Hum in my gainClone

MadFinn · 13th June 2006, 06:32 AM

I have a strange problem with my gainclone. It's a Brian GT LM 3886 kit Made a own preamp but when i connected it to the Amp i got a pretty loud hum from the amp. When i use a older Pioneer Preamp there is no hum Can anyone explain this for my Why hum when connected to one preamp (and my surrond recivier) but not the Pioneer preamp

sreten · 13th June 2006, 11:11 AM

Hi,

probably ground loops. Hum when preamp is earthed, not when fully isolated ?

/sreten.

Craig405 · 13th June 2006, 11:39 AM

Hi,

You might want to check your shielding of leads from the pre to the power amp. You must only have the shields grounded at one end (either pre end or power amp end) to avoid a potential ground loop.
Also dont connect signal grounds to chassis or mains earth grounds, you may have done this with your preamp.

Regards
Craig

DJ Exprice · 14th June 2006, 07:17 PM

Did you place BIG capacitors across the + and -? For good quality, more than 4700µF makes a clean output. I once made the mistake of using a single 2200µF for a BR smoother and got a big ol' hum

DIAR · 14th June 2006, 07:37 PM

I have only 2 x 100+1000 uF (Black Gate) with LM3875 and I can hear humming (100 Hz) when my ear is right next to the cone.

DJ Exprice · 14th June 2006, 07:43 PM

Oh...well i guess I was wrong then...
I guess the amp i was making was having a different hum problem

13th June 2006, 06:32 AM	#1
MadFinn diyAudio Member Join Date: Jan 2006 Location: Småland	Hum in my gainClone I have a strange problem with my gainclone. It's a Brian GT LM 3886 kit Made a own preamp but when i connected it to the Amp i got a pretty loud hum from the amp. When i use a older Pioneer Preamp there is no hum Can anyone explain this for my Why hum when connected to one preamp (and my surrond recivier) but not the Pioneer preamp

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13th June 2006, 11:11 AM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, probably ground loops. Hum when preamp is earthed, not when fully isolated ? /sreten.

13th June 2006, 11:39 AM	#3
Craig405 diyAudio Member Join Date: Jul 2005 Location: Sussex	Hi, You might want to check your shielding of leads from the pre to the power amp. You must only have the shields grounded at one end (either pre end or power amp end) to avoid a potential ground loop. Also dont connect signal grounds to chassis or mains earth grounds, you may have done this with your preamp. Regards Craig

14th June 2006, 07:17 PM	#4
DJ Exprice diyAudio Member Join Date: Mar 2006 Location: San Francisco, California	Did you place BIG capacitors across the + and -? For good quality, more than 4700µF makes a clean output. I once made the mistake of using a single 2200µF for a BR smoother and got a big ol' hum

14th June 2006, 07:37 PM	#5
DIAR diyAudio Member Join Date: Jun 2004 Location: Capital City Area	I have only 2 x 100+1000 uF (Black Gate) with LM3875 and I can hear humming (100 Hz) when my ear is right next to the cone.

14th June 2006, 07:43 PM	#6
DJ Exprice diyAudio Member Join Date: Mar 2006 Location: San Francisco, California	Oh...well i guess I was wrong then... I guess the amp i was making was having a different hum problem

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