Gear / Technical Help > Pre's, A/D's and Processors
DIY: Graham Patten DMIC-20 variable gain/trim mod
Brian Skalinder:
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.
(((KB))):
Does anyone know who did the Mod(or orig owner) on this DMIC-20?
http://taperssection.com/index.php?topic=59434.msg784291#msg784291
(((KB)))
poorlyconditioned:
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
cmoorevt:
--- Quote from: poorlyconditioned 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
--- End quote ---
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
poorlyconditioned:
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
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