Got my total recall built and I'm getting one beautifully clean repeat after biasing and adjustments. Mod works, delay time works...everything is great with exception of repeats. There's just one repeat. Feedback pot has no effect. Voltages are all right on the money. Using xvive mn3005's. I swapped ne570, same result. Don't have other bbd
chips to swap but I think if they were bad they wouldn't give me any repeats at all. Any ideas where to start? I've double checked component values and tested the fdbk pot itself and it's good.
I should probably add that one of the first things I did at power up was slip with my multimeter probe and ground out the DC jack. Ugh!! But like I said all voltages are good and I got the repeat right off the bat with trimmers all at noon. I went with the one repeat during calibration as my fdbk pot got turned low flippingbit around. When I turned it up it just stays at one repeat always. Anyhoo..
Only component value I found that's off is C20. I was short on 2n7's so it's a 2n2. Still just the one repeat.
I've traced continuity through out the feedback circuit and everything seems good. I've tested the ohms of the fdbk pot in use as I turn it and it's good. Again, i'm left with the conclusion my bbd chips didn't like the power supply arc. I'm going to re-order all new IC's including the 3005's...just asking one more time if anyone has ANY suggestions why this circuit might act like the fdbk pot is stuck at it's lowest setting before I spend the money. Thanks
It's not the BBDs and probably not any of the ICs if you're getting some delay, you'll have to wait until I have time to help though i'm afraid unless someone else steps in.
In the mean time post some pictures of your board.
I agree with Scruffie. The fact that you get any repeats tells me that your BBD is good and most likely... your other ICs as well. Pics of the PCB would be nice. Here are some other things to think about....
1) Did you use the specified 10KA pot for Feedback? Maybe you accidentally used a 10KB or 10KC?
2) Is the pot "wired" to the PCB or is it a 90 degree PCB pin pot? If it is wired, are the wires connected properly? Are they possibly backwards?
Good Luck ;)
Thanks! I'll send pics and voltages tonight. Fdbk pot is right angle pcb mount. I'm pretty sure it's 10kA. I'll check.
I built one not too long ago. I'm not looking at the schematic now and am far from an expert on bbd's. So take my suggestions with a grain of salt
Two things popped to mind. There is a jumper wire on two pads at the bottom of the board. Is it in there?
Second. Did you play around with the gain trimpots? I forget which one but one of them changes how early in turning the feedback knob that it starts to self oscillate. Maybe if it's turned to an extreme point it limits the repeats?
The leg of C28 that meets R34 wasn't soldered. It hides under a pot. Idiot move. Won't be my last. Sounds so good now! Thanks for the replies and making me look harder before I spent more $.
Couldnt help but glad its working now!!