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tzenobite

(newbie) pickups and volumes

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hi! i'm new here. 

i'm pretty good at soldering, i've already made some little things (for example an earbud amp), but now i need help even if i'm sure it's a silly question...
briefly, i have a heavily modified dulcimer, with 6 strings: 2 for the melody and 4 drones, i use a slim archtop humbucker turned 90° so one coil picks the two melody strings and the other the drones, i need a volume control for the drones only
i simply put a volume pot to the drones coil out and soldered the pot out to the jack together with the melody strings coil out, it doesn't work
if i use the pot to "mix" the two coils it works but obviously the volumes are all wrong
i know it's probably a silly error somewhere but i can't understand what's wrong and where... sorry
thank you all so much!

vol.jpg

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I'm no expert but I think your first drawing is problematic because you want your ground on the 1 or 3 lug not the 2 lug.  the way drawn it's going to send your entire signal to ground, or it will send the b coil to ground.

You also want the ground hitting the b coil and NOT the live signal... so I would put ground on lug 1, b coil on lug 2, and connection to vm on lug 3.  hope that helps and note that there is no implied warranty or liklihood of my answer being remotely correct!

 

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Bonus points awarded for using a schematic to lay out your circuit rather than a wiring diagram :thumb:

Version 1 of your diagram is actually closest to what you need. By rotating both pots by 90 degrees and leaving the wiring as-is you get the required behaviour:

image.png

Vb allows the bordoni coil to be variably shunted away to ground, leaving the cantini signal unaffected. Vm then behaves as a master volume affecting both signals overall. The mute switch will operate better if it shorts the signal to ground, rather than disconnecting the signal from the output as you had it drawn.

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On 3/10/2019 at 10:26 PM, curtisa said:

Bonus points awarded for using a schematic to lay out your circuit rather than a wiring diagram :thumb:

thank you but i made it that way only because it's easier to draw :D

just to be clear, since i'm newbie at this, the "arrow" is the center pin, right? 
any advise about the pot values?
and: the humbucker tone is a little "darker" than the natural tone of the dulcimer and i saw somewhere that the usual tone pot design (250k pot and .022 or .015 cap) cuts high frequecies. is it possible to cut the low frequencies instead?
thanks again!

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so...a little problem, here. 

On 3/10/2019 at 10:26 PM, curtisa said:

Bonus points awarded for using a schematic to lay out your circuit rather than a wiring diagram :thumb:

Version 1 of your diagram is actually closest to what you need. By rotating both pots by 90 degrees and leaving the wiring as-is you get the required behaviour:

image.png

Vb allows the bordoni coil to be variably shunted away to ground, leaving the cantini signal unaffected. Vm then behaves as a master volume affecting both signals overall. The mute switch will operate better if it shorts the signal to ground, rather than disconnecting the signal from the output as you had it drawn.

so, a little problem here: vb pot affects both b and c volumes.
between vb and vb there are two other pots (high and low tones controls), then vm, the switch and the jack.
all works fine, but while the vm volume works as expected the vb acts weird: full down (so to speak) it's almost ball, then suddendly is something like 50/50, then at full up is almost all c. 
maybe a diode between vb out and c can help?

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7 hours ago, tzenobite said:

so, a little problem here: vb pot affects both b and c volumes.... while the vm volume works as expected the vb acts weird ...

You may be asking too much from a single pickup. What's likely happening is that the B coil is also sensing C strings and vice versa. Perfect separation of each signal from one humbucker turned 90 degrees is impossible as the two coils and groups of strings are simply too close to each other.

 

7 hours ago, tzenobite said:

full down (so to speak) it's almost ball, then suddendly is something like 50/50, then at full up is almost all c. 

The other thing that may be affecting your expected behaviour is the noise-cancelling nature of the humbucker itself. Perhaps the way you have the humbucker wired you're adding the C strings in-phase and B strings out-of-phase, so that when Vb is fully up you're mixing the two signals to subtract rather than add. Try swapping the connections on the  B coil of the humbucker and see if that improves things.

 

7 hours ago, tzenobite said:

maybe a diode between vb out and c can help?

Unfortunately no.

The 'correct' way to make this work would be to use a piezo under-saddle pickup with one element per string, each piezo element then being mixed to produce the two groups of B and C string outputs for you to control as you need. But that also increases the cost and circuit complexity by a significant amount.

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thank you.
this couple of photos may help you understand my level of madness :D
the strings groups are as far from each other as the humbucker body allows, but the fretboard is slighter larger with some more space for the strings on both sides
actually you'll be right about phase cancellation, since i tried only one "+" wire from every coil
anyway, all that needs to understand if and how the idea of two channels works, the next step is build (or find somewhere) some small single coils for melody strings and drones
a friend on mine in germany makes his own coils for his electroacoustic hurdy gurdy, i'll do something similar, this humbucker works well enough to find how to play the dulcimer with this strings scheme and some electronics, once i figured out every ascpect of the matter i'll make the next step

regarding the under-saddle piezo, i thought somethink like what you said: cut the saddle and (somehow) put one piezo under the melody half-saddle and another under the drones, but the luthier that helped me in those "upgrades" told me that one can't cut an under-saddle piezo to a desired lenght... is that true?

IMG_20190321_205735.jpg

IMG_20190321_210234.jpg

Edited by tzenobite
added pics explanation

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thanks again! i just tried to invert the humbucker wiring and it works! i assumed that the "outside" wires are the "+"s anche the "inside" wires the "-", but using one outside and one inside as "+" the drone volume pot works a lot better

On 3/21/2019 at 6:11 AM, curtisa said:

The 'correct' way to make this work would be to use a piezo under-saddle pickup with one element per string, each piezo element then being mixed to produce the two groups of B and C string outputs for you to control as you need. But that also increases the cost and circuit complexity by a significant amount.

wait.
i just learned that a under-saddle pickup can be cut. is it true? maybe i'll try two flexible under-saddle pickups under a two-pieces saddle...

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