EH Memory Man needs repair...any techs in Canada? | Page 3 | The Canadian Guitar Forum

EH Memory Man needs repair...any techs in Canada?

Discussion in 'Effects Pedals, Strings and more' started by 335Bob, Dec 15, 2009.

  1. mhammer


    Nov 30, 2007
    Ottawa, Ontario
    Well, certainly consult this thread, and see if there is anything I might have missed: Deluxe Memory Man, MN3008 building

    Actually, reading through it now, it seems the schematic showed what a guy was going to do, not what exists in the 4xMN3005 issue.

    However, here's another potential source of noise. It is common on delays where there is a single bias trimpot to "decouple" the bias voltage by means of a cap between the wiper of the trimpot, and ground. Think of it like smoothing the power supply, but at a micro/local level. As near as we can tell, EHX skipped out on that part. It likely isn't make or break, but since it is dead easy to experiment in a nondestructive way, try sticking a cap to the relevant solder pads on the solder side of the board for each of those trimpot, and see if it makes any difference. A quick scan through the schematics of a number of well-loved commercial analog delays says that a 1uf electrolytic (+ side going to the trimpot wiper) ought to do it.

    Finally, part of the objectionableness of the hiss is the way in which it seems almost gated. Here is most of the schematic of the 2xMN3005 reissue:
    You can see that there is a 1uf capacitor from pins 1 and 16 of the NE570 compander chip. This sets the attack/decay constants of the compressor (pin 1) and expandor (pin 16) halves of the compander circuit. Pin 16, however, has an additional 1.5M resistor in parallel with the cap. This helps to produce a slightly faster decay in the expansion than in the compression (normally, they would be identical). Just for the hell of it, if you have a 1M resistor, and can find the pads where the 1.5M goes, tack on the 1M on the solder side for a moment, and listen to what happens. It might produce a more gated sound, or maybe decay fast enough that you don't notice the hiss as much. Hard to predict.

    Now, the NE570 is touted as being a bit quieter than the NE571, so there is that to consider, but I've never heard anyone rave about how much quieter anything was, now that they stuck an NE570 in there. So it may not be worth the trouble and cost to source one. In the case of the 4558s, though, an NE5532 or LM833 (both easily and cheaply available) is a quieter pin-for-pin replacement.

    Conceivably, there is some sort of magic voodoo cap replacement, of the sort that guys like Keeley does, that may be quieter in this context. Unfortunately, I have no words of wisdom to provide here, other than it might be possible.
  2. surfguitar


    Dec 15, 2010
    Surrey, BC
    I have a DDM that sounded like "eggs frying" as I turned up the level and I've tracked it down to some cold solder joints (they didn't exactly flow solder these boards). With that fixed, I found the schematic link you posted for the DMM and it seems to match mine. Mine being an EC_2002_Rev_E with an SA571, CD4047, 4558's, 2 x MN3005's.

    I noticed you mentioned replacing the 4558's with the lower noise NE5532 and I've ordered some of those to try out (Im going to socket them so I can swap with the 4558's). Kind of a spring project...

    Any way, apart from my chance to say THANKS for posting that schematic I was wondering if you have any information on the procedure for setting the trim pots? I have a function generator and dual trace scope.

    I'm still debating about changing the lower quality caps on the board for better ones. Just not sure it would make a big difference. Or for that matter any difference...

  3. kugua


    Jan 29, 2012
    I made a clone DMM.sounds good ,but hiss at background .I test it maybe the hiss is come from NE571 .I took of the resisitor of pin 16 .the sound is not like originally sound it's be very good.not fade in.[video][/video] here is the hiss sound.I wanna find some ideas toreduce it.I tested it today.the noise of hiss frequency 2000HZ---4000HZ.
    Last edited: Jan 31, 2012

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