Hi all,
I'm a tube guy, I know some SS stuff, mainly simple Wurlitzer EP boards. I'm completely bewildered when it comes to these JC schematics, they're a bit intimidating!
I was hoping someone could point me to the location of the output bias voltages.
Mainly, the issues are subtle crossover distortion on both channels, plus the distortion effect doesn't seem to work. Also on the second channel, there is noise behind the test signal. When you kill the signal, the noise persists for a second and then goes quiet. It may be my imagination but the noise has a chorus effect on it.
The PSU is fine, +/- 43V & +/- 15V rails are making it to each board.
Any tips would be appreciated! thanks for your time
I'm a tube guy, I know some SS stuff, mainly simple Wurlitzer EP boards. I'm completely bewildered when it comes to these JC schematics, they're a bit intimidating!
I was hoping someone could point me to the location of the output bias voltages.
Mainly, the issues are subtle crossover distortion on both channels, plus the distortion effect doesn't seem to work. Also on the second channel, there is noise behind the test signal. When you kill the signal, the noise persists for a second and then goes quiet. It may be my imagination but the noise has a chorus effect on it.
The PSU is fine, +/- 43V & +/- 15V rails are making it to each board.
Any tips would be appreciated! thanks for your time
Attachments
Measure across R52 or R53 (0.3R each), but there is no bias adjustment for the amplifier.
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What am I looking for?
If I plug in 1Khz @ 15mV, I do see a voltage across 52,53,152&153, relative to the volume/tone controls, of course.
If I plug in 1Khz @ 15mV, I do see a voltage across 52,53,152&153, relative to the volume/tone controls, of course.
The output stage DC idle current is V / 0.3, where V is the DC voltage across one of the 0.3R resistors.
For example, if you measure 0.03V, the idle DC current is 0.1 A.
For example, if you measure 0.03V, the idle DC current is 0.1 A.
Idle current, which is 0 when there is no signal. These tests are with 15mV input and controls at 12-o'clock.
Input ch 1:
Amp 1:
R52 - 0.053vdc, 0.176A
R53 - 0.056,
Amp 2:
R152 - 0.058
R153 - 0.056
Input ch 2:
Amp 1:
R52 - 0.040vdc - 0.133 A
R53 - 0.042
Amp 2:
R152 - 0.042
R153 - 0.042
Input ch 1:
Amp 1:
R52 - 0.053vdc, 0.176A
R53 - 0.056,
Amp 2:
R152 - 0.058
R153 - 0.056
Input ch 2:
Amp 1:
R52 - 0.040vdc - 0.133 A
R53 - 0.042
Amp 2:
R152 - 0.042
R153 - 0.042
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There is a connection between the amplifier and the effects circuit.
What does the 3 position SW2 switch do, does the center position change the noise?
How about switch SW3?
What does the 3 position SW2 switch do, does the center position change the noise?
How about switch SW3?
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Sw 2 at central position kills the vibrato/chorus effects. Sound is normal, besides the crossover distortion. In each respective position the effects work as normal.
In the vibrato position, when signal is applied, has an immediate whooshing background noise that diminishes a second after the input signal is killed. In chorus position, I get a slow build whooshing background noise that also disappears a second after input signal is killed.
Sw 3 is the distortion control pot - it tends to cut off a bit of the high end as soon as its switched on, but doesn't really affect the signal much at all as the rotation is increased. No distortion effect whatsoever.
Also, neither of these switch positions affect idle current.
In the vibrato position, when signal is applied, has an immediate whooshing background noise that diminishes a second after the input signal is killed. In chorus position, I get a slow build whooshing background noise that also disappears a second after input signal is killed.
Sw 3 is the distortion control pot - it tends to cut off a bit of the high end as soon as its switched on, but doesn't really affect the signal much at all as the rotation is increased. No distortion effect whatsoever.
Also, neither of these switch positions affect idle current.