Recomendation for FX-X Monthly Challenge: SAD512D Retrofit

[heyniceguy]

I have a recommendation for the next Monthly Challenge, or just for anyone that already knows if this have been done.

Most old flangers/choruses/delay pedals use a SAD512D BBD chip to produce delay effects. Of course we are all too familiar with the tendency for these things to plummet into the ocean like lemmings. But at least lemmings have the courtesy to leave offspring behind to replace them.

My challenge is to develop a circuit to replace the SAD512D using another BBD chipset. SAD1024, MN3--- series, R5106, etc. Something to the effect of "take 8 wires from the SAD512D footprint from this old timer pedal and plug them into these 8 pads of this new little circuit board." Viola. No more dead Micro Chorus/Flanger. No more dead analog delay.

Requirements:
1) Circuit must be "drop-in", using the 8 pads of the SAD512D pinout. Using additional points outside of the 8 pins will result in penalty points taken and a stern talking-to.
2) No size restriction for PCB layout. But the smaller the circuit, the more bonus points you get. Bonus points will be given by me. Maximum bonus points allowed = 1,000,000 (that's if you can build the whole thing right on the SAD512D socket. Using a working SAD512D will result in no bonus points and forfeiture of said SAD512D to my possession. That's what you get for hoarding, you greedy asshole.)
3) Although they are always welcome and will help everyone along, no points will be given for "theories". This contest is for proven methods only, you lazy smarty-farty bastards.

[Rylan]

Dang, so no takers? Sorry to bump a 7 year old topic but people are still seriously looking for these chips! If someone created and sold a workalike for say $30 they'd surely make some $$$.

[Scruffie]

Dang, so no takers? Sorry to bump a 7 year old topic but people are still seriously looking for these chips! If someone created and sold a workalike for say $30 they'd surely make some $$$.

The out lined plan in the first post cannot be done, creating a new chip can also not be done (without heavy investment that no one is going to put in to such a chip, if anything that'd be the SAD1024 or MN3005 but that's not happening either).

Possiblyyy, a 4011 to split the single clock pulse the SAD512D takes in to a 4049 to buffer it to overcome a 3207 clock pins capacitance but that's above my pay grade as i've never really bothered to look in to the workings of the SAD512D

The micro chorus has been made to work with a 3207 or 3207 by tapping the opposing pulse of the multi-vibrator but that's not the case for all SAD512D Pedals.

[Mark Hammer]

Yeah, the "perk" of the 8-pin SAD512D was that it did the doubling of the clock "tick" into a tick and tock internally, such that all you needed externally was a single-phase HF clock to drive it.

Producing a retrofit replacement for this rare beast would require a sub-circuit to produce complementary clock pulses to drive a 3207, but would also require changes to the host circuit as well, such that dividing down what the host circuit provides as clock would still keep you in the appropriate delay range,given the use of a BBD with double the stages.

None of that is impossible.  It's just clumsy, may not fit in the available space, and not for beginners.

[armdnrdy]

Without scouring every word of the data sheets, it appears that the easiest retrofit for the SAD512D would be making a daughterboard for a RD5107.....if you can find one!

These two BBDs share similar properties. Both produce a dual phase clock from a single clock signal, both are 512 stages, the pinout is the same except for pin 3 which is N/C on the 5107 and one of two outputs on the SAD.

The SAD can accept a higher voltage +17 max  where the 5107 only +13 max.

[Fender3D]

...all you needed externally was a single-phase HF clock to drive it.

Actually you don't even need a proper clock... anything that just pulses will work...
look at MXR Micro Flanger's clock...
It will also work with R51xx (ask Greg...  )

[Rylan]

Yeah the datasheet says 5v (or higher) single-phase clock in. Clock is 2x sync. It outputs 1 even 0 odd, then 0 even 1 odd every clock cycle.

The device creates a delay range from 0.0002 to 0.2 seconds. Fabrication: silicon-gate, MOS transistor/storage capacitor, bucket-brigade, charge-transfer. Doesn't look that advanced really, just a ton of charge-transfers on a wafer or something. The pinout of course doesn't matter but here it is:

1 clock
2 gnd
3 odd out
4 even out

5 vdd
6 sync
7 input
8 vbb

[armillary]

I ran across this thread recently. Having had some success using an MN3205 on a daughterboard to replace the SAD4096 on a DOD680, I think it's worth a try to replace the SAD512D in a DOD670 using a daughterboard with a R5106.

I also got good info from these:
http://www.diystompboxes.com/smfforum/index.php?topic=30056.0
http://www.diystompboxes.com/smfforum/index.php?topic=76604.msg626624#msg626624

I understand the SAD512D may never come back. Maybe the R5106 was also rare 5 or 10 years ago, but today it's not hard to find a R5106 for $20.

I took some measurements of the SAD512D in a DOD 670 to compare with an R5106 replacement.
             SAD512D         R5106
Vdd      15.26V             12V is typical. 13 is max. So try 12.
Vbb      15.26V             Vdd-2, so try 10V.
Clock    15.26V             5V to Vdd, so try 10V to 12V.
Gain      .8dB                3dB   (from the datasheet) 

Using the .diy file from the DOD 680 fix as a starting point, I came up with this:
http://www.aronnelson.com/DIYFiles/up/DOD670fix.pdf

Right now I'm waiting for parts, but should have an update in a week or so. Comments welcome. 

Made several changes to the DOD670fix.pdf file and uploaded it again this morning.

   

[armillary]

Private armillary reporting in on efforts to replace a SAD512D with a R5106 in a DOD 670 Flanger.

Parts arrived. Constructed daughterboard from pdf posted above and installed. Vdd=12, Vbb=10, clock=~9, adjusted bias to 7.6. Tested and got a very very weak effect, and only if Regen was above 3 o'clock. Below that, just clear guitar signal.

Abandoned the daughterboard idea, deciding instead to put the R5106 in the SAD512D socket. It's pin compatible after all. To prepare, socketed regulator and replaced LM78L15 with a LM78L12. Replaced power supply caps for good luck. Now Vdd=12, Vbb=12, bias trimmer only goes up to 6.1V. Tested anyway, with the R5106 in the SAD512D socket, and the results are very similar to the daughterboard, including the Regen having to be at 3 o'clock for any effect at all and even then it's pitiful.

But here's something interesting. Looking at that DOD Flanger 670 schematic with the cryptic scribbling (posted below), I was looking for a way to juice up the output of the BBD. The schematic shows a 22K resistor to ground, with the scribble, "100K (5106)". As in, maybe, R5106?

And below the input bias pot on the schematic, there's a crossed out scribble that looks like it could say "100K pot 5106". Actually, replacing the 5K ohm bias trimmer pot with a 10K trimmer will allow adjustment to 7.6V. Or reducing the R1 dropping resistor from 4K7 to 2K2 will let the 5K trimmer go to 7.6 volts without having to replace the trimmer. So now I'm thinking some of that scribbling really could be about R5106.     

DOD 670 schematic here: http://www.aronnelson.com/DIYFiles/up/DOD_670_Schematic.pdf

For now, I'll replace the 4K7 bias resistor with a 2K2, and the 22K output to ground with a 100K and keep trying. 


         

[Mark Hammer]

It's certainly feasible.  But considering the extra parts required, what may not be so feasible is fitting it into the existing space in the pedal.  After all, the big benefit of the 512D and the 510x chips was that they only required a single-phase clock and did the division internally, saving a flip-flop or other CMOS chip and the associated space.  Using a replacement chip that requires a two-phase clock means making space for that flip-flop.  If you can do it on an SMD board, there's hope.  But I have no idea where in the deuce I could fit a board accommodating an MN3004 and a flip-flop, if the 512D in my MXR Micro-Flanger ever went kaplooey.

If it was a bigger chassis, quite possible.  But not in anything around 1590B size.

[armillary]

I made an audio probe from the helpful post here:
http://www.diystompboxes.com/pedals/debug.html

The wet signal stoped at the 1uF cap between the 4558 and the expander side of the NE571. The cap measured 0 uF.  After replacing it, the R5106 works.   

So I switched back to the SAD512D at 15V and it works too. I'm going to just enjoy the pedal for a few days and then go back to work on the R5106. 

[Mark Hammer]

I salute your diligence. 

[armillary]

Thank you, kind sir!

[hanky6000]

So do you have a working Dod 670 now, Armillary?

[DrAlx]

For now, I'll replace the 4K7 bias resistor with a 2K2, and the 22K output to ground with a 100K and keep trying.     

The resistance to ground on the BBD output determines the BBD gain.
If its too low value you'll get low gain and distortion. Sounds like the FETs on the BBD outputs have higher drain-source resistance in the R5106 and so would need higher resistance to ground to give good gain.  I haven't checked the datasheet but if the R5106 is higher gain than the SAD512 then make that resistance to ground trimable so you can get the gain to match the SAD512.  In general you are not going to be able to make a daughter board that will fit any circuit that took the SAD512. The need for different resistance to ground can have knock on effects to other components so you can end up changing other things that hang off the BBD.