Bass preamp for homerecordings

[SupaTmu]

Anyone know a good bass preamp for home recordings? I found many diy preamps but I don't know what would be good for bass. It would be great if someone could give some pointers or maybe post a link where I could find some instructions how to build one. Anything goes but tubepreamp would be greatest. :lol:

[Chris Goodson]

I remember seeing the schematic somewhere on the internet for an Alembic tube preamp.  I had the opportunity to play around with one about a year ago and thought it was nice.  It even works well for guitar, I believe David Gilmore uses them in his live rig.

[MarkB]

Acoustic 360+

http://www.moosapotamus.com/360+/360+.htm

"-)

[SupaTmu]

I found schematics for alempic F-2B preamp from geofex. It looks pretty simple but I'm not into working with hi voltage so can someone help with this one. I though that maybe I could do this with a wallwart powersupply. The question is how?

[SupaTmu]

And here's the link to the schems

http://www.geofex.com/FX_images/alembpre.gif

[SupaTmu]

I found some threads about this preamp and I think this one can wait a while. Not my thing, yet. :wink:

[downweverything]

wow that alembic circuit looks really simple.  whats the transformer secondary... the one that makes B+ doesnt appear to be labeled

[SupaTmu]

That's the thing that crashed my project. hey downweverything if you can figure out what's B+ would you post it here, I couldn't.

[Eric H]

It's a clone of a Fender preamp (Showman --IIRC) the Alembic website is honest abut this. There are tons of Fender schemes available --that include all voltages. I'd suggest doing your homework, before tackling High-voltage designs.

-Eric

[moosapotamus]

Do a search of prevoius threads. Apparently, B+ for the Alembic is something like ~160V to 200V, but the PS uses a doubler. So, secondary might be ~100V... But, don't take my word for it... do a search!

btw, I wouldn't mind trying one of these myself.

~ Charlie

[SupaTmu]

I looked up th Dual Showman schematics and if I'm right B+ is 225V. This is not a fact, I'm just guessing.

[Greg Moss]

Here's another vote for JC maillet's 360+:

http://www.lynx.bc.ca/~jc/pedals.html

despite the hubub surrounding tube amp stages, Acoustic produced some of the best bass tones.  I highly recommend....

[MR COFFEE]

I've built a customized 360 style preamp using a built-in opto compressor and an updated first amp stage using a JFET that sounds pretty good to my ear for recording -  and also sounds good live driving a high power clean SS amp.

I wind my own toroid inductors instead of using the GIC-based design because the GIC adds a small amount of noise, and I am rather fanatical about reducing noise, but the GIC-version sounds very good too.

Run it on 25-30 volts to get it to sound right. A 9 volt battery won't cut it.

[downweverything]

can i see a schematic of your fet stage?  i was going to do that too... isnt it possible to use the existing layout just changing values... i think i have seen fets biased like that before.  also you need to teach me how to wind that inductor that would be awesome...

[Eb7+9]

I wind my own toroid inductors ...

I haven't found the GIC circuit noisy but I would like to compare ... can you share the details of your winding pls ?!

... jc

[downweverything]

i just ordered some pot cores and torroidal cores so hopefully ill be able to compare soon too.

[MR COFFEE]

Dear JC and Down,
Haven't drawn up a schematic - I went straight from the breadboard to PCB layout. Just use a N-chan JFET with a medium Vpinchoff (2-3 volts) and low noise in a low-gain circuit. I use a selected J210 with a gate resistor to ground of 1M, a source resistor of 2-5K unbypassed, and a 10K drain resistor. I take the signal off the Drain which gives a gain of 2-4, and use it to drive the photocell voltage divider for the compression function followed by another JFET gain (restoration) stage that drives the volume-control stage of the the 360 preamp.

OK, maybe mod isn't the right word exactly, but it's all pretty straight from the book stuff. Designed like this, it tolerates bass "popping" gracefully without sounding "solid-state" (as the non-techies describe the audible artifacts of stages that make unmusical sounds when overloaded).

No 9 volt batteries though, right? You need the headroom to overload politely.

Winding high value toroids is no big deal. Make a shuttle out of a popsicle stick (or longer piece of maple wood or plastic). File the ends with a 1/4" rat-tail file so the ends are concave instead of convex. Wind the wire around the shuttle longways (you make the ends concave so it won't slip off, right?) and pass the shuttle through the hole in the toroid as you wind turns and don't let the wire kink. Commercials during movies and listening to music keep this from being terribly burdensome or boring. Cover them with RTV or epoxy afterwards.

Buy toroid cores that have high mu (5000 is high mu) for getting an inductance in the range of 1.5 henries. Avoid saturation for most applications. A 0.75 - 1" dia. toroid is probably big enough - I use a 2.25" dia core in the 360 bass preamps I make. The math techies calculate the turns; I just use a multimeter that measures inductance and I have a few "standards" when precision is important (it isn't that critical here) because I didn't buy an expensive multimeter (<$100).

[downweverything]

i ordered some torroids with a mu 10,000 and some of 15,000 i figure that way ill have less turns...  how do you avoid saturation...also i got some pot cores to try them out too....i figure those would be much easier to wind.  i dont have the fancy multimeter so ill have to do the math...i figured it out to be about 300-450 turns depending on the cores i ordered.  im going to set up some other test circuits to measure them later.  what gauge wire did you use, i have a bunch of magnet wire laying around?

your jfet stage sounds cool, prob not suited to me though cause i like the compression after the tone controls that way i can even out the dynamics of the various alterations i make.  (my amp has an awesome compressor on it anyway) i think i figured out a way just to use my existing layout to make the first two stages jfets i figure that will really quiet the circuit which is a bit noisy now.  i actually want to get it to the point it will run off a 9V (well two actually for 18V i agree the headroom is an issue) if i can get the current consumption down low enough... i think i can get it to that point if i tinker a little more... batteries are really nice for the studio because they are super quiet... or i could just throw this wallwart out the window and build a worthy supply,  who knows.

thanks for all the help, let me know if something sounds wrong in my ideas.

[Bluesgeetar]

If you really want to do DIY then by all means go with what these guys say.  For me trying to figure out guitar DIY is a big time consuming headache enough.  If you are just wanting a excellent job for recording then I'll tell you.  If you get a Line 6 BASS Pod Pro (rack) you will be the happiest you'll ever be with you bass setup.  If you can afford the unit.  I did much much research before I bought mine and way plenty bass pros are using this monster in the studio.  But then again it is not DIY.  If your just trying to keep busy then go DIY.  If your pressed for time and want a awsome do it all unit and got the dough then go BASS Pod Pro.  I'm pretty young so I hate DIY.  I am not passed the age of making it in the music biz so I try to just build what I need then go back to recording.  I love my BASS Pod Pro with a passion.  I see why the pros use it.  Funny thing is that the setting I like most on it is the Acoustic 360 Bass amp with Marshall cab.  Sweeeeeeeeeeeeet!  

[Eb7+9]

No 9 volt batteries though, right? You need the headroom to overload politely.

Bart, thanx for all that construction info and bias details on your FET front-end stage - the opto-compressor is a very cool add-on !

Just wanted to say that there's two basic "headroom" philosophies that exists so far ... some players want the slight growl that can occur when large amounts of signal is running through the back end of the 360 circuit while some players want a totally clean response ...

The two far-end gain stages with 680-ohm emitter resistors will clip first ... when the circuit is powered at 24vdc there is hardly ever any clipping present in those stages at normal playing levels (very little when you push the circuit hard) - when you run the circuit at 9.6vdc the headroom drops to a point where that clipping sensitivity starts to increase a bit ... one of the reasons why I've experimented with running a modded version of the circuit at 9.6vdc is because of the availability of low-noise Boss wall-warts ... I haven't yet found a 24vdc circuit that was quiet enough for the 360 - noise is paramount here ...

... more later - thx for all the inductor building info you guys !

jc