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Old 22nd July 2001, 12:10 PM   #1
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Iím interested in what others have used for attenuation (i.e volume control) for the Balanced Zen line stage. Iím inclined to use relay switched resistors, however am interested in other ideas also.

Cheers,

Pete
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Old 22nd July 2001, 01:29 PM   #2
jam is offline jam  United States
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Pete,

You must be busy building your preamp.

The best volume control I have used is a shunt control. It has only one element (resistor) which can be a high quality Vishay, for example, in series with the input of the gain stage. The other part consists of a string of resistors which progressively shorts the input to ground.
The above can be realised with a four gang rotary switch or two, two gang switches.
Relays could be used to acomplish this but are noisy, these were used in early Pass Labs preamps. Today Pass uses a string of transistor switches to acomplish the same thing.
The shunt volume control is also used by Balanced Audio Technology in all their preamps (they acomplish this with cmos switches).

Cheers,
Jam
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Old 23rd July 2001, 11:49 AM   #3
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Lightbulb Switched volume controls

Actually, I suspect Nelson got the idea from one of the DIY'ers on his website gallary page ....

"... and an interesting electronic volume control. The volume control uses precision resistors and bipolar transistors to do the attenuation of the signal. Check Maik's web site for the complete description of the project.", viz:

http://members.tripod.de/MaikHerzog/...eamp_text.html

This is VERY NEAT ;-)

cheers, mark
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Old 23rd July 2001, 06:03 PM   #4
hifi is offline hifi  Sweden
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that seem like a nice idea.... will probobly use that in my next design...


just match the demux with a counter then one could just two switches for upp down..and maybe make it reset it self to zeor when turned on ;-)


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Old 24th July 2001, 12:16 AM   #5
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Default SS switching

Yes I've come across this before and I agree it will probably be the way I will go. I was, however, leaning towards a ladder type control, although I confess that in this application it probably won't make a huge difference.

Cheers,

Pete
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Old 2nd August 2001, 12:27 PM   #6
Alex M is offline Alex M  United Kingdom
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I've never understood the theory that varying only the
shunt component of an attenuator should give a performance
advantage. Would anyone care to enlighten me?

Alex
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Old 2nd August 2001, 01:55 PM   #7
hifi is offline hifi  Sweden
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why would relays be noicy?? if one would slow them down with som small caps to get mbb operation i cant se how they would be noicy? or do you mean the klicks from the relays themselfs???


/micke
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Old 2nd August 2001, 10:36 PM   #8
jam is offline jam  United States
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Micke,

I ment to say the mechanical noise due to the relays clicking could be annoying.

Jam
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Old 2nd August 2001, 10:47 PM   #9
jam is offline jam  United States
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Alex,

If you look at a shunt control there is only one resistor in series with the next stage and in theory the shunt element should not affect the sound as it shunts the signal to directly ground. So that the signal that needs to be amplified only passes thru one high quality resistor and no switches.

This actually works but you have to be careful in the selection of resistors as noise and loading effects can come inyo play.

Jam
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Old 3rd August 2001, 09:21 AM   #10
Alex M is offline Alex M  United Kingdom
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Jam,

"...in theory the shunt element should not affect the sound
as it shunts the signal to directly ground"

I'm not aware of this theory. The only theory I know of is
the expression for an attenuator made of two resistors,
which says that the attenuation is R1/(R1+R2), where R1 is
the shunt resistance. The whole output signal is present
across this component, and the output is DIRECTLY
proportional to its value, so it might be expected to have
the most effect on the sound quality. I'd love someone to
convince me otherwise, but until then I suspect it's a
clever excuse by manufacturers to spend less on parts.

Alex
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