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Rodent (ProCoTM RatTMDistortion Replica)Instructions

Version 2009February12 Copyright 2009 JD Sleep

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This is the Rodent Distortion kit, a replica of the ProCoRat. There were/areseveral versions of the Rat. This project and kit is based on an older version of theRat circuit sometimes known as version !. "t does not include a #$%T on theinput of the circuit as version & had. %'perimentation has shown the input #$%Tdoes not have much effect on the sound and is probabl( not worth the e'tra parts toinclude it in this project.

The OpampThe ori)inal Rat used the *+-, which is now obsolete and e'pensive to bu(,thou)h still available from some sources. The datasheet for the *+- states that

the special characteristics of this opamp are ver( low input bias current, low suppl(current, and )uaranteed drift characteristics, characteristics not normall( important toaudio. $urther checkin) of the datasheet shows the slew rate of the *+- -.012/microsecond3 is dismal compared to a t(pical audio opamp, like a T*-40, which "think is the ke( to wh( it sounds )reat in the R&T circuit.

Comparin) the *+- to both the T*-50 and the T*-40, the T* opamps sound 67 inthe Rat circuit, the( are bri)hter and more of a heav( metal t(pe of tone, and thereis some plinkin) to the attack. The *+- )ives a warmer tone, less treble, and

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with a smoother, more tube9like attack, no plinkin). The dismal slew rate ma( beresponsible for this 9 the opamp simpl( cannot reproduce the pick attack at hi)h )ain.

The *+0- or a *+:- should work the same as the *+-, the specs are the samee'cept the 0- and :- are )uaranteed over a wider temperature ran)e. There arealso other opamps like the *+0- or the 6P9-% with ver( similar specs.

This kit uses the 6P-4 opamp that is used in the current model Rat distortions.;e compared the sound of this circuit with the *+- "C and the 6P-4 "C and found

little or no difference in the sound. se the project documents provided, startin) with the ?eneral !uild "nstructions.There are a couple of options for populatin) the small ceramic capacitors. @ince the(are usuall( available in two different lead spacin)s and itAs sometimes difficult tosource the caps with just the ri)ht lead spacin), there are optional lead spacin) holesfor C and C8. @ee the dia)ram below for placement.

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The output capacitor C0- placement is similar. The kit includes a )reat soundin)aluminum electrol(tic capacitor, but 0u$ film cap can be used if (ou are sourcin)(our own parts.

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BereAs an inside view of the unit we built to )ive (ou a real view of our construction.

Bere is a chart of volta)es taken at the "C pins. >se these volta)es as a )uideline.

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