LS 100 Tube Phono Upgrade!
As many of you know, our LS 100 tube preamp is available with optional DAC (USB/RCA – 24.192 fully asynchronous) OR tube Phono.
The Phono was designed and intended for MC use. As designed, with 12AU7 and 12AX7 tube, it is capable of driving cartridges down to .30mV without a stepup transformer. Below this, a step-up is likely desired.
Because there is no MM/MC switch, it came to my attention later, that the phono stage WILL distort when used with cartridges of 2-3mV or higher. It is fine with a 1.5mV Dynavector and a .4mV Shelter that I use for testing, but higher output MC carts and MM carts WILL drive the phono stage to overload and distortion.
Well, I did some research into this and found a way to lower the phono gain by approximately 15dB, without any sacrifice in sonics.
The phono stage uses a single 12AU7 in the first stage, and a single 12AX7 in the second stage. For max gain, this is the tube complement that should be used. Substituting a 12AU7 for the 12AX 7 (now two 12AU7’s are used for phono board), the phono stage provides 15dB less gain and will allow for a greater range of cartridges.
Thanks and please don’t hesitate to call with any questions about upgrading an existing LS 100 to add DAC or Phono. Please note that only ONE option, DAC or Phono may be installed in the LS 100 however.
The KWI 200 Integrated amp DOES allow for installation of both DAC and SS phono stage.
ModWright Instruments Inc.