Newbie has a simple A40 power supply question

[dubai2000]

Hi everybody,
some time ago I purchased a A40 amp built as two mone blocks. I find it's a very nice amplifier - especially with Quad ESL57.

But when using it with more sensitive speakers it esxhibits some hum - I suppose due to its simple PS - simply two caps per mono amp.

Now I would like to add a choke and one more electrolyte cap after the choke - hoping to get the amps a bit more quiet.

Can you please advise if my indended wiring is correct - sorry for that simple question but I have not done that before 🙄.

Currently one cap runs a wire from its positive side to the amp board (and from negative to the - on the amp board from the other cap).

I understand that I connect the choke - in my case a Hammond 159ZE - to the plus side of the original cap. The other side of the choke goes to the plus side of the new cap and from there (+) another wire goes to the amp board. And the negative side of this new cap goes to the negative side of the original cap.

And for the negative rail I do the same thing just reversing + and - in my description - correct?

Please again bear with me for such a newbie query 😉.

Thanks in advance for any response.

 

[rayma]

I would like to add a choke and one more electrolyte cap after the choke - hoping to get the amps a bit more quiet.

Yes, this is called a pi filter because the schematic is a similar shape when drawn out.
Be sure to keep the chokes away from the audio circuitry and input sockets.
Twist the choke leads tightly.

Sometimes the hum is caused by the way the grounds are connected instead.
If the chokes don't help enough, the amplifier's ground wiring may need attention.

 

[dubai2000]

Thanks for the response - will have a go at putting in the chokes first.

 

[woody]

Or you could look at what was done here in this power supply it might give you all the hum reduction you need. http://www.firstwatt.com/pdf/prod_f5_man.pdf

 

[dubai2000]

Thanks for all the input - I installed chokes and caps. I have not tried the amps at sensitive speakers yet - because they were playing quite well on my Quads, but now they are actually noticeably better sounding - more three dimensional and more detailed - I am mightily impressed by that rather 'ancient' amp.

 

[Gladiator33]

Still use my A40 🙂

http://www.diyaudio.com/forums/pass-labs/138453-once-i-had-40-a.html

 

[dubai2000]

Have spent some more time with the amps - wow - this power supply upgrade was really worth it - this is the most holographic amp I have used with the Quads so far - and that includes a 20 watts Hiraga.