trainwreck express master volume

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bagudan

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Joined 2010
#1
I have built myself a trainwreck express. It is the best amp I have made yet, but it is unreasonably LOUD. I know it is supposed to be loud, and I know it´s not meant for master volume. but I wanted to try it anyways.
I made a simple master volume with a 1meg pot, and it was horrible. Anyone out there who has had succes with a different type of master volume on an amp like this?

shematic:
http://www.ampspecs.com/wp-content/uploads/2015/07/Trainwreck-Express-Schematics.png

Master volume (no good)
http://music-electronics-forum.com/attachments/39070d1462878995-trainwreck_mv_type3.png

Best regards - Kasper
 
#2
As I see in the schematic above posted, there is in my opinion, a mistake. The two coupling capacitors of .001µF makes no sense for me. I believe one of them must be almost .1µF.

Also, I see a master volume following the first ½12AX7. If you need another one, add it at the input end, in the same mode as this other, and remove the 1MΩ grid leak resistor.
 
#3
Osvaldo de Banfield said:
As I see in the schematic above posted, there is in my opinion, a mistake. The two coupling capacitors of .001µF makes no sense for me. I believe one of them must be almost .1µF.

Also, I see a master volume following the first ½12AX7. If you need another one, add it at the input end, in the same mode as this other, and remove the 1MΩ grid leak resistor.
Click to expand...

No mistake - the parallel coupling caps of different construction are a Trainwreck feature.

Where did you put your attempted MV?
Have you thought of the valvewizards PI MV?
 
#4
I don't believe that "Type 3" cross line master is suitable for a fixed biased amp. It is going to mess with the output tube bias.
Go back to the Trainwreck pages - I think what you need is the Type 1.
https://robrobinette.com/The_Trainwreck_Pages.htm

The Master Volume performance will be somewhat compromised because it will then be inside power amp feedback loop, but many have successfully used it anyway.

You can also scan the Trainwreck discussion forum here:
http://ampgarage.com/forum/viewforum.php?f=1

Cheers,
Ian
 
#5
I have the "Lar Mar" in my Express. Have a NF loop doesn't matter IMHO. When on "10" the schematic is identical to not having a MV. It works very well.

Also added one to my '71 Deluxe Reverb and it works even better in there. I often don't bring pedals to jams any more with the DR since I have Reverb, Trem and overdrive all inside.
 
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