Rat chips

suspiciousminds

I'm building a clone of a rat pedal - would a TL072 chip work or does it have to be LM308?

stickyfiddle

I think it would work but not have quite the same character. Can't you get LM308s on ebay for very little money? 

All I know for sure is that my official ProCo Rat 2 doesn't have an LM308 and was my favourite pedal in the world until I built another with a LM308 for interest's sake and now *that* is my favourite pedal...

suspiciousminds

Yeh, have just ordered some now.
Any idea whats in the rat 2?

Magnetic_Effects

A TL072 will not work as it is a dual opamp so it is not pin compatible. You need a single opamp.

You can try:

LM308

LM301

OP07

LM741

TL071

Magnetic_Effects

The LM741 and TL071 don't need the 30pf compensation cap, the other opamps do. 

english_bob

Found this:

http://www.diystompboxes.com/smfforum/index.php?topic=55234.0

Beexter

suspiciousminds;1075244" said:

Yeh, have just ordered some now.
Any idea whats in the rat 2?

The earlier Made in USA ones had the LM308 but the later Made in China ones don't. I don't think I have the most sensitive ears when it comes to tone but I definitely noticed a difference. Tried a modern one in a guitar store and hated it. Decided to take a chance on an older LM308 equipped one on Ebay and realised what all the fuss was about. I'd say the LM308 is worth seeking out.

ICBM

I hear a difference between old and new Rats too, but I'm not convinced it's due to the chip. There are other component (type/quality) differences as well, even though the circuits are the same.

In fact all the varieties of Rat (vintage, II, Turbo and You Dirty Rat) are essentially the same circuit with minor component type and value differences, and they sound *hugely* different from each other.

stickyfiddle

If the US ones definitely all had the right chip then mine must do, so it's the other components that make them sound different. Will see what's in there tonight.

And +1 for the other versions - the YDR in particular is brilliant.

Johnnyseven

ICBM said:

I hear a difference between old and new Rats too, but I'm not convinced it's due to the chip. There are other component (type/quality) differences as well, even though the circuits are the same.

This.

I had 2 US made Rat2's at one point, one with an LM308 and one without, and they sounded the same. I have also had Turbo Rats with and without and they also sounded the same, I even fitted LM308 chips to 2 that didn't originally have them are there was no noticeable difference in sound. The difference in the sound between the US and chinese Rats are, IMO, down to other components, the pots being one of them.

english_bob

ICBM said:

I hear a difference between old and new Rats too, but I'm not convinced it's due to the chip. There are other component (type/quality) differences as well, even though the circuits are the same.

In fact all the varieties of Rat (vintage, II, Turbo and You Dirty Rat) are essentially the same circuit with minor component type and value differences, and they sound *hugely* different from each other.

Yep. It would be very difficult to do any sort of reliable A/B testing since many of the other components in the circuit have an effect on the sound, so just A/Bing two RATs with different chips isn't really a fair test. Switching two different chips in the same pedal might be slightly better, but aural "memory" is very short term so by the time you've pulled one chip and put in another you can't rely on how you thought the first chip sounded. 

A guy on this thread from Madbean: http://www.madbeanpedals.com/forum/index.php?topic=17420.0  built a "RAT lab" with external controls for various things including a switch to swap between an LM308 and another IC. Seems like the differences are subtle at best.

Johnnyseven

stickyfiddle said:

If the US ones definitely all had the right chip then mine must do, so it's the other components that make them sound different. Will see what's in there tonight.

And +1 for the other versions - the YDR in particular is brilliant.

They don't all have the right chip.

lasermonkey

Apparently the CA3130 and CA3140 sound good in a Rat. I have some, buy haven't got around to it yet.

The LM108 and LM208 will most likely sound identical, if you can find any. The UA308 is the same, just a different manufacturer.

I've read that changing 30pF compensation cap on the OP07 to a 100pF makes it sound more like the '308, but the newer Rats also have the knobs glued on, and removing them to get inside is a right pain.

Swapping the clipping diodes to different types (germanium/LED/ asymmetric, etc) will probably change the sound more though.

suspiciousminds

Superb info, thanks chaps!

ICBM

Johnnyseven said:

stickyfiddle said:

And +1 for the other versions - the YDR in particular is brilliant.

They don't all have the right chip.

No, but we've already more or less established that it's not the chip which makes the difference .

lasermonkey said:

Swapping the clipping diodes to different types (germanium/LED/ asymmetric, etc) will probably change the sound more though.

Not probably - massively. It's the single biggest difference between any of the versions, although there are also other less important component value changes.

This is very useful…

http://music-electronics-forum.com/attachments/26656d1387061571-multi-rat.png

Magnetic_Effects

lasermonkey said:

I've read that changing 30pF compensation cap on the OP07 to a 100pF makes it sound more like the '308, 

The is true and is often overlooked.

Having modded quite a few Chinese Rats I have noticed that a number of them had 0.0027uf instead of 0.0033uf cap in the tone control part of the circuit. A minor difference but does make the Chinese pedal very slightly brighter on some settings if doing a shootout with a USA Rat set the to the same settings. A slight turn of the tone control fixes that of course. 

Heartfeltdawn

Beexter said:

The earlier Made in USA ones had the LM308 but the later Made in China ones don't. I don't think I have the most sensitive ears when it comes to tone but I definitely noticed a difference. Tried a modern one in a guitar store and hated it. Decided to take a chance on an older LM308 equipped one on Ebay and realised what all the fuss was about. I'd say the LM308 is worth seeking out.

Some USA ones did have the OD007DP. Somewhere between serial numbers 228745 and 255436. Yes I have records. Yes I possess the sort of absurd geek knowledge that makes good women run away. 

Vintage Rat reissues do it for me now.  

Lebarque

Bump for the best thread name ever!

ICBM

Just to resurrect this…

Does anyone know when they changed to the god-awful reverse-taper pots? Same time as the crap 3PDT and the different chip, or some time after that? I've got a later RAT II here for a repair - turns out there's nothing actually wrong with it other than it being built by idiots. The reason for the 'fault - that all the controls have all their useful range over the first quarter turn and then do nothing all the way to the top - is because some cretin decided to change the Audio Taper (Log) pots to reverse Log.

I don't remember having come across this before, so either I'm just dense and have been living under a rock, or it's something relatively new.

It's shit, anyway. It makes the controls *very* touchy if you want anything other than loud high gain mud. My favourite setting on the old Rats was with all three controls at about 1 o'clock - to get the same(ish) sound on this one, they're all at under 9 o'clock and it's difficult to dial in.

Sorry for the rant. This kind of stupidity just annoys me . I'm going to suggest he sells it and buys a proper Rat, actually.

stickyfiddle

Could just be a run on a day their regular pot delivery was late, so they used whatever they had in the factory rather than not deliver any Rats that week..? That's the sort of thing a low-spec chinese place would probably do.

Completely agree on the best sound - on mine it's everything dead on 12'oclock but I figure that's a very similar thing with different tolerances.

Heartfeltdawn

ICBM said:

Just to resurrect this…

Does anyone know when they changed to the god-awful reverse-taper pots? Same time as the crap 3PDT and the different chip, or some time after that? I've got a later RAT II here for a repair - turns out there's nothing actually wrong with it other than it being built by idiots. The reason for the 'fault - that all the controls have all their useful range over the first quarter turn and then do nothing all the way to the top - is because some cretin decided to change the Audio Taper (Log) pots to reverse Log.

I don't remember having come across this before, so either I'm just dense and have been living under a rock, or it's something relatively new.

It's shit, anyway. It makes the controls *very* touchy if you want anything other than loud high gain mud. My favourite setting on the old Rats was with all three controls at about 1 o'clock - to get the same(ish) sound on this one, they're all at under 9 o'clock and it's difficult to dial in.

Sorry for the rant. This kind of stupidity just annoys me . I'm going to suggest he sells it and buys a proper Rat, actually.

What's the serial number on it? USA or China? I had one I sold last year as a repair job. Definitely Chinese.