Schemo for DOD 460 Mini Chorus?

[StephenGiles]

 

[Mark Hammer]

I never could understand why balance controls where not included on chorus pedals - probably a marketing decision!!

Keep in mind that as delay-time gets longer, variations in pitch start to get more obvious.  When there is a clean signal to retain some semblance of pitch stability, then those wobbly sharp-and-flat variations around the true pitch are reasonably acceptable.  Take the clean signal away and, in a sense, you start to need a sweep-depth pot with much greater range of fine control to be able to dial in pure pitch wobble that does not induce nausea.

Part of what makes different makes of chorus sound dissimilar is the delay-range selected.  Certainly longer delay time (e.g., 12-20msec, as opposed to say 7-15msec) imparts a "thicker" sound, but having only delay signal in that delay range does a few things.  If the shortest delay time you're gonna be able to achieve is, hypothetically, 10msec, then you're stuck with the same sort of problem that 1st generation guitar synth players had - namely latency and how it throws off your timing.  Second, once you start delaying the signal enough, the amount of lowpass filtering needed to keep the clock noise in check becomes significant enough that switching from a dry+wet to a wet-only signal is likely to result in a fairly noticeable shift in tone, not just chorus-vs-vibrato.  If the delay range is short enough, fine, but many aim for the longer range to satisfy those who want "thickness", or who already own a flanger and want sounds they can't get with the flanger (i.e., need the longer delay range).

Finally, the vast majority of chorus-makers use a single JFET to "bypass" the effect by lifting the wet connection to the mixer stage.  Being able to have both chorus and vibrato requires a different sort of switching scheme.  Not orders of magnitude more complex, mind you, but perhaps enough to significantly alter the profit margin.  This is true of both chorus AND phaser pedals.

So, from where I stand, there are probably a lot of manufacturers that simply couldn't see a justification for including this feature (vibrato capability) in their product.  Too many design problems, not enough profit, if you're aiming for the non-boutique crowd.  Once you get into the realm of >$200 pricepoints and that type of consumer, you move into a different range of features.

[Joe Kramer]

All this talk about lack of features--wet/dry controls and vibrato options--is exactly why I'd venture into designing my own Frankenstein chorus.  I've got a CE-2, CE-3, etc.  But I want controls for mix, speed, depth, initial delay and a waveshape selector, not to mention true-bypass and low current consumption.  Nothing on the market today has all those features.  Come to think of it nothing on the market ever had those features, which was why I started building my own effects long long ago.

To add one thing to your fine rundown Mark, another big factor in chorus sound is the LFO waveshape.  I'm finding I like a sine wave over the conventional triangle--sounds less "plastic" to me, and lends itself better to stereo apps (e.g., amp 1 wet, amp 2 dry).  But as you suggested, something like the default  triangle LFO is probably an accounting rather than and audio decision. . . .

PS: Anyone remember the MXR stereo chorus, Old Yeller?  I used to love that thing, but mine croaked years ago. 

[Shed_FX]

Joe, sounds like you are pretty handy with designing your own pedals, how about making an ultimate chorus in the Lovetone vein with changeable LFO settings and with all of the wet/dry vibrato settings! 
That would be great I'd thought about doing the same with an ultra configurable delay also.

Just a thought!

[Mark Hammer]

I have one of the MXR Commande Series Flangers (Why it is called a Stereo Flanger I'll never understand ).  It uses an SAD512D chip as well, and is also fairly sparse in the parts department, much like the 460.  I'm not all that impressed with the degree of control provided to the user (Speed and Regen only), but the sound is pretty dang crisp. I must say.

[Joe Kramer]

Hey Tom, thanks for the encouragement!  A chorus/vibrato is definitely on my to-do list, and I have a file of sub-circuits ready to be cobbled together.  That's why I said "Frankenstein" earlier-- because I basically borrow various bits and sew them together rather than actually "design."  The features I mentioned wouldn't be really hard to do.  A wet/dry control could be as simple as a passive output mixer using a dual pot.  The waveshape selector could be similar to the Boss CE-3 mod I posted with a rotary switch for the different LFO shapes.  It's just a matter of getting time to breadboard it, polish it, perf it up.  That said, I seriously doubt I could even come close to something as involved as the Lovetone stuff.  I tend to go the minimal, one-box, one-function route.  But any and all suggestions welcome!

Joe

[analogguru]

sorry about the delay for the requested parts, but since some days i don´t have an access to my homepage (webspace) that I can upload the picture.  I hope the problems will get sorted out within the next days.

analogguru

[Stompin Tom]

Hey Joe... the old yellow MXR choruses (both mini and stereo) are easily my favorites (ce2 is a close third)... there's something so gross and watery about them. But watery in a different way then the boss. Hard to explain. I've long wondered what the differences were... how it gets those wonderful tones. I've tried a lot of choruses and none of them sound quite like the MXRs...

[Ben N]

I have a 460, and always liked its sound as a kind of subtle sweetening rather than a thick chorus sound like the CE2 (my other favorite). But it just isn't versatile enough to keep on the pedalboard. I also found that it has a distinct volume drop, and it is hard to jam even a simple recovery stage in that enclosure.

I would love to see that schemo, though, fellas.

Ben

[Joe Kramer]

Hey Tom,

Agreed on the old MXR.  I'd guess a couple reasons for its sound: the higher supply voltage, the cool MANUAL control (initial delay), and possibly the BBD chip.  The only schemo I've found on the web shows an MN3008 as the delay chip, but I seem to remember seeing an SAD chip in mine.  I could be remembering wrong.  I have no idea what the new Dunlop units use, but some people seem to like them.

BTW, have you seen this:

http://www.diystompboxes.com/smfforum/index.php?topic=56723.20

Jeorge Tripps (Way Huge) has some original MXR boards, populated except for the BBDs.  I haven't asked him which BBD chip it needs. . . .

[Stompin Tom]

Holy crap... I didn't see that. Thanks for pointing it out joe. It'd be hard to get up to 50 for me.... but I'll probably have to try.

I had the micro chorus for awhile (it was stolen)... although it did sound different, it had the same vibe as the stereo chorus... it ran off a single 9volt and only had a rate knob.

My friend still has his strereo chorus... I'll try to borrow it soon and take some shots of the guts.

The new dunlop is pretty cool, but way sterile compared the gritty old ones. It's got a lot of options, but it's not really my thing.

[Joe Kramer]

Hey Tom,

I just shot an email to Mr. Huge asking what chip the MXR takes.  He's near Hollywood, only twenty minutes from where I live, so I can pick up a PCB and ship it out if you'd like.  Caveat: I tried to hook up with him a month or so ago, but he said he's very busy, so it didn't happen. . . .

Gut shots of the old MXR would be cool!

[Stompin Tom]

Hey Joe... I just thought I'd post here instead of PM in case someone else was interested in the progress... totally hi-jacking this thread though. Sorry!

No gut shots, yet. I did find this schematic... I think its for ol' yeller as it has a power supply section... MN3008 chip (my friend thinks this the one in his strereo delay... but is going to check again tonight...). Of course you might be right about different versions (one of mxr's favorite tricks!) with the reticon chip... I thought my micro chorus had the mn3008, too, but I really don't remember that well.

http://www.freeinfosociety.com/electronics/schemview.php?id=572

[Stompin Tom]

Oh! just found this, too... at least we know that some of them used the mn3008

http://cgi.ebay.com/MXR-Stereo-Chorus-134-Vintage-NOS-PCB-MN3008-yellow_W0QQitemZ3774784032QQcmdZViewItem

[Joe Kramer]

Hey Tom,

That Ebay PCB looks like a pretty good deal--thanks for posting!

I'm intrigued now thinking about why they used a 3008 2048-stage BBD instead of a shorter one.  Here's a theory: use a longer BBD and clock it higher, so you still get into the short delay range, but you get much better frequency response, lower noise, more sparkle in the wet signal.  Sound reasonable?  Unfortunately, the higher the clock, the higher the current consumption, hence the AC.

[Stompin Tom]

I was wondering about the longer delay chip, too. Although it makes sense that they could clock it higher and get better frequency response, it's exactly because the old mxr choruses are so gritty and dirty sounding that I like them. There's absolutely nothing pristine about them... very organic(?)... well, you get the picture. It's also what I like about the ce2... There was a recent post about the differences between the ce2 and ce3 (the ce3, IMO, is too clean and sparkly despite being basically the same pedal)... and I wonder if it's as simple as the input buffer (one of the few differences between the two)? But, aside from that, there is a different character to the old mxrs...

[Joe Kramer]

Hey Tom,

Right, I do remember the endearing grunge of Old Yeller.  As for other sound differences, I was looking at the schemo you linked (thanks) and found something interesting.  The MXR LFO uses clipping diodes to convert the triangle wave into a sine.  IMHO, the sine LFO for chorus sounds less "plastic" than the triangle wave.  Coincidentally, about two weeks ago, I was advocating using clipping diodes for triangle LFOs here:

http://www.diystompboxes.com/smfforum/index.php?topic=57655.0

I think the CE-3 thread you mentioned is here:

http://www.diystompboxes.com/smfforum/index.php?topic=57655.0

I've done both the clipping-diodes mod and the input mod on my CE-3 and like it a lot now.  Makes a good vibrato, and sounds as good as, if not better than my CE-2!  Of course, nothing like Old yeller though.  That Gear Trader deal keeps tempting me. . . .

[Renegadrian]

I stumbled on this DOD fx and I tought it would be interesting to know more...
Schems are not so difficult to find (but you have to pay for them, found them at 5$ here http://www.ronsound.com/index.php?main_page=index&cPath=11_17) but I read it's almost impossible to get some SAD chips nowadays...
So I guess it's a dead project/used chipset?! quelle dommage...

[thedefog]

Just a heads up to people interested in this pedal, you may have to fiddle with some resistor values in that schematic for hotter pickups (humbuckers, etc). I clearly remember that on my original before I sold it that it would often clip when I played too hard. Perhaps a higher voltage would give it some more headroom?

[notchboy]

I have one of the MXR Commande Series Flangers (Why it is called a Stereo Flanger I'll never understand ). 

IIRC if you plug a TRS cable into the output jack, you get stereo output.  But there are a couple of different versions of the circuit (SAD512D vs R5107, for one thing), so maybe they're not all that way.