This Week on the Breadboard: Rat Sorbet

[Chuck D. Bones]

This started out as a request for a Rat with more gain and less midrange.

I stuck a booster-limiter in front of the Rat, with a BASS cut at the input to the booster and and a MID cut at the output of the booster. The booster provides up to 40dB gain. D1 & D2 keep U1B from saturating at high GAIN settings. With MID & BASS dimed, the freq response is flat from 110Hz to 5.2KHz. The MID cut is centered at 800Hz, near the Rat's mid peak when DISTORTION is dimed. The BASS cut varies from 110Hz to 670Hz.

I tweaked the Rat circuit slightly to accommodate an A250K DISTORTION pot. The gain range and freq response are about the same as the original Rat. The FILTER circuit was modded so that the volume doesn't change when FILTER is rotated. I also tuned the FILTER range slightly darker. Like the Rat, the FILTER knob is like a reverse TREBLE knob.

It's sounding pretty good, so I'm committing it to Vero.



The Rat is on the left, booster is on the upper right.
Knobs (L-R): LEVEL - FILTER - DISTORTION - MID - BASS - GAIN


Rat Sorbet

 

[temol]

for practice over coffee..

 

[bluedmc777]

Oh nice!

 

[Chuck D. Bones]

Done been verified.
And updated to include the missing cut at P6.

 

[bluedmc777]

Figured there’d be more interest in this cause the Rat has never seemed like a finished product to me. Useable but much more potential.

 

[jimilee]

I need to make a pcb etch layout.

 

[Chuck D. Bones]

The Vero layout in post #4 was missing a cut at P6. Building this bitch was a &^$* ordeal. A broken wire, a missing cut and a ground wire that looked soldered, but wasn't. It's working now!



Knobs:
LEVEL - FILTER - DISTORTION
BASS - MIDDLE - GAIN

 

[genXslacker]

Help a brother learn something: What about R18 makes carbon film the prescription there? I'm guessing it does something favorable to the power filtering, but what?

 

[Feral Feline]

I'm guessin': It'd be a way to use up old carbon resistors and leave the audio path to the more accurate and quieter metal-film resistors.

---

So, CDB, you could say this is now Verofied?
(I chose P7 instead of P6)

 

[Chuck D. Bones]

I'm guessin': It'd be a way to use up old carbon resistors and leave the audio path to the more accurate and quieter metal-film resistors.

Pretty much. Metal film, wire-wound or even carbon comp would work.

 

[HamishR]

I'm curious, and I promise I'm not being snarky or anything, but I notice you often use just a dab of solder for joints. For example where the ground wire meets the IN jack lug. I was taught to "fill the hole" with solder so that the wire had nowhere to go. Apart from a probably vastly lower solder bill do you ever experience issues with the wire breaking away or anything?

Also wondering - what brand of SM caps are you using? Mr Psionic is very disparaging of "SM" marked silver mica caps, so for amps I steer away from them. Do you reckon that the "SM" branded caps are ok at the voltages present in a pedal?

 

[Chuck D. Bones]

I wrap the wire around the hole so it stays put while I solder it. As long as there is enough solder to encapsulate the joint, it's good. I've had to unsolder leads that were attached that way, and they don't come apart easily. Where leads go through a hole in a PCB or Vero, I fill the hole. The other reason I keep the amount of solder to a minimum is heat. It takes more heat to melt more solder and if one applies too much eat to a switch or connector, we risk melting the plastic and damaging the part. If I put more than one lead on a switch or connector terminal, then I fill the hole to make sure both wires are securely attached.

I use whatever brand of Silver Mica caps I can get. I've had no trouble with any of them. Voltage rating is no problem with pedals because Silver Mica caps are all rated for at least 50V. If they're going into a tube amp, then a 500V rating is more appropriate.

 

[HamishR]

That all makes sense! And all the silver mica caps I have are 500V. I rarely use them them in pedals because they're kinda big.