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Ryssen 9th March 2004 06:52 PM

Help on Brute force
 
2 Attachment(s)
I have done some messuring on my Brute force (Glass Audio) headphone amp and as I can see there is something with 50 and
100hz that I donīt like.It must be something whit the power feeding or?I do not use any stabilizator in the power,but I am planing to use one will it help for this?I am messuring through my souncard,and when I messure only the soundcard thereīs almost a straight line even at 50 and 100Hz.But when I listen with headphones (No signal) I hear hum,then I disconnect the line in to the headamp.the hum dissapears,whatīs this hum from the computer?Is it some grounding problem how to solve this?

fdegrove 9th March 2004 10:51 PM

Hi,

Quote:

whatīs this hum from the computer?Is it some grounding problem how to solve this?
The PC PSU is a switched mode supply rectifying at HF so 50/60 or 100/120Hz shouldn't originate from that one.

It sounds as if you have a groundloop somewhere.


Cheers,;)

Ryssen 1st May 2004 10:27 AM

2 Attachment(s)
A tips and a question.I have made some changes on my brute force,I have added a ground loop breaker: http://headwize2.powerpill.org/projects/meier_prj.htm
and an extra ground wire to from the amp to the coumputer chassie,so now it is a little bit better,but I am wondering about the thing from ca 40-500hz itīs a little bit higher than the rest.I have tried to change the capacistors in the signal path to different values,but there was no difference.When I mesaure just with the soundcard it is a flat line,so it must be the brute force.Any suggestions?

SY 1st May 2004 01:40 PM

I think you still have a ground loop, but inside the amp. Are you returning all grounds to a single point?

Ryssen 1st May 2004 06:13 PM

Yes,from the input and output RCAīs,they are isolated from the chassis,I have thick solid wire,where the cathode resitors are soldered to,and from that solid wire another solid wire to the first
e-lyt in the power supply where all other grounds meet,eccept for mains ground wich is connected to chassis.and between chassis and the solid wire is the ground loop breaker.

Ryssen 2nd May 2004 10:07 AM

I have now moved around the grounds in the amp and now I cannot hear any hum at all,I coulīd even remove the extra wires to the PC chassis,in fact I got more hum if they where there.But the peak in the frekv.response is stil there.The frekv.rexponse is from +1.6db-0,75db,what is good ,(acceptable)?The next step is to try Regulated supply.
Thankīs for the answers.


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