Top Cut Circuit

[quayhog]

Do I need to make the capacitor value larger or smaller to increase useable range on a top cut circuit, (Vox type)? I currently have a 250kl in line with a .0068uf cap. That was the nearest value I had on hand.

The Vox AC15 schematic show .005uf for normal/treble models and a .01 for bass models. The Weber AC30 kit shows a .01uf. Has anyone here experimented with the circuit limits? It is counterintuitive to me. It seems it should act like a master volume.

Does the type of cap have an effect on tone? Poly, P&O, orange drops etc.

Jonathan

[iknowjohnny]

the bigger the cap the bigger the cut because basically what it's doing is cutting only the frequencies the cap can pass. So the larger the cap the wider range can be cut. Try a .022uf. It may seem big, but it really smooths things out nicely in some amps. It may be too much in some. but where i've tried it it was nice. It gives a smoother and wider cut sorta like gradually cutting a graphic EQ from say 500Hz to 10k on a linear curve. Going with what you have will be a more sharp transition because it's cutting along a much lesser width. Not saying it's better, but give it a shot. I liked it best. In fact, try a pair of alligator clips and just go thru various values. then once you fin the one you like find the deepest cut you'd ever use and measure the pot then use one of a close value to that measurement. just some suggestions for you from my experience. But one more thing....realize that the more you cut the more volume the amp will lose because basically all a cut control is is a frequency dependent volume control. I ended up not keeping that circuit because to get the tone i wanted the amp's volume was cut way down.

[Darkbluemurder]

It really depends on whether you want to shape the tone color with the cut control (then a bigger cap would be better) or if you want to only remove the most offensive high frequencies to smoothe out the overdrive(then use the smallest cap that gives you the desired response). There is no single best solution here - your ears decide what is the best value for this particular amp. Values I have seen range from 2200pf (Matchless), 4700pf or 5000pf (Vox) to 10nf (=0.01uf, Dr. Z). I use 3300pf in my Club Deluxe clone (Top Boost preamp circuit).

Cheers Stephan

[Darkbluemurder]

It is counterintuitive to me. It seems it should act like a master volume.

Does the type of cap have an effect on tone? Poly, P&O, orange drops etc.

Jonathan

If you leave the cap out you have the cross line master volume that is found in many Matchless amps. Personally I don't like how it sounds when turned down.

The type of cap for the cut control does have an effect on tone but this is rather subtle. I used PIO, Orange Drops and Sozo, all with good results.

Cheers Stephan

[M Fowler]

I use what I have in stock as long as it's .0047