ShortScale.org

Somewhere around 10 years back I built a customized RAT on perfboard, and it sounded amazing for the noise-rock stuff I like to do. Played many shows with it, until the shoddy solder connections eventually didn't stand up to the abuse, and it started crackling and cutting out. I retired it for a Sans Amp GT1, but after finding out how rare that pedal is and coming back to play music again in bands, I wanted to revive the old RAT.

Things are very different today, you can get actual pro PCBs made for you extremely cheap. Back in the day, your option was paying insane amounts for a pro job, or DIY laser printing a transfer and drilling it yourself, which I did a few times and it really, really sucked. So I decided I was going to re-make my custom circuit, with some improvements based on lessons learned from the old one, and most importantly, I wanted it to be two-channel.

The stock RAT, and my version, used 100k for the Gain pot. This value is way too high, you get to peak gain within the first half of the pot, and it just turns into a useless knob turn after that. I wanted a better sweep, and also wanted to replace my transparent Boost pedal at the same time. I swapped in a 10k pot to test it out, and the circuit is a surprisingly good OD pedal at very low gain settings. After more testing, I found a 25k pot was sufficient for going full-enough gain for distortion. So the plan is now, put a 10k and 25k pot on a footswitch in the gain-feedback loop of the circuit. I might need to up the 25k to 50k, but I'll see how that works out.

The other real customizations I'd done to the circuit, aside from the RC network in the gain-feedback loop, was to remove the Tone control entirely, as I absolutely never turned it up, and there was signal loss (volume) from it simply being in the circuit. One of my frustrations with the stock RAT was that it sometimes wouldn't even be at unity volume at full bore, so I wanted more volume. The tone wasn't really useful, it caused a volume drop, so it got chucked. Really wasn't a problem. I still wanted more volume, though, so I replaced the output buffer stage with the output boost stage from the Big Muff. In a BM, the high-low-pass filter on the tone knob caused massive volume loss, so a pretty hefty boost was required on the output. I stuck it on the RAT. It was fucking LOUD.

Since I now had the volume to spare, when I redesigned it this time, I decided to put the Tone back into the circuit, on a switch so it could be disabled. I set it up so that only the low-pass filter could be populated on the board, to get a stock-RAT tone, or a high pass could also be soldered in to give a full Big Muff scooped tone control. Honestly I'm probably going to be setting it up like a when I build the first one, a scooped Tone control on a RAT sounds like a good thing. I'll see how it works out.

Other minor options I had put in was switches for the slew rate on the opamp, there was the stock method, and then there was the datasheet method, with different slew rates. As best as I could learn, that would control how quickly the chip responds to changes in voltage, ie a bit like tube amp power sag. When I tested that out on the first prototype, it didn't seem to make much difference, but then it was hard to get the gain turned down enough to really hear a lot. Once I lowered the gain pot into OD territory, I could actually hear a difference between the two, so that switch stayed.

The last switch was to swap one of the diodes, to produce asymmetrical clipping. The standard diodes are 1N4148s, and then one of those gets swapped to an LED using a switch. It sounded interesting, but I think I'm going to mess with some other diodes I have instead of an LED this time.

I am still debating on whether I will put in separate volume controls for each "channel", I probably should, but then it might make it harder to set levels when playing a show. That's all off-board wiring anyway, so I can determine that later on.

I just got notification that my PCB boards have been finished and shipped, I went with the cheap shipping so I'm looking at 2-3 weeks for that, but I'm not in a rush. I'll post updates as I get the pedal moving along.

Sounds cool!

Oh man, this sounds so close to the TWAT pedal I made by rehouse and fucking with my old LM308 (special magic chip) version years ago. Before I somehow fried it in a feedback loop pedal, frown.
Your mods sound actually good though, next level shit!

Yeah, the LM308 is the magic sauce for these pedals. I managed to buy one (maybe have another one in a drawer somewhere) and that's what I'm using. However, I also bought and tested out the LM318, and there really wasn't any noticeable difference that I could tell. I really don't know why that wasn't the chip chosen to replace the 308 by ProCo. If I were going to make more of these, I'd use the 318. They are plentiful on Mouser still.

When I get this thing built up I'll do some sound sample recordings. I'm still unsure how the Tone net is going to work out, but I know the rest of the circuit sounds badass through a Twin.

Sounds good! Look forward to seeing/hearing it.

Sounds interesting. Are you going with two full circuits in there or some sort of dual pot arrangement?

I went on a bit of a RAT binge just before the pandemic. Got a DRV clone, an Idiotbox Blower Box and ended up with what seemed to combine all my favourite bouttique mods into one pedal, a Broughton Locust Star (was also eying up an EAE Longsword). That's the one on my board, but the other two both did some other stuff really well and I couldn't bring myself to get rid of them.
The DRV famously excels at the lower gain stuff, has a boost going into the front end and runs at a higher internal voltage (I think it also has a klon buffer in there) and the blower box does filthy high gain sludge real well, not sure what version of the RAT it is but replaces the tone stack with a BAX eq. The broughton has LED clipping on a switch, also runs internally at double voltage and has a bunch of extra EQ options. I actually use it more as boost into other dirt for extra clank with the diodes out, very little gain and the low end shelved off a bit for palm mute fun.

dub wrote: ↑Wed Sep 28, 2022 4:43 am Sounds interesting. Are you going with two full circuits in there or some sort of dual pot arrangement?

Sorry, missed this question. I am using a single circuit, with the gain pot on a footswitch, and there are now two of them. The switch flips between them. One is a 10k, one is a 25k, which is more than enough gain for this circuit.

I got my PCBs last week. There's some kind of weird pride to see a professional-looking PCB board that you designed, almost like creating a painting or something.


I had some build errors to sort out, but I got it complete yesterday. I am still waiting for some switches, the one I had for "slew" which controls the compensation method on the opamp broke when I was installing it, which was weird. I just hardwired one of the methods, I still haven't decided if I really want a switch for that. As I've been playing with it, I think I might change that switch to change the capacitor value in the gain feedback stage, to change the frequency response of it. Not positive yet.

Another happy mistake when building it, I scavenged one of the toggle switches from another old broken pedal, and realized it was an ON-OFF-ON switch. I decided to make that the toggle for the diodes, to give one more option. Up is the same diode as pointing the other way, down is a zener diode (diode alt, might change that one for something else), but the middle is the most interesting to me. It disables the diode in that direction entirely, so there's only one diode doing any clipping. I ended up using that setting in band practice last night, I really like how that sounds.

I haven't done any recordings yet, I don't have a recording setup anymore though I'm probably going to be changing that soon. Also, when I first finished it and put it through my bedroom practice amp, I was really, really disappointed. It did not sound amazing. It sounded like a normal ol RAT. I use a small Fender Mustang amp, set on the Twin model, so it's not exactly great for handling pedals. I took it to practice last night to test it on the big amps, and holy shit was it exactly what I was trying to accomplish. I normally use a EH Transparent Boost as an overdrive, and a Sansamp GT1 for distortion. This pedal replaces them both, and the overdrive sounds even better than the old setup. Plus, I always had the problem of going OD->Dist, in that the OD would still be engaged. This solves that problem as well. The distortion keeps definition which was my primary goal here, while still having a heavy sound.

I don't really know how to capture the exact sound of this thing, unless I set up my Twin and do a loud ass recording that way once I get a new USB interface. Either way, I'm pretty fucking happy with it.

That PCB does look classy.

Looks great

Pens wrote: ↑Tue Oct 11, 2022 3:05 pm I don't really know how to capture the exact sound of this thing, unless I set up my Twin and do a loud ass recording that way once I get a new USB interface. Either way, I'm pretty fucking happy with it.

I've had surprisingly good results using a phone - my iPhone 6 or iPad aren't all that good, but my work Samsung records guitar pretty much as it sounds in the room.

Yeah, I've honestly had some very "realistic" guitar recordings made by absent-mindedly throwing a phone near a guitar amp; the compression will help pick up some of the room to remove some of that kind "close mic sterility"

I have been using my phone with a recording app to capture stuff in band practice, though I normally position it further back to get the drums and both amps. I can try that out with it closer to the speaker. I will likely have to hook up the Twin and piss off my cat to get a proper recording, but ah well.

They'll understand

Yeah, so this pedal is just fucking weird. I keep messing with it and discovering different sounds that don't make sense. I think the massive volume boost it is capable of is part of it, I think when the volume is too high it's severely overdriving any input stage on the amp, and changing the tone of it. With near-unity volume, it has a lot of highs. Switch in the different diodes, and it goes from normal Rat, to what I consider a better, more natural sounding distortion, but when I set it to only one diode, a massive volume increase happens and the tone changes. Makes it really difficult to demo.

But the tone control is the weirdest part. It causes a volume drop, but that's fine. The pedal has plenty. At middle, it's a scooped metal sounding thing. Drop it to about 11 o'clock, and it's a nice bass rich tone. Turn it down to 7 o'clock, and it suddenly goes back to boosting some highs again?? Obviously, turning it up filters out the low end and it's really ick, kind of hurts my ears. It's basically unusable for me at those settings.

I may need to tweak the high-pass cap values to make it less shit on that end of things. I also do not understand why all the way down goes from low-pass filter, back to boosting highs again. Maybe I'm changing the midpoint or something? I used a tone calculator years and years ago to get these values, but I don't remember why I chose them.

I need to find someplace to upload sound files to show what I mean. Or, can I just attach it to a post like with a picture? I don't know how this new Shortscale works.

And also, I simply cannot get my phone to register how fucking LOUD this goddamn thing is. I have my Twin at 1, and when I turn on the pedal at max volume settings, it shakes your body. Phone apps are only registering like a 5-8 db increase, though.

http://www.guitarscience.net/tsc/bigmu ... pot=Linear

This is a web version of the software I used years back to calculate the tone stack values. It does in fact seem like the values I chose push the mid scoop point further to the higher end on the lower end of the pot sweep, which explains why I get more highs at the furthest point of the low setting. Not sure if I want to change that. I need to play around with the higher side and see if I can get a better sound out of that side of things.

At least that mystery is seemingly solved.

Pens wrote: ↑Mon Oct 31, 2022 3:54 pm At least that mystery is seemingly solved.

Always satisfying.