KMD - Distortion 70's  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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ppluis0
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Post by ppluis0 »

DjPsychic wrote: 21 Sep 2021, 18:30 Finally getting a chance to play around with this circuit. The vintage unit has an incredible sound but the amount volume is quite limited.

What components could be altered to provide a bit more volume/headroom?
Hi Dj,

As Soulsonic wrote in a previous post:
Soulsonic wrote: "If you replace the two germanium diodes with silicon ones, like 1N4148, and it will likely be very obviously louder. Replace them with red LEDs and it will be very loud. But this also changes the tone of the distortion, but maybe in a way that you will like.
If you remove the old diodes carefully, you can put them back and make it "original" again if you ever wanted to sell it."
All the volume issues are due the two germanium diodes: good sound but at lower junction voltage.

Cheers,
Jose

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Intripped
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Post by Intripped »

what Ppluis0 and Soulsonic said.
...If you have two others germ diodes you could try and put them in series with the originals: in this way the character of the distortion should be similar, while having some more volume available.

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DjPsychic
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Post by DjPsychic »

ppluis0 wrote: 21 Sep 2021, 19:22
DjPsychic wrote: 21 Sep 2021, 18:30 Finally getting a chance to play around with this circuit. The vintage unit has an incredible sound but the amount volume is quite limited.

What components could be altered to provide a bit more volume/headroom?
Hi Dj,

As Soulsonic wrote in a previous post:
Soulsonic wrote: "If you replace the two germanium diodes with silicon ones, like 1N4148, and it will likely be very obviously louder. Replace them with red LEDs and it will be very loud. But this also changes the tone of the distortion, but maybe in a way that you will like.
If you remove the old diodes carefully, you can put them back and make it "original" again if you ever wanted to sell it."
All the volume issues are due the two germanium diodes: good sound but at lower junction voltage.

Cheers,
Jose
Probably should've read that before asking. Thanks for pointing that out!

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DjPsychic
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Post by DjPsychic »

Intripped wrote: 21 Sep 2021, 21:32 what Ppluis0 and Soulsonic said.
...If you have two others germ diodes you could try and put them in series with the originals: in this way the character of the distortion should be similar, while having some more volume available.
I was hoping there was a resistor at the output I could play with like on a MXR Dist +

I've actually removed a diode in situations like a D+ with good results. But this particular pedal sounds really nice as is, just wish I had a little more volume.

Thanks!

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Intripped
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Post by Intripped »

well, this circuit is very close to the MXR Dist+ (same topology, some values changed), so you can modify it in the same ways.
here are some examples of mods from Mr. Wampler, also member on FSB, on PremierGuitar:
https://www.premierguitar.com/gear/mxr- ... -plus-mods

Regarding the output resistor R5, yes, you could try and lower its value; but because it forms a low-pass filter with C5, you should increase the value of this cap accordingly.
here's a tool that may help you, the target is to keep the corner freq the same:
http://www.muzique.com/schem/filter.htm
for example you could try R5=1k and C5=47nF, or R5=5k and C5=8.2nF

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