I just got time to open up a DEAD RAT a friend gave me and it's missing the Chip to my supprise, maybe there are more thing's wrong than just this, but it look's like a Brand new pedal, I checked The Rat schematic and it looks like it had a LM308 in it, is there anything worth subbing in it's Place ?
And what would be the best mod's for somebody that like's old classic Rock ?
Thank's,
JD
Go to AMZ and Jack Orman has a e-book on the RAT pedal what mods are the Best etc. I bought a Keeley RAT and I am very dissapointed with the lack of communication from him. Basically the Pedal with his mods has that much gain a slight jolt on the Distorition pot send the pedal crazy I have changed the pot to a different taper. But it still needs major work. I will never buy a Keeley pedal again
The LM308 is a compensated OA, for that circuit that's what you'll need if you want it 'right'. I don't know that it'd even 'work' with another. I never tried, werd has it the 308 is the RAT's best friend. Probly squeals with a TLxxx or something. There's a compensation cap that Tailors the high end...I experimented with different caps there,...
Might not be much wrong with it really, but I wonder how cleanly the bottom of the board under the OA is, you can probably clean that up with desoldering braid.
:D I know I'd be socketting the chip for sure, [heat damage preventer], and getting a 308 to try in there!!!
You should be able to resurrect it!!! Rebuild it, better, stronger than before, turn it into a RATKILLER !!! Whoops, I better let you try getting it going first.
May the Force Be With You!
Thanks Guy's,
The 308 was socketed on this pedal, that's why I think the chip was missing off the board, I'll pick one up next trip into town.
There is one thing though that I never liked about a Rat, I don't care for the Notch filter, wish there was someway to change it where it did do something for me, still though, these were and can be good sounding pedal's.
JD
Quote from: JDThanks Guy's,
The 308 was socketed on this pedal, that's why I think the chip was missing off the board, I'll pick one up next trip into town.
There is one thing though that I never liked about a Rat, I don't care for the Notch filter, wish there was someway to change it where it did do something for me, still though, these were and can be good sounding pedal's.
JD
BTW I'm also looking for a LM308, but it's not an easy IC to come by !!!. I know that some alternatives seem to be the NE5534, TL070.
Another question, what I have found is some LM3080. Is this the same as a LM308?
Small Bear carries the LM308. I built a Rat clone and put a control on it to control how hard it clips. This is a very useful feature. Here is a link to a thread I started when I built mine. Mark Hammer suggested the Clipping control and it is explained in the 2nd post.
http://diystompboxes.com/sboxforum/viewtopic.php?t=20540&highlight=
Also search this forum for more Rat mods. There is come good info here.
Thank's Dosman, Will do.
And whats the best GE diode's for Clipping ?
JD
JD,
I also found this in some of my saved files if it helps any:
QuoteI wasn't satisfied with the stock clipping diodes (once again), and used a slightly different arrangement. The switch on the top side selects between these two diode arrangements:
(1) silicon + silicon (in parallel)
(2) silicon + red LED (in parallel)
Version (1) is smoother and more "vintage" sounding while (2) is more aggressive. This pedal is capable of copious amounts of distortion and sounds great with single coils and humbuckers through all my amps. With the gain (BITE) way down and level way up on setting (1) it provides a great Overdrive tone as well. Excellent tone!
Peace!
Arn C.
Thank's Arn, I found a LM308 in some stuff I had'nt looked through so I think I'll socket the diode section so I can experiment with different diode's and LED's,
JD
Thank's to Aron and the Forum, Jack, and R.G. Keen, I now have a Rat pedal that's working,now to do some mod's to it, I tried going to Tonda's mod's but could not get it to open for some reason, are his mod's still availible ?,
JD
Quote from: petemooreThe LM308 is a compensated OA, for that circuit that's what you'll need if you want it 'right'. I don't know that it'd even 'work' with another. I never tried, werd has it the 308 is the RAT's best friend. Probly squeals with a TLxxx or something. There's a compensation cap that Tailors the high end...I experimented with different caps there,...
Might not be much wrong with it really, but I wonder how cleanly the bottom of the board under the OA is, you can probably clean that up with desoldering braid.
:D I know I'd be socketting the chip for sure, [heat damage preventer], and getting a 308 to try in there!!!
You should be able to resurrect it!!! Rebuild it, better, stronger than before, turn it into a RATKILLER !!! Whoops, I better let you try getting it going first.
May the Force Be With You!
According to Jack Orman, in his Fat Rat mod section:
"The op-amp was changed to a high speed, ultra-low noise chip (NE5534AP). This chip also has the advantage of being able to better drive capacitive loads such as the tone control of the Rat. You could alternately use an LM741, which is a single opamp similar to the sections of the 4558, to see if that provides a better tone, but it does not have the drive of the 5534. A TL071, TL081 or similar opamps can also be tried for slightly different sounds. "