This is very helpful and thanks for sending.
One other question remains - do you have to add some type of input buffer or can you just hook up straight to the EVAL1 board?
You are welcome for the info.
Regarding input buffering you do not have to buffer. What Purifi calls the EVAL1 is a three module set including a interface board that plugs into a stereo pair of 1ET400A amplifier modules providing simple secure connections. The EVAL1 interface circuit board has a buffer about which the user guide states "pre-gain stage is made with a dual OPA1612 configured as Balanced/single-ended to balanced gain stage". The manual also describes how gain can be set OR the buffers bypassed and input signal fed directly into 1ET400A.
If you are a DIYer who wants to use EVAL1 as an entry to Purifi amplification the quick easy way is to connect signal input directly to the EVAL1 XLRs. If your source is single ended take note of user guide instruction in section 3.5 "If a single ended input is need then connect GND and IN- to the negative analog input."
Some of the discussions I referenced deal with direct connections to the 1ET400A modules. More advanced DIYers and manufacturers looking to differentiate their product will ditch the OPA1612 buffer. Like Hypex and ICEpower the 1ET400A have medium input impedance in the 2k to 4k range. That falls in the range where any op-amp or other gain device
should have no problem driving it. Yet perceptive listeners report improvements in subjective sound when a preamp with more drive capability is employed.
