Double Bass line + Mic preamp

[ilfungo]

Hi
I want to build a box for double bass with this characteristics:

input
1- Hi-Z input preamp for piezo
2- Mic preamp with phantom and variable phase

output
1- sum of Hi-z +mic to amp
2  sum of Hi-z +mic to mixer
someone can give me some help or suggest me some project to start?
THANKS!!!

 

[SSLtech]

There is no project for this.

So far as I know, there is no 'variable phase' project. Nor do I know of a project that has outputs for amp and mixer separate (though there may be)...

I'm surprised that anyone would be able to reliably make decisions of this nature from a player's position, and given the limitations of an 'in-between-phase' type of unit (it  doesn't do one very important thing, which is DELAY) I really question that this would be of any real value.

If you want to test the value of the concept first (which I would strongly recommend, given my reservations) try a Rupert Neve 5017 or a Littlelabs 'IBP' and see what it does for you first.

 

[sahib]

Check out my MICPRE ONE.

http://groupdiy.com/index.php?topic=52443.msg668674#msg668674

It has independent mic and instrument inputs/outputs. Instrument input Z is 1.5M but can be raised further.

I can supply the front facia in horizontal format if needed.

 

[JohnRoberts]

Hi
I want to build a box for double bass with this characteristics:

input
1- Hi-Z input preamp for piezo

I helped a junior engineer with one of these a couple decades ago and at the time I suggested a discrete JFET in front of an op amp. Today I'd probably just advise using a low noise JFET input op amp, they have gotten quite good. 

2- Mic preamp with phantom

There are many decent mic preamp chips discussed on this forum.. do a search.

and variable phase

This is a little more uncertain. A generic variable phase that works for all frequencies is not a possible circuit. There are some popular circuits where you can effect a variable phase adjustable over perhaps an octave or two. For a bass amp application you could probably dial something in to taste.

output
1- sum of Hi-z +mic to amp
2  sum of Hi-z +mic to mixer
someone can give me some help or suggest me some project to start?
THANKS!!!

If you want somebody else to design it for you, that might cost money. I don't see any heavy lifting, while the phase shift circuit may take some trial and error to get the effect you want. 

JR

 

[PRR]

As said, the "phase fixer" is a complicated thing. Buy the IBP.

> sum of Hi-z +mic to...

This is a simple mixer. Twice.

You could spend much time figuring it out. Or just get Behringer's cheapest mixer. It has two inputs mix/rout to two outputs. It has tolerably OK mike amplifier with Phantom. It does not have super-high impedance instrument input; find a buffer on a stomp-box forum. TL072-based buffers can be built to excellent performance for this application.

The instrument output probably wants to be much lower than the PA rig output. To avoid needing extremely different knob-settings, work to PA level then use say 2.2K+470r voltage-divider on the instrument output.

 

[ruairioflaherty]

I had an IBP for years and when I sold it I really only missed the DI and not the phase trickery.  The important thing to remember is that an allpass filter like the IBP can only rotate the phase at one frequency (okay you have a choice of two in that case).

The rest of your plan sounds good but if you are really determined to figure out the IBP style thing borrow one or buy used and resell, you may be surprised at how meh it is.

 

[Dr Gris]

Another approach might be a Hi-Z input with a variable low pass filter
and a Mic input with a variable hi pass filter and a phase flip switch.
I guess the filters have to be pretty steep to get a good x-over....

Don't know if this is a good idea but it helped me in one situation but the filtering
was done by a mixer using two channels.

Best
//M

 

[JohnRoberts]

I had an IBP for years and when I sold it I really only missed the DI and not the phase trickery.  The important thing to remember is that an allpass filter like the IBP can only rotate the phase at one frequency (okay you have a choice of two in that case).

The rest of your plan sounds good but if you are really determined to figure out the IBP style thing borrow one or buy used and resell, you may be surprised at how meh it is.

IIRC the actual circuit is pretty simple (one op amp and a pot) but you do need to dial in the cap to be just right for the application...I never had much use for them but I suspect it might fix a one note suck-out caused by mic path delay if cap is sized correctly... or not.

What you really want is a delay but that is harder.

JR

 

[ruairioflaherty]

Typically when I tracked and mixed (almost all mastering these days) I would use mostly one or the other mic or DI.  I've messed a lot with delaying the direct signal (or rather advancing the mic'd signal in the DAW) with mixed results.  Generally the mic has the real lows and woof and the DI can add some nose or bite but that same effect os often available using just eq on the mic'd signal.

As ever a great player can rock either DI or mic and a bad player is rescue scenario from the off...

I've also experimented with the crossover style approaches way back in the day and it was pretty much a disaster (sorry Doc).

 

[Dr Gris]

I've also experimented with the crossover style approaches way back in the day and it was pretty much a disaster (sorry Doc).

No problem. It was a one-time last resort thingy on one track I mixed. The recording and the double bass itself was a disaster.
And yes, the result wasn't that good, but the best I could get at that time.
I only record double bass with ONE mic if it's in a controlled enviroment.

I guess this box is for live use?

Cheers
//M

 

[djgout]

I actually designed something like this a few years ago. One of my friends/clients is a rockabilly player and wanted 2 piezo inputs for live use. They play with amps and it gets very loud. I also added a low cut on the neck channel at 500 because that's all the click, on the bridge channel I had a phase flip and a variphase control that is only effective to 180 degrees below about 2k. I also created a blend control that let's you dial in the balance between the two inputs. Each input has its own gain control as well as a master amp out, and a balances line level out. We got as far as designing the circuit boards but then have piddled out on actually going into production. Its totally possible to do. I made some smaller Jr versions that he gigged with for a few years but doing everything on veroboard didn't really hold up. I think a redesign with a jfet input would make it much better and take less battery power.

 

[ilfungo]

Thanks to all for the suggestions!!!
djgout have you something that  can be shared?
Thanks