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Restoring/Modding Boss CE-300
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gavgomad



Joined: Jan 29, 2006
Posts: 69
Location: Canada

PostPosted: Sat Dec 08, 2007 5:32 am    Post subject: Restoring/Modding Boss CE-300 Reply with quote  Mark this post and the followings unread

Hey all!

I've always loved that big stereo Roland chorus sound, but the SDD was way out of my league either in terms of DIY (board layout would KILL me!), and certainly "vintage value".

So.... I managed to score something in the same "family" - the CE-300. Mine is a little cosmetically rough, but functionally seems OK.

I love this box, but I can't help but think that its sound could be cleaned up a bit.... It's a little "hummy", so I'm going to go in and clean up the power supply anyway (BTW, anyone know what one should really do with that odd ground wire connector on the back panel? ;-P )

I thought maybe keeping the front input jack "as-is", and then putting a decent preamp on the rear input jack might help feed the initial gain stages better - much like Scott did with his Dim-C clone....

Maybe a general re-capping of the electrolytics....

Any other ideas from the list?

Gav
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johans121



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PostPosted: Tue Dec 11, 2007 9:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Hey man, can you please keep this thread updated with your mods? I have one of these units. I love it however it doesn't play very nicely with line levels - mine clips with relatively low input levels, and the output seems extremely low.

Any adjustments to allow professional gear to be used with it would be awesome! I would love to be able to simply return this on an aux return on my mixer rather than having to route it through a preamp.
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gavgomad



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PostPosted: Tue Dec 11, 2007 9:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Hiho!

Will do.... I'm still trying to figure out how "appropriate" this topic is in this particular forum, but I think it's at least somewhat on topic as the key is getting this unit going with my existing keyboard and DIY rig....

So far, two of the three power supply electrolytics have now been replaced (had them lying around, so I thought I'd see if it made a difference on the hum). The answer is YES.... If you haven't replaced the electrolytics in the supply, you won't regret the few pennies in parts! I'm doing the last one as soon as a replacement part comes in....

I'm going to play around with Scott Stite's preamp from his Dim-C and see if that helps the distortion/bandwidth issue. I can't help but think that if those compressors were seeing a better matched signal from a preamp, the hiss on the top end would be reduced....

I may also get a replacement set of higher quality electrolytics and replace everything on the board - Roland used some pretty cheap electros, and they have to be dry by now (if the supply caps are telling - and they are!) It's not too expensive, will take some time, but I think it will be worth it in the long run.

Will keep you posted!

Gavin
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johans121



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PostPosted: Tue Dec 11, 2007 10:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Gavin, thanks a lot!!

To address your concern, you are making the mods/repairs yourself - so I would imagine this is the appropriate place for this thread.

Now back to the topic on hand. Seriously please keep this thread updated! I would most certainly appreciate it as I would like to breathe some new life into my ce-300!

-Jim
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PostPosted: Tue Dec 11, 2007 10:14 am    Post subject: Reply with quote  Mark this post and the followings unread

gavgomad wrote:
I'm still trying to figure out how "appropriate" this topic is in this particular forum


Both appropriate and interesting Very Happy

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germaniac



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PostPosted: Tue Dec 11, 2007 1:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Gavin and All,

You might have seen my OT post on the CE-1 chorus thread, but coincidentally I just finished doing a whole slough of mods on my CE-300, and IMHO it sounds a bit better than stock now. I can get to posting all the technical details later today, but for now here's a short sample of how the mods sound.

Regards,
Joe


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gavgomad



Joined: Jan 29, 2006
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PostPosted: Tue Dec 11, 2007 2:49 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey germaniac!

Yes, I did note your post on the CE-1 thread.... I was trying to decipher what was going on in the circuit diagram to figure out where one could potentially sneak in some bypass caps or something.... Not sure if that was one of your solutions....

In any event, I would be MOST interested in hearing your mods! The mp3 you played sounds great - less hissy than what I'm getting at present.... Any chance of getting a sample of some brighter material to get a sense of the noise floor?

Any info you can share would be fantastic! I think the potential is in the box to be a very sweet chorus.... not quite a Dim-D, but still.... Wink

Gavin.
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germaniac



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PostPosted: Tue Dec 11, 2007 3:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

gavgomad wrote:
. . . . I was trying to decipher what was going on in the circuit diagram to figure out where one could potentially sneak in some bypass caps or something.... Not sure if that was one of your solutions....

In any event, I would be MOST interested in hearing your mods! The mp3 you played sounds great - less hissy than what I'm getting at present.... Any chance of getting a sample of some brighter material to get a sense of the noise floor?

Any info you can share would be fantastic! I think the potential is in the box to be a very sweet chorus.... not quite a Dim-D, but still.... Wink

Hey!

Yes, bypassing was part of the solution--some might say to a maniacal degree. . . . Laughing

Thanks on the MP3. I could do some more samples no problem, but the thing about that one is, it's only the flute sound itself (or whatever I used) that's dark, so that would actually tend to accentuate any hiss in the CE-300. So the noise floor is pretty decent with line level signal. . . .

I agree the CE-300 has potential--mine is almost there! I've almost got my catalog of mods together. Will post soon.

Regards,
Joe
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germaniac



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PostPosted: Tue Dec 11, 2007 5:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Friends,

As you said Gavin, it seems like the CE-300 should fill the bill as a Dimension-type effect just by glancing at the circuit. But I was frankly a little disappointed when I got hold of one. It had a strange, washy, back-and-forth sound when used in stereo, and didn't have any of the floating ethereal effect that my DC-2 has. So I went probing and poking around to figure out what could be done. Here's a run-down of all the mods I did to my CE-300 in the last month or so.


INPUT LEVEL:

I reduced the input level by changing both R3 and R4 to 10K. With those values, you get unity gain at max, but if you're using line-level signals like synths, you'll almost never need to boost the gain. Also, lowering those values to 10k lowers the input noise a little.


LFO SYMMETRY:

I found several weird things here. The DC on the PS pins of the BBDs and clocks was fluctuating more than a volt in sync with the LFO. Whether this really caused an audible problem or not, it seemed wrong. Also, it seemed to me the sweep of the LFO was off-center in terms of rising and falling equally on either side of a "zero" point. Finally, at full CW of the DEPTH control, one of the LFO inverters clipped the bottom half of the triangle wave because there's too little headroom for it to reproduce the LFO output (see attached o-scope shots). Here's what I did to try and fix these problems:

--Reduced LFO output slightly by changing R58 to 120K. This prevents LFO waveform clipping at max DEPTH. You do get a little less depth of course, but there's another fix for this later. . . .

--Increased resistance of LFO output dividers to >1M. These are the resistive dividers consisting of R44/R69 on the "A" side and R64/R65 on the "B" side. For testing purposes, I tacked in a 1M pot and adjusted it for a more symmetrical LFO sweep, then measured the pot. The ratio was about 1-5, so I replaced R65 with 200K and R64 with 1M for the "B" side. On the "A" side I replaced R44 with a 1M and R69 with a 500K ten-turn trimmer. The trimmer helped dial in the symmetry, which is important for a good sound. Also, the higher resistance seemed to reduce the PS fluctuations down to a couple hundred millivolts. After these changes, I went through and adjusted RT8 and the 500K trimmer using scope/ears to get the best symmetry and sound.


BBD and CLOCK SECTIONS:

To further match the A and B side, I subbed matched polystyrene caps for C27 and C41, and then adjusted RT5 so that both clocks were dead nuts. The clock freq on mine came out to about 135K, which is fairly high for a chorus unit--that's only about 3-4ms of delay with a 3007. My next mod will be to try and drop that down to around 10-12ms, which will likely make up for some of the range lost by the DEPTH control in the earlier mod. I think this can be done by changing R46/R62 in the VCO from 100K to about 33K, but I haven't tried it yet. . . .


POWER SUPPLY DECOUPLING:

I didn't think the caps on the "digital" supply line were big enough, so I changed C12 and C22 to 470uf. Also, on the trace side of the PCB, I added 2.2uF tantalum caps to PS pins of all op amps, compander chips, BBDs, and clocks, plus on BBD bias, Vref, and Cancel supplies. Some might call this overkill, but I'm a big fan of heavy PS decoupling. It always seems to makes op-amp circuits sound much smoother and cleaner to my ear, and especially in this case, where spurious clock signals might dirty-up the PS lines. There wasn't any general PS hum in mine like Gavin mentions, so I left the power supply pretty much as-is.


As for the o-scope shots, the unmodded one shows the waveform clipping with the unaltered output level. With trimmer RT8 adjusted for equal-sized waves, there was no way to avoid this clipping at 100% DEPTH. With the LFO level decrease mod, you see a little less amplitude at max DEPTH, but the clipping is nearly gone.

The Ditty sample (previous post) was done with full DEPTH and fairly slow RATE. Sounds nice and clean I think, and not as swimmy and warped as the stock version.

Anyway, sorry the avalanche of info, but I hope it helps a little. Very Happy

Regards,
Joe


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CE300 LFO DEPTH @ 100%.jpg
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Last edited by germaniac on Sun Jan 06, 2008 4:49 pm; edited 1 time in total
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johans121



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PostPosted: Tue Dec 11, 2007 5:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

germaniac wrote:
Hey Friends,

...Here's a run-down of all the mods I did to my CE-300 in the last month or so...

Regards,
Joe


Excellent Info, Joe!

Gavin, I'm excited to hear what your thoughts are too!

Also, can either one of you share your schematics with me?

-Jim
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gavgomad



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PostPosted: Tue Dec 11, 2007 6:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks germaniac for all the info! Great work, and a great point for dissecting this beast!

An interesting point.... When Scott did his Dim C clone, he was quite surprised to find that the LFOs were not tri or sine, but AFAIR actually (like the clipped version) - "trapezoidal".... He was looking at his clone though.... Have you checked on your DC-2 to see what the shapes there are?

I seem to recall Scott doing a sample of just one of the two trapezoids (one side of the stereo mix) and it was FUGLY.... yet when you bring in the second trapezoid on the other side, it's magic time....

Just curious if you have a chance to check them, not a make work project.... Wink

I'll test out the buffer amp from the Dim-C clone and let you know if that improves things.... A slightly different solution on the front end problem, but is simply inserting a small daughterboard as opposed to yanking bits of the mainboard.

I'll definitely be following your lead, germaniac, and investigate the bypass cap issue on the ICs. Your unit has a sweet wide sound to it for sure.... Wink

I seem to recall someone (maybe scott can chime in if he's trolling - ;-P) saying that there was some additional eq'ing in the DC-2 that the CE doesn't have? Maybe some choice caps and resistors on some ICs down the line could add this to the effect?

Gavin.
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germaniac



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PostPosted: Tue Dec 11, 2007 6:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

I seem to recall Scott's remarking about the fugly Dim C waveform too, but I never did measure what it was in my DC-2--not yet anyway!

I'm sure the dynamic Mr. S will appear here eventually, but I think weather conditions in KS are a bit on the foul side right now. Alas, he may not even have electricity at the moment, but let's hope for the best. . . .

EDIT: I'm curious as to how your input buffer scheme sounds. Also, keep in mind the CE-300 already has a buffer situation at the input. You have a noninverting unity-gain stage with 1M input impedance built around IC1a, and then the LEVEL pot feeding into IC1b which is set up for a little bit of gain. IMO, the gain of IC1b isn't necessary for line-level stuff--even with my mod, the control usually sits at about 50% and still hits the +3 dB mark easily. You could knock the gain down by decreasing R3 to 47k, but two 10Ks will be quieter and still present no particular loading problems for the preceding buffer.


Hey Jim: the CE-300 schemo can be found here:

http://www.freeinfosociety.com/electronics/schemview.php?id=121

Regards,
Joe

Last edited by germaniac on Sun Jan 06, 2008 4:51 pm; edited 1 time in total
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johans121



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PostPosted: Tue Dec 11, 2007 8:14 pm    Post subject: Reply with quote  Mark this post and the followings unread

germaniac wrote:
Hey Jim: the CE-300 schemo can be found here:

http://www.freeinfosociety.com/electronics/schemview.php?id=121

Regards,
Joe


Sweet!

Thanks!
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gavgomad



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PostPosted: Sat Dec 15, 2007 11:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Quick question.... The schems for the CE-300 are easily located online, but does anyone have the rest of the service notes (or want to comment on what we should be looking for at the test points when tweaking the trimmers?)

Just thinking mine might be due for an overall tune up once I get the buffer amp in there.... Wink

Gavin.
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PostPosted: Sat Dec 15, 2007 1:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, certainly the response to the LFO is trapezoidal - and that's the way it is in the original DC-2 as far as I know (seems to me I remember Mike Irwin commenting on that?). It's an amazing experience to hear only one delay line in that thing going, then hear the difference it makes to add the other one.

In the meantime, I've been lucky enough to have had a ring-side seat in Germy's CE-300 restoration. I gotta tell you, he turned that thing around 180 degrees. He gave me a listen to the thing in the state it was in when he got it - not too good. Not too good at all. When he was done with it, man, did that thing sound bitchin'!

I don't recall him having any issues with hiss, though. His sounds very quiet to me, and the DC-2 is quiet as a churchmouse, for whatever that's worth.

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gavgomad



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PostPosted: Sat Dec 15, 2007 5:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

That's brings up the question (which I was pondering when reading about germaniac's mods)....

Is the clipped/trapezoidal lfo wave critical, or is it better to smooth that out as germaniac did?

Germaniac's CE-300 sounds sweet indeed! If I can only get mine purring like that.... Wink

Gavin.
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germaniac



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PostPosted: Mon Dec 17, 2007 1:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Scott Stites wrote:
When he was done with it, man, did that thing sound bitchin'!

sunny



Hey Gavin,

I can't comment on the trap wave question, since I haven't got to measuring my DC-2, but I'm sure it's exactly as Professor Schtietz has said. As for the CE-300, mine at least seems to put out a tri wave, up until the point where it clips, and even then the clipping is only on one of the two waves.

I don't have the service papers either, but here's the best I could make of the trimmers and test points. TP9 and TP8 give you the LFO waveforms inverted in respect to each other, with the purpose of trimmer RT8 being to match the amplitude of those two wave outputs. My o-scope shots show what happened to the TP8 output at max DEPTH when I attempted to balance them with RT8 (before and after modding).

TP11 and TP3 give you access to the pulse outputs of the clocks, with RT5 as the trimmer to match the two as closely as possible. And as Scott emphasized to me early in my mod process, the matching of everything in the delay and modulation paths is VERY important: in fact it's crucial to an effective "dimension" illusion.

The rest of the test points seem either to check the cancel and bias functions for the BBDs, to check for signal present at various compander and filter outputs, compander distortion, etc. Probably none of these should need tweaking under normal circumstances, whereas the LFO and delay sections are open season. . . .

Regards,
Joe
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gavgomad



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PostPosted: Tue Dec 18, 2007 8:05 am    Post subject: Reply with quote  Mark this post and the followings unread

Sounds like I have some fun ahead with my o-scope! Wink

Thanks for all of the info, germaniac, particularly on the test points and critical adjustments!

I'm tempted to try and adjust the compander THD settings, but not being entirely aware of what I'm looking for at the TPs, I may just leave these as is.... Same thing with the BBD bias trimmers....

After reviewing Scott's comments and yours, I think I'll try your solution to the line input issue first - simply subbing new values.... Maybe that will help the "hiss" I'm getting when a signal is present at the input.

If I can smooth out the lfos with your mods and the bypass caps, get the clocks dead on, and lightly de-hiss and de-hum (could simply be the aging electros), I'll be a happy camper! ;-P

Gavin
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ENDIF



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PostPosted: Wed Dec 19, 2007 12:43 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm... I found a Ce300 in a shop here recently. I think it might be a floor model, certainly looks new..

Something I should snap up, even if just to resell?

Seems a shame to let it languish in a glass case, even if it has a tr707 and 626, ddd1, and a bunch of midiKITI's as company....

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johans121



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PostPosted: Wed Dec 19, 2007 7:00 am    Post subject: Reply with quote  Mark this post and the followings unread

ENDIF wrote:
Hmm... I found a Ce300 in a shop here recently. I think it might be a floor model, certainly looks new..

Something I should snap up, even if just to resell?

Seems a shame to let it languish in a glass case, even if it has a tr707 and 626, ddd1, and a bunch of midiKITI's as company....


FWIW, they sell for < $125 on ebay (regardless of the condition). I've been watching the price on these for well over a year as I've been contemplating getting a second one for a while now.

So, if they have it priced as anything above $150 - 175, I'd let it sit as you can get a better deal. As for waiting for one to be posted, I'd say at least one or two a month become available.

-Jim
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germaniac



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PostPosted: Wed Dec 19, 2007 12:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

ENDIF wrote:
Hmm... I found a Ce300 in a shop here recently. I think it might be a floor model, certainly looks new..

Something I should snap up, even if just to resell?

Seems a shame to let it languish in a glass case, even if it has a tr707 and 626, ddd1, and a bunch of midiKITI's as company....


Sure, snap it up if the price is right! I got a pretty good deal at $80, so I figured I couldn't really lose. As you've prolly gathered by now, the opinion here is the CE-300's got potential, but, who knows, you may like the stock sound.

And while you're at it, rescue that 626! I love mine--analog trigger output! (The 707 still has lots of fun left in it too. . . .)

Regards,
Joe
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PostPosted: Wed Dec 19, 2007 10:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, I do have an offer in on the 707 for $80, and asked what they could do on the rest of the stuff hiding in the back.

Sales guy says he has to ask the owner or manager or whoever, and has all the info on a card.. I'll check back with them tomorrow. =]

If I get the CE300, I'll likely just resell it, and if that happens I'll ping this thread. Ditto on the others.. prolly keep the 707, at least for a little while.

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PostPosted: Wed Dec 26, 2007 10:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Gavin, how's your ce300 mods coming along?
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gavgomad



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PostPosted: Wed Dec 26, 2007 2:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Merry Christmas all!

Hi Johans121.... Actually was sitting down to try and tweak the clocks today, although my experiments were short-lived - the old 0.5A fuse in there finally quit on me....

I did start eying some things up, but I am a somewhat NEWB when it comes to my scope (it's a Hameg HM-103 a buddy gave to me)....

Germaniac, when you got those shots of the tri waves, were those from TP3 and TP11??? I seem to be seeing pulses that get wider, then narrower as the LFO pulses - nothing looking like a tri.... I see a slow "blip" of a tri on the near end of R58, though....

Also, STOOPID question.... How do you scope both TP3 and 11 at once? I have two cables - one with a combo probe and alligator clip (I often use this, grounding the clip), and another with two alligator clips. There are inputs on the X side (Trig Ext and Hor Ext)....

Hoping I don't have repair work first before I start properly tweaking.... :-/

Gav.
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PostPosted: Thu Dec 27, 2007 1:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey guys, Merry Christmas at ya!

Gav, don't feel bad about 'scope inexperience: not only is mine a hand-me-down too, but I'm just using bare wires jammed into the probe inputs and alligator clips on the other ends! Wink Whatever works!

IIRC, I took the tri waves from the anode sides of D8 and D7, just after the voltage dividers R44/R69 and R64/R65. But I think you can also get virtually the same thing at TP9 and TP8, the outputs of the inverters after the LFO. BTW, it's kind of strange that the schemo calls RT8 "VCO LEVEL" when it's more like an LFO level. . . .

EDIT: TP3 and TP11 access the clock frequencies going to the BBDs. You'll need some kind of frequency counter to see these. My DMM has an FC, and with RATE and DEPTH controls fully CCW, it says I've got both clocks at about 135K, which equals about 4ms of delay.

To get both tri waves at once, I think you need a "dual trace" scope, with two inputs. This old one I've got has a set of buttons, one for each individual input and one for the "dual" function.

I still haven't got to trying to increase the delay time in my CE-300, but I'm looking forward to doing that mod for some more range in the DEPTH control.

Keep us posted on your progress and I'll do the same. . . .

Regards,
Joe
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