Chunk Chunk Gain Questions

[H.E.L.Shane]

Hey..  I've been lurkin around a bit, finally got my Chunk CHunk built, it works, and sounds GREAT..


All for nodes set to 4.5V, all controls work..  pot is the 1M Audio taper as on the build sheet.

but the Gain, while great, is pretty much unuseable past 12:00 on the knob...  you only get a very little bit of "break up" distortion just after "0" on the gain knob, and then its right into "tear your face off,, and then melt your face off"

not that this is a bad thing mind you...... but, a little more versatility might be warranted,

I guess the question is..

its is supposed to be like that with the J201's...

would a different value gain pot change things?



I've got a second board all but built, but I'm thinkin about trying the 2N5457's in it instead

[H.E.L.Shane]

one thing i did note is that the caps i used for c3 c9 and c14 were 1uf multilayer ceramic, and quite tiny compared to others i've seen on peoples builds


while it appears that eveyone else is using the larger, higher voltage film caps,


diference???


(I build guitars...  i usually only deal with three caps, and i usually use vintage PIO's!!)

[juansolo]

There is another way, we get stonking results doing the following:

First you'll need to make yourself a Fet matcher and grab a multimeter. It's also worth reading this article on Fet matchery by RGKeen.

Ours run J201s in Q1 and Q2, and 2N5457s in the other positions. The J201s had the cutoff voltages measured at about -0.3v, and 2n5457s about -1v.

Using the fetzer valve formula for biasing, (0.6*supply voltage)+(0.7*positive cutoff voltage), everything has sounded great straight away. As an example a 2N5457 with -1v cutoff would be biased at 5.4v + 0.7v = 6.1v.

For buffer stage at the end we used a 2N5457 with the highest cutoffs we had. We also swapped out C16 for a 10nF to remove some high end fizz.

This makes the effect a hell of a lot more versatile. It'll still chug with the best of them, but you'll find that at the end of the gain dial now. Elsewhere it can do stuff like this:

[pryde]

What JS said above, I followed his method and had great results with the chunkie-chunk. Helped the pedal do either a nice, mid-rangy marshall or a scooped boogie. found a nice sweet spot in between.

[Hangingmonkey]

Thanks for the tip juansolo. I might just build another dr boogie and try it that way

[H.E.L.Shane]

Ok....   so i know enough about electronics to be  dangerous!!


I see the Jfet tester board has:



Drain - Source- Gate and Drain...


why two drains when a Jfet only has one??

Oh...  and ANY op amp...  i got a few laying around from building Fuel Cut Defense circuits for RX-7 Turbo II's!



PS.. thanks  a lot for the reply, definaly going to build the next one your way

[juansolo]

So you can plug in Fets that are DGS or DSG (check the datasheet for the Fet to find out which way it is) without having to bend the legs. The two drains are linked on the Fet matcher.

[H.E.L.Shane]

So you can plug in Fets that are DGS or DSG (check the datasheet for the Fet to find out which way it is) without having to bend the legs. The two drains are linked on the Fet matcher.

Ooooooooooooooo   DUH... I saw that they were linked across the bug board, but the answer was so stupidly obvious that it didnt click....

Thanks!!!

I'm pretty obtuse for a smart guy sometimes....

[H.E.L.Shane]

OK.. one more thing....

THe gain pot...

would switching this to 500K give you about half of the overall gain, just bradening the control sweep

(Ie full bore is now 50% of what the 1 meg would give)

Or would it alter the circuit (like switching the volume pot on a humbucker guitar from 500k to 250k  pushes the resonant frequency around)

[juansolo]

The problem you have is that each stage has too much. It depends how you want to tame it. It's a more useable effect (IMO) done our way.

[H.E.L.Shane]

OK.. gonna make an FET board..

but.. what the heck is this prototyping board actually called??

[juansolo]

It goes by the following names: prototyping board, vero board and strip board. Not to be confused by perf board which is also called prototyping board and just features little copper circles rather than strips

[H.E.L.Shane]

uuugh... thanks... i was putting "strip board" into the item search and nothing.... remove the space and put in "stripboard" and they come up...