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DirtBag v3205 distortion

Started by madbean, December 12, 2011, 10:42:32 PM

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madbean

See this thread first for newer modifications: http://www.madbeanpedals.com/forum/index.php?topic=3366.0

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Here is the solution (copied from the updated project doc) to eliminate the distortion issue with the v3205 version of the DirtBag. As promised, it's a super-easy fix!

REVISION (CRITICAL): Some builders of the v3205 version of this project have run into distorted repeats. There is a simple solution to this issue. Replace R21 (1k) with 100k and C14 (33n) with another 100k resistor. This forms a voltage divider which eliminates overloading the lower headroom of the v3205. The original 1k/33n forms a low pass filter with a corner frequency of about 4825 kHz. Even though this fix eliminates this filter, it seems that the low overhead of the v3205 does not impact the delay tone in a significant way. Further tests also found that R10 could be omitted from the compressor portion of the NE570, but this is not critical. As a reminder, you will want to use 47k for both R11&R12 when building the v3205 version.

The project document has been updated with the revision: http://www.madbeanpedals.com/projects/Dirtbag/DirtBagDeluxe.zip

I'm really sorry for those who felt frustrated over the past few days. But, I hope that frustration will quickly go away once you hear how much better your new delay is going to sound :)

Mich P

I think you mean C14 for the 33nF.

madbean


LaceSensor

Thanks for the fix
Im in Denmark but will try this wednesday night
Im a bit sad as I know that I tried in vain to remove c14 already.
Hopefully I wont mash my board getting it out.

RonaldB

THanks Madbean,
I will change this on my board and check my delay tonight.

RonaldB

LaceSensor

Didnt completely solve things for me.

Scruffie

Bean, did you see in the 'Dirtbag Troubles' thread the stuff I mentioned about the Compander voltages? It's set too hot at the moment, R11 & 12 should both be 24k, not 47k and we also need to change the other output, looking at some DMM voltages, while it should be about 1/2 supply, it's under that so i'd suggest rather than the 'correct' value of 24k for R42 we use a 33-47k there.

Then rather loosing a low pass filter, it may be preferable to change both R13 & 14 to 33k to reduce clipping, give that a whirl and see if it improves stuff.
Works at Lectric-FX

madbean

Scruff,

Thanks, I've actually been tweaking with those values. I'll try the 33ks, too. It's getting closer....I have a few final ideas to try out today. I'm also comparing voltages to the AquaPuss on the compander, and just generally audio probing both circuits.

Interestingly, I was reading a little review by Culturejam yesterday complaining about the repeats on his EHX Memory Boy yesterday. Those use four 3208s. They are so cheap I might pick one up just as a reference point to improve the DirtBag.

Scruffie

Quote from: madbean on December 16, 2011, 01:18:54 PM
Scruff,

Thanks, I've actually been tweaking with those values. I'll try the 33ks, too. It's getting closer....I have a few final ideas to try out today. I'm also comparing voltages to the AquaPuss on the compander, and just generally audio probing both circuits.

Interestingly, I was reading a little review by Culturejam yesterday complaining about the repeats on his EHX Memory Boy yesterday. Those use four 3208s. They are so cheap I might pick one up just as a reference point to improve the DirtBag.
I've got a Memory Toy, I think the repeats are fine! Then again I think culturejams admitted now he just doesn't like BBD Delay. Anyway, could be a good idea to grab one.

22/24k for R11 & 12 is fine, relatively, pin 7 is biased to around 7V on a normal Memory man (from the voltages I saw) so that's half the 15V supply, 22 or 24k in R11 & 12 got Lace Sensor 4.5Vish when I suggested he try it.

But on the other output of the Compander, on the Memory Man voltages I saw it was a lot lower than half supply (where it would normally be) so 33k should lower it down below half supply, as once again Lace Sensor got 4.5Vish when I told him to use 24k for R42.

Works at Lectric-FX