MXR Micro Flanger?

[Arn C.]

Hello,
    I have the above mentioned and I am having a problem.   The flanger bypasses correctly ,  but when the flange circuit is engaged,  I hear the same signal as if it were bypassed.   The rate and regen pots do nothing.  Any suggestions?

Thanks!
Arn C.

[Mark Hammer]

Did you play with the 250k bias trimpot on the board yet?

[Arn C.]

Hey Mark, no I didn't.  I wasn't sure how to mess with it, I guess I can mark it first then move it a bit. 

Thanks, I will try this tonight!

Arn C.

[Thomeeque]

Did you play with the 250k bias trimpot on the board yet?

Hi! Is there schemo somewhere available? I've tried to find it but it's M-117 only everywhere.. Thanks, T.

[Mark Hammer]

Stephen Giles referred me to one, but it seems to run out of information near the output section on the right side of the diagram.  That is, I can't see how the bypass switching is done.  I'm sure one of us will post it later today.  Like several MXR time-based pedals of that era, it uses the 8-pin SAD512 that only needs a single-phase clock input.  These are an absolute bear to find, if damaged.

[Thomeeque]

..Like several MXR time-based pedals of that era, it uses the 8-pin SAD512 that only needs a single-phase clock input.  These are an absolute bear to find, if damaged.

Hmm, that brings a question what BBDs they use in actual reissues of their flangers, does anybody know?

[Mark Hammer]

I don't "know" but I can't see the 8-pin SAD512D being resurrected.  Espeicially when Coolaudio is already cranking out MN3207 clones.

Emulation of the Micro Flanger and Micro Chorus is easy enough to do with 3207 chips and an invertor stage to supply the complementary clock pulse the SAD512 didn't need (but the 3207 does).  Neither of these beasts did especially startling tricks, employing simple modulation sources, and neither used full bypass.

The reissue Micro-Chorus manual indicates a 3.9msec-5.4msec delay range (w/4.5khz rolloff).  Easily accomplished with a 3207.  

Somewhat trickier is the 3.9usec-4msec  delay range claimed in the Micro-Flanger manual.  Less than four usec....on a Panasonic chip?  We're talking damn near through-zero flanging, a sweep ratio of well over 1000:1 (!?) and well beyond what the A/DA can do.  Something doesn't smell quite right.  The sort of current drive required to push a Reticon chip to achieve 200usec is considerable, so how in the hell could they get under ten microseconds of delay from a Panasonic/Coolaudio chip?  Especially since the smallest capacity BBD they currently make is 1024 stages (which would necessitate a VERY high clock frequency).  Finally, the Commande Series Stereo Flanger (I have one), which is but an eyeblink and a plastic box different than the original Micro Flanger does not sound anywhere near what the stated delay range would sound like.

So, it would seem that, unless Dunlop has done an end run and arranged to resurrect the SAD512 as a proprietary chip, there are likely to be substantial differences in the circuit of the re-issues....and some proofreading of the manual required, too.

[Thomeeque]

Somewhat trickier is the 3.9usec-4msec   delay range claimed in the Micro-Flanger manual.  Less than four usec....on a Panasonic chip?  We're talking damn near through-zero flanging, a sweep ratio of well over 1000:1 (!?) and well beyond what the A/DA can do.  Something doesn't smell quite right.  The sort of current drive required to push a Reticon chip to achieve 200usec is considerable, so how in the hell could they get under ten microseconds of delay from a Panasonic/Coolaudio chip?  Especially since the smallest capacity BBD they currently make is 1024 stages (which would necessitate a VERY high clock frequency).  Finally, the Commande Series Stereo Flanger (I have one), which is but an eyeblink and a plastic box different than the original Micro Flanger does not sound anywhere near what the stated delay range would sound like.

So, it would seem that, unless Dunlop has done an end run and arranged to resurrect the SAD512 as a proprietary chip, there are likely to be substantial differences in the circuit of the re-issues....and some proofreading of the manual required, too.

Wow, nice, that's obviously nonsense.. even if they would use some custom BBD chip with less possible BBD cell count yet acceptable for 4msec delay for guitar (let's say 32 cells? 4msec ~ f_s = 8kHz), they would have to go to f_s = 8MHz for 4usec.. hmmm.. Plus this 1000:1 ratio should be audible somehow on their soundsamples..

[Mark Hammer]

Here's the schem of the original.  You will note that we sorta run out of schem on the right.  I never really did understand the purpose of those three series diodes at the start of the wet path.

[TELEFUNKON]

Here's the schem of the original.  You will note that we sorta run out of schem on the right.  I never really did understand the purpose of those three series diodes at the start of the wet path.

would they drop the opamp`s output-DC for setting the BBD-bias?

[Fender3D]

According to "the other site"

quote:
"Take notice biasing is set in practice to VREF minus four (4) diode drops, as Q1 is an emitter follower whose output is one diode drop below its base. This arrangement varies with temperature. Wether it matched the variation required by the SAD512 or not, that's another story."

Serch for MXR Micro Chorus