Xotic BBpreamo bass no Gain
Good afternoon.
I have a xotic bb preamp bass that when activated does not generate any distortion. At the maximum travel of the potentiometer it is as if it were in the 1/4 of the same
I have changed the two ICs for testing, also change the 1N4148 diodes, but still the problem persists.
I have noticed that in the Volume potentiometer the voltage fluctuates between 4.5V and drops to 2V, without moving the potentiometer.
In the 10uF capacitor connected to the potentiometer, the voltage also fluctuates between 4.5V up to 2V, change it but the problem still persists.
The footswitch works smoothly.
I am following this scheme, but I cannot detect the problem.
Regards
I have a xotic bb preamp bass that when activated does not generate any distortion. At the maximum travel of the potentiometer it is as if it were in the 1/4 of the same
I have changed the two ICs for testing, also change the 1N4148 diodes, but still the problem persists.
I have noticed that in the Volume potentiometer the voltage fluctuates between 4.5V and drops to 2V, without moving the potentiometer.
In the 10uF capacitor connected to the potentiometer, the voltage also fluctuates between 4.5V up to 2V, change it but the problem still persists.
The footswitch works smoothly.
I am following this scheme, but I cannot detect the problem.
Regards
Thanks for answering, these are the voltages:
Q1
E 3.08
C 9.10
B 3.56
Q2
E 3.09
C 9.10
B 3.67
IC1
1 4.48
2 4.50
3 4.48
4 0
5 4.50
6 4.69
7 4.48
8 9.10
IC2
1 4.51
2 4.55
3 4.51
4 0
5 4.50
6 4.52
7 4.51- 4.52
8 9.09
Q1
E 3.08
C 9.10
B 3.56
Q2
E 3.09
C 9.10
B 3.67
IC1
1 4.48
2 4.50
3 4.48
4 0
5 4.50
6 4.69
7 4.48
8 9.10
IC2
1 4.51
2 4.55
3 4.51
4 0
5 4.50
6 4.52
7 4.51- 4.52
8 9.09
- Manfred
- Tube Twister
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Does the base voltage at Q2 also change when you move the volume potentiometer?
- plush
- Cap Cooler
Volume pot is tied to bias voltage and AC coupled with nearest stages.
Fluctuation means that bias is not stable or/and coupling caps are shorted or defunkt.
Check C14 and C15 for possible shortages (desolder at least one pin of each and measure dc resistance)
Check resitances of R25-R26, check C17, C18 and D6 for possible shortages or malfunction.
plush wrote: ↑03 Jun 2020, 14:25
Volume pot is tied to bias voltage and AC coupled with nearest stages.
Fluctuation means that bias is not stable or/and coupling caps are shorted or defunkt.
Check C14 and C15 for possible shortages (desolder at least one pin of each and measure dc resistance)
Check resitances of R25-R26, check C17, C18 and D6 for possible shortages or malfunction.
The resistance of C14 (10uF), depending on how you measure, positive-negative, or negative-positive, ranges from 500K to 6M. C15 (100nF), measures infinity (1)
- plush
- Cap Cooler
I have changed the 10uF capacitor, and checked the other components (the ones by the source, they are all ok) but the problem persists
- Intripped
- Cap Cooler
Perhaps the potentiometer itself is bad. Sometimes one or more pins loose the mechanical connection with the internal carbon trace, creating an intermittent contact.
This could explain the fluctuating voltage.
Edit
You should have noticed that also the volume of the pedal fluctuates though...
This could explain the fluctuating voltage.
Edit
You should have noticed that also the volume of the pedal fluctuates though...
Yes, you are absolutely right! The volume also changes, when it is at 0, the signal continues to pass ...Intripped wrote: ↑04 Jun 2020, 04:36 Perhaps the potentiometer itself is bad. Sometimes one or more pins loose the mechanical connection with the internal carbon trace, creating an intermittent contact.
This could explain the fluctuating voltage.
Edit
You should have noticed that also the volume of the pedal fluctuates though...
What I don't understand now is, how could it be that when putting the audio probe on Pin 1 of IC1, no distortion is heard, since there should be have the greatest distortion, but it is not ...
Sorry for my Bad english
- Manfred
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Hi Shiflet
The error is difficult to find without measurement, what measuring equipment do you have?
The error is difficult to find without measurement, what measuring equipment do you have?
- Manfred
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With an normal multimeter you can also measure AC voltages in the lower frequency range.
The output signal of the guitar generated with low E-string or A-string should work.
Up to which output of the OP-amps you can detect the signal with the audio probe?
The output signal of the guitar generated with low E-string or A-string should work.
Up to which output of the OP-amps you can detect the signal with the audio probe?