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In Reply to: RE: Sound Practices Information..... posted by drlowmu on June 27, 2012 at 21:14:01
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: 06/28/12Follow Ups:
"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
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