DOD 210 FET Preamp built; mildly overdriven sound?! How to get it clean?

[Speeddemon]

Hi,

just for funsies I built a DOD 210 FET Preamp (I got the original schematic from DOD, but here's Andy's vero layout with schematic:
http://www.aronnelson.com/gallery/main.php/v/DRAGONFLY-LAYOUTS_0/album14/album143/DOD_201_JFET_PREAMP_VERO_001.gif.html)

and I tried a J201 in it. It boosted allright, but slightly overdriven. Measured Source voltage, around 0,6V (and it needs to be 1,5V according to the DOD schematic).
Today I found the correct J113 FET; threw it in and while slightly less overdriven, it still distorts. In a medium-pleasant way (think early CCR), but it's supposed to be clean, right?
Source voltage was 1,29V now. Could it be that the overdriving goes away once I fine-tune it to 1,5V?

[dschwartz]

replace the 22k resistor for a 50k or 100k trimpot and tweak until you get clean sound , or the cleanest you can get...

judging for the schem, this shouldnd give a lot of boost...

if you want clean, you´d be far better off with a simple opamp boost.

[familyortiz]

SD, those FETs can really vary from part to part. I might try a few different ones , if you haven't already.

[Speeddemon]

Yeah, I have 2 J113's, that were pretty consistent (1.3V and 1.27V), and a bunch of MPF102's, most of them around 2,1-2,5V, but one of them at 1,6V. Although even that one also sounded mildly overdriven.

[CynicalMan]

You will get the cleanest sound when you bias the drain to 4.5V.

[Johan]

original factory schematic http://www.aronnelson.com/gallery/main.php/v/johan_0/dod_booster.jpg.html?g2_imageViewsIndex=1 says FET is selected for Vgs~1.5volt
J

[Renegadrian]

I built one and liked it - I have a 2n5457 in it and have a good boost and no extra gain. Maybe some luck, but who knows, have you got some handy to try?! Their bias point is not so close so you should get some improvement...

[Speeddemon]

I've built it on breadboard, with both the 10k and the 22k resistors replaced by pots, but so far no luck. It remains dirty, eventhough it's mild, but it's very much there nonetheless.

[Speeddemon]

@Renegadrian: But let me get this straight, it SHOULD be possible to get it totally clean then?

[Renegadrian]

ehm... It seems my memory is getting old...
I think that my memory of a clean boost is of another circuit, maybe the AZ booster.
I took it back in my experiment box, yeah no clean sound from this circuit - it adds some grit, can't get a decent clean sound out of it...Sorry!

[saucer4]

mine is a DOD FET Preamp (not a 210)  Grey, white lettering

it has a great clean boost between 10:30 and 12:00 (halfway) and a pleasant smooth distortion comes on after that

level into the amp is the same at about 10:30 on the dial (dot pointing to the "e" in 'volume')

hope that helps

I've got some pictures, can email