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Wiring , pot value(s) for ( 2 xAldrich HB's) with EMG SPC ?

 
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StarBuck83



Joined: 01 Jul 2017
Posts: 1

PostPosted: Sat Jul 01, 2017 2:29 pm    Post subject: Wiring , pot value(s) for ( 2 xAldrich HB's) with EMG SPC ? Reply with quote

Intro : I have an awesome modern ( faded trans blue whale carve maple top ) that brings me joy every day Smile ( Thank you Suhr!! LOL )
I ordered it a few years back with AHB1's and an EMG SPC.
However, I'd like to switch out the Blackouts for some passive Aldrich HB's.

So naturally I have questions.

As I'd like to keep the option of going back to actives, I'd like to keep the SPC . However this brings up the question of the volume pot size etc.

Normally one would use a high pot value ( 250 or 500K not sure what Suhr default would be ?) with passives so as not to load them , roll off freq response etc. With the AHB1's there's a 25K pot. ( makes sense , given the low output impedance and high SPC input impedance .
From EMG.. "oh use a 250K " ... uuummmhh yah NO .. that didn't work at all... Think.... sounds like crap :-0 A high pot value into the SPC produced some interesting sounds but none of them usable. Smile
So low(er) value pot ?
The SPC 250K input impedance leads me to believe it is expecting a 25Kpot ( 10:1 loading rule)...
Yet a 25K pot across the output impedance of the Aldrich would severely load it and quite probably alter it's frequency response ? ( Even 50K would affect the passive picks ?)

So... to keep the SPC I would have to add a pre amp/ buffer to the passives ? Then use the 25K VOL and SPC..
The SPC effect is subtle yet noticeable and like I said I'd like to keep it ... but...

Any suggestions with type of setup ?

On the off chance that it's just simpler to remove all the active stuff and go back to stock... what are default values for vol and tone pots and roll off cap. ( I like 80's metal.. so maybe 500K ?)

I did search for the forum but only came up with some old posts about mid boost . but little tech info etc.
Any advice would be greatly appreciated.

Ok, Having thought about this some more, and having made a schematic for the SPC , it makes a little more sense.

I did read that ENG shipped out a number ( 350 or so ) SPC's with a component missing that caused people untold grief when attempting to use it with passive pickups... Not sure if I have one, but it's behavior suggests I do. Looking at the schematic, I don't' see anything grossly wrong with it.. signal wise it makes sense.. for a cheap mid booster.

So , yes the SPC does have a unity gain buffer with a 200K input impedance ... as that would , match ( sort of...) with a passive single coil that would normally have a 250K pot across it.
So at a minimum ( to use the SPC with HB's) the SPC input impedance should be increased to 500K . I get it that the SPC wasn't' really designed for humbuckers , ( Strat Presence Control) but hey, every day should be a series of experiments.
Having said that, given the humbuckers output impedance @ resonance ( A quick approximation would seem to put the Aldrich Bridge @ roughly 450Kohms around 4KHz) then to avoid loading and changing tonal characteristics too much, perhaps we should use a 1MEG VOL pot and up the SPC input to match. Yes at some point as we raise the impedance we will run into noise susceptibility but let's see what happens.

Wish me luck Smile

SB
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Suhr



Joined: 25 Jan 2005
Posts: 2127

PostPosted: Mon Sep 04, 2017 10:48 am    Post subject: Re: Wiring , pot value(s) for ( 2 xAldrich HB's) with EMG SP Reply with quote

I would advise you use our mid boost. PS that "rule" is a minimum, not optimal. 10:1 is no loss or negligible. 1K is not a problem feeding 1M but shouldn't feed lower than 10K
StarBuck83 wrote:
Intro : I have an awesome modern ( faded trans blue whale carve maple top ) that brings me joy every day Smile ( Thank you Suhr!! LOL )
I ordered it a few years back with AHB1's and an EMG SPC.
However, I'd like to switch out the Blackouts for some passive Aldrich HB's.

So naturally I have questions.

As I'd like to keep the option of going back to actives, I'd like to keep the SPC . However this brings up the question of the volume pot size etc.

Normally one would use a high pot value ( 250 or 500K not sure what Suhr default would be ?) with passives so as not to load them , roll off freq response etc. With the AHB1's there's a 25K pot. ( makes sense , given the low output impedance and high SPC input impedance .
From EMG.. "oh use a 250K " ... uuummmhh yah NO .. that didn't work at all... Think.... sounds like crap :-0 A high pot value into the SPC produced some interesting sounds but none of them usable. Smile
So low(er) value pot ?
The SPC 250K input impedance leads me to believe it is expecting a 25Kpot ( 10:1 loading rule)...
Yet a 25K pot across the output impedance of the Aldrich would severely load it and quite probably alter it's frequency response ? ( Even 50K would affect the passive picks ?)

So... to keep the SPC I would have to add a pre amp/ buffer to the passives ? Then use the 25K VOL and SPC..
The SPC effect is subtle yet noticeable and like I said I'd like to keep it ... but...

Any suggestions with type of setup ?

On the off chance that it's just simpler to remove all the active stuff and go back to stock... what are default values for vol and tone pots and roll off cap. ( I like 80's metal.. so maybe 500K ?)

I did search for the forum but only came up with some old posts about mid boost . but little tech info etc.
Any advice would be greatly appreciated.

Ok, Having thought about this some more, and having made a schematic for the SPC , it makes a little more sense.

I did read that ENG shipped out a number ( 350 or so ) SPC's with a component missing that caused people untold grief when attempting to use it with passive pickups... Not sure if I have one, but it's behavior suggests I do. Looking at the schematic, I don't' see anything grossly wrong with it.. signal wise it makes sense.. for a cheap mid booster.

So , yes the SPC does have a unity gain buffer with a 200K input impedance ... as that would , match ( sort of...) with a passive single coil that would normally have a 250K pot across it.
So at a minimum ( to use the SPC with HB's) the SPC input impedance should be increased to 500K . I get it that the SPC wasn't' really designed for humbuckers , ( Strat Presence Control) but hey, every day should be a series of experiments.
Having said that, given the humbuckers output impedance @ resonance ( A quick approximation would seem to put the Aldrich Bridge @ roughly 450Kohms around 4KHz) then to avoid loading and changing tonal characteristics too much, perhaps we should use a 1MEG VOL pot and up the SPC input to match. Yes at some point as we raise the impedance we will run into noise susceptibility but let's see what happens.

Wish me luck Smile

SB
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