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KHOZMO ACOUSTIC PASSIVE PREAMPLIFIER

12-01-2023 | By Steve Lefkowicz | Issue 130
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Over the many years that I've been involved in high quality home audio, there's
been no part of system that has given me more concern, and kept me from making a
decision for what my system needs, than the preamp or linestage. Seems silly, as
in theory at least, a preamp or linestage should be a fairly easy device to get
right. All it really needs to do is take your various signal sources and pass
them on to your power amp. It might or might not add some gain, and these days
it may or may not have a phono preamp or DAC built in. Most importantly, it
needs to attenuate the signal to control loudness. There are numerous choices
available in the market ranging from about $49 (for a passive Schiit Audio Sys)
to well over $100,000 for some of the extreme High End models (like the Boulder
3010 for $158,000). All you need to do is decide what you need and how much
you're willing to spend.

In reality though, it isn't that easy. At least in my experience it seems the
preamp may be one of the most significant and critical components in terms of
setting the overall sound and presentation of a system. Tone, soundstage,
transparency, and virtually every other aspect of the sound of your system is
affected by the preamp, and whatever it does will be consistent regardless of
your source. Get the preamp wrong and you might never be happy with your system.

Since I went to all separate components in 1981, I've primarily used three
turntables, three CD/SACD players, four power amps. But in that same period of
time I've used six different preamps. During the thirty-plus years that I used a
PS Audio 4H preamp, I found that switching out its active line stage and using
it as a passive preamp (the power supply then only powering the phono stage)
gave me a wonderful transparent sound that satisfied fully over all those years.
It was just that as it aged, it started getting noisy. Also, it did not have a
remote, so I retired it several years ago.

In the twenty-four years that I have been reviewing gear, I have tried numerous
active preamps, both solid-state and tube, trying to find one that was just
right to my taste. The ones I really liked were all just out of my price range,
so I never acquired one to keep. In 2016, as much as a stopgap measure as
anything else, I started using a solid state Burson Conductor Virtuoso as an
active linestage. I didn't care much for its built-in DAC, but it had two line
level inputs, a remote and was clean, neutral and fairly transparent. It worked
well with my two primary amplifiers too.

Also in 2016 I asked my buddy (and longtime master audio tinkerer and DIYer)
Russ Stratton if he could build a little passive linestage for me. End result
was a tiny (4¾ "W X 2½"D X 1½"T) passive device using a high quality TKD Audio
Taper 10KOhm pot with two inputs and two outputs, one fixed and one bypassing
the pot to feed a headphone amp. All told it was about $99 in parts. The
shocking part was it outperformed the Burson in almost every category expect
maybe ultimate dynamic punch. I loved the sound of my system using this
low-cost, little device. Unfortunately, its lack of a remote for volume meant it
had limited use for the way our system is used at home. A remote for volume is
an essential part of the system, as my home office and the audio system share
space in our home's living room. Being able to quickly adjust volume or mute the
system is critical when work calls come in.



But using this DIY device made me realize I would more likely find happiness
with a good remote controlled passive than any active line stage that falls into
my generally low-cost price range. Listening to a few very high-end systems that
used the microprocessor-controlled, passive, autoformer volume controlled (but
at $14,000 very expensive) Townshend Allegri Reference Mk. II preamplifier
clearly demonstrated just how good a passive preamp can get. The Townshend
Allegri Reference is an amazing product for those who can swing it.

It all seemed to fall into place when in 2021 I saw the Khozmo Acoustic Passive
Preamplifier mentioned somewhere. I seemed to recall some nice (and pricey)
preamps on the market that used the Khozmo Attenuators in their design, but
hadn't been aware that Khozmo sold complete passive preamps, too. The
interesting thing about their website was that when you selected the options for
your unit, you could specify both the model of attenuator you wanted and what
type of resistors you wanted used. For example, for the "STEREO with Input
Selector - RCA" version that I have in house:

 * 48 steps SERIES (manual) $369
 * 48 steps Series (remote) $569
 * 64 steps LADDER Vishay (remote) $589
 * 64 steps LADDER AMRT (remote) $649
 * 64 steps LADDER AMRG (remote) $749
 * 64 steps SHUNT AMRG+Vishay (remote) $569
 * 64 steps SHUNT ZFoil+AMRT (remote) $789



Having it fully balanced and with XLR connectors adds from $70 to $230 dollars,
depending on which version you order. I remember way back in the early days of
high-end audio when Vishay resistors were considered an expensive upgrade, so to
see them as the low cost "entry level" was both surprising and encouraging.

Another interesting option, one that I hadn't planned on asking for but was
included on my review sample, was an active gain stage based on a Dual Discrete
OPAMP module supplied by Danish company NewClassD which added $500 to the list
price. It offers a fixed 6dB of gain and a stable input and output impedance,
something very beneficial for some systems, especially those using long
interconnects. The active stage can be fully bypassed with a rear mounted toggle
switch.

With the active stage bypassed, the Khozmo offers a fixed input impedance of
100KOhms, though its output impedance still varies based on the volume setting.
This may have a negative impact with some amplifiers, though I am lucky I guess,
and both of my primary amplifiers have always mated well to passive linestages.
The Burson Timekeeper Virtuoso has an input impedance of 30kOhms and the Antique
Sound Labs MG-SI15DT-S input impedance is listed as 100kOhm. Seems to work fine
for me.

My review sample is a Stereo with Input Selector (RCA) with 64 step LADDER AMRG
(remote) attenuator and the NewClassD Active Stage. Its MSRP was $1249. Without
the active gain stage it would have been $$749.

Khozmo, originally based in Poland, was in the process of relocating to Spain,
so there was an understandable delay from the time we communicated about a
review and when I received the device. It arrived very nicely packaged and in
good working order. It was pretty quick and easy process after unboxing to get
my photos and set it up in the system.

Because of the active gain stage, instead of a wall-wart to supply power for the
remote control, this came with a very nice outboard filtered power supply that
supplied both +5VDC for the remote and +/-15VDC for the gain stage. It came with
a one meter long umbilical to connect it to the main chassis, but it did not
come with a power cord. Since it used a standard EIC connector getting a power
cord was easy as I simply used the one previously plugged into my old preamp,
though it was nothing fancy.



I was a little concerned that there was no indicated ground post to secure a
ground cable, as I did have a slight ground hum issue with my previous DIY
passive, but much to my surprise and delight, after hooking the Khozmo into my
system and turning everything back on, there was no noise at all, just the type
of dead quiet background I constantly try for, but rarely achieve. Using
Vermouth Audio Black Pearl interconnects, two of the three inputs were taken up
by my iFi iPhono2 and iFi NEO iDSD, and one of the two outputs connected to my
Antique Sound Labs MG-SI15DT-S amplifier. I was ready to go. To start, I chose
to leave the active stage switched out, and run purely passive.

A quick run through with the remote to make sure everything was working showed
easy, single-step changes in volume when tapping the Vol+ or Vol– buttons. The
Mute button worked correctly and the Display button stepped through off, dim,
medium and bright on the two-digit display. When set to the brightest display,
it was easily readable from across the room and even off at an angle when I was
at my work desk. The Standby button seemed to power the unit off while leaving
the power supply on, but it might just be blanking the display. I'm not sure.



Before talking about the sound of the system with the Khozmo in place, let's go
over some more details about the unit itself. Opening the case, if you weren't
reminding yourself that this is a passive unit, the fact that it is largely
empty inside might be a bit of a surprise. Behind the front panel there is a
small PCB for the display. The display itself is a two-character display made up
of thirteen LEDs each to create a very basic number display. When muted it shows
a dash, otherwise it shows which of the 64 unique steps is selected.



On the left side there is a shaft from the Select knob to the rear PCB and on
the right is actual Khozmo 64 step ladder attenuator. Since this has the active
gain stage installed on the rear PCB there is the module for the active stage,
two small discreet PCBs attached via an 8-pin connection.



The rear panel is nicely laid out with the aforementioned three inputs and two
outputs, with enough distance between then to accommodate most interconnects. I
had no issue tightening down the locking RCA connectors on my Vermouth cables.
In between the input and output connections are the connection for the power
umbilical and the toggle switch for the active gain stage.



That's pretty much it, simple, clean and looking very much like a serious effort
to pass a signal unaltered through it.

Expectations, nah, not me…

Alright, let's get this out of the way first. No matter what anyone says,
reviewer, reader, measurer of specifications, etc., we all have expectations,
biases, and preferences. There is no way around that. The key is understanding
what your own expectations, biases, and preferences are, so you recognize them
and work with that understanding.

For me, based on my past history, my expectations for a passive line stage would
be neutrality, transparency, clarity, and possibly a lessened sense of dynamics
and soundstage size as compared to an active preamp. My biases are for simple
products that don't cost too much and that exceed my expectations. I
surprisingly have no bias towards technology or design factors, and don't care
if a device is solid-state or tube, analog or digital. But I do have a bias
against things where the price seems to have been driven up mostly to just cost
more, meaning where the price is to support fancy cases or other things that
could have been done simpler to keep the cost down. That is one reason I don't
review very expensive gear, as I understand I would start off biased against it.
I mean I can appreciate expensive gear that actually sounds better too, and
believe me, the best systems I've heard have always been way out of my target
price range. I just choose not to write about it.

My preferences, which are different from my biases, are to make my system sound
its best within a target price range for the majority of the music I want to
listen to. I specify it that way as I have seen too many times where High End
audio is defined as getting "the best possible sound out of the best
recordings." The difference, as I see it, are that most systems I've heard that
really make "the best recordings" sound their best, tend to highlight or focus
on the flaws in all other records that aren't "the best" leaving them less
enjoyable to hear. This leads to audiophiles who select their music based on the
quality of the recording rather than the enjoyment of the music. Since I collect
and listen to music based on how much I like the music, I rarely look for
specialty audiophile releases or albums that were released primarily to just
sound good. My system has to be able to extract the most enjoyment possible out
of whatever record or digital file I queue up. Yes, even the poorly recorded
ones.

With that in mind, let's get on to the Khozmo Passive Preamp and how it worked
in my system.

For the first few days I didn't do any real evaluative listening, and had the
system playing all day streaming from Qobuz while I worked from home. My desk is
actually way off to the side of the system (at a 30-degree angle to it), but the
system fills the room with music and I tend to have it running all day while I
work, just pausing it or muting it when I need to get on the phone. But then I
thought, since each of the 64 steps are a unique set of resistors, any break-in
happening would only be for the certain volumes I selected. The idea of having
to step through each to let it break-in over time did not seem appealing, so I
skipped the whole idea of break-in and just listened.

My initial reaction though, was one of surprise and somewhat unexpected. I
didn't really think this device would sound very much different from the DIY
passive I had been using. The only real difference would be the TKD pot versus
the Khozmo attenuator, but the difference was substantial. Maybe all those super
high quality resistors really do make a difference as the clarity and
transparency of the system was immediately and significantly improved. I was
instantly captivated.

It really didn't take long at all, a day or two maybe, to have most of my
initial thoughts sorted out. And over the next couple months while I continued
to listen for characteristics to write about, it only reinforced my initial
impressions.

Simply put, this is the best linestage/preamp I've ever had in my system. No it
isn't perfect, and we'll discuss those reasons soon, but from what I wanted a
linestage to do, the Khozmo does all of it at least as good, and generally
better, than any other preamp or linestage I've tried in the past.

For starters, and using a term I maybe overuse a bit, was the overall
transparency through the system. It was exceptional. Some readers may remember
that when I listened digitally I used the analog volume control of the iFi NEO
iDSD DAC to feed directly into the power amp. The DIY unit was only used to
control volume when listening to LPs. The iFi unit has a nice analog volume pot,
but it is still just a pot. Setting the iFi to bypass the pot and send the full
signal through the Khozmo was a big step up. Music universally had a clarity, a
spaciousness, a presence born of pure transparency. It sounded more like I
removed a component from system that had been cluttering up the sound rather
than adding a new component. The overall transparency of my system had been at
an all-time high for the past several months already, as an overhaul of my
Antique Sound Labs amplifier (new tube sockets, capacitors, and a new set of
Svetlana and Tung Sol tubes) had it sounding better than ever.

And yet, using the Khozmo Passive stepped that characteristic up substantially.

The Khozmo played no favorites when it came to frequency response. I suppose if
I were to plot the response it would be a straight line through the audible
spectrum. Nothing sounded accentuated or diminished. By comparison my Burson
Conductor Virtuoso now sounded slightly bright and edgy. My highly modified and
upgraded older Jolida Fusion, though recently serviced, sounded bloomy in the
bass and noisy. My DIY passive sounded (sometimes at least) like it rolled off
lower frequencies slightly.

I expect a passive device to produce a smaller soundstage than an active one,
even if possibly with better defined images within that soundstage, but that
just wasn't the case here. From all of my primary speakers and both power amps
(see my equipment list by clicking on my name at the top) the soundstage was at
least as large as I've been able to achieve here, and in all cases with better
definition. Remember though that I'm not someone who prioritizes imaging over
other characteristics, and my speakers get positioned for best tonality and bass
response, not to optimize soundstage or imaging. I know I could get better depth
for example, but not without a negative impact on upper bass smoothness due to
room size and placement limitations.

Rather than list a bunch of LPs and digital files, just look back over my old
reviews to get an idea of what I listen to. Suffice to say I listened to close
to 100 LPs and several hundred digital files (16- and 24-bit PCM files and DSD)
and streamed lots of CD quality and 24-bit files from Qobuz. Rock, Jazz,
Classical, Folk, Americana and what my wife insists is just "weird shit" were
just some of the genres played. Regardless of genre, complexity, emphasis or any
other factor, the Khozmo didn't seem to care. It just sent the signal off to the
amplifier with as little added or lost character as I can describe. It didn't
make bad recordings sound better, but it didn't make good recordings sound worse
either. Whatever came in, just went out at the volume I selected.

Wonderful!

Any quibbles? I missed having a fixed level output to send the signal to my
headphone amps. But, on the other hand, I had surprisingly good results running
interconnects from the second variable output to my Schiit Valhalla headphone
amp. I turned the volume all the way up on the Khozmo, set the Schiit just a
little louder than I would want to listen and then used the remote to adjust the
Khozmo to my desired listening level. I have tried that with active preamps in
the past with very disappointing results. This time, it worked like a charm and
I had remote volume. So maybe not a quibble at all!

I'll be trying some new monoblock amplifiers early next year, and had thought
about using longer interconnects to then use minimal (maybe one meter or less)
speaker cables. Long interconnects are a no-no with a passive line stage so I
won't do that. Not really much of an issue, as I only need about seven or eight
foot speaker cables for a stereo amp and can get by with four foot cables with
mono amps.

I'm kind of looking for something to criticize, and honestly, it is more about
your system setup than any issue with the Khozmo Passive. Either your system
will work well with a passive or it won't. I'm lucky in that mine always has
been very agreeable to passive linestages.

Regarding the optional active gain stage, I'll bet inexperienced listeners would
have a hard time detecting if it was switched in our out, as there was no
frequency response differences to speak of, just a difference of 6dB in output.
However the final sound was not the same. Mostly there was a drop in
transparency, as there was clearly now something in between me and the music. It
wasn't offensive or irritating or bad but it was noticeable. In fact it sounded
like a very good moderately priced active preamp. The sound fit neatly into a
somewhat smaller sound field, and the system didn't disappear as it did without
the active stage. But, having said that, I'd be hard pressed right now to think
of a similarly priced active linestage that would sound better than this,
especially since they would likely have a simple volume pot (like an ALPS Blue
Velvet). The Schiit Audio preamps that use their own design relay attenuator
would be a nice comparison to try. Maybe I'll check that out in 2024.

But unless you are running long interconnects, have a power amp with a low input
impedance, or use sources with insufficient output level, there's no need for
the active stage. And not only would that simplify the system it would drop the
price substantially too. In my case with this unit, it would be $749 without the
active stage. For this level of sound and build quality that is beyond "bargain"
territory and practically a steal.



To sum up, though this may be viewed by some as a good low cost, budget or entry
level product based on its price, in reality it is a real, honest-to-goodness
High End linestage that could be at home in a system many times the cost of my
own humble setup. It gets my highest recommendation.

Khozmo Acoustic Passive Linestage

Retail: $1249 as reviewed, $749 without the Active Gain stage

https://khozmo.com/

Images by Steve Lefkowicz



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STEVE LEFKOWICZ'S SYSTEM

All components in BOLD are loaned; all components in standard face are owned by
me.

LOUDSPEAKERS

Tekton Perfect SET 15, Tekton Lore, Magneplaner .7, ELAC Debut F5, ELAC Debut 2
B6.2, ELAC Debut B6, Emotiva Airmotiv B1, Sound Dynamics 300ti

ELECTRONICS

Khozmo Stereo Passive with AMRG Ladder Attenuator and "NewClassD" Active Stage,
Antique Sound Labs MG-15DT-S, Burson Timekeeper Virtuoso amplifier, DIY
2-input/2-output switch-box with TKD 10K pot for volume control 

SOURCES

Analog: Linn LP12 (MOSE/Hercules II power supply), Ittok arm, Dynavector 10X5
Mk.II Low Output cartridge, iFi iPhono2 phono stage w/iPowerX

Digital: Geekom Mini PC (i5, 16GB RAM, 512GB SSD, JRiver Media Center 29), iFi
NEO iDSD, iFi iUSB3, iPurifier2, Audioquest Jitterbug FMJ

Streaming: Tidal HiFi and Qobuz, using their Windows Desktop apps. The NEO iDSD
is a full MQA decoder/renderer.

CABLES

Interconnects: Morrow Audio MA1, Vermouth Audio Black Pearl, Audioquest
Evergreen, Nordost Solar Wind

Speaker cables: Morrow Audio SP4, Vermouth Audio Red Velvet, Audioquest Type 5,
Nordost Solar Wind, Nordost Flatline

Digital cables: iFi Gemini Dual Head USB cable, Aural Symphonics Digital
Standard xxv USB cable, Straightwire USB Link

Power cords: All power cords are stock as supplied by the manufacturers except
one older Cardas Twinlink power cord I use for power amps.

POWER CONDITIONING

Pi Audio Group Über BUSS, Monster HTS2000 power-line conditioner, 

ACCESSORIES

Sound Organization wall mount turntable stand, Mondo equipment racks, Pangea
Audio Vulcan equipment racks, Pangea Audio LS-300 Speaker Stands (28 and 32
inch), Sound Organization 24-inch speaker stands, 12-inch tall wood speaker
stands for the Sound Dynamics and other larger stand mount speakers, Kinetronics
anti-static brush for dusting LPs, Pro-Ject VC-S vacuum record cleaner, Spin
Clean record cleaner, Wally Tractor and VTA Gauge.

PORTABLE/TRAVEL SYSTEM 

Questyle QP1, Beyerdynamic DT770 Pro (600 ohm) headphones, Meze 99 Classic
headphones, Meze 99 Neo Headphones, 1More Triple Driver Over Ear headphones,
1More Triple Driver IEMs.

All the music on the Questyle QP1 is full resolution copied directly from my
music server, ripped from CD or downloaded as high resolution 24 bit PCM or
DSD. 

OTHER NOTES

This is a relatively low cost system, with no single piece of equipment having a
list price over $3000 and most being well below that. It is eminently musical,
and close enough to full range to be very satisfying on all types of music. It
does not make me choose music to fit its limitations or characteristics.

The Tekton Perfect SET 15 are my primary speaker and are usually powered by the
15 watt Antique Sound Labs MG-SI15DT-S. I find the PSET-15 to give me a very
detailed yet highly musical presentation without the need for a subwoofer. They
are designed to operate best in the loudness range I tend to listen at (mid 80s
dB average, peaks into the upper 90s) and work fine with regardless of an
amplifiers power rating. I’ve used amps from 3 watts to 200 watts with them. We
rotate three primary speakers in the system regularly (Perfect SET 15, Tekton
Lore and Maggie .7) selecting the most appropriate amp also. All the other
speakers in my list are lower cost references only used when price appropriate
for gear being reviewed.

The Sound Dynamics 300ti is a speaker I've had since 1997, and keep mostly to
have an extra option when reviewing amplifiers. Not a high efficiency design,
they still match up well with lower powered tube amps and higher powered solid
state amps. I also have a pair of VMPS RM2neo towers that I love, but they are
in storage as they are too big for my current listening room. They also sound
best when biamped, which makes them less effective as a reviewing tool.

I've had my Linn LP12 since 1984. The addition of the MOSE/Hercules II power
supply to replace the Valhalla PCB leaves me thinking I'll keep the Linn for
many more years to come. The Dynavector cartridge I use is a brand new 10X Mk.II
Low Output, the first low output model in the long history of the 10X series.
The iFi iPhono2 stage is surprisingly good for the money, and a great reference
point for a cost-conscious listener.

My listening room is the shared family living room, and somewhat oddly laid out.
From the wall behind me to the wall behind the speakers, it is 12.5 feet. The
room is 23 feet wide, but I use about 13 feet from one side wall for my system,
making for an asymmetrical setup. The left speakers is only about 15 to 24
inches from the left side wall while the right speaker is about midpoint along
the wall. Distance from the wall behind them depends on which speakers are being
used, placed for best overall tonal balance and bass response. I don't
particularly place speakers to maximize imaging or soundstage characteristics,
as those are secondary to me to musical and tonal considerations.



 





About a third of my record collection (all the rock albums alphabetized from M
through Z, plus a bunch of other stuff) was stolen sometime in the 1990s, and
it's been a slow process replacing many of those albums. Though more than half
my digital collection is on CD, I currently do not have a CD player hooked up.
All the CDs were ripped to my server either as Apple Lossless or FLAC files. The
rest of my digital collection is high resolution 24 bit or DSD files (dsf
format). 

I've been collecting records since I was nine year old, and still buy LPs
whenever I find something I want in that format. I do not buy, nor have interest
in, so-called audiophile releases, where the sound quality takes precedence over
the musical content. I would rather listen to a mediocre recording of music I
really like than an audio spectacular of uninteresting or boring music. I do not
own Jazz at the Pawn Shop or any Diana Krall. I am an admitted old Prog Rock
junkie, and still listen regularly to bands like Yes, King Crimson, Genesis
(Gabriel era only), Gentle Giant, Camel, Van der Graaf Generator, many of the
Canterbury scene bands, and other progressive rock and jazz acts. I love all
forms of music that are intricate, and demand attention. About the only forms I
don't listen to very much are mainstream pop tunes, bad rap (some of the early
or more artistic rap is quite good), 80s arena rock, most forms of metal or hair
bands. In spite of how that sounds, over half my LP collection is classical.
Give me something interesting to listen to or I'll probably watch a hockey game
instead.



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