MXR Distortion Plus -- Script vs Block differences?

[Sample]

I have two MXR Dist+ pedals that have different value pots in them.
Can anyone confirm or explain these? And could anyone also explain
what effect the different values will have on the sound of the pedal?

1978 Block logo with script bottom:
Volume pot = 90+k
Distortion pot = 561k

1980 Block logo with block bottom:
Volume pot = 40k
Distortion pot = 1.2meg


All of the schematics I've found on the www appear to specify a 10k
pot for Volume and a 1meg pot for Distortion. I found one textual
description of what the author called an 'original script' model which
said that a 500k pot was used for Distortion.

thanks
ashley

[Andreas Schmidt]

Post by Sample
I have two MXR Dist+ pedals that have different value pots in them.
Can anyone confirm or explain these? And could anyone also explain
what effect the different values will have on the sound of the pedal?
Volume pot = 90+k
Distortion pot = 561k
Volume pot = 40k
Distortion pot = 1.2meg
All of the schematics I've found on the www appear to specify a 10k
pot for Volume and a 1meg pot for Distortion. I found one textual
description of what the author called an 'original script' model which
said that a 500k pot was used for Distortion.

A lower value for the volume pot will reduce the output impedance.
There will be no difference in the sound.
Values down to 10k are possible.
If you use a high value (eg 100k), set the volume to 50% and
drive a long output cable this combination would build a low pass filter.

A higher value for the distortion pot will increase
the maximum gain & distortion.

hth
Andreas

[Sample]

Thanks for the information.

ashley

Post by Andreas Schmidt
A lower value for the volume pot will reduce the output impedance.
There will be no difference in the sound.
Values down to 10k are possible.
If you use a high value (eg 100k), set the volume to 50% and
drive a long output cable this combination would build a low pass filter.
A higher value for the distortion pot will increase
the maximum gain & distortion.
hth
Andreas

[Dwight McNamara]

Post by Andreas Schmidt
A higher value for the distortion pot will increase
the maximum gain & distortion.

Actually, a higher value pot in an mxr dist+ or dod overdrive 250
type circuit, will allow for less distortion when the setting is
attenuated. In a circuit like a proco rat, tubescreamer or ibanez
sonic distortion, where the distortion pot is in the feedback loop
of the opamp, a higher value pot will cause more gain and distortion.
In an mxr dist+ the closer the distortion pot is adjusted towards
ground, the more distortion you will get. To get more distortion than
the circuit is designed for, you need to lower the value of the 4.7K
resistor. Try changing it to 3.3k or for even more distortion, 2.2k.

[Sample]

Post by Dwight McNamara
To get more distortion than
the circuit is designed for, you need to lower the value of the 4.7K
resistor.

What cap or resistor can I change to get an increase in ouput volume?
Now, when the output is maxed, it is about the same volume as when the
pedal is bypassed. With my Rat and Big Muff (especially) the
output/volume control is capable of making the signal much louder than
the Distortion + box.

thanks

[Dwight McNamara]

The .047uf cap in series with the resistor. Lowering the
value of the resistor will increase distortion. You should
increase the value of the cap to keep the bass responce the
same. If you make the resistor 2.2k, then make the cap .1uf.
If you want to increase the amount of volume you get
then change the 10k resistor just before the diodes to 1k.
Then change the diodes from gemanium to silicon (1N4148).
At this point you will probably want to add a tone control
to roll off the highs. The one in the Rat works well for this.
see schematic:
Loading Image...
I did to my mxr dist+ the above that i described. Istead of
using the .0033uf cap in the Rat circuit, I use a 100k pot
and a .0047uf cap and leave the 1.5k resistor out. This
works better in my opinion in the mxr circuit. It works fine
without a buffer at the end of the circuit. Just pop the tone
control between the diodes and the volume control. At this point
the .001uf cap, that is in the mxr circuit, is not really needed
anymore.
Good luck.

[Sample]

Very nice! Thank you.

I did the 1k-ohm resitor change in order to increase output volume and
sure enough it did. I then went to a 100-ohm resistor and it was even
better. Now, the pedal is already louder than my guitarat when I get
to three o'clock on the knob.

About the distorion increase:
Does simply changing the resitor and cap change the reknown sound of
the pedal? Or, will the same distortion sound that the pedal used to
have at 10 now be found at 7?

The Diodes:
Does the type of distortion change when you switch from germanium to
silicon and vice versa?

ashley

Post by Dwight McNamara
The .047uf cap in series with the resistor. Lowering the
value of the resistor will increase distortion. You should
increase the value of the cap to keep the bass responce the
same. If you make the resistor 2.2k, then make the cap .1uf.
If you want to increase the amount of volume you get
then change the 10k resistor just before the diodes to 1k.
Then change the diodes from gemanium to silicon (1N4148).

[Dwight McNamara]

Post by Sample
Does simply changing the resitor and cap change the reknown sound of
the pedal? Or, will the same distortion sound that the pedal used to
have at 10 now be found at 7?

Basic same sound, but more saturated.

Post by Sample
Does the type of distortion change when you switch from germanium to
silicon and vice versa?

That will change the tone a bit. The silicon are more harsh sounding.
If you think of the distortion as crushed glass, the silicon are more
crushed than germanium. A bit more saturated, but I think the germanium
color the sound more. If you add the tone control with the silicon,
then you basically have the sound of a Rat. Maybe try adding the
tone but leave the germanium diodes. It sounds pretty good. I have
experimented with both. You have to listen and decide for yourself.

Post by Sample
ashley

Post by Dwight McNamara
The .047uf cap in series with the resistor. Lowering the
value of the resistor will increase distortion. You should
increase the value of the cap to keep the bass responce the
same. If you make the resistor 2.2k, then make the cap .1uf.
If you want to increase the amount of volume you get
then change the 10k resistor just before the diodes to 1k.
Then change the diodes from gemanium to silicon (1N4148).

[Sample]

I have a vintage white-face Rat already, and a vintage Big Muff as
well so I don't need my Dist+ to sound like a rat. Increasing the
output level was my big concern. Thanks for the tips.

ashley

Post by Dwight McNamara

Post by Sample
Does simply changing the resitor and cap change the reknown sound of
the pedal? Or, will the same distortion sound that the pedal used to
have at 10 now be found at 7?

Basic same sound, but more saturated.

Post by Sample
Does the type of distortion change when you switch from germanium to
silicon and vice versa?

That will change the tone a bit. The silicon are more harsh sounding.
If you think of the distortion as crushed glass, the silicon are more
crushed than germanium. A bit more saturated, but I think the germanium
color the sound more. If you add the tone control with the silicon,
then you basically have the sound of a Rat. Maybe try adding the
tone but leave the germanium diodes. It sounds pretty good. I have
experimented with both. You have to listen and decide for yourself.

[Dope mcSmoke]

As i see it the pot only defines the range of control, max dist is whan the
pot is zeroed, hence the resistor in series with if defines max gain, lower
it to get more. a higher value on the pot only allows you to go lower in
gain and a low value gets a shorter range and you'll be able to finetune it
more.

Post by Andreas Schmidt

Post by Sample
I have two MXR Dist+ pedals that have different value pots in them.
Can anyone confirm or explain these? And could anyone also explain
what effect the different values will have on the sound of the pedal?
Volume pot = 90+k
Distortion pot = 561k
Volume pot = 40k
Distortion pot = 1.2meg
All of the schematics I've found on the www appear to specify a 10k
pot for Volume and a 1meg pot for Distortion. I found one textual
description of what the author called an 'original script' model which
said that a 500k pot was used for Distortion.

A lower value for the volume pot will reduce the output impedance.
There will be no difference in the sound.
Values down to 10k are possible.
If you use a high value (eg 100k), set the volume to 50% and
drive a long output cable this combination would build a low pass filter.
A higher value for the distortion pot will increase
the maximum gain & distortion.
hth
Andreas