I wrote Wayne Colburn of Pass Labs yesterday as to why his phono preamps use single-ended inputs instead of balanced:
Hello Wayne,
I am hoping you can explain to me why you use single-ended inputs only on your phono stage designs. I always think of any output from a coil transducer, be it a phono cartridge, tape head, microphone coil, transformer secondary etc, as inherently balanced, center tapped or not.
I think I remember Nelson saying better noise performance is obtained with a cartridge by strapping one side of the coil to ground, am I remembering that right? Please see attached. So, diagram 1 beats digram 2 for noise, even though they are (in my mind) equivalent series circuits? Assuming the same differential pair input.
There seems to be a debate between external tape head preamplifier design guys as to which is best, with Nick Doshi firmly in the balanced camp. I was told my Studer A80RC mkII reproduce card has balanced input stage, I looked up the schematic it does not. It got me thinking as I couldn't imagine why a balanced configuration like diagram 2 or 3 wouldn't perform better.
Please clarify this for me, I would be extremely appreciative.
Kind regards,
Brett Schuler
p.s. I still have my DIY aleph 2s I built 18 years ago!
Wayne Colburn:
The single ended configuration is typically quieter by 6 dB and since noise is the biggest part of THD+noise at these levels I prefer it.
Balanced can work and I have done it but prefer single ended for phono an area I agree with Michael Fremer on. For some higher output cartridges it may be fine.
Balanced tends to be more complicated and this is the part that adds noise.
I would love to see a center tapped coil on a cartridge but was told by some cartridge makers it would be very difficult.