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Old 28th December 2011, 05:34 PM   #1
adason is offline adason  United States
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Default AY Symphonies preamp

Hi all,

I got this preamp from ebay, already modified with better caps, just had some hum. I got rid of the hum. Now I have it open, so I was thinking, what else can I modify before I put it back in and close it?
Can I completely remove first cap?
Thanks!
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Old 28th December 2011, 07:51 PM   #2
DF96 is offline DF96  England
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No, C1 is an essential DC blocker. In this particular design it is even more essential than usual, because the first stage grid is not approximately at ground potential.
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Old 28th December 2011, 08:06 PM   #3
adason is offline adason  United States
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good to know, thanks DF96
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Old 28th December 2011, 11:48 PM   #4
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Audio Experience Symphonies and Concerto [English]

I purchased one of these new back around 2004. With cap upgrades and good tubes its not much of a threat to other designs out there.
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Old 31st December 2011, 11:37 AM   #5
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Have you tried other 12AX7 tubes in it? These units came with EI 12AX7's. I noticed a marked difference when I changed the tubes to some NOS GE's.

I have the power supply schematic on my computer somewhere but it is missing the power supply voltages which would be nice in analyzing the circuit further.
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Old 31st December 2011, 12:09 PM   #6
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Interesting circuit. Current feedback over 3 stages ! (Keep in mind that this increases output resistance)
But why is R5 only 100k ? Because C2 is so large, V1's load is only 100k||330k. Which produces much more distortion. But maybe that's the reason for the good sound.
And what are R12 and C3 for ?
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Old 31st December 2011, 12:23 PM   #7
adason is offline adason  United States
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It has Tung-Sol 12AX7s in it...
I have some Electro-Harmonix, new
and some old Magnavoxes and DuMont
I have not done much tube swapping so far because of little hum. Now I got rid of that, so I can do some more listening. But the preamp is not assembled now. I was wondering while I have it guts out, what mods can I do.
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Old 1st January 2012, 02:55 PM   #8
DF96 is offline DF96  England
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Quote:
Originally Posted by the_manta
Current feedback over 3 stages ! (Keep in mind that this increases output resistance)
No, the output voltage is sampled (by R9/R10) so it will reduce output resistance.
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Old 1st January 2012, 03:35 PM   #9
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Which power supply in it?
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Old 2nd January 2012, 11:48 AM   #10
adason is offline adason  United States
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with tube rectifier...
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