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rat TO-92's ??


 
7/8/1998 11:01 AM
hys chip
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rat TO-92's ??
It seems many like the sound of the pro co. rat and I would like to try my hand at a p.c.b. layout for it. at uarberta.they have 2 scems one with 2 (bf245a) fets ?? I can't find em, and the other one type "b" it says uses a bipolar (2n5458) I found this one but it says its a jfet ?? anyone mess with the rat scems ? comments? go to he!! #@!$ chip
 
7/8/1998 12:21 PM
hys chip
email

also the scem shows it needs +4.5 volts in some places does this come from pin 7 (v+) on the LM308 op amp ? or is this wild stab in the dark way off ? chip
 
7/8/1998 1:16 PM
R.G.
I drew up that version of the Rat schematic back when dinosaurs roamed the internet. I'll take a look.
 
7/8/1998 1:22 PM
hys chip
email

after reading your tech on the tube screamer I see now the + 4.5 V is a after the 2 100k and 1uf cap, and this leads down to the 1m right? the tru bypass looked like your stuff R.G. the low noise set up without the 1megs to ground. very neet. chip
 
7/8/1998 5:15 PM
R.G.
Taking a look at  
 
http://www.ee.ualberta.ca/~charro/cookbook/audio/guitar/pcrat.gif  
 
I see immediately that I messed up the schematic in two places ...  
 
The JFETs are used as source followers, and on that input JFET, the 1uF cap leading to the 1K to ground should be AFTER the resistor to ground, which serves as the source resistor for the first stage. Also, the 1M resistor on the input JFET is misplaced, and should be from the gate of the JFET to ground, not on the outboard side of the 0.022uF cap.  
 
Those errors being noted, the JFETs are only used as source followers, and the BF245 can be replaced in this app. by 2N5457 or 2N5458, and probably MPF102, 2N5485 or 2N3819 as the specific device parameters don't matter too much in a source follower hookup.  
 
The 100K to the (+) input does go to the +4.5V source and biases the opamp into the middle of the 9V battery voltage.  
It wouldn't hurt the ratt to have another 1M resistor from the input terminal on the OUTSIDE of the input coupling cap to ground where the -erroneous- 1M is now for click suppression.  
 
"But R.G." I can hear you saying "how could you make such an egregious mistake? In public?" All I can say is, that was a time when I was squeezed for time, and it was drawn from a scan of a hastily hand drawn tracing that was sent to me. I didn't personally trace it. But you're right, I should have noticed. (There are a couple of bugs in the ualberta univibe schematic, as well. The one on GEO is correct.)  
 
The Ratt is obviously a member of the Distortion Plus family, characterized by a gain stage driving back-to-back diodes through a resistor. This isn't important to you, probably, but I'm hot on the topic as that's a key element of the book I finally decided to write on effects.
 
7/8/1998 6:07 PM
hys chip
email

wow thanks for the info R.G. I hold you all in the highest and an erroneous mistake from a hand drawn scem. and pressed for time, I seem to make them all the time and fumble around (Learn wile you burn) and still get some great tonestuff's  
I would love to buy your book R.G. on the N.G.s it seems like the fuzz face and tube screamer are faves with the rat as an also ran,I printed this out and now I will get to work on a board,thank you Chip
 
7/11/1998 3:52 PM
hys chip
email

ack! this was harder than it looked, so I did a fuzzface layout, anyone care to check my artwork ? thank's chip
 
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