The current draw is quite different, the AD8139 is about twice the draw of the AD8132. The DS’s analog supply regulators would sag too much and get hot, they weren’t designed for that level of current. The two opamps aren’t interchangeable in the DS. The wider frequency response of the AD8139 is also a (smaller) concern.
A 100MHz will miss details of the pulses. Letting more ultrasonic noise thru will work fine with some systems and can destroy others (not just a theoretical problem.)
Yes PPS.
Some of the needed output filtering, the muting and the attenuator are implemented between the transformers and the outputs. The output transformers also are a part of the filter.
In the simulator make sure you are using models of caps that have accurate ESL and ESR (as well as at least the first level of parasitics on other components.) Forgetting the parasitics will cause a big discrepancy between the simulation and real-life. The SRF of all of the caps were chosen carefully.
Also, the rejection needs to be better than about -120 at 5MHz and needs to stay down to past, say 22MHz.
They are low inductance power supply caps. X7R. I’d use NP0/C0G or film caps there if they had enough capacitance to be useful for this purpose, but they don’t. I wish that those spider caps I used on the DS were still available, but all of the vendors have stopped producing the higher capacity, higher voltage versions of them. It’s hard to get that level of capacitance at 22MHz.
Since the voltage on them is very static I don’t feal that the voltage dependent capacitance of non-NP0/C0G caps are a problem here like it is when they are directly used in the audio path.
Yes I can agree with that. Ceramic microphonics remain, but maybe of small concern here as PSU bypass basically. What size range capacitance are these?
I haven’t seen the spider caps you mention. Happen to have a link?
That’s what I call the 8-legged MLCC capacitors I believe you are talking about. They aren’t array capacitors (e.g. four capacitors per unit) instead they are IDC (inter digitated capacitors), a single capacitor with multiple leads for each terminal. I used the LLA series from Murata. They go by different names from different manufacturers. E.g.
Ted, I’m confused on the 60R (2x120R in parallel) in series with the plus and minus output, just before the XLR conns. There is no further C after these; what is their function here?
One use is as a part of the 20dB attenuator. If the 120 resistors are always inline you don’t have to have a relay “in the signal path” that switches them in, out, bypasses them or whatever. You avoid problems with inconsistent contact resistance, etc. With them there the attenuator can be implemented with a 15 Ohm shunt to ground - which, in a handwaving sense “isn’t in the signal path”. Tho everything is really in the signal path there is value to keeping the two channels as equal as possible as any difference in relay contact resistance between the two channels would mess with the soundstage, etc. With a differential output signal the shunt resistors are basically in series between the two outputs and hence non-ideal relay behavior will affect both channels identically. In single ended mode there’s still balanced/identical behavior between the “+” rail and ground.
60 Ohms is small enough compared to any normal equipment with a 22k, 47k or 100k input impedance that it doesn’t mess with the frequency response even with, say, 1nF of cable capacitance. There’s plenty of drive so the 15 Ohms shunt isn’t a problem.
Partially because of the 60 Ohms in series in each output line the DS is comfortable with a dead short on its output indefinitely.
Phase 1 proof of concept complete. Oh yeah! (Tech note- my preamp has uber high quality input DC blocking caps so the Vcm is not a problem for this test).
The DSD version of “Take 5” on this system now sounds so good I’m just letting it play in a loop for awhile lol… Resolution and “correctness” are off the charts.
Everyone on the list should have received a PM with Priority Mail 2 day tracking info.
Let me know if I missed anyone.
Thanks,
Merry Christmas &
Have a great Holiday!
Yeah man I do like the TRT caps, and they were ~ top 5 finishers in my cap search. I put some into the xover of my DIY Invictus speakers even (and my “Super Kans” project years ago". But they weren’t the top
I do like the TRT caps, and they were ~ top 5 finishers in my cap search. I put some into the xover of my DIY Invictus speakers even (and my “Super Kans” project years ago". But they weren’t the top