relay volume attenuator for PASS pre - diyAudio
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Old 17th January 2005, 08:38 AM   #1
kiyull is offline kiyull  South Korea
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Default relay volume attenuator for PASS pre

Hi,

I plan to make 255 step relay attenuator for PASS pre (P1.7 or BOZOS) using ICL7109 ADC(using 8 MSB).
I calculated impedances of the attenuator using the R values of P1.7 and other values(startng with 1K, 2K, 4K etc. just trial values). However, calculated impedances using R values of P1.7 is very low (less than 500 ohm, left fig in attached file). The impedance with other R values shows 2 to 5 kohm which is much higher than those of P1.7.

I am not sure about the proper R values for the BOSOZ where the 10K pot are recommended, since I am not an expert in this field.

Kiyull
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Old 24th February 2005, 07:48 AM   #2
kiyull is offline kiyull  South Korea
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Hi,

More than 300 diyer read this post, but : Probably, I missed "?".

Meanwhile, I have assembled the relay volume control (with R set 2 of previous post)and I attached to the Atmel AT89C51 which I want to use it for a VFD (or LCD). Display contains input source, attenuation and some flying characters as you see in the picture.

I want to use it with Henrik's X-BOSOZ and Aleph-X at the moment (both are not finished yet).

I have two questions:
1) What is the best position of this volume, i.e., input or output?
2) Can I use this at P1.7 without changing the resistors of R set 1 ?

Any comments will be appreciated .

Kiyull
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Old 24th February 2005, 08:03 PM   #3
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To answer your 1st question... The volume control should be at the output for reduced noise.

On your 2nd question, checkout what Till added in this thread regarding relay attuenation. Nelson made helpful comments here as well.
Aleph P Attenuation Circuit

Till is banned, but is taking questions on the circuit on http://www.diyhifi.org

-David
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Old 26th February 2005, 02:30 AM   #4
kiyull is offline kiyull  South Korea
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Thanks David, I was not sure about the proper reason to put the pot at the output.

-Kiyull
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Old 26th February 2005, 02:56 AM   #5
Illusus is offline Illusus  Canada
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A pot at the input attenuates the signal going into the line amp, at the output there is full gain from the linestage including all noise it creates. A pot at the output attenuates the signal coming from the line amp including it's noise level. So...when you turn down the music volume you are also turning down any hiss and hum coming from the linestage.

EDIT: "I was not sure about the proper reason to put the pot at the output."
I guess my post was pointless...I misread you.
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