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In Reply to: RE: Hey Tre! posted by DanK tubes on June 26, 2012 at 13:31:56
A friend of mine built this with the help of Dennis, etc. The component values were all given to him.
I ask Dennis over the phone what the differences were between this circuit and his and he wouldn't really say. He did say that he uses multiple small by pass caps on the cathodes. My friend used only one but he used the right brand and the right size main cathode bypass caps.
Dennis complained that the current was a tiny bit to high in both the driver tube and the output tube and that the voltages were a tiny bit (and I mean a tiny bit) too.....I can't remember, I did take notes, I will have to see if I still have them.....well, high or low.
What he did say lead me to believe that it was very (my word) close.
When push came to shove Dennis said that 1" of the wrong wire will ruin the whole amplifier???!!!
I had it here for a few days. I circuit traced it and drew these schematics myself.
It's sounded awful.
On the test bench the PS was unstable even when not playing and the HF rolled off starting at 11kHz. Dennis has said (here on the AA) that his amp starts to roll off at 15kHz. He said the tubes he uses have less Miller capacitance than NOS. Dennis said (here on the AA) that his amps will start to roll off at 11kHz with Sylvania NOS 2a3's and 9kHz with RCA.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Got quite a few mistakes in there, Guy.No wonder you don't think it works-- I don't think THIS schematic does, either!
I hope nobody built this thing-- what you have here is a clock-radio amp.
There are wrong parts values and entire sections are left out... or the proper connections into circuits are in the wrong places.
Voltages are also off.
Hey! I don't mean to be mean here-- part of my technology is proprietary-- it isn't a freebie, so if you don't have it, it's not your fault.
The operating principles that I have shared and the concepts are what's really valuable anyway.
Good builders will get most of it right without me, although they won't get the entire result, it will be good.
I would refer people to Sound Practices articles on Loftin-White amps. If one studies those enough, he will invent ways to get the desired bandwidth for music.
---Dennis---
Edits: 06/27/12
What do you mean by that?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Here's my original post, and yes I was coached by both J and D as the project was made. And yes, there's what I'll call micro differences, some of which "may" have been improvements....
http://db.audioasylum.com/mhtml/m.html?forum=tubediy&n=153234&highlight=Satan+patiently&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dtubediy%26searchtext%3DSatan%2Bpatiently
I had not "yet" tried multiple by-pass caps, because I didn't have any at the time. I did however make an effort to minimize wire, see the pictures (much less than what Dennis does, I've seen the underside of his amp BTW).
I also had a much lower DCR power trans than Dennis uses, whatever that's worth, and I used dual 5R4GY's instead of one 5U4GB, which Jeff should like. I had custom made filament transformers with a tab for a CT that the R and Ck directly soldered to, from there to ground, (no wire).
Yes the voltage on the 2A3 was a little bit higher than what was "recommended", I didn't think that could "ruin" anything as the 2A3 was still operating UNDER max dissipation. I tore the amps apart 2 years ago or more. Before I did, I changed the driver to a CCS loaded lo mu triode,
instantly cleaner, better. I also changed the PS to "normal" which made other noise go away, but we now know that the original PS was "no good".
Jeff later felt happy to thrash my build, yet thankfully admits having misadvised.
See:
http://db.audioasylum.com/mhtml/m.html?forum=set&n=69636&highlight=grant+handley&r=&search_url=%2Fcgi%2Fsearch.mpl%3Fforum%3Dset%26searchtext%3Dgrant%2Bhandley
Hello GSH,You relied primarily upon me, and I was NOT correct in values and voltages in several areas, as my understanding of the circuit was not as good back then, as it would be today.
We both should disclose the fact that I told you to make the AC cord (ONLY) out of inexpensive Carol 300 VDC or 600 VDC 12 AWG wiring, and the audio out of TCSS and silver wire.
The TCSS never got installed. You wired the amp mostly with the inexpensive 12 AWG Carol, which has a "big wire" (very negative) thick and out-of-time sound to it.
Use of huge Carol 12 AWG hook up wire, in places other than the AC cord, guaranteed poor sound IMHO.
I also had the B+ supply filtering and shunt regulators mis-done, totally my fault back then, as far as obtaining low ripple. I made the same error with Slownlo, and even my own implementations in 2008-09.
You also never sent me a finished schematic of what you made, so that I could comment on voltages, and various obvious errors I would have spotted. IMHO, we BOTH made errors back then.
That a CCS improved things is not surprising at all to me, it was a band aid for numerous implementation and circuit errors. You gave up on the project, before fully informing me of exactly what you built and allowing me to suggest corrections. About two years later, in 2010, I told you quite precisely in what three areas that amp was "boogered", and it certainly was.
Its a shame you have never heard one of Dennis 2A3 amps, to know what performance level is possible. I have, that is what keeps me active.
Live and learn.
Cheers,
Jeff Medwin
Edits: 06/28/12
"The TCSS never got installed. You wired the amp mostly with the inexpensive 12 AWG Carol, which has a "big wire" (very negative) thick and out-of-time sound to it."
Yes, true BUT: the Carol 12g wire was only to the rectifier (yellow and red), and the ground (less than 6" total in one uncut piece from the HV CT
to the input, through the cap terminals. There's no other wire in the circuit, period, except for the lead to the OPT which was paralleled with silver wire. BTW we both know Dennis uses the stock red and yellow leads out of the stock Hammond power transformer to his 5U4GB. That sure isn't TCSS. So, the ONLY real wire "flaw" is the 6" ground, that actually only counts from C2 to the input, which is less than 3".
So the 3" ground wire of heavy copper, was "bad". OK
The difference in the op points is NOT large, as stated, still UNDER max dissipation for the 2A3, and the 7B4 was "close". I don't see how this could dramatically change anything. I don't think the small voltage differences could be "heard", in fact, they could easily blur between "perfect" and what you would call "way off" just with the line voltage changing. So I veto that.
The missing multiple by-pass caps is the largest "flaw" and I admitted that from the word go (see original post)
I also got tired of the hum and installed a Bourns pot, which fixed that.
I'm not really trying to defend or prove anything, just state the what is.
I do believe that the paralleled caps (if done whatever right is) could be an area of improvement for ANY CIRCUIT, which is why I brought it up in my other recent post. I give Dennis direct credit for having pursued this, although I don't have any direct experience with "what exactly" he has done, other than note that he said "it's expensive, and will cost more than the sum of the rest of the parts". With that, it's hard to get moving, expensively, into darkness, to maybe achieve light.
Furthermore, I think a direct coupled SE amp is a good sounding thing.
Perfecting it, is just an interesting set of possibilities.
I and many others may not prefer the 7B4-2A3 to what I or those others are preferring now, but overall improvements in PS, wire and caps are still valid for other circuits, so whatever real findings Dennis can show,
can likely "help" other designs in these areas. I wish this "tone" could be upheld in this discussion.
"There are wrong parts values and entire sections are left out. Voltages are also off."
So....If it's wrong tell us where and how.
This is what you and your friend told my friend to build. If it's wrong it's not the builders fault. He just built what he was told to build.
Entire sections? What do you mean by that?
You amps is a two stage DC 2a3 amp? Correct?
What sections are missing?
"No wonder you don't think it works-- I don't think THIS schematic does, either!"
So tell us what is wrong with it.
Put up or shut up!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Correction! I don't tell anyone to build anything-- or completely how to build it.
Others do, and their contributions sometimes help, sometimes don't.
I, for one, admire them and appreciate their efforts. Remember, that these guys are working for nothing-- on other people's behalf. Now, that's pretty decent in my book, even if a few honest mistakes are made. (They will be-- SO WHAT? It's free- just use the GOOD parts of it, for God's Sake!).
That's life! Full of advice-- and only a few things actually work. Then, the real problem is-- as always-- how to APPLY some of that advice-- and maybe what to leave out also!
Again, that's life! Get used to it-- I happen to enjoy it and like to live on Planet Earth-- with all its faults!
As you should expect, I don't give out schematics or tell people exactly how they should build their own projects, since I'm part proprietary, and part understanding-- of the fact that every guy has the right to build anything any way he wants anyhow!
All we're doing-- at least that's me-- is allowing a peek into the THINKING PROCESS that can lead to excellence. You DO NOT get schematics, pre-designed kits, or any advice on how to build things-- except as general accurate, honest thinking processes that can-- if properly understood, lead to sheer excellence.
That's what you get for free from me. Nothing else. Be happy that it's available! Learn from it! Or-- don't. It's your call.
Developing an antagonistic attitude over it is childish.
---Dennis---
The overall concept of "modern" SE tube amplifiers is what is important, not the rote copying of a schematic.
I took a lot of information from Jeff Medwin aka Drlowmu and but I did not copy what he did exactly.
I adapted the overall "modern" approach to my circuit and came up with something useful and good sounding to my ears.
The detractors are not willing to buy the recommended parts, build a circuit or learn anything.
They want to publish poorly executed/incorrect Serious Stereo schematics and say that "modern" SE tube amps don't sound good.
The negative people just want to police the AA tube forums and try to bully other builders into silence.
dt 667
Don't you-- or others-- worry about it. They don't have anything that could work-- the mistakes are just too numerous to bother mentioning.
Their thing can't, and won't perform as they have it drawn up/perverted.
Now you know why I don't give out schematics-- I don't want them butchered.
---Dennis---
The only antagonism I have for you is because of the misinformation you spew to the detriment of the neophyte.Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/29/12
Sound Practices, Issue #5, Spring 1994, Page 3, "A Direct Coupled Single Triode Amplifier" by Ciro Marzio and Cristiano Jelasi".
Very nice article.
I'd suggest a modern power supply.
Jeff Medwin
Well, guys, what are you waiting for? Good Ole' Jeff has given you the goodies!Now, you can read the articles and learn WHY these Italians liked this approach better than anything else. Remember, they were listening to Italian Opera-- which is demanding musically.
Sure, I have perfected it. But, you cannot deny that their version of the concept did sound very realistic-- musically, even though it was operating in a narrow bandwidth-- measurement-wise..
Of course, that didn't really hurt it much.
Why is that? Even after rolloff of both highs and lows, the thing still responded well to micro-signal input. What happened is that although highs were rolled-off, THEY WERE STILL THERE!
That is FAR better than an amp that is measured flat-- say-- out to 35,000 HZ, but WILL NOT RESPOND to micro signals in frequency ranges even well below that, but must be POWER-DRIVEN to give even a passing nod to those energies.
Of course, the Miller-Effect eliminated amp will not drive a H.-EFF. speaker well at all, even though it measures well AT FULL POWER..
What happens here is that the rolled-off Italian design reproduces FAR more highs than the amp that has much more H.F. extension-- but not into a H.-EFF. speaker-- the extension to 35,000 HZ (as an example) is only on paper-- it is real enough if the amp is driven hard, but it DOES NOT occur in a H.-EFF. SPEAKER when the amp IS NOT driven hard..
In this case, amp measurements on paper don't prove power-response to SMALL signal input. The Italian's amp does respond-- at small signal levels, and that is the secret of it.
It can be rolled-off at both ends of the audio frequency extremes and yet deliver FAR more input of those rolled-off frequencies into an actual speaker-- than can the Miller Effect-Eliminated amp that measures perfectly, but will not respond to micro-signal input..
Now, I'm NOT interested in another mud-slinging contest over this. This is FREE, valuable information, TRE, MACH1, and GEO.
TAKE it or LEAVE it.
The Italians liked it and had fun with it. And, that wasn't even close to what is possible.
Oh, I KNOW-- several of you don't think that these are serious amplifiers. What did they use in the front-end-- a 12AX7?
Oh, but that can't work! It's that horrible Miller stuff! Yeah, sure. But it DOES work.
Have you ever asked WHY? I did.
---Dennis---
Edits: 06/28/12
"What happens here is that the rolled-off Italian design reproduces FAR more highs than the amp that has much more H.F. extension-- but not into a H.-EFF. speaker-- the extension to 35,000 HZ (as an example) is only on paper-- it is real enough if the amp is driven hard, but it DOES NOT occur in a H.-EFF. SPEAKER when the amp IS NOT driven hard.."
So, if it IS "driven hard" then are we back to equal (other than gain) ?
The main reason I left the hi mu driver, was I didn't need the gain, in fact a mu of 18 is still more than I need. This means that I'm using more than half of my available 2V of signal from the source, whether a CD player or a phono-pre, and, of course, ATTENUATING LESS. Is this "driven hard" ?
In addition, regardless of Rp or Miller issues, selected lo mu drivers can be measurably if not also audibly, lower distortion, because they are more linear, period. This is usually a good reason to use such an item, right?
I always thought hi mu triodes were for situations where hi-gain was needed, accepting the fact that there's a distortion "penalty" for such an "advantage". I think this is basically still true?
The real question is whether or not hi mu equates to higher low level sensitivity. "technically" is doesn't...
I'll admit, that once I made a direct coupled SE parafeed amp with a CCS loading a lo mu driver, I hadn't heard anything better, and was also amazed by the low level retrieval. The amp also had 2 less caps in the signal path...You may want to try it Dennis, use your front end if you prefer.
I neglected to mention something very important in this kind of amp-- it's critical.
When you're running a High-Mu, low current device as a driver-- that item must have unlimited plate power available, and it must have very tight voltage regulation.
If you attach a constant-current device-- either to the plate or the cathode of the driver stage, the performance should degrade because of the added phase problems initiated by the Band-Aid thus applied.
If, instead, the sound improves, and the amp has more power with the C/C applied, then that is proof of a power supply problem on the driver's plate supply.
The supply should have very tight voltage regulation-- you can't do this with any regulating device-- it will fail to closely enough follow music's changes. Instead, you use resistors for shunt-regulation. Ideally, you can run up to 40 ma., to ground, and use only 8 tenths of a milliamp of that for the driver plate current-- maybe slightly more-- one milliamp with a single section of 12AX7A-- which is recommended because so many excellent varieties are available today.
Sorry I neglected to mention this. If you've had problems, look here.
---Dennis---
Very intelligent and good questions-- all of them.Let's see if I can shed some light on them, not all of this may apply to your own situation, so don't consider it the only things you can do.
My approach to anything is how can I get it perfect... that may require changing more than the unit in question-- it may require designing a whole system to get everything as perfect as I can make it. So, again, this may not be gospel for your circumstances-- I'll do it for your discussion:
(1) I'm not sure that paragraph makes as much sense as it can-- let's take another look at it-- let's try and improve on my wording:
What I mean is that the Italian design- with its low-plate current driver stage responds better to small-signal inputs than an amp that has a higher plate-current driver installed for the purpose to overdrive Miller-Effect on the output tube grid.The low-plate current driver is easier to drive with input signals entering the amp than the higher plate current driver is.
This is an advantage where the amp is not pushed to full output-- as in the case of High Efficiency speaker..
Should one wish to push the output tube to full output, then the higher plate current driver will get much more input from the source components, and we will enter the area where it can perform better. It will also have a wider bandwidth because it is now overdriving the Miller Effect on the output tube grid.
We run into a severe fidelity problem when we DO NOT push this high plate current driver amp to full output. In that case, the hefty input tube plate current acts as an incoming signal blocking device, rendering the amp hugely less transparent and dynamic. As you probably already know, amps have to be power-sized to their speakers.
A much more honest appraisal would be-- the amp DRIVER STAGE must be sized to the SPEAKER.
-----This is far more important than matching the output stage to the speaker-----!
The thing that I notice most when using tube amps is that the power from the amp with the low-plate current driver, while delivering less total watts available from that amp-- puts out audio power that is infinitely more powerful and potent-- and has far greater ability to drive the speaker AS LONG AS that speaker doesn't need more power yet.
If the speaker does, you have to have a larger driver stage. In such a case, you give up a LOT of fidelity-- you would be much better off to change the speaker out and opt for more efficiency.
(2) If the amp is driven hard with the high-current driver stage, more input is being put onto its grid. This overcomes some of the limitations that the high-current driver exhibits under lower drive conditions. Is this performance as good or as potent as running the low-current driver stage into a speaker that is efficient enough to place that driver stage into its correct operating range?
NO! NOTHING will outperform the amp with the High-Mu, low-current driver stage-- IF the speaker loads the amp properly-- and never overloads the amp.
(3) "I didn't need the gain". The above discussion is for a 2-stage amp, so the high-gain input stage is needed. The overall gain of such an amp-- using a 2A3 output tube-- is in the range of 19-20 db. This is discussed in Jim Smith's book "get better sound". In there, you can read what Jim considers ideal gain for an amp. That is the range we have here..
Typically, with this kind of amp, we'll use a CD player, computer Sound Card, or a Phono stage that outputs-- ideally-- 3.2 to 3.6 volts Single Ended. In such a case, no preamp stages are needed, the 2-stage amplifier is directly driven by the source component. Volume control is accomplished by a Ladder Attenuator, or an L-Pad Attenuator.
Series and transformer or autoformer type attenuators are not used because series types cannot maintain an ideal load on the source regardless of volume setting.
Transformer or Autoformer types are OK for good midrange and voice performance, but fall short of maximum transparency-- compared to what we can get by eliminating them. Another thing that MUST be eliminated, in any really good system is all active preamp stages except for the Phono stage-- which is, unfortunately, necessary.
(4) Don't let linearity charts or other data fool you into thinking that they always apply to all situations under all musically-driven conditions. These can certainly mislead, although you will often catch me looking at them, and trying to find the more linear areas-- IF everything else is ALSO OK. IF NOT, then a workable balance must be thought-out across the entire amp's operating range and conditions.
Remember this: all devices, be they tubes, solid-state devices, caps, resistors, transformers and inductors-- have ranges where they operate well and ARE NOT being stressed-- thermally, signal-input, or power dissipation-wise. When parts are not ever stressed, they are far more dynamic and transparent, and MUCH more musical. With some tubes, this WILL NOT be the most "linear" portion of the tube curve. SO WHAT?
Basically, getting too hyped-up over theoretical "linearity" or "low distortion" can cause one to make overall engineering mistakes in amp design that will rob one of the musically linear, distortion-free presentation that you really want----- IN THE SPEAKER.
(5) High-Mu triodes are used where they can eliminate an extra gain stage. An extra gain stage-- regardless of intent-- is always a sonic disaster if it can be avoided. The more parts and gain stages you have, the slower your amp is, and the less transparent it is.
Anytime you can eliminate a coupling cap-- do it! NO cap exists that can be accurately put in series with an audio signal.
---Dennis---
Edits: 06/28/12
"What happens here is that the rolled-off Italian design reproduces FAR more highs than the amp that has much more H.F. extension-- but only on paper."BS
"TAKE it or LEAVE IT."I'll leave it and argue that it is a flawed design.
"Oh, but that can't work! It's that horrible Miller stuff! Yeah, sure. But it DOES work.
Have you ever asked WHY?"
It doesn't work so I have no reason to ask why it works.
You still haven't answered my question.
What do you mean when you say, referring to the schematic I posted, "the proper connections into circuits are in the wrong places"?
The plate of the 7b4 is connected to the last cap in the PS filter with a plate resistor. Just like in your amplifier.
The cathode of the 7b4 is connected to ground through a bypassed cathode resistor. Just like in your amp.
The grid of the 7b4 is connected to ground through a grid resistor. Just like in your amplifier.
The plate of the driver is directly connected to the grid of the output tube. Just like in your amp.
The plate of the output tube is connected directly to the output transformer. Just like in your amp.
The output transformer is feed from the second C of the PS filter. Just like in your amplifier.
The cathode of output tube is connected to ground through a bypassed cathode resistor using the CT of the filament transformer. Just like in your amplifier.
So tell us Dennis, what connections are in the wrong places?
You say some awful silly stuff some times.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 06/28/12
Saved me some trouble.
Dan
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