Hello!
I have a Noise ( sounds like pink noise ) problem with this amp after i push the low pass button, the problem doesnt occur if i press the hipass button.
The problem is present on both channels.
The amp works well without the low pass button pushed.
I have no schematics, but this is what i have done so far:
- RCA-Ground is ok, i desoldered the RCAs completely because it was hard to see if they are broken when installed, but they are fine!
- i measured RCA-Ground to main ground: i have around 1000 Ohms.
- i scoped the inputs and outputs on the NE 5332 which i marked:
after pushing the low pass button i get a negative offset of 60mV with visible noise on the outputs of the opamp i marked on top.
the Opamp marked in the center has also an offset of around -20mV but no noise if i push the low pass button.
Can somebody give me a hint what to check next?
Any help is much appreciated and thank you in advance!
EDIT: i forgot to mention that the opamp on top is new but that changed nothing.
I have a Noise ( sounds like pink noise ) problem with this amp after i push the low pass button, the problem doesnt occur if i press the hipass button.
The problem is present on both channels.
The amp works well without the low pass button pushed.
I have no schematics, but this is what i have done so far:
- RCA-Ground is ok, i desoldered the RCAs completely because it was hard to see if they are broken when installed, but they are fine!
- i measured RCA-Ground to main ground: i have around 1000 Ohms.
- i scoped the inputs and outputs on the NE 5332 which i marked:
after pushing the low pass button i get a negative offset of 60mV with visible noise on the outputs of the opamp i marked on top.
the Opamp marked in the center has also an offset of around -20mV but no noise if i push the low pass button.
Can somebody give me a hint what to check next?
Any help is much appreciated and thank you in advance!
EDIT: i forgot to mention that the opamp on top is new but that changed nothing.
Does it do this with no RCAs plugged in?
Some possible problems:
The pots are out of sync. Sometimes the shaft gets pulled out and one pot is turned before the shaft is reinserted. Make sure that all pots have the same amount of rotational range. 270°?
Same level of noise on both channels?
Is the 'noise' actually a high-frequency oscillation?
Some possible problems:
The pots are out of sync. Sometimes the shaft gets pulled out and one pot is turned before the shaft is reinserted. Make sure that all pots have the same amount of rotational range. 270°?
Same level of noise on both channels?
Is the 'noise' actually a high-frequency oscillation?
Thank you for your reply, Perry!
Yes, also noise with RCAs plugged in, it doesnt change if i have a source connected or not.
The pot-shaft is a very good point - thank you, i will check all pots next.
The noise is audible and sounds exactly or very similar like test signal " pink noise "
Yes, also noise with RCAs plugged in, it doesnt change if i have a source connected or not.
The pot-shaft is a very good point - thank you, i will check all pots next.
The noise is audible and sounds exactly or very similar like test signal " pink noise "
I checked all pots and they are all the same and noise is still present, but i did not mention that the noise is gone with gain pot totally counterclockwise.
i also found out if lowpass button is pressed and gains set high - noise present, but if i press the highpass button, noise disappears...
another thing to mention is when i use a gain pot and turn the first and the second at the same time, noise grows. But if i pull the shaft and only turn the
outer pot there is no noise. The same with the second channel.
i also found out if lowpass button is pressed and gains set high - noise present, but if i press the highpass button, noise disappears...
another thing to mention is when i use a gain pot and turn the first and the second at the same time, noise grows. But if i pull the shaft and only turn the
outer pot there is no noise. The same with the second channel.
Yes, both channels clean even if lowpass switch is pushed.
With only one channel gain increased also clean audio , both channels good!
The noise comes with increased gain settings in lowpass-mode.
With only one channel gain increased also clean audio , both channels good!
The noise comes with increased gain settings in lowpass-mode.
Do you know any of the history on this amp?
Has anyone else tried repairing it before you received it?
Do you see any noise on the supply terminals of the op-amps?
On the rail voltage?
Does the amp have noise at the speaker terminals with no speaker connected?
Has anyone else tried repairing it before you received it?
Do you see any noise on the supply terminals of the op-amps?
On the rail voltage?
Does the amp have noise at the speaker terminals with no speaker connected?
I have no idea about the history, it looks original and the seal on the back was intact!
i dont see noise on the suppy terminals on the opamps and also not on the rails.
i scoped the supply voltage of the opamps and the rails and in that moment i push the lowpass button, the voltage drops for a short time and i
see the cone of the woofer coming out a bit with a " pop ".
i dont see noise on the suppy terminals on the opamps and also not on the rails.
i scoped the supply voltage of the opamps and the rails and in that moment i push the lowpass button, the voltage drops for a short time and i
see the cone of the woofer coming out a bit with a " pop ".
Is there a way you could contact the owner to see when this problem started?
Do you see excessive DC offset on one or more of the op-amp output terminals?
Do you see excessive DC offset on one or more of the op-amp output terminals?
i can try to contact but this will take some time i guess...
I checked all outputs of all opamps, there is no significant DC offset.
but there is also a 16 pin dual opamp , JRC 13600d , it has 200mV negative offset at output A ( pin 5 ) and 400mV negative offset at output B ( pin 12 ) .
Pin 1 is -13.6V and pin 16 is also -13.6V
I checked all outputs of all opamps, there is no significant DC offset.
but there is also a 16 pin dual opamp , JRC 13600d , it has 200mV negative offset at output A ( pin 5 ) and 400mV negative offset at output B ( pin 12 ) .
Pin 1 is -13.6V and pin 16 is also -13.6V
The 13600 is a transconductance amplifier. Pins 1 and 16 are the control terminals.
Do you ever see the noise on the output of this IC?
I need to go check something but I'll get back to this. I don't remember offset on the output terminals of a 13600 but I'll see if I have one to check. It may be normal. Were you using a close ground?
Do you ever see the noise on the output of this IC?
I need to go check something but I'll get back to this. I don't remember offset on the output terminals of a 13600 but I'll see if I have one to check. It may be normal. Were you using a close ground?
here are the results:
Pin 5: -130mV after lowpass button pressed : -330mV
Pin 12: - 360mV after lowpass button pressed : -550mV
Pin 5: -130mV after lowpass button pressed : -330mV
Pin 12: - 360mV after lowpass button pressed : -550mV
I don't think there is a problem there (with the 13600).
I'm waiting on a couple of replies to see if anyone has a diagram but I don't think a diagram will help if both channel work flawlessly when driven alone.
I'm waiting on a couple of replies to see if anyone has a diagram but I don't think a diagram will help if both channel work flawlessly when driven alone.
Thank you very much for your help so far. 😊👍
The amp works great without lowpass pressed.
I remember that a very similar amp , the MTX Thunder 2300 didn’t make the speaker pop when lowpass button is pressed.
The amp works great without lowpass pressed.
I remember that a very similar amp , the MTX Thunder 2300 didn’t make the speaker pop when lowpass button is pressed.
Is the noise present at both ends of the crossover frequency?
The pop is generally due to an op-amp with slightly too much DC offset. Since the DC affects the level in the 13600, I doubt that it's the issue.
Does the noise remain the same when the level (overall gain) is controlled via the remote level control? In other words, if the gain is set low with the 13600, can you increase the gain pot's setting and have no noise?
The pop is generally due to an op-amp with slightly too much DC offset. Since the DC affects the level in the 13600, I doubt that it's the issue.
Does the noise remain the same when the level (overall gain) is controlled via the remote level control? In other words, if the gain is set low with the 13600, can you increase the gain pot's setting and have no noise?
If i change the crossover frequency nothing is changing, i have constant noise.
I am sorry, i cant answer your second question because the owner doesnt have the remote control 🙁
Is there a chance to simulate this with a spare gain pot which i can pull off a dead amp? I believe i should have some 5k pots somewhere.
Regarding the opamp DC : do you think i should try to exchange the first opamp after the RCAs?
I am sorry, i cant answer your second question because the owner doesnt have the remote control 🙁
Is there a chance to simulate this with a spare gain pot which i can pull off a dead amp? I believe i should have some 5k pots somewhere.
Regarding the opamp DC : do you think i should try to exchange the first opamp after the RCAs?
I scoped the 13600D again and i have noise on the following pins without lowpass button pressed.
Pins 5 , 7 , 9 , 12
all with negative offset
The inputs look ok and i checked the surrounding resistors, i cant find an open resistor 🙁
I would not hesitate to replace that 13600 but its not available in my country, is there a substitute for it ?
There is a lm 13700 available..
Pins 5 , 7 , 9 , 12
all with negative offset
The inputs look ok and i checked the surrounding resistors, i cant find an open resistor 🙁
I would not hesitate to replace that 13600 but its not available in my country, is there a substitute for it ?
There is a lm 13700 available..
As far as I know, they are interchangeable. Why not bypass it for now to eliminate it as a possible problem?
The DC is likely OK. If I earlier stated that there should be no DC, I was wrong. If the output pins have a slight DC offset, it will be about 1.5v more negative if they're using the output buffer. To bypass it, you're remove the input and output coupling capacitors and run a jumper wire between their terminals that did not connect to the 13600.
Attached is a sample diagram.
The DC is likely OK. If I earlier stated that there should be no DC, I was wrong. If the output pins have a slight DC offset, it will be about 1.5v more negative if they're using the output buffer. To bypass it, you're remove the input and output coupling capacitors and run a jumper wire between their terminals that did not connect to the 13600.
Attached is a sample diagram.
