# Breadboard a Rat



## fig (Dec 5, 2021)

I hadn't planned on it, but the urge struck when Derek mentioned never having played one so I downloaded the schematic from electrosmash and put one together. It's a fairly simple build, with a low component count. 

IC1 = LM308N, Q1 = 2N5457, clipping diodes are 1N4148s. I tried stock pots, but found I liked W50K for distortion and B250 for tone.







It sounds pretty groovy as is, but I may try out Derek's proposed mods. It's much easier to adjust a circuit to one's liking by breadboarding it first, whether it's someone else's mod, or your own. 

This is bypass for reference...a 150Hz sine @ 500mV






This is engaged, close to unity (6-ish) with the tone rolled back to 3-4






Distortion dimed






Vol maxed...why not?






It's a classic for a reason.

I'm going to tighten up the layout, but I'm pretty happy with placement.


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## fig (Dec 5, 2021)

Just had a thought....if anyone has a groovy mod they'd like me to try, I will try to get a makeshift recording rig together so I can share the results.


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## Coda (Dec 5, 2021)

You’re gonna record examples, how about swapping out some op-amps?…


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## peccary (Dec 5, 2021)

fig said:


> Just had a thought....if anyone has a groovy mod they'd like me to try, I will try to get a makeshift recording rig together so I can share the results.


I bought a few Rat boards and was planning on giving this mod a shot with my bass as it seems pretty simple. If you're looking for something to do!

https://www.google.com/amp/s/marcuseffects.wordpress.com/2016/06/20/proco-rat-bass-mod/amp/


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## BuddytheReow (Dec 5, 2021)

A rat is on my list to breadboard. I built one on vero and it’s pretty dark unless I dime the tone knob. For some reason mine can almost sound gated at times even though it’s opamp based


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## jimilee (Dec 5, 2021)

Instead of silicon or LEDs, how would it sound with a couple of BS170s clipping to ground?


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## fig (Dec 5, 2021)

Coda said:


> You’re gonna record examples, how about swapping out some op-amps?…


I'll use my little ZIF socket breakout...






I've got several single opamps, tons of diodes, and a bag of BS170s_. _I'll try to get them all in before losing interest, LOL.


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## Dan0h (Dec 5, 2021)

You are a mad scientist, a level worthy of aspirig towards. and not the Aspiration that is created in 90% humidity and lether seats in summer, but the other aspiration.


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## fig (Dec 5, 2021)

peccary said:


> I bought a few Rat boards and was planning on giving this mod a shot with my bass as it seems pretty simple. If you're looking for something to do!
> 
> https://www.google.com/amp/s/marcuseffects.wordpress.com/2016/06/20/proco-rat-bass-mod/amp/



That looks easy enough...


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## tcpoint (Dec 5, 2021)

Try the VFE Red Wolf.  That's my favorite Rat variant.  I have an extra pcb, if you'd like one.


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## fig (Dec 5, 2021)

The opamp auditioner is online!


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## fig (Dec 5, 2021)

peccary said:


> I bought a few Rat boards and was planning on giving this mod a shot with my bass as it seems pretty simple. If you're looking for something to do!
> 
> https://www.google.com/amp/s/marcuseffects.wordpress.com/2016/06/20/proco-rat-bass-mod/amp/


The only difference I see is that in the schematic I used for the build, it would go in between R5 (not R7) & C6. I've got the parts out and will graft it into the breadboard. I'll add another switch to swap from BS170s to 1N4148s.


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## vigilante398 (Dec 6, 2021)

fig said:


> I tried stock pots, but found I liked W50K for distortion


You already got my favorite there, I went with A50k though. I never turned my Rat's distortion up all the way anyway, and a lower value pot opens up some nice mid-gain areas that are otherwise lost in the taper with a 100k pot.


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## caiofilipini (Dec 6, 2021)

Speaking of Rat opamps, does anybody know if this is accurate?






If it is, it appears the LM308Ns I got from GuitarPCB are not the real thing.


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## Big Monk (Dec 6, 2021)

What are common opamps subs for this? I want to breadboard one this weekend.


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## benny_profane (Dec 6, 2021)

OP07 is in new production Rats. You can try any single op amp provided the pinout is compatible. Hi-fi / fast op amps will be wasted here. Note that the LM308 / OP07 require external compensation, some others will not. This is typically indicated by TRIM, COMP, or offset nulling in data sheets. You can experiment with the compensation cap to shelve high frequencies and limit bandwidth.


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## fig (Dec 6, 2021)

Here's the bass mod Joe..


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## fig (Dec 6, 2021)

benny_profane said:


> provided the pinout is compatible.


The ZIF socket makes it much easier to re-pin by swapping wires at the socket.


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## fig (Dec 6, 2021)

caiofilipini said:


> Speaking of Rat opamps, does anybody know if this is accurate?
> 
> 
> 
> ...


I couldn't say if that conclusiveIy determines legitimacy, but I checked a couple of my LM308Ns and OP07s...nothing betwixt pins 1 & 5 on the DMM.


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## caiofilipini (Dec 6, 2021)

fig said:


> I couldn't say if that conclusiveIy determines legitimacy, but I checked a couple of my LM308Ns and OP07s...nothing betwixt pins 1 & 5 on the DMM.


My 4 LM308Ns from GuitarPCB read around 2.38KΩ between pins 1 and 5. 
My LM308AH metal cans read over 8MΩ.


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## peccary (Dec 6, 2021)

fig said:


> Here's the bass mod Joe..


Using the fancy tant caps and everything!


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## fig (Dec 6, 2021)

caiofilipini said:


> My 4 LM308Ns from GuitarPCB read around 2.38KΩ between pins 1 and 5.
> My LM308AH metal cans read over 8MΩ.


I'd build out the circuit and see how they sound.


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## fig (Dec 6, 2021)

peccary said:


> Using the fancy tant caps and everything!


I brought out the nice tableware for you folks.


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## fig (Dec 6, 2021)

The opamp auditioner is really coming in handy... 
So far I've confirmed these;

LM307N
LM308N (duh)
LM310N
LM741
TL061
TL071
TL081
OP07
OPA27
OPA602 (swapping pins 1 & 5)
NE5534 (swapping pins 1 & 5)


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## jeffwhitfield (Dec 6, 2021)

fig said:


> The opamp auditioner is really coming in handy...
> So far I've confirmed these;
> 
> LM307N
> ...


OP07 is what is currently being used in the newest ProCo Rat pedals. It's supposed to be the closest equivalent to a LM308N. Technically, it's a better op-amp...but to my ears it's still a little different. Very, very subtle difference though. Still a Rat though.


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## fig (Dec 6, 2021)

100Hz sine sounds close on most, but I've been listening to it all day so everything sounds mushy. We'll see how they look to the scope, plus I'll run/record a loop through each and post them. I'll use the production opamp for testing the clipping options and the bass mod. 
I'm also going to make a switch bank for the breadboard.


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## vigilante398 (Dec 7, 2021)

When I build for myself I use metal can LM308AH because mojo. When I build for customers I use OP07 because I can get them in SMD package and pick-and-placed. Plus they're cheeeaaaaaap.


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## fig (Dec 10, 2021)

Update - I've done quite a bit more undocumented tinkering and swapping, mostly to get my bearings on how to best demonstrate variations within the option matrix [op-amp/clipping/bass mod]. Rather than audition every possible combination, I'll choose an op-amp, then match the clipping to my personal preference. For the bass mod I will use both my chosen configuration & stock (and any others you'd like me to try Joe).  My audio interface died..probably of loneliness since I never used it..so I have a replacement incoming for the comparison samples. I have some cool scope shots to share as well.


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## Harry Klippton (Dec 10, 2021)

What interface died and what did you get as a replacement


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## fig (Dec 10, 2021)

That Scarlett 6i6 (remember? I tried to give it to you, LOL)....the replacement is a Scarlett solo 3rd gen. If the space is right when we move I'd like to get something with more versatility, like an RME Fireface.


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## fig (Dec 18, 2021)

I'm still putzing with the comparisons, but hands down the LM308 sounds better than the other dozen or so auditioned [insert subjective harumph]. The circuit on my breadboard as is below is how I'll build it out (minus the zif and superfluous wiring). I'll get some measurements, but the diodes are black glass OA7s and bring quite a punchy growl to the table. Mica and C280s for tone-jo. 

Joe, I ran into a delay on your request, but will circle back to it. 

There's phaser island in the foreground....which is also the reason for the delay...LOL


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## Paradox916 (Dec 18, 2021)

Punchy growl?!  Phaser island?! You have my attention now.... tell me more about these magical OA7s you speak of. How do they compare to the 1N34As?


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## fig (Dec 20, 2021)

@Paradox916

Apologies for the delay. To answer your question; the Vf range of the 2 are fairly close in the samples I tested (within 10mV), but the curve response seems quite different.

Using my signal gen. and scope together, I ran a ramp wave into the diode (DUT) and connected channel 1 probe between the input and diode and set the measurement to amperage. Channel 2 was connected between the other pin of the diode and common to make a simple XY curve trace. The sampling memory depth is 7m so it's a thicker, 3D sort of trace.

Here is a 1N34A.






...the waveform distortion..







Now the OA7...






...and it's waveform..






..and a 1N4148..






..you guessed it...






I'm still planning to put together some audio samples but I've been otherwise occupied of late. These visuals are helpful to demonstrate a difference, but for our purposes matching those squiggles to audible recognition would go a long way.

"Phaser Island" is just a MXR 90 I want to use to determine a lower threshold for Vgs-off, no connection to this project. This may already be common knowledge amongst those in the know, but I operate outside that magical bubble so empirical evidence accompanied by input from youse guys is king.

Edit: I uploaded the square wave response images rather than the saw waves...the other waveforms displayed respectively.


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## Paradox916 (Dec 20, 2021)

That’s interesting... just by the wave form it looks as if the OA7 are some where between the 1n34a and the 1n4148... I don’t know exactly what I’m looking at but now It’s m even more curious. Thanks for doing that!


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## fig (Dec 21, 2021)

Okay Joe, yer up.

I had to redo the switch as I misread the blurb the first time and used an on-on-on-and-on-indefinitely instead of an on again-off again-on again type.

The 4u7 option is the green EC, and the 10u a tantalum.






You might notice the absence of the clipping diodes...I removed them for this demo....btw this damn thing is LOUD without them. I have a little Roland MG-10 at the end of the bench I use for audibles, and had it set for a _clipped_ rat...yikes!

Anyway, so I ran a squiggly line through the circuit - 80Hz 1Vpp sine

The first view is the stock value setting (center off)






Next is the 4u7 option...more pronounced hump..






...and the 10u option...look more like a Fedora..






Once again, sound clips will be even more useful but I hope this gives you an idea...The 10u side begins to clip @ 65Hz as seen here






Thanks for reading! If you spot an error or have feedback I'd love to know!

Edit: The 10u side begins clipping @ ~98Hz...

Second edit (due to duhhhh): The first edit should read the 4u7 side begins clipping @ ~98Hz.


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## peccary (Dec 21, 2021)

fig said:


> Okay Joe, yer up.
> 
> I had to redo the switch as I misread the blurb the first time and used an on-on-on-and-on-indefinitely instead of an on again-off again-on again type.
> 
> ...


Thanks, Fig. I have to admit that I'm not sure what I'm looking at here but I am now picturing a fedora wearing rat on the front of the enclosure. 

I'm thinking of getting myself a cheapie scope just to be able to see what I'm hearing, I feel like that experience would be really helpful. Being able to see the clipping is pretty cool. 

How'd your Ric sound through it?


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## fig (Dec 21, 2021)

peccary said:


> Thanks, Fig. I have to admit that I'm not sure what I'm looking at here but I am now picturing a fedora wearing rat on the front of the enclosure.
> 
> I'm thinking of getting myself a cheapie scope just to be able to see what I'm hearing, I feel like that experience would be really helpful. Being able to see the clipping is pretty cool.
> 
> How'd your Ric sound through it?


I haven't gotten to play through it with the mod yet, but it's on my fig-do list. 

How's your vision? If a smaller screen is not an issue I'll send you this Hantek 2D72. It's a 2-channel scope, a signal gen and DMM all in a handheld. The bandwidth is fine for the display but pushing it to an external via the USB port introduces a good bit of lag.


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## peccary (Dec 21, 2021)

fig said:


> I haven't gotten to play through it with the mod yet, but it's on my fig-do list.
> 
> How's your vision? If a smaller screen is not an issue I'll send you this Hantek 2D72. It's a 2-channel scope, a signal gen and DMM all in a handheld. The bandwidth is fine for the display but pushing it to an external via the USB port introduces a good bit of lag.


My vision is awful but the glasses help 🤓

That is very gracious of you, Tim, thank you. I think it would be a pretty handy learning tool. I'll drop you a PM.


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## phi1 (Dec 22, 2021)

Something that might be a fun/easy mod while on the breadboard. A pair of red led soft clippers changes the feel at higher gain levels. You get less of the woofy fuzz stuff and a tighter clearer sound by avoiding op amp clipping. the op amp clipping is super cool in its own way, this is just a simple way to get a feel for how the op amp clipping (before the hard clipping diodes) is affecting the sound.

Also, in my build a put the ruetz sweep mod, which I almost always back off a bit compared to stock. Just a 1k pot in series with the 47R.


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## fig (Dec 24, 2021)

phi1 said:


> Something that might be a fun/easy mod while on the breadboard. A pair of red led soft clippers changes the feel at higher gain levels. You get less of the woofy fuzz stuff and a tighter clearer sound by avoiding op amp clipping. the op amp clipping is super cool in its own way, this is just a simple way to get a feel for how the op amp clipping (before the hard clipping diodes) is affecting the sound.
> 
> Also, in my build a put the ruetz sweep mod, which I almost always back off a bit compared to stock. Just a 1k pot in series with the 47R.


I'll give that a shot, thanks!

I played around with the pedal controls and found a nice spot to demonstrate the bass mod a bit clearer...



https://imgur.com/ZOhdhIV



Unfortunately, sharing the GIF is more difficult than creating it, LOL.


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## peccary (Dec 24, 2021)

With animation, even! Very fancy.


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## benny_profane (Dec 24, 2021)

fig said:


> I'll give that a shot, thanks!
> 
> I played around with the pedal controls and found a nice spot to demonstrate the bass mod a bit clearer...
> 
> ...


Nice! What are the axes and legends?


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