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Hi, I'm having issues with a recent Chorus pedal build. Hoping someone can help me out!

- I get sound when the pedal is off (bypass works)
- I get sound without the effect when the pedal is on
- LED blinks and responds to the Rate
- Turning the trim pot can take away all sound or result in a lot of distortion - but still no chorus effect

I think I'm getting the following voltages. Let me know if I should measure anywhere else.

4558
Pin 8: 7.28VDC
Pin 7: 3.07
Pin 4: 0VDC
Pin 1: 3.07VDC

3207
Pin 1: 0VDC
Pin 5: 7VDC
Pin 8: 7.26VDC

I'm also happy to upload pictures but getting an error that they are too big when I try to add them as an attachment.

Attachments have a file size limit of 1 MB. Try reducing either their size or color depth to get the file size down. Most any image editor will let you do this, even MS Paint. I like Irfanview for this purpose, and it's free.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Here are the pictures - thanks for taking a look at it!

I swapped batteries because the V+ voltage was really low. Still have the same symptoms, but her are the updated measurements:

4558:
- Pin 8: 8.81VDC
- Pin 7: 6.88VDC
- Pin 4: 0VDC

3207:
- Pin 8: 4.6VDC
- Pin 7: 4.6VDC
- Pin 5: 8.46VDC
- Pin 4: 7.9VDC
- Pin 2: 4.0VDC
- Pin 1: 7.9VDC

TL022:
- Pin 8: 8.8VDC
- Pin 4: 0VDC

The voltage bias is also set at 6.2VDC (I think - I'm measuring from the third leg of the bias pot).

Here are the voltage values for the 3102:
- Pin 1: matches Pin 5 of the 3207
- Pin 2: 3.7VDC
- Pin 3: 0VDC
- Pin 4: 3.7VDC
- Pin 5: variable
- Pin 6: 7.45VDC
- Pin 7: Variable, about 2.5VDC
- Pin 8: 7.26VDC

I forgot to add that I traced the audio back to pin 7 of the 4558. The clean signal comes out of pin 7. I could not get any audio signal from pin 6 of the 4558 or further back in the path, but it may simply be too low to come through my amp.

Is it possible that I have a bad 3207 or could there be an issue with the 3102? I am not sure what the voltages for the 3102 should be.

BTW, debugging these is almost as fun as building them

Hi - Will you please re-check these readings and make sure that you are reading the correct pins? The MN3207 is IC2. Pin 1 should be grounded and have zero volts.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Sorry, not sure how I messed up those measurements. Here is what it is:

3207:
Pin 1: 0vdc
Pin 3: variable
Pin 5: 7.9vdc
Pin 7: 4.15vdc
Pin 8: 4.15vdc

The notch is oriented up.

Do you have a signal tester?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

I have the one from BYOC. I could only get audio out of PIN 7 from the 4558. I was not able to hear anything back beyond that in the circuit. Where else should I test?

Listen for input signal on pin 3 of the BBD and then output signal on pins 7 & 8. The output signal will be vibrato as it is pre-mixer. Try adjusting the trim pot if you don’t hear any output.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

I can hear audio on pin 3 of the BBD. It's lower volume than the full output signal so I think I'm hearing the correct input. However, I cannot hear anything on pins 7 or 8. Given that the LED is blinking, am I correct in assuming the LFO / Clock works correctly and the BBD is likely dead?

Yes. The voltages overall look pretty good. I think the BBD is probably dead. I would email BYOC and request another one of you don’t have one hand. Do you happen to have another pedal with the same BBD in it?

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

I got a new chip from BYOC and swapped it in. I still have the same behavior - weak audio on pin 3 of the 3207 and no audio on pins 7/8. I had good audio coming into R13, before Q2, so I'm not sure if there is an issue there. I do have another chip on order that I'll try. Is it possible the audio on pin 3 is too weak to get delayed by the 3207 or is the lower volume normal? Thanks!

Perhaps you have the wrong value in for R14. I can't tell from the pic.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

Right. I was going to suggest testing signal at IC1 pin 1 and on both sides of R15. Let's see where that wet signal path is dying.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

R14 = 10K
R15 = 4.7K

The signal drops directly out of Q2. It's normal volume on R13, drops in volume coming out of Q2. Looking at the board, top to bottom, I hear a *very* faint sound on the bottom leg of Q2 and the same volume of signal I hear on R15 coming out of the top leg.

Verify this by pulling the BBD from its socket and test again. Want to make sure the BBD is not dragging down the signal.

If it is the same with the BBD removed, you want to rework your R11/C5, R12/C6, R13/C7 networks by verifying values, resoldering the connections, and verifying ground connections, as well as resoldering Q2, checking those voltages (full supply on the collector, less on the base and emitter), and verify R14's ground connection.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

I checked with it pulled and had the same result. I'm pretty sure Q2 is broken so I'll order another transistor.

Hi, Guys - thanks for sticking with me and helping me out. Hopefully, this will be instructive for someone else. I keep getting the same results:

- Replaced Q2 with another 2N3904
- Validated R11, R12, R13, and R14 all at 10K with a multi-meter
- Visually validated the capacitors and they seem fine
- Tested Q2 and I'm getting v+ on the collector and less on the other legs

Again, I'm getting sound but it decreases in volume on the emitter of Q2. I get no output on pins 7/8 of the BBD.

One thing I noticed that seemed strange was that R16 is not connected to v+. Instead, it's connected to ground on the back of the board (shares a trace with R21). Is this correct? According to the schema it should be going to v+. It's missing the trace on the front of the board like the older versions of the PCB.

That is actually correct for an MN3207 BBD. I posted the incorrect schematic above (older version with an MN3007 - sorry about that) and the current schematic must be wrong because you should give the output of a 3207 a ground reference, not a V+ reference. I missed that before.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

So, we had a little weirdness there because I was confusing which BBD in this circuit (I didn't realize that BYOC had switch the BBD from a MN3007 to a MN3207), and the schematic has an error in it (this is being fixed now). Your BBD voltages as previously posted look good, and you've swapped the BBD, so this shouldn't be a BBD issue.

The current schematic for this circuit is posted here: http://www.byocelectronics.com/analogchorusschematic.pdf

I think you need to focus on IC1a (the input amplifier) and the R/C networks between IC1a and the BBD (C4-C7, R10-R15, Q2). You've replaced Q2, so that probably isn't the issue.

Some other things to check:
- Remove the BBD from the socket and leave it out. We're looking to get strong signal at pin 3 of the empty MN3207 socket. That is the goal for now.
- Verify that you have strong clean signal on IC1 pin 1, and that the signal is noticeably reduced at pin 3 of the empty MN3207 socket.
- Make sure your bias voltage is good. Measure DC voltage on pin 5 of IC1 and adjust the trim pot so that voltage there is 1/2 of what it is on pin 8.
- Once the bias is set, measure and post the voltages from all pins of IC1.
- Report voltages from both sides of R10.
- Verify with your meter that only one end of C5 and R14 are grounded.
- Measure and report voltages from both sides of R15.

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MasterDelayer/Reverbrador/Ampaholic/TopJacker

Have you tested the voltage at the base (middle leg) of Q2 yet? I'm not seeing that in the thread. If not, could you please test that?

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com

The voltage of the collector of Q2 (bottom leg) is 8.14vdc. The voltage of the base (middle leg) seems to vary. The voltage of the emitter is .5vdc. What value should I be looking for?

I'll test the signal, etc., tomorrow.

That may be your problem. I don't have a unit handy to actually test (perhaps Morgan does), but I believe the bias voltage on the base of Q2 should be around 4 or 4.5V, not variable as you've described. R10 connects to 1/2v and sets the bias for Q2 and the BBD. Pin 3 of the BBD should be around 4 or 4.5V as well. That bias voltage has to go through all that low pass filtering (R11, 12, and 13, and C5, 6, and 7) so there are a number of places that something could be going awry.

If you have some sockets handy, you should socket Q2.

_________________
*patience is a virtue*

Please do not PM me. email is prefered. keith@buildyourownclone.com