Did I get real MN3005's?

[shawnee]

Hey guys, I bought the spare Dirtbad pcb from Jacob that wasn't working and found the problems. I knew that it had to be related the the two IC's and a couple of caps that he removed so I pulled up the schematic and ohmed everything out until I found a few places that were open. A few wires on the outside of the board and it's working like a champ. My delay pot is exactly 100K and C42 is 250pF. I bought 4 MN3005's from Polida (EBAY) and tried them all. I know it's a little crude but I set the delay pot to max and feedback to max and counted the number of repeats in 30 seconds. I got 68 repeats in 30 seconds no matter which combination of two chips I used. That should be about 441ms (68x2=136 repeats in one minute. 60 divided by 136= 441ms). The delay time seems a little short but I don't think you can get that much out of 2 MN3008's. All four give the same delay time so I can't be using one MN3005 and a MN3008 (which would explain 440ms). So did I get 4 real MN3005's?

[jkokura]

no help here, cause Scruff is better at this than me, but glad you got it working. I knew it would be a simple fix.

Jacob

[shawnee]

Thanks Jacob. I spent several hours on it but I finally got it working. It sounds great and 440ms is enough for me but I was just curious as to what everyone else thinks about the delay time.

[gitaar0]

I build a dirtbag with mn3005 form te same source.
I get over  550 ms with 300pf and a 130k pot (250k pot with a resistor across)
No clock noise.
Maybe experiment with the delay pot and that cap and you could get more out of it.

[shawnee]

I just tried closer to 300pF in place of the 240pF at C41 and retimed. The delay time went up to 517ms so I think I got four real MN3005's from Polida! I actually think it sounds better with the original cap in it though. Just a heads up, all I did was pull the CD4047 and put a tiny 47pf cap into the chip socket at pin 1 and pin 3. 240+47=287. Then I just pushed the chip back in to test. That way you don't have to solder anything to try different values. My cap has really thin leads though so you can't do it with some big silver mica cap.