Replacing electrolytics in old effects.

[GREEN FUZ]

I recently purchased this thing off ebay.
The legending describes it as a Programmable Filter. In brackets it has, Synth Driver



It was made sometime around the late seventies early eighties and is some sort of Autowah/Variable filter along the lines of a Mutron, I guess.
It`s a particularly rare model from an obscure British company which didn`t seem to last very long and which there is very little information to be found. It`s part of an interesting Modular system that, along with attempts by other companies, never quite caught on.
It was described as not working but is in fact making recognisable quacking/sweeping sounds. The design seems fairly simple and I hope to reverse engineer it in time.

The issue I have with it is that the filter sweeps are very noisy and there is a constantly evident wind-like noise in the background. My question is, is it likely that replacing all the electrolytic capacitors will help get rid of the noise? I have read that many repairmen advocate replacing them, as a matter of course, in effects over 10 years old.

[Papa_lazerous]

Windy noise yup that'll be yer caps

[DavidRavenMoon]

Sounds like noisy op amps to me.

[Papa_lazerous]

Naaaaaaaaa not opamps, opamps arent known for aging and becoming bloody noisy and whooshy, sure you get noisy ones but they are niosy because of their design and it may be you can improve on them in this effect by purring in better ones, But electrolytics are known to drift and go bad after 10 years or so.  Its a classic cap noise, have heard it first hand when messing with a few old pedals

[R.G.]

Naaaaaaaaa not opamps, opamps arent known for aging and becoming bloody noisy and whooshy, sure you get noisy ones but they are niosy because of their design and it may be you can improve on them in this effect by purring in better ones, But electrolytics are known to drift and go bad after 10 years or so.  Its a classic cap noise, have heard it first hand when messing with a few old pedals

Actually, they do. Give a read to "When Good Opamps Go Bad" at GEO, in the "Circuit Sweepings" folder.

Sounds like noisy op amps to me.

Could be either. Leaky caps AND opamps doomed by bad circuit design both do this after a while.

... there is a constantly evident wind-like noise in the background. My question is, is it likely that replacing all the electrolytic capacitors will help get rid of the noise? I have read that many repairmen advocate replacing them, as a matter of course, in effects over 10 years old.

It's a first step in any old pedal.
(1) go to GEO, http://www.geofex.com
(2) upper left hand corner, "Guitar Effects Debug"; click on the link
(3) item 4, "Resuscitating the Elderly Stompbox"
(4) read and enjoy, especially item 5. I can't prove this, of course, but it is likely that most of the repairmen that advocate replacing them as a matter of course read that here, as this has been up on the net for many years and although it was common to do this as a "cap job" on tube amps before that, I never heard a repair tech say it until after I put this up.

Electro caps may live a long time, but they have a definite design life, and that life is SHORTENED by sitting un-polarized, no voltage on them. Shelf life of electros may be as short as five years. Think of electros as a funny kind of battery that you have to keep charged all the time just for the side effects.

[GREEN FUZ]

(4) read and enjoy, especially item 5. I can't prove this, of course, but it is likely that most of the repairmen that advocate replacing them as a matter of course read that here, as this has been up on the net for many years and although it was common to do this as a "cap job" on tube amps before that, I never heard a repair tech say it until after I put this up.

Thanks R.G, I`d already read that article. Probably where I got the idea to replace the caps in the first place. In any case, after replacing the electrolytics (all two of them) the wind is still a-howlin` in my pedal. I guess that leaves the possibility of dodgy IC`s or perhaps more likely your other pointer about poor design.
Any suggestions on how to proceed?

[drewl]

Could be both
replace the damn caps first

[GREEN FUZ]

As I mentioned, I`ve already replaced the Electros without any discernible difference. Any other suggestions welcome.

Although I could replace the op-amps I was wondering if there was a way to test them in situ.

[DavidRavenMoon]

What kind of op amps are they?  Some old pedals used things like 741's, and they are pretty damn noisy.

I had a Phase 90 once that had an op amp go bad.  I couldn't find which one it was, so I pulled all of them and replaced them with sockets.   

While I was at it, I replaced the 741's with quieter op amps.

[R.G.]

In any case, after replacing the electrolytics (all two of them) the wind is still a-howlin` in my pedal.

That's mildly amazing. I'd think there were maybe a dozen electros in something like that; but hey, could be.

I guess that leaves the possibility of dodgy IC`s or perhaps more likely your other pointer about poor design. Any suggestions on how to proceed?

Yep. Now it's time to whip in new opamps, possibly new transistors. And we get into the issue of what opamps they used. Hope for singles or better yet, duals. Almost all singles and all 8 pin duals have the same pinout. Some of the early stuff has different pinouts and quads were a mess. What's on the board?

Might as well list the transistors too.

[GREEN FUZ]

Yep. Now it's time to whip in new opamps...

OUCH! Last thing I wanted to hear.

There are quite a few of them. All very common and readily available from what I can tell, bar the CA3080`s possibly.


CA3080E X 2
TL074CN X 2
TL072CP X 1
CD4016E X 1

Transistors

BC149 X 3

[R.G.]

That's not too bad.

The CA3080's have a reputation for being noisy, but I'd start with some cheap stuff.

Replace the transistors and the TL07X stuff first.

The thing is a state variable filter, done with the two 3080 OTAs. The TL907x form a safe environment for the 3080's to work. The transistors are likely to feed temp-compensated currents to the OTA current inputs.

On the opamps, (1) note the orientation of the chips as they sit there (2) cut off the legs of the chips right at the body (3) stick the hot end of a soldering iron in the body-side crook of the legs left over and (4) lift the leg out when the heat flows the solder in the hole. Use braid or a thin toothpick to open the hole. Then it's your option, sockets or new parts in the board.

Look for board contamination, dust, dried liquids, etc.

[DavidRavenMoon]

The CA3080's have a reputation for being noisy...

To say the least!

[Paul Perry (Frostwave)]

Before doing all this work, maybe build an audio probe (that is, a 0.1uF cap going to an amp!) and sniff around to see if it is possible to find where the 'windy' noise starts up.
Try tapping components as well. Worth doing a little thinking before yanking chips.

[ayayay!]

The CA3080's have a reputation for being noisy, but I'd start with some cheap stuff.

They do?  Why are they popular in the Dyna Comp then?  What would be a good substitute for it?  (In this pedal or the DC?)

Trying not to hijack the thread...

[StephenGiles]

Before doing all this work, maybe build an audio probe (that is, a 0.1uF cap going to an amp!) and sniff around to see if it is possible to find where the 'windy' noise starts up.
Try tapping components as well. Worth doing a little thinking before yanking chips.

Eminently sensible suggestion. I can't get to grips with the recapping and replace all opamps with the most expensive you can find, because at 9v it will make little difference I'd wager.

[GREEN FUZ]

Before doing all this work, maybe build an audio probe...

That`s been on my things to do list for too long. Now that the faulty pedals are beginning to pile up, it`s probably a good time to make one.

... I can't get to grips with the recapping and replace all opamps with the most expensive you can find, because at 9v it will make little difference I'd wager.

I forgot to mention, it`s actually running at 18v. It`s got a seperate mains power supply that it can be plugged into.