acoustic pre-amp - help!

[jubjub]

I've got an important gig coming up. I need to build some sort of Passac type fishman type pre-amp.
I have a transducer pick-up and a sound hole pick-up and I would like to mix them both if posible. Please help.  Any suggestions ?
I'll need cuircut diagrams or at least a point in the right direction.
:roll:

[Bluesgeetar]

Good luck getting anything.  Although I love it here it is a very very very very biased forum.  It almost seems like it is anti acoustic and anti bass here.  Which is a damn shame cause the acoustic is still the sweetest sounding instrument.  I have tore this place up looking for stuff on acoustic but pretty much nothing.  They don't seem to like acoustic guitars here.  I hope you get something. :cry:

[moosapotamus]

Hey Bluesgeetar, it sounds like you are the biased one. This forum is anything but anti-acoustic, anti-bass or anti-anything, for that matter. You want to hear a bunch of audio clips of effects played on bass, go check out my web site. As for acoustic, well... folks can only respond to topics that are raised (not too many folks asking, "what's the best distortion for my acoustic guitar?"). This is a DIY stompbox forum, after all. :roll: In the future, consider waiting to see what sorts of helpful and constructive responses get posted before jumping to conclusions. I mean, why risk coming off like a schmuck? Your response was neither helpful nor constructive. Didn't you ever listen to your mother... "If you can't say anything nice..." [/flameoff]

[ontopic] There's lots of info available on acoustic instrument preamps. It'll come down to your specific requirements and building skills. For example, here's something very simple...
http://www.till.com/articles/GuitarPreamp/index.html

... and, here's something a bit more complex...
http://www.rane.com/ap13.html

Then, it sounds like you want to incorporate a mixer, too. The AP13 seems to deal with that. But, you may not want to get that involved. Try searching up some options for preamps and two-channel mixers. Then look at how they might be integrated.

Maybe do some searching around here and google, vivisimo, etc... to find some specific things that fit your particular needs for both. I'm sure folks here will be able to lend some advice on putting things together.

peace, luv & woodstock
~ Charlie

[jubjub]

ok, I have a plan. I'm going to build 2 of those simple pre-amps. It looks ideal. And from the 2 outputs go to a little 2 channel mixer. I already have a little mixer but If I have time i'd like to make a little all in one unit.
That would be cool. I've got an albumns worth of stuff to learn in two weeks so time is the issue. However to build 2 of those simple pre-amps won't be a prob. Thanks for your help.
I'll let you know how I get on.

[downweverything]

my barcus berry piezo preamp (for piano) i opened the other day just uses a simple opamp amplifier stage, and those sell for a decent amount of money and are fairly high regarded, i was somewhat disappointed.

[jubjub]

Using op amps for an acoustic pre-amp scares me a bit. The frquency range for an acoustic is so much broader. Does anybody know what fishman use? Thier stuff sounds pretty good. I've had some unpleasant experiences tonaly with op-amps and just don't use them any more.

[bwanasonic]

I've had some unpleasant experiences tonaly with op-amps and just don't use them any more.

Generally speaking I'm suspicious of the little things myself, but make sure to try the Burr Brown OPA2064 and OPA2134 before you write them off completely.  I'm still laughing about the idea of an anti-acoustic bias in a forum for DIY stompboxes though!  That's a bit like saying there is an anti-oboe bias here.

Kerry M

[Bluesgeetar]

I did have jubjubs best interest at heart.  I knew dang well that posting my response would get him an answer or two.  I just wish I had of thought of the reverse psych. trick the last few times I saw someone ask an acoustic question.  That PeterJ guy had to ask twice and still no go.  Acoustics just seem to fall to the way side around here.  Just an observation of an acoustic lover.  I guess the problem is that to truly capture the sweetness of an acoustic you need tube circuitry and a nice mic and that is not a focus of this forum.  Tube circuitry is a mean animal to deal with and I understand that.  I feel like crying everytime I even think about building a tube project.  There is though no place on earth that even comes close to being equal to this place for electric guitar effects and stuff.

Plus an acoustic is not as easy as plug and play and twist a few knobs like electric.  Acoustic guitar, mic placement you have to sit in one spot, put in sound hole cover.  Set up onboard stuff to sound good with mic signal, compressor limiter, etc.etc.

Electric:  Plug in and rock!

[David]

Jubjub:

Relax, dude!  This ain't that hard.

Solution:
   Jack Orman's "Simple Mixer" on AMZ -- just do 2 input channels instead
   of 4

   On each input channel, build:
       A preamp based on the first op-amp buffer in the AMZ article "Basic Buffers".  Replace the jumper with a 100K audio pot and a 1K or 10K ratio resistor to ground.

       The tone control from the "Pocket Rockit" on Mark Hammer's site

        A 386 to provide biasing per R.G.'s post.

        Use one TL072 or 5532 op-amp per channel.  Use a TL071, 5534 or the Burr-Brown to do the mixing honors.

If you've got a decent axe and fairly good pickups, this should do the job for you IMO.  Of course, I'm not an acoustic purist because I usually play electrified -- but I know what sounds good with less tinkering.

[Mark Hammer]

Ironically, I was going to post a request for acoustic pre-amp suggestions myself.  A neighbour plays in churches and I set myself the task of helping him sound great.  He has a Fishman thingie on board, involving a ribbon piezo in the bridge and a condensor on a small goose neck.  Unfortunately, the guy who installed it for him has it coming out two separate (height-staggered) phone jacks with no onboard controls (he has to go over to the mixer to turn down or up).  I just finished building him a little retrofit box that packs two phone plugs (also staggered to match the jacks) and a dual-ganged 50k volume pot so he can turn down from the guitar...finally...and have one single stereo cable coming out of his guitar instead of two cables hanging off the end..

I'm planning on eventually making him one of those "Harmonic Sweeteners", and maybe an SSM2166-based dynamics/noise processor, but in the interim I'm pondering a simple junction floorbox he can get at nearby with dual buffers, a mono-stereo switch and maybe some sort of anti-feedback control.

...And that was going to be the nature of my query.  There are a variety of approaches to reducing feedback risk, depending on the type of venue and type of signal source.  Does anybody here have any experience with acoustic guitar in a church-like environment?

I'm pondering a few approaches:
1) Simple sweepable notch filter.
2) Simple signal invert  (if what comes from the speakers and guitar are out of phase, they shouldn't sum....as much)
3) Variable allpass - Essentially a 2-stage phase-shifter with big caps and a passband so wide that the whole guitar signal passes without audible notches.  This would allow for speaker/source phase differences in-between 0 and 180 degrees so that  use pf phase differences to prevent summing/feedback could be tweaked.
Naturally, all of these could be used together., or packed into the same box.

I'm curious about what others find helpful in reducing feedback in such environments, and also whether (and how) the feedback control issues are different for the two mic-ing systems (piezo vs condensor mic).

[bwanasonic]

I just wish I had of thought of the reverse psych. trick the last few times I saw someone ask an acoustic question.

I don't think anyone's response was a result of your *psychology*. They most likely wanted to offer some help to the original poster. When a thread doesn't get replies, it shouldn't imply indifference on the part of forum members. Maybe it just got lost in the shuffle. I don't think using any kind of *trick* will make this forum a better place.

Kerry M

[casey]

hey mark,

ive been playing in churches for years.....one of the most useful i have
found was a notch filter on a peavey "ecoustic" amp.  the amp itself
sounds horrible, but it had a very useful notch filter on a sideways
mounted slider pot.

here is a picture:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=38076&item=3716291728&rd=1&ssPageName=WDVW

you can see the fader above the second knob to the left.

it sweeps through all the frequencies with a very narrow Q.

anyway, i played through one (my mistake) at a church one time
and i had quite a bit of feedback.....i moved it from one end to
the other until it notched it out.  even though i didnt like
the sound of the amp, i was really impressed by the knotch filter.

[Mark Hammer]

Thanks, Casey.  Much appreciated.  The e-bay picture didn't show, but I looked up the Ecoustic and found some nice summaries of its features and comparison products.  I gather the phase-reverse tends to be pretty popular not just because of feedback issues but also because you never know what the phase relationship of all the sources of a multi-mic'ed acoustic instrument are going to be.

[casey]

yeah, i dont think the newer peaveys have them...(the sideways slider)
but it was very useful....  of course there is the l.r. baggs way of
doing it.  they have both phase reversal and a notch filter on their
para-acoustic d.i.

[Nasse]

:shock: My acustic cheap gtr is so bad sounding it is better to leave it unamplified. Or it is just my playing technique.

I could not just now find one very old circuit come my mind when read this thread. But maybe someday. Anyway it was idea in old National Semiconductor Audio Handbook. LM387 one half low noise opamp or preamp connected as buffer amplifier (switchable gain, input impedance was 820 k) for piezo pickup and second half was three band baxandall tone control. Quess tweaking that tone control to suit for your guitar would be interesting.

Maybe a simple peak limiter would help somehow in the feedback problem. And maybe highpass filter in the input to cut unwanted lows.