Cepheid Chorus no effect

M

Megachunk

New member
Hello
I read through some of the other like threads on this issue, but can’t seem to figure mine out. LEDs work, LFO flashes, passes signal, but no effect. Even with slight adjustments to the trim pot, all I get is clean signal, and in some areas of the pot loss of signal. I did have an IC Chip, the TLO22, in backwards, which fixed a lot of the noise present. Just no chorus effect. I have built another one that I use all the time but this one is so close. I posted my voltages and an image of the board. If any of you experts notice anything, would appreciate a starting point.
Thanks, Mike

IMG_1048.jpeg IMG_1049.jpeg
 
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Do you have a DMM with a frequency feature? If so, you should measure pin 2 or 6 of the BBD to make sure your clock is working. No clock = no delay. Should measure ~40kHz. Should also vary with the rate and depth knob.

You can also measure the voltages on the transitors. If you check madbean's pork barrell build doc there are voltages to compare to. I might reflow Q2 and Q4 too.

The basic sections of a chourus are the clean signal (seems good), the LFO (working), the delay line + clock (suspect), and the mix section.
 
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Bio77 said:
Do you have a DMM with a frequency feature? If so, you should measure pin 2 or 6 of the BBD to make sure your clock is working. No clock = no delay. Should measure ~40kHz. Should also vary with the rate and depth knob.

You can also measure the voltages on the transitors. If you check madbean's pork barrell build doc there are voltages to compare to. I might reflow Q2 and Q4 too.

The basic sections of a chourus are the clean signal (seems good), the LFO (working), the delay line + clock (suspect), and the mix section.
Click to expand...
I got a DMM with frequency feature. When I measure pins two and six on the V3207D to ground, I get around 50 or 60 Hz for about two seconds and then it goes right to zero and stays there.
Could you please point me to where mad bean’s pork barrel build dock is please? I would like to measure the transistors next. i’m just having trouble finding it.
Thanks for your help Bio77!
 
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Megachunk said:
I got a DMM with frequency feature. When I measure pins two and six on the V3207D to ground, I get around 50 or 60 Hz for about two seconds and then it goes right to zero and stays there.
Could you please point me to where mad bean’s pork barrel build dock is please? I would like to measure the transistors next. i’m just having trouble finding it.
Thanks for your help Bio77!
Click to expand...

IMG_3726.jpeg


First search return on Google s the 2019 version:

Looks like the newer version is the second hit.
 
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Since the clock is firing up and then leaving, maybe you have a loose connection. Might be worth reflowing some suspect solderpoints. The voltages can help you identify the area on the circuit you want to address carefully. Also, with this circuit the trim sets the bias for the BBD but also the bias for the other opp amps (it's a weird design that I don't like). Anyway, that means that you should have the trim pot in the middle (where you were getting sound in your video) when you measure voltages. Also, the volatges won't be the same as the doc but they should be close and realative to each other, if that makes sense.
 
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