O.k. , the problem is in both cannels and in the MM input mode you have also noise with open input.
What happens with the noise in the MM input mode, no cartridge connected, when you short circuit pin 3 of the XLR input.
It should not make any difference, but when it does it points in the direction that something is oscillating.
Hans
Hans,
in MM mode there is no difference, if pin 3 is shorten or not. I think something with the LME49710 is wrong (MM-Stage).
Dieter
in MM mode there is no difference, if pin 3 is shorten or not. I think something with the LME49710 is wrong (MM-Stage).
Dieter
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Does anything change when you change the gain in the MM mode.
I can imagine that one Lme is wrong, but both ?
And the plus and minus supply voltages are both checked ?
Hans,
the +/- supply is Ok, bute the Buffer Op-Amp is one LME47920 for both channels.
regards
Dieter
the +/- supply is Ok, bute the Buffer Op-Amp is one LME47920 for both channels.
regards
Dieter
Yes the buffer is one chip for both. Have you tried with and without rumble filter?
Thanks fir the pics.
In the MM input mode with open input, while producing bad noise, what are the DC voltages on Amp 3 and Amp 5, pins 1 2 3 and 5 6 7.
In the MM input mode with open input, while producing bad noise, what are the DC voltages on Amp 3 and Amp 5, pins 1 2 3 and 5 6 7.
Hans,
here the resukts:
left right
Pin 1 -2,6V lsmall ripples 0V osz
Pin 2 -0,52V 0V
Pin 3 -0,52V 0V
Pin 5 0 V 0V osz
Pin 6 0 V 0V bad osz
Pin 7 -0,3V -0,52V osz
Output OP Amp
1,2,3, 5,6,7 0V DC, but oszilating...
Dieter
here the resukts:
left right
Pin 1 -2,6V lsmall ripples 0V osz
Pin 2 -0,52V 0V
Pin 3 -0,52V 0V
Pin 5 0 V 0V osz
Pin 6 0 V 0V bad osz
Pin 7 -0,3V -0,52V osz
Output OP Amp
1,2,3, 5,6,7 0V DC, but oszilating...
Dieter
This was to be expected, because only oscillation can spread itself through both channels.
The problem is always, which part is causing this misery.
One way to find out is to take the 3 LME circuits from the board, mount IC sockets instead, and insert the op-amps piece by piece in a socket, starting with the output buffer and see when and where it goes wrong.
The other way is to isolate the LME's piece by piece from their power supply by cutting +/- traces on the pcb. With resistor values of several ohms, the traces can be repaired step by step, op-amp by op-amp, at the same time giving a better supply isolation and better resistance against oscillation.
Hans
Hans,
I have ordered spare LMEs, but the owner told me, that there is still Warranty on the preamp. Mr. Schaefer died a few month ago, but maybe there is a predecessor of Mr. Schaefer who handles the warranty cases. SAC is going out of business.
Dieter
I have ordered spare LMEs, but the owner told me, that there is still Warranty on the preamp. Mr. Schaefer died a few month ago, but maybe there is a predecessor of Mr. Schaefer who handles the warranty cases. SAC is going out of business.
Dieter
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