Obsidian with BS170's ?

[MartyMart]

Is it just a matter of making it a "negative ground" version for use with these "N channel" mosfets ?
I guess the biasing setup could be different too !
3.9k's could be perhaps 10k or 20k pots ....

MM.

[pyrop]

Is it just a matter of making it a "negative ground" version for use with these "N channel" mosfets ?
Yep I believe so. You also need to flip the electrolytic caps as Joe says
I guess the biasing setup could be different too !
3.9k's could be perhaps 10k or 20k pots ....
a 10k trimpot would do the trick I would say

MM.

You could use 2N7000 as a sub for the BS170's
I've built the pos ground BS250 version and it's real nice although it does have a little noise and the N channel version is supposedly a lot noisier.

pyrop

Edit: I have PCB layout if interested

[WGTP]

The original Obsidians had N channel 2N7000s and LEDs for protection.  I bet someone around here has them.   

[Gringo]

I have those schems, pm me an email address if interested.

I built an obsidian with 2n7000 (one of the older versions, i had no bs250s) and tried it with a big muff/marshall tonestack at the end. I can't tell about it being noisy, because it's on stripboard and not boxed, but the sound...very very nice. The marshall ts gave it more versatility (doh!) but the simple big muff ts was not bad at all.

[MartyMart]

Thanks, PM sent

MM.

[burnt fingers]

Anybody still have the schem for the 2n7000 obsidian?  I have not been able to find it anywhere. 

Scott

[Joe]

2N7000, BS170 work fine, the BS250 is just quieter. I'm not sure about the biasing on this thing, seems that MOSFETs from the same reel are pretty closely matched, but between batches they can vary quite a lot. I usually just test the stages on a breadboard to get the right drain resistor values, instead of fiddling with trimpots. Another point, if the drain resistor required to get 4.5v is too high, say over 10k, then I would adjust the gate bias too.

[MartyMart]

Thanks Joe , another great sounding circuit
I built a BS170 version and got close to 4.5 v drains using 6k8 resistors
It's a little noisy, but I dont have any "high gainers" that are silent !!

Cheers,

Marty.