ProCo Rat DIY Not Too Successful

[orson198305]

I built the following circuit without the two FETs, (as i cannot find any and don't know of a equivelent) I'm in the UK it's ****.

http://www.generalguitargadgets.com/diagrams/rodentsc.gif

I tried (as the site suggested) a TL061 & TL071 just to test the circuit. The 71 just sounded clean no matter the pot config. the 61 couldn't be more in opposition. It sounded dead fuzzzy. The wierd thing is though, when i turn down the volume or treble control in my telecaster i got this horrible buzzing through the amp. With the 61 the guitar needed to be struck pretty hard for any sound to come through. My only alteration was removing the 2 FETs and swapping the 30pF capacitor with two 15pF ceramic capacitors in parallel.

 

[tschrama]

I've build a hand full of RAT clones .. also whitout the input or output buffers..the opamp should really be the LM308 .. it's a low power (300uA?) and low slew rate opamp that makes it sound so typical .. really a TL071 won't give you the sound .. you really need a low slewrate for that sound

They should work fine.. check you circuit again... did you bias the input at 4,5 Volts?...

 

[orson198305]

Yeah, i bulit & Tested that seperatley.

 

[orson198305]

Does anyone know of any good books, that are aimed at effect processor DIY? I could use a tutorial on why this and that is used, i may be able to diagnose problems in the future if i actually understood what i was building.

Chears

 

[icurays1]

head on over to www.diystompboxes.com and check out their articles, forum, and wiki. absolutely everything you could ever want to know about guitar effects, from the simplest analouge fuzz to crazy weird envelopes and other digital madness.

 

[orson198305]

Thanks for that - great site

 

[Voltaic]

I built the following circuit without the two FETs, (as i cannot find any and don't know of a equivelent) I'm in the UK it's ****.

I've never bought anything from them before, but here's an ecommerce company out of London that has a good selection of FET's, including the 2N5458, might be worth checking out. Mark V

for valve amp stuff check out AmpMaker


cheers,
daniel

 

[orson198305]

Thanks for that, i can see myself using that site in the future, i managed to build the switching system with a standard npn transistor, just had to tweek the resistors. I also bought a bogstandard FET to replace the 5458, it's a little loud due to this fact but, better than nothing. I wonder why there's been so much hassel about the millenium switching circuit. The earlier rats suffered from very dim led's, surely the proco engineers are better than that?

 

[Voltaic]

You would think so.. but, some might say we think too much

BTW, where abouts in scotland are you?

 

[orson198305]

Kilwinning - Sadly

 

[tschrama]

the real proco RAT opmp uses just 300uA of current, the LED are obviously disigned to be dimm, as it saves power... the RAT not only sounds very good, is it goes a long way on one battery..

then again, I have a second generation RAT, and the led is dimm when switched off, and quite bright when switched on....

grzz,
Thijs

 

[orson198305]

I don't know if these different generations have different valued volume pots. The millenium switch can't be used for every value of pot, it has to be configured for each value.

 

[orson198305]

You are only talking about a couple of milliamps between bright and dim LED, replacement with a "ultrabright" LED which needs less current would sort out the dim LED problem.