Does anyone care to ask an amplifier designer a technical question? My door is open.

@fsonicsmith

Let me ask you this Roger; other than one of Ralph’s amps, which modern era top-tier tube amps have you actually sat down and listened to with not just your own planar speakers, but also modern coned speakers across a decent spectrum?

Other than designing amplifiers Roger has a pretty robust repair business and is an authorized repair shop for Allnic. Lots of vintage and modern equipment, solid state and tubed, crosses his path. I know because for the last 3 years I have been the repair intake person. As he has mentioned previously, Roger also measures anything he can get his hands on and has notebooks full of test notes for equipment that spans the ages. Also, Roger does not design planar speakers, he designs electrostatic speakers, there is a difference, perhaps you might read up on that.

Are you living in a cave?

Actually he has quite a nice house with a very nice system.

When we’re bored we go visit local folks to hear their modern systems (this past weekend we heard Avantgarde horns with their associated electronics) and Roger is pretty active with the SFAS, with the responsibility for running the upcoming phonostage shootout in January. My point is that Roger is very up to speed regarding current designs and design "philosophies," but testing and measurements are still critical to producing quality components and the principles behind these measurements go back in time. Ohms Law is still Ohms Law after all. Unless I missed something it hasn’t been updated or modernized.

Same is true for balanced amplifier design. Today we see all sorts of designers referring to their equipment as balanced. In many cases the design is just balanced at the input, not throughout (then there are the pseudo balanced designs). The only person I know that has been doing true balanced tube designs consistently (and in adherence to the balanced standard) has been Ralph Karsten and he’s been at it for over 40 years. However, the concept is not so modern, in fact it wasn’t developed for home audio use, but rather first utilized by the phone company to drive long cable lines (although I am unclear if the phone company developed the standard which I have heard referred to as the 600 ohm standard).

So Fred Sonic Smith (I assume that’s what your handle references) perhaps you should leave us. You bring zero value, you do not possess the knowledge or credibility to refute anything Roger says and although their opinions greatly differ, at least Ralph has the credentials and reputation to partake in those discussions. Let him do so if he wishes, he needs no help from you.

I re-entered because I could not resist. I saw that your irascible behavior has continued and not just towards me, so I felt better about re-entering.

Actually that was your cue to leave and stay away. You re-entered because you enjoy trolling here.

Haha... Nimble Tube-Roller Society! That exchange must have been just before I started buying stereophile (1986). I agree that having the freedom to choose different power tubes for the same amplifier is liberating from an owners standpoint (well, at least THIS owner!). It is also a very good point that buying something designed around a “single source” part is risky. I had an H.H. Scott LK-150 power amp (built in 1961) that I’ve used 6550, KT88, and now KT120 power tubes in. My son is using the amp now. That’s still a great amp (in my opinion). My point is that even though those tubes are from the same “family”, it was great to be able to try different flavors in the same amp. Regarding preamp tubes; I’ve had preamps that were built around different tube types, and they all had their strengths and weaknesses. I didn’t really attribute those differences to tube A vs tube B. But I knew not what made them sound the way they did. That’s why I wanted to take this opportunity to ask someone who has to make a decision about which to use. As you said, how can one compare between tubes used in completely different units?

Regarding the issue of cartridge loading, in a past thread here Jonathan Carr (Lyra cartridge designer, who I believe has also designed some phono stages) stated as follows:

I should now debunk another myth regarding loading, which is that low-impedance MC cartridges are insensitive to capacitive loading. OK, the MC cartridges themselves aren’t particularly sensitive to capacitance, but the inductance of the cartridge coils will resonate with the distributed capacitance of the coils and the capacitance of the tonearm cable to create a high-frequency spike, and this spike certainly is sensitive to capacitance. In general, the less the capacitance the better. Having more capacitance (across the plus and minus cartridge outputs) will increase the magnitude of the high-frequency spike and lower its frequency, neither of which is good news for phono stage stability or phase response.

Generally speaking, the greater the capacitance across the plus and minus cartridge outputs, the heavier the resistive loading needs to be to control the resulting high-frequency spike. Conversely, less capacitance allows the resistive load on the cartridge to be reduced, which will benefit dynamic range, resolution and transient impact.

The relevance of the Hagerman link Ralph provided in his previous post is that it illustrates the high frequency resonant peak (i.e., the "spike") formed by the interaction of the inductance of the cartridge and the load capacitance that it sees.

I am not in a position to say whether or not the **only** relevance of resistive loading of a low output moving coil cartridge is to control that peak, and its potential effects on the particular phono stage. However I certainly wouldn’t consider the possibility that it could often at the very least be an important factor in the performance of a system to be "out of the world," as Roger stated.

Also, while I don’t recall the exact numbers, Ralph has stated in some past threads that he has observed remarkably high levels of energy emanating from LOMC cartridges at ultrasonic or RF frequencies.

Also, FWIW, I’ll mention that Keith Herron, whose company and products (especially his phono stage) are about as non-controversial and highly regarded as they come, suggests that with his particular phono stage no loading whatsoever will often be found to be preferable with LOMCs, regardless of the cartridge type. (The LOMC input of his phono stage is FET-based, and it applies a load resistance to the cartridge that is nearly infinite when load resistors are not connected externally, to RCA jacks that are provided for that purpose). And I have found that to be the case in my own system, with an AT-ART9 cartridge having a recommended load of "100 ohms minimum."

Finally, without placing blame (although I have my own thoughts about that) I’ll just say that it’s a shame that an otherwise wonderful thread is compromised by the fact that two long-time designers of highly regarded audio electronics can’t deal with each other in a more respectful and matter-of-fact manner.

Regards,
-- Al

I read both links. The first is common knowledge and nothing about RF. The second is long so if there is something in particular you want to me to read please quote it here. Are we playing "Wack A Mole’ here?

Im really tired of RF being the devil for everything. Usually if there is RF sensitivity you will hear an AM radio station. If there aint no radio coming in there aint no RF. Lets get real please.

For the What’s Best forum, just look at JCarr’s posts. No whack a mole- not even sure what that comment is even supposed to mean.

No-one has said RF is the devil for everything except you, just right now. But these two links did point at RFI (or ultrasonic or near ultrasonics, in the case of MM cartridges) being a problem with LOMC cartridge operation... I don’t see how that can be construed as ’everything’.

Ralph has not honored the stated purpose and rather come here to once again to hawk his paradigms and unusual ideas about cartridge loading and RFI. You are into vinyl I see. Do you agree with his loading suggestons? Dont we load a cartridge to change its sound? That last one about loading a cartridge for the sake of the preamp was so out of the world. Most of just a juse a ferrite bead to stop RF from coming in.

This statement is outlandish and false. Please note though that I am not attacking you, just the veracity of this statement, unlike you who sees fit to attack me personally. I have honored the stated purpose, as I am a designer of amps and my door is open.

If you say you looked at both links and came away with the idea that RFI has nothing to do with it, the only conclusion that can be drawn is that you didn’t in fact read the links or failed to comprehend their significance. When we are talking about noise in the MHz range, that’s RFI, especially when it is the result of excitation of a tank circuit.

I do agree, Ralph should have never entered this thread nor should you. I dont see a question and I dont see a contribution. You left, said you wouldnt come back, but you did.

Roger, you seem to appreciate my being courteous when I offer corrections (which you seem unwilling to accept), but you seem unwilling to be civil in return.


Contrary to yours and others impressions, this is not your thread- its a public forum.


As a bit of a hint, I find that keeping decorum in spite of personal attacks (including outright untruths) is a simple tool to maintain credibility. FWIW I have an EE just like you and I don’t engage in pseudo science any more than you. I can prove everything I say. I suspect that you are not *as* acquainted with equipment from the old days- 1960s and before, as I might be. You have said that my talk about the Power Paradigm and the Voltage Paradigm is the pseudo science to which you refer; to me that just suggests that you don’t have a grounding in history. This despite my showing an example of what I was talking about (one that we have discussed prior); in spite of that evidence (the Fisher A-55 I linked, and any amplifier with a ’damping’ control) right in front of your face, yet you still accuse me of pseudo science!


But:
You are getting out of hand here. This entire thread is in violation of Audiogon posting rules, for the simple fact that you primarily use it for promotion.
On occasion I get accused of the very same thing, but those that do so will note that I have yet to start a single thread on this site (despite being active on it since its inception in the 1990s), let alone one that focuses primarily how great I am in tandem with how great my products are, all the while demeaning (in some cases, falsely) others. I do mention my products when asked and also in the context of related questions (such as balanced operation; quite often because there is much misunderstanding about how balanced lines are supposed to work).

This is not your thread! - if that were the case it would be on your website. Instead you are posting on a forum that is open to the public. My presence here has mostly been to keep the record straight when things have gone off the rails. The 6SN7 thing and the cartridge thing are two examples.

I can see that it bothers you as much as it does me when you see things that are untrue. If I can offer a bit of advice:We often go thru live with made up stories. In fact we live as if those stories are true. When life and the stories don’t agree we suffer. At that point, to end the suffering the best thing to do is drop the made up story. You will note that I do not attack the voltage rules as being made up. I regard them as an engineering solution, but one that has some bad applications. I’ve pointed out why earlier and don’t need to repeat myself. The old power rules are one way out of the resulting colorations of the voltage rules, but they come with their own price (limited market, for one, more fiddling and more careful equipment matching for another).


IOW, if you think I made up the idea of the power rules, you are simply not grounded in history.


I am perfectly happy to have that conversation on a different thread. I’ve been having this conversation for the better part of 30 years and its not been debunked by any engineer that listens- only those who don’t and are further unaware of how the voltage rules were developed.

I dont mind any designer coming here if we both understand electrical science in its accepted current form and speak the proper language. If you want to read made up science there are pleanty of other threads on here for that.

I have a a question for Ralph, Why have you not sent an amplifier to Stereophile for review? They have reviewed all of mine and preamps too.

I got my degree at the UofM. I don’t subscribe to anything made up. Enough with the innuendo already- if you don’t get what I’m talking about, just say so, otherwise lay off. John Curl got it, Nelson Pass got it, other engineers on this site got it...

Regarding Stereophile:
We sent a preamp to TAS for review. It did quite well- the reviewer bought it and said so in the review. Then he moved over to Stereophile prior to the publication of the review; it got published there. At that point we knew we were in trouble when we got the news that he had jumped ship to Stereophile, as we had been warned by people from several companies (ARC among them) that if you can’t afford advertising with them, they will treat you as a sacrificial lamb to show how hard hitting their reporting is. Sure enough, some months after the initial review was printed (in which I had to challenge JA’s measurement comments, as the Audio Precision at that time didn’t properly support a balanced input, despite it appearing so- a different conversation), and after being asked if we would advertise in the magazine, the reviewer was later instructed by Stereophile editors to print a followup. Apparently when he was installing defecting tubes in the preamp, it didn’t work right. We tested several of those tubes; one was a Telefunken that was so dead that I thought my tester was at fault as it got no reading at all when the Telefunken was lit up. I had to test some known good tubes to know that I was not going nuts! To date I’ve yet to see another 12AT7 that bad that still had a vacuum. We got blamed in the followup for that failing on the part of the preamp. Do you have amps and preamps that function correctly on bad tubes?

A second product, the MA-2, was destined for a nice review in 2004 by Paul Bolin when he was with Stereophile, but a company that was trying to take over my company threatened Stereophile with a lawsuit if they didn’t give the amp back to them. Paul let me know this was happening, and since we owned that amp I went and picked it up. While the lawsuit never went down, JA was sufficiently rattled by that event that he removed Paul from the Stereophile staff.

@krelldreams What prompted my question regarding tube types was the discussion in this thread about 6sn7/12au7/6sl7/5751/12ax7 tube type use for preamps and amp inputs. But there is also the question of power output tube choices - el34/6550/kt88/kt120/kt150, etc. It appears that some designers use the same tube types in their products, however there are instances where designers switch types year to year, or even have concurrent products performing the same function (amp or preamp) but using different tubes. Consumers and reviewers, also, sometimes prefer only 6sn7 or 12au7 based preamps, or kt120 or el34 amps, for example. I was hoping to get the viewpoint of someone who makes this choice.

Thanks for an on point question. For years Everything ARC made used 6550s. Some makers are similarly fond of EL-34s. Some consumers are in love with that little 9 pin EL84.

Part of the tube choice is driven by, you, the consumer. I built an EL84 amp because I know there a lot of people who love that tube. I did do someting different and got 35 watts per pair rather than 17 watts. I raised the power, kept the safety and life of the tube and made somethig to this day people do not believe possible. The application is laid out in my 2018 Burning Amp presentation.

On the other hand I built the RM-9 to take any octal power tube, of which there are many. Power stays the same, only the negative bias changes. I did this so that users could compare widely different power tubes on the same platform. In my thinking how can someone say something general about a particular power tube when they are comparing it in two different amps? David Manley got very upset over the RM-9 and we exchanged several letters in pubic in the Stereophile. They are fondly known as the Manley/Modjeski letters. I hope to get them up on the HIFI school site. At the same time we coined the term "Tube Rolling" and I made buttons imprinted "Member, Nimble Tube Roller Society" This was way back in 1983 so young folks may have missed it. David was totally opposed to tube rolling.

You can take an old RM-9 and use 4 of the KT 120s or 150s instead of 8 of the earlier tubes. Will still produce full power with half as many tubes.

What I see in the market place now is that New Sensor (Tungsol) is creating larger power tubes and there are those designers who appear to get out a new amp with the new tube as fast as they can, which does worry a bit. If a designer goes for the full power of a KT-150 and you have to go back to the 120 or 88 you will loose power. If the Russians do something bad the KT 120 and 150 could disappear until someone else takes it up. You can add your own "ifs" to the list. HP and other equipment makers had a policy any part had to have at least one other supplier. Single source parts not allowed.

Tube cost is another criterion. EL84s are very inexpensive, EL 34s next. then 6550/KT88, KT 120s. However the KT150 cost to me is about twice the KT 120. The look and power are quite a departure and I will not be surprised it the next bigger KT is already in the works.

KT, stands for Kinkless Tetrode in the UK. We use Beam Power Tube in the USA for the 6550 which is essentially the same thing. The first beam tube was the 6L6, a great tube that no one uses because the public has someting against it, for no good reason.

In essence, You, the buyer are controlling the tube choice as much or more than the designer. Hope you choose well. :)

Roger;
I have not deleted any of my posts. Not a one. 

fsonicsmith., you seem to troll my threads, this is not the first time I have encountered you.

I think you are mistaken. I don't recall ever entering into any debate of any kind let alone some type of trolling-skirmish with you. IMO, you are once again confused. 
Let me ask you this Roger; other than one of Ralph's amps, which modern era top-tier tube amps have you actually sat down and listened to with not just your own planar speakers, but also modern coned speakers across a decent spectrum? I ask because as I have said previously in this thread, you keep referencing ancient amplifiers of the remote past which you conveniently choose to piss all over. Others have asked you this same question too and you have not responded. Are you living in a cave?
I re-entered because I could not resist. I saw that your irascible behavior has continued and not just towards me, so I felt better about re-entering. I do respect you and your knowledge base, but it also pays to be a gentleman. Towards the end of his life, Charley Hansen (you misspelled his name a few posts ago-shame on you) was very vocal about MQA and his debate with JA on another forum became quite heated. Throughout that give and take, both managed to remain polite and civil. You could take a lesson from them. 
I brought up Charley Hansen's interview towards the end of his life about his latest iteration of amps finally-in his opinion-capturing the sound of the best modern tube amps. Have you sat down to listen to any of his amps? Have you analyzed why they might sound as they do from an engineering standpoint?
I am into vinyl, thank you. I am the proud owner of a Manley Steelhead, which I bought new. I love it and love Manley. I wish the aesthetics of their amps suited me more. I acknowledge that letting aesthetics get in the way of a purchase decision seems silly. I also acknowledge that Ralph's views on cartridge loading differ from my own. But as you quoted me (accurately), I have 1% of your engineering knowledge and his too. But I have years and years of empirical experience and based upon that, I have chosen to disregard Ralph's views on cartridge loading as simply not applicable to my particular system and experience. 

@ georgehifi
" I've set a 6sn7 in a preamp up on the oscilloscope and talked at it, and watched my voice being duplicated on the scope as wave forms superimposed on the 1khz test wave, and was quite eyebrow raising just how loud it was compared to the test wave."
Very interesting!
I would also amplify - lol - the sentiment that this is truly a wonderful thread!  :-)

What prompted my question regarding tube types was the discussion in this thread about 6sn7/12au7/6sl7/5751/12ax7 tube type use for preamps and amp inputs. But there is also the question of power output tube choices - el34/6550/kt88/kt120/kt150, etc. It appears that some designers use the same tube types in their products, however there are instances where designers switch types year to year, or even have concurrent products performing the same function (amp or preamp) but using different tubes. Consumers and reviewers, also, sometimes prefer only 6sn7 or 12au7 based preamps, or kt120 or el34 amps, for example. I was hoping to get the viewpoint of someone who makes this choice. 

@fsonicsmith

Ralph-you should never have entered this thread. You tried to kill the OP with kindness and camaraderie, and he spit on you every chance he got. I think most of us reading through this thread can see the OP for what he is; entrenched in the remote past and bitter. His hubris is out of bounds. I have been around long enough to suspect that there must be something else going on in the OP’s life that is causing him to behave so poorly.

As Oldtech noted, this is my thread.

Hi,

fsonicsmith., you seem to troll my threads, this is not the first time I have encountered you. Aren’t you the one who said you knew only 1% of what designers know. I was looking for that one.. It appears a lot of your responses are now missing.

Ralph has not honored the stated purpose and rather come here to once again to hawk his paradigms and unusual ideas about cartridge loading and RFI.  You are into vinyl I see. Do you agree with his loading suggestons? Dont we load a cartridge to change its sound?  That last one about loading a cartridge for the sake of the preamp was so out of the world. Most of just a juse a ferrite bead to stop RF from coming in. 

I was happy to discuss his points till it got out of hand. Ralph can run his own thread if he wants to promote his paradigms. You write well, perhaps you could edit the one on Power so it makes some sense.

I do agree, Ralph should have never entered this thread nor should you. I dont see a question and I dont see a contribution. You left, said you wouldnt come back, but you did.

I dont mind any designer coming here if we both understand electrical science in its accepted current form and speak the proper language. If you want to read made up science there are pleanty of other threads on here for that.

I have a a question for Ralph, Why have you not sent an amplifier to Stereophile for review? They have reviewed all of mine and preamps too.

What causes a designer to choose a certain tube type for an audio circuit? Is the circuit designed around a specific tube, or is the best tube type found for the circuit that’s been/being designed? I know there are different electrical properties (I’m not an EE, so that is my untrained understanding), but does one choose the tube primarily for its electrical ability, sound, reliability, or some combination?

I know you would prefer that RM or RK answer this but I have something I can add. I asked this question of ARC's techs (I don't recall which one I spoke to) about their current penchant for designing power amps around the Tungsol KT150 and before that, the KT120. In ARC's case, I was told that they did the former-designed their amps around these tubes. If you happened to follow the history of the Ref series of amps, this is fairly obvious. The KT120 hit the market and the then-current Ref series of power amps were shipping with KT88's. They were able to handle the increased transformer demands presented by the KT120, but just barely. ARC reacted by beefing up their transformers to accommodate the KT120. Then the KT150 came out and this time, ARC was ahead of the curve rather than behind it-it seems they were got their hands on the KT150 before it was released to the public and were able to come to market with their Ref 75SE and Ref 150SE with KT150's installed. This was true of the GS "Galileo" Series as well. The tech I talked to told me that they felt the KT150 was far more linear and "accurate" than all of the predecessor power tubes, and also more durable. Too bad (for me) they are also significantly more expensive. That said, I used an ARC VS110 for about ten years and went through about six sets of various KT88's, 6550's, and even tried KT120's. I know, without a doubt, that I am getting far superior sound with my present amp, the Ref 150SE. The VS110 had a sweet slightly euphonious sound. Bass was good, but nowhere close to the solid slam I get with the Ref 150SE. The treble is far less grainy with my present amp as well.  

What causes a designer to choose a certain tube type for an audio circuit? Is the circuit designed around a specific tube, or is the best tube type found for the circuit that’s been/being designed? I know there are different electrical properties (I’m not an EE, so that is my untrained understanding), but does one choose the tube primarily for its electrical ability, sound, reliability, or some combination?

This is a golden nugget of wisdom;

(In their book "Control Design And Simulation", Jack Golten and Andy Verwer discuss (in chapter two) with regard to applying mathematical models to the real world: "...mathematical models invariably involve simplification. Assumptions concerning operation are made, small effects are neglected and idealized relationships are assumed." 

Ralph-you should never have entered this thread. You tried to kill the OP with kindness and camaraderie, and he spit on you every chance he got. I think most of us reading through this thread can see the OP for what he is; entrenched in the remote past and bitter. His hubris is out of bounds. I have been around long enough to suspect that there must be something else going on in the OP’s life that is causing him to behave so poorly.

Here is a great example of what I consider the proper use of 6SN7 and 6SL7. Note all the preamp and phase inverter are SLs. Interestingly the SN is used as a push pull output tube... So cool. Its worth reading some of the thread.

https://music-electronics-forum.com/showthread.php?t=16661

@oldtecg05
 Whose thread is this?

I thought it was mine. I dont mind a bit of controversy as long as its Gentlemanly and with some sense of humor. Its the sense humor that I find lacking.

Power is equal to volts times amps and is also equal (thru Ohm's Law) to current (squared) times Ohms.
In this case, to make 100 watts into 8 ohms, you divide 100 by 8 and take the square root, which is about 3.4 amps. That's all thats needed to make 100 watts if the load is 8 ohms and it makes no difference what kind of amplifier it is. So what is the 29 amps??

HI, I was involved in that discussion about the Benchmark amp. Some of us were trying, without much luck, to advise the owner not to bridge the amps into his speakers. Then we got into current. Then the whole thing fell apart and I left. 

To answer your question. 100 watts at 8 ohms is 40 volts peak. If you have an electrostatic or other speaker that goes down to an ohm or two you will need a lot of current to play trumpet music at full level. You may need 40 amps to get your 40 volts at 90 degree phase and most amps will be very unhappy. The Beveridge ESL required 1500 VA to play Miles. There was no way to get that through a reasonable transformer so we made Direct Drive 3000 volt amplifiers that provided 1/2 amp of current. 

@atmasphere It is in no way an excuse for bad specs- and in fact our amps have some pretty good specs (if proper measurement technique is used, which means **don’t ground a speaker terminal during testing**, which is the mistake that almost everyone except Charles Hanson made/makes). I suspect you didn’t read the paper at the link very carefully, since you claimed that you read it, yet still with the remonstrations!

Do you think I am so stupid as to ground floating outputs. GEEEEZ Get off my back. I go into the balanced input of the Soundtech. Ive given your amplifier every opportuinty to meet your specs and it just does not. Would you like to send me one that does?

Ive measured you feedback to be less than 0.1 db with an 8 ohm load. I simply disconnected the feedback and the meter moved less than 0.1 dB. Is that how you measure it? Output regulation is about 9 dB at 450 mA idle and is certainly idle dependent.

Distortion I can never get below 1% unless I really want to heat up the tubes.

Ive read you paper to death and makes little sense to me or anyone skilled in the art. Rather than me keep reading it how about you work on re-writing it. Im happy to help.

The history of the 6SN7, has nothing to do with its current use. Shall we publish the 6SN7 application notes for the whole RC series? Will the writing make it a better tube?

All I know about your amplifier is that if I add 12 dB of feedback it sounds a lot better to everyone that has come to hear it. Perhaps you have not tried this much. Because the amp has good stability it takes this feedback nicely and gets us under 1% THD and a regulation of 3 dB vs 9 dB. Makes the QUAD 57 sound really nice in brushes, clean tuneful bass, clear vocals. Why are you so opposed to feedback? Ive read Crowhurst, he taught me how to make good transformers.

I dont go looking for amps to modify, other people modify my amps. All they do is put in silly fast rectifiers. WOW. People modify cars. If 12 dB of feedback makes the M-60 sound better to all the people I have demonstrated if for then it does for them. Look, It seems we have hit a nerve here, lets be nice and lets all try to make better amps and less story.

Actually Roger, I did that earlier. You must not have read the post?
The loading is for the benefit of the preamp, if its sensitive to RFI. If not, no loading is needed. IOW if you need loading to deal with brightness, the preamp has a problem with RFI. The loading resistor detunes the tank circuit caused by the cartridge and tone arm cable and thus knocks out the RFI caused by the tank circuit when driven into excitation by the energy of the cartridge. Here’s a couple of links that address this in greater detail; the link to the What’s Best forum includes posts by Jonathan Carr, a noted designer of LOMC cartridges. The one to Jim Hagerman’s website has some of the math and some charts that show whats going on:
http://www.hagtech.com/loading.html
https://www.whatsbestforum.com/threads/cartridge-loading-a-misnomer.15077/

I read both links. The first is common knowledge and nothing about RF. The second is long so if there is something in particular you want to me to read please quote it here. Are we playing "Wack A Mole' here?

Im really tired of RF being the devil for everything. Usually if there is RF sensitivity you will hear an AM radio station. If there aint no radio coming in there aint no RF. Lets get real please.

Whose thread is this?

What can I expect to pay for a recap (plus any normal servicing)? I can actually drop off the amp at Krell myself (they are an hour or so away).

While it might be old enough that some of the filter capacitors could be getting near failure, that is not the problem here. Filter caps don't make static noise. Is this problem in both channels or just one? If one, I would suspect the input transistors.

My pre amp is a Conrad Johnson Classic II. Output is 200ohms.
The Krell input 47K--despite this, I am using an attenuator before the amp inputs.

The input impedance has nothing to do with whether you need attenuation or not, FWIW. I'd get an estimate from Krell before deciding your course.

When an amp specifies a maximum current what exactly does that mean and how is it relevant? On another thread there's discussion of an amp that has max current of 29 amps and puts 100 watts into 8 ohms. Since 29 amps would be a whole lot more than the current into 8 ohms at 100 watts or into any normal load this must have some other relevance. 

Power is equal to volts times amps and is also equal (thru Ohm's Law) to current (squared) times Ohms.
In this case, to make 100 watts into 8 ohms, you divide 100 by 8 and take the square root, which is about 3.4 amps. That's all thats needed to make 100 watts if the load is 8 ohms and it makes no difference what kind of amplifier it is. So what is the 29 amps??

Let's do the math the other way- 29 squared is 841 watts if into a 1 ohm load, but if this amp can double power as impedance is halved, clear down to 1 ohm, the wattage would 800 watts, not 841! The math can't lie about stuff like this, so clearly if the 29 amps is real, it has to be something else. Often it is- its the amount of current that can flow if the power supply is shorted for 10 milliseconds. Mostly that's a measure of storage that the capacitors in the power supply have and probably does not say much about how the amp measures or sounds. Also FWIW, there are tube amps that have that much 'current'. IMO, the 'current' (please note quotes) is often a misleading figure as current can't exist without voltage no way no how.

When an amp specifies a maximum current what exactly does that mean and how is it relevant?  On another thread there's discussion of an amp that has max current of 29 amps and puts 100 watts into 8 ohms.  Since 29 amps would be a whole lot more than the current into 8 ohms at 100 watts or into any normal load this must have some other relevance.  

OK--could use some advice. I am currently using a Krell KST-100. (solid state) Amplifier since around 1992. I think age is setting in--getting first signs via noise/static like through speakers. I have isolated the Krell.

What can I expect to pay for a recap (plus any normal servicing)? I can actually drop off the amp at Krell myself (they are an hour or so away).

Now part two (which impacts part one)
My pre amp is a Conrad Johnson Classic II. Output is 200ohms.
The Krell input 47K--despite this, I am using an attenuator before the amp inputs.

So--do I recap and refurbish my Krell (a great amp) or do I switch to another amp (I like the solid state CJ's for around $2-3k). 
Thanks!

Please explain. Im all ears.

Actually Roger, I did that earlier. You must not have read the post?
The loading is for the benefit of the preamp, if its sensitive to RFI. If not, no loading is needed. IOW if you need loading to deal with brightness, the preamp has a problem with RFI. The loading resistor detunes the tank circuit caused by the cartridge and tone arm cable and thus knocks out the RFI caused by the tank circuit when driven into excitation by the energy of the cartridge. Here’s a couple of links that address this in greater detail; the link to the What’s Best forum includes posts by Jonathan Carr, a noted designer of LOMC cartridges. The one to Jim Hagerman’s website has some of the math and some charts that show whats going on:
http://www.hagtech.com/loading.html
https://www.whatsbestforum.com/threads/cartridge-loading-a-misnomer.15077/

Why, because it was made for audio, not B&W television.

There are some great books on the history of Heath written my people who were there.

This other stuff about sawing tubes in half make no sense. Ive taked to tube designers and they dont talk that way... at all.

With regards to the 6SN7:

From the RCA Receiving tube manual, RC-19, published 1959, page 229:
2nd sentence (after the part about being used in television circuits):
"Each unit may also be used in multivibrator or resistance-coupled amplifier circuits in radio equipment"
The same phrase about ’resistance-coupled amplifier’ is used to describe the 6SL7, 12AX7, 12AT7 and so on.

Roger, when you say that you don’t know of anyone that used the 6SN7 in audio applications, as in this post:

The 6SN7 was made for black and white TV and was never, to my knowledge, used in the audio chain.

And then turn around and say this:

My dad built the WM-2 in 1956 so I am very aware of 6SN7, as was Heathikit who used them everywhere they could. Are you aware that most of their early products were built largely from WWII surplus of which there was tons. They would buy tons of surpus and then figure out what to do with it. 6SN7 were in great abundance.

--- Could you clarify what you meant here? These statements appear contradictory.

Regarding the sawed in half comment, sure, tube manufacturers don’t talk that way and for the record, I don’t manufacture tubes. But I do use them. Look at a 12AU7 and compare it to a 6SN7 (GE 6SN7s are the best example for this) or a 6CG7; the 12AU7 plate structure is half the height. And when you look at the specs, extremely similar to the 6CG7/6SN7; the geometry and spacing was maintained. So ’sawed in half’ is a good layman’s description. It makes plenty of sense.

To those who write up pages of pseudo science and create paradigms to make excuse for bad specs I no longer care to see here. Skilled people in this industry have come up with some minumum standards for noise, distortion and output impedance.

"Skilled people"? Do you mean marketing?
Uh, Roger, in a way this seems aimed at me (the use of the word ’paradigm’; I’ve not seen anyone else here use that word). If so, you’re way off base (and I regard the attack as un-called for). Don’t think for a minute that we built our amps without feedback because we couldn’t apply it! In case you don’t know what is meant by the Power Paradigm, as opposed to the Voltage Paradigm, I did explain it at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

It is in no way an excuse for bad specs- and in fact our amps have some pretty good specs (if proper measurement technique is used, which means **don’t ground a speaker terminal during testing**, which is the mistake that almost everyone except Charles Hanson made/makes). I suspect you didn’t read the paper at the link very carefully, since you claimed that you read it, yet still with the remonstrations!

Briefly:The Power Paradigm is what was around prior to the Voltage Paradigm; the ground work for the latter being laid down by MacIntosh and EV in the late 1950s (it was not until the early 1970s that it had fully taken root). At the time, the only way to build an amplifier that acted as a voltage source was to use enough negative feedback to get proper output regulation. But it was well known at the time that this didn’t work for all speakers made- the speakers had to be built to work with the concept as well. That is why I use the term ’Paradigm’ (and I *also* use it because any thought outside of that platform is often regarded as heresy).


Here is an interesting example that at which you should take a look so you know I’m not making this up:
https://www.google.com/search?client=ubuntu&channel=fs&q=fisher+a-55&ie=utf-8&oe=utf...
The first hit of this Google search for a Fisher A-55 is an image from a YouTube video. In the image we see the damping control of the amplifier. It is labeled at full counterclockwise " Constant Voltage", at noon "Constant Power" and fully clockwise "Constant Current". And yes, we’ve had this conversation before.
Speakers built in the old days that were under the Power Paradigm were usually equipped with midrange and tweeter level controls. These controls were not there to adjust the speaker to the room, they were there to adjust the speaker to the voltage response of the amplifier, which was an unknown (examples: vintage horn systems, Acoustic Research AR-1, 1960s KLH loudspeakers, the large Advent...). The Voltage Paradigm was an attempt to get away from having to do that- more ’plug and play’ so to speak.

Like any problem, the solution introduced its own problem- that of brightness as a coloration. This is a problem in every amplifier that employs loop feedback. How bad the problem is depends on the skill of the designer. The brightness is not caused by a frequency response error of course, it is due to residual levels of higher ordered harmonic distortion caused by the feedback application itself. See Norman Crowhurst.

The traditional argument is that the residual distortion is negligible. It is not!! The ear *uses* higher ordered harmonics to sense sound pressure; adding them in even trace amounts results in brightness that does not show up as a FR error because the ear converts the distortion into tonality.

(In their book "Control Design And Simulation", Jack Golten and Andy Verwer discuss (in chapter two) with regard to applying mathematical models to the real world: "...mathematical models invariably involve simplification. Assumptions concerning operation are made, small effects are neglected and idealized relationships are assumed."

It is the mark of a good engineer to know when and which things should be assumed, neglected or idealized. I maintain that violating one of the human ear/brain most fundamental perceptual rules is not good engineering.)

That the ear converts distortion into tonality is well-known. That the ear uses higher ordered harmonics to sense sound pressure is also well understood and non-controversial. It can be demonstrated by a test using simple test equipment.

Many high end designers recognize the brightness-as-coloration problem; the issue is what to do about it? That is why you see so many zero feedback amps that have "bad specs" but for some reason sound quite good. As I’ve pointed out many times, the "specs" don’t recognize the human hearing perceptual rules so what looks good on paper does not always translate to what sounds good as well. This fact is also non-controversial- we see it all the time in the pages of Stereophile, where a reviewer liked an amplifier quite a lot, and yet John Aitkinson is perplexed because the equipment measured poorly. The simple explanation, offered by HH Scott’s head engineer, is that the wrong thing is being measured.

BTW, these comments are not to be construed that every amp that measures poorly must sound better than it measures! There are some bad products out there and you and I are likely in agreement on many of them.

Tim - yes the hafler amps
what great fun and value
see you soon !
jim

@tomic601   

  thanks for awesome thread Roger

i got to page 27 of the Williams book and he says “ but as you learned in your AC theory course... “

so....now what book do I need ? Dont answer, I will figure it out...
Tektronix scope is on order...@$&*(#### this is fun.

You are the first one here to report diving into the pool!  Dont worry too much about the AC theory, thats is likely to get into AC power, 3 phase motors, things not important. Read how tubes and transistors work and then the simple circuits to the complex. He does that very well.

If power supplies interest you that is fairly easy stuff. I forget if he does much or anything with tubes, but for now transistors do the same basic things, they amplify. 

@fleschler

Maybe microphonics are not an issue with cathode followers.

I just don’t understand VAC using only 6SN7s in all their current amplifiers if they are worse than 6SL7s.

VAC is likely using them because thats what the current customer base has been told its the tube to have.

Cathode followers have a gain of 1. 6SN7s have a gain of 20 when used for line gain. The Microphonic sensitivity is thus 20 times less in the follower.

SNs and SLs are not interchangeable, nor meant to be. They are two different animals. SNs run at almost 10 times the current and most circuits would not bias up properly.

Do you know if your circuit is a cathode biased or a constant current biased follower? Makes a big difference when you swap tubes. big big big

2 seconds and a schematic will answer that question.

I thank you for this question because, with additional information and some simple schematic understanding, we might come with an alternative answer to what is going on. We really dont know why these differences between tubes exist. Or if these same things would be heard in another preamp that had the other kind of circuit. In other words, is the difference really in the tube alone or more likely how the tube performs in your circuit.

thanks for awesome thread Roger

i got to page 27 of the Williams book and he says “ but as you learned in your AC theory course... “

so....now what book do I need ? Dont answer, I will figure it out...
Tektronix scope is on order...@$&*(#### this is fun.

Here is the best data I found for the 6H30. The curves look right and the table of parameters done at different plate voltages and currents are very interesting. The first 3 columns are his set up values and the rest are the results. 

 http://www.triodeel.com/6h30.html

Is this like a 6FQ7?  Granted the pin out is the same.

After I get a few responses I will give mine. I want the questioners to do a little thinking on this one. Kinda like Homework.

I’ve tried a dozen 6SN7s for my amps’ cathode followers. What a huge range of sound characteristics.

The worst (thinnest,brightest) were Russian 80s or 90s ones under the Sovtek label, which looked identical to the Counterpoint branded ones and an English branded one. NOS GEs were generally noisy/distorted sounding.

The best were Raytheons for my amps, with the older VT-231 my favorite for its huge dynamics and warmth. Raytheons from the GT era can be more neutral sounding and harmonically thinner than the VT-231.

Sylvania’s Chrome dome had too tipped up sound for my amps but very clean and dynamic too.

RCAs, for decades of production, were warm sounding but less dynamic. My amp manufacturer uses 60's RCAs to great effect in the same amps but with very different speakers.

Ken-Rad was similar to VT-231s.

Any of the NOS tubes are superior to the 80s/90s Russian made tubes. I haven’t tried the latest tubes. In my application, the tubes can last possibly 10,000 hours (I know it’s lasted 5,000 hours already).

Maybe microphonics are not an issue with cathode followers.

I just don’t understand VAC using only 6SN7s in all their current amplifiers if they are worse than 6SL7s.

@ramtubes

First, the concept of your building the type of switch box I mentioned is very intriguing.  I'm not sure the idea still fits well with my system, which has become more complex (I'm introducing subwoofers, crossover etc).But I will certainly cogitate on the idea.

Also, love your idea for building switch boxes to text cables etc!  If the timing were right financially for me, I'd likely take you up on that (just out of my own interest.  I'm far from sold on the worth of high end cables, but I do have access to a bunch and it would be fun to test under more ergonomic circumstances, fast switching, etc).

@ramtubes. I’d like to personally thank you for taking the time to sift through all these messages and provide your input on many of them. There’s a lot of valuable information here. I’d like to thank @atmasphere as well! Differing viewpoints gives us all a variety of things to consider. One should never stop seeking knowledge. 

@atmasphere   Roger, you might want to do some reading at the links I posted in my prior post. Most of this post (except perhaps the comments about subjective listening) is incorrect. As I pointed out earlier, the load is not for the cartridge's benefit- its about the preamp.

Please explain. Im all ears.

There's plenty of old school audio electronics that used the 6SN7. As you know, its geometry is similar to that of the 6CG7/12BH7 and 12AU7 (the latter being the same as the 12BH7 but with the entire structure sawed in half)

My dad built the WM-2 in 1956 so I am very aware of 6SN7, as was Heathikit who used them everywhere they could. Are you aware that most of their early products were built largely from WWII surplus of which there was tons. They would buy tons of surpus and then figure out what to do with it. 6SN7 were in great abundance. I think a 6SL7 might have made a better choice and I snuck one in a Williamson, changed a few resistors, and really liked it . Much more linear tube (low distortion). Why, because it was made for audio, not B&W television.

There are some great books on the history of Heath written my people who were there.  

This other stuff about sawing tubes in half make no sense. Ive taked to tube designers and they dont talk that way... at all.

As to it being lower in microphonics, the tone is of course different as the structure is different. But I would not say they are less microphonic than a modern 6922.  But this is just my experience of testing over twenty thousand 6922s

Love the idea of a switchbox to test various power cords and fuses!

@roberjerman   I have found more data on the 6N30 tube. Same pin-out as 6DJ8 and 6CG7. Plate dissipation 7 watts max. Plate voltage max at 250. Looks like the 6CG7/6FQ7 will work!

The Russians copied many of our tubes as did the Chinese. What you want to do next is compare Mu, Gm and Rp of the tubes at similar operating points. Let me know what you find out. Great question.
 
Low noise 6CG7s can be a little difficult to fine but I have found some.

For EVERYONE,

My new/old/previous technician Ben arrives today and I will be spending most of my time with him and not so much here. I will continue to answer valid questions. We will be making and posting videos at the Berkeley hi fi school site. http://berkeleyhifischool.com/ and on You Tube. Videos are what I want to spend my time on.

In the last week we have gotten off track. This thread is intended to answer questions and not to have people give opinions of my or others answers. I am always willing to debate a point that can be supported. That means supported from a recognized authority. For instance, concerning tube characteristics, ratings and applications that means data books from RCA, GE, Sylvania. Take your pick, they all agree with each other because RETMA made them. Did you know that all brands of tubes had exactly the same price lists? In otherwords you could carry a RCA price list in the 70s, as i did, and a 12AX7 was the same list price even if Telefuken made it. One list.

In some cases I have offered to build a A/B box for those interested in really hearing what is going on. It is my firm belief that is the most revealing way. Others may differ and continue to differ.

I thought the other day, Why not build a switch box with several IEC inlets and one standard outlet and a relay or switches. Let people listen to power cords on the fly. Two would be enough, or more doesn’t matter. Fuses too. What is wrong with that test? Lets do some real research.

I am not interested in de-bunking pseudoscience. Established science needs no de-bunking. To those who write up pages of pseudo science and create paradigms to make excuse for bad specs I no longer care to see here. Skilled people in this industry have come up with some minumum standards for noise, distortion and output impedance. I happen to agree with John Atkinson on these. Best wishes if you care to minimum standards. There are always outliers and they will be most adament.

One thing I have learned in this popular and intense thread it that many audiophiles have created a religion with various belief systems. I’m sorry but that interests me not at all. You can’t design a good ampifier on religious principles. You may get one to work, to make some music, but there will be much missing. Sorry.

I thank all for making this thread the most popular for two weeks on Agone. Im not leaving, just shifting my focus back to my real work.

Short questions without a lot of unnecessary information will get my first attention. Most questions can be asked in one or two sentences.

@bdp24 

@ramtubes, Roger, I know you consider the 6DJ8 superior to the 12AX7 for use in a phono stage, but let me ask you this anyway ;-) : how do you feel about substituting a pair of 5751’s in place of a phono amp’s 12AX7’s? I know the 5751 exhibits lower gain and noise (in the 1980’s I had a Dynaco PAS 2 that was "modified" by Frank Van Alstine, and he put in 5751’s. That pre was very quiet.), but are there trade-offs involved between the two tubes? Is the 5751 a true direct replacement for the 12AX7, regardless of application? Or are there circuit considerations? If used in an RIAA moving magnet phono stage (gain of 42dB or so), will the 5751 automatically provide a little more headroom/freedom from overload than the 12AX7?

The 5751 is slightly different froma 12AX7 and close enough to be tried. We have plenty of very low noise ones. CJ has used them for years. I use one in the integrated I am developing. I could have used a 12AX7 but like the 5751 better. it also happens to be a "Premium" tube which means they took more care on consistancy and long life. It falls under the "industrial" category where failures are not appreciated. Headroom is more of a circuit parameter than a tube parameter. 

I think microphonics can sound euphonic. I built a Bottlehead be pre-and while it was fantastic the tubes in that application were very microphonic. It lends everything a rounder more robust sound as it’s like a delayed Feedback.

That's a new one on me- usually microphonics causes harshness!

tomic601, DH-500 and DH-200. Are you referring to the Hafler's? I had a DH-200, and a DH-220 and DH-110 pre, that I built from kits. Great little amps and what a blast to build from kits! Quite the learning experience. All mine worked from the first try after assembly.

I think microphonics can sound euphonic. I built a Bottlehead be pre-and while it was fantastic the tubes in that application were very microphonic. It lends everything a rounder more robust sound as it’s like a delayed Feedback. 
 That is ultimately what made me get rid of it 

 @mrdecibel indeed.....I think IF memory serves correctly we sold at least 4 pair of them including to a bar owner who loved his music while tending bar....
On a lark one night at the store, while owner away, we biamped them w DH500 on the low end and a DH200 on top ( we had better amos but wanted similar tranfers function )..Played Peter Gabriel - Security...that CD has some low end wallop !!!!!
wow...

I would buy a pair today just for grins....ha

Thanks.
I didn't totally follow all that, but that's due to my level of ignorance.

@prof

Don't feel bad. A lot of designers don't get it either!

Good question. Cartridges are very different in how they respond to loading. My Denon 103 is a 14 ohm cartridge (as I recall) and likes 100 -200ohms load. More load drops signal level, dont ever go that far, and makes the sound rather dead. No load is rather bright.

On the other hand the Lyra cartridges are so low in impedance that they dont respond to loading so we, in the SF audio society did some tests and found the Lyra best unloaded.

There is not any relation to speakers and amps that I would care to make. A cartridge is a source, the load is a resistor. Not much else going on.

Roger, you might want to do some reading at the links I posted in my prior post. Most of this post (except perhaps the comments about subjective listening) is incorrect. As I pointed out earlier, the load is not for the cartridge's benefit- its about the preamp.

The 6SN7 was made for black and white TV and was never, to my knowledge, used in the audio chain. 

There's plenty of old school audio electronics that used the 6SN7. As you know, its geometry is similar to that of the 6CG7/12BH7 and 12AU7 (the latter being the same as the 12BH7 but with the entire structure sawed in half). If you need examples, Google:
https://www.google.com/search?client=ubuntu&channel=fs&biw=1440&bih=729&tbm=isch&...

Now if the 6SN7 is not really a good audio tube, why does VAC use it on the entire line of amps as input tubes?  He could have used a 6SL7 or 6CG7 or variant.

Its because it *is* a good audio tube. That is why so many manufacturers used it on the old days, prior to octal based tubes being replaced by miniature tubes. Its considerably less microphonic than 6DJ8s, although almost any signal tube has to be hand picked for low microphonics.


Folks, you can't just pull a tube out of a box and expect that it going to do the job. It really should be tested, but testing for microphonics means listening to the tube to see if its acceptable.


I don't agree with George's comments about microphonics equating to euphonic character! As anyone who has played with tubes knows, microphonics is *not* musical or euphonic. If you hear that quality in a microphonic tube, its doing that **in spite** of the microphonics!

Also plenty of choices for the 6N30 - from low-to-high prices (Saratov-made DR versions). Shame on ARC and others calling it a "super" tube - and boosting the prices for the gullible!

I have found more data on the 6N30 tube. Same pin-out as 6DJ8 and 6CG7. Plate dissipation 7 watts max. Plate voltage max at 250. Looks like the 6CG7/6FQ7 will work! 

Are the pin-outs identical? If so, then the 6CG7/6FQ7 would make a cheaper substitute for the pricey Russian tube!

Is the Russian 6N30 (6H30) a copy of the 6CG7/6FQ7 dual-triode 9-pin base? I suspect it is! And not some secret "super" tube as claimed by ARC and others! Plate voltages and GM appear similar.

Krelldreams, I use an Luminous Axiom II, Walker Mod, 3 rca in, 2 rca out, with remote, and I feel it does not have a sound of it's own. $1249. retail. Tim Stinson from Luminous spent a lot of time with me on the phone, and I could not be happier. Enjoy ! MrD.

Tomic, the ADS L 2030 was ( likely still is ) an awesome speaker.....Enjoy ! MrD.

Quote analogluvr , " I’ve tried power cords from Shunyata and XLO and have not heard any difference.  Shunyata one was there flag ship that was selling used for almost 2K. Nada."

 
The only place where I, personally, find inarguable, obvious difference/reason, in brand, cost and attention to details where cables or wiring are used is in Tonearms and Phono Cables. I would rather direct extra value/dollars into the power supply parts than the cord to the wall beyond a solid firm contact/shielding. I too couldn't hear obvious value of the much higher cost of exotic power cords , especially vs. just a portion of that cost put into better parts in the power supply circuitry. 

I wanted to weigh in on the power cord debate. I purchased a few of them several years ago. I did it because so many people were raving about how great they are, including one friend of mine in particular. When I replaced my stock cables, I did so without doing an intensive A/B comparison. I just took the stock ones out and put the “good” ones in. Sounded great... but it sounded great before. Not much to say other than that. If I have to work really hard to detect a difference, it’s not worth it. I honestly don’t have very expensive cables, considering the cost of my gear. I use Anti-cables for my speakers, and a mix of moderately priced Tara Labs and Audioquest for interconnects. My friend uses VERY expensive cables, and has components and speakers that are more expensive than mine, but we both agree that my system sounds better. I wouldn’t argue with someone who tells me their cables make a huge difference. To them maybe they do. But to me, so far, they haven’t. I have no problem hearing differences in different pressings of the same LP. I hear differences between amps, preamps, LP playback systems, speaker positioning, etc. But cables, not so much. It’s also odd that people who love cables get so angry and defensive when other people don’t get excited about them. Hey, if you dig ‘em, get ‘em, and be happy with what sounds good to you. You don’t have to get so mad. 

 I’ve tried power cords from Shunyata and XLO and have not heard any difference.  Shunyata one was there flag ship that was selling used for almost 2K. Nada. 
 That was before I really got into the hobby and started building some things and learned a little bit about how this stuff works. I thought there was something wrong with me that everybody could hear these drastic changes and I couldn’t! 

almarg
None were microphonic initially, as determined by lightly tapping on them with a pencil eraser. Two of them eventually became severely microphonic, however.

Yes Al there are so many that are and owners don’t even know they have them, they think it’s "euphonics" but in fact echo.
I test "every tube" not just 6SN7’s that come by me, with a tap of the fingernail and watching the oscilloscope.
Or in the listening system turn the volume up to normal and get someone to listen in front of the speaker/s while you flick gently with the finger nail.
A "bonk" microphonic, with a "tinkle" can be loose/shaky heater filaments as well.
A "runway" bonk (rotating feedback) that just gets louder and louder, a severely microphonic tube have your spare hand on the poweramp power switch.

Cheers George

@ramtubes. 

I will measure the Axiom with a meter. Actually, after considering your comments regarding my experience with the passive, I reinstalled it in my system. This time I reduced the gain of my phono preamp, and I’m giving it another go ‘round. I’m using a variety of albums by a variety of artists in a variety of genres. I made my judgement in haste the first time, because the first LP I played sounded bright. I know better than to make a judgement so quickly without giving the component in question some time. I’m glad you questioned my impressions! This passive was never intended to take up residence in my main system, but I’m beginning to think a higher quality passive unit may indeed be a good fit. As to the phono preamp, I would actually prefer to used a tubed unit if possible. I appreciate you taking the time to discuss the details of these things. Clio gave me a contact email for getting information about products, which is outside the scope of this thread. I will continue to evaluate this passive in my system for awhile to get a handle on its strengths and weaknesses. It is sounding quite nice. Maybe it was revealing a bright recording that the preamp was taming..? Anyway, I’ll keep at it. Thank you again