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JGAN 28th May 2012 03:17 PM

Buzzing in preamp circuit?
 
Hey guys,
I finally finished my tillman preamp circuit :D I will be posting more on it later, but it seems to be helping the tone quality already. However, I do have a problem with buzzing/humming from the circuit. It happens whenever plugged in and switched on, and I don't think its the battery. The buzzing does go away when I short the input though. Could I have bad jacks?

Thanks,
JGAN

Osvaldo de Banfield 28th May 2012 03:30 PM

... or improperly wired or shielded.

JGAN 28th May 2012 03:49 PM

I don't think I did anything wrong when soldering, but how do I go about shielding?

Osvaldo de Banfield 28th May 2012 04:46 PM

Which is the input impedance of such stuff?

JGAN 28th May 2012 04:54 PM

Discrete FET Guitar Preamp

3.0M Ω input impedance.

Osvaldo de Banfield 28th May 2012 05:06 PM

3Megohm is a very high input impedance. So a good shielding is imperative. Shield al conections from board to the input plug, and tie the shield to gnd of the circuit at only one point. Also, I suggest to add a source follower at the output of your circuit to come from low impedance to a cable then to the amp.

JGAN 28th May 2012 05:10 PM

I actually may have built the circuit wrong. For a n-channel JFET transistor, which is the correct schematic (drain vs source)?
http://www.cliftonlaboratories.com/u...c%20Symbol.gif
Or...
http://upload.wikimedia.org/wikipedi...dep_symbol.svg

doozerdave 28th May 2012 05:13 PM

You may be creating a ground loop with the input equipment. Have you been careful with power and signal grounding in your pre-amp to avoid power noise running along with signal ground?

Osvaldo de Banfield 28th May 2012 05:49 PM

No, most JFET have D & S interchangeable, ans in the particular case yours not, it will not work properly, but isnīt the cause to hum. Distortion may be, but not hum/noise.

JGAN 28th May 2012 09:16 PM

Quote:

Originally Posted by doozerdave (Post 3039953)
You may be creating a ground loop with the input equipment. Have you been careful with power and signal grounding in your pre-amp to avoid power noise running along with signal ground?

I'm not exactly sure what that means?


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