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Author Topic: DIY: Graham Patten DMIC-20 variable gain/trim mod  (Read 3741 times)

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Offline Brian Skalinder

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DIY: Graham Patten DMIC-20 variable gain/trim mod
« on: August 02, 2004, 12:21:20 PM »
Thanks to Dr. Phob for this one!!


NOTE: this doesnt replace the use of the dip switches, it just gives you the option to fine tune the gain in-between the 5db increments that the dip switches give you.

was doing one this weekend for someone, so i decided to take some pics along the way....

open the dmic20 up, slide out the board and locate the 2 internal gain pots..


they are located at R65 and R66


flip the board over and locate the solder points. you will need a de-solder tool for this.


after de-soldering, you should be able to remove the pots with a small pair of needle-nose pliers or a pair of electronic tweezers.



you should be left with nice clean holes on R65 and R66..


use some good 3 conductor wire, and prepare the ends with a fine coat of solder.



solder your wires to the board, making sure the colors are consistant in each hole. its best to pull the wires thru the back as far as possible. then solder the back enuf to secure the wires. clip off the exess the same height as the other soldered compenents, and add another drop of solder.



make sure to use matching rated potentiometers. they are 5K ohm, .25w   Calrad is pretty much the only manufacturer you will find easily.


i clipped off the little solder contacts sticking out sideways, and soldered the wires directly in the holes. this is the easiest and most compact way to do it. this is the right channel pot. i mounted then with the contacts on the side facing away from eachother. given the way i have the wires soldered to the board, the wiring of this pot is backwards.  so youll have to flip the white and the bare wires.


drill holes the front faceplate. i have a template, but its best to trace out the outline of the pots the way you can fit them the best, and measure out were to drill the holes. drill a guide hole with a tiny bit first. you dont really have much chances to redo this part. the very first one i ever did was pretty bad, but i coaxed GP into sending me a new faceplate :) 

use whatever knobs suit your fancy.  here are 2 options:




a good way to test it hook up everything with mics and all in a quite room, put your deck in record and slap some headphones on and crank the gain dip switches up as high as possible, and move the knobs around, shake the unit, etc to see if you hear any static or unusual noises. its best to do this before and after your mod, so you know if you have introduced a problem.


See some follow-up discussion in the original thread.
« Last Edit: February 14, 2005, 10:22:34 AM by dmonterisi »
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Offline (((KB)))

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Re: DIY: Graham Patten DMIC-20 variable gain/trim mod
« Reply #1 on: February 24, 2006, 11:46:00 PM »
Does anyone know who did the Mod(or orig owner) on this DMIC-20?

http://taperssection.com/index.php?topic=59434.msg784291#msg784291

(((KB)))
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Offline poorlyconditioned

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Re: DIY: Graham Patten DMIC-20 variable gain/trim mod
« Reply #2 on: February 25, 2006, 02:10:49 AM »
Hey, I just bought a DMIC-20.  Now I have some questions.  Late, but anyways...

- can I get SPDIF from this thing, eg., to input to a microtrack?  I read somewhere that I have to attenuate the signal as well as make a cable from XLR>RCA.  Also, is the standard OK, for SPDIF input?  Eventually I want to put a TOSLINK output right inside the device if the standard is OK.

- can I change the clock from 48 to 44.1?  It is a crystal, right?

- has anyone used an external clock?  I'm thinking of running SPDIF (RCA) from my UA5 to keep the clocks in sync, and record SBD with the UA5 and mics with the DMIC.

  Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
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cmoorevt

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Re: DIY: Graham Patten DMIC-20 variable gain/trim mod
« Reply #3 on: February 25, 2006, 10:49:02 AM »
Hey, I just bought a DMIC-20.  Now I have some questions.  Late, but anyways...

- can I get SPDIF from this thing, eg., to input to a microtrack?  I read somewhere that I have to attenuate the signal as well as make a cable from XLR>RCA.  Also, is the standard OK, for SPDIF input?  Eventually I want to put a TOSLINK output right inside the device if the standard is OK.

- can I change the clock from 48 to 44.1?  It is a crystal, right?

- has anyone used an external clock?  I'm thinking of running SPDIF (RCA) from my UA5 to keep the clocks in sync, and record SBD with the UA5 and mics with the DMIC.

  Richard


Re: question #1: Yes.  If you want to use the bnc output on the front, you'll need a BNC>RCA adapter and then whatever coax cable you want into the MT.  I bought my supplies at markertek and would suggest getting a right angle bnc>rca as the regular straight ones stick out quite a bit.  There was a picture of a leegeddy bnc>rca cable around here, but I can't seem to find it. 

If you want to use the AES output on the back:

http://www.taperssection.com/index.php?board=14%3baction=display%3bthreadid=7676

Offline poorlyconditioned

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Re: DIY: Graham Patten DMIC-20: change clock 48k > 44.1?
« Reply #4 on: February 25, 2006, 03:09:04 PM »
Does anyone know if/how to change the clock on these?  I've got (I think) a 48k model and want to run at 44.1k.  I suppose I could either change the clock (crystal or some part of circuit?) or try to sync to an external clock (eg., from a UA5).

Thanks,
  Richard
Mics: Sennheiser MKE2002 (dummy head), Studio Projects C4, AT825 (unmodded), AT822 franken mic (x2), AT853(hc,c,sc,o), Senn. MKE2, Senn MKE40, Shure MX183/5, CA Cards, homebrew Panasonic and Transsound capsules.
Pre/ADC: Presonus Firepod & Firebox, DMIC20(x2), UA5(poorly-modded, AD8620+AD8512opamps), VX440
Recorders: Edirol R4, R09, IBM X24 laptop, NJB3(x2), HiMD(x2), MD(1).
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Offline Chuck

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Re: DIY: Graham Patten DMIC-20 variable gain/trim mod
« Reply #5 on: February 11, 2007, 09:00:44 PM »
Hey, I just bought a DMIC-20.  Now I have some questions.  Late, but anyways...

- can I get SPDIF from this thing, eg., to input to a microtrack?  I read somewhere that I have to attenuate the signal as well as make a cable from XLR>RCA.  Also, is the standard OK, for SPDIF input?  Eventually I want to put a TOSLINK output right inside the device if the standard is OK.

- can I change the clock from 48 to 44.1?  It is a crystal, right?

- has anyone used an external clock?  I'm thinking of running SPDIF (RCA) from my UA5 to keep the clocks in sync, and record SBD with the UA5 and mics with the DMIC.

  Richard


Richard, I want to do all of that. Did you ever figure it out?
I want to sync my V3 to a DMIC-20 to sync SBD recordings to microphones. I want to add an optical output and I want to do a gain knob mod. I suspect you can make the knobs continuously variable and do away with the switches. I don't have the DMIC-20 yet, so I don't know if that's the way to go, or if it is best to keep the switches and use the knobs for trim control, like on the V3.

It appears you can switch the DMIC-20 clock from 48 kHz to 44.1 kHz with DIP switches inside. I'd like to know if this works too. There is a chart somewhere. I'll post it when I find it.
« Last Edit: February 11, 2007, 09:43:22 PM by Chuck »
Reality is merely an illusion, albeit a very persistent one.

Microphones: (2) Microtech Gefell M300, (2) AKG C 480 B comb-ULS/ CK 61/ CK 63, (2) CAD GXL1200 (cardioid and sub-cardioid capsule & electronics mod), (2) Audix M1290-o, (2) Micro capsule active cables w/ Naiant PFA's, (2) Naiant MSH-1O, (2) Naiant AKG Active cables, (2) Church CA-11 (cardioid), (2) CAD C9, (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Tascam DR-680, iRiver iHP-120 (Rockboxed & RTC mod), Denon DTR-80p

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline (((KB)))

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Re: DIY: Graham Patten DMIC-20: change clock 48k > 44.1?
« Reply #6 on: February 12, 2007, 05:41:20 PM »
The DMIC20 will sync to an external clock w/ the rear BNC "AES SYNC" INPUT.
-Seems to me that this is the easiest way to run 44.1k with a 48k box.

I've read that you CAN swap crystals and change the internal dip to change it over to 44.1, of course assuming that you already have obtained a 44.1 crystal to begin with.

I have to be honest in saying that I personally do not have the technical expertise to attempt this myself, but if someone knows what they're doing with this, it can be done. I'd be interested in seeing photos if anyone tries it.

-Kevin
« Last Edit: February 12, 2007, 05:50:49 PM by (((KB))) »
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Offline Chuck

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Re: DIY: Graham Patten DMIC-20: change clock 48k > 44.1?
« Reply #7 on: March 02, 2007, 10:41:57 PM »
The DMIC20 will sync to an external clock w/ the rear BNC "AES SYNC" INPUT.
-Seems to me that this is the easiest way to run 44.1k with a 48k box.

I've read that you CAN swap crystals and change the internal dip to change it over to 44.1, of course assuming that you already have obtained a 44.1 crystal to begin with.

I have to be honest in saying that I personally do not have the technical expertise to attempt this myself, but if someone knows what they're doing with this, it can be done. I'd be interested in seeing photos if anyone tries it.

-Kevin


The DMIC20 will sync to an external clock w/ the rear BNC "AES SYNC" INPUT.
-Seems to me that this is the easiest way to run 44.1k with a 48k box.

Yes, this does indeed work.

I've read that you CAN swap crystals and change the internal dip to change it over to 44.1, of course assuming that you already have obtained a 44.1 crystal to begin with.

Having coorisponded with a tech at GP, I learned that this can be done. He told me it would require swapping out the crystal, which is soldered to the circuit board. He also indicated that there would need to be some calibration done. He even said he could send me the crystal, if I wanted to do it myself.

I hope to be done moding my DMIC-20 in the next week or so. I'll post photos if anyone is interested.
Reality is merely an illusion, albeit a very persistent one.

Microphones: (2) Microtech Gefell M300, (2) AKG C 480 B comb-ULS/ CK 61/ CK 63, (2) CAD GXL1200 (cardioid and sub-cardioid capsule & electronics mod), (2) Audix M1290-o, (2) Micro capsule active cables w/ Naiant PFA's, (2) Naiant MSH-1O, (2) Naiant AKG Active cables, (2) Church CA-11 (cardioid), (2) CAD C9, (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Tascam DR-680, iRiver iHP-120 (Rockboxed & RTC mod), Denon DTR-80p

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

Offline Chuck

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Reality is merely an illusion, albeit a very persistent one.

Microphones: (2) Microtech Gefell M300, (2) AKG C 480 B comb-ULS/ CK 61/ CK 63, (2) CAD GXL1200 (cardioid and sub-cardioid capsule & electronics mod), (2) Audix M1290-o, (2) Micro capsule active cables w/ Naiant PFA's, (2) Naiant MSH-1O, (2) Naiant AKG Active cables, (2) Church CA-11 (cardioid), (2) CAD C9, (1) Nady SCM-1000 (mod)
Pre-amps: Naiant littlekit v2.0, BM2p+ Edirol UA-5, Church STC-9000
Recorders: Tascam DR-680, iRiver iHP-120 (Rockboxed & RTC mod), Denon DTR-80p

Recordings on the LMA: http://www.archive.org/bookmarks/ChuckM
Recording website & blog: http://www.timebetweenthenotes.com

 

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