Help With Left Channel Hum

Monjul · 19th April 2010, 07:26 PM

Hi.

After enjoying some sonically significant upgrades to a Cary SLA 70A Signature EL-34 P-P amp which includes a complete re-tube, new filter caps, coupling caps and cathode bypass caps I'm dissapointed that a low level hum still exists in the left channel. Although you have to place your ear close to the speaker to hear it, I'm somewhat surprised that the issue wasn't resolved along with the recent component changes. The right channel is dead quiet, btw.

I've attached a schematic but need to warn you I am somewhat of a novice when it comes to utilizing them. Any advice would be welcome. Thanks.

bigwill · 19th April 2010, 07:28 PM

Does it go away with only one channel connected from the preamp?

Monjul · 19th April 2010, 07:32 PM

Quote:

Originally Posted by bigwill

Does it go away with only one channel connected from the preamp?

No, and forgot to mention that. It is originating somewhere in the power amp.

bob91343 · 19th April 2010, 11:14 PM

The resistor in the filament wiring is marked SELECT so maybe you need to change that one. That's the one at the bottom of the diagram.

Else you may have a heater-cathode leakage on the 6SL7; did you swap them?

If the two channels are operating from separate power supplies perhaps one supply is not properly filtered; look at the 500V electrolytic capacitors.

Are the two units wired identically? You could have a ground loop injecting hum into the amplifier input.

Monjul · 21st April 2010, 10:24 AM

Quote:

Originally Posted by bob91343

The resistor in the filament wiring is marked SELECT so maybe you need to change that one. That's the one at the bottom of the diagram.

Else you may have a heater-cathode leakage on the 6SL7; did you swap them?

If the two channels are operating from separate power supplies perhaps one supply is not properly filtered; look at the 500V electrolytic capacitors.

Are the two units wired identically? You could have a ground loop injecting hum into the amplifier input.

Both the inverters and filter caps are new. All the tubes have been replaced.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Left channel dead	doubled	Solid State	10	11th April 2010 11:19 AM
Can I have the sub woofer channel and the left and right channel as one?	Boscoe	Chip Amps	7	21st February 2010 05:56 PM
Hum in left channer - rogers cadet 3	cr0wl3y	Tubes / Valves	6	7th January 2010 11:44 PM
Hum left channel on Threshold SA3 (I know its not a pass labs but...)	Tino	Pass Labs	3	30th May 2008 02:53 PM
Need help with hum and faint left channel on my S5 Electronics kit	Neville	Tubes / Valves	4	15th January 2007 10:58 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

19th April 2010, 07:28 PM	#2
bigwill diyAudio Member Join Date: Dec 2004 Location: UK	Does it go away with only one channel connected from the preamp?

19th April 2010, 11:14 PM	#4
bob91343 diyAudio Member Join Date: Mar 2010	The resistor in the filament wiring is marked SELECT so maybe you need to change that one. That's the one at the bottom of the diagram. Else you may have a heater-cathode leakage on the 6SL7; did you swap them? If the two channels are operating from separate power supplies perhaps one supply is not properly filtered; look at the 500V electrolytic capacitors. Are the two units wired identically? You could have a ground loop injecting hum into the amplifier input.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)