lm339.... in a fuzz?

[pinkjimiphoton]

a friend gave me a sack of these a while ago, and being a total EEDIOT, i figured i'd ask.
i know its a 4 stage voltage comparator or something to that effect, but looking at the pinout thru
my fuzzmonger eyes, it looks like it could be used as 4 opamps.
think it could be used to make a fuzz? any caveats?
just trying to figure out a use for 'em
thanks guys!

[Aph]

I've never tried it. Always heard a comparator is too unstable as an amplifier.

[PRR]

http://www.ti.com/lit/pdf/snoa654

[DIY Bass]

Sure I have seen them used on LED VU meters?  Could make a cool little input/output meter on a pedal or amp.

[Mark Hammer]

If the Anderton Ultra-Fuzz can use a comparator made of a single op-amp, then surely the LM339 can be used to make a similar category of fuzz.  Of course, once you've passed the signal through a comparator to yield a square wave, there's nothing much you can do with the other three comparators, unless you've divided up the signal into discrete bands and square them up individually.

If a person had a hex pickup, an LM339 and a LM393 dual comparator would provide six strings worth of square waves for filtering.

[anotherjim]

Paul linked the application notes for a reason... the answers are within.
Find page 27, figure 30. Note that gain is R2/R1 just like an op-amp and frequency response is fast enough for guitar.
...also find oscillators, one-shot, flip-flop functions in there.

[Aph]

I've never tried it. Always heard a comparator is too unstable as an amplifier.

Dumass, go ahead and live a little:
Instant fuzz (taken from the app notes... thanks Paul).

[EBK]

Ok, now we need someone to design a fuzz using one of those LED bargraph driver chips. 

[pinkjimiphoton]

I've never tried it. Always heard a comparator is too unstable as an amplifier.

Dumass, go ahead and live a little:
Instant fuzz (taken from the app notes... thanks Paul).





hmmmm. mebbe i gotta play with this. why not use the other opamps as an input/output buffer, and maybe to drive a tone stack?

very interesting, thanks everyone!!

i'm gonna look hard at the doc paul posted (thanks bud!) and try and see if my dumb ass can figure something out.

i mean, they're used in eq's, so should be able to adapt them to use more than a single stage i'd imagine

[Aph]

Hey, pinkjimi, I hope you realize that dumb ass comment was directed at myself! 

[anotherjim]

Has that been tried? I've got a suspicion that the speed response is really slow. (15k & 470n = 22Hz).

[pinkjimiphoton]

Hey, pinkjimi, I hope you realize that dumb ass comment was directed at myself! 

hahahaha i guess we must wear the same size shoes bro, its all good no worries!!!

[Rob Strand]

Has that been tried? I've got a suspicion that the speed response is really slow. (15k & 470n = 22Hz).

Not only that  when it clips the output is going to be a saw-tooth as the o/p transistor will short out the cap quite easily in the negative direction but the cap can only charge slowly in the positive direction.

The whole problem about adding the cap is to make the device stable with a feedback loop around it.  And the reason it's a problem is is because a comparator has no compensation or any means for it.  Fig 28 (PRR's link) is the crudest way to achieve stability but it's not without its problems.

Another dodgy method is to add a divider on the input (inside the feedback loop, note fig 28 has a lot of division from the feedback network already).  That reduces the forward gain. Then a smaller cap might be possible.

All the issues are pretty much summarized in section 21.

There's other ways to stabilize amplifiers and the ideas are pretty much packed into Fig 30.     As soon as I saw fig 28 a circuit like fig 30 popped into my head and then magically appeared on the next page as I read through the text.   Fig 29 shows the significant improvements achieved with fig 30.   It might help to add a resistor from the emitter of Q1 to ground.  The DC biasing on Fig 30 might need some tweaking.  Also I'm pretty sure Fig 30 assumes the circuit driving the input is low impedance.  If not, it might go unstable.

You could spend a lot of time tinkering around with a circuit like that.   The number of parts it takes to fix it could be replaced by a transistor stage 

[Edit1: You can also do an inverting version like fig 30
Edit2:  Sometimes these ideas are used for real opamps:
    http://www.datasheetlib.com/datasheet/849337/an140_philips-semiconductors.html
]

[Aph]

Has that been tried? I've got a suspicion that the speed response is really slow. (15k & 470n = 22Hz).

I usually (usually...) don't post schematics unless I've tried them. This one is on the breadboard now. It actually doesn't sound too bad!
I'm not gonna box it up... and it is far from commercially ready (in my opinion). But, I've heard a lot of "boutique" noise-maker type boxes that don't sound any better than this. 

[Aph]

Ok, now we need someone to design a fuzz using one of those LED bargraph driver chips. 

Sounds like a challenge...

[Rob Strand]

Here's another contribution to the "IC's Abused as Opamps" scheme,

TL431 Regulator:   (about 1/3 down)
http://www.techlib.com/electronics/crystal.html#AudioAmp

Thermionix's LM10:
http://www.diystompboxes.com/smfforum/index.php?topic=119691.0

What else?
LM723 Regulator;  might not sound too bad.
The LM3900 is just asking for it.  There's a possible compressor out of that one.

[thermionix]

Thermionix's LM10:
http://www.diystompboxes.com/smfforum/index.php?topic=119691.0

I actually built that, well the board, not in a box yet.  I was able to use a scrap piece of perf that I had damaged with the Dremel.  I socketed the IC so I can swap to 741 etc.  Pins 1 and 8 are hardwired together for the LM10, but pin 8 is NC in most singles, so no problem.  All film caps except a 47u power filter, 1S1588s for clippers.  I'm thinking of calling it the C- because I think it's a little better than a D+.   



(yeah hot glue strain relief for the wires)

[anotherjim]

Has that been tried? I've got a suspicion that the speed response is really slow. (15k & 470n = 22Hz).

I usually (usually...) don't post schematics unless I've tried them. This one is on the breadboard now. It actually doesn't sound too bad!
I'm not gonna box it up... and it is far from commercially ready (in my opinion). But, I've heard a lot of "boutique" noise-maker type boxes that don't sound any better than this. 

Because the chip output can swing most of 0 - 9v (*), what is left on the 470n cap is probably still guitar level, at least over 2 octaves or so.
* it isn't an active swing to +9v. The comp chip outputs are simple NPN to ground (aka open-collector) and must have the pull-up resistor to Vcc.

[Kipper4]

Would using diodes in parallel with the 100k (nfb)make it musically fuzzy? If that's a thing?


Edit:
I've seen positive feedback used with comparators before but not nfb....

[Aph]

Here's a demo of the LM339 fuzz circuit:

https://soundcloud.com/nicenportly/lm339-fuzz-demo

Complete with unintelligible guitar playing by yours truly.
I may also upload a sample of the LM3914 fuzz... yeah, that's a threat.