Need Help With A New ADA Flanger Problem

[Paul Marossy]

Yeah, I guess that I might have to break out the audio probe. I did replace the input cap just for kicks... no results there, either.

Since the ICs are in sockets, it's real easy to start by replacing them and see what happens. Based on the suggestions I'm getting here, I think I will concentrate on the BBD section of the circuit. Maybe it's a bad cap or something.

[oskar]

Audioprobe and voltages are off course no.1, and a schematic!

But I think the problem is really early on. The loZ signal going through as it should indicates that something is pulling down (or up!!) the signal at an early stage (before any internal amplification). Basically you've got a short. A cap, a resistor... or like the first transistor buffer if there is such a thing in there. Are there diods protecting the input?

[Paul Marossy]

Audioprobe and voltages are off course no.1, and a schematic!

But I think the problem is really early on. The loZ signal going through as it should indicates that something is pulling down (or up!!) the signal at an early stage (before any internal amplification). Basically you've got a short. A cap, a resistor... or like the first transistor buffer if there is such a thing in there. Are there diods protecting the input?

Yeah, I have the same feeling about that, being early on. I have tried replacing every active component except for the MN3010, which appears to be working. So yeah, there may be a short or something like that because it works, but only with a very strong signal on the input. I did check the voltages on all of the IC chips, they are getting the right voltages.

I have suspicions about C7 as it was soldered onto the wrong side of the PCB, and some of the traces were pulled up, but not broken. I haven't checked for continuity with that cap and the diode array on IC-1B, but I will do that when I get a chance. Maybe something is up with that.

Here's the schematics for Rev 3 & Rev 4: http://www.diyguitarist.com/Schematics/ADA-Flanger/ADA-FlangerSchem.pdf
I have the Rev 4 version on my bench right now.

[Paul Marossy]

OK, I did some audio probing today. I haven't found the exact source of the problem yet, but here is what I have found so far, referring to the Rev 4 schematic here: http://www.diyguitarist.com/Schematics/ADA-Flanger/ADA-FlangerSchem.pdf

1 - Input signal at IC1A & IC1B is OK. Input cap C1 was replaced just for the heck of it with no results
2 - IC2B has a very weak effected signal at pins 12, 13 & 14
3 - I can hear about half the effect if I put a jumper across R9, but it also raises the gain to where you can hear a little distortion, too
4 - I replaced C7 and checked for continuity on the diode array on IC1B, found no problems there
5 - Pin 3 of the MN3010 is getting a good signal, and I can hear that it is "pulsing" at pins 8 & 9, so I think it is working fine. This also makes me think that IC4, IC5 and IC6 all doing their job, too.
6 - I replaced C2, C5, C15 & C27 with no results
7 - I tried replacing C17, no results there, either.
8 - I tried all new IC chips (except for MN3010), and get the same results. All have been verified to be getting power.
9 - I am getting what sounds like a somewhat normal effected signal at pin 8 of IC2C, which has Q1 between it and the output stage, IC2D
10 - Replaced C21 (output cap, 1uF tantalum) thinking that maybe it got fried somehow, no results with that either
11 - Bias voltage has been verified, appears to be no problem with that

So, this all leads me to believe that the problem is somewhere in the Enhance, Range or Threshold section. All of those controls are working, so I am not sure if the problem is there, either.

I am wondering if possibly Q1 (LS4393, NPN JFET) has some sort of problem. It appears to me that it is not even getting any power, so I don't know how it could go bad. What does it do anyway? Is it acting like a variable resistor in this circuit?

Anyone with ADA Flanger experience have any suggestions for what to look for? I am kind of really baffled now. 

[StephenGiles]

I never used the noise gate at Mike Irwin's suggestion, so why not disconnect it and see what happens.

[Paul Marossy]

I never used the noise gate at Mike Irwin's suggestion, so why not disconnect it and see what happens.

Disconnect what? The entire noise gate section?

BTW, I have no replaced every single electolytic cap on the PCB, still have the same problem. I don't know what else it could be since I have replaced all the electrolytic caps, all of the ICs, and the bypass switch. This is really kind of baffling. I wonder if a resistor drifted in value or something. I don't know how that could happen, but I'm at the point where I think I'm going to measure every single resistor and compare it to the color bands.

As far as I can tell, the MN3010 is also functional. This is just really weird. 

[carrejans]

I'm at the point where I think I'm going to measure every single resistor and compare it to the color bands.

Don't forget that you can't measure resistance inside a network.
You will have to take em out first. 

Good luck at finding the problem.

[oldschoolanalog]

Please take V readings from the 3010 and post. I'll open up my 3010 A/DA when I get home from work later and compare.
And... have you played around with any of the trimpots (yet)?
Stay  ,
Dave

[Paul Marossy]

Please take V readings from the 3010 and post. I'll open up my 3010 A/DA when I get home from work later and compare.
And... have you played around with any of the trimpots (yet)?
Stay  ,
Dave

OK, thanks, I will measure those voltages on the MN3010 and report back. I did mess with all of the trimpots, none of them have any affect on the situation...

[StephenGiles]

"Disconnect what? The entire noise gate section?"

Yes.

[Paul Marossy]

oldschoolanalog-

Here are the voltages on the MN3010 chip:

Pin 1 - 14.58V
Pin 2 - 7.49V
Pin 3 - 7.11V
Pin 4 - 1.00V
Pin 5 - 7.11V
Pin 6 - 7.49V
Pin 7 - 0V
Pin 8 - 7.44V
Pin 9 - 7.46V
Pin 10 - 7.49V
Pin 11- 0V
Pin 12 - 7.49V
Pin 13 - 7.37V
Pin 14 - 7.44V


StephenGiles-

I may do that as a last resort, but I'd rather not do that at this point since it's not even my pedal.

[oldschoolanalog]

Hey Paul,
Mercifully, I found my notes from the last time I opened up this beast (A real pain in the ass. Requires total disassembly.) One difference is pins 3 & 5 (the inputs); and pins 8, 9, 13, & 14 (the outputs) all measure ~1.4 V  higher than the ones you posted. Give or take a tenth or so. Inputs = 8.6V. Outputs = ~8.7V. All the other pins are within .1 V of the ones you posted. Since adjusting the bias trimpot had no affect on your effect I suspect (Holy crap! I'm rhyming! ) the FET in the gate. From what I can decipher, this is pretty much the only active component that hasn't been changed. If you have a J201, try it there. It's worth a shot at this point, IMHO. Let's face it. The unit is basically rebuilt at this point. What's one more component amongst friends? Try this before disconnecting the gate. Keep us posted.

Dave

[Paul Marossy]

Thanks for the info oldschoolanalog, I'll try messing with Q1.

Interesting that your voltages on the MN3010 measure higher than what I have in this one. I wonder if that is a contributing factor here?

[oldschoolanalog]

Interesting that your voltages on the MN3010 measure higher than what I have in this one. I wonder if that is a contributing factor here?

T1. Bias trim adjustment. That's why I asked about any trimpots being moved around. T1 will have to be set properly at some point.
Is there any chance you could post close up photos of both sides of the board now that the unit is disassembled? They might come in handy now or for future reference.
Thanks!

[Paul Marossy]

Interesting that your voltages on the MN3010 measure higher than what I have in this one. I wonder if that is a contributing factor here?

T1. Bias trim adjustment. That's why I asked about any trimpots being moved around. T1 will have to be set properly at some point.
Is there any chance you could post close up photos of both sides of the board now that the unit is disassembled? They might come in handy now or for future reference.
Thanks!

Well, it appears that Q1 was the culprit after all, after I tried everything else under the sun first.  But I did learn a lot more about this circuit and troubleshooting a complex circuit, so it's all good.

Anyhow, I put a transistor socket in there and tried some different FETs. The J201 seems to work the best out of the ones that I tried (some didn't work at all, or had the same result as the problem that I was initially trying to fix).  I also had to tweak a few of the trimpots to where it sounded best.

Unfortunately, I don't have any equipment that will take really good close up photos of the PCB for everyone... 

[oldschoolanalog]

Gotta' love the J201. Glad to here you got it up and running.
Dave

[Paul Marossy]

Yeah, it was a pain in the rear though! 

BTW, do you think that substituting the RC3403s (IC1 & IC2) with TL074s will make much of a difference to the sound of the circuit? The RC3403s are supposed to be these ground sensing high slew rate chips, don't know how important that is for the overall sound...

[Paul Marossy]

Disregard that last question. I compared data sheets and the TL074 outperforms the RC3403. The slew rate of the TL074 is 10 times the slew rate of the RC3403! But, I guess the RC3403 was a high performance IC chip in the late 70s...

[newperson]

Hi,
A few questions about this pedal.  I have one that passes clean signal but does not have an effect.  The clean signal gets a bit weaker when the switch is on.  I believe I have Version 4, MN3010 chip.  My first guess is that it seems that the internal transformer has gone bad.  I am looking at the link earlier in the thread to see the layout of the pedal.  The power transformer has 120VAC on side and 4.5V dc on the other side.  From what I can tell it should be 15VDC correct?  Not 15VAC right?  IC7 has 11.4V DC, 0 Volt DC, 10.1 Volt DC, and when measure with AC on the meter 24.3VAC, 0V, 21.5VAC.  I am taking my ground reading from pad A which is connected to the black ground wire from the jacks.  Should this part be putting out 15VDC?  Step on in the calibration test procedure says IC7 Pin 3 +15V.  My IC7 is marked 7812C LM340.12.  So does this make it a LM340 with 12v out?  Is it the wrong part and should be LM340.15?  Or is the power transformer making it have the off reading?

Am I reading this right and need a new power transformer?  If so can someone point me to a part number for this transformer?  I am in the US and mouser or digikey would be a nice place to order from.  If need be I could order a wall wart and wire that.  In that case would I need 15VDC .5 to 1 amp?

I am a little confused on why the AC reads on my meter.  That is my second learning question from this.  Why does the AC read on this part?  Or why can one read AC?

Thanks for any help,
Paul.

[Paul Marossy]

The power supply is regulated with a power regulator IC chip. If you are getting DC voltage readings of 15VDC after that regulator, then your transformer sounds like it's fine.

I had one pedal on my bench that had similar symptoms, and it turned out that Q1 was bad. I replaced it and then the pedal worked again. The problem is finding an exact replacement for it is nearly impossible, however. The unit didn't work quite up to factory specs with a substitute FET in there, but it still worked.