Need Help With An ADA Flanger

[Paul Marossy]

So... I got this guy's flanger the other day to do this "Paul Gilber mod" on and it's DOA. I plugged the guitar in and I get no sound at all when the effect is supposed to be on.

Here's a little dialogue I have had so far with the pedal owner:

PJM: I got it this afternoon, but there are some complications - I tested it out and it is not functioning. It works in bypass mode, but I get nothing when I try to switch in the flanger. Did you verify that it was actually working before you shipped it?

It looks like it hasn't been plugged in for a very long time, I had to clean all of the corrosion off of the power cord plug and the jacks before I even plugged it in to test it. It also looks like someone has been inside this pedal before, too, and did some kind of mod to it. I'm currently trying to figure out what might be preventing it from working.

DB: it was working when i had it.  you had to tap the front..... i think it was an issue with a connection or something.  let me know if you can come up with anything otherwise i will just take it back to the guy i got it from. 

PJM: Tap the front? That's really odd. That would seem to indicate a loose connection somewhere, but I didn't see anything that looked like it was loose. I'll look at it again once more tonight.

DB: that what i had to do when i bought it from the guy at this shop.  he opened it up and said he fixed it and it worked fine.  i really hope we can get this to work.

PJM: Huh, maybe something get tweaked during shipping. I'll look at it and see if I can figure out what's up with it.

DB: how is it looking?

PJM: I spent an hour on it last night, still no luck making it work. Tonight I will measure voltages and see if everything is getting power.


So... I've tested the footswitch, the jacks, cleaned the pots looked for any bad solder joints, broken wires, fixed someone's botched attempt at replacing the harmonics switch, still get nothing. I can get a very faint signal thru it in effect mode, so I think it might be possibly a bad IC chip. If it were an IC chip, what do you think would be the most likely candidate?

Any ideas on what might be the problem here, and what I should look at first? I'd really like to get this thing working as DB wants to use this in the studio on the next album to be released soon. Any help would be much appreciated!!

[Johan]

moosapotamus has the schematic...
here is a link.. http://moosapotamus.net/IDEAS/ADAflanger/ADAflangerSCH.gif
hope this helps
j

[Gripp]

Checked the bias trimmer for the BBD?

[moosapotamus]

Yeah, tried recalibrating? Calibration and bench test procedure is here...
http://moosapotamus.net/IDEAS/ADAflanger/ADAflanger.html
Or, maybe one of the trim pots is just gone bad.

Can you hear any sweeping in the faint signal that you can get out of it?
If so, that would be a really good sign. Maybe check opamp outputs with an audio probe?

Could be a real bummer if you can't get any sweeping (blown out BBD chip). What BBD is in there? Or, not too bad if it's only a bad opamp in the LFO.

Do you know what version you have? The link to the schematic that Johan posted may or may not match the pedal you have. There were apparently a number of different versions, some with SAD1024, some with MN3010. One of the schemes in this *.zip file might be a better match to what you have...
ADA Flanger Archive.zip

~ Charlie

[Paul Marossy]

Yeah, tried recalibrating? Calibration and bench test procedure is here...
http://moosapotamus.net/IDEAS/ADAflanger/ADAflanger.html
Or, maybe one of the trim pots is just gone bad.

No, I did see your page, but I haven't got that far yet. I did fiddle with all the trimpots, but to no avail. They all seem to have some effect as well, especially the BBD clock trimpot.

Can you hear any sweeping in the faint signal that you can get out of it?
If so, that would be a really good sign. Maybe check opamp outputs with an audio probe?

I seem to hear some kind of "swooshing" sound, I think. It's a pleasant kind of chorusing, I guess. All the knobs have some effect on the sound.

Could be a real bummer if you can't get any sweeping (blown out BBD chip). What BBD is in there? Or, not too bad if it's only a bad opamp in the LFO.

Do you know what version you have? The link to the schematic that Johan posted may or may not match the pedal you have. There were apparently a number of different versions, some with SAD1024, some with MN3010. One of the schemes in this *.zip file might be a better match to what you have...

I'm not sure if it's Rev 3 or Rev 4, but it does have the MN3010 chip on it.

EDIT: It's a Rev 3, as the serial number on the unit is before the number stated on the Rev 4 schematic at the lower RH corner.

[johngreene]

I seem to hear some kind of "swooshing" sound, I think. It's a pleasant kind of chorusing, I guess. All the knobs have some effect on the sound.

I would say that means that 90% of the pedal is working. You are hearing white noise going through the delay path. So the problem is most likely before that. Either the foot switch (input side) or input buffer. You can usually just poke with your finger along the signal path (use a pair of tweezers for pinpoint accuracy) and by the hum you couple in, find where the signal path is broken.  Start from the input to the BBD and work backwards toward the input.

--john

[Ry]

You've probably already thought of this, but you could try an audio probe to see where the signal gets lost.  I know there's a lot more to this pedal than just the signal path...

[Paul Marossy]

An audio probe might be helpful. But it is also a pretty complicated circuit.

Since all the chips are in sockets, I could almost just replace them all. If I can get an MN3010, that is.

[johngreene]

An audio probe might be helpful. But it is also a pretty complicated circuit.

Since all the chips are in sockets, I could almost just replace them all. If I can get an MN3010, that is.

I use my finger as an 'inverse' audio probe. In other words it injects signal rather than monitors it. You just have to work from the output toward the input and use the amplifier to monitor your progress. I think this problem is going to be a pretty simple even though the pedal itself is complicated because you can hear the 'swishing' means the LFO is working, the clock is working, and the MN3010 is more than likely working. If you touch the input to the BBD and hear AC hum 'whooshing', you know everything from that point to the output is working. So just move towards the input from there. Touch the inputs of things and when you finally hit something that doesn't result in hum, you found the problem area.

--john

[Paul Marossy]

Well, I think I hear a swishing sound. It's so faint, but it sounds like a gentle chorus type sound.

I did verify that the circuit is getting power, I measured 15.33 VDC, and the schematic says 15 VDC.

[moosapotamus]

Since all the chips are in sockets, I could almost just replace them all. If I can get an MN3010, that is.

Since you can hear some faint swooshing, I would not touch the MN3010. But, maybe seeing what happens if you just replace some of the opamps might be worth trying. I would start with the input buffers. IIRC, anything that's pinout compatable with TL07x should work.

~ Charlie

[Johan]

how about just pulling and reseting all IC's one by one?...solved a lot of odd problems I had on a  EH Memoryman I once owned...could explain why it worked taping on it at one time...
j

[StephenGiles]

Some feint swooshing would seem to indicate that the LFO, clock and BBD could be OK. I agree with Charlie, you should trace the audio signal to the BBD input. You could also try injecting a signal after the BBD to see if it passes through the output and regeneration sections. Then there is the possibility of a dry joint of course.

[Paul Marossy]

But, maybe seeing what happens if you just replace some of the opamps might be worth trying. I would start with the input buffers. IIRC, anything that's pinout compatable with TL07x should work.

I have some TL084s sitting around that I could try using for testing. I have had a hunch from the start that it possibly has something to do with the input buffer(s), but I have been sick all weekend, so I haven't had a chance to get to it.

EDIT: There's two RC3403ADB IC chips on the board, which are "ground sensing quad opamps". Can I use a TL084 in place of those? If not, what can I use?

how about just pulling and reseting all IC's one by one?...solved a lot of odd problems I had on a  EH Memoryman I once owned...could explain why it worked taping on it at one time...

So, to do this, do you just pull them out one by one and then put them back in? I also had a thought to do this, but it didn't seem like it would yield any results...

Some feint swooshing would seem to indicate that the LFO, clock and BBD could be OK. I agree with Charlie, you should trace the audio signal to the BBD input. You could also try injecting a signal after the BBD to see if it passes through the output and regeneration sections. Then there is the possibility of a dry joint of course.

I looked on the PCB for any damage to the soldering, but I couldn't find anything that looked suspect. I did notice that the enhance pot had the nut missing and someone put a piece of foam in the inside to try and keep the PCB from flexing. I don't think the PCB was damaged for however long it was like this, but I will revisit this area - maybe there's a hairline crack on the PCB somewhere?

[Paul Marossy]

OK, I rounded up all of the data sheets for the IC chips. It appears that the RC3403 might have a higher slew rate than the TL084, but I think the TL084 ought to work for testing purposes...

[Paul Marossy]

Well, good news - I replaced all of the dual opamps and the single opamp and the pedals works now. It sounds great as a chorus pedal, but the flange doesn't seem as pronounced as I am accustomed to. How does it compare with the MXR flanger for example?

Now, I have two questions for anyone with more knowledge in this area than I:

1. Does a TL084 have a high enough slew rate to be a suitable replacement for the RC3403?
2. Are there some sound samples somewhere that I can compare this one with?

And to confirm some of my earlier questions in a different post, messing with T2 does get you that strange detuned spaceship sound. Pretty fun pedal all in all! 

[oldschoolanalog]

I have 4 vintage MXR's and a reissue. I also have a reissue (3010 based) A/DA as well as 3 I have built. I've always had a spot in my heart for the MXR's. I purchased my first one in 1979 and it still works great and is lots of fun. However... they don't come close to the A/DA in terms of sonic flexability and "extremeness".

TL084's should be just fine. Some folks reported using LM324's (Now that's a low slew rate op-amp!) in their A/DA/Moosapotamus builds with no issues.

Sound samples:
http://www.modezero.com/ada-flanger.htm

All the Best!
Dave/osa

[Paul Marossy]

Thanks Dave. Mine doesn't flange quite as well as those sound clips,  I need to tweak it just a little bit more.

Thanks for the info on the TL084s, I concluded last night that they sound good to my ears, so I am going to leave them in there.

EDIT: On those sound samples, was the fuzz before or after the flanger?

[slacker]

Glad you got it working. For my Moosapotamus clone I used TL074s and a TL072 and it works fine so I'd think you should be fine with TL084s.

Charlie gives some excellent tuning advice in this post from the monster ADA Flanger thread. http://www.diystompboxes.com/smfforum/index.php?topic=49929.msg434438#msg434438 might be worth going through that to make sure you're getting the most out of it.

[Paul Marossy]

Thanks slacker, I'll check that out.