Restoring/Modding Boss CE-300

[gavgomad]

Hey Germaniac! Thanks for the reply!

I'm thinking the dodgy fuse was clouding what I was getting on the scope.... I'll give it another hack this weekend.... I think I need a better meter with frequency on board, as my scope is definitely a single input.

BTW.... Germaniac (or anyone!).... Another stupid question.... When replacing the PS fuse, if I recall correctly, the key rating I should worry about is the amp rating? The schems call for a 125V/.5A fuse. All that seems to be local are 250V/.5A, but in my mind that shouldn't make a dif? Mains voltage around here is same as US, so 250V is really about double - odd that would be the standard....

Will get back to this on the weekend for sure (gotta sneak into work for a bit today! AAARGH! ;-P)

Gavin.

[gavgomad]

Here's an update for those following my trials and tribs....

Fuse replaced, and supply is purring again.

Modded the input resistors R2 and R4 to 10k, with noticeable drop in noise and "heat" on the inputs.

Eyed up the LFO waves, and basically found that when adjusting RT8, at some point the tri waves started bending awkwardly, so I backed off the trimmer until it was just clean again.

As for the clock, my DMM has a frequency setting, but I don't know how accurate it is. It would give repeatable results on the same output though, so once I set the benchmark frequency from the one set of BBDs (strangely mine came in at 116k - could be error between the DMMs?), I adjusted RT5 until I had the same reading. Germaniac - did you try and adjust this by ear afterward? The stereo chorus effect seems a bit narrower by comparison.... I might play around and see how the audio is actually affected by RT5....

That's it for now.... Quieter, but a bit narrower in the stereo field and less "lush".... I'm starting to find my way around the circuit now, though!

Will post anything new as I go.... I think that decoupling the ICs is next on the list, but dunno if I'll get to that this weekend!

Happy New Year all!

Gavin.

[johans121]

Gavin, post your address and I'll send you a RedBull

Looking forward to your updates!

[gavgomad]

Hey Johans121 'n all!

Thanks for the offer of Red Bull! If I can get rid of this blasted cold that hit me hard yesterday, I think I'll make a bit more progress!

As for a "mini" update, I decided to take my scope and DMM into the studio, so I can measure AND ear what's going on. A few tweaks of RT5 to tighten things up even more (this DOES actually narrow the stereo field as, of course, the differential between delay lines is decreased - but seems critical in keeping that clean, not-washed-out chorus).

RT8 was a little out of adjustment, so a little tweak there got rid of the clipping (although as Germaniac noted, the tri doesn't seem as symmetrical as I'd like - will have to add his symmetry-adjust trimmer and see if I can fix that up a bit....)

I also scoped up a straight ol' saw, and adjusted the cancel trimmers for the least clock noise - it's a little tough to see on my scope, but the ends of the trimmers are really "dancy", and you can see a sweet spot in the middle where the waves look the cleanest).... The "hiss" I was referring to seems to be gone now, although I don't know if this is due to the other round of changes or not....

Really liking the new levels from the 10k resistors on the inputs. VERY manageable now....

Now, for decoupling, I don't have 2.2s, but I do have a bunch of .1s.... I've often seen smaller caps such as this for decoupling purposes, but I'm open to words from the gallery on this one!

It's coming along quite nicely, I must say!

Gavin

[germaniac]

Glad to hear you're making progress Gav!

[gavgomad]

Hey Joe! Thanks for the additional info!

As for "too much info" for this stage of the proceedings.... PLEASE provide, and I will thank you much in advance and apologize upfront for my slow digestion! Frankly, it's nice to know that someone else is moving in the same direction on something and, hey, if you've started blazing that trail before me, I certainly don't mind benefiting from whatever knowledge you feel like sharing!

I will have to dig around for the 'styrenes.... Those are small caps, to say the least!! I firmly believe that your symmetry mod is critical, though.... From what I can see of the tri's I'm getting, they're not clipping as yours were, but they definitely do NOT look like perfect symmetrical tri's....

Strange.... On my CE-300, I can drop the rate knob to minimum, and the box almost sounds like a comb (it sounds THAT narrow).... Give it just bit of rate, though, and crank the depth, and there's at least enough there that you can hear the sound start to "breathe" like the ol' Dim-D.... Not there yet, but I think following your lead will move in that direction!

Methinks I'm due for a recap of all of the electros though.... I'm detecting some instabilities in the circuit that, short of aging electros and possibly ill NEs or Op Amps (I think the former more probable), I can't account for.... Plus, although much quieter than before, I still think the quiescent noise in this beast can be further silenced....

Oh well, I completely recapped and re-trimmered my OB-8, this should be a walk in the park, eh??? ;-PPP

Keep me posted on that VCO mod.... I am MUCHO interested in hearing your results, and will likewise keep all posted on my developments!

I shall sneeze along with you my friend, whilst the iron burns hot!

Gavin

[germaniac]

Okay, here's the result of some delay mods, and frankly I'm STOKED about this! My theory about the VCO resistors didn't play out, so I resorted to increasing the clock caps, C27 and C41. At first I tried 100pf which upped the delay to about 7ms, then I went to 220pf which I find ideal. The clock freqs are now about 33K, for about 14ms of delay. I didn't have any polysty in that value so I used polypro for the time being.

For these samples I used a sound with a little more teeth and harmonics in it than before. The first example is the dry uneffected sound.

The second example is my previous mods before the delay adjustment. It's pretty tame, and you can hear a bit of comb-filtering/flanging, just as you mentioned with yours Gav. FWIW, I don't care for that sound in a chorus.

The third example is with the same settings as the second, so it sounds rather exaggerated to make a point. But now it definitely sounds like a CHORUS. That's with the DEPTH control full CW, so there's lots of room to tame it down. But I really like having all that depth to spare because you never know how it might be useful in a mix somewhere.

On the fourth example, I start with the effect engaged but the DEPTH control at full CCW. I slowly raise the DEPTH control, then the RATE control, and then back it down to a reasonable speed.

As I say, I'm just about totally happy with the sound of this thing now--as far as I'm concerned it finally sounds the way I EXPECTED it to when I first got it! Let me know what your opinions are. . . .

Well, there's nothing like solder fumes to clear your sinuses. I'm beat for the day, so it's off to take a nap. . . .

Regards,
Joe (snooze)

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CE-300 Delay Test 1.mp3
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CE-300 Delay Test 2.mp3
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[gavgomad]

Hey Germaniac!

Thanks for the update! Sounds like I'm going to be on the hunt for some 220pfs myself, as that sounds MUCH better than the stock 300.... Way to go, man!

I too dislike the "comb-filter" kind of sound - which is why initially I started to get concerned about the sound of mine after I locked up the two clock signals.... The sound seemed to have "thinned out". This is NOT the sound I had come to know from the likes of the Dim-D or even Dim-C, which was wide and lush, just without the "wash", if you will, of a typical chorus. If anything, it was adding a nasal quality to my nice fat Obie pads, which is NOT a pleasing addition!

I think you are dead on when you say that Boss/Roland seemed to rely on imperfections in the circuit, including variations between clocks, to obtain a stereo image on this box. The theory seems to have been that the more random differences between the left and right channel, the more likely the ear would pick it up as a stereo image.... Most distressing when all of the critical components for a really good chorus - quality companding etc. - were in the design from the start.

In any event, it is clear that with a little work, this box can step into the shoes of a dimension chorus - but certainly NOT out of the box!

At work for a bit today, but may try and start bypassing those ICs today!

Question Joe, where did you decide the ideal spots were for decoupling the bias, vref and cancel supplies?

Gav.

[germaniac]

[gavgomad]

Hey Joe!

Thanks for the tips on decoupling.... What I was aiming for was the best spot on the overall bias, ref and cancel circuits - I know you need to get it as close as possible to the circuit your decoupling (easily spotted with an IC!), but I just wasn't sure of the best spot on those. Sounds like the best place to stick 'em is on the rail prior to the passive components in the circuits.

I think I need to pay a bit more attention to Mouser - there was a time when they had a ridiculously high minimum order for shipments to Canada, but it looks like that is no longer the case? Will find out soon enough!

The CE-300 is certainly a puzzle.... When I picked mine up, there was some scuttlebutt around on the net that it was a good sub for the Dim-C, and as I wasn't going to get around to building a clone any time soon, I thought I'd take a risk on the 300.... It seems so ridiculous that Boss went as far as they did with this design, only to drop the last 1% of the work and lose 90% of the benefit of what they actually did RIGHT in the design.... Oh well, keeps this piece of kit affordable for those of us who can tweak them to our benefit!!

I'll try and get some samples of my OB through the 300 in the next day or two - it will also show where my CE is at this point as well, in case someone hears something unexpectedly awry in there!

Happy New Year!!

Gav.

[wolzow]

Hi germaniac,
I'm quite interested in the mods you made having just got hold of a beaten-up CE-300 myself. However, I'm a bit confused about the statement:

[germaniac]

Hi Margus!

[wolzow]

Hi,

[germaniac]

[germaniac]

Hey Gav and Jim and Others:

I want to offer a special apology for my mistake regarding the "R2" mix-up. All this time I've been meaning R3, NOT R2 for the input level reduction mod. So, to clarify once and for all, the input-level mod spoken of in this thread should be to reduce resistors R4 and R3 to 10K. All my previous posts have now been edited to reflect the correct designation.

As I mentioned previously, my schematic wasn't too clear, but I'm very sorry if this messed you guys up in any way! My bad, and I'll try to be as clear and precise as possible from here out. I hope your mods are going well, and I'm sorry again if this mistake caused any trouble. . . .

Regards,
Joe

[johans121]

[germaniac]

[germaniac]

It's been quiet on this thread--hope you've all been busy with your mods. Just in case anybody's in the market:

http://cgi.ebay.com/BOSS-CE-300-Rack-Chorus . . . .

EDIT: Bidding ended, sold for $77.


I'm pretty much finished with all my mods, and will have a run-down of all of them in a while, as well as a few samples. . . .

Regards,
Joe

[johans121]

[germaniac]

Hi Folks,

Well, I've been using my modified CE-300 for several weeks now, and I'm pretty well satisfied with it.

Most of my mods have been posted previously in this thread, but I thought it might be helpful to have them here in one place. I should also mention here that the earlier problem I had with the LFO distortion seemed to have disappeared, so I undid all the changes relevant to that. I can't explain why this happened in the first place, though I do have the o-scope shots to prove it existed!

Anyway, without further ado, here's a run-down of all the modifications that I think helped move my CE-300 a little closer to the Dimension family tree. Attached is a color-coded schematic.

-----------------------------


INPUT LEVEL AND IMPEDANCE MODS:

The CE-300 originally may have been aimed at guitarists, and so there is a 1M input impedance. For synthesizers or general line-level use, R2 can be reduced to 10K for lower input impedance and less noise. To retain low frequency response, C1 should be increased to at least 4.7uF. (Thanks Margus for this info!) In my case, I used a 4.7uF Panasonic nonpolar electrolytic, along with the original .047 film cap bypassing it on the trace side of the PCB.

There's a fair amount of gain after the LEVEL control, and again for line-level use, this gain isn't necessary. Also the gain-setting resistors around IC1b don't need to be as high a value as they are, since input buffer IC1a can drive a fairly heavy load. Both R4 and R3 can be changed to 10K, which will give slightly lower noise and unity gain at full CW on the LEVEL control. With those values, a typical synth output should have no problem driving the level meter into the red even at 50% of the LEVEL control. If you want to keep the gain of the stock unit, the input noise still can be lowered by changing R4 to 10K and R3 to about 22K.


LFO SYMMETRY ADJUSTMENT:

Trimmer RT8 is for the purpose of matching the inverted and noninverted outputs of the LFO. This is important because a suitable "Dimension" effect requires fairly tight symmetry between the two BBD outputs. If you have an o-scope make sure the LFO outputs at TP8 and TP9 are as equal as possible before moving to the next mods. . . .


LFO SYMMETRY MODS:

Listening to the way the LFO modulated the clock and BBD on my CE-300, 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. The resistive dividers consisting of R44/R69 on the "A" side and R64/R65 on the "B" side serve the purpose of setting this "zero" point, as well as reducing the LFO level somewhat. For testing purposes, I tacked in a 1M pot in place of the "B" divider network and adjusted it for a more symmetrical-sounding LFO sweep, then measured the pot. The ratio was about 1-5, so I replaced R65 with a 200K and R64 with a 1M resistor. Because the symmetry was slightly different on the "A" side, there I replaced R44 with a 1M resistor and R69 with a 500K ten-turn trimmer and adjusted it to match the other side. (On my particular unit, after adjusting the trimmer by ear to match the sweep symmetry of the "B" side, the resistance measured about 235K.) This mod could also be done effectively by replacing both sets of resistor dividers with 1meg trimmers and adjusting to taste.

As a footnote here, the higher resistance of the dividers also seemed to reduce the PS fluctuations I noticed on the PS pins of the clock and BBD chips. Previously they were varying more than a volt in sync with the LFO, but now they were down to a couple hundred millivolts. Whether this has any effect on the overall sound is open to question, but it does seem like a strange design glitch.


DELAY TIME MODS:

The stock delay time is a bit on the short side for a chorus device in my opinion, somewhere in the range of 3 or 4 milliseconds on my unit. The clock caps C27 and C41 can be increased from 47pf to 100pf or even 220pf. I prefer the value of 220pf, which in my particular unit gave a clock frequency of about 33K, or about 15 ms. This gives plenty of range in the DEPTH control, everything from subtle to warped, and the longer delay also diminishes the flanger/comb-filter effect apparent in the CE-300, which I find inappropriate.

Polystyrene caps are recommended here for more accurate timing of the clock and hence smoother sampling in the BBD. To keep the delay times of the "A" and "B" sides equal, capacitors C27 and C41 should be matched as closely as possible, and then the frequency of the side "A" clock can be adjusted by RT5 so that both BBD delay times are identical.

A sidenote: any change in the 500K symmetry trimmer will slightly change the overall clock frequency of IC8. Therefore, a bit of recursive adjustment is necessary between the 500K trimmer and RT5, until the "A" side clock finally matches the "B" side clock.


OUTPUT LEVEL MOD:

It's easier to get a decent amount of input headroom if the output gain is increased a bit. With the all previous mods instituted, S/N for my CE-300 was measured at about 115dB with no effect, and about 100dB with effect. Substituting 200K metal films for R105/106 on IC13a/b boosted the output gain about 12dB over stock without adding too much extra noise. With those values in place, S/N with no effect was about 100dB, and with effect about 85dB. For my purposes, a worst case S/N of 85dB is nothing to worry about, and I think the improvement in ease of adjusting input level for max headroom while still having plenty of output gain is a worthwhile trade-off.


POWER SUPPLY DECOUPLING MODS:

Some extra PS decoupling is optional, but it never hurts, especially where spurious high frequency clock signals might dirty-up the PS lines. The CE-300 has a bare minimum of decoupling. The "digital" supply rail caps C12 and C22 can be increased to something like 470uF. On the trace side of the PCB, anything in the range of .1 to 10uF decoupling caps can be added to PS pins of all op amps, compander chips, BBDs, and clocks, as well as the BBD bias, Vref, and Cancel supplies. Some might call this overkill, but heavy PS decoupling always seems to makes op-amp circuits sound much smoother and cleaner to my ear.

That's all for now. Happy Modding!

Joe

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[gavgomad]

Hey Joe, Jim and all!

Sorry for disappearing for awhile.... Then truth is, my CE remains "sans chassis" on my bench, as "work" has substantially impeded my progress....

That being said, I am excited to see the complete set of mods! Well done!!

If you get the time, a couple of samples showing off the finished article would, of course, be most welcome!

I hope to get back on the mod wagon soon with my CE - I think I'm going to replace the electrolytics while I'm in there for "safety" sake, but I'm going to implement these mods for sure.... Almost time to put in a parts order, methinks!

Gavin.

[germaniac]

Hey Gav!

I missed you.

Definitely sympathize with you as far as "works in progress" with all those JH PCBs sitting lonely on my shelf and still so many other projects to do. . . .

Thanks for props! As you can see by my touched-up schemo (my first foray into MSPaint, BTW), the actual mods don't look like much, but I guess most of the work was the R & D, so to speak.

I'd be happy to do some samples. I've been meaning to run some guitar through the CE-300, but other than that, is there anything particular you'd like to hear in terms of types of sounds or A/B comparisons, etc? Be as specific as you like, and I'll try to get something recorded that gives a clear idea of how this thing sounds now.

Hope you get some bench/fun time soon. . . .

Joe

[gavgomad]

Hey Joe!

I too have a lot of projects on the shelf - JH Triple Chorus, JH Phaser on the way, MB6582 8-voice SID synth (got a tube of CEM 3372s awaiting me to design a dual Xpander filter board for this one, which I then gotta duplicate four times!), bits of a Moog Prodigy style synth, between 8-10 vcf modules for a processor controlled filter bank.... Then I have my repairs, my MKS-70, my buddy's Arp 2600, my CE....

PHEW!!!

The problem is I'm still wired on some of the new ideas coming down the line - JH's fixed filter bank, mebbe a real Dim-D clone.... It never ends!

For now, I'm settling with getting the CE modded and going, and fixing the crackly chorus in my MKS-70. The big stuff is just gonna have to wait....

In terms of A/B, I think some samples where the CE is cut in and out a couple times would be helpful. Guitar is a great source, as would be a softer pad type sound, that way you can get a sense of how the chorus behaves with swirling sounds as with percussives?

My CE is going to be used as a stereo treatment for my analogs, and in particular my beloved OB-8 - a very thick beast at times to say the least! ;-P

Given the thickness of something like the OB, I'd be very interested in how the modified CE handles complex "moving" sounds without adding the typical chorus "mud".... Might be a nice "stereo-izer" for the Triple Chorus, no?

Whatever you can post to let us enjoy your work is most welcome!

Hopefully I'll have a report for you soon, then I can finally post those OB-8/CE sounds I promised! ;-P

Gav.

[germaniac]

. . . . And now, Chapter 12, in which we find our Hero surrounded by the aboriginal peoples of the mysterious planet, and lacking any means of communication in their native tongue, he reaches for a portable music generator in his utility pack, and begins to improvise a tune to the wonderment of his hearers. . . .


. . . . A slight variety of samples with the modified CE-300. For reference sake, unless otherwise noted, all examples were done with the controls set at the exact middle of shaded areas on the CE-300's front panel.

PSS-480 PAD:
First few bars are dry mono, the remainder with stereo CE-300.


XP-60 STRINGS:
First figure is a dry saw wave mono. Next figure is the saw wave with mono "hex chorus," a Solina-like sound. Next is saw/hex chorus and stereo CE-300. Last is saw wave sans hex chorus with stereo CE-300.


ELECTRIC GUITAR:
First figure, dry guitar with very slight overdrive. Second figure, same guitar sound with stereo CE-300. Third figure, with stereo CE-300, but with controls adjusted for more DEPTH and slower RATE (which I prefer for this type of sound).


SK-1
This is a pipe from a pipe organ (blown into by mouth) sampled into the SK-1. The periodic glitches you may hear are the crude loop points. There are actually two tracks mixed together here, both with CE-300 set to almost full DEPTH and rather slow RATE.


A sidenote: I found recording through the CE-300 with a mic a bit touchy on the levels still. I now understand the argument for increasing the CE-300's output levels. This would allow a much better margin of headroom at the critical input, with make-up gain set to a fixed level at the output. A quick glance at the schemo and I would guess at raising R105/106 to 100K or so, if that didn't increase the noise too much. And I thought my mods on this thing were finished . . . a DIYer's work is never done!


Regards,
Joe

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PSS-480 Pad & CE-300.mp3
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XP-60 Strings & CE-300.mp3
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Electric Guitar & CE-300.mp3
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SK-1 & CE-300.mp3
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[blue hell]