Proco Rat bottoming out?

aron · April 27, 2009, 07:09:51 PM

>What does the diode in the input of Joe Davisson's Vulcan overdrive do? It says "The diodes in the bias network prevent hard-saturation of the transistors."
Anyways, I wonder if something needs to be added to the front of both circuits? A buffer, or maybe something to limit the input?

The diode input is awesome, but can add noise. I had the same overload with a FET Muff long ago. Basically input resistance or voltage dividers will control the level and stop this from happening.

grolschie · April 27, 2009, 07:13:58 PM

Quote from: aron on April 27, 2009, 07:09:51 PM
The diode input is awesome, but can add noise. I had the same overload with a FET Muff long ago. Basically input resistance or voltage dividers will control the level and stop this from happening.

I noticed that the Professor Tweed has a 68k in the input, and the Eighteen doesn't. Would such a resistor on the Rat help me? I guess then it would cause a problem with low output pickups? I am guessing it would form a voltage divider with the input resistor?

aron · April 27, 2009, 07:32:18 PM

OK, the question is, if you take your guitar and turn down the volume a little, does it sound OK? If so, then you probably can increase the 1K input resistor to a larger value. I think this will do what you want.

grolschie · April 27, 2009, 07:38:00 PM

Thanks Aron. That won't work for me until I put a treble bleed on my guitar's volume pot. All these things I never get around to....

What typical value would be suitable to increase the 1k to please? Or should I try a trimpot or something?

aron · April 27, 2009, 07:38:58 PM

Yeah, just put a 100K pot and turn it until you hear something good (I hope) :-)

grolschie · April 27, 2009, 07:41:02 PM

Thanks Aron.

grolschie · April 28, 2009, 06:34:38 AM

Well, firstly I tried the 100k pot in front of the Eighteen. No joy. However, I solved most of my Eighteen's bad sound by increasing the resistor before the 3rd J201 from 8.2k to 76.2k (a 68k in series with the 8.2k). I ended up throwing to 68k's in series (144.2k total), but the first made the most difference.

EDIT: Now to mess with the Rat....

aron · April 28, 2009, 12:41:45 PM

Hey great!

I think I am going to put in a 250k pot for the rat distortion. I think my original had more distortion and sustain than this new one. I read somewhere that the original big box rat had a 150K instead of 100k.

aron · April 28, 2009, 01:26:07 PM

Hey I just had a thought. I think the Rat would be a very cool pedal to make an Octavia effect with. I'm going to look into that.

grolschie · April 28, 2009, 05:02:38 PM

Octavia, interesting. Please keep us posted.

My Rat seems to have not a heap of volume (2-3 o'clock is unity on volume knob), but heaps of gain. Above 12 o'clock on the gain knob starts fuzzing out. I got it 2nd hand, so I don't know the year - suspect its a 90's one. It's got a serial number and is made in the USA.

grolschie · April 28, 2009, 11:48:06 PM

I opted for a quick fix. Changing the 1k to a 68k turned the sound to mud. So it's back to 1k and back to the drawing board.

Aron, that sagging like-effect you mentioned, well my Eighteen still does that when my compressor is in front of it even when comp is bypasses. Must be the buffer in the compressor perhaps? No compressor in front and it's ok. Weird.

aron · April 29, 2009, 12:36:11 PM

Ok, yeah that's weird. I definitely cannot have anything in front of my Rat. I get the same thing. Guitar straight into Rat and everything's OK.

So changing 1K to something else didn't work??? Hmmmm...

grolschie · June 06, 2009, 01:50:18 AM

I think it's solved. I replaced the LM308N with a CA3130EZ and it seems so much better, even sounds good with my compressor in front of it. Probably a combo of the previous mods and the IC swap perhaps. Thanks everyone.

News:

Proco Rat bottoming out?