Hi, been restoring a CJ MF2500 solid state amp.
After recap, change of blown parts it now works 🙂
Could dial in 0Vdc dc offset on both channels and bias is fine.
Without a source connected it is dead silent on speakers. No hum, hiss and amp transformer is also silent. So far so good.
However, with my preamp connected there are some hiss/hum in both woofer and tweeter. I am able to hear it from approx 2m distance. Quite annoying.
The preamp is totally silent with other amps and also as headphone amp, it also measures extremely well.
With other sources the result is the same.
I have not tried shorting the inputs yet.
Any suggestions?
Any typical reason for something like this can happen? Both channels are infected.
After recap, change of blown parts it now works 🙂
Could dial in 0Vdc dc offset on both channels and bias is fine.
Without a source connected it is dead silent on speakers. No hum, hiss and amp transformer is also silent. So far so good.
However, with my preamp connected there are some hiss/hum in both woofer and tweeter. I am able to hear it from approx 2m distance. Quite annoying.
The preamp is totally silent with other amps and also as headphone amp, it also measures extremely well.
With other sources the result is the same.
I have not tried shorting the inputs yet.
Any suggestions?
Any typical reason for something like this can happen? Both channels are infected.
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desoldering a mass on rca at the input of the amp, right or left no matter,
to see if you do not have a loop in the amp
to see if you do not have a loop in the amp
He means to disconnect the ground connection on one side, to avoid the possible ground loop.
Sajti
Sajti
I will try that. Uncertain if it will be today.
But can a ground loop cause that much "damage"? Alot of harmonics spurs.
But can a ground loop cause that much "damage"? Alot of harmonics spurs.
Guess the answer is yes in your case...all harmonics from your measurement come from psu, the most visible ones are all odd order (x 50Hz)
Hi there 🙂 Yes we have a ground loop problem.
Connected directly to my dac (with volume control) it plays just beautiful. No hum, hiss og anything. No problem. The dac is not connected to safety ground (yet).
Any suggestions how to get rid of it with this amp?
Connected directly to my dac (with volume control) it plays just beautiful. No hum, hiss og anything. No problem. The dac is not connected to safety ground (yet).
Any suggestions how to get rid of it with this amp?
Hmm - how to explain it?
Here is a picture anyway.
RCA out is the pair on the left.
It is dead silent on my other amp. (Ovation-SX).But got a real ground loop with the CJ mf2500.
Here is a picture anyway.
RCA out is the pair on the left.
It is dead silent on my other amp. (Ovation-SX).But got a real ground loop with the CJ mf2500.
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I see the protecting grouond connected to the chassis. How the signal ground connected to the chassis?
Sajti
Sajti
Well actually it is connected via the headphone (3.5mm) out to the left of the rca´s.... If I remove that I got no ground connection fram rca to the chassis... Hmm - probably not the best grounding scheme..
Yes I will try that.
Anyway - the main issue here was the mf2500 and it seems perfect 🙂 Just not with my particular preamp. After a couple of hours use it dials in 0mv dc offset on both channels and bias is spot on according to CJ.
I can fix the preamp on a later occasion.
Anyway - the main issue here was the mf2500 and it seems perfect 🙂 Just not with my particular preamp. After a couple of hours use it dials in 0mv dc offset on both channels and bias is spot on according to CJ.
I can fix the preamp on a later occasion.
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