First, I believe that the vu meter mod should de done. It looks gorgeous ! just make sure that this has no consequences on the clarity of the signal...
- will do my best, a small interface has to be provided (4 germanium diodes, 1 resistor, 1 small capacitor perchannel + one switch (Average / Peak), so the connection to the signal has about 3KOhm.
Powersafe mode : I see that there are some long cables (to go to the Switch and to come back) coming from the pins of the tube. Are you sure that this do not alter tha sound ?
- the wires are following the same path as the exsisting power lines, the switch only connects or disconnects a static voltage of 1.4 volt to pin 1 of the dl92, so switchted on, no change to before, switched off - just no current floating.
DAC ? Will it be internal ? Which one have you choosed ?
- formfactor, sound quality, price/performance ratio - HRT microstreamer DAC - a small little box i will provide an internal slot and two connectors for, could be removed and externally used at any time, fully powered by USB. an alternatiy would be the meridian explorer with 24bit 192 Khz, but a windows driver would be needed, not that universal and usable in the office with no right to install drivers.
Question: what is the benefit of having balanced input and balanced output is the internal design is NOT balanced ??
- a four pin mini xlr firstly is much better than a normal 3.5mm stereo jack. that you can connect a balanced source is a add-on. balanced equipment was primary designed for studio use with long cables because much better resistance against rf and other interferences. i think a double mono design is half way to balanced, only one amplifier per channel, but better channel separation as with one power supply and ground for both channels.
- a 4 pin xlr jack for headphone out makes sense, as this is the way the signals come out of the tu-05, two output transformers. also if you use a normal 3 pin stereo 6.3mm jack, you have to connect ground to ground, and then you have a connection between both amp parts. also it is the most universal connector. at the moment i am thinking of saving space by providing xlr to 2 speakers / 4 jacks and xlr to 6.3mm headphone out adapter cables instead of different jacks.
Anyway, I love the project and believe that all the rest is for me very good ideas, including the XLR headphone plugs that offer better contacts and rigidity than a JACK.
- what i forgot but will look if and think that the standard transformer output could also be used as preamp out, it makes no sense to implement an preamp out after the df91 stage as both df91 and dl92 stage together make this great tu-05 sound.