RR+

Classic distortion circuit used by Randy Rhoads

 

 

The RR+ distortion rack effect module compares to the MXR Distortion +, multiple versions of the DOD 250 Overdrive Preamp, and the DOD YJM308.  It is a simple, rough-and-tumble distortion that has been in production for a long time.  There are loads of mods available for those that want to add a little polish to this unrefined circuit.  Or leave it as-is and play it loud and proud like Randy Rhoads did.

 

Description

The MXR Distortion + borders on crude in design.  It has been in production for decades and is still popular today for its nasty distortion.  It was the starting point for designs of many subsequent distortion and overdrive circuits from Maxon, Ibanez, DOD, and many others.  The circuit provides lots of opportunities for tweaks and modifications, so we offer quite a number of them.  However, this is a lean circuit, raw and crude.  Piling up the options on it can get you a long ways from its base character.  Nothing wrong with that necessarily, but it may be indicative that another circuit may be a better match for what you're after.

 

Configurations

  • RR+ - compares to MXR Distortion +

    

  • RR 250 V1 - compares to first grey version of the DOD Overdrive Preamp 250
  • RR 250 V2 - compares to second and third grey versions of the DOD Overdrive Preamp 250
  • RR 250 80 - compares to 80's versions of the DOD Overdrive Preamp 250
  • RR 250 90 - compares to 90's version of the DOD Overdrive Preamp 250

  • RR 308 - compares to DOD Overdrive Preamp YJM308 Yngwie J Malmsteen version

There have been several versions of the DOD250.  There were at least 3 versions in the gray pedal, 2 versions in the yellow pedal, and a special Yngwie Malmsteen 308 which is almost identical to the 250's.  Ignoring some tiny changes that have to do with the non-audio part of the circuit, the second and third grey versions were the same, and differed from the first grey version by a single capacitor.  The first yellow version was also very similar to the grey versions, but used a different op amp.  Later yellow versions and the YJM version used yet another op amp, which isn't pin-compatible with the previously used op amps.  The MXR Distortion + used the same op amp as the grey DOD 250s. 

 

Options

  • Smooth Switch - There is an input capacitor that reduces the bass allowed into the circuit.  This switch lets you select from 3 values to allow different cutoff points for what is allowed to pass into the circuit.  One setting is the stock circuit value.  Another one filters out more bass for a more open sound.  The third one allows more bass in, for a smoother sound.  These don't always result in big differences, but they are there.
  • Script Option, Block Option - The Distortion + came in two versions, the Script and Block versions.  They differed only in the brand of op amp they used.  The Script version used an LM741 and the Block version used a uA741.  It's doubtful that there is enough difference between the two to be audible, but you can choose whichever you prefer.  You must choose one of these options or the Custom Op Amp option for the RR+ configuration.  These options don't apply to the RR250 configuration.
  • Custom Op Amp - For either configuration, you can choose a different pin-compatible op amp.  Not compatible with Script or Block options for the the RR+ configuration.
  • Noise Cap - This option adds a filter cap to get rid of very high frequencies.  The Yellow 250 Option includes a noise cap, but the RR+ and RR 250 do not normally include noise caps.  It is probably a good idea to let us add a small one in if you use high gain or have noise issues in your setup.  We can also change the size of the one included with the Yellow 250 option.
  • More Highs - The RR+ and the default RR 250 circuit both reduce the highs at the input to the circuit.  This is even before the capacitor changed with the Smooth Switch option.  The Grey 250 v2 and Yellow 250 Options do not include this high cut.  We can adjust this cut so that more highs are allowed to pass into the circuit.  This is not presently switchable.
  • More Bass - The RR+ and RR 250 circuit doesn't have a Tone control.  Instead, as you increase the Gain, the bass is reduced to prevent the sound from getting muddy, leaving it bright to cut through the mix.  At high gain levels, the sound can be pretty thin and bright.  We can adjust this so that less bass is lost as the Gain is increased.
  • Gain Control - This option changes the character of the circuit, which may not be what you want.  Normally, as you adjust the Gain, you are also adjusting the tone, more gain cuts more bass.  We can change this behavior so that the tone doesn't change as you change the Gain.  Only the Gain will change, and it will have a bit larger range of gain available.
  • Soft Clipping Switch - This option allows you to add soft clipping in the gain stage, a new feature for the circuit.  We allow for one or two simple clipping configurations of your choice, along with the option of no soft clipping.  We recommend that you select no clipping for one switch setting, then add one or two types of clipping for your second and (optional) third switch settings.
  • Hard Clipping - The RR+ configuration uses (2) germanium 1N270 hard clipping diodes.  The RR 250 configuration uses a pair of silicon 1N4148 hard clipping diodes.  You can change those to some other diode configuration.  If you find the circuit doesn't have enough volume for instance, you could double the clipping diodes to make it a bit louder.
  • Hard Clipping Switch - Add a second hard clipping configuration you can select with a switch.  Optionally also include a third switch setting to turn hard clipping off, perhaps so you can use soft clipping.
  • Tone Control - Adds a simple high cut tone control near the end of the circuit.  You'll probably lose a bit of volume, too.  Interacts with Gain and Volume controls.  Might be more interesting along with the Gain Control option.
  • Improved Volume Control - This option just changes the size of the output potentiometer to give it a different feel.  It does not affect the available volume.
  • Carbon Comp Resistors - The original Distortion + used some carbon comp resistors.  By default we use metal film to help keep the noise down, but you may want carbon comp if you want to be closer to the original circuit tone or you just like the sound of carbon comps.
  • Components - We use metal film resistors and a selection of capacitors that provide good tone and low noise. 

 

Front Panel

  • On/Off indicator LED
  • Volume/Level
  • Gain
  • (optional) Smooth Switch
  • (optional) Soft Clipping Switch
  • (optional) Hard Clipping switch
  • (optional) Tone

 

Rear Panel

  • Audio In
  • Audio Out
  • On/Off Footswitch
  • On/Off Override
  • DC Power
  • DC Power LED

 

Module Width

  • 1.5" standard
  • 2.0" with options
  • 2" left wing available for standard 4-control configuration
  • 1.5" right wing available for standard 4-control configuration

 

Power Consumption (aprox)

10 - 15mA

 

Base Configurations

Part # Description List Price
MOD-RR+ RR+ module $209
MOD-RR250V1 RR 250 V1 module $209
MOD-RR250V2 RR 250 V2 module $209
MOD-RR25080 RR 250 80 module $209
MOD-RR25090 RR 250 90 module $209
MOD-RR308 RR 308 module $209

 

Options

Part # Description List Price
MOPT-RR-SMSW Smooth Switch $19
MOPT-RR-SCRIPT Script $0
MOPT-RR-BLOCK Block $0
MOPT-RR-OPA Custom Op Amp $0-TBD
MOPT-RR-NOISE Noise Cap  $0
MOPT-RR-MHI More Highs $0
MOPT-RR-MLO More Bass $0
MOPT-RR-GAIN Gain Control $0
MOPT-RR-SCLIPSW Soft Clipping Switch  $19-TBD
MOPT-RR-HCLIP Hard Clipping $0-TBD 
MOPT-RR-HCLIPSW Hard Clipping Switch  $19-TBD
MOPT-RR-TONE Tone Control $19
MOPT-RR-VOL Improved Volume Control $0 
MOPT-RR-CCRES Carbon Comp Resistors $5 
MOPT-RR-CC Component Changes $0 - TBD