Crapped out ross flanger... what are the symptoms of a bad sad chip?

[Stompin Tom]

This is what's happening with my unit: I get all the right flanging sounds, etc, but the effect is extremely quiet (its fine when bypassed). There's also a fairly loud hum... the hum makes me think it might be the power supply (which is on-board like the mxr flanger... in fact it's basically the mxr flanger. You can find the factory schemo here: http://www.shredaholic.com/mxrflanger.html). I know if I was getting sounds like this out of a tube amp I'd change the filter caps, but I'm not sure this applies to stompboxes. In any case, I haven't had a chance to thoroughly go through the unit, yet, but I was hoping someone with more experience could tell me what the symptoms of a bad sad 1024 are (I couldn't find this in the archives). I'm just hoping to ease my mind a little before I have time to sit with the thing and fiddle some more.

[lvs]

Hello Tom, my sole experience with a bad BBD was with a SAD512 in a DOD chorus. The pedal had stopped working and I hoped the defunct part was the LFO but unfortunately, it was the hard to find BBD (but I found one). The symptoms were not at all like you describe : with chorus engaged, the pedal worked but did nothing as if it were in bypass, without any hum or volume loss. Maybe that helps you a little.

[heyniceguy]

In my experience, a bad BBD often resulted in zero delay/flange/chorus. So effect mode sounded just like bypass mode.

What you are describing sounds like U4 has a problem. like the op amp chip is bad and mucking up the signal gain.

if you really wanted to check that BBD, easy way is to do this:
check pin 2 and 15. there should be a clean signal at both.
check pins 11/12 and 5/6. there should be a delayed signal at both.

if you get no delayed signal, then move onto:
check pins 3/14 and 8/10. there should be complementary clock signals there.

if clock signal exists, it's likely your BBD is bad (granted you have elimated bad solder joints, power supply problems, and all the other "standard" fare).

[StephenGiles]

"if you get no delayed signal, then move onto:
check pins 3/14 and 8/10. there should be complementary clock signals there."

...of the same voltage.

[Stompin Tom]

Wow. Thanks everyone. Very helpful. Now I have some ideas to go with when I have a chance to check the pedal more closely.

Quick question for nice guy. Why would you think it's U4 and not U1 or U2?

[oldschoolanalog]

This is what's happening with my unit: I get all the right flanging sounds, etc, but the effect is extremely quiet

The BBD is probably OK. (Probably; not definately.)
Put in new power supply caps. This is always a good idea w/old fx.
Audio probe it. Start at the input and work your way thru the circuit. This should let you find the point that it "becomes quiet".
Just my 3 cents. Good luck, and keep us posted.

[Stompin Tom]

Yeah, as I said I haven't had a chance to sit down with it for very long. I'll probably have time tomorrow. At that point I'll go through all the debugging checks, like the audio probe, to try to figure out what's going on. I just had no ideal how to check the SAD1024 (and I was hoping it wasn't the problem). I think changing the power supply caps no matter what is a good suggestion... it's close to 30 year's old and, on top of that, I have no idea how much (or little) it's been used. I'll update when I have more information.

[heyniceguy]

the reason i suspect U4 is that you said you said you are getting "right" flanging sounds, only that it is very quiet. so that tells me you are getting a good signal to your delay ckt, a good delayed signal, and a good mix of the two. U4 looks like a gain recovery / mixing stage to combine the wet/dry signals and to bring the signal up to the proper volume. because the flanging sounds "right" then the mixing seems to be good. but the gain recovery seems to be mucked  up. if the power supply checks out OK, and you have hum on your line, in my experience, that can be attrtibuted to a bad active component (IC, FET, tranny, but most often an op-amp).

just rampant speculation on my part...

[Mark Hammer]

And quite reasonable speculation it is.

The BBD is one of those chips that if there is a weak link anywhere in it (and there are a lotta links), you will get no audible time delay of any sort, whether quiet or hummy.

Hum invariably finds its birthplace in the power supply.  Based on the schematic you linked to, you should probably consider replacing whatever is the equivalent of C24, C20 and C9.  T'wer I, I'd replace C24 with a 1000uf/35v unit.  Electrolytics are a mere fraction of the size and price they were when your pedal was made, and more filtering will not hurt.  So spring the 80 cents or whatever for a nice substantial cap that will make the power lines behave better.  I'm confident it will fit the space.

Is U4 necessarily the culprit?  Possibly, but not necessarily.  What I will say is that the choice in op-amps since the production date of that pedal has mushroomed.  Even if the pedal were working just fine, it should be possible to replace all U1-4 with a more recent and better choice so as to improve noise specs.  Shouldn't cost you more than a couple of dollars.  U5 can be left as is because it is not part of the audio path.  Half of U2 is also not part of the audio path, but I can't see any step up for the audio half of U2 detracting from the performance of the non-audio half of U2.  A TL072 is probably a decent choice.  You *can* get quieter, but in the absence of any companding in the pedal, I suspect anything better than a TL072 would be wasted effort.

THE BIG BUT.....  (Remember Pee-Wee's Big Adventure where he had a heart to heart talk with the waitress about "her big but"?)

The SAD1024 has essentially two 512-stage delays in it.  These can be used in parallel or in series.  Here they are used in series.  Audio goes in pin 2.  The two complementary outputs from the first 512 stages comes out pins 5 and 6 and gets DC filtered (via C6) and fed to the next 512 stages via pin 15.  This is why the bias voltage from R49 is fed to both pin 2 and 15 via separate 100k resistors (a DC bias voltage is always necessary at the input to a BBD).  The complementary outputs of the 2nd 512 stages arrives at pins 11 and 12.

You will see a trimpot labelled R48 on the output of the BBD.   As shown, the trimpot seems to adjust the level of the output from the BBD.  Trimpots can get bumped out of place or can oxidize over time, and this one may merely be presently mis-set or need some cleaning.   Now, even though this is a "factory schem", I've seen errors on factory schems before.  Typically, circuits using SAD-1024 chips will incorporate some means of balancing the final two outputs, such that clock noise is maximally cancelled out and optimal sound is obtained.  In this schematic, there is no means for precisely achieving clock cancellation.  Is it possible that R48 is shown wrong and it is really wired up differently (as a balance pot between pins 11 and 12)?  Yes.  If the schematic accurately depicts the circuit in your pedal, then the faint flange thing may really BE a question of simply turning the BBD output level up to where it is supposed to be.  If the schematic is in error and the trimpot is really a balance control, then you will hear no great change in the level of flange when adjusting it, but primarily a change in the quality of the audio you do hear.  Either way, I think the question you really want an answer to at this moment is "Will I damage anything by adjusting the trimpot?".  Happily, the answer is "No".  Worst case scenario is you end up with a temporary reduction in sonic quality and have to keep tweaking until you recapture original sonic quality.

Since a trimpot adjustment poses the least overall risk to the pedal, I would suggest starting there.  Save any chip or cap changes until you have safely ruled out trimpot drift as the source.  It may well be the case that you get the level back to where it should be but the hum still persists.  THEN you replace the power supply caps.  While swapping op-amps may well be a desirable path to pursue, leave it to the very end of your trouble-shooting since their removal and replacement poses the greatest threat to the board (and likely the greatest test of your skills).  I would highly recommend desoldering braid with a smidgen of liquid flux wiped on it if you need to remove anything. I would also highly recommend installing decent DIP sockets on the board, THEN plugging in the op-amps.

[oldschoolanalog]

Just realized. I have an old  Ross flanger ( Red; 4 knobs; AC cord; specs on back plate.) Works perfectly. Totally forgot there for a while  .
If your initial "going over" doesn't work out; post voltages. I'll be glad to compare/help out.

[Stompin Tom]

Again, thanks everyone. I understand the logic behind that IC now, nice guy. Makes perfect sense.

And Mark, as usual, you've very patiently and clearly laid everything out... a great help. I'll start with the trim pot.

If I can't figure it out I'll take you up on the offer to compare voltages, old school... that'll be a great resource if I need it!

[Stompin Tom]

So... I finally had time to sit down with an audio probe and dmm. I checked the signal path through all of the op amps... everything sounded fine. So I started checking from the output backwards... turns out what is the equivalent to c19 in the schematic (the electrolytic near the output) was the culprit. I changed it and the other electros and so far it sounds great! I'm psyched! Thanks again!! FYI the mxr and the ross are in fact a bit different. For starters, all my opamps are rca4558p and, strangely, all the electros (except the big 470uf filter cap) are 10uf. I think they then adjusted other components around that change because all the components in the signal path from the last opamp out are slightly different. I also changed the big filter cap from 470 to 1000uf per Mark's suggestion.

My next step might be to make it true bypass, but I'm going to wait to see if the tone suck bothers me enough to bother... I had an old mxr chorus for awhile and it's switching never bothered me.

[Mark Hammer]

Glad to hear its working again.

Just to satisfy my own curiosity, does the trimpot I mentioned adjust delay level or adjust BBD balance?

[Stompin Tom]

You know, Mark, I'm not sure what it does... I guess it mixes in the delay signal because the effects gets somewhat more intense(?) when I turn it up, and I don't hear any clock noise no matter where it's set.

By the way, it sounds great with my big muff in front... at times it's totally whacked out and futuristic sounding, in an 80's sort of way.

[Stompin Tom]

Ok, an update and another question...

I've been using this at practice/gigs since I changed the caps and I'm still very happy with the sounds I get. It does a pretty good phase type tone at medium speeds and a nice (and a little gross.. in a good way) leslie-ish warble on fast speeds. I actually like it better than chorus for this. And, of course, it does that jet airplane thing at the other extreme. Not through zero, but nice.

In any case... I have a hum problem. It's not terrible, but somewhat irritating and probably louder than I'd want to record with. For a while I thought it was this cheap adapter I use with my delay, but its actually the flanger. I assume this is a filtering problem in the on-board power supply. Per Mark's previous suggestion, I changed and upgraded the filter cap already. I've also changed all the other electros. Any suggestions for reducing the hum? I'd rather not pull out the power supply and use a wart.

[Snaxster]

Ok, an update and another question...

In any case... I have a hum problem. It's not terrible, but somewhat irritating and probably louder than I'd want to record with. For a while I thought it was this cheap adapter I use with my delay, but its actually the flanger. I assume this is a filtering problem in the on-board power supply. Per Mark's previous suggestion, I changed and upgraded the filter cap already. I've also changed all the other electros. Any suggestions for reducing the hum? I'd rather not pull out the power supply and use a wart.

Hello, Tom. It's been years since your post, but just in case you haven't see the "Vintage Ross Flanger Noise Mod": http://www.thegearpage.net/board/showthread.php?t=663820.   

Best,

Snaxster