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September 20, 2020, 04:31:29 PM

Author Topic: Bias pots and selector switch  (Read 142 times)

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Offline Samsquatch

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Bias pots and selector switch
« on: April 23, 2020, 07:58:44 AM »
Hi Bottlehead Forum.

I have just begun my Stereomour II build and am just wondering if there is any benefit from upgrading the 10 Ohm pots and the 4 pole 3 position switch. And if so what would the recommendations be?

Thanks in advance!
Mike
Winnipeg
Stereomour II   Seductor/Smash  Crack HD650 HD700
Rega Planar P3 Reduction Ortofon Bronze
Nuforce DAC 80
Fostex FE126EN in DIY backloaded horn enclosures
Best sounding system I've ever owned

Online Paul Birkeland

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Re: Bias pots and selector switch
« Reply #1 on: April 23, 2020, 08:09:26 AM »
The 10 ohm pot is a hum pot (the Stereomour is an auto biasing amp).  There are very, very few choices available that would work well in that position, so I wouldn't recommend changing out that part. 

Some folks have changed out the 4P3T switch for a Goldpoint. 
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline Samsquatch

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Re: Bias pots and selector switch
« Reply #2 on: April 23, 2020, 11:53:54 AM »
Thanks Paul.

So would the hum pots become obsolete with the DC filament upgrade?

Mike
Winnipeg
Stereomour II   Seductor/Smash  Crack HD650 HD700
Rega Planar P3 Reduction Ortofon Bronze
Nuforce DAC 80
Fostex FE126EN in DIY backloaded horn enclosures
Best sounding system I've ever owned

Online Paul Birkeland

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Re: Bias pots and selector switch
« Reply #3 on: April 23, 2020, 12:20:07 PM »
The DC filament upgrade does not create, ripple free DC, so the humpot is still quite useful. 

The 2A3 filament itself is a 1 ohm resistance that sits across the hum pot and 22 ohm balancing resistors, so this isn't a mission critical part.  With the DC filament upgrade, there are also some big caps in parallel with the 2A3 filament that are even lower impedance than 1 ohm (at most frequencies).
Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man