Wow, that is quite a bit of peaking. Didn't run across that info in my quick search. Interesting. I've become a 'Local Live Music' fan and am slowly assimilating some of the technical info.

 

A typical guitar speaker has a frequency response worse than a lousy old AM radio or telephone.
A typical 50 years old man also has a poor hearing's frequency response.
I am 78 years old and my hearing aids work fine with a high frequency peak that is more than +60dB.

 

I had to measure it. The output from the guitar pickup is about 100mV rms into the oscillscope probe (10MΩ input).

 

some tests done on pickup output

https://sound-au.com/articles/guitar-voltage.htm

 

Of course the output level depends on how hard you strum the strings. A proper string picker also increases the output level.

 

Of course the output level depends on how hard you strum the strings. A proper string picker also increases the output level.

picks n fingertips n townshend windmills ..yeh .

 

ok. op amp arrived.

measured: -0.036 .

 

ok. op amp arrived.

measured: -0.036 .

Audio measurements are at a certain frequency and the voltage level should be "peak" so that your oscilloscope can show when the amplifier output is clipping with extreme distortion.
An ordinary multimeter usually measures the levels of only 50Hz and 60Hz electrical sinewaves accurately. It does not show amplifier clipping.

Then your 0.036 number has no meaning.

 

I don’t think @MrChips was asking for a DC voltage measurement after the opamp, he was asking you to use your signal tracer (amplified speaker + capacitor gadget) to see if the signal makes it there. And, as always, you need to strum the guitar while doing so.

 

I don’t think @MrChips was asking for a DC voltage measurement after the opamp, he was asking you to use your signal tracer (amplified speaker + capacitor gadget) to see if the signal makes it there. And, as always, you need to strum the guitar while doing so.

oh yeh!!! ooops .. too much time in between . thanks for that

 

so . have done the right test . I'm back ... I'm focused . so I have a strong signal coming through the powered speaker now . faint hiss in the back ground .

 

so . have done the right test . I'm back ... I'm focused . so I have a strong signal coming through the powered speaker now . faint hiss in the back ground .

Okay, so that opamp was bad. I would connect the speaker back to the amp, it might just be fixed.

 

As Bob says, the acid test is getting proper sound out of the loudspeaker.
If no joy, go back and do the test on post #128.

 

Okay, so that opamp was bad. I would connect the speaker back to the amp, it might just be fixed.

hooked up amp speaker and Im still getting white noise but the guitar signal seems a bit louder than before . does that make sense ? on to the next op amp ???

 

hooked up amp speaker and Im still getting white noise but the guitar signal seems a bit louder than before . does that make sense ? on to the next op amp ???

You never mentioned anything about the guitar signal in previous tests.

Go back and do the test from post #128.

 

You never mentioned anything about the guitar signal in previous tests.

Go back and do the test from post #128.

I hook up the powered speaker and play a string ...that's what I'm calling the signal ,right ? Have just done this test on no. 128 and there is no signal , no hiss . nada.

 

You have four remaining uA741CP op-amps to check.
The pinout of uA741 and TL071 are the same. The output signal is on pin-6. Try to probe the signal at pin-6 without shorting to any adjacent pin.

 

You have four remaining uA741CP op-amps to check.
The pinout of uA741 and TL071 are the same. The output signal is on pin-6. Try to probe the signal at pin-6 without shorting to any adjacent pin.

View attachment 306968

View attachment 306967

ok . powered speaker test : one lead on GND .. and other lead/probe on pin 6 of each op amp . yes ?

so.. on the pic above . pin 6 would be, top pins 3rd from the left . ?

 

ok . powered speaker test : one lead on GND .. and other lead/probe on pin 6 of each op amp . yes ?

Yes.

Let us identify the op-amps #1 to #5 starting from the left. Describe what you hear from the PC speaker while probing pin-6 and playing the guitar or bass. Get an extra pair of hands if you need it. Shorting pin-6 to another pin will be disastrous.

(I am going to be on the road for the next three days. You may want to start replacing each op-amp one at a time.)

 

Yes.

Let us identify the op-amps #1 to #5 starting from the left. Describe what you hear from the PC speaker while probing pin-6 and playing the guitar or bass. Get an extra pair of hands if you need it. Shorting pin-6 to another pin will be disastrous.

(I am going to be on the road for the next three days. You may want to start replacing each op-amp one at a time.)

OK . thanks for that . will be careful with my probe . safe travels ...going anywhere exciting ?

so #1 have signal .
#2 , 3#, # 4 , #5 all no signal.

will begin replacing # 2 next ... then test and move on