Informant Drive tweaks

O

Orson Anton Welleson

New member
I finished the Informant drive over a week ago. It is nice enough, but it didn't grab me. Everything that made the Rat so enjoyable is missing from the ID.

I've heard people talk about trying other op-amps. I think that's my next move. I'm assuming the LM308 would work. The idea being to give the circuit some of the snarl and bite of its progenitor.

Any thoughts from anyone else underwhelmed by the ID?
 
Orson Anton Welleson said:
I'm assuming the LM308 would work.
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It won't - the informant has two TL072 dual op amps and a charge pump, the LM308 is a single op amp.

You could try a different dual op-amp but I suspect the difference won't be that big.

If you can identify what it is you don't like and would like more, then you could tweak other parts of the circuit. I wasn't a huge fan either (at least on a strat), I tried kludging in an extra low pass filter in the middle of the circuit (it was too bright on a strat, for my taste), but it didn't work very well. I probably should have put in something before the main circuit itself (although the buffer makes that annoying), since turning the tone control down worked fine for me, but I just sort of gave up on it. Maybe I'll revisit it at some point.
 
Hmm, okay. I thought one of those two TL072 was for the buffer. Back to the schematic then.

It's really simple. The Rat has more bite, more mids, which is a big part of that bite, and more harmonics. I'll revisit it one day down the line. Until then, it's to the box of disappointing or boring effect boxes. It's a box full of things that were disappointing, or are in need of repair.
 
Orson Anton Welleson said:
Hmm, okay. I thought one of those two TL072 was for the buffer. Back to the schematic then.
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Oh, do you mean you would replace one of the TL072 with an LM308 and also skipping the buffer? That would work op amp stage wise, but a.) not sure if the pinouts are compatible, b.) you need a compensation cap for an LM308 I believe, and c.) you would be changing the first stage of the pedal which is not the doing the heavy lifting, so I still don't think it would make a big difference in sound.

If you want more bite and more mids, switching out the op amp is not going to get you that.
 
That was the idea. I didn't expect anything in particular from changing the op amp, except possibly possibly imparting some Rat-like qualities, making it a bit less polite.

I'm guessing that since most of these LM308 are Chinese fakes, that explains what I've noticed, namely that different fake LM308s have different audio qualities from each other. This is in the same circuit, of course. Meaning that Rat clone "A" has a fake LM308 of a given source. I swap it out for another brand of fake LM308, in clone "A"and it sounds somewhat different from the original LM308 the pedal came with.

Someone will almost inevitably tell me this can't be so, but it was aurally conspicuous with two different Rat circuits I have here.
 
For Rat's the closest thing I hear to the LM308 is an OP07, which is more reliably sourced.
I also bought LM308's from Jameco that appear to be genuine.
 
maybe try pulling out the charge pump, running at 9v might be less headroom and more interesting?
I wasn't that impressed by this one either--it's like they neutered a rat.
 
gtfields13 said:
For Rat's the closest thing I hear to the LM308 is an OP07, which is more reliably sourced.
I also bought LM308's from Jameco that appear to be genuine.
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Ooh. How about an update when you try them out? Better yet, run Chuck's test drive:https://forum.pedalpcb.com/threads/pandoras-box-fizzle.25875/post-329869
Chuck D. Bones said:
LM308 test
Build this circuit on a breadboard:
LM308 pin 2 to pin 6.
pin 3 to gnd via 100K.
Pin 3 to +9V via 100K.
Pin 4 to GND.
Pin 7 thru a DMM set to measure μA to +9V.
Apply power and measure current into pin 7. Typical current draw is 300μA. I have measured as low at 250μA and as high as 360μA. Most other single opamps draw at least 1mA.
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I'm a 308 purist; it's a curse. And I've been too cautious (and broke) to find out for myself
 
Curious, I was only notified of one response here recently. Okay, never mind that.

gtfields13 said:
For Rat's the closest thing I hear to the LM308 is an OP07, which is more reliably sourced.
I also bought LM308's from Jameco that appear to be genuine.
Click to expand...
I've heard about the Jameco LM308s, and there seems to be some doubt and disagreement about their veracity (?)
I've been buying metal can 308s off of a couple of electronic parts supply houses on eBay. Not cheap, but not out of reach. The parts are from the US, and by all appearances and claims from the sellers, they are genuine metal can 308s. They certainly sound quite a bit different, if not better, than the various more modern LM308 opamps (8 pin DIP? Not sure how they are identified by form). I may take another look at the Jameco, although if more that 10.00 a piece, I'll stay with the metal can type.
spi said:
maybe try pulling out the charge pump, running at 9v might be less headroom and more interesting?
I wasn't that impressed by this one either--it's like they neutered a rat.
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I'll try that. Neutered is right. I'd love to know what that guy was thinking. He removed everything that was cool about the Rat. The Rat can be pretty smooth on its own, so if he was trying to smooth it out, then that seems misguided.
 
gtfields13 said:
For Rat's the closest thing I hear to the LM308 is an OP07, which is more reliably sourced.
I also bought LM308's from Jameco that appear to be genuine.
Click to expand...
I would have to agree, that the Jameco are legit. They aren't as big as Mouser and Digikey, but to lie about these op amps, claiming they are from National Semiconductor? That seems pretty foolish. Maybe I'm naive, but what is the advantage to lying about this. They aren't charging huge sums. In fact, they have one of their LM308 on sale currently for 3.98. Maybe it is because they are Chinese fakes (chakes? chinakes?)

I went ahead and bought a few for 3.98
 
IIRC, the jameco ones have 2-3 date codes that align with some from Chinese sellers.
The logo is maybe funky too.
I have some. Need to test the skew rate at some point...
 
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