LM-741 OP AMP based amplifier circuitry. Design is based upon a DOD-250. Hand-wired and soldered. Shielded signal wires. Real heavy box! Controls are 1 VOLUME and 1 GAIN. The gain potentiometer value is 1M! (over twice the value of the leading DOD-250 copy) 1 nonfunctional foot switch. Modified to use either a 9 volt battery or a 9 volt external power source.

This petal is the same type used by Yngwie Malmsteen to hotten up the Marshalls he uses.

He is famous for endorsing the DOD-250 and attributes this petal (or the modern clone he now uses) for his signature sound when used with an old Marshall 50 watt amplifier.

The MRR-250 is a simple guitar signal amplifier that will give a low or high gain amplifier a boost with no frills (just a gain and a volume knob).

Actually, its the DOD-250 from the Guitar Effects web site (http://www.generalguitargadgets.com/). I would have loved to put all of the information on how to build it, but this is forbidden by the guitar effects web site.

This petal makes the clean channel of my Marshall sound like its switched to the boost channel (not quite the same sound, but more of an 80's sound like Randy Rhodes). Used with the gain on your Plexi-50-type amplifier, you can increase the sustain and drive the sound real hard (compress the hell out of it).

The sound I get with the amps high gain and this petal to hotten it up is great for playing real heavy (but clear articulation is possible). I see why Yngwie stuck with this one tone for all of these years.

I am able to dial in a good sound with this petal.

As I said, the Guitar effects web site prohibits posting the good information on building this petal, but does a much better job of consolidating everything you need to build it.

See the DOD-250 project page at: GENERALGUITARGADGETS.COM

The build took me an evening and one morning.

Most of that time was spent preparing the box to be used.

I used hand-twisted connections with solder glaze, and then trimmed short to under 1/4 inch.

I used shielded cable for the input and some possible high gain whistler wires, but I did not hook up the ground wires. As it turned out, I did not have to.

The cost was $26.00 in parts.

Radio Shack had all of the parts I needed, except a 500 K linear potentiometer and a 0.05 uF capacitor.

I substituted the 500 K linear for a 1 Meg linear and the 0.05 uF capacitor was substituted for a 0.047 uF (its within 20% tolerance of 0.05 uF anyway).

The testing went rather well.

I did not have to do anything but assemble it after testing.

This was because I checked each connection several times, and did not try to build it in one night (in one sitting).

I was concerned that the substitution I did on the capacitor and the gain control would have made part of the ranges unusable. But as it turns out, this was not the case.

The petal (to my pleasant surprise) operated as you would expect. It works with both the PLEXperimental-50 and my transistor G100R Marshall head, and is fully functional.

The only issue was that I wired the gain potentiometer backwards, so it goes the 'wrong' way. This is no big deal, as it really does not matter!

The board is a rough hand-wired copy of the design given on the guitar effects web site (http://www.generalguitargadgets.com/). It measures about 7 square centimeters and uses 22 gauge wire (left over from the PLEXperimental 50). This is a basic OP AMP amplifier circuit that is almost exactly copied by the MXR Distortion+ petal.

 

This is the final assembly (after the successful test). The monster box allowed me to spread everything out. Note the (un-depleted) shielded cable used.

I noticed that the R6 in the schematic and layout guide is referred to as a 4K7. I am sure this was a typographical error. I found that the MXR distortion + schematic properly referred to it as a 4.7K resistor.

I used 1N4148/1N914 diodes as what was recommended (I believe these where the original values DOD used on their 250 petal).

I used insulated jacks.

The 1M linear (gain) works well and does not do more than turn into the Jimi Hendrix (Live at Woodstock) sound when cranked up. There are no other effects to this substitution.

The shielding did seem to have an effect (moving the wires around during testing seemed to suggest this).

I recently wired the power jack to accept a 9 volt input (or a battery).

I burned up the 741 in the petal while testing the Mr Theremin with the petal. Nothing on the petal worked until I replaced the 741 with a new one (this circuit may be sensitive to voltage from the input).

I did not include sound files, as this petal sounds like any other distortion petal I have heard or owned (also I am running out of room my ISP allows for server space).

The selection "Hate Farm" (on my MP3.COM site) used the petal for all of the solo work. The petal allowed the already high gain amplifier to get even hotter. I got the dark Yngwie-tone with this combination, but mostly used this combination for the great sustain and rich harmonics.

http://artists.mp3s.com/artists/278/michael_r_rogers.html