More BBD Insanity Micro Chorus/Reticon/Mistress

[T-rask]

For the one-line question of this story, skip to the bottom...



To try to make a long story short I have an old busted MXR Micro Chorus with the SAD512D chip in it that I've had for almost two years now, all the while trying to find the answer to revive this plague.  

I read on analogman's site a while back that the Reticon 5106's can pop in pin-for-pin (which is great because mxr was nice enough to socket the 512 in the factory), but that the bias supplies would need changing in order to function properly. So I found one, and then wrote him, and if I remember correctly he didn't have any info on the chip, so he knew that they'd probably need to change, but not what to.  

fast forward a few months

I've looked at the BBDmentia files, and there is no mention of the 5106, just the 5601 which gave me false hope at a quick glance.  So I still don't know what this thing takes to run...

fast forward a few more...

So I also read in the new Analog Man book that the Deluxe Electric Mistress re-issue uses the R5106 chip, but when I had the schematic faxed to me, it was barely legible, and by what i could make out, it didn't look like it actually had the chip in there, but something else. I've got a hardcopy arriving in the mail any day now, but I'm still doubtful.


***So the great question...***

Does anyone have any info on the R5106 chip (not the 5601).

-or-

Does anyone have a re-issue D.E.M that they can check for me?  


and, another question,  would it be safe to assume I could possibly drop the power down to say 4.5v's to try to run the chip that way, without fear of blowing it up? Are there any chips that do only take less than 4v??

And, if I would be able to try it at 4v's, then slowly working my way up the voltage ladder if it didn't work, would I need to possibly change the input signal as well?

Are there any good general BBD rules somewhere that I may have missed other than the bbdmentia site?

Thanks for sticking through this terribly long rant, i promise they're much shorter here on out, but I'm new, so I had to vent my frustration....  

Whew!

[puretube]

here`sthe datasheet for RD5108 - read the 2nd sentence!
http://experimentalistsanonymous.com/diy/Datasheets/RD5108.pdf

some stuff on the topic I came across:
http://diystompboxes.com/sboxforum/viewtopic.php?t=818&highlight=rd5108
http://diystompboxes.com/sboxforum/viewtopic.php?t=11884&postdays=0&postorder=asc&highlight=rd5108&start=0

I guess the MM now uses either a MN3005, or 2 MN3007s - do search...

[Vsat]

T-rask,
I have the R5106 data sheet here in the 1983 Reticon databook, it is 6 pages (but no scanner...)

The note says supply voltage on pin 8 is (+)18V ABSOLUTE MAX... and the recommended operating voltage range is (+)5V to (+)13V. One schematic shows it connected to (+)15V thrugh a 10 ohm resistor with a 0.1 uF bypass cap. Also says it is pin-compatible with the SAD512. Pin 7 (the SYNC pin) should be grounded if only one chip is being used.
Cheers, Mike

[Mark Hammer]

If my site says 5601, then it is a typographic error, and SHOULD say 5106.  My apologies.  (BTW, I didn't find anything terribly aggressive or offensive in your note, so don't sweat the tone of it.  Sounded level-headed to me.)

Thanks to Ton for the link to the 5108 datasheet.  Replacing the 5106 with a 5108 is essentially the same as replacing a MN3005 with a MN3008 (or vice versa), or replacing a 3207 with a 3209, etc.  In those cases where a chip is pin-for-pin replaceable BUT has more stages (or fewer), some change to the clock circuit may be necessary.  

For example, the difference between a chorus and flanger is essentially the choice of delay range.  To produce that delay with the number of stages available from that chip, the clock has to step the signal through those stages at a certain rate.  Slower, and the delay time increases.  Faster and it decreases.  If I have a box using an MN3009 (256 stages) for flanging, I *can* pull it out and stick in an MN3007 instead.  The pedal WILL work, but the delay time will be increased x4, putting it into the top of the chorus range.  Restoring the same range of delay times with x4 the number of stages would involve increasing the clock rate x4.  This, in turn, would probably mean decreasing the value of the timing cap in the clock circuit by a factor of 4.  So, if the existing cap is 220pf, the new one should be 55pf to maintain the identical delay time.  If the switch went the other way (i.e., a 1024-stage chip was replaced with a 256-stage device), then the clock rate would have to be slowed down by increasing the timing cap by x4, from 220pf (in the example) to 880pf.

While this is *sometimes* possible to do, it isn't *always* possible to do, for a variety of reasons.  First, BBDs have a certain input capacitance on their clock pins which tends to round off and distort the clock pulses as the clock frequency goes up.  There are ways around this, but here we're talking about a simple substitution of a chip and not a wholesale redesign of the board or installation of a daughter board, so let's just say it can't be done easily sometimes.  If we're only talking about a "mere doubling" of clock rate, the odds are pretty good it will work, but quadrupling starts to verge on the border "maybe not".

Going in the other direction, while BBDs can certainly handle slower clock rates, there ARE limits to clock rate on the low end since the FET/cap stages leak current, and leak more if you force the "sample" in each stage to hang around longer before moving on to the next stage.  More importantly, though, there is a huge noise penalty to pay or slowing the clock rate down to achieve a desired delay time.  Typically, the lowpass filtering you see after the BBD and before the dry/wet mixing stage is calculated to provide good bandwidth, but provide a real obstacle for clock frequencies within the audio range that might leak into the signal path.  So (and these are made up figures), if the clock reaches 10khz at longest delay time, the design might have 4-poles of lowpass filtering at 5khz to make sure that any 10khz whine in the audio path is down 48db.

Okay, now imagine the pedal in question has filtering set at 5khz, in anticiopation of a clock that never goes below 10khz, and you replace the BBD with another that requires the clock to descend to 2.5khz in order to achieve the same effective delay time.  Pretty noisy, huh?  You bet.

This situation is not unrealistic (well, the absolute numbers are, but the idea isn't), but it is not unsurmountable.  You CAN swap BBDs and slow the clock, but the filter corner frequency/ies will need changing so a bit of filter math and some additional caps will be in order.

[puretube]

Mark: the way I understood T-rask is:
he can get the 5106, but can`t get the datasheet from Analogman;
that`s why I suggested to read the "08" sheet, coz it seems the same xcept for the # of stages - I didn`t wanna suggest swapping the chips...
so he will keep the clock and filtering.

the 5601 is, IIRC, some "cursing" ( :shock: ) or so filter-chip [joke!]

If I`d remembered, that the 5108 was in the "dementia", I would`ve linked there, of course...
(have to admit, that I printed it out, but haven`t looked in there for
quite a while - but remembered that our friend Colin    was talking about a big RD510X deal...)

ooops: But re-thinking the whole deal, and re-reading the 08 datasheet,
does that mean, that the "06" got only 256 stages? As compared to the SAD512`s 512?

In that case, of course - pincompatible or not - measures have to be taken
concerning clock/filter, a.s.o.
Thank you for clearing that up.  

sh*t, got to go thru my old vaults/stashboxes, to see if I can`t find those surplus TCA350 chippies, that GOT to be somewhere...
:roll:

[Ben N]

Nice little tutorial, Mark--as always, perfectly lucid and comprehensible even to the technically challenged.  A saver.
Thanks!
Ben

[T-rask]

I still have no clue why I didn't register here 2 years ago when I first looked at this forum.. You guys rock, a kind thank you to all of ya.

I'll do some more fiddling (hopefully this weekend) and see what I can come up with on the big swap.

And a quick note for Mark, it wasn't your site per-se, but the actual Reticon Documents only showed a R5601 (CCD or something I believe), so no fault of yours. Thanks for the great resource for all the other BBD's though!

I'll post anything interesting I come across after all this...

[Jason M.]

T-rask,

Maybe I can help...I have both versions of the MXR Micro-Chorus.

Here are some pin voltages:
First, the SAD512D

Power supply= 9.54V

1) 5.2-5.7V (from LFO)
2) & 7) Ground
3) & 4) 4.5V
5) & 8) 9.54V
6) 2.35V

Now, the R5106
Power supply= 8.8V (Battery goes through a 1N914 for reverse polarity protection)

1) 4.1-4.7V (from LFO)
2) & 7) Ground
3) & 4) 1.69V
5) & 8) 8.78V
6) 3.63V

I used the same battery for both sets of measurements, which read 9.6V out of circuit.

Both versions have the exact same pc board and the circuit values look almost identical. I didn't check *every* resistor, but did check the ones around the BBDs and they are the same.

The one difference I DID find is the output of the TL062 opamp that feeds the lo-pass filter, which goes to the input of the BBD (pin 6).

On the SAD512D version, pin 1 of the TL062 is connected to three 1N914 diodes in series.
These three diodes are located in the center of the pc board.

On the R5106 version, the two outside diodes are replaced with jumpers and the middle diode is replaced with a 6.8k resistor.

Try that change before you put in the R5106 and you should be all set.
You may have to adjust the trimpot for best sound.

Now, I don't know if it is the delay chip or not, but my Micro with the R5106 has A LOT of background hiss. I even swapped it out with two other chips with the same result.
My Micro with the SAD512D has no background hiss, and sounds much better than the R5106 version, which sounds kinda muddy and warbly.

Let us know if it works out.
Good luck!
J.

[thatjanke]

I realize that this is an old posting but I just thought that I would let you all know that old Organs use the SAD512 chip. Not too long ago I found some at an Organ repair shop. The shop is out on the Web but I can't remember the name of it. Why modify when you can get the real thing?

[Fret Wire]

It would be nice to find a few.

Question to Mark and Ton, on the other thread I got the impression you didn't think much of the Micro Chorus.
http://diystompboxes.com/sboxforum/viewtopic.php?t=28773
Are you thinking of the "Stereo Chorus", which is the plastic Commande Series? The Micro Chorus and Micro Flanger are 1590b cased fx, the Micro Chorus having only a rate control. Both really sound better than you'd think for small fx. The Micro Chorus reminds me of the Phase 90, in that MXR gave you a rate knob and decided the depth for you. Not super versatile, but every setting of the one knob is usefull.

Back to the 512D question, do either of you guys have a schematic for the Micro Chorus or Flanger?

[analogmike]

Now, I don't know if it is the delay chip or not, but my Micro with the R5106 has A LOT of background hiss. I even swapped it out with two other chips with the same result.
My Micro with the SAD512D has no background hiss, and sounds much better than the R5106 version, which sounds kinda muddy and warbly.

I have done a few mods from SAD512 to R5106. I thought there was a problem with the pedal, as it was REALLY noisy with the 5106. But I did another one and it came out the same... does anyone have an R5106 version that is NOT noisy?

[Thomeeque]

RD5106A/RD5107A datasheet (found somewhere around some time ago)

Oh, now I see how is this thread old, everybody interested has it probably now as well..