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PeeCeeBee V4H GB

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R

redjr

Member
Joined 2011
Amp Repair Success

redjr said:
Thanks for that explanation. I will pull the boards at some point and replace both the resistors and Q3 and Q4.
Click to expand...
Hi shaan,

I repaired my V4H PCBs and my amp is singing lovely once again. I only had to replace R25 and Q3, as R26 and Q4 survived the incident. Good as new. I also had to make some minor changes to the Yarra preamp, and now the power up/down cycle is working better.
 
O

Onemangang

Member
Joined 2011
Hi shaan

First time stopping by and seeing your amplifier. Looks nice :)
Hope I am not repeating a question already asked, haven't read all posts yet.
But here we go..

You are using almost the same input I used in my line amp many years ago ( no diamond ). Mine however, is dc coupled. And I was wondering if you have tried your amplifier without capacitors c3,c4,c9,c10?
In my line amp, these would be shorted directly to ground ( they where actually never there in the first place ), and the css's Q7 and Q8 would draw their current from the other side of the two 100 ohm resistors R3 and R4.
Q7 and Q8 then need to draw additional current because the input transistors do not open before the voltage across R3 and R4 go beyond ~0.6 volt.
Meaning the css's should draw an additional 6 mA. I also use a servo to balance my css's for zero offset.

Does my question make sense?

Edit:
All component references are for the schematic shown in post #1

Regards and thank you for sharing
Jørgen
 
Last edited:
shaan

shaan

Member
Joined 2009
Onemangang said:
Hi shaan

First time stopping by and seeing your amplifier. Looks nice :)
Hope I am not repeating a question already asked, haven't read all posts yet.
But here we go..

You are using almost the same input I used in my line amp many years ago ( no diamond ). Mine however, is dc coupled. And I was wondering if you have tried your amplifier without capacitors c3,c4,c9,c10?
In my line amp, these would be shorted directly to ground ( they where actually never there in the first place ), and the css's Q7 and Q8 would draw their current from the other side of the two 100 ohm resistors R3 and R4.
Q7 and Q8 then need to draw additional current because the input transistors do not open before the voltage across R3 and R4 go beyond ~0.6 volt.
Meaning the css's should draw an additional 6 mA. I also use a servo to balance my css's for zero offset.

Does my question make sense?

Edit:
All component references are for the schematic shown in post #1

Regards and thank you for sharing
Jørgen
Click to expand...

Hi Jorgen.

Does either of the two designs in the post (#2) linked below look similar to the design you mentioned?

simulating-building-simple-symmetrical-amplifiers-post2

If yes, then there you have it. This design works pretty well, but due to high sensitivity of the input pair to temperature changes a servo is needed, as you mentioned. With the capacitors installed there however, offset is very tame even if the input pair is not thermally coupled to each other.
 
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Onemangang

Member
Joined 2011
Hi shaan

I'd say the left one is close. I drawn up a quick sketch. To the left it shows how my 25 year old line amp works. To the right it shows what I was asking.

Regards
Jørgen
 

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