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Old 28th May 2003, 08:05 AM   #31
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Ok so even if the OPT isn't contributing any appreciable load, the other tube half is. Why is the CCS use at all, and why is it negated with caps?

Lesse... 6N6P mu circa 20 IIRC (was talking with Colt and he looked it up for me), but since the OPT's winding ratio is 40:1, or 20:1 for one half the transformer as is used here, net gain won't be greater than one. Though it will provide additional current if the signal source is high impedance, and adds a volume control to the string.

I bet if you changed the CCS to a resistor, and got rid of those spare caps (at the CCS and PSU), you'd have enough money to squeeze in a choke.
Lesse... 75mA choke... AES sells a 10H 90mA Triad choke, $18. As for the circuit, you can use the same PT and caps, paralleling the two last ones as shown. Should be good and solid and sim shows the same negligible level of hum.

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Tim
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Old 28th May 2003, 08:10 AM   #32
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Hi John,

The inductance is a problem - one additional reason for more current through the triode to reduce Rp a bit more.... Using a cheap OPT one is always going to suffer with poor bass extension. The circuit actually cheats a bit - the 220uF yields a small tip up in bass response before it drops off - so subjectively the effect is a bit like the LS3/5a. This is fixed by using Hammond 1609s at another 50euros cost - it's also worth using a twin LC psu removing the decoupling caps and going true PP. Replace the pot with a TVA doing PP splitting and you have my own pre Well almost...

ciao

James
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Old 28th May 2003, 08:18 AM   #33
dhaen is offline dhaen  Europe
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Default Calling Henry..

Hi James,


Quote:
one additional reason for more current through the triode to reduce Rp a bit more....
Well of course that's a very good reason for the 220u.
With Tim's proposal, the Rp would be much higher.

Anyway Tim, are you up early, or late to bed?

Cheers,
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Old 28th May 2003, 08:19 AM   #34
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Hi Tim,

Actually I tried that and it breaks the bank. Look at the cost breakdown and the two ccs costs a total of 1.3 euro...

Of course, the decoupling caps add up to the choke cost and one could throw them away - but I know the difference between having the Audyn bypassing the psu output and not and I wouldn't be without it - I think..

I don't think it's a perfect or even an optimum design - I thought it interesting to do a WOT pre for 100euros and interesting enough to post...

I hadn't intended to build this but I might knock this up with the psu your way to see what it sounds like and then try my way and see which works better as I really don't know which would be better.

Thanks

James
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