Scratch built Proco Rat

Discussion in 'Pedals' started by ivan H, Jul 11, 2017.

  1. ivan H

    ivan H Member

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    I have never owned or even used a Rat pedal, but hearing a demo of another guys build (general guitar gadgets kit) impressed me enough to want one. As the Aussie BYOC distributor was out of Mouse kits I decided to scratch build. Before starting on a pedal I'm unfamiliar with I like to research the circuit, so hit the stompbox forums. Suitably enlightened, I started ordering components, the most important being a couple of the "metal can" type (TO-99) Motorola LM308HZ chips. I was lucky to get two of these for 3 bucks more than one new (probably Chinese) LM308 would cost me over the counter at my local electronics outlet. As I had read of people experiencing squeal problems at extreme settings with Vero board rat builds (probably due to poor construction techniques) I decided to do the board "point to point" style on prototype board. I stuck with component values from the first series of rat pedal, though as electrolytic caps have such large tolerances I substituted close tolerance tantalum caps for the filter controls two frequency dumps & the two places in the audio path where the originals had electrolytics. All other caps are mylar as per originals. Resistors are 1% metal film types. So here is the board before fly leads were attached WP_20170701_005.jpg & the underside WP_20170702_004.jpg & the completed pedal WP_20170702_007.jpg WP_20170702_010.jpg not yet labeled. I added a SPDT "on-off-on" type mini toggle switch that selects between the stock Rat's clippers, adds another diode in series with the positive clipping diode or, in the center position lifts the ground on the positive clipping diode so that only the negative half of the waveform is clipped. As its for myself & doesn't need to be fancy I (roughly) labelled controls with a white paint type marker WP_20170706_001.jpg
    I also wired the filter control in reverse as I had read it gives more useable sweep doing this with the audio taper pot. And it sounds fantastic. Now I know why these pedals have been so well liked. How did I ever get by without one. For rhythm type riffing, power chords etc, the stock Rat clipping option is my favorite. Adding in a second series'd positive clipping diode (asymmetrical clipping) makes it a bit more aggressive & a tad tighter sounding with a smidge more volume. Lifting the positive clippers ground (even more asymmetrical) makes it again more aggressive & tighter with a very noticeable volume increase. To do it over, I would go with just the stock clipping arrangement & the ground lift on the positive clipper which I would put on a footswitch along with an LED indicator. This would be a handy feature when taking a lead. As I still have another TO-99 type LM308HZ IC I might also do a "You Dirty Rat" variant (germanium clippers), even though these never used an LM308 chip. Cheers
     
    Last edited: Jul 11, 2017
  2. rjshare

    rjshare Senior Member

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    :applause: seriously good job!
     
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  3. scrumm21

    scrumm21 Silver Supporter Premium Member

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    Very Nice ! would love to hear a demo clip...
     
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  4. MUSTANGCAT

    MUSTANGCAT Senior Member

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    First time I seen one of your post on here Ivan! You've helped me out a number of times modding stuff. I'm currently gearing up to mod my JH-1 wah. I got all the parts but since I've been working, I have not had the time to start tackling it yet. Next week I'll probably get started after I finish the show I'm doing. By the way I picked up some of the metal can type Motorola LM308 from ebay. I plan on checking it out on my Rat2 which I soldered a socket in a few years back. ( With your encouragement ). Great seeing your posts on here. Cheers! The C Man.
     
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  5. MUSTANGCAT

    MUSTANGCAT Senior Member

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    Ivan I hope you decide to build a YDR. I dig my Rat2 but my YDR has even cooler tone to my ears.
     
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  6. ivan H

    ivan H Member

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    Thanks for the kind words guys. I can't promise a clip but if I can enlist someone's aid in recording in a suitable format I'll get one up (digitally challenged). Hi MUSTANGCAT, yes, I will get a YDR done, probably make it switchable between germanium & LED clippers, so a YDR & a Turbo Rat, that way I'll have all bases covered. I'd also like to try the OP07DP chip in both just to see if I can hear a difference. Looking forward to hearing how you wah turns out. Cheers
     
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