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

Damn, now I REALLY wish I still lived in San Jose!

Regarding the A/B testing, while we began last weekend Roger spent the better part of the week optimizing the set up, no easy task said he. He has now been inviting folks over to listen and I took another stab at it today. This time I brought some go to CDs that I like to use, simple music for the most part, trios and duos, but there are certain things I’ll be listening for. In some cases it’s not even the music, Edgar Meyer’s and Yo Yo Ma’s breathing, Keith Jarrett’s chirping and Gary Peacock’s fretting, The footsteps in Todd Garfinkle’s Jun, the resin on the bow, stuff like that. In other cases it’s the bass, piano, strings, cymbals and high hats.

My session lasted an hour or so and in addition to some unique experiences there were some consistencies across all the music. I originally commented in my notes that the bass produced by the un-modded amp sounded fat but pleasing. However, after more listening, and especially as the bass notes went lower, it was clearly bloated. Not to mention that while the individual bass notes during the solo on Keith Jarret’s version of When I Fall in Love on the modded amp were clearly defined, they were at times smeared on the un-modded amp. In addition, the cymbals and the high hats were slightly muted on the un-modded amp and I could hear a bit of hash as well.

A couple lessons I received in the process. If I didn’t get it before, and I thought I did, I now know for certain the effects a low output impedance amplifier has on a speaker and the resulting sound. In addition, while I can easily hear the effects of an amplifier that clips or has higher amounts of distortion, I think for the first time I could clearly hear the effects of low amounts of IMD as I A/B'ed the amps. Now Roger has invited a few folks from the SFAS to be part of the next group who will participate in the listening test. It will be interesting to hear others impressions and compare notes.

@mrdecibel Roger, this is a GREAT thread, thank you. I agree that all of the nasty comments and bickering should be kept out of this thread ( as well as all threads ). This thread is about learning, as I see it, and I am learning a great deal ( maybe understanding 1 % of it ) And yes, this thread has me thinking about trying tubes again in a power amp. : Going back to damping. In my early years, I owned several ss power amps, a few high powered. Two in particular, were an original Ampzilla, and a factory built Dynaco 400. Having many speakers at the time ( DQ10, AR 3, Klipsch Lascala, just to name a few ), the Dynaco had a bloated, slow, ill defined bass in comparison to the Ampzilla. Both were rated at 200 wpc into 8 ohms ( as I mentioned, these characteristic were also in all of the tube amps I had at the time ). Can you explain if these characteristics between the Amnpzilla and Dyna had anything to do with damping ? Thank you in advance. Enjoy ! MrD

.

Thanks, the nasty comments and bickering are charateristics of the people who make the comments. I ignore most of them. When I look at the threads they get on I can hardly imagine what sort of person they are. I am happy to have little of them here. I guess every forum has its trolls. 

At to your sonic observations. Ampzilla was and is a great amp. I think Jim B designed the Dynaco also, but I am unsure. If you find a schematic I can likely tell. People should know that some designers art is easy to spot, just as an artist’s paintings or sculptures. Bongo Jim, as we called him, was a really great amp designer, great pianist and all round fun guy. I have a picture of him Bacsom King, Mike and Laura Elliott at a BBQ at my home in Santa Barbara many years ago. Ill try to find and post it.

 Sounds like you have had some bass issues. Both SS amps should have good damping, I know Zilla did. Tube amps with poor damping = bloated bass and other problems. Would love for you to hear the listening test we have going on right now with two identical amps except that one has been modified to have 4x damping and 1/4 x distortion. The bass difference, clairty and air on the QUAD 57 are quite apparent. We are doing some serious listening with a very tight setup.

@teo Some Ignorance is so manifold that it is used to commit to attacks so libelous and underhanded... that the person initiating is practically kicked off a given forum. So obvious to all, that there aren’t even words for it.And then that illiteracy and ignorance is paraded about as somehow being informed. That we can all be that dense. Jebus. What a horrific world that would be. So far gone that it can’t even be explained to a given person how far off base and wrongheaded a given comment might be.

I think im being called out but so poetically I can hardly be certain. I think Teo has a better future as Poet and Philosopher. 

His verse is  almost Shakespearian

  https://en.wikipedia.org/wiki/Sonnet_94

Bruce De Plama (Brians brother) often quoted the last of this. 

For sweetest things turn sourest by their deeds;
Lilies that fester smell far worse than weeds.

@atmasphere  A choke is helpful as it can be used to help filter out the 60Hz sawtooth waveform that is part of the rectification process.

Ralph, Im sure you meant to say 120 Hz ripple, not 60 Hz unless you are using half wave power supplies.

Chokes are indeed great things and not found in many amplifiers these days because its just too much trouble for some designers to have them made. I put two in the RM-9 MK II as Ultralinear amps benefit from them greatly. The G2 on an ultralinear has the same ripple as the plate. Where a pentode amp can have additional filtering for the G2.

@cardiff  Here is one nobody seems to have asked yet...

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?

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. When you pull current on a IEC it gets hot, is that good?

Before audiophiles got into power cords most manufacturers went to IEC connectors for no other reason that it makes the amp easier to handle and pack up, not so people could go fooling around with wire. 

Here's a schematic of the ST-120 version (sans values for resistors and capacitors), which is apparently the same schematic as the ST-70 except for resistor sets.
https://drive.google.com/open?id=1IMaAaaWRuIU8v-_OZ3jfrcQCI5a0gpP8 

Nice circuit, simple. The 16 ohm tap is a bit silly and taking the feedback off it can have both good and bad effects. Otherwise, classic Marantz, Heath, Eico, etc.

@bifwynne  Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

Btw, I owe you two quads of KT-150s for matching. The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

We have been awaiting your tubes. Time has passed and we have to get back on the same page as to the specs for current and G2 volts. Better not to wait on these things. Strike while the iron is hot as they say.

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. 

@prof  So my question is: What exactly is happening to cause the type of sonic changes on hears when changing impedance settings for a cartridge?

My know-nothing layman’s hunch is that it’s similar to how speaker impedance interacts with certain tube amps, where some combinations contour the frequency response...and (sorry for the word) damping factor? (The changes in the bass in lower impedances do give me that "lower damping factor in the bass" vibe).

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. 

@andrew 

This has been a great and informative thread. Thank you for sharing your time, knowledge, and insight. I've learned a lot.

A question for you: any further thoughts on ARC's M300 monoblocks? They're a fairly...unique design and perhaps the best evidence of your view that WZJ's ARC designs were often over-complicated. That said, I enjoy them, and they've only blown up a couple times over the years. Any further comment?

(As to your point about the reliability of ARC products, I also have a pair of Ref 600s and pray every time I switch them on that they don't go up in flames.)

One other question: for those of us with super-inefficient speakers like Magnepans, what should we be looking for in an amplifier?

Look at this from Stereophile 

Peak Current (via 1 ohm, 2ms pulse)
8 ohm tap: +13.7A -13.5A
4 ohm tap: +16A
2 ohm tap: +18A
1 ohm tap: +24A
Read more at https://www.stereophile.com/content/audio-research-m300-monoblock-power-amplifier-measurements#8yHmL...
That is an impressive amount of current. The damping factor of 30 and 0.05 THD are impressive also. The full review is good reading. 

A continuing wonder of Audio Research's designs is how they can sound so good with such a complex signal path.
Read more at https://www.stereophile.com/tubepoweramps/585/index.html#REEwDyeIIFoMddwp.99

We can see that current ARC amps are no where close to what Bill achieved. One problem with complexity is fixing it. How bad did yours "blow up" 2 times?

If you can handle the the praying for no smoke and afford the rather short tube life then carry on. For those who cant I would go SS. 

There comes a point when tube amps just get too big. The alternative is get a high power tube amp with transmitting tubes. One pair of moderate sized transmitting tubes, like 833s,  can produce 300-1000 watts. Having a lot of smaller tubes in parallel is not so practical. One pair of 833s is about the same cost as one pair of KT 150s. or other KTs. And they look really cool. Id make you a pair if you wanted. Thats the big tube WAVAC Uses SE but I would go push pull. 

What is the re-tube cost on the 600?

I said I was done in this thread and once again, I lied. I swear this question is in good faith and not meant to challenge or make a point. While looking over at Tungsol's website I saw this;

Engineers and musicians have long debated the question of tube sound versus transistor sound. Conventional methods of frequency response, distortion, and noise measurement have always assumed linear (clean) operation of the test amplifier and have shown that no significant difference exists. In actual operation most amplifiers are often severely overloaded with signal transients. Under this condition there is a major difference in the harmonic distortion of tube and transistor circuits.

http://www.tungsol.com/html/faqs14.html

Please be aware that this paper was not written by any Tungsol engineers who are long gone as well as their factory and any tribal knowledge. 

This is the work of New Sensor who has taken over the name, probably with no resistance, and making the tubes in Russia. Im not saying these are bad tubes but they are not Tung Sol of America.  The KT series apperars to be good and I have tested the 120s and 150s. The data sheet for the 150 is in Tungsol style but not of Tung Sol quality. No plate curves, Gm seem too high. Not informative as in the good old days. I have offered to help them.

Also keep in mind that New Sensor sells to the guitar amp market by 100 to 1. Nothing wrong with that. Thanks to the guitar guys for keeping the demand for tubes going. We audio users are a drop in the bucket. 

That article is from a guitar amp perspective where it’s more common to overdrive. 

I said I was done in this thread and once again, I lied. I swear this question is in good faith and not meant to challenge or make a point. While looking over at Tungsol's website I saw this; 

Engineers and musicians have long debated the question of tube sound versus transistor sound. Conventional methods of frequency response, distortion, and noise measurement have always assumed linear (clean) operation of the test amplifier and have shown that no significant difference exists. In actual operation most amplifiers are often severely overloaded with signal transients. Under this condition there is a major difference in the harmonic distortion of tube and transistor circuits. 

http://www.tungsol.com/html/faqs14.html

RM or RK, there has been this overriding premise (by RM) that most of us have more power and overhead in our amps than we really need. What is your response to the premise above (and everything else in the link provided)? I can find the link if you like, but in one of Charley Hansen's last interviews with Stereophile he stated that after thinking throughout most of his engineering career that tube-o-philes' preferences were largely imagined, he had come around to the thinking that it is in fact extremely difficult to engineer a solid state amp that captures the same magic that a tube amp can have (and in the meantime Charley acknowledged that he had come around to believing that there is in fact a certain tube magic) and that he thought his latest amp design had captured that magic. I only bring up Charley's arguably unrelated "epiphany" because it may or may not be related to the premise of Tungsol that most amps are severely overloaded in actual operation. So what do you say about this? I happen to have 150 watts of glorious tube power (actually more) with my ARC 150SE matched to very efficient and easy to drive loudspeakers-DeVore O/93's-and I have no problems with audible hum and I am very happy with how my system sounds. 

I just want to say thank you Roger. With respect to tube amp output impedance selection, I had never heard that you should “Always use the lowest tap that gives you enough volume without distortion (clipping)”. I have a pair of Kef LS50s in an acoustically treated room (16’ x 11’ x 10’) that I’m driving with a pair of ASL DT200 hurricane mono-blocks (100 watts per channel). I’m not worried about clipping. I immediately tried your suggestion by switching the LS50s from the 8 ohm tap to the 4 ohm tap. And, just like you said, the bass tightened up, so much so that it shifted the tonal balance of the system up. This caused the system to actually sound a little strident. Well, I had used a parametric equalizer to boost frequencies around 10KHz a few decibels to offset the acoustically treated room, I thought. I removed the boost and Voila’, things are noticeably better all the way around.

I have another set of tube mono-blocks that use 4 EL34s each. I think that these are more sonically pure than the Hurricanes but they don’t seem to be able to control the bass on the LS50s to an acceptable level. I can’t wait to try the 4 ohm tap on those. Thanks again for sharing this knowledge with us.

Clio09
I am curious how you settled on the 60 Hz cutoff and what other levels you may have experimented with.

Clio09
atter much experimentation I found the 57's positioned the way they are in my space to be the most room filling and linear top to bottom - down to about 50-55 hz. Still, to get the bottom octave and bass impact (it's a large room) I needed to add subs. I used to have a big HSU set up in nearfield next to me. It was fine as long as you were sitting in one spot. But if one uses the room - walks around, and sits in different spots around the room;  multiple subs are the answer to eliminate the bass nodes. Adding the two 12" Dynaudio subs improved on the single large HSU. Keeping the HSU as a slave would have been interesting, but my son took it. 8^0
The lowest crossover point on the Dynaudio BM12s is 60 hz. So that is where they are set. I have tried higher settings in the past with other subs and felt it interfered with the 57's bass too much. 

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

VAC seems to be doing some good work these days. I have worked on one of their big preamps, it was nice but picked up hum from a power amp 2 feet away. We were surprised.

Yes, we were! Hey Roger. Great thread!
Bill

@ramtubes

You wrote the following regarding ARC:

Im sorry, but you asked. I'm sorry to be so negative about ARC, but I was a dealer for them from 1975 to 1980. If you have not heard about the "pink papers" thats a story in itself. ARC treats dealers with a heavy hammer, large opening order and threats if you do not follow the party line. Bill called us up one day because he heard we were doing A/B comparisons for our customers. He said "stop immediately or I will pull the line"

Of course I respect your technical experience and ARC anecdotes, but let me just weigh in on ARC.  Perhaps I have been crazy lucky, but I have owned ARC gear for quite awhile and my anecdotal experiences are quite different than yours.  

In particular, as far as linestages go, I've owned the Ref 3, Ref 5, Ref 5SE and now currently, the Ref 6.  As far as amps go, I've  owned the VS110, the VS 115, the Ref 150 and now the Ref 150SE.  My CDP is the Ref CD-8 and my phone pre is the PH-8.    

To date, I have had only one problem; namely:  blown bias resisters in my older amps.  Other than that, no other problems whatsoever.  In the case of my Ref 150SE, I am running KT-150s. So far, … fingers crossed, ... no problems with arc'ing or blown bias resisters.

As far as bench tests are concerned JA tested the Ref 150 amp, an earlier version of the Ref 150SE.  Here is his report:    https://www.stereophile.com/content/audio-research-reference-150-power-amplifier

Notably, JA reported that "Fig.1 indicates that the Ref150 has a wide bandwidth, particularly into loads higher than the nominal tap value, which correlates with a well-defined 10kHz squarewave (fig.2). While this graph reveals a small but critically damped overshoot on the leading edges of the waveform, presumably due to an ultrasonic transformer resonance, no ringing is visible."  By comparison, the Ref 75 did not test as well.  And you noted the same in your prior post.  

I can't speak to whether the circuits in my ARC gear are elegantly simplistic or labyrinthically complex .  I am not a EE.  But so far, my gear is holding up pretty well.

As far as SQ is concerned, … no comment.  I have not had an opportunity to A/B ARC gear against any other brands.  But to my untrained ears, my gear seems to sound OK.

Perhaps your views about ARC might change if you road tested some of their current models.  I understand that ARC opted to simplify the circuits in its latest offering, the Ref 160 mono blocks.  Haven't heard them, but it doesn't matter.  I am not going to drop $30K on mono blocks.

Btw, I owe you two quads of KT-150s for matching.  The 3rd party vendor from whom I purchase the tubes didn't match the tubes to ARC spec.

Regards,

Bruce

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?

There is a voltage drop across any power cord that can influence the output power of the amplifier. What is less well understood is that it can affect distortion too. Much depends on the amplifier design of course, but these effects are measurable and no surprise in some cases that they can be heard too.

Question about the effects of different impedance settings and phono cartridges.

The loading is there for the preamp, not the cartridge! I know this sounds counterintuitive but here's how it works:
The cartridge has an inductance and the tone arm cable has a capacitance (along with the input capacitance at the preamp). Together they form a tuned circuit. With a Low Output Moving Coil cartridge, this resonance can be at several MHz. If the preamp is unhappy about Radio Frequency Interference (RFI) at its input, it will affect the sound- the additional distortion will likely make it bright. The loading resistor detunes the resonant circuit and thus prevents the RFI. Problem solved?
The downside is usually two things: 1st, by loading the cartridge in this manner you are causing it to do more work. The energy has to come from somewhere and that means the cantilever will be more stiff- less able to track higher frequencies! The second problem is that (generally speaking) a preamp that requires loading to sound right probably also has stability issues, usually because the designer hasn't sorted out the facts in the 2nd paragraph below your quote. This instability often results in excess ticks and pops that **actually would not be audible were the preamp actually stable**!

This latter fact comes as a surprise to many people, but when you are exposed to a stable phono circuit, it is very relaxing to not be hearing so many ticks and pops. This has nothing to do with bandwidth BTW. For more on this seehttp://www.hagtech.com/loading.htmlandhttps://www.whatsbestforum.com/threads/cartridge-loading-a-misnomer.15077/

What are the symptoms of the supply caps being on the way out and at what general age do they become seriously at risk?

Sometimes caps can last a very long time, depending how hot they got how close to the limit the voltage was ect ect.
Look for bulging.
http://embedonix.com/wp-content/uploads/2015/09/good_bad_ugly_capacitors.jpg
Top Leakage
http://www.southseascave.com/wp-content/uploads/2014/12/IMG_1820sml.jpg
Base leakage
http://protectyourpower.com.au/wp-content/uploads/2016/05/Brisbane-Airport-UPS-Call-1.jpg

Cheers George

I have an amp maintenance question, if I may.

I favour amplifiers that are either Class A or at least have very rugged power supply capacity (I use several Classe DR3 VHC, a Belles A, a Rowland 5).  What are the symptoms of the supply caps being on the way out and at what general age do they become seriously at risk?  The Classe amps, for instance, are hitting 30 years old now.



Got into these way back to be able to drive 1 ohm speakers but stuck with them after speaker changes as I love the sound.

@ct0517 - nice set up. I sometimes use my RM-10 with my ESL 57s in biamp set up. The Class AB amp I use for the bottom is a Luxman M-02. I use the Beveridge RM-3 (no remote) to crossover at 100 Hz, 4th order crossovers for both high and low pass. Rather than two woofers I use four in an asymmetrical array. I am curious how you settled on the 60 Hz cutoff and what other levels you may have experimented with.

Roger
this is related to a question you raised in past post on subs and remote controls.

ramtubes - The amp is any old SS 100+ watt amplifier. Currently a nothing special Denon. The woofer level control is on the crossover.

This solves a lot of problems with powered subs. Unless they have a remote (do they now?) it is difficult to adjust the level for different CDs,

Firstly I Agree, especially if someones subs are setup in typical fashion across the room with the main speakers.

My solution
I am using for the last two years, two Dynaudio BM12s studio subs in Room B with my Wayne Picquet restored Quad 57's. They (BM12s) are one example of a solution with a credit card sized remote control that handles db and crossover levels, phase, and allows you to save 4 settings. Classical is typically a higher DB setting then compressed popular music.
The BM12s are handling 60 hz and down and the RM10 has full control of the 57's. The subs come with their own Class A/B amps and on the boxes are heat sinks. Mine are now positioned on either side of the listening couch. This allows for the db levels to be set the lowest, phase 180. The sub amps heat sinks don't even get warm. Very little vibration from the boxes.

************

We last conversed about a year ago when I inquired about slope cards for an RM3 that I own. I was thinking about a project to bi-amp my Matrix 800's at the time.

btw - A nice surprise coming back here for winter conversations to find you have the most popular thread on Audiogon. 8^)

Cheers Chris

@tomic601, Oops, I had you confused with clio09! He DOES have a professional relationship with Roger. I’ll put the Decca info up in a thread, for all to see, hopefully tomorrow---Eric.

as for factorials for decimals, try the gamma function

the gamma ray is also effective for trolls who add ZERO

 @bdp24 I would love to see the Decca notes as well !

  and I might add that the 5A rated power cord is reasonably priced on the RAM tubes website.

@ eric - no mentoring relationship w RM other than this thread which I am greatly enjoying....and learning...the Analog circuits book arrived today and I am diving into it with a glass of Malbec and some Peter Gabriel on the box ( shock the monkey ? ) I think my trajectory will include burning amp 2019 IF they will have me. Just about to order the scope, R Vandersteen who I do consider a mentor recommended a used Tektronix TDS 220... but Amazon has a new w warranty Tektronix for not much more than the hawks at ebay want used..

big fun

QUESTION: Roger (or Ralph?)...

Question about the effects of different impedance settings and phono cartridges.

I’m a newbie with high end turntables (just replaced my old turntable with a much better one). My phono stage is convenient in that it allows easy access to changing the impedance levels from the front panel. I actually enjoy playing with the impedance settings to alter the sound to taste depending on what I want.

Mine is an MC cartridge and I find an impedance setting of 100 Ohm to be just about right in terms of sounding tonally accurate (like my digital source).

I won’t be telling anyone here what they don’t know when I mention that as I set it to higher impedances, the sound gets brighter and more taught (to more "pinched" and less relaxed/natural sounding towards the high end of the impedance settings). And the sound becomes darker (more rolled off in the highs), richer, more spacious and the bass seems to bloom a bit more in size and lose some tightness. I actually often enjoy just dipping down the impedance from the 100 Ohm setting to the 33 Ohm setting, to enjoy the slightly richer sound sometimes.

So my question is: What exactly is happening to cause the type of sonic changes on hears when changing impedance settings for a cartridge?

My know-nothing layman’s hunch is that it’s similar to how speaker impedance interacts with certain tube amps, where some combinations contour the frequency response...and (sorry for the word) damping factor? (The changes in the bass in lower impedances do give me that "lower damping factor in the bass" vibe).

Thanks..

Exclamatory math.

The little under the bridge creatures have caught the scent Roger.

We get requests from folks who want their old RM-9s refurbished. One of the common side requests we get is to put in an IEC inlet in place of the captive power cord, which from Roger’s perspective is more than adequate for the job, of reasonable length, and quite flexible. We try to talk folks out of this as there is just not enough room between the transformer cover and the edge of the frame to add an IEC inlet. In addition, the RM-9 frame makes this task rather difficult as you have to cut into the wood and there is risk of damage if not done properly. So for those who insist we advise them we will chop the stock cord about 6" from the top plate strain relief, attach a male IEC, and finish it off with shrink wrap and the customer gets to choose the power cord of their choice. Now the signal comes from the Romex in the wall, through the designer power cord, then that last 6" through the original stock power cord into the power supply.

However, some may not be aware that Roger does acknowledge a power cord can make a difference in the system. In this case, a power cord that addresses hum caused by having DC on the line, which can be a hard problem to fix. So he designed a power cord rated at 5 amps that removes DC and will quiet troubled transformers.

And I thought the unanswered question was who wants the last piece of pie?

@jdjohn   Any thoughts on kits like this modeled after the Dynaco ST-70?  http://www.tubes4hifi.com/bob.htm#ST70  This isn't a mod or upgrade for stock ST70s, but a kit for building a brand-new amp. Some of the design changes are listed under 'ST70 amplifier features' if you scroll down the page a bit.

Looks good. I like to see the 3 tube driver board. Do they have a schematic?

The original single 7199 tube driver was flawed by tube to tube variations. Some good 7199 would bias up in a region that actually produced a lot of distortion and reduced power. There are many 3 tube drivers. I would like to know more about theirs.

The kit looks good and priced well.

Here's a schematic of the ST-120 version (sans values for resistors and capacitors), which is apparently the same schematic as the ST-70 except for resistor sets.
https://drive.google.com/open?id=1IMaAaaWRuIU8v-_OZ3jfrcQCI5a0gpP8 

The real question left unanswered is what is pi squared factorial? 😳

Hi Ian (Ieales),

Surely you realize that pi squared, rounded off slightly, equals:

3.14 x 3.14 = 9.86

Best regards,
-- Al

π² != 6.28
2π = 6.28

@cardiffkook, I’m sure Roger will get to your question, but in the meantime you should know that he does NOT share your feeling that "the PC is a fundamental part of the electronic device", and does not "optimize the cord for the device in building it." He infact includes NO cord with his power amps! Further, he says his reason for doing so is that everyone has a spare computer power cord laying around ;-) . Anyone wanting a 'better" pc can get a 3’ long 10g Signal Cable one for $59.

@noromance, I respect Roger’s directive to keep this thread focused on amplifier design, and questions about that topic alone. I brought up Harvey Rosenberg and the Decca only in response to tomic601’s (who has a close relationship with Roger, if I'm not mistaken) mention of mentoring. I’m happy to share what Harvey had to say to me about the Decca, so I’ll start another thread dedicated to that subject. Let me find my notes and collect my thoughts, and I’ll lay it on ya! I know you have a Decca or London, and are therefore very interested in what Harvey had to say about them.

Thanks for offering to answer questions!

Here is one nobody seems to have asked yet...

What is the role and importance of significantly upgraded power cords in component design? It seems to me that the PC is a fundamental part of the electronic device and that the manufacturer should optimize the cord for the device in building it. What are your thoughts on the matter as someone who actually builds electronics?

I’m sure you misspoke when you referred to pi-squared. The 6.28 factor you referred to is of course correct, but that is 2 x pi, not pi-squared

Yup- thanks for that. My medication is a bit too powerful today...

It adds better isolation on high frequencies between power supplies.But what do you think does it have any real effect?

What do you think about separate power  supplies between left and right channels for 300B SET amplifier? Does it do a significant difference?

A choke is helpful as it can be used to help filter out the 60Hz sawtooth waveform that is part of the rectification process. They can be quite helpful in that regard, as to do it with resistors and filter caps essentially requires more filter caps and also means a bigger voltage drop in the power supply, where voltage might be at a premium. IOW you can have a fairly low voltage drop across the choke due to a low DC resistance, yet still filter out noise in the supply.

Separate supplies is not a bad idea at all, although in a class A1 SET you shouldn't have a lot of noise in the supply. If you have separate supplies though, you could also have separate chassis for left and right. This would give you the ability to run shorter speaker cables, which is really helpful when working with amps with a higher output impedance such as an SET.

The trick is that when things stereo share a common power supply its possible for them to talk to each other (the term is 'crosstalk') and essentially interact unless great care is taken to deal with the power connections and ground connections correctly.  Otherwise you can increase IM distortion and IM needs to always be kept as low as possible. 

Hello @atmasphere ,

Thank you a lot for your reply.

I know some people like to put chokes between output and drivers B+.
It adds better isolation on high frequencies between power supplies.
But what do you think does it have any real effect?

What do you think about separate power  supplies between left and right channels for 300B SET amplifier? Does it do a significant difference?

Regards,
Alex. 

Roger, this is a GREAT thread, thank you. I agree that all of the nasty comments and bickering should be kept out of this thread ( as well as all threads ). This thread is about learning, as I see it, and I am learning a great deal ( maybe understanding 1 % of it ) And yes, this thread has me thinking about trying tubes again in a power amp. : Going back to damping. In my early years, I owned several ss power amps, a few high powered. Two in particular, were an original Ampzilla, and a factory built Dynaco 400. Having many speakers at the time ( DQ10, AR 3, Klipsch Lascala, just to name a few ), the Dynaco had a bloated, slow, ill defined bass in comparison to the Ampzilla. Both were rated at 200 wpc into 8 ohms ( as I mentioned, these characteristic were also in all of the tube amps I had at the time ). Can you explain if these characteristics between the Amnpzilla and Dyna had anything to do with damping ? Thank you in advance. Enjoy ! MrD. 

Ralph (Atmasphere), thanks for your characteristically very constructive and informative post above. A very minor correction, though, for the record. I’m sure you misspoke when you referred to pi-squared. The 6.28 factor you referred to is of course correct, but that is 2 x pi, not pi-squared.

Thanks again. Best regards,
-- Al

Roger nice job handling Teo. IMO he embodies everything that is wrong in high end audio these days.

Some Ignorance is so manifold that it is used to commit to attacks so libelous and underhanded... that the person initiating is practically kicked off a given forum. So obvious to all, that there aren’t even words for it.

And then that illiteracy and ignorance is paraded about as somehow being informed. That we can all be that dense. Jebus. What a horrific world that would be.

So far gone that it can’t even be explained to a given person how far off base and wrongheaded a given comment might be.

Hi Ralph. Im curious if you use an inverse RIAA network to check your EQ. If so where did you get the values? I built mine from the advice of Peter Moncrieff, Mitch Cotter and Dick Sequerra who were the first to discover that many RIAA EQ curves were off. Of course I used precision parts.

Of course! Its been a really long time and I do not remember where I got the values, but when used I got flat response. FWIW it also plays flat when I cut a lacquer on my lathe and play it back on the preamp. The Westerex has pretty tight curves in this regard; the electronics are matched to the cutter head.

5. What is the best and cost effective way to separate power supply between output tube B+ and driver tube B+?

@alexberger

You can of course make sure that the timing constants in the power supply are low enough that the driver and output section can’t talk to each other. Here’s the math:

F = 1/RC times Pi squared.

That formula results in some hard to work with numbers, since F is frequency, R is resistance and C is capacitance in Farads, which is really inconvenient. So I usually useF=1,000,000/RC * 6.28
(6.28 being Pi squared).  This formula results in F in cycles per second (Hertz), R in ohms and C in uf (microfarads), which is more real-world.


In your power supply, C is the power supply bypass capacitor, which is probably an electrolytic device. R is the resistor between the power tube B+ power supply filter cap and the filter cap for the driver. The thing is, there will be a certain amount of current that the 6SN7 needs, so you have to make sure the resistor is large enough wattage to survive that.

For that you need Ohm’s Law which is R=V/I


R is resistance in ohms, V is volts, I is current (C was taken already so I is the convention for current).


To calculate wattage (of the resistor) W=V x I


So for example, if you use a 40uf filter cap, and the driver tube is drawing 9mA (0.009amps) between the two sections, then for the power supply to have a cutoff at 0.5Hz the resistor value will be 8,000 ohms. There will be a 72 volt drop across the resistor and it should be a 2 watt device.


Now the trick here is to make sure that the coupling capacitor has a cutoff frequency higher than the power supply cutoff! Otherwise, the circuit can become unstable, prone to ’motorboating’ (a low frequency oscillation) and IMD will be higher. Use the same formula to calculate the value of the coupling capacitor; R will the resistor in the grid circuit of the power tube that the capacitor is driving. To get 0 phase shift at 20Hz, the coupling cap should go 10 octaves lower, or to 2 Hz; our power supply cutoff is safely below that (although it would not hurt to go an octave lower by doubling the value of the filter capacitance). The problem here is that SET output transformers often don’t have good low frequency bandwidth, and the 300b is right on the cusp of where 20-20Hz is actually sort of possible with a good output transformer. Even though your speaker may not go that low, its a good idea to get as much bandwidth as you can to preserve phase relationships that the ear uses to detect soundstage width and depth. So get a good output transformer.


If the manufacturer has issues with low frequencies saturating the transformer, you can reduce the value of the coupling capacitor, but I would be hesitant to do much of that as phase shift in the bass robs the amp of perceived bass impact, even though its flat on the bench.


A less cost effective way to do the power supply for the driver is to use a separate power transformer and power supply for it. In this way no matter what signal condition exists in the output section, no amount of noise in the power supply of the output tube (such as a general voltage sag) can talk to the driver section. However in SETs, this usually isn’t a problem unless you run the power tube in class A2 or class A3. The latter classes of operation can draw more power from the power supply as output power is increased; class A1 does not do that.

Hello @ramtubes,

I have a DIY 300B SET.
Input tubes are 6sn7, driver are 6f6 in triod mode.
I use coupling capacitors (Duelund Custom Cu) between input, driver and output tubes.
I use 5K output transformer James Audio.
My speakers Altec 604E ~100dB sensitivity.

I have a number of questions:
1. What is optimal transformer load for 300B? When I don't need extra power with my very sensitive speakers.
2. What do you prefer for inter-stage coupling, transformers or capacitors?
3. I'm thinking to upgrade to Hashimoto output transformers? Do you have experience with Hashimoto?
4. When you design your amplifiers, how do you calculate optimal idle current for input and driver tube stage?
In the past, I increased idle current in both, input and driver tube. And in both cases it gave me a significant improvement in sound.
For example, I increased current in 6sn7 from 4.2mA to 5mA. And I can to increase it let say to 5.5mA. How do I know what is optimal or good enough?
5. What is the best and cost effective way to separate power supply between output tube B+ and driver tube B+?

Regards,
Alex.

@teo_audio  Please keep posting. Your contributions are valued.

@grannyring  Bill, an Excellent post. Well said, Sir.

@teo_audio actually made some reasoned and reasonable comments. Why attack him and his business here? Seriously,  I am reading far to many words stating others are “dumb, morons, snake oil marketers, build poor gear” etc... Goodness it’s time to be more humble and professional about other people’s business, hard work and achievements in life.

Others have areas of expertise and experience we can all learn from. I learned long ago when I feel most everyone has it wrong and only I have the answers and truth, then it’s time for me step back and really look at my myself.

This has the potential of being one of the best threads I have read here on Agon in years. Great posts by the OP and others. I simply ask for us to please stop demeaning and name calling builders, business, posters and people we may disagree with. Plenty of very smart and experienced people like the products from these other companies and can appreciate the sonic differences that are found in these pieces of gear. Many appreciate the sonic differences and fine tuning that can be found in parts, wire, and even fuses.

What some call snake oil might, just might, be a blind spot for the person judging. No individual knows it all and there are products out there that just plain old do as advertised even though we might not fully understand why........yet!