electroharmonix - memory man solid-state echo / chorus debug

[the3secondrule]

picked up one of these: http://www.effectsdatabase.com/model/eh/memoryman/echochorus off a fellow forumite as a project.

all tants / electros have been replaced (except for the power filter caps - waiting on an order). also replaced the 4558's and 2n5087.

there is delayed signal, but the repeats are significantly quieter than the clean signal, repeats are thin / distorted, and at full feedback, i'm only getting 1 or 2 repeats. also there is no chorus on the chorus setting.

I've audio-probed the circuit, and i'm getting good delayed signal out of the MN3005 on pins 3 and 4, but the repeats drop in level after the 2n5087.

getting the correct voltages from the ne554
pin 14:   15.6v
      11:  -15.6
      3 :    0

MN3005
0
-7.73
-7.6
-7.3
-.15.4
-7.7
-0.11mv
-14.48

cd4047be
-15.2
-.1v
-.01
0
0
0
-15
-15
-15
-7.7
-7.7
-15.
-15
0

More voltages coming shortly, and I also have a factory schem (not sure if it is cool to link to it?)

but anything else I should check? anything else jumping out?

Cheers,

J

[the3secondrule]

also, it has been suggested that I attach a heatsink to the ne554 - but im not sure how to go about heatsinking a 14 pin chip...

J

[theehman]

You may need the trimpots adjusted.

[the3secondrule]

should have mentioned - trimpots have been adjusted.
no scope, so I had to do it by ear - first i adjusted the bias for the strongest delay signal, then the clock cancel and hi-freq to get rid of the most clock noise.

As i mentioned - audio probe gets good strong delay signa out of the 3005, l, and then it weakens later in the circuit... (after the 2n5087, before the feedback pot)

J

[the3secondrule]

It lives!

found a tiny short to ground off on of the caps in the filter section. after weeks of staring at the pcb, it jumped out at me.

Still no chorus, yet... tbc

[theehman]

Check your echo/chorus switch.  Sometimes they get really dirty/oxidized on the contacts.  The slider inside may be missing as well.

[the3secondrule]

Sweet, will do - Just redid the wiring on the chorus switch, but i'll check for continuity on the switch as well...

J

[the3secondrule]

have checked the echo/chorus switch, and i'm getting continuity across the lugs in chorus position, so i assume the switch is ok.

Voltages for the lm1458 -
pin 1: -0.13
-0.13
-0.13
-15v
-0.17
-0.17
-0.1
+15v

i'm assuming there should be oscillating voltages somewhere around pins 5,6,7. any suggestions as to what to check?

Cheers,

J

[the3secondrule]

Also, just wondering if there is any way to improve the blend control.

with the blend control set with the clean signal at unity, the repeats are too quiet. with the blend control set with the repeats at unity gain, the clean signal is too quiet.

wonder either if the blend control could be rewired as a wet - level control, or if subbing the 10k blend pot with something smaller, say 5kB would allow more of both the clean and wet signals with the blend at 50%.

thoughts?

Also, Ron, I believe I obtained the schem off you. Are you happy for me to post it here to help with debugging, etc?


J

[theehman]

Also, Ron, I believe I obtained the schem off you. Are you happy for me to post it here to help with debugging, etc?

J

I didn't draw it so post away.

[the3secondrule]

schem here:

http://img163.imageshack.us/img163/5990/memorymanschem.gif


J