A2 operation

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Paul Barker
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#1 A2 operation

Post by Paul Barker »

In my early days of valve audio when discussing with people like Steve Bench and Bob Danyelek (sorry if spelling wrong Bob), I learned quite quickly about the special sound of A2 operation.

Normally many people, Darren especially, find the 211 thin midrange and bass.

I had a really poor quality Music Angel (I think) Chinease 845 amp, bought from Andrew Ivemey, written off as a completely hopeless case, because it's sound was just awful. There was no hope for it. The original circuit used a voltage doubler for the HT.

Anyhow I ripped the whole lot out, but in the process discovered a major error in the way it was hooked up, that would have been responsible for the terrible sound, and quite dangerous. The Chinease will get it right, but this one was bad, very bad.

I hooked up a very simple A2 211 amp with ecc35 parallel as driver.

Though there isn't much power to drive very far into A2 the low powered resulting amp hgas non of the aforememntioned 211 weaknesses. It really is a superb midrange sound. OK there isn't a great deal of bass, to be expected.

I'll probably have to change the input/driver to 6em7 and add interstages. Shame those won't fit on board. But it shows great promise.
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Nick
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#2

Post by Nick »

Interesting.

The GM70 amp that I have put together to drive Colins Electrostatics should manage a fair bit of A2, maybe +20v, at least thats what I saw when testing it.

I was using a pair of Lundahl LL1677 which were good in that the primary was happy with a 300b at 80ma, and the secondary could be wired to give a 1:1 ratio, but crap because the FR of them had a nasty peak that I tried to remove with a zobel, but never got rid of.

I removed the AE 1:1's from the 45 amp last weekend, they did a much better job of driving the gm70's grid.

If I get the chance this weekend I will try it again, and see how far it goes into A2 with the AE TX's.
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Paul Barker
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#3

Post by Paul Barker »

Let us know how it goes.
Darren
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#4

Post by Darren »

Blimey Paul,
Not sleeping?
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Paul Barker
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#5

Post by Paul Barker »

You know how it is. Then five minutes before the alrm is due to go off you are sleeping sound as a log.
Darren
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#6

Post by Darren »

Yes, too often these days.

Must be age....
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