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Topics - Tomsouthtrader

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Tubes and Hybrids / VHT Classic 18 Preamp Modification
« on: September 21, 2020, 08:14:49 AM »
Hello There
I have been trying to modify my VHT Classic 18 (basically a cheep Chinese amp based loosely on a Marshall 18w circuit).
Essentially I am trying to completely bypass the awe full input gain stage that uses a TL072. And wire the guitar straight to the input of the first preamp tube..
I have found the schematic for the amp, and working from that I got the soldering iron out..
My aim was to completely remove the TL072 from the circuit and wire the input straight into the tube.
The schematic I have attached shows what I have done to the circuit.
The amp didn't blow up thankfully.
And it does make a sound... And The tone itself is not to bad (at least through the LO input).
However it now has a couple of issues  :-[

The input is now incredibly noisy. There is some sound even when the master is at minimum.
Also the treble control when turned all the way up makes make an awful noise (almost like some self oscillation). However I had never turned this all the way up before attempting this modification.

So I am asking for you knowlage and advice on how to fix my 'mod'  <3)

Link to the schematic and my 'MOD'..
https://drive.google.com/drive/folders/1Q-AdViC60HTd6p0KYzZEajgf1M5A8tYZ?usp=sharing

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