Double neck acoustic/ B-band pickup ....balancing volumes on necks?

[rockjunky]

Hi guys.

I bought a double neck acoustic like the below \/ and I'm trying to find an easy fix on a volume balance issue between necks



It has a B-Band dual pickup with no volume pots. There is a dip switch that does a 27 dB at off, and 0 dB at on, but that is too much.

Rather than installing any pots I was wondering if I could install a small resistor in the circuit somehow just to chop off a little DB.

It is routed to a stereo plug....the 6 is just a little louder than the 12.

Any idea how I could do this?

[Mick Bailey]

To get an output drop you need a voltage divider, which in essence is what a pot does - it's a variable voltage divider. If there's a preamp fitted it makes things easier as the output will be low enough impedance not to get loaded down.

So, your two resistors need to be arranged like a pot set midway. Connect two resistors in series (1/4W metal film), ground the end of one, hot feed to the end of the other, and your output comes off the junction. If you had (say) 500k total, to get half the voltage output you'd connect two 250k resistors in series. Hearing is logarithmic, so you'd need to experiment to get the best values for your setup.

My approach would be to temporarily wire in a pot and establish the correct levels, then measure the resistance either side of the wiper and replace those with fixed values. If it were mine, I'd probably use a small trim pot soldered to a piece of veroboard, wire it up, set the position and then insulate the assembly, leaving it inside the guitar. I could always then re-trim the balance if I got the urge. You can get 6mmx6mm trimmers.

The overall resistance value comes down to the preamp - check the manufacturers spec to see if the pickup can be wired to a pot and use that value.

[52 Bill]

Wouldn't it just be easier to plug the two outputs into two channels of an amp with separate volumes and tones? Or into a simple stereo mixing box with separate volumes?

What are you plugging this into?

[rjb]

Wouldn't it just be easier to plug the two outputs into two channels of an amp with separate volumes and tones? Or into a simple stereo mixing box with separate volumes?

That is how they were designed to be used- run a Y-cable from the stereo output jack to two separate inputs.
B-Band Ltd - Acoustic Guitar Pickup Systems
Refer to the installation instructions:
http://www.b-band.com/uploads/Produc...-A2-manual.pdf

B-Band also makes a dual-input single-output preamp, with attached volume & mix control thumbwheels.
B-Band Ltd - Acoustic Guitar Pickup Systems

[rockjunky]

Hi Guys,

Thanks for the replies!

rjb the dual input b-band with vol and mix IIRC only does AST & UST not two UST's like the chimaera has.

As far as how I am going to run it, a few different ways with the Y cable but I've put in a switch that I can go between mono/stereo and the necks too.

So rather than lugging AB switches/mixers etc was looking at switching between necks but also having the balance there.

Especially when using something like the tonewood amp here ToneWoodAmp | Reimagining the acoustic guitar
Don't want any pedals etc then!! just a small switch on the guitar itself switching between necks and using tonewood to amplify/effects etc.

I might try Micks idea...any other input is welcome!

[rjb]

rjb the dual input b-band with vol and mix IIRC only does AST & UST not two UST's like the chimaera has.

Going by the descriptions, neither preamp "does" two UST's...
But the AST and UST are based on the same electret film.
I think they just never imagined anyone using two undersaddle transducers in one guitar.

As far as how I am going to run it, a few different ways with the Y cable but I've put in a switch that I can go between mono/stereo and the necks too.

I'm not sure I follow.
How are you getting mono out?
Are you switching either the tip or ring to an instrument cable's center conductor?
Or are you shorting tip to ring?
Or....?

[rockjunky]

Hi rjb

From the manual of the A2

The A2 is a two input / two output endpin preamp. Designed
as a platform for two sources, the best performance is with the
combination of UST and AST. The #1 channel input can support
UST or AST pickup.
The #2 channel input can support a UST or AST pickup, or can
also be configured for use with the B-Band AG-MIC condenser
microphone or a passive magnetic pickup with the mini dipswitches
inside the A2.


I remember seeing the A2.2 and thinking this might be a solution but I was pretty sure it didn't support both on the 2nd channel, I could be wrong on this!
The other thing is the mix goes from one pickup 100% to a 50/50 on the furthest sweep going by the manual.
So that wouldn't suit me.


I have a 4pdt 3 Way switch installed that on position 1 does the 6 in mono (sleeve not connected), middle position does stereo for both necks & position 3 the 12 in mono (again sleeve not connected).

[rjb]

Hi rjb

From the manual of the A2....

I read that too. The website "features" overview doesn't tell you that part.

A2 (2009 upgrade) Features:

• Dual input and output channels: Channel 1 - UST or AST, Channel 2 - AST or sound-hole condenser microphone or magnetic pickup

I remember seeing the A2.2 and thinking this might be a solution but I was pretty sure it didn't support both on the 2nd channel, I could be wrong on this!

Well, "technically", you could plug in two UST's; both channels have the same gain and input impedance.

A2.2 SPECIFICATIONS
Voltage gain: AST channel, +15 - +30 dB;UST channel, +15 - +30 dB
Input impedance (both channels): 50 Mohm || < 10 pF
Output impedance: < 3 kohm
Nominal output level: -10 dB u (0.245 Vrms)

The other thing is the mix goes from one pickup 100% to a 50/50 on the furthest sweep going by the manual.
So that wouldn't suit me.

That's a biggy. And, after skimming the manual, I see that the mixer incorporates a crossover- they call it an XOM (cross-over mix) circuit.

The ideal process for authentic acoustic sound comes from combining the high frequencies of the AST and the low frequencies of the UST

I have a 4pdt 3 Way switch installed that on position 1 does the 6 in mono (sleeve not connected), middle position does stereo for both necks & position 3 the 12 in mono (again sleeve not connected).

I'm still confused. You're floating common (sleeve)?

Sorry I'm obviously not providing much help.
But at least I learned something.

[rockjunky]

I'm still confused. You're floating common (sleeve)?

Sorry I'm obviously not providing much help.
But at least I learned something.

With position 1 & 3 I am floating the sleeve.
It comes from the A2 to the switch and floats there.


In position 2 the tip is for one neck the sleeve the other...this was the way it was wired originally (there were two other wires, one for ground, the other as well that closes a circuit when a jack is inserted)

So essentially in position 1 & 3 the jack is mono (floating sleeve at the switch) and only 2 is stereo.

It all seems to work fine...is there any issue doing it this way?

[rjb]

With position 1 & 3 I am floating the sleeve....
It all seems to work fine...is there any issue doing it this way?

I think I'm just a visual person- the words are tripping me up & I'm not going to understand without a schematic.
But don't worry about that- if it seems to work fine, it probably does.
I second the motion to try Mick's voltage divider. This may be helpful:

A2 Specifications
Output impedance (both channels): 150 Ω
Nominal output level (both channels): -10 dB u (0.245 Vrms)

EDIT:
OK, after a night's sleep, I think I see what you're saying.
I assume you meant to say that in switch position 2, the 6-string neck goes to tip and the 12-string to ring.
And in switch position 1 (6-string mono), you float the common (sleeve) to the cable for the 12-string.
And vice-versa.

The confusion arose because I had in mind my own definition of "mono"- I thought you were sending the combined outputs over a single unbalanced cable.

[rockjunky]

I think I'm just a visual person- the words are tripping me up & I'm not going to understand without a schematic.
But don't worry about that- if it seems to work fine, it probably does.
I second the motion to try Mick's voltage divider. This may be helpful:

A2 Specifications
Output impedance (both channels): 150 Ω
Nominal output level (both channels): -10 dB u (0.245 Vrms)

EDIT:
OK, after a night's sleep, I think I see what you're saying.
I assume you meant to say that in switch position 2, the 6-string neck goes to tip and the 12-string to ring.
And in switch position 1 (6-string mono), you float the common (sleeve) to the cable for the 12-string.
And vice-versa.

The confusion arose because I had in mind my own definition of "mono"- I thought you were sending the combined outputs over a single unbalanced cable.

Sorry totally my mess up there! Yes in the mono positions 1 & 3 it goes to the tip for the desired neck and I float the ring! (not the sleeve my bad!!!)
In position 2 its tip (ex 6) and ring (ex12)

I messed up calling ring the sleeve

[rjb]

I'd never heard of Chimaera guitars before, so went searching around.
Found this neat-o clip of a double 6-string.

/

[rockjunky]

I'd never heard of Chimaera guitars before, so went searching around.
Found this neat-o clip of a double 6-string.

/

There is a pretty cool clip of a guy with a chimaera that has a bass for one neck and a 6 string on the other using a looper

[Mick Bailey]

You can wire a resistive divider into the jack plug - that's probably the easiest solution and avoids any work disturbing the guitar electronics.

[Steve A.]

You can wire a resistive divider into the jack plug - that's probably the easiest solution and avoids any work disturbing the guitar electronics.

Yes!!! You suggested this earlier in direct response to the OP's question of using a single resistor to balance the two pickups. (On-line manuals often do not reflect minor design changes in a product.)

Steve Ahola