Cepheoid CE-2 Chorus - Service Notes - Adjustments

equinox

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There is a trimmer on the board, bit NO information in the documentation sheet or online on how to adjust this!! :O

I've been searching around and see in the Service Notes of the original CE-2, it says to apply a 200Hz +3dB since wave to the input and adjust the Q3 emitter (one of the 2SC732TM-GR) until clipping equally on the top and bottom!

Is this how you do it on Buggs' design?? If not, please advise and oh, how to adjust to +3db?? I have an Audio Signal Generator and so can set a sign wave frequency, but adjust amplitude in x.xxV. What voltage is +3dB??!??

PLEASE ADVISE and thanks in advance.
 
Thanks for the feedback. Oh yeah, I forgot about what the Service Notes and previous posting years ago said on the dials.
They actually have the Rate off and Depth on full (see below). The BOSS CE-2 "Service Notes" has the dials set the same and Rate off and Depth on full (see attached). Hope this helps as again, there was no directions in the thread no the Document Files! Not sure what a Pork Barrel is and why not the same as BOSS service directions! That just confuses which way to go!! :O Hope this helps.

CE-2 BIAS PROCEDURE:

This is a quick how-to for the CE-2 trimpot adjustment, or more correctly "how to set the BBD operating point".

Just done this to my MIT ACA CE-2 and it will work on any CE-2.

Tools
- You will need a scope. No way around it. I bought an old Tektronix 2215A off eBay for $100. A worthwhile investment...
- Phillips screwdriver to remove the back plate.
- Small flat-blade screwdriver to adjust the pot.

Procedure
0) Go get the service notes from here: http://www.godiksennet.com/images/sch/CE2.jpg

1) Remove the backplate and swing the board out

2) Obtain a 200Hz +3dBm signal source. I used CoolEdit on my PC to generate a 200Hz wave, then put it through a little Behringer mixer I have to boost it up to +3 dBm. Power the pedal with a known good battery (or the correct Boss power supply). Plug a lead carrying the +3dBm signal into the pedal input and turn on the pedal. Turn the "rate" pot fully anti-clockwise and the "depth" pot fully clockwise.

3) Set the scope to 500mV/division, 1ms/division sweep, and "AC" in. Use the service notes to locate Q3 on the board. It is quite near the trimpot. Connect the scope probe to the emitter of Q3 - it is leg of Q3 furthest from the trimpot. I just held my probe tip onto the solder pad on the solder side of the board.

4) Increase the incoming signal until you see one of the three waveforms on the service notes. If your signal is too low, the waveform will look like a perfect sine wave - wind up the signal until it starts to clip and looks like one of the three waves. Once you see a clipped waveform, "center" the waveform by turning the trimpot (i.e. until there is equal clipping on top and bottom of the waveform).

5) Once the waveform is centered, lower the incoming signal until one of the sides of the waveform stops clipping - this will look like either the top or bottom waveform on the service notes. When this happens readjust the trimpot until the waveform is again "centered" (there is equal clipping on top and bottom of the waveform).

6) Disconnect everything, and close up the pedal. You are done!

Note that at no point in the adjustment are we looking at DC-offset. Just leave the scope input set to "AC".

Looking at the CE-3 schematic, this same process will also work for the CE-3 (only change is the measuring point is Q8 in the CE-3, not Q3). You are on your own finding the emitter of Q8...
 

Attachments

  • BOSS CE-2 Service Notes.pdf
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Thanks for the feedback. Oh yeah, I forgot about what the Service Notes and previous posting years ago said on the dials.
They actually have the Rate off and Depth on full (see below). The BOSS CE-2 "Service Notes" has the dials set the same and Rate off and Depth on full (see attached). Hope this helps as again, there was no directions in the thread no the Document Files! Not sure what a Pork Barrel is and why not the same as BOSS service directions! That just confuses which way to go!! :O Hope this helps.

If you’re using an oscilloscope, Rate will only affect the period of the sine wave it’s being sent, so being half or full won’t really matter, it’s the max depth that matters.

The Madbean Pork Barrel is another PCB for the CE-2 circuit, and though the madbean instructions are not as exact as feeding the pedal a perfect sine wave and measuring it on an o-scope (after all, not all DIYers have signal generators and o-scopes, and biasing by ear is often more than good enough), it’s essentially shooting for the same goal - bias the circuit so that it produces the effect but doesn’t clip.

(Same process for the Caesar as well)
 
In the BOSS Service Notes, they are measuring the emitter of Q3.
What is the transistor on the PedalPCB that should be measured and as the BOSS uses 8 transistors (3 including Q3 that are 2SC732TM-GR and 5 that are 2SC945-P), but the PedPCB version only uses 5 and all are 2N5088!
Please advise. Thanks in advance.
 
"Emitter of Q5." - Thank you for the confirmation!
Stickman 393 - Welcome!
Now, just to understand what "+3 dBm" coorelates to?!?? Is it .100V, 1.00V? 1.2345V?!?? SO I can set my Audio Signal Generator to the appropriate amplitude.
 
Last edited:
That's +3dBm.

[dBm][Watts][Volts]rms[Volts]p[Volts]pp
30.200E-02315.853 mV446.616 mV893.232 mV

Ok. I'll set the audio frequency generator to ~315.853mV RMS. Thanks Buggs.
Using the orignal ICs (3101/3007)and zener. Just got a magnifier yesterday to get the pads. Good Lord they are small and my eyes just went recently for seeing up-close! Would have preferred a standard .100" (i think it is) pads and solder in headers and just use computer jumpers so set the mode. Much easier. This is soo close...gonna me a bitch to not bridge. Wich me luck! Else...have them connected and just cut the connection(s), but jumping would be better and more versatile.
 
The solder jumpers have been spaced a bit more on the newer revision of the board to prevent bridging, but since they're set-and-forget I preferred that method over removable jumpers.

If someone (who doesn't know better) gets in there fooling around with the jumpers they could burn traces or destroy the BBDs.
 
Well, I got the pedal built, but not working nor getting anything that resembles the Service Notes response off of the Emitter of Q5 (probably because not working)! Soo, I'll need to go thru it hieristically and see what's up.

I was able to bridge the pads on the right side for the 3101/3007 ICs (see pic).

I hope to get this going soon. Everyone loves a good CE-2 pedal! :) Not sure if the other ICs called out are improvements are not (always up for improvements and lower noise floor in the modern age), but had a couple other CE-2 clones from days past lying around with original ICs and see people having issues finding them, soo decided to just pull them out of the old pedals as the PedalPCB will be the one I'm using.

I'll let you know how it turns out.
 

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  • IMG_20210630_140743172_HDR.jpg
    IMG_20210630_140743172_HDR.jpg
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