I don't, but coincidentally I was just in contact with a fellow who owned one and he was quite impressed with his. Nice wood case, too.
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I have a couple DIY preamps using fully balanced Khozmo stepped attenuators which I really like. Hattor is the brand used for complete preamps from the same company. I prefer an active output stage, which Hattor also offers.
I have not tried the AMRG resistors, but have read good things about them. My first build uses the Takman REX resistors in the shunt positions with a Vishay Z-foil series resistor. This combination sounds excellent with exceptional transparency. My other Khozmo use Takman REY shunt resistors and an Audio Note silver tantalum series resistor. I'm still working on tweaking this preamp which uses different power supplies and output buffers, so I'm not ready to say whether I like this combination better or not.
I have a balanced version with the AMRG Trans resistors. I am using it with an ARC Ref 75SE at the moment. It is superbly well built and the remote works really well. It controls volume, input, balance and has a mute. Once set up I am not sure you need much else. The sound is superbly natural, not surprising given there are only 2 high-quality resistors in the path. The only thing to watch out for is impedance mis-matches and it sounds like you have that sussed. It has equalled some very expensive preamplifiers in naturalness and clarity. If you want to alter the sound then this is not for you but if you want a neutral preamp then the value is great. It comes in a flight case and is really well made. I ordered a buffer input and all it required was to add a board, job done.
Short answer is that yes, I actually own a Khozmo and two Hattor preamps, and the Hattor Active Tube Stage, and I really like them.
The longer answer is that I became acquainted with Hattor as way to remotely control the volume in my system. I own a very nice sounding active, unity gain SMc Audio TLC-1 preamp, which has been upgraded to a similar sound quality as their VRE preamp. Unfortunately, the onboard Shallco VC does not allow remote control of the volume. I worked with Steve McCormack to modify the TLC-1 so it is now a unity gain buffer achieved by removing the VC from the circuit and replacing it with two large AN silver tantalum resistors.
With the TLC-1 as a buffer, I still needed a method of controlling my system volume and gave Khozmo a try with one of their inexpensive passive units. I really liked the sound and the interface/remote so when I saw a Hattor Big Preamp for sale used at an attractive price, I purchased that. Some months later, I wanted to try their tube active stage and Arek (the owner/designer) gave me a good price on a package with a Big Preamp, which is how I came to own two of them.
In my main system, I use the Hattor Big Preamp in passive mode, which provides me with a system interface that is as good as I have had with any of the preamps I have previously owned. With the Hattor Big Preamp, you get rca and XLR inputs/outputs, a large display in your choice of color, input selection, and selection of mute, volume, and balance, all controllable using the remote. My unit has the optional NewClassD OPamp active stage, which provides your choice of 3/6/9 dB gain, also selectable by the remote control.
Sonically, the Hattor Big Preamp is great, IMO. I have literally owned about 20 preamps with at least two costing north of $10K before I found the SMc unit I have now, and IMO the Hattor would hang with all of them, particularly in passive mode where it seems to have close to zero impact on the sound. You do get your choice of resistors and I chose the Amtrans AMRG carbon film resistors, which are made in Japan by the former distributor for Riken resistors. In my Khozmo unit, I had Takman REY shunt resistors with the Vishay Zfoils in the series position, and IMO the AMRG Trans resistors in the Hattor sound more musical.
Regarding gain, I could be happy with the sound of the discrete OPamp board in the Big Preamp. I could also be happy with the Khozmo Active Tube Stage, which sounds very good (a bit more musical/natural than the OPamp board) and better than the Tortuga and Purity Audio tube buffers I have had (on loan) here in my system. My unity gain SMc TLC-1 buffer sounds better than all of them to me, so that is what I use - with the Hattor in passive mode providing my system interface.
I hope this helps. I would be happy to answer any specific questions.
I have been using Big Hattor Dual mono (AMRGtrans, active phase of NewClassD for two years now - but I usually listen in passive mode) in conjunction with the SimAudio Moon W8 power amplifier. It suits me perfectly. Compliance with the input impedance of the amplifier is an important consideration for operation in passive mode.
I have one that’s got all the upgrades and the tube stage as well. It’s a superb preamp for sure. In my system, the tube stage adds a lot to the sound being amazing. I recently compared to the Benchmark and there was no comparison, the Hattor is worlds better. This piece oozes quality and sounds incredible.
I've used a Khozmo volume control/ "preamp" for several years now in two different iterations, and I would be hard pressed to go back to an active preamp despite having owned a few excellent ones through the years. Sonically, it's about as transparent as you can get and is the embodiment of simplicity. Build quality is top notch, and customer service from Arak (despite being in Poland) has been exemplary. My highest recommendation.
I purchased a Khozmo preamp a few months ago. I had been using a 12AU7 tube buffer. I did not like the volume control. Not linear but sound was good. I bought the Khozmo to keep the cost down(vs Hattor) I have upgraded resistors. The build quality is superb. Aesthetically, this is a unique and nice looking piece. Sound is transparent. Their equipment is customizable with the intent of unaltered sound.
Arek is very easy to deal with. I emailed Arek and hoped everything was OK in Poland. He is housing a Ukrainian mom and her child. What a noble gesture.
The impedance issue can be more involved than simply verifying a 1:10 ratio (which many consider a minimum with a more desirable number being 1:20 or higher). For example, many preamps (and particularly tubed preamps) have output impedance that is significantly higher at frequency extremes (particularly at bass frequencies) than at 1K Hz which is the typical frequency where the output impedance is reported. In those cases, the reported output impedance (i.e., at 1K ohms) can result in one ratio while the actual ratio at frequency extremes could be much different (i.e., lower). JA at Stereophile used to regularly report about this in his measurements of (mostly tubed) preamps. Below is an example from his review of the Lamm LL2 Deluxe:
It also becomes important with passive volume controls (i.e., passive linestage) where the output impedance is dependent on the impedance value of the volume control, and where the IC cable impedance becomes more important without active circuitry (which is why most recommend very short cables when using passives).
Regardless of what Paul says in the video, there are still solid state amplifiers with input impedance as low as 10K ohms. This is rarely a problem when using active solid state preamps, which typically have output impedances in the range of 100-200K ohms, or lower. However, amplifiers having low input impedances will not likely reach their full sonic potential when driven through a passive line stage. For this reason, the sonic impact of using a buffer (i.e., active circuitry to address output impedance) between a passive preamp and an amplifier can vary significantly depending on the differences in input impedance between amplifiers.
I just wanted to update this thread. I received my preamp about a week after ordering it. Working with Arek was a pleasure. It is extremely well constructed and solid. When you factor in the quality build and the flight case it ships in, you can understand he’s not getting rich at this.
It is very transparent as you might expect, but dynamic as hell too. Just gets out of the way and let’s your amp do it’s thing, which is exactly what I wanted. Highly recommended.