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EH Deluxe Memory Man

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1/31/2000 1:38 PM
Bob	EH Deluxe Memory Man I've got an out of whack, 4-knob, older Deluxe Memory Man. There are alot of gain and bias trimpots inside this unit. Does anyone know the calibration /setup procedure for this so I can get this thing sounding reasonably good/better. Thanks, Bob

2/1/2000 7:32 AM

The Bias trim of an SAD1024 is set by observing the chip's output (see below) on an oscilloscope. With a maximum-level signal input, adjust the trimmer for minimum output distortion on both positive and negative signal peaks. (Please don't tell anyone this is also how you bias a guitar amp.)

The Gain trims are set to preserve successive output levels from chip to chip.

The SAD1024 is a dual 512-stage BBD. The EH-7550 (Memory Man Deluxe) uses four 1024's, each serially configured. They are IC4 (A&B), IC5 (A&B), IC7 (A&B), and IC8 (A&B). There is a 4558 buffer between IC's 5 and 7.

I don't have a component layout for you but the wiper of each of the four Bias trimmers (10kB) is fed simultaneously to both A and B inputs (pins 2 and 15) of its particular SAD1024. Each is fed through a 100k resistor.

Three of the four Gain trimmers (5kB) are 2-legged, hanging on a 1024's B+B' output (pins 5 and 6 connected together). In the case of IC8, however, the trimmer is hooked between B and B' (between pins 5 and 6), with the wiper feeding the junction of a 16k and a 2.4k resistor. That final-stage wiper should typically read 4.6 V DC.

To set the first (IC4's) Gain trim, match its A output level (pins 11 + 12) to its B output level (pins 5 + 6).

Good luck.

2/1/2000 11:22 AM

Anders Westerberg

Bob, are you sure the bad sound is because of improper trimmer settings? The symptoms you'll get is clock noise (high pitch tone in the background, pitch affected by delay time knob), distortion (if a gain trimmer is set wrong) or if you get outside the limits; no delayed sound at all.

I don't know what your definition of bad is, but loss of high frequencies is a part of this old BBD-technology. The low-pass filter starts cutting at 3kHz (if memory serves me).

2/1/2000 11:47 AM

Anders,
I'm dealing with a unit that was badly abused and cannabalized for parts (SAD 1024) before I got it and there is some physical damage to it and the CB. I don't know much about them and I'd thought that it would be a fun little restoration project. There appears to be alot of un-original parts of dubious quality and evidence of excessive soldering inside. (it looks nothing like my buddy's (inside) and it doesn't sound like his either). I've got it working but it is limping along right now and I thought a setup procedure would be worth checking, while I'm at it. I'm not compelled to adjust trimpots, unless, of course there seems to be a good reason to do it. I am getting a bad distortion on the delayed sound. It's just nice to have the info while you're doing it.

And thank you for the info,
Bob

P.S. My definition of bad is: 'not good'

2/1/2000 12:13 PM
Anders Westerberg	>There appears to be alot of un-original parts of dubious >quality and evidence of excessive soldering inside. Sounds just like Electro-Harmonix . If you've replaced the SAD1024's, you have to do a little tweaking. Probably one or two gain trimmers if you get distortion. Follow the guidelines provided by Rich and get back if you get stuck.

2/1/2000 12:16 PM
Bob	Anders, Thank you, Bob

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