Rat op-amp

[Shrtyska9]

I just picked up a Rat 2 from a high school friend. It has the op07cp chip and so far I like it alot but I was wondering if swapping that for the lm308n would really make it that much better.

Thanks in advance.

[mremic01]

I don't hear the slightest difference.

Most demos of the two chips are done with two separate Rat units. The units will already sound slightly different because of component tolerances, so that's not a valid way to compare the ICs. If you socket the IC, you still have to take time to stop playing to make the swap. You don't get to do it while playing and listen for any difference in tone.

I built a Rat Lab with several circuit variants on switches. The one I was most interested in was the op-amps. It's got two IC sockets that can be switched between with a 3PDT. Originally, I was using a 4PDT and having the two ICs share one leg of the same compensation cap, but that was causing issues. So I changed it so they each had their own cap. I can flip the switch with one hand while strumming with the other. Honestly, the tone cap makes more of a difference. The OP07 and LM308 sound identical.

People will throw in all kinds of sciencey stuff about slew rate and the comp cap. The OP07 doesn't even need the cap, as it's internally compensated. The LM308 will sound gross and sputter without it. But in my Lab, the LM308 sounds the same with the cap as the OP07 does with the cap as the OP07 does without the cap.

[Shrtyska9]

Awesome man! I probably would have found the answer had I not overlooked that the DIY stompbox thread you started a few years was more than one page. Thanks for the very informative response.

Richard

[mremic01]

Which thread was that? I was really into the Rat when I was first starting out, so there're probably a few were I was asking questions that I'd now consider kind of dumb.

As far as I know, no one has bothered to test these things on a switch. Most guys just use sockets, and then have to remember how the previous IC sounded. So they convince themselves that the things still sound different. I did too, before I tried it this way. Beavis Audio did the ScreamerLab, but stacked the ICs, which has several pin then in parallel. I wanted to avoid doing that. I plan on building my own ScreamerLab, but I'm going to use a 6 pole rotary switch, which I have on order from Mouser. Then we can see how different the 4558 chips are and whether or not fancy Burr Browns make any difference.

[Shrtyska9]

http://www.diystompboxes.com/smfforum/index.php?topic=91080.0;wap2

That's the thread. Comparing old and new rats.

This is my first rat and probably will be my only production one. It was one of those rare deals where it was vastly cheaper to buy instead of build. The slow loris is definitely on my to do list now that I know how much I like the sound of the rat.

The screamer lab sounds like a great idea man. Definitely interested in the results.

Richard

[culturejam]

I think different op amps sound different ... in a Rat. It's not that any one is better than another, but there are differences. LM301, for example, sounds to me to have a bit less gain at some mid and higher frequencies. It's a bit more mellow than a 308. I suspect that some of that has to do with the value of the compensation cap, but I haven't done extensive testing.

I just recall the first time I really did some testing between the op amps, I was very surprised that I could hear a difference that was definite.

What would be awesome would be a Rat PCB with two op amps and a trimmer cap. That would make testing a lot easier.

[GrindCustoms]

Pretty much anyone now a days, have access to an audio interface and recording programs.

The rest time of your ear when swapping components sure makes a difference... add to that that no matter how you try, you're a human and never playing the same riff in both pedals will have the same dynamic.

That's why i use a looper, record a riff and let it play in loop in the pedal, bypass pedal, change the IC or whatever the component you are testing.

If you want to have recordings of all that and hear the true difference between them, simply take the output of your pedal, run it in a DI or directly in the instrument input of your audio interface. What you want to hear is the difference between components so no need to mic and go through your amplifier, speaker and microphone that simply add a shitoad of color over what you're really trying to hear.

And if you don't have a looper........ re-amp a guitar track or anything that can get that job done, we're not in the 70's anymore... no need to have a lab big as a football field to have concrete results.

Just my 2db.

Rej

[Shrtyska9]

Cool thanks for the response CJ. Its good to know there are options out there when I decide to swap through some op-amps. I'll probably hold off for a while to see if the rat loses its charm. Plus I'm all out if dip8 sockets and I'm not sure if the sip strips I have will fit as they have been too large for any board I have tried them on.


Seeing as i dont have a looper the re-amping idea is awesome Rej.

Richard

[mremic01]

I just don't hear it. Nothing. Not even the subtlest difference, switching while playing. 

[Shrtyska9]

^^^ that thing is sweet! Could you record a clip direct into an interface like rej was talking about and switch between chips?

Richard

[culturejam]

I just don't hear it. Nothing. Not even the subtlest difference, switching while playing. 

That's a bitchin' rig! Nice!

I'm usually the guy who doesn't hear any difference between caps, trannies, op amps, etc. Maybe it was just that one build on that one day that I tested. But I know I heard a definite difference between LM301 and LM308, the latter having more apparent gain in the mids (which I would describe as "more aggressive" sounding). I also tested CA3140 and CA3130. My impression is that the "aggressiveness" ranks like this: CA3130 > LM308 > CA3140 > LM301.

Having said all that, you'd never not know it was a Rat regardless of the op amp. So it's not something I'd spend a whole lot of time worrying about or futzing with. I was on the hunt for a cheaper, easier-to-find alternative to the LM308, which is why I tested several at once.

[mremic01]

^^^ that thing is sweet! Could you record a clip direct into an interface like rej was talking about and switch between chips?

Richard

I could give it a try. Maybe the amp and speaker are filtering out frequencies where you could hear a difference. I haven't install the drivers since my last os install, so I'll have to get my interface set up again.

[Shrtyska9]

Right on CJ good to know.

Richard

[Shrtyska9]

^^^ that thing is sweet! Could you record a clip direct into an interface like rej was talking about and switch between chips?

Richard

I could give it a try. Maybe the amp and speaker are filtering out frequencies where you could hear a difference. I haven't install the drivers since my last os install, so I'll have to get my interface set up again.

Yo man its not that big of a deal. Like I said in my first post I'm really enjoying the pedal as is. I was just wondering if the lm308n lived up to the hype that it is given by some. Thanks again for the info guys!

Richard

[Guitarmageddon]

I've tried a few (LM308 both RCA and Chinese, metal can and op07cp) and hear a difference too...and I'm not usually that fussy.
The metal cans kill the others IMHO.  I use them in my personal rat and "shmancy' expandra builds.

Still got a few of these if anyone here is interested... (only$5 ea, shipped anywhere!)