Fet version of alembic f2b

JebemMajke · March 07, 2012, 07:16:25 AM

I ve just built Alembic F2B with FET's. It sounds wicked both on guitar and bass.
FET's are BF245b's, and used trimpots to set voltages to 4.5 v on both.
Schematic I've used

Questions:
1. Is this supposed to give me some overdrive? Because it's a clean boost all the way.
2. That volume pot ( 1 meg ) gives almost max vol after 11 o'clock, there is no big difference between 11 and 5 o'clock. I've used linear pot.

anchovie · March 07, 2012, 07:36:00 AM

Quote from: JebemMajke on March 07, 2012, 07:16:25 AM
Questions:
1. Is this supposed to give me some overdrive? Because it's a clean boost all the way.
2. That volume pot ( 1 meg ) gives almost max vol after 11 o'clock, there is no big difference between 11 and 5 o'clock. I've used linear pot.

1. The chain is gain stage -> lossy tone stack -> gain stage. The second gain stage is basically a recovery for the tone control losses, so you've only got one stage of boost which isn't a guarantee of clipping. Try tweaking the trimpots for best sound rather than just measuring the voltage - you might get some grit if FETs are biased off-centre.
2. Use a log pot.

JebemMajke · March 07, 2012, 08:12:24 AM

Ok. Don't need it for dirt, i like it clean, but i wasn't sure if its supposed to be clean, so i asked.

Mike Burgundy · March 07, 2012, 03:16:53 PM

The "dirty" F2-B cascaded both preamp sides (it's a stereo unit) one after the other. Bass into L, L out into R, R out into amp - that's supposed to give a very good distorted bass. Has the added benifit of pre- and post distortion EQ, should be cool, but haven't played with it myself. Have a crack at building a second one and see!

JebemMajke · March 10, 2012, 10:43:42 AM

This thing did a splendid job on the last night's gig. @#$%in A, my cheap yamaha sounded like a fender jazz. And the crowd liked it too, only the sound guy and guitar player gave some mean looks, screw them. It was bass all the way. That last post got me thinking ... i ll make a second one in the same box with a true bypass, but i would like to have a different eq on it. Partly because i want to do it tonight and i don't have any 250k pots and the other reason is i would like to experiment. So any advice on the tone stack? Have in mind that i will be using this ting on both bass and guitar. But probably more on bass.

artifus · March 10, 2012, 10:49:31 AM

QuoteAnd ~~the crowd~~ my friends said that they liked it too

Quote from: JebemMajke on March 10, 2012, 10:43:42 AM... only the sound guy ... gave some mean looks, screw them...

screw them, they screw you. cos you could be screwin' the gear they're paid to take responsibility for, not to mention the public's ears . had the sound guy taken a di feed from your fx before your amp? did you explain the diy nature of said fx and the possible output levels? had you much of a sound check, if any?

*edit* in other words, did you communicate your required needs to the hired help so that they may have assisted you in attaining your goals? communication is key. unless you got some dick having a bad day they are actually there to help you. help them to help you.

JebemMajke · March 10, 2012, 11:20:40 AM

I think u got it wrong. We didn't play in front of our friends, we played 100 km away from our town, so we had no friends and family in the audience. Soundguy is a "guitar-must-be-the-loudest-instrument-on-stage" kind of person. And i don't really care for that since we play rock music with darker sound, and lots of bass. He didn't have any feedback. He was just angry because I am not the bass player who is somewhere in the back with volume down to 1. And the volume on the amp was on 4 ( mark bass amp ), with F2B on i didn't really need more volume. I did explain it to the sound guy that it's a diy thing and i said what is in the box. Singer was happy, drummer was happy, audience too ( lots of them came to me after the gig and gave me kudos on the tone and some solo's ). Only the guitar player and the sound guy weren't happy.

So back to the main thing, any advice on the tone stack for the second stage?

artifus · March 10, 2012, 11:24:44 AM

Quote from: artifus on March 10, 2012, 10:49:31 AMunless you got some dick having a bad day

JebemMajke · March 10, 2012, 11:26:23 AM

Tone stack man, please. No more about that gig.

artifus · March 10, 2012, 12:15:15 PM

fine. you carry on screwing and being screwed - see if it helps holding up evolution in that way.

i was simply and humbly suggesting that it may help to communicate. one notes that you are still unaware as to why your guitarist and soundguy looked unhappy. did you think to perhaps, i don't know, maybe, like, talk to them? exchange data? shared data may then be processed and later incorporated into future behaviour thus eliminating past problems.

with regards to tone stacks you may find the search function enlightening.

Ripthorn · March 10, 2012, 12:47:59 PM

I did this fet version three or four years ago. Works quite nice indeed. There are some layouts in the thread made by others, search for FET2B.

EnnPeeEff · March 11, 2012, 11:03:21 AM

The alembic is pretty much a dead on clone of the fender "black face" ab763 pre-amp. A lot of people mod the normal channel on their fender amps to have another tonal option, if you google around with that you can find versions of "Marshall", "dumble" Hi gain, etc.

Gus · March 11, 2012, 11:23:47 AM

I have a few LT spice sims of a circuit like this using two Si NPN transistors. 9VDC and 18VDC versions with different output drives. I took into account plate R and input resistance and gain of each stage for the power supply voltage. Should bias fine with no adjustments. Should have some nice distortion from the NPN stages.

Interesting paper
good graphs starting at page 12
http://www.its.caltech.edu/~musiclab/feedback-paper-acrobat.pdf
Look at BJT with emitter feedback and compare to fets and triodes

I have not had the time to build them. If I post them to the galley is anyone interested in building them?

moosapotamus · March 11, 2012, 01:31:47 PM

Hey Gus, I'd be interested in building them and seeing how they sound for bass guitar. I just can't say exactly when I could get to it. But I would like to see them.

BTW - I've already got plenty of tone controls on my bass and my amp. So my first inclination would be to simply remove the tone stack completely. Bet it would sound ace!

~ Charlie

Gus · March 11, 2012, 02:02:13 PM

I will repost. I see something I should fix

karter2000 · March 11, 2012, 04:47:24 PM

Hi Gus, I'd be interested as well!

JebemMajke · March 11, 2012, 08:52:07 PM

Quote from: moosapotamus on March 11, 2012, 01:31:47 PM
Hey Gus, I'd be interested in building them and seeing how they sound for bass guitar. I just can't say exactly when I could get to it. But I would like to see them.

BTW - I've already got plenty of tone controls on my bass and my amp. So my first inclination would be to simply remove the tone stack completely. Bet it would sound ace!

~ Charlie

I've ignored a tone stack in a second build and it gives nice, full sounding overdrive. But when i cascade the first one in the new, "toneless" build, it gets too noisy and the overdrive is over the top. So a tone stack is a must to eliminate extra noise and unwanted gain. At least for my ears. I guess i ll play around with Duncan tone calculator to find something fitting with the parts i have on my workbench.

moosapotamus · March 11, 2012, 10:24:01 PM

Quote from: JebemMajke on March 11, 2012, 08:52:07 PM
I've ignored a tone stack in a second build and it gives nice, full sounding overdrive.

cool

~ Charlie

JebemMajke · March 12, 2012, 03:30:16 PM

So here is the tone stack from Sunn 300t

So I'll use this tone stack on a second one.

Domin · September 14, 2023, 04:45:18 PM

I know Im late to the party but i made it with J201, 2SK117 and with bypass caps i have basicaly doom machine, without it its like slightly cranked Marshall, any ideas how to tame it?

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Fet version of alembic f2b