Cherrybomb and ChunkChunk

[juansolo]

I really quite like this. Crank the bass & gain, pull the treble back and it's a thick fuzz. Everything in the centre and it's a nice over drive. That and a distortion inbetween.

Though it has been a good lesson in not being a pikey. This is a recycled enclosure and for the sake of saving a few quid and buying a new one, I just made my life difficult. As the PCB has board mounted pots and both the LED and power socket got in the way (you'll note that the decal has the power where I'd expect it to be had it been a recent build).

That made it awkward, the crushed and therefore shorting power line from said socket took some finding because of this. Then I've managed to grind the head off one of the old screws. As such, a simple build like this ended up taking several hours more than it normally should. I need to be less of a tight arse!





Jaymz3: The final evolution! This was made purely to try out some tweaking of the build. I can no happily say that we've nailed how to do this one in terms of wiring, component choice and biasing. It's as quiet as the 2nd we did but way more useable. Unfortunately this means that mine (number 1) needs completely rebuilding and the 2nd needs some components swapping out...

[pickdropper]

Looks nice and clean as always.

[semicolonoscopy]

Very nice. Is that some Terry Dodson art on the Cherrybomb?

[juansolo]

Very nice. Is that some Terry Dodson art on the Cherrybomb?

Some Malleus promo art.

[Vallhagen]

This was made purely to try out some tweaking of the build. I can no happily say that we've nailed how to do this one in terms of wiring, component choice and biasing. It's as quiet as the 2nd we did but way more useable. Unfortunately this means that mine (number 1) needs completely rebuilding and the 2nd needs some components swapping out...

Very cool. Any hands-on hints you like to share? I am about to build my Chunk Chunk any day (well, any week...). PCB n stuff right here on my desk:)

Cheers

[crash]

+1 to any advise on the Chunk Chunk.

Love the artwork on both.  The Cherybomb brings back memories of the summer of 94 for me.

[chromesphere]

The Cherybomb brings back memories of the summer of 94 for me.

Did you work at a post office in 94 crash?  I also like the picture of the women licking the stamp. haha sorry just having a little joke here with myself...

That Dr Boogeys got enough room left over for a 2nd effect! Nice work!

Paul

[juansolo]

This was made purely to try out some tweaking of the build. I can no happily say that we've nailed how to do this one in terms of wiring, component choice and biasing. It's as quiet as the 2nd we did but way more useable. Unfortunately this means that mine (number 1) needs completely rebuilding and the 2nd needs some components swapping out...

Very cool. Any hands-on hints you like to share? I am about to build my Chunk Chunk any day (well, any week...). PCB n stuff right here on my desk:)

Cheers

I'll poke Mr Clegg (marauder) to respond in detail as he worked it all out. But essentially J201's clip like a bastard with very small voltages. There is an increase in gain but it comes with loads of clipping distortion. The new one has a more usable range, though you just tend to end up with the gain maxed (something you couldn't really do on the original without it going mental).

What he did was meter a load of jfets (can't remember the ones) which then allows you to work out the bias voltages. Then it's pretty much set and forget. We also swapped a cap to pull some highs from it.

Interesting to back-to-back it with the originals, mine we manged to get quite nice but it's noisy as hell due to the wiring. His was quiet but never faded out quite right (mis-biased and we just couldn't get it right). I've since swapped out the fets and cap on his and it's identical to the new one. Just got mine to dismantle now...

We both prefer how it ends up with the new setup.

[marauder]

The Fetzer Valve acticle on ROG was the starting point for the biasing and JFET choices.
http://runoffgroove.com/fetzervalve.html

I already had a JFET matcher for matching JFETs for phaser builds and sorted all my J201s and 2n5457s into cutoff voltage ranges. 
http://www.geofex.com/article_folders/fetmatch/fetmatch.htm
http://www.aronnelson.com/gallery/main.php/v/Richard-Boop-RLBJR65/album81/album75/Fet_Matcher_1.gif.html

I found that all my J201s had a very low cutoff, sometimes below the minimum spec (I chucked these out), but most were around -0.3 -0.7V.  In the above article it mentions that the cutoff voltage is the maximum input signal before clipping will occur.  No tube will clip at such a low input voltage, so a j201 probably isnt a good JFET to emulate a tube. 

The 2n5457s measured from -0.6 -1.5V, much higher before clipping will occur.  We used a range of these with cutoff voltages from -0.9 -1.1V.  Using the biasing method in the fetzer valve article, the bias on these is 6.0-6.2V.  The trimmers were adjusted to these values on the drain, and they sound spot on with low noise, and a nice decay without any gating.

The only downside is that the gain of 2N5457s is about 50% of a J201, but as I never ran the boogey much over 50% its not a problem, its much more controllable.  If you get a J201 with a high cutoff voltage then putting this into Q1 could be a way around this.

If I had a circuit to measure the idss parameter then I think it could be made even better, but the source resistors would probably need trimming also.

Another change made is C16. This was changed from 1nf to 10nf, this is to remove some high end fizz.  This came from the GuitarPCB Boogie 57 mods.

[mgwhit]

+1 on the GuitarPCB Boogie 57 specs.  That's how I built my Chunk Chunk, and no one has ever told me it's not metal enough.

P.S. Great builds -- your art work and finishing skills are phenomenal.

[Vallhagen]

Thanx Marauder and Juansolo for helpful posts. I will follow that recommendation about changing the JFETs as well as carefully read through those links.

I very much look fw to build my own one.

Cheers and thanx again.

[chuckbuick]

Very nice!!!  I'm planning on doing a Chunk Chunk when the boards are available again.  This info will be a great help.  Thanks a lot!!!

[sgmezei]

How did you like the gain pot in the Cherrybomb? I struggled with mine and tried a ton of different values and added resistors.
I ended up with a 1KC in there.....

Did you try different kinds of tranny's?

Scott

And needless to say, your finishes look awesome!

[juansolo]

How did you like the gain pot in the Cherrybomb? I struggled with mine and tried a ton of different values and added resistors.
I ended up with a 1KC in there.....

Did you try different kinds of tranny's?

Scott

And needless to say, your finishes look awesome!

Cleggy has the memory for what we used as the pot, it's still bunched up at the end, but usable.

Yeah we tried a few trannies in there. These were the first ones we put in it and after trying the others are the ones that stayed. Again, Mr C will be required for the rememberage...

I *REALLY* have an appalling memory. Incredibly so. My theory is that my brain is a finite sized container being required to remember lots of things, so I tend to trash things that I don't think I'll need to know anytime soon, and I'm a bit crap at prioritisation. That's my excuse for it anyhow.

Anyway, what was the question?

[marauder]

We used a 10KC pot for the gain.

The transistors used were BC109Cs.  Tried 2n5088, and bc239c.  The 109s sounded much better.