What to build with an SAD1024?

[erix]

I recently found a SAD1024 still in it's Radio Shack card ($11.95 in 1980!) and I want to build something with it.
Does anyone have any ideas?

Thanks,
erix

[Mark Hammer]

Probably the "best" thing you could build with it is the A/DA Flanger, using the adaptation for the SAD-1024 that Mike Irwin devised.  I've heard it and it's both real and spectacular (couldn't resist the little Seinfeld reference there).

You CAN use an SAD1024 for a bunch of other things, but quite frankly they don't show off the chip as much as the A/DA pedal does.  It isn't enough to do echoes, and choruses have survived quite nicely with run of the mill MN/BL3207s.  Flanging and 1024's go together like coffee and donuts.

[erix]

Thanks Mark!

Any idea where I coould find Mr. Irwin's schem?

erix

[StephenGiles]

Here:
http://img.photobucket.com/albums/v317/StephenGiles/ada_MI_1024.jpg

happy soldering!
Stephen

[erix]

Yoiks!

That looks lovely - nice drawing!

Is there now 'Threshold' pot on this version?

erix

[StephenGiles]

No, I never bothered with it.
Stephen

[RedHouse]

What's going on with IC-1b?, looks like a Franken-TubeScreamer in there.

[Mark Hammer]

It's essentially a limiter, and roughly similar to what you'll find in other designs.  The idea is that if you set the regen too high, the combined input+regen signal exceeds what the BBD can handle and you get the whupped-with-a-ugly-stick clipping.  One way to handle it is to simply opt for only a modest amount of regen in the first place.  This is often seen by the inclusion of a regen trimmer on the board.  The regen control is set to max during production/setup, and the trimpot set to a point below oscillation.

The other way to handle it is to set a soft-clipping/limiting action by means of diodes such that the regen ceiling is set to a known maximum (knowable by virtue of the diodes' voltage drop).  In some instances, such as in the Boss BF-2, you'll see a simple back-to-back pair of diodes in the 2nd op-amp to perform that function.  In the case of the BF-2, there is a 4k7 resistor in series with the diode pair to "soften" the action of the diodes.  It adds a small amount of grit to high level signals and excessive regen, but it keeps the BBD from clipping even uglier.

No question about it, though, the A/DA's  limiting is more complex.  One of the issues (Rev. 3) uses a simpler arrangement between the input and input+regen mixing stage, with a 2+2 diode arrangement going to ground (à la Dist+) through a cap.  Revision 4 uses that 6-diode thing in the stage where the regen signal comes back.  I haven't ever been in a position to compare how the two sound, relative to each other, but my guess is that Rev 4 likely makes maxing out on regen feasible.  Of course, you will note that the regen trimmer is also included so "max" means max of usable regen (soft clippers aren't perfect).  Also note that unlike many other flangers, the A/DA (and Morley Sapphire) does addiional lowpass filtering of the regen signal before it gets fed back.

[StephenGiles]

I actually changed the limiter on mine to the Ver 3 type at Mike's suggestion - havn't got round to changing my drawing yet.
Stephen

[Johnny Guitar]

Well I have an SAD 1024 as well (unused I believe) and was thinking of making a flanger.

Would Irwin's circuit be a lot better than a Dlx Electric Mistress (since I could get a PCB from GGG -- I also liked the way Belew could get that "elephant" roar by playing with the knobs! )

John

[Mark Hammer]

Let's be clear about this.

There are plenty of tricks that just about ANY commercially available flanger, past or present, can do.  If that's what you generally want a flanger for, then any of those will do nicely.  The Deluxe Electric Mistress has made lots of "classic" tones, and has made (and continues to make) plenty of players (including his holiness, Adrian Belew) very happy for all the right reasons.

Then there are certain tricks that require fairly exotic capabilities to do.  Where the A/DA, and perhaps a few select other designs over the years, move in and grab the spotlight is in producing those slow sweeps that feel like a jet formation coming in over the horizon and doing a fly-by.  That requires tha ability to a) produce a much shorter minimum delay time than most stompbox flangers do, and b) sweep from that minimum delay time to a much longer one, producing a broad "sweep ratio" ( = max delay divided by min delay).

The original unit used a Matsushita delay chip (MN3010) that unfortunately seemed to have one of the most limited production runs of that line.  Limited enough that it joins the ranks of the R5101 and MN3011 as far as being hard to find and expensive to buy.  Fortunately, the Reticon SAD-1024, while no longer in production, has a roughly similar architecture, and is not in terribly short supply.  Mike did not tamper with the general design features of the original, but simply adapted the existing design to be able to replace the MN3010 with an SAD-1024.

At long, slow ultra-wide sweeps, it sounds fabulous, but if you simply wanted a flanger to mimic bubbly or slow Leslie speaker sounds, a DEM will do that particular job very nicely and will make you just as happy as an A/DA clone would.

[erix]

Thanks Mark and Stephen!

I'm really interested in the ADA now. I've found a lot of posts regarding it via the search button (Stephen you are perfboard animal!) so I won't use this thread to repeat any of those questions but...

Are there a schem(s) of the originals around so that I may get some missing component values (the diodes) and see how the "Threshold" pot was implemented? There is a link in one of the post to JBLAudio's site but it is no longer active.

Thanks!
erix

[Mark Hammer]

http://www.adadepot.com/adagear/gearpages/stompboxes/ADA-Flanger.htm

[Johnny Guitar]

Then there are certain tricks that require fairly exotic capabilities to do.  Where the A/DA, and perhaps a few select other designs over the years, move in and grab the spotlight is in producing those slow sweeps that feel like a jet formation coming in over the horizon and doing a fly-by.  That requires tha ability to a) produce a much shorter minimum delay time than most stompbox flangers do, and b) sweep from that minimum delay time to a much longer one, producing a broad "sweep ratio" ( = max delay divided by min delay).

Thanks Mark!

Since I'm pretty happy with my MXR's ability to get that rather slow "woosh" flange sound and (more importantly) since I have no faith in my ability to build a complex circuit on perfboard yet, I'll probably go with the EH DEM clone.

John