I just finished assembling the B1 based on the diagram taken from passdiy. I used the pcb and jfet purchased from pass lab and I added the following material:
Panasonic ECO-S1EP153BA 15,000 uf 25V EL caps
Vishay BFC241671005 CAP FILM 1UF 63VDC 2%
Nichicon QAP2E106KRP CAP FILM 10UF 10% 250VDC
1N914 diode-VSCT general PURP 75V 200MA
Vishay Dale CMF501K0000FHEK RES 1.00K OHM 1 / 4W 1%
Vishay Dale CMF5010K000FKEK RES 10.0K OHM 1 / 4W 1%
Yageo MFR-25FBF52-15K RES 15K OHM 1 / 4W 1%
Yageo MFR-25FBF52-221K RES 221K OHM 1 / 4W 1%
Yageo MFR-25FBF52-1M RES 1M OHM 1 / 4W 1%
Vishay Dale ALSR031R000FE12 RES 1 OHM 3W 1%
Vishay P9A2R100FISX1503ML POT, LOG DUAL 50K
The result is nothing short of disastrous ..... a lot of distortion. since they are hard to find, I would like to know if anyone can give me an idea on what I can try before changing the JFET. Now I'm feeding the circuit by two 12-volt batteries in series.
Thanks
Panasonic ECO-S1EP153BA 15,000 uf 25V EL caps
Vishay BFC241671005 CAP FILM 1UF 63VDC 2%
Nichicon QAP2E106KRP CAP FILM 10UF 10% 250VDC
1N914 diode-VSCT general PURP 75V 200MA
Vishay Dale CMF501K0000FHEK RES 1.00K OHM 1 / 4W 1%
Vishay Dale CMF5010K000FKEK RES 10.0K OHM 1 / 4W 1%
Yageo MFR-25FBF52-15K RES 15K OHM 1 / 4W 1%
Yageo MFR-25FBF52-221K RES 221K OHM 1 / 4W 1%
Yageo MFR-25FBF52-1M RES 1M OHM 1 / 4W 1%
Vishay Dale ALSR031R000FE12 RES 1 OHM 3W 1%
Vishay P9A2R100FISX1503ML POT, LOG DUAL 50K
The result is nothing short of disastrous ..... a lot of distortion. since they are hard to find, I would like to know if anyone can give me an idea on what I can try before changing the JFET. Now I'm feeding the circuit by two 12-volt batteries in series.
Thanks
Can you show us some pictures?
Your power supply is producing 25+ volts unloaded. Maybe even 30V. Please measure the voltage at the battery terminals. Your power supply caps are 25V rated. I don't know if this is the problem but it's a concern. I would find an 18V "wall wart" switching power supply. I don't think the B1 is effected by psu quality very much. Nelson used a switch mode power supply in his own build. It's not amplifying any noise (it's a buffer) so psu quality is not as important.
If you used the jfets from Pass Labs I doubt they are they issue. It is probably your power supply, a mistake soldering the board or your input/output/volume control wiring. That is why it would be good to see pictures.
Are you sure your volume pot is wired correctly and all the RCA jacks are isolated from the chassis, etc?
Your power supply is producing 25+ volts unloaded. Maybe even 30V. Please measure the voltage at the battery terminals. Your power supply caps are 25V rated. I don't know if this is the problem but it's a concern. I would find an 18V "wall wart" switching power supply. I don't think the B1 is effected by psu quality very much. Nelson used a switch mode power supply in his own build. It's not amplifying any noise (it's a buffer) so psu quality is not as important.
If you used the jfets from Pass Labs I doubt they are they issue. It is probably your power supply, a mistake soldering the board or your input/output/volume control wiring. That is why it would be good to see pictures.
Are you sure your volume pot is wired correctly and all the RCA jacks are isolated from the chassis, etc?
the voltage measure al the battery terminal is 25.6. I do no have picture, at the moment the board has been removed from the case because testing it would be easier and so the rca jacks are isolated from the chassis. I also tried eliinating the volume pot by shorting the cw and w terminal.
At the moment there is no input selector.
I also tried to invert the jfet, but no result at all.
This is the measure at the output with input 1khz @1V sinewave.
I found the same signal just after R102/202.
The red one is the "blank" while the blue channel is at the output
I'll post some picture of the board as soon as possible.
My soldering skills, although in the far past I've had a lot of practice, are not so good, and the tolls I used are not very professional. that is why I fear that the Jfet could be damaged.
At the moment there is no input selector.
I also tried to invert the jfet, but no result at all.
This is the measure at the output with input 1khz @1V sinewave.
An externally hosted image should be here but it was not working when we last tested it.
I found the same signal just after R102/202.
An externally hosted image should be here but it was not working when we last tested it.
The red one is the "blank" while the blue channel is at the output
I'll post some picture of the board as soon as possible.
My soldering skills, although in the far past I've had a lot of practice, are not so good, and the tolls I used are not very professional. that is why I fear that the Jfet could be damaged.
Cipo, i built a jfet boz and got the same waveform as you, my fets were from ebay and i suspect them as you cant really screw up a jfet boz.
here are some pics of the pcb please ask for more if needed.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Just tried to power it up with a 18V switching power supplies taken formerly used to power up a laptop and I've the same issue. Could not believe that this happens on both channel the same way...
I can see severe 2nd distortion of the output.
What does the input signal look like?
Post measurements of the voltage across the output capacitor. Both AC and DC.
What does the input signal look like?
Post measurements of the voltage across the output capacitor. Both AC and DC.
@AndrewT
The input signal is a 1khz sine @1V. Red channel is measured directly at the sources while Blue channel is the output.
Looking at the pcb there is a mismatch between the pcb layout and the original scheme. cap C3 is not parallel with C2 but with series R4/D2. Does it make some difference?? looks like no.
waiting for C2 to be full charged makes the things much better. but still not perfect.
I'l try reducing C2 to 1000 uf and see what happens
The input signal is a 1khz sine @1V. Red channel is measured directly at the sources while Blue channel is the output.
Looking at the pcb there is a mismatch between the pcb layout and the original scheme. cap C3 is not parallel with C2 but with series R4/D2. Does it make some difference?? looks like no.
waiting for C2 to be full charged makes the things much better. but still not perfect.
I'l try reducing C2 to 1000 uf and see what happens
D1 is absolutely critical to the correct operation of this buffer.
If you used the wrong one or put it in the wrong way, you will have issues.
If you used the wrong one or put it in the wrong way, you will have issues.
I cannot make out any differences in the red and blue in the second pic.
Pic1 only shows output waveform.
Show both input and output waveforms so that both you and us can compare.
Just read the vert scale.
~0.5Vpp , but the input is 1Vac or ~3Vpp
The signal is attenuated/clipped to ~-15dB. a Buffer should be -0.01dB to -0.1dB
Pic1 only shows output waveform.
Show both input and output waveforms so that both you and us can compare.
Just read the vert scale.
~0.5Vpp , but the input is 1Vac or ~3Vpp
The signal is attenuated/clipped to ~-15dB. a Buffer should be -0.01dB to -0.1dB
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this is the input signal
An externally hosted image should be here but it was not working when we last tested it.
@pico
D1 should be correctly connected as you can se from one of the picture above.
Pass says that this should drawind down the dc voltage when the power supply is turned off. that is not what actually happens. the led stays on for a long time
D1 should be correctly connected as you can se from one of the picture above.
Pass says that this should drawind down the dc voltage when the power supply is turned off. that is not what actually happens. the led stays on for a long time
That input is not 1V sinewave. It is just over 1Vpp or ~300mVac
That explains why the output is showing severe clipping on the +ve side.
This is typical of a single ended stage that has too high an input for the supply voltage.
I think you have crippled the supply voltage.
It should be ~18Vdc
Measure your supply rail voltage at the Buffer.
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this is the view of both input and output
An externally hosted image should be here but it was not working when we last tested it.
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