Interesting. I think #2 is the last stage before the main amp.
Try replacing #3, #4, and #5.
I am going to guess that you will end up having to replace them all.

 

Interesting. I think #2 is the last stage before the main amp.
Try replacing #3, #4, and #5.
I am going to guess that you will end up having to replace them all.

so I have now replaced all the op-amps . hooked up the amp speaker and the signal is there but lacks volume and still some constant hiss . op amp #1 . has signal ( pin 6 hook up) but #2 ,3, 4 ,5 still no signal coming through .

 

https://soundcloud.com/rabbit1-272945711%2Fbass-audio
I've uploaded some audio . I used my phone placing it on top of the amp. you can hear the hiss and the distortion in the signal . gain is at 3 and volume is half way up . hope it helps

 

Does the hiss go up if you increase the volume?
Is the guitar volume all the way up?
Is there anything between the guitar and the amp?

 

Does the hiss go up if you increase the volume?
Is the guitar volume all the way up?
Is there anything between the guitar and the amp?

Hiya , yes it does . yes guitar is up full. nothing in between

 

Then there is still something bad in the amp.

 

That is a symptom of an open coupling capacitor. Or a partly open coupling capacitor.
But replacing all of the 741 opamps makes perfect sense also.
Time for signal tracing.

 

That is a symptom of an open coupling capacitor. Or a partly open coupling capacitor.
But replacing all of the 741 opamps makes perfect sense also.
Time for signal tracing.

so , focus is now on the caps . ok thanks

 

I heard the hiss and some electricity hum.
Are you still using 56 years old maybe fake 741 opamps? The 741 opamp was never used for audio because it has so much hiss and distortion that it is not mentioned on its datasheet.

 

I heard the hiss and some electricity hum.
Are you still using 56 years old maybe fake 741 opamps? The 741 opamp was never used for audio because it has so much hiss and distortion that it is not mentioned on its datasheet.

I really dont know . what would you say , would be the price of a low and high quality op amp ?

ah.. yes I see what you mean ... am reading about old 071's . found an article on op-amps shootout.

perhaps I can go through the board and make sure all is well first , then later ....upgrade the op amps .

 

At this point it is clear that signal tracing will be the effective method for locating the failure or multiple failures. A suitable signal source could even be an appropriate microphone in front of a small radio speaker. Then, using that small independent amplifier, using the circuit schematic, following the signal through the amplifier circuit to the point where it is lost. At the failed component there will be no signal on the output side.
I once serviced an FM radio this way, and determined that there were TWO open capacitors in the audio section, both before the volume control and just past the volume control. No wonder the original service tech could not fix it.

 

He already did the signal tracing. If I understood correctly, the signal at the opamps outputs were all similar.

@Rabbitbreth, have you put the signal from the guitar through another amp? Perhaps the signal is bad at the source.

 

At this point it is clear that signal tracing will be the effective method for locating the failure or multiple failures. A suitable signal source could even be an appropriate microphone in front of a small radio speaker. Then, using that small independent amplifier, using the circuit schematic, following the signal through the amplifier circuit to the point where it is lost. At the failed component there will be no signal on the output side.
I once serviced an FM radio this way, and determined that there were TWO open capacitors in the audio section, both before the volume control and just past the volume control. No wonder the original service tech could not fix it.

thanks for the input Bill. MrChips has been patiently guiding me through the testing with a little powered speaker probe we built , I wouldn't know how to do it on my own even. I dont quite understand circuit schematics yet .

 

He already did the signal tracing. If I understood correctly, the signal at the opamps outputs were all similar.

@Rabbitbreth, have you put the signal from the guitar through another amp? Perhaps the signal is bad at the source.

Hi Bob , yes the pick ups are good . I have another amp .

# 1 op amp ( from left to right on pics) is working but no signal on the other four op amps and when I hook up the amp speaker its hissy and low volume and crappy sound .

 

Hi Bob , yes the pick ups are good . I have another amp .

# 1 op amp ( from left to right on pics) is working but no signal on the other four op amps and when I hook up the amp speaker its hissy and low volume and crappy sound .

We never came up with a schematic for it, right?

It is possible the other opamps are not in the signal path. Does the amp have reverb? If so, that might be the function of some of the others.

Is the signal after opamp 1 noisy or is it clear?

 

We never came up with a schematic for it, right?

It is possible the other opamps are not in the signal path. Does the amp have reverb? If so, that might be the function of some of the others.

Is the signal after opamp 1 noisy or is it clear?

mr chips made a schematic of the power amp stage only . there is no reverb .

the signal after #1 is quite clear ... a tiny bit of hiss perhaps . I will get back on that .

schematic is on page 4 . #74

 

mr chips made a schematic of the power amp stage only . there is no reverb .

the signal after #1 is quite clear ... a tiny bit of hiss perhaps . I will get back on that .

schematic is on page 4 . #74

Thanks.

 

mr chips made a schematic of the power amp stage only . there is no reverb .

the signal after #1 is quite clear ... a tiny bit of hiss perhaps . I will get back on that .

schematic is on page 4 . #74

The schematic in post #74 is only the power amplifier section, NO OP-AMPS in that circuit at all. and it seems that the power amplifier is working.
Given that the op-amps are all 741 types, with a known pin-out, it certainly should be possible to probe the output pin of each of the devices. probing the inputs would require more circuit information.

 

I would probe at the base then collector of Q1 now. At this point, a signal injector would be more useful.

 

The schematic in post #74 is only the power amplifier section, NO OP-AMPS in that circuit at all. and it seems that the power amplifier is working.
Given that the op-amps are all 741 types, with a known pin-out, it certainly should be possible to probe the output pin of each of the devices. probing the inputs would require more circuit information.

so , probing the input we are looking to see if current is getting there so we can track back from there right ?