ad3208 arghh

caress · July 09, 2007, 10:36:09 PM

i put together an ad3208 using a ggg board and bl3102, sa571, bl3208, mn3205 all from smallbear and i can't seem to get any repeats out of the damn thing. i've searched the board, checked for bad soldering, wrong parts, un-grounded-ness, wrong wiring, cap/diode/ic/transistor placement, messed with the trims over and over again, etc etc...........nothing except a slightly boosted, distorted signal coming through. i'm at my wit's end here. any HELP!?

newbie builder · July 10, 2007, 12:07:59 AM

if you bought extras of the ics, have you tried replacing them/checked all their orientations, as well as the orientation of the transistors? always my first thought in builds gone wrong since I've done it more than a few times myself.

also, see this thread so that others can help you troubleshoot:
http://www.diystompboxes.com/smfforum/index.php?topic=29816.0

caress · July 10, 2007, 10:33:42 AM

1. AD3208
2. http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=48&Itemid=26
3. i used a pcb from ggg and took my time soldering everything in since i usually perf and don't pay $xx for a board

4. modifications are: i used a 10k trim instead of the 100k coming from the repeats pot to get plenty of self-osc
5. negative ground....checked all cap, diode, transistor and ic placement/orientation.
6. sound goes through and is distorted a bit and boosted a little bit, but no delays.

Rayman · September 20, 2007, 01:05:16 PM

if your sound is distotred with no delays, it sounds like you have to adkust the 10K trim pots. Sorry to point out the obvious. Have you tried adjusting the trim pots like the instructions on GGG.

markm · September 20, 2007, 03:01:37 PM

Quote from: Rayman on September 20, 2007, 01:05:16 PM
if your sound is distotred with no delays, it sounds like you have to adkust the 10K trim pots. Sorry to point out the obvious. Have you tried adjusting the trim pots like the instructions on GGG.

Good advice though.
Also, Have you read over the complete project at GGG?
It's been a long time since I built mine so I don't really remember what the info is but there may be some help there as well.

caress · September 20, 2007, 11:33:27 PM

sigh...yeah i read and reread the project notes and tried adjusting the trims for quite some time. in the meantime i've built 2 rebotes! haha i'll come back to it pretty soon. i might swap out my clock...? it might be the issue. when i figure it out though, i'll repost. thanks for the advice-s.

caress · November 10, 2007, 05:51:27 PM

sorry to bump this up, but i'm still having some problems with my ad3208.

after changing my chips, i've got delays! but they're very distorted...

close to being a nice tape-y distortion, but just a little too much. i can hear that they're a bit misbiased and i've just tweaked the trimmers for about 2 hours straight...still can't get exactly the sound i need. my issues are that my trim pots aren't doing anything in the middle range of their turns...they are set up as follows (from left to right looking down at the board):

(BBD2 Balance): turning does nothing. (i retouched my solder points as well)
(BBD2 Bias): only works at one extreme of the pot and a very small sweep at that.
(BBD1 Balance): again works better closer to one extreme, but has a large sweep (almost the whole pot).
(BBD1 Bias): works closer to the mid range with a little sweep.

BBD1 controls seem to be working more or less normal... it's BBD2 that seems off...? also, i'm not really getting delay on higher frequency notes unless i turn the BBD1 Bias trim and get a bit more distortion...?? new battery and all...
i just can't get a clean sound out of here! anyone? ideas? help!

george · November 12, 2007, 02:17:17 AM

what voltage are you getting at pin 7 of BBD2 at the 2 extremes of the bias trimpot?

And what voltage are you getting at pin 5?

It seems to me that there is a problem either with the zener you have in there or one of the 2 4k7 resistors connected on either side of the bias trimmer for BBD2 is the wrong value ....

oldschoolanalog · November 12, 2007, 04:06:01 PM

Quote from: caress on November 10, 2007, 05:51:27 PM
...new battery and all...

Are you using a 9V battery to power this? IMHO, this might be part of the problem.
If so, try a "regulated 9VDC power supply", as specified in the schematic.
Everything to gain, nothing to lose.
osa

caress · November 12, 2007, 08:04:34 PM

ok i tried a 1spot 9v adaptor with similar results, so i don't think it's the supply.

my 4.7k resistors near the bbds are 4.7k...but i can't check voltages right now because my mm is shot.

i'm going to pick one up tomorrow if i have a chance.

edit: after listening for a while, i'm kind of digging the distorted repeats. my only beef is that high freq signals aren't effected by the delay in this state...?
another thing too, it's really easy to get infinite repeats and i really mean infinite. i played a note and it was repeating without turning to mush or feeding back for well over two or three minutes...is that normal?

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ad3208 arghh