As I built my system, kind of on my own, volume control was not as simple as just putting a preamp in the system and walking away. Volume control, attenuators have many different configurations and levels of quality playback.
System specs:
DAC output: 2.0V single ended
Pass XA25: 47Kohms input impedance
Speakers: about 100 dB efficient
Streamer: Digital volume control
This has been a two year saga. My original active preamp failed. I bought a passive preamp, not knowing what it really was, except a volume control. It had an Alps volume control($15 part). It sounded OK at high volume. Why? The streamer volume "bit stripped". Twenty years of inactivity did not prepare me for this. I thought the problem was my amp. I bought a Schitt Aegir but my kids could kick out it’s touchy protection circuit. Not the amp’s fault. It was asked to play above it's comfort zone. . So I bought a Pass XA25. Problem solved. Couldn’t kick it out. But back to the preamp. So I was turning up the passive all the way and adjusting the volume on the streamer. Partially due to laziness(no remote) and partially because I didn’t understand the problem. At the same time, I had some listener fatigue from some sharpness in the trebel. So let’s try a tube buffer. A passive with a tube and it had a remote. Now we’re talking. So I had good sound, much better sound. Wait a minute, the volume isn’t linear and low level listening just isn’t right.
Enough of that, now that I understand all this input, output, impedance stuff, let’s solve this problem once and for all. I was hoping to be able to swap my current preamp for a good volume attenuator without spending a lot more than I can sell the current preamp for. Enter Khozmo. Talked to Arek Kallas. Figured out the correct impedence of the attenuator, beautiful color options, upgraded to Vishay and Takman resistors and it is remote. There is only one resistor in the signal path. There are three type of Khozmo: ladder, series and shunt. I am getting the shunt style. Cost roughly $600. Per Arek, the ratio of passive preamp resistance to the amp input impedance should be 1:4 or thereabouts. This unit will be arriving in a week or so. Khozmo and Hattor is the same company in Poland. Their preamps get great reviews. The Khozmo is a basic model. The Hattor can have op amp based gain switchable to 3,6, or 9 gain and has nicer enclosures but the volume attenuator used is the same.. The passive I ordered should be very transparent.
There are other designs but this one is known well and reasonable. There are TDR and another kind of implementation that are supposed to be good, but the cost is higher.