SOLVED Cepheid Chorus BBD Chips

[A_Stereo]

I bought 3207 + 3102 Chips from CoolAudio on Stomp Box Parts after reading they were a good seller.

After carefully reviewing this thread: https://forum.pedalpcb.com/threads/solved-cepheid-chorus-only-the-leds-work.8099/

And taking some voltage readings, I'm in line with OP minus the readings in red:

TL022

1 4.29

2 4.32

3 4.32

4 0

5 4.32

6 4.35

7 4.32

8 8.65



3207

1 0

2 0 (They have 4.2) Link to pin 4 3102D (CP4)

3 4.67

4 8.09

5 8.65

6 8.65 (They have 4.2) Link to pin 2 3102D (CP2)

7 4.2

8 4.2



3102D

1 8.65

2 8.65 (They have 4.2) Link to pin 6 3207 (CP1)

3 0

4 0 (They have 4.2) Link to pin 2 3207 (CP4)

5 0

6 8.54

7 2.84

8 8.1



RC 4558

1 5.4

2 5.4

3 5.4

4 0

5 5.4

6 5.4

7 5.4

8 8.8

I don't really know what "CP" means in the context of the datasheets:

https://www.coolaudio.com/docs/COOLAUDIO_V3207_DATASHEET.pdf

https://mediadl.musictribe.com/download/documents/coolaudio/docs/COOLAUDIO_V3102_DATASHEET.pdf

It's hard to tell what I should be checking for that is off, as these two chips basically link together on the pins with incorrect voltage readings without any components in between these links.

The resulting output signal is basically the nonmodulated sound from the output of RC4558 pin1 on the path away from the BBD chips (the path through R34 before it hits the summing amp). Using an audio probe I'm not hearing anything coming out of the BBD chips (pin 7 of 3207D). Furthermore I've confirmed that the audio signal is entering pin 3 of 3207 as intended.

In terms of the 3102 the LFO LED also glows steadily instead of pulsing.

Another thought is that my polarity is backwards on the 3207. Currently have pin1 going to ground, pin5 to 9V. However this should be in line with the datasheet as far as I can tell.

Any help would be much appreciated, thanks!

Link to page with build documentation that has the schematic: https://www.pedalpcb.com/product/pcb416/

 

[szukalski]

 

[A_Stereo]

Sure thing!

 

[A_Stereo]

Solved in case anyone ever finds this. Nothing to do with the chips. Going through the LFO section with an audio probe, I discovered that I used 33R instead of 33K in two locations. Swapping them out solved it, as well as solved the voltage readings on the two chips. Audio probe to the rescue!

 

[A_Stereo]

One more thing: Translating a couple of Brian Wampler's mods to the Cepheid:

For faster (better) rate control, change R2 on the Cepheid schematic from 47K to 150K (he recommended 100K, but 150K sounds better imo).

For more depth, change C11 on the Cepheid schematic from 47pF to 100pF.

It becomes a less subtle pedal after that in a great way. You can still turn down the rate/depth for more subtle sounds, but it makes more of the pots range useable.