Need help understanding Matchless Hotbox Clean Channel circuit

[Frankgb]

Hi,

Can someone explain the use/purpose of the paralleled 560pF cap and 220k resistor after the Clean Volume control???

I'm trying to figure out why this valve circuit sounds different to my Valve Junior, they are basically the same except for these two components, but the HB has an extra little something that I can't seem to replicate in my Junior.

many thanx

Frank Berend

[Mike Burgundy]

It has been said before (in a sticky, even) and probably will have to be said again, but links to schems will facilitate getting answers. Now people have to decide if they want to start searching for it first - or guess at how it looks.
That said, are the circuits really the same? I believe the VJ is a small amp whereas the Hotbox is a preamp. Have you isolated both stages into an identical setup?
If that's all yes, then it might just have to do with component value variation. Tubes vary a LOT, as do caps.
a 560pF cap is smallish so it either tames highs (if it's directed to ground) or all the rest (series). With a 220k and 560p in a standard highpass configuration the corner frequency would be just over 1.2KHz, so that would definitely add some audible bite.
You could take it out and see how that sounds.

[terminalgs]

the 560pf cap allows some high frequencies to pass through,  frequencies that cannot get through the  cap, must go through the 220k resistor.   more high end,,  bite.. like Mike B. posted.   depending on what schematic you find for the EVJ,  you might find one with a similar cap/resistor arrangement drawn at the point of the 1M R just prior to the volume pot with the cap drawn as "empty" (I'm guessing the circuit board has a place for such a cap, but it is omitted).

So, it seems you are comparing the 1st stage and EQ/vol circuit of the Hotbox to the 1st stage and volume of the EVJ.  although they are indeed similar in basic terms ( 12ax7 gain stage followed by a volume pot ),  there are a other differences besides the one you are asking about...  other differences: a 250k volume pot instead a 1M.  the volume pot has a 180pf bypass cap,  the EVJ does not has a bypass cap.  these would  effect tone as well.   

if you want the hotbox sound from a EVJ,  look at Vox modes for the EVJ,  or replace the EVJ preamp with the preamp from a Vox Top Boost.