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Stormrider 18th April 2013 06:50 PM

Modified Alembic F2-B
I'm going to be building a single channel bass preamp based on the F2-B. I think I have most of parts ready to go, just need to order the FET's and some caps so I can do a quick prototype. I happen to have one of the Stancor power transformers used in the F2-B, so the power supply will be identical to the original.

The buffered output should cover the main weak point of the F2-B, which is it's compromised ability to drive long cable lengths and the low impedance inputs of modern pro amplifiers.

Stormrider 18th April 2013 06:51 PM

1 Attachment(s)
Schematic attached.

funk1980 18th April 2013 09:02 PM

Cool build!
I'd up the value of the output capacitor though. If connected to e.g. a power amp with a 10k input impedance, which is quite commen, the -3dB point will be at about 160Hz(!). WAY too high for a bass amp. You want it to go down to at least around 30Hz, which is achieved with a 530nF cap, which doesn't exist, so you could use 1uF and be safe for even lower peripheral input impedances.

Stormrider 18th April 2013 09:28 PM

Of course, you're right. Pretty bad copy/paste error there. I agree, 1uF would be good.

svtb15 19th April 2013 06:26 PM


Stormrider 19th April 2013 10:15 PM

1 Attachment(s)
Updated the schematic, and placed an order for a Par-Metal 10-19082B 1U case.

I'm worried about the transformer fitting; even though the original Alembic is in a 1U case, and I have the same Stancor PS-8415 power transformer, the Stancor I have is 1.64" thick, which is the exact internal dimensions of the Par-metal case (1.74" - 0.1" for the top bottom panels)... We'll see how that goes.

Now I'll be working on the turret board layout.

funk1980 21st April 2013 08:33 AM

Cool, keep us posted.

cyclecamper 22nd April 2013 05:42 PM

Of course the F2B classic is two channels, and some of the best sounds are using both channels in series.

cyclecamper 22nd April 2013 05:44 PM

Are you talking about that Q1 as your 'buffered output'??

cyclecamper 22nd April 2013 05:47 PM

BTW when I did mine, I used two sub-mini toggle switches for the bright switch, with a much different cap on each...gave three different knees (one, the other, both).

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