CE-1 Input Mod

[Buffalo Tom]

Can someone confirm this is R11 on the CE-1 pcb? Im trying to get my CE-1 to work with guitar without distortion. I have changed the pot to 500K audio and now trying the trick with R11. I have put alligator clips and a 1meg trimmer there and testing different values I parallel with R11. But still ugly distortion.

This is the info I have:
R11 479K gain 48x
dropping it to 220k will get you 23x
dropping it to 270k will get you 28x
dropping it to 330k will get you 34x

For example, 1M and 470k in parallel is the same as 319k.

But I feel nothing above works. Only lower volume but still distortion? Any suggestion how to mod the CE-1 to work without distortion on the input.



Schematic: https://elektrotanya.com/PREVIEWS/45612216/23432455/hangszer/boss/boss_ce1-chorus.pdf_1.png

[Mark Hammer]

Find me another chorus or delay that provides more than a gain of 2x on the input stage.  Go on.  I dare ya. 
And I do hope you are not using the transistor "Mic" pre-amp.

[Scruffie]

Find me another chorus or delay that provides more than a gain of 2x on the input stage.  Go on.  I dare ya. 
And I do hope you are not using the transistor "Mic" pre-amp.

Deluxe Memory Man.

What do I win!? 

[Scruffie]

Have you checked the supply voltages of the unit? It uses a fixed BBD bias which isn't ideal in the first place (although one would hope/assume BOSS/Roland were selecting them) but with component drift, that could have shifted.

There is a divider at (I think, hard to read the #'s) R13 & R15 which would be a good spot to adjust, it would need calculating to keep filter operation the same though.

[Buffalo Tom]

And I do hope you are not using the transistor "Mic" pre-amp.

Im using the low setting

[Buffalo Tom]

Looking at the analogman video and the sound of his CE-1. This sound great.

No way I can have the level control that high on my units. I have two CE-1 and both have the same distortion problem. Does not sound anything like the analogman CE-1.  Even with 1M parallel with R11 and 500k pot.   

[Buffalo Tom]

Have you checked the supply voltages of the unit? It uses a fixed BBD bias which isn't ideal in the first place (although one would hope/assume BOSS/Roland were selecting them) but with component drift, that could have shifted.

There is a divider at (I think, hard to read the #'s) R13 & R15 which would be a good spot to adjust, it would need calculating to keep filter operation the same though.

I think you are absolutely right. I got 22.5V between +/- on IC-1. Schematic says +/- 13V (26V) here so that's a problem to start with..

[Scruffie]

Well then I'd start by replacing all the electrolytic & tantalum capacitors, that'll probably resolve the voltage issue and hopefully that'll fix your distortion issue.

[Mark Hammer]

When my local buddy Tim was designing his acclaimed Retro-Sonic clone of the CE-1, we had many off-line discussions about getting the cleanest possible sound.  Tim was very meticulous in recreating the original, right down to scoring a lot of MN3002 chips. 

One of the topics that came up was the manner in which the CE-1 addresses clock noise.  Instead of using a compander chip, or pre-emphasis/de-emphasis, as some later products might, the CE-1 used a simple noise gate for the wet signal; comprising IC-3 feeding Q12.  When the input signal dips below a given level, Q12 is turned on, bleeding off the delay signal and any clock noise to ground.  Though not the sole or even main source of distortion, often when a gate has some "chatter" and turns on and off very quickly, it gets perceived as "distortion".  This can be because the sidechain feeding the gate has more than some amount of envelope ripple.  If one temporarily lifted the connection to Q12's gate, this would defeat the noise-gating action and you'd hear whatever noise was coming through the wet channel, even if you stopped playing.  HOWEVER, if defeating the noise gate means that the clock whine and hiss remains BUT the "distortion" goes away, then that would suggest the gate section needs some tweaking.

As well, ALL bucket-brigade devices will sound distorted, regardless of input level, if the bias voltage on the input is not set right.  Generally, one would find a trimmer feeding the input pin of the BBD, that could be adjusted until the cleanest and loudest delay signal is heard, but in the case of the CE-1, this job seems to be done by fixed resistors R19 (8k2) and R22 (10k) feeding current-limiting resistor R21 (100k).  Theoretically, one could remove R19 and R22 and replace them with a decent 20k trimmer, or perhaps a 10k trimmer with 6k8 on one end and 1k5 on the other.  Alternatively if the 10uf cap that would normally stabilize the bias voltage (C15), perhaps when you go about replacing caps, start with that one and see if it ameliorates things.

[Scruffie]

Just to point out, the CE-1 does use pre & de-emphasis, it's just hidden inside the low pass filter structure. See C06.

[Mark Hammer]

Hadn't noticed it before, but it's pretty dang wimpy pre/de-emphasis, compared to say, the CE-2.  But I gather the strategy is that IC1 boosts the signal which is then attenuated by R13 (22k) and R15 (10k), R13 being bypassed by the .0068uf cap.  CE-2 and later pedals would switch things around and use differential gain for highs at the input, compared to uniform gain and differential attenuation.

But, good eye. 

Incidentally, depending on the schematic one is looking at, C06 is different.  One of the drawings I have shows a cap labelled C06 as a 100pf cap to ground from pin 3 of the IC1 op-amp, and what you refer to as C06 labelled as C09.

[Scruffie]

I've never really delved in to the costs & benefits of actively boosting the highs exclusively vs. passive highs with full signal boost, It's done both ways across the 70s, I think you picked based on what you expected your input source to be rather than one being wimpy over the other.

I think the noise gate is mostly because the MN3002 was a damn awful BBD, the signal loss is atrocious which needs making up at the end of the mix.

I'm not even sure if that really says C06 or it's some kind of ancient written language, I can't believe after all these years these are the best copies we have of that schematic.

[Mark Hammer]

The one I posted was simply one that came up on an image search, such that I could simply insert a link.  I think I have more legible ones on my hard drive.  Of course, the bottleneck in all this is that many of these were scanned and posted, or at least saved for later posting, in an era when scanners were not exactly the highest resolution.