Dragonfly Sparkle Boost possible errors

[estch71]

Among the many projects I have at hand, I built this one particular circuit, thanks to Ivark for posting on his website (I hope it's okay that I post it here).  The problem that I'm having is that at the bottom right of the layout, it shows that the connecting wire goes from the board to Vol lug 1/Gain 1 & 2.  I connected this three diferent ways; two wires going from the board to each pot, and then two wires in one hole going to their respective pots.  The third way was to have Vol lug 1 bridge over to Gain lugs 1 and 2.  Needless to say, the only thing I got out of it was buzzing at first (I had to rebuild it).  After rebuilding, I noticed that the gain pot had no effect on the tone or sound.  I'm wondering if there's something wrong in the schematic:



any advice is greatly appreciated.

[mistahead]

I think that Dragonfly used to be a local here... one of Torchy's mates? Before my time.

The below works:
http://www.aronnelson.com/gallery/main.php/v/diyuser/Sparkleboost.gif.html

[estch71]

I think I see the problem now.  There's two cuts instead of one, but that may be due to the difference in the layout.  Hopefully this helps with the 5K pot not working.

Thanks for the info.

[slacker]

Those two layouts are the same in terms of how the components are connected, they should both work.

[induction]

That layout is verified and matches the schematic, so there must be something wrong with your build.

Volume 1, and Gain 1 and 2 go to ground. It doesn't really matter how they get there.

Here's a few questions to get started:
What jfet did you use?
Did you adjust the trimpot?
What is the voltage on the jfet drain?
Have you tested the gain pot with a DMM?
Can you post some pictures of your build?

[estch71]

I've grounded Vol 1 and Gain 1 and 2.  I used a J201.  The trimpot is adjusted to relieve some of the hum, but not all.  the jfet drain is -0.16 v.  The gain pot is a 5kB at 4.66k, tested with a multimeter.  No pics yet.

[induction]

The trimpot is adjusted to relieve some of the hum, but not all.  the jfet drain is -0.16 v.

The trimpot exists so that you can dial in 4.5V on the drain. You shouldn't have a negative DC voltage there (or anywhere else in the circuit), but maybe you just reversed the leads, or maybe you weren't using ground as your reference. In any case, put the black lead at ground and the red lead on the drain, then turn the trimpot until it reads 4.5V. In the end, it doesn't have to be exact and you can use your ear to fine tune it, but for troubleshooting purposes get as close as you can. Then check if your gain pot has any effect.

The gain pot is a 5kB at 4.66k, tested with a multimeter.

You should also check the resistance between lugs 1 and 2 for the full range of the pot. Make sure it actually changes when you turn the knob. It should go from 0 to 4.66k (or pretty close).

[estch71]

The problems I had stemmed from bad potentiometers, faulty wiring, and a bad ground.  Now, this thing works great, albeit for a slight hum.  I think I'd rather have a Rangemaster though. 

[induction]

Glad you got it working, at least. The hum should go away with a battery or a regulated adapter.

[mistahead]

I like this boost over some others but love the RM.

I am playing around with dual darlington double-rangemaster neg-gnd thingy on my breadboard at the moment. If it fails I will throw some diodes at it and see what multi-stage darlington fuzz can shake out, actually the plan B idea is more interesting anyway.

[estch71]

I'm really into modding these builds.  I just bought a Jet City 20 combo and threw some Tung-Sol 12ax7s and two matched Ruby EL84s in it so I can get a better tone than my Univox.  Not knocking the Univox (it has two 6L6 power tubes in it), it's just that I see so many videos with fully tubed amps which seems to allow the sounds of the pedals come through.  It also helps me to dial in these pedals when needed.

I gotta say that I really dislike the Eminence speaker they have in that amp.  Gotta change it out.