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Originally Posted by compuryan /img/forum/go_quote.gif
Sachu, I reassessed my hum this morning. At normal listening volumes, I can't hear any hum through the headphones. However, I can hear a faint hum from the unit itself though. When I turn up the volume to about 2 or 3 o clock I can hear the same hum coming through the headphones and it is noticeably stronger through the left channel.
From talking to others, about the only way to isolate the hum is to move the transformer to a different chassis or buy a completely shielded one. I'll probably perform one of those upgrades down the road. I really should wire for SE, it'd be a heck of a lot easier for trying different phones head-fi meets, it'd require some additional wiring and a switch too. Still not sure on that one, maybe.
Thanks for the knobs site, Erik. I really like the look of some of those.
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Thanks for the info Ryan.
I think you could try a few things first before moving the transformer in to another chassis,
1> You have about 3-4 inches of space between the amp boards and the front panel..try moving at least the left chanel ones closer to the front panel and see if it reduces the hum.
2> Try to implement the signal input wiring with shielded wires instead of basic hook up wire (this solved my hum problem in my other amplifier taht i built for speakers)
3> Move the transformer more to the top left corner (as far as possible).
4> After you have done one or all of the above, Turn off your amp, disconnect from mains, insulate all mains wiring with insulation tape, loosen the transformer. PLug in your amp and phones, slowly turn (rotate) the transformer in either direction to see if the hum reduces in any given direction.
If none of these work, then i guess you could go with a shielded transformer or a differnet chassis solution.
I am still trying to make up my mind, but am now leaning towards the shielded one.
Already got a quote for the sumr transformers (checking to see if it needs an inrush limiter)..I was hoping to get the unshielded transformers and see if it works and use the extra 100$ that the shielded transformer would cost to get front panels made at FPX. The advantage I think of having the power supply (including the sigma 22) in a different chassis would be to be able to use it with other amps such as a EHHA which I really really liked (fantastic match with the sennheisers).
The SE wiring makes a lot of sense, and am sure many people at your upcoming meet would love to have a try at your amp with their SE phones.
I am planning my layout for a balanced and single ended operation similar to the Krmathis amp..with the exception of me adding a mute switch on it when connected to speakers.
