Request for trainwreck clones owners (new sound on a switch)

[roberto]

Hi everyone,

I would like to ask a favour to the owners of a clone of trainwrecks here on the forum, to do a simple and in my opinion effective mod.
Based on the schematic posted here: https://ampgarage.com/forum/viewtopic.php?f=3&t=5691
and more specifically this one: https://ampgarage.com/forum/download/file.php?id=6854

I would like to ask to:
- disconnect R7 from the ground reference;
- install a voltage divider formed by a 1 M resistor and a 5k trimmer (plus a 10u pot to stabilize the voltage) from the PI node to ground;
- connect R7 to the wiper of the trimmer;
- raise the reference voltage of the grid of the 3rd stage until you get the same polarisation as it has 1k5 on its cathode (à la Fender);
- play it and report the impressions.

The reason why I don't do that is that I don't have a similar amp on hands to test the idea, but it gave good results on ther circuits.
Of course the trimmer can be set wherever you like it most. This is also part of the results I would like to see based on everyones' tastes.

Just not it will not sound like a 3 stage Fender, because many parts of the circuit are different, but it seems to me an easy way to get more sounds from a very simple and effective circuit.

Thank you in advance

Roberto

[norburybrook]

is this for Express or Rocket builds?...or any?




M

[norburybrook]

is this for Express or Rocket builds?...or any?



:edit just seen it's for express sold my 2. Just have a rocket.




M

[roberto]

You can extend the same concept to the Rocket as well.

Based on this circuit: https://ampgarage.com/forum/download/file.php?id=8003
taken from here: https://ampgarage.com/forum/viewtopic.php?f=3&t=5684

Disconnect the grounded side of the pot P1 and connect it to the same configuration as above.
On the other side, you can try to give negative reference to the grid of V1a and set it colder (like it had 2k2 or higher on the cathode) by scaling down the 1 M resistor and connecting it to the first filtration stage of the bias supply.

Thanks in advance.

[roberto]

One important note before anyone does this mod: pay attention you are configuring a voltage divider from an high voltage supply node.
Maximum attention must be paid to all steps!

[stephenl]

Express V2a Mod.pdf

[roberto]

Exactly that! This is what I sketched on my phone to describe it to a friend of mine.

mixed bias gain stage - Roberto.jpg

PS
1 Mohm should be right, but if you find the 5 kOhm pot not to have effect, lower the dropping resistor from 1 MOhm to 470 kOhm.
It also depends on the voltage on the node.