The MXR Flanger-Doubler

[Mark Hammer]

Eddie/Sebastian in Germany was kind enough to provide this schematic for us of the old (early 1980's) blue rackmount Flanger-Doubler from MXR.
http://forum.musikding.de/gallery/albums/userpics/10045/normal_flanger-doubler.jpg

Given the recent discussions on automatic double-tracking, I thought folks would find this interesting and a useful addition to their schem collection.  Eddie was primarily interested in extracting the flanger portion and trying to turn it into a pedal, or at least something smaller than the full unit, but that's no reason why folks interested in the other half shouldn't see it.

Looking over the schematic, you can see a number of interesting aspects.  First, there is a diode-clipper pair in the regeneration path.  Second, there is a CLM6000-based limiter of sorts in the delay path back to the mixing stage.  The unit uses two different BBDs.  The BBD for the flanger section is an SAD-1024, apparently, but the one used for the doubler section does not conform to anything I have datasheets for.  If the pinout or other properties rings a bell for anyone here, or if Eddie knows, please chime in. This is a real head-scratcher.  The only thing I can see is that the signal conditioning required for the input and output of this device is considerably more complex than for the SAD1024, and for any BBD I've ever seen, so I gather it must be either something borrowed from another type of technology or else a much earlier generation chip.  You can still see by the inclusion of a balance trimpot, however, that it involves two parallel-complementary signal paths like the SAD1024 and many others.

Selecting between the flanger and doubler effects involves two things.  The switch selects between the outputs of the two different delay devices, and appears to introduce two different DC offsets in the circuit section between the LFO and the clock generator.  You might also notice that the clock generator itself outputs not two, but THREE clock pulses.  One of these is unique to whatever the delay chip is in the doubler, and the other two drive the SAD1024.

There are 9 poles of lowpass filtering in the delay-only path that I can see, with the same filtering applied to both the doubler and flanger section.  Both the flanger and doubler sections have their delay outputs severed from the rest of the filter and mixing path when the effect is bypassed.  I gather this is to prevent any clock noise whatsoever from leaking into the audio path downstream.  If you look in the upper right hand corner, you can see a simple clock formed by the 4069 inverter chip, and an output called "TG" to its right.  Cast your glance to the outputs of the two delay chips, and you can see that the TG goes there and essentially engages/disengages a 4016 CMOS switch.  Never having used one of these units, I can't comment on whether this approach provides any noticeable difference in noise levels.

With the provision for "hi" and "lo" inputs and outputs, and the fact of its rackmount form, the unit seems intended for studio or other professional use, and seems to anticipate a relatively low impedance input.

Eddie has indicated in his note that the flanger sound from this unit is superior to that found in the little grey box of the same era.  Though Dunlop promotional literature and the recent EVH flanger would suggest otherwise, he wonders whether this might not be the MXR flanger that is associated with Van Halen material of that era.  I'll let you folks chime in on that.

In any event, here's yet another thing to send Stephen Giles and Scott Stites scurrying.   Enjoy, and thanks Eddie/Sebastian.

[Eddie]

The other delay chip is the Reticon R5101 not on that world anymore......So the doubler part is nothing to think about in diy.
I would like to build  the flanger only. So a new schematic/pcb layout is needed.
I could post some more  pictures of the circuit board if wanted. And do some audio samples as an appetizer..........

Thanks goes to Stephen!

Eddie

http://forum.musikding.de/gallery/displayimage.php?album=random&cat=10045&pos=-1000
http://forum.musikding.de/gallery/displayimage.php?album=lastup&cat=10045&pos=4


Promo:
http://forum.musikding.de/gallery/displayimage.php?album=lastup&cat=0&pos=0

[Eddie]

Nobody interested?

Really?


Eddie

[StephenGiles]

Ah, I certainly scurried when I first got that circuit Mark! I've never been able to track down an R5101 in the UK though.

[therecordingart]

Is it a lost cause to want to DIY one of these?  Should I just keep hunting eBay for the real thing?

[Jason M.]

Thanks for sharing the schematic.

I think Dimebag used one or two of these units.

The Reticon R5101 is almost impossible to find by itself, but is used in the Boss DM-1 and some versions of the vintage MXR Delay.

[trixdropd]

I'd love to build one of these. Dimebag and Zack wylde and eddie van halen all used this to great effect. It's an awesome unit!!

[therecordingart]

Is there a comparable replacement chip?  Would a company like TI or someone like that do a short run reproduction?