Recently I undertook a rebuild, complete with a new chassis of the old AEM 6010 series preamplifier.
I am delighted with the results, with the exception of a low level hum when the phono stage is selected.
The hum appears to be at a constant level, and despite trying alternative earthing / grounding arrangements, I am unable to locate the problem.
I have attached a picture of a CRO screen shot (it’s the best I can do, thanks to Photoshop) of the output waveform.
The waveform as shown is at 8 khz with an input voltage of 5mV. The waveform has been taken form the normal preamp output.
All of the high level inputs are perfect with no problems.
As you can see, the waveform is nice and clean on one side, but becomes dirty on the downward leg of the cycle.
I have swept the frequency from 20 hz to 20 khz, and the dirty waveform first appears at about 3.5 khz, and gets progressively worse.
However, the “rise” section of the waveform is always clean.
Unfortunately my knowledge of interpreting CRO results such as this is somewhat limited.
I would be very grateful for any assistance, or if anyone could shed any light on this matter.
Thanks in advance.
Regards
George.
I am delighted with the results, with the exception of a low level hum when the phono stage is selected.
The hum appears to be at a constant level, and despite trying alternative earthing / grounding arrangements, I am unable to locate the problem.
I have attached a picture of a CRO screen shot (it’s the best I can do, thanks to Photoshop) of the output waveform.
The waveform as shown is at 8 khz with an input voltage of 5mV. The waveform has been taken form the normal preamp output.
All of the high level inputs are perfect with no problems.
As you can see, the waveform is nice and clean on one side, but becomes dirty on the downward leg of the cycle.
I have swept the frequency from 20 hz to 20 khz, and the dirty waveform first appears at about 3.5 khz, and gets progressively worse.
However, the “rise” section of the waveform is always clean.
Unfortunately my knowledge of interpreting CRO results such as this is somewhat limited.
I would be very grateful for any assistance, or if anyone could shed any light on this matter.
Thanks in advance.
Regards
George.