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Old 26th June 2012, 06:03 AM   #1
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Question Help with preamp build

Hey all.

I've built a Velleman preamp but am having problems with it working. Besides soldering mic cables and crossovers, I haven't had any experience with building kits. Here are some pics of what I've done. I will gladly send it to someone to fix for me (will pay, of course) unless you can tell me something to try, I just don't know. I would love to have this work.

Preamp Project pictures by nonsuchpro - Photobucket

Thanks in advance!
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Old 26th June 2012, 07:20 AM   #2
godfrey is offline godfrey  South Africa
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What's wrong with it? What does it do (or not do)?
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Old 26th June 2012, 10:17 AM   #3
DF96 is online now DF96  England
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You have a meter, and some knowledge of how to use it?
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Old 26th June 2012, 10:30 AM   #4
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Quote:
Originally Posted by godfrey View Post
What's wrong with it? What does it do (or not do)?
It doesn't pass signal. If i turn up the volume, it does make a slight buzz. Not sure if this is the issue but it only has 2 pins for IN and 2 or OUT. Since I'm using XLRs, I assumed I would do hot where it say "signal" and pair the black and ground on "ground". The trim pot is working, just no audio. Mic works direct into amp, but not through my box.
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Old 26th June 2012, 10:31 AM   #5
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Originally Posted by DF96 View Post
You have a meter, and some knowledge of how to use it?

I have a multimeter and have some knowledge on how to use it. I know how to test voltage, ohms and amps.
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Old 26th June 2012, 01:53 PM   #6
godfrey is offline godfrey  South Africa
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Hmmm.....
  • Maybe the input's not connected correctly.
  • What kind of microphone is it? Does it need phantom power?
  • What kind of wall-wart power supply is that? I hope it's DC and connected the right way around. (Don't try reversing it if you're not sure).
  • Sorry, but this is a lousy circuit for a mic preamp anyway.

[OT]
Seems like there's a gap in the market for decent kits. A few weeks ago someone else had problems with another, even worse kit in this thread.
[/OT]
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Last edited by godfrey; 26th June 2012 at 02:00 PM.
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Old 26th June 2012, 02:09 PM   #7
DF96 is online now DF96  England
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Check DC conditions e.g. opamp output pins 1 and 7. It should be about half the supply voltage. Unplug the input, and put your finger on the input pin. Do you get a loud hum?
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Old 27th June 2012, 04:50 AM   #8
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Quote:
Originally Posted by godfrey View Post
Hmmm.....
  • Maybe the input's not connected correctly.
  • What kind of microphone is it? Does it need phantom power?
  • What kind of wall-wart power supply is that? I hope it's DC and connected the right way around. (Don't try reversing it if you're not sure).
  • Sorry, but this is a lousy circuit for a mic preamp anyway.

[OT]
Seems like there's a gap in the market for decent kits. A few weeks ago someone else had problems with another, even worse kit in this thread.
[/OT]
I double checked the input. Maybe I should try with something other than a mic. I know this is a bs circuit. I just want it working
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Old 27th June 2012, 04:51 AM   #9
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Quote:
Originally Posted by DF96 View Post
Check DC conditions e.g. opamp output pins 1 and 7. It should be about half the supply voltage. Unplug the input, and put your finger on the input pin. Do you get a loud hum?
Will try this, ty!
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