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Old 10th February 2011, 03:32 PM   #1
dano12 is offline dano12  United States
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Default Reverse engineering a phono pre, help these old eyes

I've spent the last two days reverse-engineering a low-cost commercial phono pre. I've been as diligent as I can in getting it right, but after many hours my eyes are going crossed. Anyone have some free bandwidth to see if I'm on the right track?

Here's the schematic I have so far, does it look remotely like a discrete phono pre? I can't figure out why there is no DC supply to the collector of Q1...

Click the image to open in full size.



Doh, I guess it would be helpful for me to include the photo of the PCB with the parts legend. Here's the link because it is a rather large file:

http://www.beavishifi.com/ComPhono_PCB.png

Last edited by dano12; 10th February 2011 at 03:54 PM.
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Old 10th February 2011, 04:29 PM   #2
alayn91 is offline alayn91  France
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Hello,

According to the PCB picture, you have forgotten R12, 270KR, from Vdc+ to Collector of Q1 and base of Q2.

Regards.
Alain.
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Old 10th February 2011, 05:37 PM   #3
dano12 is offline dano12  United States
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Quote:
Originally Posted by alayn91 View Post
Hello,

According to the PCB picture, you have forgotten R12, 270KR, from Vdc+ to Collector of Q1 and base of Q2.

Regards.
Alain.
Thanks very much for the good catch. I've updated the schematic--it is looking more like a valid circuit now.
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