Repairing a Class A MOSFET headphone amp.
I say repair but it turned out to be quite a simple job! Members may recall I recently sold my Iota Audio headphone amp which I was very fond of. As a result I decided to get out an old DIY amp that I'd bought cheaply which had a hum (that got louder as you turned it up) and a channel imbalance at low (but regularly used) levels. I also thought it lacked a bit of bass.
I ordered a cheap stereo pot and fitted it the other night once the kids had gone to bed.
https://www.ebay.co.uk/itm/Stereo-Ve...-/123868039337
I plugged in a pair of cheap headphones to test, which still had the hum, but then I changed to my HD650s and there was no hum at all. I've no idea why, could it be an impedance mismatch? I'd initially put it down to the closeness of the transformer to the PCB.
Also, it sounded lovely and just had an imbalance right at the bottom of the volume range below listening levels. Still not as rich a bass as I'd ideally like, but very neutral and, more importantly, natural sounding. So all in all a great result and a good value replacement for the Iota amp.
What I find most interesting is the name on the PCB. It appears to be by Yulong Audio but I can't find any reference to the model on the internet. Could be a prototype design? The guy I bought it off was Chinese and said his friend made it.
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