Acoustics 360 Bass Preamp DIY

[Sweetalk]

Hi!, I'm new at the forum, it's great!!!!....

I'm trying to build the Acoustics 360 Bass preamp from http://www.lynx.net/~jc/pedals360.html but there's no ready-to-transfer board there... Does someone have it?... Another question: the power supply it's 9v, 18v or 25v? I've been looking across the net and always says a different value...

Thanks for all!!!!

[Bernardduur]

I just wanted to make the same one, but than as a preamp for my bass amp.

The original voltage is 25V

[Eb7+9]

the active inductor 360 clone will work on 9volts but without rebiasing two gain stages (ones with 680 ohms between emitter and ground) the headroom is a little low ... that's good if you like lots of growl, obvioulsy more players find the circuit sounds better working at 24vdc ... you've got the option ...

~jc

[moosapotamus]

Does the 360 require a certain (minimum) amount of current at 24vdc? filtering and regulation too, I presume? I never had much luck running mine above 9vdc.

Thanks
~ Charlie

[MR COFFEE]

Charlie,

It will run cleaner at higher voltages, which don't need to be regulated, but the PS does need to be filtered well. Any PS ripple goes straight into the signal chain. Current drain is pretty minimal. Any 18 -20 volt transformer will handle the current drain.

I use a simple emitter follower type of hum-reducing regulator on my 360 preamp supply (collector to dc input, emitter to circuitry, 1K resistor from collector to base, 220uf (or more if you like) from base to ground. Simple, works well. Don't short the emitter output to ground, though. No hum at all.

The preamp is a lot less wooly-sounding on 18 volts or better. The original PS was 25 volts from the original schematic.

[moosapotamus]

Cool, Mr C! I'm going to have to try that out.
I remember trying a 24V regulator with filter caps some time ago with no luck. Have also tried various wall warts, too (18VDC, 24VDC). Got nothing but 'hummm' at the output.

Thanks!
~ Charlie

[MR COFFEE]

Charlie,

Those IC regulators have a several-volt dropout voltage, and my guess is they weren't dropping enough voltage to regulate right.

If you hook it up the same again, see how much voltage you have *before* the regulator. They need 5 or more volts above the output voltage or they cut in and out. Especially if you haven't got a good-sized reservoir cap hanging off your full-wave rectifier (few thousand mfd). 

It's a pretty-sounding preamp circuit. I use a toroid coil for the Variamp circuit, and it is about as quiet a preamp as I've heard for bass.

Two 9 volt batteries work pretty well, too.

Bart

[lowstar]

i´d like to chime in with sweetalk asking for a pcb.
anybody ??

cheers,
lowstar

[moosapotamus]

Those IC regulators have a several-volt dropout voltage, and my guess is they weren't dropping enough voltage to regulate right.

Makes sense. I ran into the same issue when I was building the hamptone jfet pre.

It's a pretty-sounding preamp circuit.

It cretainly is.

I use a toroid coil for the Variamp circuit, and it is about as quiet a preamp as I've heard for bass.

Do tell... Is that toroid stock or DIY? Part #?

Two 9 volt batteries work pretty well, too.

Yeah, I did discover that. But for me, three 9v batteries worked even worse than just one. Whatever... I don't think this is really practical or doable with batteries, anyway.

I'm going to give that hum reducer you described a try when I get a chance.

Thanks again, Bart!
~ Charlie

[Eb7+9]

Thx for the info Bart,

never seen that hum reduction circuit, makes sense ... the base is AC-grounded through the cap ...

I think the problem about feeding the 360 circuit with a kind of EMITTER FOLLOWER regulated supply (eg. LM7824) happens if the down side of the regulator doesn't see a big enough cap ... in the Boss PSA-120T 9.6vdc wall-wart there's a 1000uF cap at the output of the 7809 ... I remember hearing something in design school about these NFB regulators going unstable if they weren't loaded with enough capacitance AND current draw, but I never did the analysis so I don't know for sure how to draw the line on that ...

definitely, winding a coil for the variamp section is the way to go if you have the time to do it ... gives best noise figures ...

cheers, jc