Please meet JOCELYNE (Express)

[Lonely Raven]

Very nicely laid out!

[godi]

For some reasons, I don't like the presence control, not very effective in my opinion. I follow exactly the layout in the Trainwreck file section using a 5 K pot. My little 4-4-0 and the Liverpool are using 25 K presence pot, any suggestions to make the presence pot more usable ?

Thank, Jean

[martin manning]

Godi, you could try increasing the size of the 0.1uF presence cap to move the knee frequency of the feedback network lower. That will cause the presence control to reduce the feedback over a wider range of frequencies. It should be easy to clip an additional cap across the existing one to try out larger values. You can also increase the amount of feedback by decreasing the value of the 100k feedback resistor, which will also accentuate the effect of the presence control. Since you want to lower the value of the FB resistor, it is again easy to clip another resistor across the existing one to try it.

[jelle]

Also keep in mind that you changed the grounding scheme. That affects things a bit as well.

Jelle

[godi]

He Martin Manning, good suggestions, in fact I did both mods, I add a 0.047uF cap to the existing 0.1uF (for a total of 0.147uF) and I reduce the feed back resistor from 100K to 85K, it's a little more effective.

Iv'e learn someting, thank

I also change some wires at the pots, pink diden't match with the green.

Jean

[martin manning]

I also change some wires at the pots, pink diden't match with the green.

That must be what did it ;^)

[godi]

Here is JOCELYNE with a completed face plate :

[img525]http://www.jeangodbout.com/trainwreck/express-11.jpg[/img]

I use a Robert CRUMB train drawing I found on Internet

Theses Trainwreck amps play loud, even with 6V6