Tighter sounding Rat mod. Any idea?

[Xavier]

Just built a Rat based on Gaussmarkov's layout, in my case I didn't have any single opamp so I used half of a TL072 - I keep changing opamps although all sound pretty much the same, 4559, OPA2604, etc...-

I have the input cap on a DPDT so it switches between the original 20nF and a 220nF.

Even the 20nF I find too fat and I would like this circuit to be MUCH tighter sounding. At high gain settings there's so much bass that it's all mud.

Would something like a 2n2 input cap do the trick or should I look anywhere else in the circuit? I don't think Ruetz mod is what I'm after...........

[Chugs]

I would leave the input cap at 22n.Try replacing the 4.7uf cap that connects to the 560R resistor with something smaller. Say 2.2uf or 1uf. This will lower the amount of gain in the low end and tighten up the sound.

[tubelectron]

Hi Xavier,

Discard the TL072 and go for the LM308N, which is the original OP-amp used in the 1981 Rev.B "big box" ProCo RAT. Believe me, as I have done it : it's an improvement worth to do, also. Way less harshness, better harmonics and sustain... An approximation would be the 741, the 1458 or 4558 : it's better than the TL072 as it reduces harshness, but meaningly inferior to the LM308N about the harmonics.

A!

[FlyingZ]

Definitely don't do the Ruetz mod. I would suggest a smaller gain pot because best performance is 55% or below with the existing pot. If that don't nail it for you save it, on some amps I hate it but on others its incredible. This is stock at about 50% gain; understand I simply threw my headset in front of the speaker for haste. http://www.aronnelson.com/gallery/main.php/v/FlyingZ/Line-In+2_Mic+2+2009-12-2+11-57-48.mp3.html

[Xavier]

I played a bit more with my rat circuit and so far I'm happy, here's what I did:

- I had a switch with 2x1n4148 in one side -stock clipping- , and 3x1n4148 -assymetric- clipping in the other side. I exchanged these 3 diodes by 2x5mm red leds and it's more usable.

- Swapped the TL072IP by an OPA2604PA. No difference that I can hear, I'll try with the good old 4558..........

- I had an input cap switch between 22nF and 220nF, which had a barely audible effect. I pt the original 20nF input cap and used the switch for the Ruetz mod, which is not exactly awesome, but certainly changes the character of the pedal completely. It becomes a low gain OD and if you don't use too much gain -otherwise it gives some nasty fuzz- sounds pretty OK

- I swapped the 100KB gain pot by a 25kA pot. This made the greatest difference. Now I still have more gain than I need, but the taper feels much better and the range is more adequate, I no longer have total fuzz with the pot at 9:00.

[FlyingZ]

I no longer have total fuzz with the pot at 9:00.

Check your original, something is incorrect.

[R.G.]

(1) define "tighter"
(2) my experience is that swapping opamps results in very, very tiny changes if anything can be heard at all.

[Xavier]

Hi RG

With tighter I mean less bass, more "cutting". I think there's a reason why manufacturers don't use always 1 mF input caps in all their builds.

I guess the pot change has more to do with the taper than with the value itself. I had all the gain coming as soon as I turned up the pot a bit........now I have a usable range. I cannot say there's anything wrong in the circuit, it could be although I have spent a lot of time debugging it........ nevertheless I'm happy how it sounds now.

Funnily enough I built another one using exactly the same schem -2 weeks before- but using an LM308N, and it was a completely different animal. The one with the dual opamp has more gain and punch to it (almost too much).

The previous one I gave to a highly reputed studio guitar player, just to find out that I made a big mistake..........used a 33n cap instead of a 3n3 cap. When I called him guess what he said........."this Rat sounds much better than the stock unit I have and it doesn't need any change"......yes he likes dark guitar tones 

[Renegadrian]

- I swapped the 100KB gain pot by a 25kA pot. This made the greatest difference. Now I still have more gain than I need, but the taper feels much better and the range is more adequate, I no longer have total fuzz with the pot at 9:00.

was fiddling with RAT pots, tone remains 100k A, I have a 100k B for volume, but hey that doesn't change the pedal character, and tried a 100k B for the gain...nah, it had total gain at 9 o clock as xavier reported - no 25k A but I feel much more control with the 50k A I have now.
So after a lot of time...THX for the suggestion!!!