|
|
Post by wanderer on Mar 13, 2019 21:12:53 GMT -5
Just got a BASX A100 amp in house. Plan to try it with a Schiit SYS passive attenuater/switcher ("passive preamp"). Specs for SYS output impedance is "5K ohm MAX" and input impedance for the A100 is 27K ohms (right??). Seems a less than ideal ratio. Anybody using the a passive volume control with an A100??
|
|
KeithL
Administrator 
Posts: 9,928
|
Post by KeithL on Mar 14, 2019 9:14:27 GMT -5
That's actually an excellent impedance ratio - in terms of compatibility. All attenuator type "passive preamps" have a relatively high output impedance... which also varies depending on where the knob is set.
This means that they don't work well with long cables... and they prefer to be connected to an amplifier that has a relatively high input impedance. You DO NOT want those impedances to match - you want the input impedance of the amp to be much higher than the output impedance of the preamp. Since the output impedance of the Schiit preamp is a maximum of 5k, and the input impedance of the A-100 is 27k, that is an excellent ratio. (Although most tube amps had very high input impedances, most modern solid state ones tend to be much lower, as low as 5k - 10k in some cases.)
You should also realize that the A-100 has an analog potentiometer volume control at its input. That means that the input impedance of the A-100 is almost purely resistive, which makes it a virtually ideal load for a passive preamp.
(As with most integrated amps, the A-100 has a potentiometer at the input, feeding a gain block with fixed gain - so every A-100 has a "passive preamp" already.) Therefore, you will have a potentiometer (the preamp) feeding another potentiometer (in the A-100). In this case, by stacking two potentiometers, you will get more control range....
Since the input impedance of the A-100 is almost purely resistive, there will be no unexpected interaction between it and the high output impedance of the "preamp". I would note that you probably want to keep the interconnects between the Schiit unit and the A-100 short - and avoid running them next to power cables. (Because its impedance is higher, the output of the passive preamp will be more prone to picking up hum than the output of an active preamp, even though the impedance is still pretty low.)
Just got a BASX A100 amp in house. Plan to try it with a Schiit SYS passive attenuater/switcher ("passive preamp"). Specs for SYS output impedance is "5K ohm MAX" and input impedance for the A100 is 27K ohms (right??). Seems a less than ideal ratio. Anybody using the a passive volume control with an A100?? |
|
|
|
Post by wanderer on Mar 14, 2019 9:30:01 GMT -5
Thanks! Planning on no more than a meter, or 1/2 meter if I can make it work, low capacitance interconnect. Looking forward to the setup.
|
|
|
|
Post by jj2106 on May 22, 2019 9:17:44 GMT -5
Sorry I missed this interesting thread. If it 's too late, so much the worse.
I have a BasX-A100 driven by a fixed-output DAC. No idea what's the DAC 's output impedance.
For practical reasons, the A-100 is located 10 meters away from the DAC and hidden under a bed.
So, next to my PC and to the DAC, I have a passive attenuator.
This is simply a 100K ALPS 27/16 potentiometer packaged by Nobsound of China. I costs 40$.
I initially set the Nobsound to 12 o'clock and the A-100 to 0.
I then slowly raised the level on the A-100 until I reached a "comfortable" listening level.
It works a treat. The cables are good quality RCA, but still cheap. No noise whatsoever.
As they say, I'm a happy camper.
|
|
