Triple op amp for EH Bad Stone?

[dwmorrin]

I've just been made aware of the existence of triple op amps.
I'm working on an old Electro Harmonix Bad Stone, '74 pots, infamous mummy graphic.
This version has triple op amps with the following pinout (provided by "tube-exorcist" on fsb.org):
Pin 01: Bias
Pin 02: OP1 output
Pin 03: OP2 -in
Pin 04: OP2 +in
Pin 05: OP3 +in
Pin 06: OP3 -in
Pin 07: nc
Pin 08: nc
Pin 09: OP3 output
Pin 10: V-
Pin 11: OP2 output
Pin 12: OP1 +in
Pin 13: OP1 -in
Pin 14: V+

It uses two of these DIP, 14 pin chips. One has the numbers scratched off, and the other has been replaced by a past repair with a daughterboard that converts 2 SIP dual op amps into the DIP footprint.
The pedal is in need of repair - I haven't determined if it is a chip or not, but thought I'd try to figure out this mystery chip now, in case I need/want to track one down.
Anyone out there familiar with a part number for such a chip?

[Mark Hammer]

?????

Perhaps you should ask on one of the EHX forums. I've never heard of such a thing, but then there's a lot I've never heard of.

Is this the model/issue that uses a CD4009 chip for the control elements instead of discrete JFETs?

[dwmorrin]

Thanks for the reply Mark.
There's threads going about it on EH forum and fsb.org at the moment. Seems to be a pretty rare bird, so I thought I'd broaden my net a little.
I believe this is earlier than the CD4009 chip version.

There are discrete FETs marked "SCOTT" instead of a typical part number.

This board has two unmarked DIP 14 pin ICs, believed to be triple op amps, plus 2 741s that disappear on later boards (from what I've gathered anyways). The later boards seem to use LM324s, so this one has 2x single op amp chips + 2x triple op amp chips, for total of 8 op amps... later boards use 2x quad op amps for the same total. I'm pretty sure a trace of the board will reveal it's probably similar to the LM324 version, but with these weird triple op amp chips.

FWIW, this board is labelled EH 5800, whereas it seems like the LM324 version is EH 5850.

[culturejam]

Weird. I was *just* looking for triple op amp ICs.

There are a few DIP packages still available, but they are all expensive (like $18 each). For example: Maxim ICL7632

I would recommend going with a SOIC package (surface mount) and using a 14-pin SOIC-to-DIP adapter. It will be cheaper (by far) than buying a through hole part.

Here's a link to a SOIC triple op amp:
LMH6683MAX/NOPB Texas Instruments | Mouser

Newark has one on blowout:
LMH6683MA/NOPB - TEXAS INSTRUMENTS - IC, OP-AMP, 190MHZ, 940V/ us, SOIC-14 | Newark element14 US

[Mark Hammer]

Would any of those have been in production before 1974?

I've seen, and have, some oddball packages, like 14-pin 741s, the old Anderton favourite 4739, and the totally whack TL075 (quad bifet with an LM4136 pinut) and NE5535 (14-pin dual with inputs on one side and outputs on the other), but a triple is a new one on me.

[culturejam]

Would any of those have been in production before 1974?

I have no idea, honestly. I wasn't "in production" in 1974.

I wouldn't have even known about triple op amps other than a random thought I had yesterday. There seem to be some circuits that call for only 3 op amps, and then you have to figure out what to do with the other one (usually buffer VREF, use it as an audio buffer, tie it off and leave it fallow, etc), so I started searching for triple op amps. I didn't think they even existed, but it turns out they do.



So yeah, for a one-off repair or 1-to-1 mojo corksniffer reproduction build, I'd get the SOIC version and use an adapter for through-hole.

[J M Fahey]

Not sure they are triple op amps.
I have *faint* memories of them being single or dual voltage/current gain controlled stages (to implement the phasing/filtering effect) and a buffer, because OTAs usually use high impedance loads.
Something similar to LM13600 .
In fact somebody posted which *standard* IC would fit there.
Original ones were stamped untraceable house numbers.

[Mark Hammer]

Well, I was beginning to doubt that they were what you claimed, but I should know better than to question the word of a Brooklynite.

I took a gander at the pics that I assume you posted on the EHX forum, and the pic of the board shows it to be a sort of perversion of this circuit. The schematic corresponds to what the board photo shows, with one glaring exception: instead of using two quad op-amps (A1-4 and B1-4), it uses a pair of triples and a pair of singles, to yield the 8 op-amps required for the full circuit. Apart from that, everything else appears to be tickety-boo.

Man, weird. Just weird. But if EHX changed transistors and caps with regularity in those days, then I guess they can change op-amps. The part that puzzles me is why they would have committed to a board layout that very few chips could render usable. Although I suppose the variety of quads in those days was much less than it is now, so maybe committing to a triple op-amp chip wasn't really forfeiting much in the way of alternatives.

If a person had a bum one in the shop, I honestly can't see anything particularly special about the way in which those triple op-amps are used. A phase-shift stage is a phase-shift stage. If anything, the specs on the JFETs are probably fussier.