Si FF Debug, little help plz

Barcode80 · April 29, 2007, 05:50:28 PM

Okay, just built the Si Fuzz Face on Dragonfly's Vero layout. sound isn't bad, but i've got a couple of quirks. when i touch the pot shafts (haven't put on knobs yet) i get a buzz like i'm touching a ground. Also, i'm getting some RF noise. i know putting a small cap to ground can take care of this, but i can't remember where it goes

any thoughts?

sfx1999 · April 29, 2007, 05:56:52 PM

I am not sure about the pot thing, but as for the cap, it goes from the base of Q1 to ground. The base has a 2.2 uF capacitor and a 100K resistor on it looking at the GGG schematic.

enigmur · April 30, 2007, 04:11:40 AM

Is it in an enclosure yet?

If not, that will block out a lot of interferrance and should make sure the pots are grounded too (i've heard of people wiring the enclosure of the pot to ground).

If it IS in an enclosure, i'm not sure why it would be buzzing - check all your grounds and see if grounding one of the pots helps at all -

Cheers.

Barcode80 · April 30, 2007, 11:40:52 AM

yeah, it is already in the enclosure, that's why i thought it was so odd. i wonder if one of the pots is slightly defective and causing some problems, since both have a lug grounded. i will try swapping the pots and i'll put a 47pF cap from output to ground and see if that takes care of the RF.

sfx1999 · April 30, 2007, 06:05:54 PM

Don't put it from output to ground; put it from the base of Q1 to ground. By the time it gets to that part of the circuit, it isn't radio anymore; it has been converted to audio.

Barcode80 · April 30, 2007, 07:55:12 PM

okay, i realized that i had subbed a resistor by connecting in parallel when it should have been series, so that took care of the splatty sound and the odd ground buzz. now though, the output is incredibly low, not even unity when maxed. thoughts?

enigmur · April 30, 2007, 10:03:03 PM

Could you post a link to the layout?

What value is the resistor in line with the 9V+? I think the stock one I used was like 330R or 470R - something around there. Apparantly putting a 1k2 in there it will give it a much louder output.

Changing the input cap, which was 2.2uf on my circuit, to something lower decreased volume slightly and got rid of a bit of bass. Have you looked at the schem at fuzzcentral?

What value is the output cap?

I'd also check biasing, if it is lower it will be quiet.

Barcode80 · May 01, 2007, 01:29:32 AM

http://aronnelson.com/gallery/albums/album144/SILICON_FF_VERO_001.sized.gif

i was using a different layout, but i switched to this one and built it, and got some screwy results... but this time i socketed the transistors and once i popped a pair of 2n4401's in there, it SANG! it is still just slightly gated at the end of note decays, but it still sounds pretty damn good. pics:

enigmur · May 01, 2007, 01:57:36 AM

Great! It looks really good man!

How did you get that kind of sandy texture effect on the box? It looks nice.

Try playing around with the bias to get rid of any gating or decay, it is usually the cause.

Barcode80 · May 01, 2007, 02:20:04 AM

its rustoleum spraypaint, they make a finish called hammered. they have it in copper, silver, and a darker gun metal color.

sfx1999 · May 01, 2007, 02:56:29 PM

Is it possible the transistors you were using had a non-standard pinout?

Barcode80 · May 01, 2007, 03:04:15 PM

possible, though i looked them up by manufacturer, they were fairchild, and a thorough check of all fairchild datasheets that i can find on the 2n3904 all show the same pinout.

Barcode80 · May 01, 2007, 03:07:38 PM

if i build this again, i'll replace the bias resistor with a trim pot and tweak to my liking. even with the very slight gating on the sustain, it sounds really good.

i'm also pretty proud of my wiring on this one. realtively clean and tidy, though still room for improvement.

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Si FF Debug, little help plz