What's the qualitative difference between Zen Lite Balanced and ZV7-R ?

[Alex S]

I did a double-take because they look so similiar except the Zen Lite Balanced (fig. 16, Zen Variations 1) seems to make-do without the constant current source in the bottom half of the curcuit.

Or, in another words, what does the additional cmplexity with the constant current source in ZV7-R (fig. 1, Zen Variations 7) buy?

Thanks.

 

[Nelson Pass]

Setting aside issues of efficiency, we note that the larger the
value of the resistor (and higher voltage of the negative supply)
the more it behaves like a constant current source.

For reasonably high values of this resistance (say 8 ohms or so)
the performance between it and a CCS are not that big as long
as you are running a good symmetric balanced input. If you
go to single-ended input, then the distortion goes up. This is
true even with a CCS since a CCS isn't often that perfect at the
higher frequencies.

As a result, a CCS is superior with a single-ended input, and
generally is a little bit quieter than the resistor, depending on
the supply. On the other hand, if you have a large value resistor
(16 ohms or more), a quiet supply, and balanced inputs, I think
the resistor sounds a little better.

 

[Alex S]

Thanks for the reply, Mr Pass.

The evolution from ZV6 to ZV7-R consists of 'eliminating the negative power supply rail, and biasing with a constant current source'. These two changes were lumped and discussed as one in the ZV7 document.

Going back to the Zen-Lite Balanced circuit seem to indicate that the negative supply can be eliminated without bringing in the constant current source. It got me curious that's all. The Zen-Lite Balanced looked like ZV6.5 ; does that mean it's already Susy?

So, the CCS is optional, - useful for certain situations (i.e. single-end input, noisy supply, and to get slightly better efficiency), as your reply explained. Thanks!

 

[stefanobilliani]

Going back to the Zen-Lite Balanced circuit seem to indicate that the negative supply can be eliminated without bringing in the constant current source. It got me curious that's all. The Zen-Lite Balanced looked like ZV6.5 ; does that mean it's already Susy?

Hello Alex,

The zen lite balanced isn't Su-Sy. In fact is possible bring in the CCS even with a single rail voltage , but Su-Sy requires the current source .Depending on the circuit it can be a resistor or a CCS.

 

[Alex S]

oh I see. that's the answer I was looking for - thanks!