> "As near as I can see from tracing from one sheet to another, U29, a TLV320ACC23 DAC with integrated headphone amplifier drives the TTC-108 LIN OUT transformers directly. Headphone and speaker audio, in contrast, are derived from a second TLV320 DAC driving a LM4950 amplifier for speaker output and an LM4811 for headphone output..."
Jack, I am coming into this discussion a bit late, so my apologies to all for any redundancy. I believe the device listed as U29 on the K3 schematic may be a mis-print and my best guess is that's it's the Texas Instruments TLV320AIC23 -- as is the case with U7. The device's H/P output (presumably used for the LINE OUT function) is rated to function down to nearly a zero-ohm load. http://focus.ti.com/lit/ds/slws106d/slws106d.pdf By contrast, the device's line-level output (unused on U29) is specified to function into a Z of no less than 10K-ohm. So, absent any large variation in noise level between the two outputs, Elecraft's choice of using the H/P output was a wise one since the transformers can be driven by a very low-Z. However, currently the TI device is coupled to the transformers with 600-ohm built-out resistors. Once you receive your TTC-108 transformers for testing, it would be an interesting exercise to incrementally change the value of the build-out resistors from a low-Z source -- all the way down to zero, and note the effect of THD/IMD sensitivity as a function of driving source Z. It would be an even more interesting exercise to run the identical test using the Triad transformer you mentioned as well as the Holy Grail of all audio line transformers, a Jensen type. Paul, W9AC -- View this message in context: http://n2.nabble.com/K3-Harmonic-Distortion-tp797780p841653.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
