TC Electronic Magus Pro = Rat 308

JuneauMike

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Yeah, current Rats use the OP07. If I were a company building Rats in large numbers, I wouldn't want to have to deal with supply issues with sourcing 308s. Maybe there's enough of them out there for a niche builder to produce them for years to come, but I personally wouldn't tool up if I built them by the tens or hundreds of thousands.

Also, the specs for the OP07 and 308 are the same, at least where it should matter, which is the slew rate. Since no one has done an actual real double blind test (TTBOMK), I don't think it can objectively be concluded that the 308 does indeed sound better. And if it really is a matter of different slew rate between the two, you can actually adjust that, by increasing/decreasing the compensation cap.

...I wouldn't be surprised if most of us who swear a 308 sounds better aren't actually just fooling ourselves. This is possibly especially true if someone is trying out the latest Rat 2, because ProCo has made at least one component substitution that makes them sound audibly different.
Do you have any ideas on how you'd manipulate the slew rate of an IC? I don't know enough about it to chime in, but I'd assume that there's not too much that can't be done when it come to a circuit. I mean, we can even do digital to simulate various distortions and amp models now, right?
 

11 Gauge

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Do you have any ideas on how you'd manipulate the slew rate of an IC? I don't know enough about it to chime in, but I'd assume that there's not too much that can't be done when it come to a circuit. I mean, we can even do digital to simulate various distortions and amp models now, right?

Well, this is simply analog stuff, in the case of a simple op amp. The slew rate is manipulated by providing 'frequency compensation' in this situation, to make the op amp behave in a more stable manner.

...So, the very existence of external compensation kind of hints at just how obsolete an op amp like the 308 is, because many high performance op amps tend to have their own internal compensation. It's kind of like points and condenser in an old car engine distributor - you don't see that used with modern cars.

Long story short - with the 308 or OP07 - it's a single capacitor that 'puts guardrails' on the frequency response. TTBOMK, ProCo has always used a 30pF cap for the compensation cap (apparently, it was suggested on the 308's datasheet itself).

...Assuming the 308 does indeed have a lower slew rate than the OP07, and it's preferable (e.g. 'clearly sounds better'), you should be able to tweak the value of the compensation cap with the OP07 (by making it bigger), thereby making the slew rate identical to the 308's.

Capture03.PNG


...So, again assuming the 308 has a lower slew rate, and this is why we prefer it, the OP07 would probably have a line on the above graph that's just a little bit higher and to the left of the blue line. Also assuming that it's probably just a little bit higher of a slew rate, it probably would only require increasing the compensation cap slightly.

I've suggested to a few folks to try using a cap with a value between 33pF - 39pF, with their OP07 Rat. One or two have told me that it 'sounded better', but I think at least one person said they still preferred their 308 Rat. It's entirely possible that the compensation cap might have to be increased even more, but this is all trial and error stuff, since we aren't actually measuring anything.

Anyway, the above graph (which isn't mine, BTW, and can be found here - https://www.electrosmash.com/proco-rat) simply and clearly illustrates how the compensation cap affects the slew rate/bandwidth.

Who knows? Maybe you could make either op amp sound 'more better still' by simply increasing the compensation cap to be a bit bigger than ProCo ever did.
 

JuneauMike

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Well, this is simply analog stuff, in the case of a simple op amp. The slew rate is manipulated by providing 'frequency compensation' in this situation, to make the op amp behave in a more stable manner.

...So, the very existence of external compensation kind of hints at just how obsolete an op amp like the 308 is, because many high performance op amps tend to have their own internal compensation. It's kind of like points and condenser in an old car engine distributor - you don't see that used with modern cars.

Long story short - with the 308 or OP07 - it's a single capacitor that 'puts guardrails' on the frequency response. TTBOMK, ProCo has always used a 30pF cap for the compensation cap (apparently, it was suggested on the 308's datasheet itself).

...Assuming the 308 does indeed have a lower slew rate than the OP07, and it's preferable (e.g. 'clearly sounds better'), you should be able to tweak the value of the compensation cap with the OP07 (by making it bigger), thereby making the slew rate identical to the 308's.

View attachment 855281

...So, again assuming the 308 has a lower slew rate, and this is why we prefer it, the OP07 would probably have a line on the above graph that's just a little bit higher and to the left of the blue line. Also assuming that it's probably just a little bit higher of a slew rate, it probably would only require increasing the compensation cap slightly.

I've suggested to a few folks to try using a cap with a value between 33pF - 39pF, with their OP07 Rat. One or two have told me that it 'sounded better', but I think at least one person said they still preferred their 308 Rat. It's entirely possible that the compensation cap might have to be increased even more, but this is all trial and error stuff, since we aren't actually measuring anything.

Anyway, the above graph (which isn't mine, BTW, and can be found here - https://www.electrosmash.com/proco-rat) simply and clearly illustrates how the compensation cap affects the slew rate/bandwidth.

Who knows? Maybe you could make either op amp sound 'more better still' by simply increasing the compensation cap to be a bit bigger than ProCo ever did.
Thanks for that, I had read that before but forgotten it. I'm building a RAT pedal next and I was wondering about the compensation cap. I've got an OP07 and a can-style 741 that I wanted to try. I understand the 741 would not use a compensation cap although I could be wrong there.
 

11 Gauge

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Thanks for that, I had read that before but forgotten it. I'm building a RAT pedal next and I was wondering about the compensation cap. I've got an OP07 and a can-style 741 that I wanted to try. I understand the 741 would not use a compensation cap although I could be wrong there.

That's correct, no comp cap for a 741, or most other op amps, so no comp cap for TL071, NE5534, etc. They all have internal compensation.
 

soundxplorer

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I bought a Magus Pro on a whim, couldn't resist the small enclosure. It sounds very close to my Whiteface when I dial it in using my ears. The knob positions can be slightly different because the RAT circuit is very touchy in the lower range of the Distortion knob, where I typically use it. You can't just set both pedals to 9 o'clock and compare...dial it in by the way it sounds.

Bonus is the Turbo mode. So great to have both in one small pedal. It's a winner in my book.
 

Jbnaxx

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Not being a jerk, but why would you not get the real Rat? Is there something that is not up to par on the new ones? I have one of the Duecetone Rats. I can get some good sounds out of it, but it is huge...... not pedalboard friendly at all. it spends most of it's time in the old pedal box.
 

JustPlayItLoud

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Not being a jerk, but why would you not get the real Rat? Is there something that is not up to par on the new ones? I have one of the Duecetone Rats. I can get some good sounds out of it, but it is huge...... not pedalboard friendly at all. it spends most of it's time in the old pedal box.
It’s three very different circuits in one pedal for the same price as the regular Rat.

The Turbo and Fat by themselves are each significantly more expensive, so you’re getting a lot of Rat for your dollar.

And each setting does sound excellent.
 

Jbnaxx

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It’s three very different circuits in one pedal for the same price as the regular Rat.

The Turbo and Fat by themselves are each significantly more expensive, so you’re getting a lot of Rat for your dollar.

And each setting does sound excellent.
Nice…. I have been looking at another Rat. The Deucetone has a setting called Clean Rat that I haven’t seen on any other Rat. That was my favor setting. As I said earlier, the Duecetone just takes up too much pedalboard space.
 

soundxplorer

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Not being a jerk, but why would you not get the real Rat? Is there something that is not up to par on the new ones? I have one of the Duecetone Rats. I can get some good sounds out of it, but it is huge...... not pedalboard friendly at all. it spends most of it's time in the old pedal box.

I have a whiteface reissue RAT, love it. But I also like the Turbo RAT sound sometimes, and the Magus Pro can switch between those sounds (plus the Fat RAT setting, which I don't really use). Plus it is small and cheap.

The Deucetone is awesome, but like you said it is very large and heavy. The Clean setting is just a boost to run into the other RAT side...set it up for light crunch then boost it into heavy distortion. I think the Yeah Yeah Yeah's guitarist Nick Zinner tours with a Deucetone.
 

ahiddentableau

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If my memory is working correctly the DIY community addresses the difference between the two ICs using a small compensation cap when the OP07 is used. Most people who have A/B'd it say they can't tell them apart but as always with these things there are a few people who claim otherwise.
 

Mark617

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To my humble ears, I can’t tell the difference. I’ve had a Rat now for 15 years. It’s tried and true, gives me the tone ( I ) want a d it’s built like a tank
 

JustPlayItLoud

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so what's wrong with an American Made Pro co rat?
I bought a rat when they first came out and liked to plug it into my Fender Super Reverb a lot.
They cost 3-10x as much depending on the model on the used market.

There are no current production Rats made in the USA. All the ProCo made variants are MIA, but the Rat2 moved to China almost 15 years ago.

Since they’re both made in China and the same price, it’s hard to argue against getting 3 Rats instead of 1 unless you specifically want it to say Rat on it.
 

ping-ping-clicka

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They cost 3-10x as much depending on the model on the used market.

There are no current production Rats made in the USA. All the ProCo made variants are MIA, but the Rat2 moved to China almost 15 years ago.

Since they’re both made in China and the same price, it’s hard to argue against getting 3 Rats instead of 1 unless you specifically want it to say Rat on it.
excuse me! I just bought the darn thing way back when and can't break it, year in an and year out. A Pro Co RAT to the uninitiated is a RAT regardless of historical considerations , I mean it's nasty as hell in the sweetest way. Screw Top or Cork Bottle it rat ta-tata-tats in a black box unless it's the
JHS RAT PACK DISTORTION with nine iconic RAT tones in one compact pedal?
 

Tee1

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For me the footswitch on this is useless and really does not warrant the word 'pro' on it. It's some electronic relay which only engages the effect once you release the switch (not once you depress it), so there's a delay. That means you need to fight your natural pedal stomping instinct of being able to engage it when you actually step on it. There are switches of this type which do engage the effect when depressed (eg Boss) so i have no idea why they went with this crap version. Fine if you're a bedroom player or in a studio and don't need it timed well, but live, forget it.

It also seems unethically made. They would rather you buy a new one and throw away broken ones i.e. instead of replacing a footswitch. It's assembled in such a way that they really don't want you to open it up or peek inside unlike many other professionally made, serviceable pedals. Just my 2¢.
 

bluesholyman

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For me the footswitch on this is useless and really does not warrant the word 'pro' on it. It's some electronic relay which only engages the effect once you release the switch (not once you depress it), so there's a delay. That means you need to fight your natural pedal stomping instinct of being able to engage it when you actually step on it. There are switches of this type which do engage the effect when depressed (eg Boss) so i have no idea why they went with this crap version. Fine if you're a bedroom player or in a studio and don't need it timed well, but live, forget it.

I have an Maxon Pedal built like this - the OD9 Pro+ Not a fan they did it that way for the reasons you mention, but I have it in a loop switcher, so not really an issue. Perhaps they are using something called "negative edge triggering" where the foot switch creates a positive voltage (zero/ground being the norm) at a component and that component is then looking for the voltage to return to 0 again (the negative edge) before it activates the circuit. I imagine there was a reason to do it this way, but I am too far removed from my electronics days to have an idea of the usual suspects. Switching stability is my first thought, but we don't really see issues with others that don't do it like this.

I have always respected ProCo for building the Rat like a tank for a golf cart price. I imagine the margins on the Magus are considerable for some parts of the supply chain, and they sacrificed serviceability to get there. Electronics have been going that way (disposable products) for some time, so whats really surprising here is ProCo's continued dedication to their design and price point all these years.
 

Tee1

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I assume it's simply the cheapest way to do it. Oddly, the pedal engages only once it's released after being depressed, yet disengages when depressed. The switch is on a small pcb which then attaches to the other main pcb.

IMG_8030.jpg
 




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