Does anyone have a SPICE simulation for pickup/pot?

[PFDarkside]

I think a few of you guys have some simulations saved…. Can anyone do the frequency response simulation of a 500k vs 250k vs 25k with a Humbucker? (I think a 25k would be unusable, but I ran into some comments that a famous player used a 25k with a Humbucker, I have my doubts)

 

[beaubrummels]

500k, 250k, 25k for what? Tone? Volume? Spin-a-split? Variable treble bleed? Blend control?

25k would work for a split, bleed or blend.

 

[Teleplayer]

Basically you are looking at the inductance of the humbucker, combined with the capacitance of your cable. There is also a difference between the two cases when the volume is rolled off. Are you interested in what happens at part volume, or only with the volume knob maxed? What humbucker are you using? and how long is your cable? it seems like you do not have a tone control wired in.

 

[freefrog]

What counts is mainly the total resistive load. Volume or tone pots make little difference here when it comes to measured resonant frequencies (at least when pots are full up).

See below.

I've used my "Humbucker as a transformer" model. In this case, it models a HB with 2 conductors cables, symetrical coils, 4.4H, 8k (in the P.A.F. range, IOW).

The curves translate voltage and not current. Otherwise they would be flat before resonant frequency.

Upper left pic = HB with a single 500k volume control.

Bottom left = the same with a single 250k volume pot.

Upper right = the same with a single 25k volume pot.

Bottom right = the same with a 500k volume pot and a 500k linear tone control, itself lowered at 5% of its value. There's a slight shift of the "frequential dome" obviously due to the tone cap (whose capacitance really enters in the game when the pot is set really, really low, for the record, albeit it can affect harmonics even when pots are full up).

If we wanted the load to be exactly @ 25k, the tone pot would be to set @ approximatively 5.3% of its value.

So and to sum it up, a single 25k pot would behave largely like a guitar with two 500k pots, whose tone control would be set just above the final shift to a second resonant frequency caused by the cap...

FWIW, I've once mounted a 25k tone pot instead of a 250k because of a stupid error (not a good idea for a senior to solder in the dark)... The HB was a bright and powerful HB with ceramic mag. The tone was dull (and made me realize my mistake) but it was not as dark as I would have expected...

NOTE - 5spice sims done and pic assembled while I was sipping my morning coffee. To take with a grain of salt, so (the pic and not the coffee). ;-P

 

[PFDarkside]

What counts is mainly the total resistive load. Volume or tone pots make little difference here when it comes to measured resonant frequencies (at least when pots are full up).

See below.

I've used my "Humbucker as a transformer" model. In this case, it models a HB with 2 conductors cables, symetrical coils, 4.4H, 8k (in the P.A.F. range, IOW).

The curves translate voltage and not current. Otherwise they would be flat before resonant frequency.

Upper left pic = HB with a single 500k volume control.

Bottom left = the same with a single 250k volume pot.

Upper right = the same with a single 25k volume pot.

Bottom right = the same with a 500k volume pot and a 500k linear tone control, itself lowered at 5% of its value. There's a slight shift of the "frequential dome" obviously due to the tone cap (whose capacitance really enters in the game when the pot is set really, really low, for the record, albeit it can affect harmonics even when pots are full up).

If we wanted the load to be exactly @ 25k, the tone pot would be to set @ approximatively 5.3% of its value.

So and to sum it up, a single 25k pot would behave largely like a guitar with two 500k pots, whose tone control would be set just above the final shift to a second resonant frequency caused by the cap...

FWIW, I've once mounted a 25k tone pot instead of a 250k because of a stupid error (not a good idea for a senior to solder in the dark)... The HB was a bright and powerful HB with ceramic mag. The tone was dull (and made me realize my mistake) but it was not as dark as I would have expected...

NOTE - 5spice sims done and pic assembled while I was sipping my morning coffee. To take with a grain of salt, so (the pic and not the coffee). ;-P

Thanks, that’s what I was looking for. Not as unusable as it’s made to be? What if you had a really bright amp, could a single HB/25k volume guitar work?

 

[PFDarkside]

500k, 250k, 25k for what? Tone? Volume? Spin-a-split? Variable treble bleed? Blend control?

25k would work for a split, bleed or blend.

Just a 13k-16k Humbucker and a 25k volume pot.

Basically you are looking at the inductance of the humbucker, combined with the capacitance of your cable. There is also a difference between the two cases when the volume is rolled off. Are you interested in what happens at part volume, or only with the volume knob maxed? What humbucker are you using? and how long is your cable? it seems like you do not have a tone control wired in.

Just the Humbucker and volume, full up, straight into a wireless which eliminates the cable capacitance.

 

[Teleplayer]

I made the simulation based on a JB with 16k resistance, 8H inductance, and only about 30pF additional input capacitance for the wireless unit.

It is not a realistic simulation, because it assumes the wireless unit has high input resistance. If the wireless unit has 500k input resistance, then it will cause the 500k volume control to perform like the 250k plot on the graph.

 

[PFDarkside]

I made the simulation based on a JB with 16k resistance, 8H inductance, and only about 30pF additional input capacitance for the wireless unit.

It is not a realistic simulation, because it assumes the wireless unit has high input resistance. If the wireless unit has 500k input resistance, then it will cause the 500k volume control to perform like the 250k plot on the graph.

Thanks! That’s what I’d expect to see, mud city IMO.

You can probably guess the supposed player with this setup.

 

[freefrog]

Thanks, that’s what I was looking for. Not as unusable as it’s made to be? What if you had a really bright amp, could a single HB/25k volume guitar work?

No, it was not unusable when I've mounted accidentally a 25k tone pot. Yes, a single 25k volume pot might work with a bright amp.

 

[PFDarkside]

No, it was not unusable when I've mounted accidentally a 25k tone pot. Yes, a single 25k volume pot might work with a bright amp.

Thanks.

 

[freefrog]

Just a 13k-16k Humbucker and a 25k volume pot.


Just the Humbucker and volume, full up, straight into a wireless which eliminates the cable capacitance.

Ah, OK...

A wireless without cable capacitance will/would make the resonant peak very high pitched and potentially irritating for ears... while the output level of the pickup will/would be modifiable from the wireless unit.

Flattening this resonance thx to a low resistive pot load might make sense in this case IMHO.

EDIT - I had posted here another sim but have realized that my 5spice program wasn't working properly since the last update.... and I'll have to check if the bug noticed has not corrupted the screenshots already shared in my previous answers.

So, instead of a sim, I'll share below a measurement done this evening: the pickup is a JB style humbucker: 15.4k, 7.8H. Its resonant peak has been measured through a 450pF cable + a 500k single volume pot (in red), with a single 250k volume control (in pink) then with the lowest possible stray capacitance but with a resistive load of only 22k (in black: it mimics approximatively the case of wireless + 25k pot described above).

A differently sized vertical scale makes the curves flatter in this test than in my previous sims but people will "get the picture".

FWIW.

 

[PFDarkside]

Ah, OK...

A wireless without cable capacitance will/would make the resonant peak very high pitched and potentially irritating for ears... while the output level of the pickup will/would be modifiable from the wireless unit.

Flattening this resonance thx to a low resistive pot load might make sense in this case IMHO.

EDIT - I had posted here another sim but have realized that my 5spice program wasn't working properly since the last update.... and I'll have to check if the bug noticed has not corrupted the screenshots already shared in my previous answers.

So, instead of a sim, I'll share below a measurement done this evening: the pickup is a JB style humbucker: 15.4k, 7.8H. Its resonant peak has been measured through a 450pF cable + a 500k single volume pot (in red), with a single 250k volume control (in pink) then with the lowest possible stray capacitance but with a resistive load of only 22k (in black: it mimics approximatively the case of wireless + 25k pot described above).

A differently sized vertical scale makes the curves flatter in this test than in my previous sims but people will "get the picture".

FWIW.

That’s very interesting. A much flatter curve with a lower peak but more extended high end.

 

[Teleplayer]

I suggest to have a look at the instructions for the wireless system. Check if there is a specification for input resistance, and maybe the capacitance. This modelling doesn't tell the real story unless you know the specs of the input it is driving.

 

[freefrog]

I suggest to have a look at the instructions for the wireless system. Check if there is a specification for input resistance, and maybe the capacitance. This modelling doesn't tell the real story unless you know the specs of the input it is driving.

Absolutely!
Goes without saying that my test above was done through a 1M input but the "host" input is critical...

Years ago, someone (I think it was Malcolm Moore) had shared a screenshot showing how changing loads @ input can totally reshape the response of mag PU's. It's a pity to note that such docs are no more accessible online.
I'll share what I'm talking about if I can find it in my crowded archives (talk me about finding a single pic among thousands of files in several hard disks :-/ )...

EDIT - found it by luck. In his 2003-2007 synthesis, Malcolm Moore was saying:

The graph below shows [a] 'Strat 01' pickup with various loads on it, and it should be
very clear that if other pickups were put in place, then the shapes of the frequency
response curves would follow the same. In other words, it does not really matter
which pickup is used, with a bit of load tailoring, (adjusting the load resistor value and
the load capacitor value) virtually any magnetic pickup manufactured along these
lines can all be made to have virtually identical frequency responses.

 

[PFDarkside]

I’m sure for the artist in question it was a big name system that many used throughout the 80’s. (Schaffer–Vega)