Motorboating? (with change of op-amp?)

[BAARON]

I have a Son of Screamer style pedal (with no pulldown resistor before the input cap because I wire my switches properly and don't think I need it) which has never given me issues before.  Yesterday I decided to swap out the op-amp to see if there was a difference.  I pulled my 4558 out of the socket and replaced it with an LM1458.  "The tone is nicer," I thought, and then I noticed that it was motorboating (or at least I Assume it's motorboating) when I wasn't playing, an obnoxious "put-put-put-put-put-put-kCHHHHHHH-put-put-put-put-put-put-kCHHHHHHH" that wasn't there with the 4558.  I'd say it's a frequency of 5 or 6 Hz, maybe.  When I play with the volume control on my guitar, it changes the character of the motorboating... not the speed, just the ugliness of the put-puts.  (It doesn't get quieter, it just gets different.)  Then it disappears abruptly with the guitar volume at zero.

Things that make the motorboating disappear:
- It's not audible when I'm playing, but it might still be there.
- Putting a buffer in front of the pedal (like a SHO set to unity gain).
- Turning the volume control to zero on my guitar.  Not one or two... just zero.

The 4558 didn't motorboat, but the LM1458 does.  What gives?  Why would one chip be happy while the other isn't?  Is the 1458 defective?  (It certainly sounds just fine when I'm playing...)

What's especially odd is that I also have a Zendrive-style pedal with essentially the same input section, PS filtering, voltage divider, etc., currently using a JRC1458.  It does not motorboat.

I'm using a OneSpot adaptor, and it does this whether it's daisy chained with other pedals or not.  The fact that only my LM1458 is doing this makes me suspect the chip.



...That said, I've noticed similar a put-put-put-put-put-put-kCHHHHHHH-put-put-put-put-put-put-kCHHHHHHH in other builds before too, like a NPN silicon Fuzz Face I had on the breadboard.  It basically went away once I put in some tiny caps between the base and the collector on the transistors.  So is it a bad OneSpot and the LM1458 is just fussier about it than my 4558 was?

[ninjaaron]

NSFW

http://photofreak.org/out.php/i1646_motorboat.gif

Hope I'm not violating the terms of service.

[BAARON]

Does anybody have an actual Useful response that doesn't involve cleavage?  Believe it or not, boobies will not fix low speed oscillation in a pedal.

[ninjaaron]

ehm... I'm no pro... but try putting some largish electrolytic bypass caps from (a) the V+ in pin of the opamp to the ground pin.

No guarantees. This is just what my heart tells me... then again, my heart also told me to post the boobies, so who knows?

You could also try putting an RC low pass filter to ground at your output.

[BAARON]

A large cap going from + to -?  Already have that.

A low-pass filter at the output?  It's a low frequency that's oscillating, so I can't imagine that letting it pass will do much good.

Any advice from the pros, since ninjaaron says he isn't one?

[Vitrolin]

maybe try another 1458?

[ninjaaron]

A low-pass filter at the output?  It's a low frequency that's oscillating, so I can't imagine that letting it pass will do much good.

High pass... that's what I meant. I often mix my words up when I'm thinking about T&A. If it's a low freq that's causing the trouble, I guess bandpassing it ought to do the trick

On the other hand, Vitrolin seems to have a capitol idea. You may well have the bad-device blues.


(In other news, I'm noticing a proliferation of 'Aaron/Aron' related monikers on this board... what ever can it mean?)

[BAARON]

(In other news, I'm noticing a proliferation of 'Aaron/Aron' related monikers on this board... what ever can it mean?)

It means that the Irish Force is strong with this one... message board... or at least in the names of its members.


I know.  I need to try another LM1458 (I'm pretty sure I have one), but I'm not convinced that's the entire problem because I've occasionally run into the same problem with other pedals before.

[WLS]

Changing the op-amp would be a good place to start.


Bill

[Thomeeque]

...That said, I've noticed similar a put-put-put-put-put-put-kCHHHHHHH-put-put-put-put-put-put-kCHHHHHHH in other builds before too, like a NPN silicon Fuzz Face I had on the breadboard.  It basically went away once I put in some tiny caps between the base and the collector on the transistors.  So is it a bad OneSpot and the LM1458 is just fussier about it than my 4558 was?

To me it sounds like some electro-magnetic noise at your place, which inducts into your signal in some cases (some "lucky" combinations of everything with everything starting at your guitar and ending somewhere in the stompbox or even further).

Term "Motorboating" is usually used when "on-board" LFO ticks get into the signal..

T.

[BAARON]

Term "Motorboating" is usually used when "on-board" LFO ticks get into the signal..

R.G. would disagree with that definition.
http://www.diystompboxes.com/smfforum/index.php?topic=37802.msg266164#msg266164

So would Wikipedia.
http://en.wikipedia.org/wiki/Motorboating


P.S. Thank you, Aron, for editing that post.

[Thomeeque]

 Oh, good to know! Thanks!

[BAARON]

No problem, T!  Always happy to spread a little help around, even if it makes me seem like a dink sometimes.

[petemoore]

  Whats the rest of the circuit [power supply] ?
  A fresh battery, = true DC = a quick, excellent comparator to other power supplies can be better scrutinized.

[BAARON]

The rest of the circuit is a Son of Screamer with a few value changes.

The power supply is a OneSpot supply.  Having read some of R.G.'s comments at another forum about the OneSpot, I think we can assume it's fairly stable.

Trying it with a battery might have been a good idea, but I rarely build my own effects with battery clips because it gives me more room in the box and I prefer adapters anyway.  (I am, shall we say, thrifty.)


In the end I tried a fresh LM1458 and it didn't tick any more, so I guess the question now is "why would one op-amp tick and another not?  Why would a fuzz face tick without a smidge of local negative feedback on the second transistor?"  Etc.

Anyway, I'll just ditch the old 1458 because I know it's no good now.

[Vitrolin]

conclusion: to solve problems start with the simplest solution, no sound change cable, wierd opamp noise change opamp etc.

[AFF]

Can you build a BASS pedal using that chip? You said you were thrifty so why throw it away. At those low freq it probably wouldn't even be noticed by a bass player.

I don't really have any tech advice about it though as you probably already know ( you had to school me on LEDs from my post)
But I can sure tell you to save the op-amp and build a bass pedal and then there is recycling solution to all the low freq put-putting op-amps out there. Who knows it could be the next big thing. Dumb people like ME would buy it ... if I played a bass that is.

Glad you got it solved.

By the way seriously how much did you pay for that op-amp and/or the original op-amp?

[Vitrolin]

you could check it to see if both opamps are gone  choppin' if not you could use it as a single op amp, or just buy a new one they aren't super expensive.

[BAARON]

An LM1458 is 60¢ from www.SmallBearElec.com... I just don't like wasting parts.

The op-amp still works, but it putts and ticks and it pisses me off.  I'm not sure how to deal with it, so I'll probably just ditch it.