The LM308 OpAmp and the difference it makes in the ProCo Rat 2

[St_Genesius]

NOT A GOD DERNED THING.



That is all.


I've spent a little over a week now playing with my new (older-made) LM308-equipped Rat2 and comparing it to my old (newer-made) non-LM308 Rat2. While they sound different with identical settings, the overall flavor is very much the same and they can be very easily made to sound identical with a little knob tweaking on one or the other. Something in the neighborhood of 10 years separates their manufacture, and people seem to LOOOOVE the old ones and deride the newer ones, but I'm telling you: to my ears, they are absolutely interchangeable. I cannot find a sound on one that I can't match with the other.

I should add, perhaps, that both of these pedals are USA-made, so I don't know what differences might be heard in the newest, Chinese-made Rats.

 

[St_Genesius]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Woops, wrong room. Mods, could you move this to Amplifier Central?

 

[ErikH]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

In my MIC Rat 2, there's a difference in the sound, but only slight. It's not a drastic change.

 

[St_Genesius]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

At identical settings, I hear a little less agression out of the LM308 pedal: Thinner sound, lower volume, less distortion. By nudging the distortion knob just a bit (maybe 1 hour's worth) and the volume knob a bit more (between 2 and three hours) it sounds so much like my other Rat that when I switch between them without looking, I can't tell a difference, much less begin to guess which one I'm hearing. That's running straight out of the pedals into the preamps on my recording interface (playback through Event TR-8s).

BTW Erik, that DS-1 I bought off of you a couple of months ago has become the pedal I use to goose the Rat into fuzzier territory. I've got a couple of actual fuzzes on the board, but that DS-1 is seeing a lot more use for the noisy bits than they are.

 

[the guy who invented fire]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

I have to disagree...I think the LM308 makes all the difference in the world in a Rat. I love rat pedals and have owned a dozen or more over the past 10 or more years and the first time I plugged into a non LM 308 rat I knew something was wrong...I had to get home and read up before I knew there had been a change but I could tell by the tone that the new ones were off somehow....

 

[St_Genesius]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

My sample size in undoubtedly as small as it could be.

All I know is that these two pedals have more visual differences -- the housings are different shapes, the printed logos are different sizes, the LEDs are different -- than sonic. They both sound very much like a Rat.

 

[ratherdashing]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Op amp changes are subtle, and usually don't change the tone of the pedal per se. They do more for changing the dynamic response of the pedal. For example, with one op amp you might be able to clean up the sound by picking lightly, but a different op amp might distort regardless of pick attack. I've never heard an op amp swap that changed the fundamental tone of a pedal.

If you want to change the tone, swapping capacitors is the most effective thing. Changing the clipping diodes makes quite a difference as well. A lot of people like to put red LED's in their Rats for clipping instead of the stock diodes, but there are hundreds of possibilities there.

 

[ratherdashing]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

It's also important to point out that the LM308 is a really terrible op amp by today's standards (in terms of gain and noise floor), but it is a part of what makes the original Rat sound the way it does.

 

[the guy who invented fire]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Op amp changes are subtle, and usually don't change the tone of the pedal per se. They do more for changing the dynamic response of the pedal.

That statement is not relly a good stance to take...depeding on what the op amp is doing in the circiut it can have a HUGE effect or a very little one...

 

[ratherdashing]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

That statement is not relly a good stance to take...depeding on what the op amp is doing in the circiut it can have a HUGE effect or a very little one...

I'm not sure what you mean by "what the op amp is doing". I have never seen a pedal circuit where the op amp(s) is/are doing anything other than amplifying the signal.

 

[St_Genesius]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

After I posted my impressions of my two rats on another forum, someone posted this video. I post it here ONLY to add another voice to the conversation, not as an endorsement of their results or conclusions, necessarily. Like I said before -- the hyperbole of my first post notwithstanding -- I can really only speak to what I hear in these two pedals that, by all accounts, SHOULD sound different, but don't to me.

http://www.youtube.com/watch?v=bpTv2jAree8

 

[ErikH]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

In a circuit like the Rat, the op amp makes very little difference. The other components around it influence the sound a lot more. Heck, swapping out the diodes will have a greater impact as Matt stated.

St_Genesius, glad you're enjoying the DS-1.

 

[Vasshu the humanoid typhoon]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Well my Ibanez clone uses a TL071, and an array of germanium diodes, plus a redone filtering
Call it my little Gilmour tone.

 

[ratherdashing]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

In a circuit like the Rat, the op amp makes very little difference. The other components around it influence the sound a lot more. Heck, swapping out the diodes will have a greater impact as Matt stated.

St_Genesius, glad you're enjoying the DS-1.

Even the pots can have a greater affect on the tone than the op amp. This is something I've recently noticed. Pots vary somewhat in value. For my FTL Drive, I noticed a BIG difference in the way the tone control behaved simply by switching between a 25k pot and a 20k pot.

There is also a lot of variance within pots of the same value. I metered a 500k Alpha pot recently that read 590k, and another that read 480k. That's a big difference! Imagine two Tube Screamers with those pots for the Drive knob. The 590k one will distort quite a bit earlier than the 480k one.

This made me wonder if the differences people are supposedly hearing between two op amps are actually just pot value differences. It is WAY more likely that two pots are electrically and tonally different from each other than two op amps, especially if they're both built to the same specs (e.g. the JRC4558D vs. RC4558P debate in Tube Screamers).

 

[ratherdashing]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

After I posted my impressions of my two rats on another forum, someone posted this video. I post it here ONLY to add another voice to the conversation, not as an endorsement of their results or conclusions, necessarily. Like I said before -- the hyperbole of my first post notwithstanding -- I can really only speak to what I hear in these two pedals that, by all accounts, SHOULD sound different, but don't to me.

http://www.youtube.com/watch?v=bpTv2jAree8

I get the guy's point, but the demo doesn't seem to be designed to illustrate the things that replacing the op amp will actually change, namely the dynamic range, compression, and noise floor. I am not at all surprised that nobody heard a difference in tone. I wouldn't be able to either.

 

[cream123]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

I'm not sure what you mean by "what the op amp is doing". I have never seen a pedal circuit where the op amp(s) is/are doing anything other than amplifying the signal.

well it could be in a half rectifier or it could be in a non inverting or inverting amp, but yeah. Op-amps are also used as fundamental building blocks for A LOT of stuff. on the other hand, in guitar pedals its really just amplification

 

[cream123]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Well my Ibanez clone uses a TL071, and an array of germanium diodes, plus a redone filtering
Call it my little Gilmour tone.

I like the TL071, nice op amp. I also like stacked LM741s in some designs. very...lofi


btw, op amp stacking will change the sound. so, thats a difference. but different types won't change much

 

[Vasshu the humanoid typhoon]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Eh stacking op amps.....that can devour too much power if not being careful.
Mine has a socket, so I have tried a few different ones...LF251 also was quite nice in there.

 

[cream123]

Re: The LM308 OpAmp and the difference it makes in the ProCo Rat 2

Eh stacking op amps.....that can devour too much power if not being careful.
Mine has a socket, so I have tried a few different ones...LF251 also was quite nice in there.

true true, I usually only use two, if I stack at all.