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Old 12th June 2012, 03:08 PM   #11
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Quote:
Originally Posted by underwurlde View Post

Soooo, how to make it unity gain?
Don't use that circuit.

If I were you, I'd grab a copy of Morgan Jones's "Valve Amplifiers" and study it in detail. Lots of ideas for unity gain circuits, the correct way to use CCS loading, and the fundamental principles of design that you ought to know. Now, if what you want is basically an effects box rather than a clean amplifier, you'd do better seeing how the guitar amp guys do it, and there, Merlin Blencowe's books are excellent.
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Old 12th June 2012, 03:14 PM   #12
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OK, cool.

Hopefully there will be something as simple for me to try!

Valve design is obviously not my bag, baby. Too awkward to scratch up with all those high V's required etc. but a friend of mine has sent me a 'request'.

Thanks again for your help,

Andy.

Just for the record, & if you have a little time to explain, why "Don't use that circuit"?
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Old 12th June 2012, 03:16 PM   #13
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Do it as SY says or buy something like this: 6N3 (5670) Tube Buffer DIY Kit (Stereo) No Tube | eBay

Otherwise we will fill pages here and won't get very far.
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Old 12th June 2012, 03:38 PM   #14
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Quote:
Originally Posted by underwurlde View Post
Just for the record, & if you have a little time to explain, why "Don't use that circuit"?
It's a circuit designed to maximize gain from a given tube, the opposite of what you're looking for.
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Old 12th June 2012, 03:41 PM   #15
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@SY - OK, gotcha! I know not my valves TBH.

@the_manta: That kit you've kindly pointed out to me above seems (basically, bar the JFETs for constant current) the same as the circuit I've reproduced, other than the fact it uses different valves, i.e. Chinese 6N3 (5670) instead of 12AU7's?

So I guess the circuit I had originally assumed as OK uses the 'wrong' valve? So I guess I should start by asking "which valve"?

Andy
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Old 12th June 2012, 03:48 PM   #16
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So I guess the circuit I had originally assumed as OK uses the 'wrong' valve? So I guess I should start by asking "which valve"?
No. Ask, "Which topology?" And you'll find the answers and (more importantly) understanding in the books I suggested.
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Old 12th June 2012, 03:50 PM   #17
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Which topology? LOL

Hmmm, a learning curve me thinks. And there's me hoping for simplicity. Should've known better.

Andy
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Old 12th June 2012, 08:56 PM   #18
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A self-biased cathode follower perhaps?
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Old 12th June 2012, 09:08 PM   #19
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That's one possibility. Design it well and you won't hear it. Design it poorly and you'll get a "sound."
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Old 5th July 2012, 01:14 PM   #20
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Just built an Aikido CCDA valve circuit.

Click the image to open in full size.

It inverts of course. Does this matter?
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