Balanced line stage- input or output attenuator

nobody special · 6th April 2006, 05:21 PM

I will be building a zen balanced line stage using a uC and relay attenuator, and I was wondering about the trade-offs between attenuating the input vs. the output.
It seems to me that the output network uses some very small value resistors for the low volume settings to keep the output Z low, but has the benefit of reducing the noise of the circuit, as described in the original article.
On the input side I was considering using a matched Nchannel JFET buffer between the major (10db steps) and minor (1.25db steps) attenuators, keeping isolation and preserving the loading impedance so one doesn't affect the other. The problem there is no output noise attenuation.
I have also considered splitting the major and minor steps- minor on input and major on the output (or the opposite).
Anyone have any comments or suggestions?

flg · 6th April 2006, 06:20 PM

Steve, where in USA???
Well, the JFET input may keep the noise level down if you attenuate at the input. Recently I have seen a few threads relative to this subject(volume, gain, levels etc. May have been X or SOZ topologies). A search would be fruitful I think...
I have a question though. Is'nt there a "gain" control between a diff pair of sources in the design you have in mind. What is wrong with using the gain control as the level adjust??? There will be changes in measured performance by using this component that way but, I don't think they will be a showstopper. You might therfore want the ideal input level with the level control at the most typical setting to acheive close to optimum performace at typical listening levels. Just some idea's.

nobody special · 6th April 2006, 06:32 PM

I'm near Akron / Youngstown Ohio.
I plan on implementing an "X" topology, so the gain resistor is out. I'm not sure that it's the best idea anyway because distortion performance would change with gain settings. With more feedback at lower gain settings you would get more upper harmonics with less lowers to mask them, and it might start to sound thin and brittle.
I'll give the search a try, but there are just SO many threads and I'm feeling lazy.

Thanks for the ideas

Nelson Pass · 6th April 2006, 08:44 PM

My preference is to provide a variable input divider and output
shunt, setting the input so that with no output attenuation you
get a level somewhat higher than what you will use in real life.

nobody special · 7th April 2006, 01:18 PM

Nelson,
By shunt do you mean a voltage divider or loading the outputs to ground? Thanks for the reply.

6th April 2006, 05:21 PM	#1
nobody special diyAudio Member Join Date: Oct 2002 Location: USA	Balanced line stage- input or output attenuator I will be building a zen balanced line stage using a uC and relay attenuator, and I was wondering about the trade-offs between attenuating the input vs. the output. It seems to me that the output network uses some very small value resistors for the low volume settings to keep the output Z low, but has the benefit of reducing the noise of the circuit, as described in the original article. On the input side I was considering using a matched Nchannel JFET buffer between the major (10db steps) and minor (1.25db steps) attenuators, keeping isolation and preserving the loading impedance so one doesn't affect the other. The problem there is no output noise attenuation. I have also considered splitting the major and minor steps- minor on input and major on the output (or the opposite). Anyone have any comments or suggestions? __________________ Nobody

6th April 2006, 06:32 PM	#3
nobody special diyAudio Member Join Date: Oct 2002 Location: USA	I'm near Akron / Youngstown Ohio. I plan on implementing an "X" topology, so the gain resistor is out. I'm not sure that it's the best idea anyway because distortion performance would change with gain settings. With more feedback at lower gain settings you would get more upper harmonics with less lowers to mask them, and it might start to sound thin and brittle. I'll give the search a try, but there are just SO many threads and I'm feeling lazy. Thanks for the ideas __________________ Nobody

7th April 2006, 01:18 PM	#5
nobody special diyAudio Member Join Date: Oct 2002 Location: USA	Nelson, By shunt do you mean a voltage divider or loading the outputs to ground? Thanks for the reply. __________________ Nobody

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6th April 2006, 06:20 PM	#2
flg diyAudio Member Join Date: Jul 2005 Location: North East	Steve, where in USA??? Well, the JFET input may keep the noise level down if you attenuate at the input. Recently I have seen a few threads relative to this subject(volume, gain, levels etc. May have been X or SOZ topologies). A search would be fruitful I think... I have a question though. Is'nt there a "gain" control between a diff pair of sources in the design you have in mind. What is wrong with using the gain control as the level adjust??? There will be changes in measured performance by using this component that way but, I don't think they will be a showstopper. You might therfore want the ideal input level with the level control at the most typical setting to acheive close to optimum performace at typical listening levels. Just some idea's.

6th April 2006, 08:44 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	My preference is to provide a variable input divider and output shunt, setting the input so that with no output attenuation you get a level somewhat higher than what you will use in real life.

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