Aquaboy Deluxe-15V-distorted repeats and runaway oscillation

[MAO]

After reading through previous posts and trying many of the "fixes" I still can't get a clean repeat, in fact I can't get it even tolerable. I still have oscillation runaway too when using the Feedback knob, even with T1 all the way down.

Powered by Road Rage 2015, LT1054 and 7815.
Clock set at 7Khz with Delay pot maxed.
D1, D2 & D3 omitted. IN5817 used in place of R58
8k2 - R50 & R51 (VTL5C3)
R55 & R27 jumpered (Could this be related to the distortion issue?)

Currently have 3 unresolved issues:
1. Biasing BBD1 - distortion and high pitched whine
2. Distorted repeat
3. Can't turn feedback pot past noon or oscillation begins.

Biasing per build doc:
With IC4 removed and audio probing IC3 Pin3 I get a loud high pitched whine over the signal unless I turn the clock trimmer way counterclockwise. So when I'm trying to bias BBD1, I can't get rid of the distortion and I get a high pitched whine on top of the guitar signal (with clock set at 6.5Khz) Is that normal?

Here are the "mods" I have in place at the moment:

Compander biasing
(14.6V Pin 13-NE570)
Increased R13 & R14 to 42k. Gives  7.25V on pin 7-NE570
Decreased R37 to 8k2. Gives 7.33V on pins 10,11 - NE570

Loud Repeats:
Increased R38 to 68k to tame the volume of the repeats a bit. 

Other changes:
20k Trimmers for Bias 1 and Bias 2 (Started with 30k)
100K Trimmer for T1 (Started with 50k)

Other "mod" tried:
Lower gain of BBD 2, tried 33k for R28 & R29. This resolved the oscillation issue but not the dirty repeats so I put them back to 100k for now.

Here are my voltages:
    IC1 - LF353                       IC2- NE570                       IC3-MN3008                  IC4-MN3008
1. 0.0         8. 14.6            1. 1.03      16. 1.05            1. 14.11      8. 0.95         1. 14.11    8. 0.95
2. 7.29       7. 7.29            2. 1.84      15. 1.84            2.   7.09      7. 7.94         2. 7.09      7. 7.21
3. 7.29       6. 7.29            3. 1.84      14. 1.84            3.   6.40      6. 7.09         3. 6.73      6. 7.09
4. 0.0         5. 7.29            4. 0.0        13. 14.6            4.   6.38      5. 0.0          4. 6.75       5. 0.0
                                        5. 1.84      12. 1.84
                                        6. 1.84      11. 7.33
                                        7. 7.25      10. 7.33
                                        8. 1.84        9. 1.84

    IC5 - MN3101                    IC6 - TL062
1. 14.11      8. 0.95       1. Varies        8. 14.60
2. 7.09        7. 6.91       2. 7.36          7.  Varies
3. 0.0          6. 7.13       3. Varies        6. Varies
4. 7.09        5. 6.79       4. 0.0            5. Varies

Q1 14.6/6.55/6.24
Q2 14.6/7.19/6.6
Q3 14.6/6.70/6.12
Q4 14.6/6.10/5.52

Last note, I'm playing a Les Paul with Tone Zone pickups.

Please help, thanks!

[mgwhit]

Do you really have 0V on IC1 pin1.  That looks like a problem -- I would expect to see your op amp reference voltage (VB, 7.29V in your case) there. 

Your IC2, IC3 (MN3008 BBD) and IC6 (TL062 dual op amp LFO) voltages look good.

[teknoman2]

Your voltages are looking ok expept pin1 of IC1 which probably is a measurement error.
Despite that your compander and bbd voltages looks correct.
While turning the bias pot you should find a spot where the delay is without any distortion if your mn3008 is legit.
One time I had a couple of mn3008 which where fake and I could bias them at any point of the bias control.
Do you have any other bbds to try a different one?

[MAO]

Thanks, unfortunately those are the only 2 BBDs I have.
So frustrating.
I'll order a couple more. Is Polida a valid source on EBay?

[teknoman2]

If I was you I will probably avoid any Chinese e-bay seller.
Paul is offering MN3008, and most mebers here have buy from his shop, including me and never had any issues.
They are tested and legit.

http://www.diyguitarpedals.com.au/shop/index.php?main_page=product_info&cPath=4&products_id=123

cheers,
Panos.

[Scruffie]

Any delay coming through at all and the BBD works to a point, certainly not fake, although perhaps ESD damaged.

Use an audio probe to find the source of distortion, sounds like there's too much signal at some point, quite possibly an incorrect value or bad solder joint.

[MAO]

Thanks for your help, feeling optimistic again. Although I am going to order a couple MN3008s from Paul as I'm sure once I have this one sorted I'll be building another.

Will audio probe again in about 3 hrs or so, but last night I was getting a high pitched whine on top of the distorted signal while probing IC3 (MN3008) pins 3-4. Is that normal?

Should the signal coming into IC3 pin 7 be clean and without a whine?

[MAO]

Audio probe NE570 pin 6, clean pin 7, more gain, sounds slightly overdriven, but no ugly distortion. Swapped with another NE570, same results. Is this slightly overdriven sound expected?

BBD 1 MN3008 pin 7 same as NE570 pin 7, MN3008 pin 3 ugly distortion and a high pitched whine.

Hoping for something to try, maybe lowering gain of BBD 1 via R21 & R22? Or trying something in R55?

[MAO]

Tried 100k for R55, didn't help just seemed to limit the amount of rotation when adjusting the bias trimmer.

I just powered with 9V rather than 15V and even though the NE570 is biased high (around 7V on 7,10,11), the distortion seems better. It also allowed me to tame the runaway oscillation with the 100k trimmer I have in there. I'm assuming there must be less gain through the BBDs with the 9V supply. I'm now wondering if I should re-bias the NE570 for the 9V supply and see what happens. Defeats the purpose of the MN3008s but if it sounds better...

Guess I should try adjusting the BBD gain with the 15V supply 1st by decreasing R21 and R22.       

[MAO]

No go with R21 and R22, just lowered the gain/volume from BBD 1, distortion remained.

Went with option 2, re-biased NE570 for 9V supply,  distortion is much better. 

Don't understand why, but may have to stick with the 9V supply.

Going to stop for now until I get some pointed suggestions as I'm just going around in circles.

Thanks,
Mike

[gitaar0]

Hi,

I had some troubles that sound similar. Did you check those posts?

What are you using to test the delay? Might be that your signal is very hot. Humbuckers are driving BBDs easily to distortion. Did you check and reflow your soldering as Scruffie was suggesting?
I was very precise in what Inwas looking for and thus worked quite a bit on the distortion. Biasing is very critical, up to the point that I even made sure that the cancel pot was right, not by ear or sight but with a scope. It does matter, at least too me it did. The same goed for biasing the compander at half powersupply ( thank you Scruffie) . That makes a big differences. Did you try to change R 15 too as that might temper a too hot signal.
In my case I found out that it did matter a lot at what voltage I was running the build. Lower then 14.8 for the bbds was just not as clean as I wanted. My problem was with the roadrage that I could not get to deliver 15 volt to the Aquaboy. It would always drop too much. I worked with a dc-dc converter that keeps the voltage at what you choose and that worked way better with a cleaner signal. Problem with that was that I got clock heterodyning with my delay and the Delaytion tap tempo module that I combined it with. The roadrage did not have that problem. In the end I found the regulator for the roadrage that did keep the voltage to 14.8 minimum. Maybe it had to do with the parts I can get here. I have had that problem with other builds in combination with the roadrage before. I think you can find my posts about that. I did not work with mn3008 but maybe this info helps.
It is worth the effort so keep working at it.
Succes, Marc

[MAO]

Thanks Mark,
I did refow solder around BBD1, but not the entire build. Will do that today.

I'm using a Les Paul with Tone Zone humbucker, I did notice early on if I set the bias pots in the middle of their passing delay range and picked lightly the distorting  wasn't noticeable, so a hot signal may be the culprit. I'll increase R15 too today.

Unfortunately I don't have access to a scope.


I'm sure I read your previous post, but will reread to be sure I didn't miss anything.

[MAO]

R15 or R55 to tame hot signal?

[teknoman2]

What's your value of R55?
You should jumper or R55 and R27.
R15 purpose is only for filtering.

[gitaar0]

I'm using a Les Paul with Tone Zone humbucker

That is a very hot pickup afaik 
Maybe work with a less powerfull pickup first to see if you get your aquaboy right.