Dummy Coil Wiring

[freefrog]

Re: Dummy Coil Wiring

I have seen varying advice on the dummy coils resistance. Some say 50-80% so it removes the majority of hum but doesn't mess with the tone too badly. While an article I once read about Ritchie Blackmore's yellow strat by his guitar tech said that he prefers to have a dummy coil which is 2K more than the pickups. Having a mismatch in the coil's resistance isn't necessarily a problem when you consider hybrid humbucker with asymmetric coils.

I agree with you about assymmetric coils and here is why: the ability of a dummy coil to cancel the hum has nothing to do with its resistance.

It has to do with its number of turns IF and only IF the dimensions and shape of the coil are the same than those of the "noisy" pickup.

If the dummy coil is smaller than the noisy one, it will need more turns... and/or some iron core(s) to increase its "antinoise".

If the dummy coil covers a wider area than the noisy pickup, it will require less turns, less resistance. I have currently an "air coil" mounted in my experimental guitar: it makes almost totally silent a 13k single coil albeit the air coil measures... 255 Ohm (but it's laid in a peripherical routing measuring 23cm *15cm).

FWIW.

[idsnowdog]

Re: Dummy Coil Wiring

My dummy coil started as a coil with slugs but I removed them not knowing if I wanted them or not? I did some experimentation this morning and a 7k resistor in parallel can halve the value of the coil. What I am unsure of though is how I could wire it parallel so that it only is applied to the neck and middle positions when the dummy coil is engaged?

[idsnowdog]

Re: Dummy Coil Wiring

I wired it up tonight but it looks like the dummy coil is in parallel rather than series. I hope Artie can chime in.

[freefrog]

Re: Dummy Coil Wiring

I wired it up tonight but it looks like the dummy coil is in parallel rather than series. I hope Artie can chime in.

If I can contribute without interfering too much: Artie did say it in his answer 4 and it seems logical, since an on/off/on switch make impossible a switchable series connection.
If you use(d) an on/on switch for OOP and another on/on switch (possibly a push pull) to enable/disable the dummy, series connection would be doable (with the added 7k resistor that you want if needed)

@ArtieToo: this answer is trying to ease the online help process and not to compete with your replies. Take back the control stick when you want to. :-)

[ArtieToo]

Re: Dummy Coil Wiring

@ArtieToo: this answer is trying to ease the online help process and not to compete with your replies. Take back the control stick when you want to. :-)

No prob man. I need all the help I can get.

I personally, have never used a dummy coil. I think the newer noise-cancelling singles catch the vintage vibe pretty good. So I assume it's supposed to be wired in parallel. Remember, a standard humbucker remains noiseless whether in series or parallel.

[idsnowdog]

Re: Dummy Coil Wiring

If I can contribute without interfering too much: Artie did say it in his answer 4 and it seems logical, since an on/off/on switch make impossible a switchable series connection.
If you use(d) an on/on switch for OOP and another on/on switch (possibly a push pull) to enable/disable the dummy, series connection would be doable (with the added 7k resistor that you want if needed)

Could you modify the diagram to show that?

[freefrog]

Re: Dummy Coil Wiring

Could you modify the diagram to show that?

Will try to do it ASAP if nobody does it in the meantime. Right now, I'm at work. Thx for your patience. :-)

[freefrog]

Re: Dummy Coil Wiring

Could you modify the diagram to show that?

Hey man, below is my take.



The two swiches related to the dummy coil are DPDT's.

The dummy coil is wired in series, between the ground of your PU's and the ground of your guitar. When it's engaged, the 7k resistor is theoretically in parallel with it for neck and mid pickups only (IOW: for positions 2 to 5; you'd need a superwitch to enable selectively the parallel resistor in positions 3 and 5 only, unless there's another solution that I've not found).

I've located all the "hot" wiring, including the connection with the no load blender, on one single side of the switch. The other side has to do with the ground and dummy.

Hope it's clear. I admit to be tired and busy so I hope there's no error in my rough sketch...

Lemme know if it answers to your needs. :-)

[idsnowdog]

Re: Dummy Coil Wiring

Thanks for the diagram. I think I need to simplify things and one of the best ways to do that is just have the dummy coil in series for the neck/bridge and not try to reverse phase to make middle humbucking.

Wouldn't this work?

[ArtieToo]

Re: Dummy Coil Wiring

I'm curious to hear how this turns out. A dummy coil is just an inductor, and an inductor filters out highs. Let us know how this sounds.

[freefrog]

Re: Dummy Coil Wiring

Thanks for the diagram. I think I need to simplify things and one of the best ways to do that is just have the dummy coil in series for the neck/bridge and not try to reverse phase to make middle humbucking.

That's exactly how one of my Strats is wired.

Wouldn't this work?
[ATTACH=CONFIG]105293[/ATTACH]

it would certainly work. Would it sound good? It depends on the specs of the pickups and coil involved...

That said and to schematize what comes to my mind:

-any passive dummy coil causes a drop in output;

-if the dummy coil is wired in parallel with the existing pickup(s), the drop will be more important because the parallel signal path divides altogether the resistance and the inductance: if we put a 6k & 2H dummy in parallel with a single coil measuring the same values, we'll end with the equivalent of a pickup measuring 3k and 1H: the sound should be high pitched and weak.

-if a dummy coil is wired in series with the existing pickup, its "inertia" still causes a drop in output (essentially because the dummy adds resistance in the signal path) but the inductances of the two coils stack upon each other and partly compensate the loss in output. The dowside is a loss of high frequencies precisely due to the higher inductance but it's not necessarily so dramatic...

-Like Ilitch, I prefer a dummy coil to be wired between the pickups and ground rather than between the pickups and output: the second case works but does funky things with the frequency response and it's not necessarily satisfying musically.

More later if time permits (right now, I write this during a pause for lunch at work).

[idsnowdog]

Re: Dummy Coil Wiring

I wired it up the way I diagramed it last night and the wiring portion is a success. I have not had a chance to string the guitar up and play it though. I plugged it into a small amp and with the SSL-5 and the 5.2K dummy coil engaged hum is lessened by about 40% and 80% with the neck.

[idsnowdog]

Re: Dummy Coil Wiring

I finally got the guitar strung and set up yesterday. My impressions of the modification are positive. It's hard for me to judge just how much the dummy has cut down the hum because the shielding job I did on the guitar is VERY effective to begin with. What I do notice is when the dummy coil is engaged the amount of hum does go down to the point it is nearly noiseless. There is some tonal change (darker, thicker) when the dummy coil is engaged and the bridge/neck aren't as bright sounding and their dynamic range is slightly less. Despite the dummy coil not being specifically matched to any of the pickups it doesn't degrade the sound of the guitar. I have heard a few noiseless pickups that sound better, but I have also heard many that sound much worse than this DIY experiment. If you were performing live and engaged the dummy coil you would only need to do minor tweaks (less bass+more treble) to make up for the difference. The only thing I need to change is I put a .047 capacitor on the neck's hot lead to act as a bass trap and although it does cut the mud the middle pickup ends up sounding a little darker than the neck. So I will try a .056 capacitor to see if I can get a little more bass or possibly add another bass trap to the middle.