Dead Astronaut FET Bassman Preamp

[MJ_Sound_Cubed]

Thanks for the layout update >)

[patrick398]

edit: cant believe nobody spotted this...

scrap your layout...the fets are wired wrong...

the drain goes to v+ trim..

the source goes to r/c to ground.

the 68k goes to gate.....



watch your pinouts. 

Yeah i realised this when i was putting the trannies in but did mention in the original post that i've bent the legs so drain is top, gate middle, and source bottom

[deadastronaut]

ahh i see....

[patrick398]

Had a 22n instead of a 2n2 in the hi/lo section which i think accounted for the difference in volumes in the two settings. I've replaced the 68k input R with a 220k just to try and tame it a bit. Also have 22uf for C2 and removed C6. Sounds great!

[anotherjim]

One thing not mentioned, although lower input impedance might be ok with your guitar, other guitar types, especially those with humbuckers might sound dull.
The usual tactic to clean up the front end - is to turn down the guitar volume control. Not every player likes to do that.

As exceptions that prove nothing, check out early stuff by the UK band Dr Feelgood. Guitarist Wilko Johnson played a stock Fender Telecaster into an H||H IC100 100w combo. That amplifier was all solid state, 741 op-amps, passive James type Bass & treble tone control and a 100k input impedance - and no not ever any pedals. Although the later VS amplifiers had a tube simulation circuit, the IC100 did not and didn't pretend to either.

Probably, if I presented a design that cloned an IC100 channel, it would get yawned at.

[Ben N]

No, no -- 741 = mojo. 

[Willypp]

Necro thread revival:

Is there a verified vero layout for this now?

[deadastronaut]

havent done a vero........

[patrick398]

I did one a while ago but was never really satisfied with how it sounded on guitar. As far as i can remember the layout is correct but worth giving it a once over:



EDIT: Just realised this is the same layout i opened the thread with so disregard if you've already checked that one out

[bluebunny]

Ask me again when I get back from vacation next week. I built one of these and I can't remember if I got a board from Rob or did a Vero myself. (I might try to find the gutshot I posted in the Pictures thread.)

[bluebunny]

Looks like I did indeed do a Vero...   Back at my PC on Wednesday. 

[Rob Strand]

In the old thread there was a point where the volume control got changed to 100k.
I got confused if it was changed back to 1M or left at 100k.

[bluebunny]

So I'm back, and it looks like I have two versions of the layout.    The first one is the version I built.  Note that it has the anti-switch-pop 1M resistors mounted on the switch (you can see it in my build picture), probably because I'd laid everything out before I re-read that part of the thread!  Here's that version:



And here's a post-build tweak which incorporates the two resistors.  Note that this hasn't been built and verified, but I'm pretty sure it's correct.  But YMMV, of course... 



Even as I stare at this, I can see improvements...   

Anyway, these both correspond with this version of the circuit:



Hopefully all of this might prove useful to anyone wanting to build this circuit.

[Atodovax]

So I'm back, and it looks like I have two versions of the layout.    The first one is the version I built.  Note that it has the anti-switch-pop 1M resistors mounted on the switch (you can see it in my build picture), probably because I'd laid everything out before I re-read that part of the thread!  Here's that version:



And here's a post-build tweak which incorporates the two resistors.  Note that this hasn't been built and verified, but I'm pretty sure it's correct.  But YMMV, of course... 



Even as I stare at this, I can see improvements...   

Anyway, these both correspond with this version of the circuit:



Hopefully all of this might prove useful to anyone wanting to build this circuit.

Is this preamp ment to be plugged into a power amp or into a regular amp with its own preamp?

[bluebunny]

I've only ever used mine with a regular amp or a mixer, not into a power amp.  But I don't see why it wouldn't be OK.  Try it?  No one will die.