EH DLX Memory Man Help

[jmasciswannabe]

I know that I am supposed to write down the voltage ratings of all the opamps, and I will if need be, but before going through all that, someone might have an idea to save me the trouble. I have the MN3008 version and it works pretty good except for when I try to do long/indefinite repeats. The repeats start to clip and become more "staccato." I have diddled with the trims a bit to no avail. I swapped out the sa571 still didn't help. Pin 3 on all the mn3008s sound fine, so I assume they are all working. Maybe one is on the fritz? Any suggestions/ideas would be appreciated.

Here is a link to the schem, couldn't figure out how to attach it on here.

http://music-electronics-forum.com/attachments/10834d1283022724-deluxememorymanrevd.pdf

[rustypinto]

If the unit is delaying, the op-amp voltage readings may or may not help here. Even the BBD voltages aren't that useful because no two BBDs are the same.

It does sound like one of the MN3008 biases is off though. Are you using an oscilloscope/ signal generator to do the adjustments? If not, it gets really hard to tell which of the four MN3008 BBDs are off, or contributing more distortion than the other for a given input signal amplitude and delay time setting/ clock frequency.

Also, make sure you know exactly which trim does what, or you might be tweaking the wrong parameter. Its really easy to get mixed up if you're looking at the back-side of the PCB. I don't remember if the Rev D PCB has the trim labels or not. I know Rev E does, which is another DMM version that uses MN3008.

[jmasciswannabe]

The trims were a little confusing at first, but I've got them memorized. I learned about the voltage matching being a no go earlier on in my trials. I do not have an oscilloscope but am going to be looking into a software oscilloscope and using my sound card. Gonna start a new post about that and see what people think.

Can anyone point me to a circuit analysis of the memory man or something similar. I guess knowing how it works would be a beneficial thing. I can't wrap my head around why initial delays sound good and full but the others sound chopped.