DIY acoustic preamp/amp...

[bt2513]

I am interested in building a preamp for my acoustic and am looking for some parts and layout suggestions.  Basically, I'm looking for something I can use to practice with at home (while using effects) that can also be taken on a gig to use as a preamp/DI box.  My idea is basically to string together pieces of existing circuits, not to reinvent the wheel.  Maybe tweaking a thing or two for clean headroom as opposed to the typical overdrive/distortion most of the circuits on this forum aim for.

Here are some features I'd like it to have:

2 inputs for high and low impedance (one for an active piezo, one for a passive magnetic pickup)
blend knob for both inputs to be used at the same time (bypassed when only one is used)
gain and master volume (might be cool if master volume had an expression pedal jack as well)
signal clip indicator - not 100% necessary but if its easy to rig then why not..
tone stack (sweepable mids maybe, but otherwise open for suggestions)
maybe a very clean compressor section
line level-switchable effects loop
maybe a small clean power amp section (powerful enough to drive a small speaker)
XLR out?

What layouts should I be considering for this purpose?  If I should substitute opamps/transistors in existing designs, what do you suggest I use?  What are some other ideas to make this better?  Is there anything I'm forgetting?

[jkokura]

WOW. That's a big enterprise...

2 inputs with switching seems to me to be a bit overkill - you can buffer two inputs, but there's no need to have one for active and one for passive. It seems you want a buffered blender or mixer circuit there.

Blend knob, see above.

Gain and Master seems that you'd need to find a good acoustic preamp and work with that. Also, if you have an expression pedal, you could probably just use a Volume Pedal in an effects loop. Probably easier in my humble opinion.

Tone Stack would be incorporated into the acoustic Preamp. Don't know much, but you can search that I think.

Compressor for Acoustic... I recommend something you can blend in. I used a Ross Compressor and liked it, and I'm about to start trying to use a Boss CS-2, but I would really, really like to try using the Tonepress because it has that blend function. Again, this is something that could be in an effects loop.

Line level? Why? What kind of Line Level effects will you be using? Better to have a loop at guitar effect level I say.

XLR out requires you to build in a DI box. I highly recommend building the ones that you'd find on the website for Jensen Transformers. Google Jensen DI Transformer and you should be able to find them.

You're going to need a big box (1590DD? 1590D?), and more than layouts right now, you need to think about a block diagram for the whole unit. I think it's a doable project, and would love to see your results. Go for it, but think about what you really need.

Jacob

[bt2513]

WOW. That's a big enterprise...

2 inputs with switching seems to me to be a bit overkill - you can buffer two inputs, but there's no need to have one for active and one for passive. It seems you want a buffered blender or mixer circuit there.

Blend knob, see above.

I currently am using a B-Band active piezo transducer but it can sound pretty harsh and brittle through some of my effects.  I have played magnetic pickups in the past that sounded much better in certain situations but currently do not have a magnetic pickup.  Thus, the ability to completely use magnetic or piezo or any combination in between would be something I would find very useful.

Gain and Master seems that you'd need to find a good acoustic preamp and work with that. Also, if you have an expression pedal, you could probably just use a Volume Pedal in an effects loop. Probably easier in my humble opinion.

Tone Stack would be incorporated into the acoustic Preamp. Don't know much, but you can search that I think.

That's the thing.... I don't know of any acoustic specific circuits that have been published on the web.  That being said, I know there's a boatload of simple solid state preamp circuits out there and was looking for more of a pointer to one that I could adapt to an acoustic application (increased frequency range, clean headroom, etc.).  There are also lots of tone stack options out there... in lieu of building a specific acoustic preamp, I was thinking it may be easier to just adapt an EQ of sorts for use with this project.  I never thought of controlling master volume through the effects loop - that's a great idea

Compressor for Acoustic... I recommend something you can blend in. I used a Ross Compressor and liked it, and I'm about to start trying to use a Boss CS-2, but I would really, really like to try using the Tonepress because it has that blend function. Again, this is something that could be in an effects loop.

Again, I like this idea of putting it through the loop... I just don't have a suitable compressor and would have to build/buy that too.  If there's a simple and effective design out there that would lend itself well to acoustic applications, I would just as soon build it into the unit....  but the blend knob is a great idea.

Line level? Why? What kind of Line Level effects will you be using? Better to have a loop at guitar effect level I say.

I have no idea what I'll be running.  Right now, delay and a looper.  In the future, maybe a more sophisticated rack unit.  The line level feature really isn't important.  If is simple to implement, why not... if not, then I have no problem leaving it out.

XLR out requires you to build in a DI box. I highly recommend building the ones that you'd find on the website for Jensen Transformers. Google Jensen DI Transformer and you should be able to find them.

Again, this isn't a super important feature.  As long as the unit can drive longer cables, I have no problem leaving it off.  Given the space parameters, I would rather have the space dedicated to a power amp section than XLR connectors.  For the power amp, I had envisioned something similar to a squeaky clean version of a Small Cricket - in size and simplicity, not sound.

You're going to need a big box (1590DD? 1590D?), and more than layouts right now, you need to think about a block diagram for the whole unit. I think it's a doable project, and would love to see your results. Go for it, but think about what you really need.

Jacob

I am willing to give up features to save on size and I really appreciate the insight you've offered.  I am a total n00b and this would be my first foray into a somewhat original project.  Up to this point, I've only built things from kits and well documented project files.  Ideally, I would like this to be the size of a 1590BB (whatever the size of the new EHX pedals are - like the Ring Thing, etc.).  Whether that's even possible, who knows......

Thanks!