Different EH Memory Man

[Wild Bill]

A friend brought me his old Memory Man for repair. The dry signal is there and adjustable but the effects are totally dead.

Looked around for a schematic and although mine is marked as a "Deluxe" it is very different than the schematic from Steffen's site.

This one uses SAD1024's. The regulator pass transistor is a 2n6290 rather than a 2n6111. It appears to be regulating but to -20 volt instead of -15.

There's a mess of RC4558 op amps but no sign of a clock chip like a 4047, or anything else for a clock either.

All the op amps show close to the -20 v at the output pins, which I assume is a VERY bad sign!

Only the pcb circuit is different - from the outside it looks like the same Deluxe Memory Man.

Anyone got any hints or ideas that might make things easier?

---Wild Bill

[StephenGiles]

This is the one:
http://img.photobucket.com/albums/v317/StephenGiles/EH_MMdeluxe3.jpg
http://img.photobucket.com/albums/v317/StephenGiles/EH_MMdeluxe2.jpg
http://img.photobucket.com/albums/v317/StephenGiles/EH_MMdeluxe1.jpg

Maybe the 4047 is missing from the unit, but it is required.
Stephen

[Wild Bill]

That's it, Steve!

I'll quaff a brew (Canadian) in your honour!

You were also right about the clock chip - I was digging through old books looking for tips on how to make an op amp oscillate for a clock!

The 4047 was hiding under the delay pot!

---Wild Bill

[Mark Hammer]

Hi Bill,

One of the things I always suggest people consider with BBD-based effects that seem to "work fine but without any delay signal" is to consider that the bias trimpot for the BBD has either drifted or been jostled.  BBDs need to see the audio signal sitting on top of a DC bias.  If the bias is mis-set, a wee bit, you hear a distorted delay signal.  If it is off more than that, you hear NO delay signal.

One of the practical difficulties of those early MM's is that they used multiple SAD-1024 chips, EACH of which required its own bias trimpot.  If any one of those 3 gets buggered up, you won't hear any delay signal, even if the other 2 work great.  Of course, it wasn't exactly E-H's choice to do so, since larger capacity BBDs (the equivalent of 4 SAD-1024s) didn't come along until a bit later (when E-H happily switched over to avoid this problem).

How would you know that the bias for chip X is set right when the others are set "wrong"?  The most straightforward way is to start with IC4a and verify that delay signal is coming out the other end with either a scope or an audio probe in contact with either the output of pin 5 of IC4b or on the negative side of DC-blocking cap C22 (1uf) just after IC4b  Once functionality is verified, move on to the next BBD and the next.  If it should happen that tweaking the bias voltage does NOT produce any viable delay signal, despite assurance of signal flow up to that point, then it stands to reason you have a fried SAD1024.

There ARE other sources of nonfunctionality (with so many parts, how could there NOT be?), but this is a pretty common one.

A second place to check might be the "gain" trimpots, which would appear to maintain an appropriate interstage signal level.

[puretube]

hi again, Bill...

those 20V don`t sound good to me at all  :cry:

[Mark Hammer]

Atually, come to think of it, while many op-amps can handle it, 20v doesn't feel so good to an SAD1024 either.  There is a distinct possibility you are the proud possessor of some fried BBDs.