Author Topic: Preamp works only when JMP3 jumper is on

February 11, 2021, 09:04:09 pm
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hypnotoad

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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. 



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?

February 12, 2021, 11:17:17 am
Reply #1

JPK

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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).
« Last Edit: February 12, 2021, 11:19:41 am by JPK »
JPK

February 12, 2021, 12:53:21 pm
Reply #2

hypnotoad

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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!!

February 12, 2021, 02:58:16 pm
Reply #3

JPK

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JPK

April 07, 2021, 11:52:54 pm
Reply #4

newsoulebel

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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?!!!

April 08, 2021, 11:09:08 am
Reply #5

JPK

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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.
JPK