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So I've just bought a Chinese (AXL) 18w marshall clone (model name is Medway special...very similar to the VHT 18W standard) - it sounds very nice, but has a bit of low level hum (50hz, doesn't change with pre or post volume) ...not overbearing but I can hear it so it niggles me.
Just wondering if this is common amongst the genre?
Here's the schematic...
VHT Classic 18 Schematic.PDF
don't think it's PSU caps (as the hum is 50Hz not 100Hz) ...also the hum is getting into the signal after the master vol (because even when this is turned down I hear the hum) ...so that narrows it down a bit (possible tube issue?)
...you'll see there's some opamps at the front of the circuit...I'm not too happy about this, but if I bypass then I'll lose the pre gain control . As it goes I think the op amp's gain is too hot as it's difficult to get a totally 100% clean signal out of the amp. I was thinking of replacing the tl07 circuit with a Tilman fet amp (lower gain, better sound vs the tl072 )...anyone done this (or pondered it?)
Just wondering if this is common amongst the genre?
Here's the schematic...
VHT Classic 18 Schematic.PDF
don't think it's PSU caps (as the hum is 50Hz not 100Hz) ...also the hum is getting into the signal after the master vol (because even when this is turned down I hear the hum) ...so that narrows it down a bit (possible tube issue?)
...you'll see there's some opamps at the front of the circuit...I'm not too happy about this, but if I bypass then I'll lose the pre gain control . As it goes I think the op amp's gain is too hot as it's difficult to get a totally 100% clean signal out of the amp. I was thinking of replacing the tl07 circuit with a Tilman fet amp (lower gain, better sound vs the tl072 )...anyone done this (or pondered it?)
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