I have been putting off finishing up my Truepaths for a few months now. I have several questions about the best way to finish them up and get them in their “final resting place”.
The system is proposed to look like this (going upstream):
1. Two JBL L5 speakers (6 Ohm).
2. Two Velleman 4700s for speaker protection.
3. Two Bridged Truepaths built with default values.
4. Twisted Pear Opus DAC. Balanced output based on Wolfson 8741 chip with usb or s/pdif input.
5. PC or media server source.
I guess the best way would be just to ask a couple of questions at a time and then see what the answer is.
The L5s are 6 Ohm and seem like they would push the Truepath pretty hard since I have 61 volts coming in from the power supply. I don’t really intend to drive them hard but went with the dual amps because it seemed cleaner than adding a balanced to single ended converter. If I replace the MOSFETs with IRFp4227PbF I should be OK right? I am aware that I will have to recalculate the current limiting and change from the default values.
I hate to have a relay (Velleman 4700) in the output path. Just seems like an easy failure point that could lead to degradation in the sound quality. I think that relying on the Truepath mute circuit will not protect your speakers from a failed MOSFET however. I believe the common failure mode for a MOSFET is ON and I don’t see how the mute circuit can help with that. One thing I am considering is having the relay from the 4700 short the output to ground and have a 10 amp fuses on the positive and negative supply lines from the power supply to the Truepath. I think this would work ok once you were up and running but the startup and shutdown on the 4700 have pauses to protect against speaker pop. Would the Truepath detect the short and not un-mute until the relay is open? Or would there be trouble (maybe something I haven’t thought of yet) with this scheme?