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SET Asylum Single Ended Triodes (SETs), the ultimate tube lovers dream. |
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In Reply to: RE: Sound Practices Information..... posted by GSH on June 28, 2012 at 16:13:56:
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
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- RE: Sound Practices Information..... - tube wrangler 19:37:58 06/28/12 (0)
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