Chunk Chunk edit - J201 choice

[hammerheadmusicman]

So I built up my chunk chunk, and is passing signal, lots of volume, lots of gain (all be it a little 'gritty' sounding), all the controls seem to work, but the sound is so thin and shrill.. No bass at all?! It is also a little noisy, but I'm out at the minute and will have another poke around when I get back, and take some voltages and stuff. Just  wondering if anyone else has had an issue like this? I am thinking tonstack, but I don't know yet..

Thanks

George


So, I got it all going, and was wondering as i have a massive bag of j201's and a tester for hFe, what should I go for in the chunk chunk build? I have a few below 300hfe, loads around 330 (+\- 10), some around 360hfe enough to do the whole lot, and a few around 400hfe, should I match them all, or do the same as in an amp and use different gains for different places in the circuit etc?

Thanks again

G

[oldhousescott]

My .02, check out my post on changing the third stage to more closely match the recto schematic. That may help resolve the graininess issue. Also, you can certainly dink around with the tone stack to tailor the response. Reducing C15 to somewhere between 2n2 and 4n7 will reduce the upper mid content and shift the treble corner frequency higher. Likewise increasing C16 will allow more bass to be passed through. You can go as big as you can fit in here, 1u, 2u2, etc., although you'll reach a point of diminishing returns if you try to go much larger. Increasing R16 to 6k8 or 8k2 will scoop the mids a bit more making the bass seem a bit more prominent. Check out the Duncan Tone Stack Calculator for playing with tone stack values (perhaps you're already familiar with it). The Marshall stack is the one you're interested in in this circuit.

[nzCdog]

My .02, check out my post on changing the third stage to more closely match the recto schematic. That may help resolve the graininess issue.

Cool link never saw that thread, thanks oldhouse!  My 0.02... in my latest build I used 2n5457s instead of J201s changed C17 to 100n for a little more bass...

[pickdropper]

My .02, check out my post on changing the third stage to more closely match the recto schematic. That may help resolve the graininess issue.

Cool link never saw that thread, thanks oldhouse!  My 0.02... in my latest build I used 2n5457s instead of J201s changed C17 to 100n for a little more bass...

Yeah, I tend the build this circuit similarly.  I tend to use a mixture of J201 and 2N5457.  I also use 100n for C17.  Any more than that and it gets a really weird resonance in the bass. 

I am not really crazy about the tone stack in general.  I've been meaning to do a layout with a different one but haven't gotten around to it yet.

[hammerheadmusicman]

Thanks dudes, I've got it sounding pretty sweet with some slightly lower gain J201s, and made sure the biasing is bang on 4.50v, which made a hell of a difference! I have put a resistor in series with lug 1 (I think) of the gain pot, so that it doesn't go down all the way, as in the last quater(ish) of the travel was very quiet in volume, which was unusable as it was just too quiet. So I measured the resistance at the point which would be my 'bare minimum'. I found this to be a very simple mod, which made every part of the gain pot usable..

Still tinkering,

Thanks

George

[pickdropper]

I actually bias mine much higher than that, around 6 volts.

[hammerheadmusicman]

Really?it was sounding all. Weird and grainy though.. Perhaps it's the batch of j201s I have? Might get hold of some 2n5457s and whip em in and have a play.. You don't test your jfets gains by any chance do you?

[hammerheadmusicman]

My .02, check out my post on changing the third stage to more closely match the recto schematic. That may help resolve the graininess issue.

Cool link never saw that thread, thanks oldhouse!  My 0.02... in my latest build I used 2n5457s instead of J201s changed C17 to 100n for a little more bass...

C17?  Do you mean C11 or C10? There isn't a C17, unless I've gone a bit mad, and can't see it

George

[pickdropper]

Really?it was sounding all. Weird and grainy though.. Perhaps it's the batch of j201s I have? Might get hold of some 2n5457s and whip em in and have a play.. You don't test your jfets gains by any chance do you?

Yep, but admittedly, I haven't gone back recently and tried it at a lower bias point.  And no, I don't screen the JFET for gain in this build.  I just pre-screen them to make sure they bias in the circuit.

[pickdropper]

My .02, check out my post on changing the third stage to more closely match the recto schematic. That may help resolve the graininess issue.

Cool link never saw that thread, thanks oldhouse!  My 0.02... in my latest build I used 2n5457s instead of J201s changed C17 to 100n for a little more bass...

C17?  Do you mean C11 or C10? There isn't a C17, unless I've gone a bit mad, and can't see it

It depends which schematic you are looking at.  On the original, the it C12 was a 220nF cap.  When Bean redrew it, he changed that designator to C17.  If you look at the schematic in the build docs, You can see that C17 has one leg tied to the net with R16/C16 and the other side tied to the center lug of the mid pot.

George

[hammerheadmusicman]

^its official, I have gone completely mad, I was building a mud bunny (civil war spec) today, and opened the PDF reader on my ipad and looked at the wrong schem,  must be the food coma I have from all the eating in the last two days!

Haha

Thanks again guys,

George

[hammerheadmusicman]

Just out of interest, what positions do you put your j201s and 2N5457s?

George

[pickdropper]

Just out of interest, what positions do you put your j201s and 2N5457s?

George

It really varies as I've used a few different configurations.  I will say that I tend to prefer J201s in the front of it and 2N5457 on the back end.

[hammerheadmusicman]

Thanks, ill give it a try, I do like this circuit though I have to say, nice ballsy distortion!

G

[nzCdog]

LOL!  Hope you recover from your food coma soon