I recall that in a thread here a while back Kevin Deal of Upscale Audio also mentioned very emphatically that 6SN7s are often microphonic.
FWIW, though, during the approximately seven years in which I owned a VAC Renaissance 70/70 MkIII, which uses four of those tubes, at various times I used a total of about 20 of them. All of them were the GTB version, with the majority being NOS tubes of various makes from the 1950s and 1960s, and the rest being current production. None were microphonic initially, as determined by lightly tapping on them with a pencil eraser. Two of them eventually became severely microphonic, however.
Best regards,
-- Al
|
Roger and George,
Thanks for the insights into the 6SN7 tubes in preamps. I have a tube preamp that uses 4 of these tubes, along with a rectifier, and have upgraded from NOS Sylvania and GE tubes to both the Psvane CV181-T and the Shuguang CV 181-z tubes. The new tubes are simply remarkable, far better than the NOS tubes (other than a handful of the Holy Grail tubes) and with good longevity. I will admit that they are microphonic. Thanks again for your information and furthermore for you taking the time to participate in this forum. Your insights are most enlightening. |
That’s interesting information concerning the 6SN7 tube. My power amps use them (NOS 1948 Raytheons) as cathode followers and the 6CG7 as a pair as input tubes. Gain is probably lower there, but just try the finger nail gently flick test to see what happens. You’ll soon know if you have a microphonic, oh sorry, euphonic tube. https://forum.audiogon.com/posts/1661211I'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. Cheers George |
|
@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? |
and yes customer brought his Bob Carver Phase 400 in and wanted to hear it with Litz wire speaker cables into ADS 2030.....
kabooom......
in all fairness, we had a service department that saw a lot of fried Phase 400, you could look crosseyed at them, or so it seemed.... |
I have a garden hose MIT PC that is a PITA and made my Ayre amp sound worse...IMHO I think a well executed coldwelded moulded cord on quality Belden wire is in many cases superior to glam cables that put a ton of physical loading on connections ( internal to the connector and then into the IDc socket.....and to answer RM ? heat is bad, it is V or I converted, which means NOT good.
taking offers on the garden hose...ha
|
That's interesting information concerning the 6SN7 tube. My power amps use them (NOS 1948 Raytheons) as cathode followers and the 6CG7 as a pair as input tubes.
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. |
Roger, "What exactly is A-B-A?"
I've seen multiple comparisons where some/many were prepared to offer conclusions after a single switch from an original component (A) to something different (B). For several reasons I don't feel that is meaningful without at least going back once to the original. I also thought that was a standardized label but apparently not.
|
I'm another who has compared garden hose sized power cables to more modest but appropriately sized "stock" cables and found that both work fine with no audible differences. I do use a relatively gigantic PS Audio AC cable for a REL sub, but that's simply to impress people although no people have yet to be impressed...still...it wasn't expensive since it was "previously owned"...gotta say it looks cool...maybe thickness isn't so important after all (really? you're thinking THAT?). |
@prof, I'm sure Roger would take this into account, but keep in mind that since the CJ Premier 12 and the Eico HF81 are both tube amps and have output transformers, they should not be operated unloaded while they are being provided with a signal. So a suitable switchbox would apply load resistors to whichever amp is not selected.
Best regards,
-- Al
|
@krelldreams
Roger asked for specs... the only spec I know of is “1.2k” hand written on the bottom of the case. This was only a test anyway since I’d need more than the single input this one provides. I was not aware that Music Reference made passive devices (?).
I am considering both tubed and solid state phono preamps. Any design parameters that I should be paying attention to? Any designs to avoid? I currently only need one for a high-output MC cartridge (MM gain and loading), but I plan on trying other cartridges in time as well. I’m not opposed to getting a step up device if a cartridge I get in the future needs one.
BTW, i looked up the Axiom. If you have an ohm meter just connect it to the input jack and output jack and get some numbers. Non of them are good for long runs as we all know. If yours is 1.2 K ohms thats a rather low number unless the source is much lower. For you preamp you need to focus on S/N ratio and RIAA accuracy and distortion which should be nill. If you find a measured review I will look at it. You want at east 60-70 dB signal to noise ratio at the output of YOUR cartridge. We might build a few phono preamps on special order. The one I have developed for Clio has is all tube start to finish, 3 gains, 12 loadings, tape EQ available (he likes 15 ips tape). It uses only 4 tubes which I am rather proud of as most will use more and give you more trouble. I tried a FET front end some years ago and just did not like it. A Low noise FET is about the same noise as a SLN 6922, so there is no noise advantage there. You can get the lowest noise with transformer inputs, but then you have to deal with placement issure and the sound of the transformers. |
@ramtubes
You’re gonna hate me: My amps are Conrad Johnson Premier 12 monoblocks and an old Eico HF81.
BTW, since you asked about hearing "the other side" for power cords:
I was cured of power-cord-fever early on. I had been given a selection of Shunyata power cords to try, from their least expensive to very expensive. I didn’t think I heard any difference between the less expensive Shunyata cables and my 15 dollar power cable (On CD players, etc). But I thought the most expensive cable seemed to obviously change the sound. (Darker, smoother, more lush). To double-check I had a pal help me do a blind test between that cable and the 15 dollar cable. Once I didn’t know which cable was being used, all the "obvious" sonic differences I thought I was hearing vanished and I couldn’t tell them apart. Saved a bunch of money there! I haven’t worried about pricey cables since. (I’ve gone on to blind test other components, sometime identifying differences, sometimes not).
|
@prof
Actually, the talk of switchers raises another question I'd like to direct to Robert:
I have more than one amp I like to use for my system. It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers. (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp. Depending on which amp I wanted to use I'd just flip a switch.
At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.
Would you say a fully transparent switcher of the type I'm describing could be built?
Yes we have one, can make you one with a volume control to balance the gain of the two amps so they play the same loudnes. They, God willing, you flip back and forth, on the same speaker please, and hear of not hear the differences between the two amps. This is exactly what we are doing. Then you can invite your friends over and really have some fun. You will likely find what we have found.. Some amps sound very similar with differences too small to be sure they are real and some amps let you know pretty quickly what they are up to. We find good correlations with measurements. What are your two amps. |
@cardiffkook
Roger said.... I put the proper cord on my RM-9 but now people want me to put an IEC on there so they can use theirs. I did opimize but thats not good enough for the PC and fuse people. May I also offer that a captive cord has one less pair of connections Cardiff said.
That is what I suspected you would say. I have tested expensive upgraded power cords in my system and never noticed any improvement or difference. I notice large differences between amps, preamps, cartridges, cartridge loading and even in minor changes of speaker toe in. But in my system, I have yet to hear any difference between pc's. I am not saying there are no differences, just that I haven’t heard any so far in my system, compared to the cord included by the manufacturer. I think we need to hear more from the people like Cardiff who have tried powercords and not heard any difference. I will allow it because we have heard quite enough from the pro side, too much. Lets try to balance the issue. Lets give voice to those, like Cardiff, who can clearly dissern difference in his system. Anyone who has bought a power cord and owns an SPL meter, or oscilloscope or any measurement equipment is welcome to report their findings. I have reported mine. Anyone who has spent over $100 on cables and has no SPL meter had better go get one. :) |
@bifwynne
Not sure what you feel is deficient with the ARC Ref 150SE specs. If you care to elaborate, please do Thanks for not getting at me since you own these amps. All I am saying is that Bill was on a mad quest for low distortion and high damping and achieved that in the one amp I called out for that. My only negative was its complexity. See if you can find that post. What I feel is deficient is exactly what JA thinks. Somtimes us folks do agree. https://www.stereophile.com/content/audio-research-reference-150-power-amplifier-measurements. What interesting to me is that most audiophiles agree with each other by disagreeing with the technical people. It is still a mystery to me why people without technical knowledge want to disagree with technical people who are making this stuff (for better or worse). Sometimes I feel like im just fueling the fire. JA does me a great favor when he tests an amp, then I dont have to. I have 400 pages of test notes on 200 amps and preamps that I have measured over the past 35 years. Testing an amp is a laborious task if you really want to get into whats going on. For you and everyone out there. There are things going on in certain combinations of amps and speakers that cannot be easily predicted. However these effects are rarely present in a good amp with good performance measurements. I have tricks that go beyond what JA does. For instance I put a 0.1 uf cap (similar to some speaker cables) across the output of a big Adcom amp while was on the bench and luckily connected to an AC Line amp meter. When i touched the cap against the output terminals the 10 amp meter pegged and i quickly disconnected the cap. I just holding it. Didnt get hot though 1200 watts was going somewhere and that somewhere was the transistors. I know some people have unknown Birdies going on in there system. Birdies are brief supersonic oscillations that occurr on specific parts of the wave at specific levels. If you drive a simple woofer directly that is the easiest way to see them and they sound like clipping but you are not clipping. I have personally, in my own store in the 1980s, watched a BIG Levinson ampifier smoke when connected to a high end speaker cable that had some parameter (perhaps capacitance) that the amp didnt like. It just sat there as little trails of smoke came out, and frankly I was amused. I know im off topic but... motto is. Just because an amp passes the 2 uF load test (somewhat standard) does not mean it is stable into smaller capacitances that might be present in many cables. Whether you like lamp cord or not, It is the proper constructin for a speaker cable. Just not exotic enough for most. Hey man, its just wire. Anyone else smoked and amp with a speaker cable? |
@pryso That is a simple A-B is not adequate, even though you may find differences. I believe at a minimum you need to have A-B-A.
What exactly is A-B-A? we just go back an forth as desired. All connections are cleaned with De-oix from the start. |
whitestix
I recall you saying at Burning Amp a year ago that you did not like 6SN7 tubes in preamps. I have a preamp that uses these tubes and it is the best I have ever heard in my system. I have a friend that used these in his fully glitzed out Supratek Cabernet Dual preamp. http://www.supratek.com.au/uploads/1/2/2/5/122515010/published/corttop2.jpg?1539764225An he thought the world of them, till I went to hear what he was on about, as soon as I heard it, I said "that euphonics you say your hearing, I’ll show what it is, stop the cd and leave the volume where it is" I sat him down in the listening seat and I gently taped the chassis of the preamp and there was a nice solid loud "donk donk" out of the speakers. Your hearing "microphonics not euphonics" I said to him, then I very gently taped the actual tubes with my finger nail, and it was even louder with added "tinkle" to the "donk donk". Say no more. Cheers George |
@whitestix
Roger,
I recall you saying at Burning Amp a year ago that you did not like 6SN7 tubes in preamps. I have a preamp that uses these tubes and it is the best I have ever heard in my system. What is the problem with these tubes from a designer's standpoint? Thank you.
Have a look at the most recent BA video where i discuss the tube. I point out where the mu starts falling off, its 5 or 10 ma. but have a look for yourself. Id like everybody to look at whatever suggestion applies to them. So look it up.
As long as you can get ones that dont make noise or ring much when you tap them then you are ok. In my experience those are hard to find. Remember the 6SL7 was made for audio.The 6SN7 was made for black and white TV and was never, to my knowledge, used in the audio chain. When factories make a tube they pay attention mostly to the characterestics the tube was designed for, again not for audio, therefore they cared not about noise of microphonics. WIth 6SL7s they cared plenty.
My guess is that people use 6SN7s simply because they have the right gain, just by luck. BTW, the 6CG7. 6FQ7, 6GU7 was the 9 pin replacement for the 6SN7. Much easier to find. more modern construction. How do people like those?
YOU have to keep in mind the train has been a rolling for a long time on the 6SN7 for audio so it had a good hand on that tube for no reason technically. It also might be that this tube was just lying around everywhere with new old stock for days. People used to throw them away because after B&W televsion was replaced by color that tube was replaced by the 6FQ7... right away. |
@lemonhaze
Hi Roger,Am I glad I found this helpful thread. I have a Mark Levinson 23.5 amp that hums.The hum is loud and stays constant in amplitude regardless of the position of the volume control. I am driving it with an Aikido linestage that I built and which from driving various power amps I know to be quiet. I tried lifting the earth leg first on the line amp and then on the power amp but hum stubbornly remains. I bought the amp used. I realise that it is quite ancient and probably needs to be re-capped. I took a look inside and it appears somewhat daunting.
Has anyone suggested putting shorting plugs into the inputs of the amp. That is the true test. If the amp hums through the speakers just as loudly then it off to the shop. Nothing is lower noise than shorting plugs :) Quality amps, like yours can keep their caps for 40 years if it runs cool enough to keep your hand on continuously. Most re-capping is performed by the shotgun method. They just do them all rather than find out whats needed. Perhaps thats not bad, but many times caps arent even the problem and what they put in may not last as long. Re capping has become way overdone. |
I probably should have put this in quotes from one of bdp24's posts to eliminate any confusion: Roger Modjeski (@ramtubes) prefers the 6DJ8 for pre-amp use, but I don’t
know that he currently offers a phono amp. Roger or clio09? That was what I was responding to. In another post bdp24 did mention Roger building a passive for you. As I mentioned in my last post the Pot in the Box passive attenuator is available. The design is very simple using a Noble pot that is laser
trimmed, thick film, discrete steps. They are the same extremely high
quality Noble pots used on the Audio Research SP-6 and the Beveridge
RM-1 (which I own). Typically these are built with two inputs with a selector switch. The front switch also has a mute position (middle position). If you are interested in some specs:
Input Impedance: 50K Ohms Output Impedance: 0 - 25K Ohms Frequency Response: DC - 100K Hz The RM-4 was offered in two formats. The first a pre preamplifier, better known as a moving coil head amp for MC cartridges. Then there is the RM-4+ that adds an RIAA circuit, with optional attenuator and inputs for other sources. We have a couple of these lying around the shop. IIRC correctly one has 2 inputs and the other 6, both have an attenuator and input selector switch. You can send an email to tubeaudiostore@gmail.com if interested. |
@ieales
I'd be curious if trained listeners can reliably detect the sound of the switcher
Trained listeners have found the switcher to be transparent. Sounds like in your current setup the listener does not know which he is hearing at the moment? We could certainly go to that. With the results we are getting the difference is easy to pick up on. |
@clio09. I believe bdp24 was suggesting I consider having Roger build me a passive (for switching and level control), not a phono preamp. In addition to an input for phono, I’d like to have at least two other inputs, and preferably two outputs as well.
I searched RM4+ and found only RM4, which appears to be a MC phono preamp only (?). If there is such a thing as a phono preamp which adds a couple of aux inputs for other sources, and a level control, I’m all ears. I’m not familiar with the “pot in the box”. Would you provide some more details as to its design?
Also, in your opinion, from a designer’s standpoint, what are some some things to look for, and to avoid in choosing a quality phono preamp? Thank you.
|
@bdp24 - technically no, Roger does not offer a new production phono preamp (although we have some unique RM 4+ units lying around that in addition to phono include a volume control and inputs for other sources as well). I have a tape head/phono preamp that he designed in my system right now and which we showed at a SFAS meeting a few months back. It is a 2 box unit with separate power supply. It’s not an easy build and getting it mass produced will be tough, but if someone really wants one built to order, just phono only, and is willing to wait while it is built they can email Roger or I at tubeaudiostore@gmail.com to discuss.
Pot in the box passive preamps can still be made to order. It’s an easy build and Roger has plenty of the really nice Noble pots available that he likes. |
@bdp24.
I’m thinking that may be exactly the avenue I’d like to explore further. I’m looking at phono preamp options as we speak. I have a very simple passive device, which I did try, but didn’t care for. I am very willing to try other passives though, since the one I have was purchased to provide level control for our kitchen system, where I was using a 1960s HH Scott tube power amp.
The unit is a Luminous Audio Axiom. When I ordered it they asked what amp it would be used with so they could make one to work specifically with That amp. It is entirely possible that it is a mismatch with my primary amplifier.
Roger asked for specs... the only spec I know of is “1.2k” hand written on the bottom of the case. This was only a test anyway since I’d need more than the single input this one provides. I was not aware that Music Reference made passive devices (?).
I am considering both tubed and solid state phono preamps. Any design parameters that I should be paying attention to? Any designs to avoid? I currently only need one for a high-output MC cartridge (MM gain and loading), but I plan on trying other cartridges in time as well. I’m not opposed to getting a step up device if a cartridge I get in the future needs one.
Thanks again for the advice!
|
@krelldreams, if LPs are your main source and focus, one option is to buy as good a phono stage as you have the dough for, along with a relatively inexpensive passive pre. Passives work better in some situations than others, having to do with source gain, output voltage and impedance, along with power amp input sensitivity and impedance. Roger is a proponent of passive pre's, and will make you one. That will leave you more $ for a phono stage. |
@bdp24. All understood. Thanks. I guess the trick is to figure out what’s causing it, why it’s happening, and how to fix it. That’s what I’m hoping to learn more about.
I believe that my speakers, my amplifier, and my vinyl playback system are better able to communicate the music to me than my preamplifier is. I wouldn’t say it’s a “bad” preamp. I just have a sense that it’s not as “good” as the rest of the chain, and is therefore frosting my window, so to speak.
I initially joined this conversation to discuss options for using a simpler circuit vacuum tube amplifier in my system, but as I thought more about it, and followed the thread, it occurred to me that my preamplifier may need to be improved before I venture into replacing the amp.
It’s helpful to read the opinions and experiences of others, and it’s very valuable to have the perspective of successful component designers (Roger, Ralph, etc.). I appreciate all the contributions (except those added by the trolls... occasionally entertaining, but useless here).
I realize Roger is focused on the power amplifier, but he has created well-regarded preamplifiers as well. Ralph currently offers both. They have figured out the “What, Why, & How”. |
@krelldreams, the "cleaning of a window" is the transparency I was speaking of above. It’s the opposite of the veiled, opaque, translucent sound (a layer of "scrim", as J. Gordon Holt called it) you are trying to rise above. Transparency can and has been achieved via both tubes and transistors, being more a matter of the talent of the design engineer. For instance, though Roger uses primarily tubes, he felt transistors would work better as the input stage of his RM-200 power amp to achieve the performance he was after. |
Clio09
@ct0517 - thanks for the response. With the subs in place are you still running the Quads full range, the using the sub fior 60 Hz and under, or are the Quads completely cutoff at 60 Hz? Hi Clio09 The 57's are full out on the RM10 and in parallel to the subs. The preamp I am using in that room has two direct outputs. One output set going to the L and R 57, the other set going to the L & R sub. The subs are on each side of the listening couch, the opposite room side to the 57's. The Quads are seven feet from the front wall. So they are about a third of the way into the room. I realize that the way I have set up the Quads (see virtual system pics) and the subs is, well, unorthodox. But that is just one of the aspects of a dedicated room, that allows you to manipulate speaker placement, and affect the way the speaker output and the room gel. The hell with aesthetics. Hey, anyone with Quad 57's isn't into aesthetics anyway - 8^0. Room A is my main room, it pressurizes easily due to its shape and the speakers used in there; but Room B is a better room for entertaining due to its size. It's been a lot of fun when people visit and if any are interested in audio, watching them get a grasp that the Quad 57 is actually a speaker. Equally entertaining is when I tell them there are two subs in the room and to tell me where they are as music with a lot of bass plays. They start looking over at the 57's across the room, looking in the corners nearby. When I tell them they are on each side of the couch they are sitting on, one right next to them on the left - they are in disbelief. Cheers |
@bdp24 .. I had an older CJ preamp, a PV-8, which sounded as you describe. I replaced that with this one, a Rogue Perseus Magnum. It improved on the sound I was getting from the PV-8 in some areas, but I also felt like there was something missing when playing LPs. I didn’t realize it at the time, but discovered that the Rogue uses a ss phono stage, rather than tube... the tubes were only in the linestage. I don’t know if that was the difference in the sound, or some other area of its performance. The Rogue sounded a bit clearer and had better sounding bass, but after I got used to that improvement, I sensed that the LP playback was a bit veiled. When I tried the inexpensive phono preamp, a schiit mani, there was an obvious improvement in every parameter... like the cleaning of a window to the sound. I want more of that ;) |
Thanks for answering me. I noticed that the continuous bias VAC 200IQ sounds better than the manual bias predecessor Phi-200. The improvement is claimed on the continuous bias. I also own a backup amp, the 70 watt EAR 890 which runs really hot in Class A with autobias. It is not sonically in the VAC ballpark. It doesn’t control 3-12" woofers in my main system with 2.8 ohm low impedance but sounds fine in my second system controlling 3-10" woofers with a 3.7 ohm low impedance.
I now remember my own experiences with an ARC SP-14 preamp where the central cap melted in the middle of the circuit board and the need to replace output tubes after maybe 1000-1500 hours in a pair of Classic 60s. That’s also what worries me about the VAC 200IQ as they get 100w 8 ohms out of a pair of KT88s. Based on your lecture, it appears they are being driven too hard. The worst tube life experience I’ve had were the Dynaco Mark IIIs. 9 months and I had to replace the output tubes-bad design. |
@krelldreams, Conrad-Johnson uses the 12AU7 in their pre-amps, so I’ll guess that’s what you have. CJ products are considered to have a "warmer" sonic character than those of other companies. Some like and want that in their system, others want a different sound from their electronics. The 12AX7 and 12AT7 are used by many other designers, both of them by Keith Herron in his well-regarded VTPH-2 phono stage. I have no doubt that unit would provide a considerable improvement over the C-J, with a more "modern" (less colored---"added" warmth is a coloration, like a filter on a camera lens, more transparent and detailed) tube sound. Roger Modjeski (@ramtubes) prefers the 6DJ8 for pre-amp use, but I don’t know that he currently offers a phono amp. Roger or clio09? |
@bdp24, well that makes more sense. We are not crossing over the Quad in the test set up. However, in our respective RM-3s both Roger and I use 4th order Linkwitz/Riley crossovers, 24 dB slope cut at 100 Hz for high and low pass. Roger also adds some EQ to the low pass board that I believe he explained here or perhaps in another thread. In any event I have used the Quads with the RM-3 and my bass array in a biamp set up and like that arrangement, which I also do with my modified Acoustats. I don't run the satellites full range.
|
@ramtubes. Thank you for your reply to my questions.
You asked: “If you have a good preamp, why change?”. I’ll list a few things that have me looking elsewhere.
1.) I bought this preamp new, and after about two years it developed an issue. Every few times I switched sources, the left channel would fail to output sound. After cycling the selector the sound would return to normal. I called the manufacturer for advice. They told me to spray the switch with contact cleaner, which I thought shouldn’t be necessary for a two year old unit, but I did as they suggested. While it was open, I noticed that there was a screw missing from the vertical board that the selector switch was attached to. When I rotated the switch, the board moved around. I installed a screw in the corner of the board where it had been missing, and it no longer moved when I rotated the switch knob. That seems to have solved the problem, but made me wonder what else could have been overlooked.
2.) I recently bought an inexpensive, but well-reviewed phono preamp for another system. I decided to see how this stand alone phono pre compared to the built-in phono stage of my main preamp. The inexpensive phono preamp, through the tube linestage of my main preamp, sounded noticeably better. I asked the manufacturer, as diplomatically as possible, why this might be. They told me that the tube line section of the preamp is much better than the built in ss phono stage. Why include a phono stage that you know is inferior to the rest of the unit?
3.) I’ve read that the 12au7 is not the best tube to use in a preamp circuit. My preamp uses all 12au7 tubes (4 of them), and I’d like to try something that is designed around a different tube type.
4.) This preamp is made by one of the manufacturers whose amplifiers left you “not impressed”.
I like the way my system sounds, but for the reasons listed above, I’m feeling like replacing this preamp could allow the whole system to sound better... especially after the surprising phono preamp experiment. A system can only be as good as its weakest link, right? |
Oops, clio09, I meant to say ct0517 above. I keep conflating you two! |
Roger,
I recall you saying at Burning Amp a year ago that you did not like 6SN7 tubes in preamps. I have a preamp that uses these tubes and it is the best I have ever heard in my system. What is the problem with these tubes from a designer's standpoint? Thank you. |
@clio09, I suspect (and hope!) that clio09 (and Roger) x/o from the Quads to the subs at 60Hz using high pass (on the Quads) and low pass (on the subs) filters. But the point I want to convey to you is that such a filter (a x/o) is not absolutely at the specified frequency, but rather that frequency is where the x/o slope has dropped by 3dB, I believe it is. The slope can be 6dB/octave (1sr order filter), 12dB (2nd order), 18dB (3rd order), 24dB (4th order), or even steeper. The Quads are not "completely cutoff" at 60Hz, still putting out some sound below 60Hz, at increasingly reduced output as frequency drops due to the filter. |
Actually, the talk of switchers raises another question I'd like to direct to Robert:
I have more than one amp I like to use for my system. It's a minor pain to switch the cables, but it sure would be nice to have a switcher where I could switch between amplifiers to the main stereo speakers. (So interconnects would lead from one output of my preamp to my main amplifiers, and out the other output to a second amp. Depending on which amp I wanted to use I'd just flip a switch.
At one point I did a bit of research and saw some candidates, but for the most part they looked awfully cheap, which left me hesitant.
Would you say a fully transparent switcher of the type I'm describing could be built?
|
We abandoned switchers as they were always audible. So rather than A-B, we had C-D or C-C. We were pretty meticulous in keeping paths as identical and as clean as possible having only the relay contacts as the additional connector.
One thing we never did, but probably should have, is have a simulated load for the off item to maintain thermal characteristics more closely.
I'd be curious if trained listeners can reliably detect the sound of the switcher.
|
@ct0517 - thanks for the response. With the subs in place are you still running the Quads full range, the using the sub fior 60 Hz and under, or are the Quads completely cutoff at 60 Hz?
|
I should have mentioned this, Roger built a very accurate switch box that has a long cable with a button switch on the end. I could sit at the listening position and click the button at various intervals (3 - 5 seconds generally) so going from A>B>A again was very simple. It was also easy to see which amp was in play.
|
Roger, thank you for the reply about cartridge impedance.
|
Hi Roger,
Am I glad I found this helpful thread. I have a Mark Levinson 23.5 amp that hums.The hum is loud and stays constant in amplitude regardless of the position of the volume control. I am driving it with an Aikido linestage that I built and which from driving various power amps I know to be quiet. I tried lifting the earth leg first on the line amp and then on the power amp but hum stubbornly remains.
I bought the amp used. I realise that it is quite ancient and probably needs to be re-capped. I took a look inside and it appears somewhat daunting.
|
+1 for anything Jim B touched !!!!!!
RIP |
A point on comparison testing which I suspect Roger may agree with. It is something I've learned after long years in this hobby.
That is a simple A-B is not adequate, even though you may find differences. I believe at a minimum you need to have A-B-A. That means any connection improvements (cleaning from friction) as well as differences from something new (possibly a detail not heard in A so B seems better, but it becomes diminished in the overall picture) can be accounted for.
|
We need to stay away from the power cord debate here, imo. However, I have stated in other cable threads the subtle, to dramatic differences pcs make, to these ears. Cannot explain why, and I do not really care. But in my listening room, with my equipment and system, and with every one of my familiar recordings, I hear it immediately. I am talking about IEC cords, and those I have replaced with hotwiring. Sorry Roger, I will try and stay on point. Enjoy ! MrD. |
I put the proper cord on my RM-9 but now people want me to put an IEC on there so they can use theirs. I did opimize but thats not good enough for the PC and fuse people. May I also offer that a captive cord has one less pair of connections That is what I suspected you would say. I have tested expensive upgraded power cords in my system and never noticed any improvement or difference. I notice large differences between amps, preamps, cartridges, cartridge loading and even in minor changes of speaker toe in. But in my system, I have yet to hear any difference between pc's. I am not saying there are no differences, just that I haven’t heard any so far in my system, compared to the cord included by the manufacturer. |
@bdp24 - Eric this has truly been an eye opener. Roger can now do A/Bing on any number of amps. Fritz Heilor lives in the area recently donated a pair of speakers to us to use in a biamping experiment (Roger is impressed with his designs), so besides the Quads we have some box speakers available to us as well. The more the merrier I say. However, this listening stuff is really hard. After an hour or so I really needed a break. While some of the differences were not subtle, in may cases you really had to focus to hear the differences, and at least to my ears, there were cases where there was no difference at all.
|
Jim B did Dynaco 400, SAE, GAS and SUMO products. Brilliant guy. |
@ramtubes
Roger, you wrote:
"The difference between Bill Johnson amps and the current products is night and day. I appreciate the simplicity but not so much the performance specs. However specs arent everything. We are finding out some very interesting things on some listening tests. Very hard to get a really good handle on an amp without an A/B and a reference."
Not sure what you feel is deficient with the ARC Ref 150SE specs. If you care to elaborate, please do.
Also, have you ever bench tested the Ref 150 SE or Ref 6 linestage? Further, have you ever A/B'd any current ARC models against other brands that you think highly about?
My speakers are pretty sensitive. Rated at 92db. I can play music (rock or classical) at ear-splitting levels without any apparent sonic congestion. Of course, I can't speak to distortion because I don't have the means or ability to measure those specs.
That said, maybe it really does not matter what I think. There are a million threads where folks tout the attributes of their gear and so I guess everyone has their own favorites.
In any case, I would like to know your reactions if you bench tested or critically listened to any *current" ARC gear.
Keep an eye peeled for my KT-150s. I am also sending some old ARC winged C 6550s that I used on some older ARC amps (roughly 2000 hours on the tubes). I would like to know if they have juice left in them. Also, the 6550s might give you a clue about the tubes specs ARC used to match their tubes for purposes of matching my KT-150s. The KT-150s are da*n expensive tubes.
Regards
BIF
|
