AY Symphonies preamp

adason · 28th December 2011, 05:34 PM

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!

DF96 · 28th December 2011, 07:51 PM

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.

adason · 28th December 2011, 08:06 PM

good to know, thanks DF96

Original Burnedfingers · 28th December 2011, 11:48 PM

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.

Original Burnedfingers · 31st December 2011, 11:37 AM

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.

the_manta · 31st December 2011, 12:09 PM

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 ?

adason · 31st December 2011, 12:23 PM

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.

DF96 · 1st January 2012, 02:55 PM

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.

Original Burnedfingers · 1st January 2012, 03:35 PM

Which power supply in it?

adason · 2nd January 2012, 11:48 AM

with tube rectifier...

31st December 2011, 12:09 PM	#6
the_manta diyAudio Member Join Date: Nov 2006 Location: Munich, Bavaria	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 ? __________________ Терпенье и труд все перетрут

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28th December 2011, 07:51 PM	#2
DF96 diyAudio Member Join Date: May 2007	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.

28th December 2011, 08:06 PM	#3
adason diyAudio Member Join Date: Nov 2004 Location: home sweet home	good to know, thanks DF96

28th December 2011, 11:48 PM	#4
Original Burnedfingers diyAudio Member Join Date: Nov 2002	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.

31st December 2011, 11:37 AM	#5
Original Burnedfingers diyAudio Member Join Date: Nov 2002	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.

31st December 2011, 12:23 PM	#7
adason diyAudio Member Join Date: Nov 2004 Location: home sweet home	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.

2nd January 2012, 11:48 AM	#10
adason diyAudio Member Join Date: Nov 2004 Location: home sweet home	with tube rectifier...

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