Buzz on preamp

alexmoose · 13th December 2006, 02:07 PM

Hello everybody.

I recently built a simple 5687 preamp found on Diyparadise. The preamp has a great, rich tone, but has an annoying buzz. The Buzz is only present when the volume is NOT turned all the way up. The preamp uses a dual chassis design, and I am really up the creek on this one!

I thought maybe if I physically placed the Output/coupling Cap directly on the RCA jack instead of on the plate, (and having a wire connecting the cap to the RCA jack) that would fix it, but I don't know! please any suggestions would be very appreciated.

-Alex

SY · 13th December 2006, 02:51 PM

This is most likely a grounding issue; the "buzz" gives it away as ripple pickup. A few photos would help trace it down. Moving the coupling cap is unlikely to do much.

alexmoose · 13th December 2006, 04:32 PM

Would a ground issue really get quiter as the volume knob went up?

SY · 13th December 2006, 04:50 PM

Depending on where it is in the circuit, yes indeed, it could.

alexistheo · 13th December 2006, 05:22 PM

Is the body of the volume pot grounded?

alexmoose · 13th December 2006, 06:04 PM

it is attatched to the metal chassis, however I will most deffinatly attatch it to the ground in a better wat once I get a chance

alexmoose · 15th December 2006, 04:22 PM

I grounded the pot case, and It still makes the same buzz. It almost sounds like interferecne....

jayme · 15th December 2006, 04:56 PM

Do you have star grounds?

I had buzz until I separated my star ground into 2: One for the PSU section and one for the Signal section. I then connected the Signal star ground to the PSU star ground with a 10R resistor.

That fixed up the hum issue very nicely!

Oh, and make sure your case is ONLY grounded at one point...preferrably very close to the power IEC socket and connected directly to the ground pin on the power input.

Joel · 15th December 2006, 06:12 PM

Quote:

Originally posted by jayme
...preferrably very close to the power IEC socket...

RCA recommends at the signal input jack.

alexmoose · 15th December 2006, 07:17 PM

I have two gounds, one for the bias circuitry, and one for everything eles. I have a dual chassis design, so ground directly to the IEC connector is impossible. I will try to make everything ground in the same place when I get a chance

13th December 2006, 02:07 PM	#1
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	Buzz on preamp Hello everybody. I recently built a simple 5687 preamp found on Diyparadise. The preamp has a great, rich tone, but has an annoying buzz. The Buzz is only present when the volume is NOT turned all the way up. The preamp uses a dual chassis design, and I am really up the creek on this one! I thought maybe if I physically placed the Output/coupling Cap directly on the RCA jack instead of on the plate, (and having a wire connecting the cap to the RCA jack) that would fix it, but I don't know! please any suggestions would be very appreciated. -Alex

13th December 2006, 02:51 PM	#2
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	This is most likely a grounding issue; the "buzz" gives it away as ripple pickup. A few photos would help trace it down. Moving the coupling cap is unlikely to do much. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

13th December 2006, 04:50 PM	#4
SY diyAudio Moderator Join Date: Oct 2002 Location: Austin, TX Blog Entries: 1	Depending on where it is in the circuit, yes indeed, it could. __________________ “Listening to records is like ****ing a picture of Brigitte Bardot.” - Sergiu Celibidache

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13th December 2006, 04:32 PM	#3
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	Would a ground issue really get quiter as the volume knob went up?

13th December 2006, 05:22 PM	#5
alexistheo diyAudio Member Join Date: Jun 2004 Location: New York City	Is the body of the volume pot grounded?

13th December 2006, 06:04 PM	#6
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	it is attatched to the metal chassis, however I will most deffinatly attatch it to the ground in a better wat once I get a chance

15th December 2006, 04:22 PM	#7
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	I grounded the pot case, and It still makes the same buzz. It almost sounds like interferecne....

15th December 2006, 04:56 PM	#8
jayme diyAudio Member Join Date: Sep 2005	Do you have star grounds? I had buzz until I separated my star ground into 2: One for the PSU section and one for the Signal section. I then connected the Signal star ground to the PSU star ground with a 10R resistor. That fixed up the hum issue very nicely! Oh, and make sure your case is ONLY grounded at one point...preferrably very close to the power IEC socket and connected directly to the ground pin on the power input.

15th December 2006, 07:17 PM	#10
alexmoose diyAudio Member Join Date: Mar 2006 Location: Michigan	I have two gounds, one for the bias circuitry, and one for everything eles. I have a dual chassis design, so ground directly to the IEC connector is impossible. I will try to make everything ground in the same place when I get a chance

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