hello fellows, I have o problem feed directly tube dac( 2x 6922 not SRPP, which has lower impedance.)anybody tried to up input impedance for aleph x? from 20kohmbalanced to 40-47kohm balanced. as I understand this is not only changing input resistors to 10kohm resistors to 20-23kohm..
anyone tried?
greetings
Rolandas
anyone tried?
greetings
Rolandas
anyone? is no one can anyone put me in right direction. I think many people would like to conect high impedanse sources(like tube dac) and have the same problem. I was very surprise that 10V rms(!) output (manufacturer claims 5V rms non HDCD and 10V Rms HDCD)are so weak comparing to 2V RMS low output impedanse ordinary opa amps dac. not speaking about muddy ,undynamic,not controled bass..
elviukai said:
input impedance is roughly sum of two series resistors (+ and - side);
you can up them to ,say, 27 K -but you must scale up 100K resistors for same factor (2,7x) . Also you must scale up (2,7x ) 10K resistors from inputs to gnd.
after that you need to scale down (2,7x) 10pF caps across (now) 270K resistors
try it like that-and if you have some problems with sensitivity, we will re-think what to do;
Elviukai-
Do you have an oscilloscope?
I found using a high input impedence caused a phase variation between the channels of my aleph-mini amp. It was only a few degrees at 20kHZ, but could be seen very clearly at 100kHZ.
I don't know if it was from bad devices, or if this might be typical of all the amps, (unless someone took the time to match input devices in circuit).
If you do have a scope, once you have implemented Choky's resistor values, just feed the same signal to both channels and check the signal at the gates of the input devices to make sure it matches. Check both positives against each other at the same time, then both negatives.
Do you have an oscilloscope?
I found using a high input impedence caused a phase variation between the channels of my aleph-mini amp. It was only a few degrees at 20kHZ, but could be seen very clearly at 100kHZ.
I don't know if it was from bad devices, or if this might be typical of all the amps, (unless someone took the time to match input devices in circuit).
If you do have a scope, once you have implemented Choky's resistor values, just feed the same signal to both channels and check the signal at the gates of the input devices to make sure it matches. Check both positives against each other at the same time, then both negatives.
Nelson Pass said:Not by much, as it turns out.
It's not a deal killer to most people. Just thought I'd throw it in. Stuff like that bothers me, but I realize that I'm in a distinct minority in my quest for wide bandwidth (preferably accomplished with little or no NFB--any idiot can get wide bandwidth with oodles of NFB).
Note for the record that I prefer higher input impedances whenever possible--a holdover from my tube days--but that bandwidth matters more to me now than high impedance. If I've got a circuit that, like most of the Aleph variants, starts rolling off ca. 100kHz and I do something that drops that to 80kHz I stop and ask myself just how badly I want that modification of the circuit. I nearly always go back to the 100kHz version.
Someday I'll discover a definitive explanation as to why it takes a solid state circuit with 250kHz bandwidth to sound as open as a tube piece with 50kHz bandwidth. It's not logical that it should be so, but if audio were that cut and dried, it probably wouldn't be nearly as much fun.
Grey
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