No Signal through BBD's in aquaboy deluxe

[Timo]

Hi,

this weekend I put the final components on the aquaboy deluxe (2013 version) PCB I had lying around for years. However, no repeats/feedback/whatever is heard when the effect is engaged, only the dry signal. I went over the pcb with both a DMM and an audio probe and found that the problem is probaby somewhere in the BBD's. I get audio on pin 7 of IC 3, but none on pins  3 and 4 (the output pins). Also, the voltages on the DC in pins of the BBD (that should be 5 and 8 if im not mistaken) are way low, which I think causes the issue. I don't have D2 or D3 on the board and I'm using a 15V power supply (3PRR.)

So, does anybody have an idea what can cause this issue? I won't be able to check again until next weekend, but that gives me some time to digest your advice, I guess. Thanks! 

[jimilee]

What are your voltages on IC 2 like and do you have another you can throw in there? They're very sensitive, I went though 3 troubleshooting my total recall.


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[Timo]

Oof, thats exactly what I wasn't hoping for haha. Im using an NE570 and I only have one, but I'll try to find a couple extra just in case. I'll get back to you with those voltages!

[Scruffie]

If signal is reaching IC3 but not coming out of it, it's nothing to do with IC2 (and not to chastise you jimi as I know people seem to have problems with them, but they're really not that sensitive, they're an op amp and a bunch of transistors in a package, nothing we don't usually deal with, just don't want that becoming the next 'thing'.)

Post your voltages, then we'll talk

[Timo]

Ah thats good news, I looked around online and those NE570's are rather expensive. Another thing I just noticed is that I hear a high pitched whine, which I assume is clock noise (the pitch seems to be modulated slightly in the same rhtyhm at which the rate LED blinks), when audio probing pins 3 and 4 of the two BBD's, as well as on pin 7 of the second BBD (IC4).

I've got some voltages for you; (measured against gnd)

pin - voltage

IC1:
1 - 7.09
2 - 7.09
3 - 7.09
4 - 0
5 - 7.09
6 - 7.09
7 - 7.09
8 - 14.15

IC2:
1 - 1.15
2 - 1.8
3 - 1.8
4 - 0
5 - 1.8
6 - 1.8
7 - 3.09
8 - 1.8
9 - 1.8
10 - 4.7
11 - 4.7
12 - 1.8
13 - 14.15
14 - 1.8
15 - 1.8
16 - 0.8

IC3
1 - 13.9
2 - 6.94
3 - 3.10
4 - 3.10
5 - 0
6 - 6.93
7 - 2.03
8 - 0.95

IC4
1 - 13.9
2 - 6.94
3 - 3.10
4 - 3.10
5 - 0
6 - 6.93
7 - 2.03
8 - 0.95

IC5
1 - 13.96
2 - 6.94
3 - 0
4 - 6.94
5 - 6.21
6 - 7.41
7 - 6.33
8 - 0.93

IC6 (I used a TL072 here instead of a TL062)
1 - 6.13
2 - 6.9
3 - 6.61
4 - 0
5 - 6.98
6 - 7.07
7 - 7.34
8 - 14.16

Q1
1 - 5.35
2 - 4.27
3 - 14.15

Q2
1 - 2.46
2 - 2.97
3 - 14.15

Q3
1 - 2.86
2 - 3.33
3 - 14.15

Q4
1 - 2.26
2 - 2.74
3 - 14.15

[Scruffie]

Your BBD bias is way too low, you should have in the 6-8V range on pin 7 of each BBD. I hate to ask but you have tried tweaking the bias trimmers while probing, haven't you?

TL072 isn't a great alternative for IC6, don't think it's related to your issue but you might find it adds LFO tick and its higher current draw might explain why you have a low supply voltage. LM1458 would be suitable if you don't have any TL062.

Yes the high pitch whine is clock whine.

[Timo]

Oh man I feel like such an idiot. You're right, that was it! Can't believe I didn't realize that that was the problem.

I agree on the TL072, but it was the best alternative I had at hand. I'm on gonna replace it with something more suitable as soon as I have to order something from a store that sells them :p

Anyway, thanks a lot for your help! Can't wait to box this up!