### Post by cooltone on Dec 16, 2012 8:35:51 GMT -5

I am submitting some ideas about the circuit design for a humbucker coils configured in parallel. I am planning to use these ideas on my Vintage V100 and would appreciate any comments/criticism/improvements from the forum.

Summary of circuit features

- Simplifies setting the characteristic guitar sound. L_hb, C_res and R_Q act like a an equaliser giving good control of the characteristic sound - experiment with C_res values first, then R_Q values.

- The characteristic sound is preserved at nearly all vol pot levels - treble bleed is not needed.

- Some provision for centre position volume mixing is available

- A second characteristic sound created when tone pot set to zero, which is user definable.

1) Humbucker resonance

First some background ideas triggered by the fine work of JohnH, thread ref: A better treble bleed circuit.

My approach is to think of the humbucker inductance as making a resonant circuit with the all the surrounding components, up to and including the cable and amp impedance.

With multiple capacitors there are multiple modes of resonance. Each mode of resonance is defined by a particular LCR combination which defines the resonant frequency and the Q factor. When R is high there is little resonance (low Q). LCR combinations with a low resonant frequency attenuate higher frequency resonance of other LCR combinations.

2) HB Parallel Coils (compared to series coils)

- the inductance is roughly divided by four

- the series resistance is roughly divided by four

- Coli capacitance is multiplied by four - in practice the multiplier is 2~3 times

(For reference see: www.buildyourguitar.com/resources/lemme/table.htm )

3) The MacSpice Net List for the design

***********************

ParallelHumbuckerCircuit

*

* By Cooltone

* Input voltage

vin 1 0 ac 1.0 dc 0.0

* Humbucker Parameters (estimated)

L_hb 1 2 1.65

R_hb 2 3 2K

C_hb 3 0 200p

*Load Capacitor and Resistor - to define resonant freq. and Q

R_Q 3 4 0.01k

C_res 4 0 1.5n

* Volume Pot

R_vol1 4 5 0.01k

R_vol2 5 0 550k

* Tone Pot and Capacitor

R_tone 4 6 550K

C_tone 6 0 10n

* Mixer Resistor

R_mix 5 7 50k

* Amp and Cable Load

R_amp 7 0 1Meg

C_cable 7 0 200pf

.control

* dispose of any 'save' statements from previous runs

delete all

* perform an ac analysis

ac dec 200 200Hz 4kHz

* plot the magnitude of the voltage at node 7 vs frequency

plot db(v(7)) xlog

.endc

.end

*******************

4) Circuit description

- At Vol pot = 10, L_hb and (C_hb +C_res) define the prime resonant frequency (see R_mix info). As the volume pot is reduced the resonance of L_hb and C_cable is attenuated by the resonance characteristic of L_hb and C_hb+C_res. This means the resonant frequency is quite stable over all vol pot levels.

- R_Q is used to manage the Q factor. Since series wiring reduces the pickup resistance, the Q factor is increased, R_Q is used to reduce the Q factor.

- R_mix, provides some mixing function when selecting both neck and bridge pickups. Since R_mix feeds into the R_amp (~ 1M), the signal loss is relatively small (< 1db). R_mix also provides further isolation of C_cable from L_hb which reduces its influence on the prime resonant frequency.

- C_tone is increased by a factor of four, since L_hb is reduced by a factor of four. As the tone control pot is reduced, the resonance of L_hb and C_tone attenuates the resonance of L_hb and (C_res + C_hb). When the tone control is close to zero, a new resonance is formed from L_hb and (C_res + C_hb + C_tone).

- Connecting the coils in series results reduced output compared to the parallel configuration, but I do not believe it is halved, I believe it is dependent on power transfer characteristics (a bit too complex for me to work out). However, I believe this can be compensated by turning up the pre-amp without introducing significant amp noise.

5) Caveats

- Many of the circuit values have been estimated, since manufacturers rarely provide characterisation data for pickups.

- I have only performed model analysis on MacSpice, so there may be some variations in practice

- Choosing a value for R_Q is just a guess. Setting R_Q to zero yields a Q of 13db, which is aggressive. 6.8k reduces this to 8db.

- I used 550k pots from CTS/Bareknuckle

I would really appreciate any comments and a sanity check!

Summary of circuit features

- Simplifies setting the characteristic guitar sound. L_hb, C_res and R_Q act like a an equaliser giving good control of the characteristic sound - experiment with C_res values first, then R_Q values.

- The characteristic sound is preserved at nearly all vol pot levels - treble bleed is not needed.

- Some provision for centre position volume mixing is available

- A second characteristic sound created when tone pot set to zero, which is user definable.

1) Humbucker resonance

First some background ideas triggered by the fine work of JohnH, thread ref: A better treble bleed circuit.

My approach is to think of the humbucker inductance as making a resonant circuit with the all the surrounding components, up to and including the cable and amp impedance.

With multiple capacitors there are multiple modes of resonance. Each mode of resonance is defined by a particular LCR combination which defines the resonant frequency and the Q factor. When R is high there is little resonance (low Q). LCR combinations with a low resonant frequency attenuate higher frequency resonance of other LCR combinations.

2) HB Parallel Coils (compared to series coils)

- the inductance is roughly divided by four

- the series resistance is roughly divided by four

- Coli capacitance is multiplied by four - in practice the multiplier is 2~3 times

(For reference see: www.buildyourguitar.com/resources/lemme/table.htm )

3) The MacSpice Net List for the design

***********************

ParallelHumbuckerCircuit

*

* By Cooltone

* Input voltage

vin 1 0 ac 1.0 dc 0.0

* Humbucker Parameters (estimated)

L_hb 1 2 1.65

R_hb 2 3 2K

C_hb 3 0 200p

*Load Capacitor and Resistor - to define resonant freq. and Q

R_Q 3 4 0.01k

C_res 4 0 1.5n

* Volume Pot

R_vol1 4 5 0.01k

R_vol2 5 0 550k

* Tone Pot and Capacitor

R_tone 4 6 550K

C_tone 6 0 10n

* Mixer Resistor

R_mix 5 7 50k

* Amp and Cable Load

R_amp 7 0 1Meg

C_cable 7 0 200pf

.control

* dispose of any 'save' statements from previous runs

delete all

* perform an ac analysis

ac dec 200 200Hz 4kHz

* plot the magnitude of the voltage at node 7 vs frequency

plot db(v(7)) xlog

.endc

.end

*******************

4) Circuit description

- At Vol pot = 10, L_hb and (C_hb +C_res) define the prime resonant frequency (see R_mix info). As the volume pot is reduced the resonance of L_hb and C_cable is attenuated by the resonance characteristic of L_hb and C_hb+C_res. This means the resonant frequency is quite stable over all vol pot levels.

- R_Q is used to manage the Q factor. Since series wiring reduces the pickup resistance, the Q factor is increased, R_Q is used to reduce the Q factor.

- R_mix, provides some mixing function when selecting both neck and bridge pickups. Since R_mix feeds into the R_amp (~ 1M), the signal loss is relatively small (< 1db). R_mix also provides further isolation of C_cable from L_hb which reduces its influence on the prime resonant frequency.

- C_tone is increased by a factor of four, since L_hb is reduced by a factor of four. As the tone control pot is reduced, the resonance of L_hb and C_tone attenuates the resonance of L_hb and (C_res + C_hb). When the tone control is close to zero, a new resonance is formed from L_hb and (C_res + C_hb + C_tone).

- Connecting the coils in series results reduced output compared to the parallel configuration, but I do not believe it is halved, I believe it is dependent on power transfer characteristics (a bit too complex for me to work out). However, I believe this can be compensated by turning up the pre-amp without introducing significant amp noise.

5) Caveats

- Many of the circuit values have been estimated, since manufacturers rarely provide characterisation data for pickups.

- I have only performed model analysis on MacSpice, so there may be some variations in practice

- Choosing a value for R_Q is just a guess. Setting R_Q to zero yields a Q of 13db, which is aggressive. 6.8k reduces this to 8db.

- I used 550k pots from CTS/Bareknuckle

I would really appreciate any comments and a sanity check!