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super high pitch 'whine' with treble boost on active preamp?


goonieman
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Hi All,

I just installed in a Spector Tonepump into my 2 x humbucker bass using this diagram:

http://michalik.cz/images/pdf/bp-4_2volume_rev2_en.pdf

Only I used a 250K vol pot, and added the ground from the bridge assembly into the ground on the jack (where the brown wire goes).

I gut this intermittent 'whine' when boosting the treble pot:, FYI:

[color=#333333][font=Verdana, Arial, sans-serif]• Powered by 9V battery[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Current consumption 1,2mA[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Battery lifetime cca 420 hours, when using quality alkaline ones up to 1000 hours.[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Gain +12dB[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Tone controls:[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Bass: +14dB/-4dB @55Hz[/font][/color]
[color=#333333][font=Verdana, Arial, sans-serif]• Treble: +14dB/-12dB @6,5kHz[/font][/color]

[color=#333333][font=Verdana, Arial, sans-serif]I reckon its battery related because the 'whine' reduces and drifts when I move the battery around the compartment. Should the battery be shielded?[/font][/color]

[color=#333333][font=Verdana, Arial, sans-serif]thx[/font][/color]

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I've never heard of a battery being the cause of electromagnetic interference - though if you're moving the battery about that probably means you're also moving bundles of wires about with the possibility of movement at poorly made connections maybe? Looking at Tonepump wiring diagrams I see that some suggest using 250K volume pots and some (including the BP-4 module that your diagram indicates) say use 500K - are you sure the 250K pots are ok? This assumes you've got passive humbuckers too.

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More likely there's something in the vicinity which is causing the previously imperceptible whine, and the treble boost is enhancing it. The battery could well alter the pattern by which it's being picked up.
All kinds of things can cause electromagnetic interference.. cabling, lighting, transformers, mobile phones.. you name it! Tried switching things off to see if anything in the house is the cause?

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[quote name='HowieBass' timestamp='1438269716' post='2833100']
I've never heard of a battery being the cause of electromagnetic interference - though if you're moving the battery about that probably means you're also moving bundles of wires about with the possibility of movement at poorly made connections maybe? Looking at Tonepump wiring diagrams I see that some suggest using 250K volume pots and some (including the BP-4 module that your diagram indicates) say use 500K - are you sure the 250K pots are ok? This assumes you've got passive humbuckers too.
[/quote]

I would have thought that 500k would bring out the higher spectrum even more?

I have MEC passive soapbar pups.

It's odd, because my passive single coil MECs on my warwick corvette with glokenklang pre are totally silent!

I've emailed the designer of the tonepump, so i guess i'll wait to hear back.

thanks

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Humbuckers usually take 500K pots but if you've enough treble and you like the sound then stick with the 250K. How well is the bass shielded? I'm just wondering if the high pitched whine when you boost the treble is evidence of interference that needs screening out.

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  • 2 months later...

If the pickup is passive and is controlled before the signal enters the preamp, then sometimes the higher value pots are used, as the pickups are essentially functioning in passive mode.

By not wiring the bass exactly according to the schematic, you may have introduced a loop that caused the preamp to become unstable and induced oscillation.

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