Stepped Attenuator 4 pole = quad?

The mains reason for adopting balanced impedance connections is to attenuate interference from a noisy environment.

This requires precise matching of impedances.
Conventional attenuators are not impedance matched
Stepped attenuators could be impedance matched. But these usually use +-1% resistors.
For good interference attenuation you need better than 0.1% matching of impedances.
That would require +-0.05% resistors. AND the cabling+connections must also give an impedance match over many years of use/misuse.

Look at B.Putzeys
His balanced impedance volume control uses:
Balanced impedance input >> bal to unbal stage >> active vol pot >> unbal to bal stage >> balanced impedance output
That's the way to do it effectively, if you need the advantages that balanced impedance connections bring to your system.
 
Look at B.Putzeys
His balanced impedance volume control uses:
Balanced impedance input >> bal to unbal stage >> active vol pot >> unbal to bal stage >> balanced impedance output
That's the way to do it effectively, if you need the advantages that balanced impedance connections bring to your system.
Thanks, Andrew.
So, if I'm trying to incorporate 'volume control' into a system with a Pass Balanced Line stage (BOSOZ 'preamp')- with unbalanced input & balanced output- and a Pass Aleph J power amp (balanced inputs).... I should put a stereo volume pot on the unbalanced input side of the preamp, not on the output?
 
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Had a look at the one quoted above on Ebay, looks like a 4 pole switch to produce the stereo attenuator. Herein lies the confusion.

Thanks, that makes sense to me.
I've asked the seller for a wiring/connection diagram, but I'm not hopeful on that. :)

So, IF that's what I need (want) I'll probably be sticking to 4-gang pots - which are quite limited in availability (Bourns minis only at Mouser and Digikey).
From Andrew T's comment, it looks like I'd be better off doing the attenuation on the unbalanced side, between the source (CDP or DAC) and the 'preamp'/amp.
 
Have a look at B.Putzeys' balanced vol pot.
Compare his output to the one shown in Jensen's an003

You have unbal to bal.

So I suggest you make this:
unbalanced source >> selector >> vol pot + Buffer >> unbal to bal >> balanced receiver.

The ONLY part that needs to be balanced is the final unbal to bal convertor. This is the part that will tolerate long leads in a noisy environment.
All the preceding should be on shorter leads and enclosed in screening enclosures.

Are there any balanced impedance experts out there that disagree on that system topology?
 
Sorry to get a bit off the original topic.....but the attenuator choice is really dictated by other decisions on 'topology'...
You have unbal to bal.

So I suggest you make this:
unbalanced source >> selector >> vol pot + Buffer >> unbal to bal >> balanced receiver.

The ONLY part that needs to be balanced is the final unbal to bal convertor.
The 'preamp'/buffer I'm building is the BOSOZ - Pass Balanced Line Stage. It's the first time I've ventured into 'balanced' circuits; I plan to mate it with a Pass Aleph J diy power amp which can accept balanced inputs.
The BOSOZ can have attenuation at both the input and output, as well as a 'gain setting' control. Nelson Pass and some builders have commented that the volume control is better at the output - but your comments about tracking/balance issues on the balanced side make a lot of sense.
So, pehaps I'd be bette to put the control at the (unbalanced) input end - this would also allow me to insert a L-R 'balance control' which my room environment really needs as there is a large doorway/arch on the L side.
This is the part that will tolerate long leads in a noisy environment.
All the preceding should be on shorter leads and enclosed in screening enclosures.
Andrew- in your opinion are there any advantages to balanced connections in a 'normal' - short leads and no big electrical noise issues- home environment?
How much will I be 'missing' from the possible performance of those Pass designs by running them unbalanced?
Thanks for your input, as always.:)
 
There may be a small gain in audio performance from using an all balanced impedance and balanced +fully differential amplification in a system that is designed from the ground up to take advantage of what the topology can give.

One downside and it has already been mentioned. Balanced is usually very slightly noisier, but if you take on the fully differential with the extra 6dB of signal, that noise will be masked by the higher signals.

The big advantage of balanced impedance is for the connections and their rejection of interference. In a domestic system, this may not show any advantage, except if you were to distribute over long distances to the far ends of a long house from a centralised source/selector. And where you will pass around areas of known noisy switching/interference.
 
I'm pretty sure that ebay item in the first post is a ladder type 2-channel stepped attenuator. only two resistors per channel are involved to form an attenuator at any given position, that's why a 4-pole switch. I had one of these myself. The Chinese made 4x24 switch has a crappy detention feel that's hard and bumpy throughout the range, and the travel from step to step is somehow slightly unevenly spaced. The positive side is it does what it should quite well. The switch has make-before-break contact transition so the stage that follows it does not get its input open-circuited.
 

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Nattawa:
Thanks for that diagram- it explains how the 4-pole switch is wired for 2 channels. I have a couple of those in my parts collection which I bought but never used - I really prefer the 'continuous adjustment' of a pot, but I know they don't track as accurately as a good stepped attenuator.
DIY-ing one of those switches (to get a 4-gang equivalent if needed) isn't my idea of fun, but one never knows what the future may hold!