Sound Skulptor forums
Build help and troubleshooting => MP573 Microphone preamplifier => Topic started by: hypnotoad on February 11, 2021, 09:04:09 PM
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Hi! build the preamp last week and when testing everything worked fine. The readings I got when checking with my multimeter was 24.4V in the first test (TP2 <-> V+) with power transformer out, and 24.3V with power transformer in.
Everything sounded fine, and I have only recorded bass guitar D.I with it since I buid it.
However, tonight I was gonna record some vocals and there's no signal at all from the preamp. Did the setup guide once again and found out that the preamp only pass microphone signal when the JMP3-jumper is on.
So I read on this forum from another person that there could be something wrong with the diode's on the D.I module. I checked them with my multimeter and both where fine. I did all the measure points in the guide on this forum, and got the readings:
A - 2.59v
B - 4.08v
C - 22.4v
D - 13.50v
E - 2v
F - 12.87
G - 0.92v
H - 4.11v
I - 0.347v
J - 3.51v
K - ? couldnt measure as there was no point to attach my probe.
L - 3.02v
To me they all seem to be more or less fine.
Should mention that the bass guitar sounds wonderfull thru it also!
However, In the process of building it I made an error. I soldered the pins on the D.I-module the wrong way and had to redo it. In the process of heating away the solder I think a ring conecting the pin to the pcb got lost.
I include a picture so you can see what I mean.
(https://www.dropbox.com/s/xr7cgderjk082tc/IMG_0647.jpg?dl=0)
Could this be why the preamp dont pass signal?
If that's the case, can I maybe jump the bad pin to where it should connect?
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Check that all the connections of the DI connector (red lines in the picture) are OK.
If all OK then try changing the 2N7000. This device is sensitive to static electricity and should be handled with your body grounded (removing your shoes is generally enough).
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Hi! I bridged the second last pin to where it would be connected via the pcb, and now everything works =)
Thank you very much!!
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Congratulations!
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Check that all the connections of the DI connector (red lines in the picture) are OK.
If all OK then try changing the 2N7000. This device is sensitive to static electricity and should be handled with your body grounded (removing your shoes is generally enough).
man I have blown a few of these doing the DI boards. Its a pain in the ass.
I have a DI board right now that is not working because othe 2n7000.
JP, just exactly how sensitive are these?!!!
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I never blow any, simply by removing my shoes when I handle them. It keeps the body at ground level.
Some careless vendors may supply already damaged devices. I have had several. The ones in our kits are 99.999% OK.
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I'm not sure anyone will check this again but if OP happens to have those pictures I'd love to check them out to see if that would point me in the right direction. I'm not sure I made the same initial error but my end result is similar. Works amazing with JMP3 on through the mic, works great through the DI when its off but never both.
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You probably have a damaged 2N7000 on the DI board.
This unit is sensitive to static electricity and must be handled with your body grounded (shoes removed).