another case of gainclone hum

adolphe · 24th April 2006, 04:16 PM

Okay, so I've had a few of Peter Daniel's gainclone kits running for a few months now, and I can't get rid of the hum. It's definately audible through the speaker from the listening position when no source is connected to the amp and gets slightly louder when I connect a source. I've tried rewiring it a couple times now, and I've got it at it's quietest, but I still consider it unacceptable (compared to my Denon receiver hooked up in the same room to the same source and speakers which has no hum unless you have your ear right up the driver and even then, basically negligable).

So I'd like some help in troubleshooting this. I have a theoretical background in electronics, but this is the first amp I've built. I've made a diagram showing how I've wired things. I'll take a picture of the actual construction later if need. I built it on a piece of MDF for now.

The first time I used strainded hookup wire, and the newest hookup revision I've used solid core copper. The chips are mounted to heatsinks using mica/thermal compound. You can consider my mains "poor" as the electricity in my neighbourhood is pretty dirty, and the wiring in my house is equally poor, but as noted my Denon amp runs fine.

Suggestions!?!?

-Scott

adolphe · 24th April 2006, 04:21 PM

the forum is saying my image has errors, just trying to upload it again.

-Scott

Cortez · 24th April 2006, 06:52 PM

Look how the high current wires are so close to each other, not forming a great loop.
And not just the rails, but also the speaker wires are close to the rails, and to each other.
The signal should go from the RCA directly to the PCB and just after that to the MAIN GND !
Keep the wires really close to each other, and the signal wires far as possible from high currents.
With a layout like this you shouldnt get any hum, I promise !

But if this doesnt solve your humm, you have something other problem wich doesnt appear on yourt drawing,
like wirings between to two amps, or with using the safety earth a wrong way, or inappropriate shielding, etc.
Good luck !

billdinva · 25th April 2006, 10:30 AM

You are missing a connection to earth. Connect the house safety earth wire to the chassis. If you transformer has a metal case also connect this to ground Then connect the PG+ and PG- to that connection. That should take care of the hum.

To test: short the input. You should only hear a quiet hiss which is the residual noise of the system. Try hooking up a battery powered CD player. You should not have any hum. The try a mains CD player. If you have now have hum you have a earth loop. See the article on earthing at http://sound.westhost.com/

Computer audio has an inherently noisy ground. This creates other issures. But that is another thread.

Fossil · 25th April 2006, 12:29 PM

I thought it's OK to isolate the safety earth from the circuit ground?

In any case, check whether the RCA body is touching the chassis. If both RCA body touching, it may form a grd loop

kvholio · 25th April 2006, 01:50 PM

If you have audiosector-pcb, signal-ground(sg) and output-ground(og) are connected at the pcb.If you run wires like in your drawing you are causing groundloop by connecting those two at your wiring-terminal.try running shielded wire from rca-input to sg at pcb and in at pcb.

Klaas

billdinva · 25th April 2006, 02:03 PM

Fossil, I think that what is meant by an "isolated ground" is one which the chassis ground and circuit are separated by a ground breaker (resistor and capictor).

The circuit ground needs to be referred to earth otherwise it will float.

adolphe · 25th April 2006, 03:01 PM

Thanks for the replies everyone. I think my RCA's may not be properly isolated from the chassis. I'll try reworking that, as well as seperating in-gnd and o-gnd from the terminal block.

-Scott

Fossil · 26th April 2006, 01:53 AM

Quote:

Originally posted by billdinva
Fossil, I think that what is meant by an "isolated ground" is one which the chassis ground and circuit are separated by a ground breaker (resistor and capictor).

The circuit ground needs to be referred to earth otherwise it will float.

what's wrong with floating the DC ground?

billdinva · 26th April 2006, 02:51 PM

Assuming the ground floats halfway between V+ & V-. any difference between V+ & V- will be amplified at the output. I'll try to simulate this evening (USA EDT).

24th April 2006, 04:16 PM	#1
adolphe diyAudio Member Join Date: Jun 2005 Location: Ontario / Kentucky	another case of gainclone hum Okay, so I've had a few of Peter Daniel's gainclone kits running for a few months now, and I can't get rid of the hum. It's definately audible through the speaker from the listening position when no source is connected to the amp and gets slightly louder when I connect a source. I've tried rewiring it a couple times now, and I've got it at it's quietest, but I still consider it unacceptable (compared to my Denon receiver hooked up in the same room to the same source and speakers which has no hum unless you have your ear right up the driver and even then, basically negligable). So I'd like some help in troubleshooting this. I have a theoretical background in electronics, but this is the first amp I've built. I've made a diagram showing how I've wired things. I'll take a picture of the actual construction later if need. I built it on a piece of MDF for now. The first time I used strainded hookup wire, and the newest hookup revision I've used solid core copper. The chips are mounted to heatsinks using mica/thermal compound. You can consider my mains "poor" as the electricity in my neighbourhood is pretty dirty, and the wiring in my house is equally poor, but as noted my Denon amp runs fine. Suggestions!?!? -Scott

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25th April 2006, 10:30 AM	#4
billdinva diyAudio Member Join Date: Mar 2006 Location: Virginia	You are missing a connection to earth. Connect the house safety earth wire to the chassis. If you transformer has a metal case also connect this to ground Then connect the PG+ and PG- to that connection. That should take care of the hum. To test: short the input. You should only hear a quiet hiss which is the residual noise of the system. Try hooking up a battery powered CD player. You should not have any hum. The try a mains CD player. If you have now have hum you have a earth loop. See the article on earthing at http://sound.westhost.com/ Computer audio has an inherently noisy ground. This creates other issures. But that is another thread.

25th April 2006, 12:29 PM	#5
Fossil diyAudio Member Join Date: Sep 2001 Location: SG	I thought it's OK to isolate the safety earth from the circuit ground? In any case, check whether the RCA body is touching the chassis. If both RCA body touching, it may form a grd loop

25th April 2006, 01:50 PM	#6
kvholio diyAudio Member Join Date: Jul 2005 Location: leeuwarden	If you have audiosector-pcb, signal-ground(sg) and output-ground(og) are connected at the pcb.If you run wires like in your drawing you are causing groundloop by connecting those two at your wiring-terminal.try running shielded wire from rca-input to sg at pcb and in at pcb. Klaas

25th April 2006, 02:03 PM	#7
billdinva diyAudio Member Join Date: Mar 2006 Location: Virginia	Fossil, I think that what is meant by an "isolated ground" is one which the chassis ground and circuit are separated by a ground breaker (resistor and capictor). The circuit ground needs to be referred to earth otherwise it will float.

25th April 2006, 03:01 PM	#8
adolphe diyAudio Member Join Date: Jun 2005 Location: Ontario / Kentucky	Thanks for the replies everyone. I think my RCA's may not be properly isolated from the chassis. I'll try reworking that, as well as seperating in-gnd and o-gnd from the terminal block. -Scott

26th April 2006, 02:51 PM	#10
billdinva diyAudio Member Join Date: Mar 2006 Location: Virginia	Assuming the ground floats halfway between V+ & V-. any difference between V+ & V- will be amplified at the output. I'll try to simulate this evening (USA EDT).

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