Author Topic: Dirtbag Resistor values and Treble Adjust  (Read 1665 times)

Trash Cadillac

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Dirtbag Resistor values and Treble Adjust
« on: July 01, 2012, 09:22:16 PM »

There are a couple of resistor values I have a question about in the Dirtbag schematic.
R56 and R57 are 27k, in the original DMM these values appear as 27k and 2.7k.
Is this just an original typo or does this difference affect anything?

Also, there are a few posts in the forum about getting a little more treble in the Dirtbag delays.
This seems to be the only area where comparisons to the original DMM fall a bit short.

Which are the best areas to play with (cap and resistor changes)for some extra treble, or maybe bass cuts.

Any tweaking advice greatly appreciated.


« Last Edit: July 18, 2012, 02:24:28 AM by Trash Cadillac »

Trash Cadillac

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Re: Dirtbag Resistor values and Treble Adjust - Follow Up
« Reply #1 on: July 18, 2012, 02:40:19 AM »

Just a quick follow up on this topic.

I finished a new MN3005 Dirtbag and did find it very dark on the repeats.
Lucky the chips I bought worked first time, and even repeated without a bias when I fired it up.
Way darker than an old DMM I could compare it to.
It still sounded fantastic, just dark repeats. Very strong repeats as well.
And a lot darker than the MN3205 version I built earlier.

So I checked all my components and found nothing wrong component value wise.
I had a good look at posts here and info from other sources.
I swapped all the TL072P chips out for old school 4558's and that actually thinned it out a bit,
and did not make it appreciably noisier or worse sounding.  Just a bit less hi fi.

I also checked a couple of schematics and found that the values for C32 and C4 near the output were different on a couple.
Nearly every other component was the same or equivalent value. Great job done by Mad bean on
his schematic.
So I swapped those, and voila, old school charm. Brighter and clearer.
C32 became 10uf (not 22) and C4 became 22uf (not 47).
These could be switched in and out I suppose.
I lost some delay time so I  changed C41 to about 270pf and that was enough extra.
No obvious weirdness in the longer delays either.

Maybe someone more techie than me can explain the changes/interactions caused by the swap.

Basically this now sounds really, really close to a DMM.

There is some great info others have provided that show how to thin repeats by adding a tone control to
the feedback area.
Swap C5 for about 3300pf and put the 22nf off one leg of a 500k pot to allow fatter or thinner repeats.
I have not tried this, but some seem to like it for variations on a theme.
Sounds like a great add on though.
Link below.

Eventually I will do a proper audio or YouTube comparison between:

Dirtbag MN3205, Dirtbag MN3005, DMM and BOSS DM2(has MN3005 chips).




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Re: Dirtbag Resistor values and Treble Adjust
« Reply #2 on: July 19, 2012, 09:33:45 AM »
Brilliant I'm going to try this. Thanks.


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Re: Dirtbag Resistor values and Treble Adjust
« Reply #3 on: September 01, 2012, 05:42:24 PM »
Really nice!

I had the same problem, but decided to build a new one with low profile parts and maybe even the stupid electrolytic arrangements (it doesn't look series wiring, as the anodes, or catodes in our case, are facing each other) as in the original DMM.

I also noticed those different values you mentioned, except for the 2.7K, made the changes but they haven't made my dirtbag sound like the original one. I may be missing something there, but I'll pay more atention on my new build... Anyway, for now I have really nice sounds coming from the unit, but it is a different beast for sure.

One thing I noticed is that the repetition starts with low volume (maybe have to tweak the gate around the ne570). That kills the crispy strat string attack on the repetitions, and maybe is responsible for what I perceive as dark first repeat.

The tone control is a really nice feature! I have done something similar to my DM-2 and it is really cool now. That piercing 12th or so repeat before going into crazy oscilation is gone, and it didn't affect the first repeats.

Will let you guys know how that went.



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Re: Dirtbag Resistor values and Treble Adjust
« Reply #4 on: September 06, 2012, 02:12:40 AM »
Interesting, it appears the values are from the new factory schematics, I doubt the change of C32 makes much difference but C4 should as it's a high pass filter. Changing that changes it from a 0.1hZ corner frequency to 0.2hZ.

You could play with R5 to get some brighter or darker tones too.
Works at Lectric-FX


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Re: Dirtbag Resistor values and Treble Adjust
« Reply #5 on: December 01, 2012, 07:49:29 PM »
Hey guys, just wanted to add some feedback to this discussion since it's been helpful to me.

I can say that changing both C4 and C32 makes a difference in the tone of the effect. I first tried swapping C32 to 10uf and found that it did offer brighter repeats. C4 was next and it had the effect of making the final sound of the blended signal a little brighter as well. I did like the sound of the dirtbag before these changes but even more so now.

I'm not sure how these changes would result in a shorter delay time as was mentioned above.

Between those changes and changing R11 and R12 to 39k I am quite pleased with the results.