Review of Khozmo Passive Preamplifier

George 47

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With the Reviews section in abeyance, I thought I would still go ahead and give you my thoughts on the little Khozmo passive preamplifier:

Khozmo.jpg

It was twenty years ago that Sgt Pepper taught the band to play…

Well it was actually 34 years ago (yes 34 years!!) that CD hit the (audio) world. It brought a whole range of plusses and minuses that have been worked on for the last 34 years. Real progress has been made. It took some time but it has become the mainstay of music delivery even though now it is being overtaken by streaming.

One of the possible plusses involves the audio bit of the DAC. Nearly all DACs use opamps or discrete components that provide an output of 2V. This has become an unofficial standard, although the XLR variant gives 4V. With power amplifiers requiring about 1V for full output, this allows a change in the role of the preamplifier. If the output of CD/DACs was 2V and the power amplifier required 1V then all that was needed was to attenuate the output signal down to 1V or less. This brought about the possibility of using very simple single/two component (preamplifier with no amplification) attenuators. The birth of the passive preamplifier/attenuator.

To make the thing less hair shirt some added source switching and heaven forbid……..remote control.

This brought great promise. There would only be 1/2 components between the DAC and the power amp. How could it get any better? Stunning sound quality, cheap costs and everyone would be smiling, bar preamp manufacturers. But it did not work out that way. Everyone and their dog built a pot in a box, one set of input and output connectors and stunning sound flowed………er not quite………or not always.

For me, I saw this happening and bought a CD player with volume control built into the CD player. It had a digital volume controller. How could anything go wrong? It did and I preferred my active preamplifier. In fact, the in-built volume controller sounded terrible. Why? Well despite the great promise, the volume controller worked by ‘decimating’ the signal. It reduced the volume by chopping off some bits. 16 bits to 4 bits to 12 bits. Awful. They have got better now by using more bits in the volume controller.

OK along comes Creek who actually put together what I regard as a cracking item, the OBH 22 preamplifier. It has three inputs and two outputs. A source selector and volume control using a high-quality Blue Alps pot with a natty remote control. With my ARC valve preamplifier, it would require a really brilliant preamp to sound better. And it did. All it would do that was negative was to lose some bass impact and soften the overall dynamics. But it was incredibly natural, ultra-detailed and very easy to listen to even on rock music. However, occasionally it just did not work with some equipment and it sounded soft and quite mushy. Not often but it required care in matching impedances. Using long interconnects between the attenuator and the power amp could also lead to problems. But taking care to keep interconnects short (1m) then all was OK. However, it is no more as Creek does not make them anymore. A pity.

Recently there has been a huge interest in passive attenuators and that has produced many variations on a theme. There are many simple pots in a box. There are more sophisticated stepped attenuators where individual resistors are soldered onto the volume controllers and instead of the volume being continuously variable it is attenuated in steps. There are variations of even this type including shunt attenuators where one resistor is always in circuit and another is used to provide the steps of the volume control. There are Light Dependent Resistors (LDRs) where a change in the voltage of a small light source affects the LDR, it changes its resistance which is connected to the output volume. And of course, there are transformers that attenuate the signal either through Transformer Volume Controllers (TVC) or auto-formers. As you may expect all have their advocates.

I am looking at the Khozmo Passive Preamplifier (Attenuator), which is a stepped shunt attenuator. This is a company I have not come across before. They are based in Poland and you buy direct from them via the Internet. This is something that is becoming more common and promises to give good products at a reasonable price as the mark-ups from the distributor/shop are not added to the price. However, you have to buy blind and rely on any money-back promises and reviews like this one and people’s experiences.

It is possible to buy this shunt attenuator with different quality resistors for both the shunt resistor and the switched-in resistors. Khozmo sells the standard attenuator with Caddock and Vishay resistors with upgrades possible to the Takman Rex and Vishay Z foil resistors.

They are sold with either 10/20/50/100/200Kohm input impedance and in my case the 10K variant was recommended as I was using it with the Nord Class D power amplifier. The attenuator goes from -60 to 0dB in 48 steps (2dB increments from 1-11 and 1dB from 12-48) with make-before-break switches, hard-gold contacts, ±0.1dB channel matching, just two resistors in the signal path at any given setting, CNC-machined PA11 aluminium bodies and a precision ball-bearing support. Everything is hard-wired with solid silver core wire.

Because I listen slightly off-centre I asked for the dual mono version which is slightly less convenient than using a stereo version but you do get control over the balance. My attenuator had three inputs and two outputs with phono connections (which led to an odd problem later). The box is very well made. It is quite weighty and looks the part with wooden cheeks and the controls have a nice solid feel. Overall, including the attenuators, it is well-built and it is hand-made to boot. If you buy the stereo version, it can be remotely controlled at extra cost. The really good news is the basic model costs $300. My model cost $400 which with postage made a landed priced of £320.

So how did it sound?

Well, I wanted to use it with my Auralic/Aries+Audionote DAC2.1x front end, the Nord Class D power amp and Audionote E/HE speakers. I, therefore, had an issue with the power amp needing XLRs and the Khozmo using phonos. Maybe I should have got the XLR variant. Anyway in goes two amorphous make XLR/Phono adaptors and I get a sound out that it is very good. But I can surely do better with a Cardas XLR adaptor. I buy a pair and things did not work out. So eventually I go for the Neutrik XLR/phono adaptor and all is well.

Well, enough prevarication how did it damn well sound?

Well as you may expect from having just a couple of resistors in the circuit extremely neutral and natural. The 3D soundstage is big and it has great width and depth and dare I say it height. It also shows up a lot of studio recordings as being very dry and artificial with their limited soundstages. I used the old demo favourite of Misa Criolla featuring Mercedes Sosa and you can hear the large acoustic it was recorded in and the echo fading away. As you may expect there is no noise coming from the speakers with a passive attenuator and an extremely low noise power amplifier. You can therefore easily hear the echo from the acoustic as it gently fades down to zero with no cut-off. The bass was big and powerful with no overhang. The bass tonality was very good. It was possible to easily hear the different types of bass and the tricks done in studios.

Onto something musically different, Dystopian Overture from the new Dream Theater album in 24/96. The tricks used in this studio creation were easy to hear and very clear. In the middle of this track there is ‘kitchen sink’ moment where all sorts of instruments are added and taken out of the mix. The different instruments added echo and layering was easy to hear. After listening to that section of music it feels like you have been on an audio assault course. I was audio overwhelmed and given a feeling of being taken over which may have been what the band wanted to paint for this desolate future. Other preamps can become confused by this passage making it messy and less unnerving.

Of course, it is not perfect. Despite using high-quality resistors the dynamics are not as sharp as those from active preamps and the high frequencies do not have the air of transformers or active preamps. Active preamps still have that huge drive and attack and this resistor-based attenuator is a little softer. But for me, it is more relaxed and easier to hear for longer periods of time. Maybe not as showy as actives.

If you are concerned about whether everything will work and need to check the impedances Arek is great with advice and always responded to my e-mails very quickly and allows a return of the product if it does not work out for you, within a reasonable time period.

]In conclusion, given that some of the other preamplifiers I used (Nuforce P9 active preamplifier, Audionote M6, Creek OBH 22) were far more expensive than the little Khozmo and it was not embarrassed or shown to be deficient apart from a few minor areas makes it a bit of a bargain. It is highly recommended and you can get any variant you want.

So let me introduce to you
The one and only……….Khozmo….
.


Khozmo.jpg
 
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Lee Henley

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Nice write up George, I ise one his pre amps myself, it's called a Hattor which is supposedly the higher end version, I must admit they are a fantastic preamp to say the least, anyone looking for a passive preamp then buy with confidence on the stuff that they sell

 

ff1d1l

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Thanks for that, George. I must say I obtained a Khozmo with Z foil upgrade from Arek a few months ago, and I'm very happy with it. If your system is not clean and revealing you might feel a bit short changed on dynamics and bass drive. If your system is clean and capable of reproducing presence and dimensionality you may well find the upped game in this area addictive. When I go back to active preamps its a bit like returning to CRT or LED tvs after a good projector - things can look hyped and glossy, but you realise they're not as accurate.

At a recent bake off in an unfamiliar system it was bettered - not enormously -  by a Music First pre - I thought a fuller rounder sound and a smoother treble - but at many times the cost. In my own system at home, it seems not to have any real shortcomings - with the right material instruments are very present and in the room, sometimes shockingly so. I use the second output to run two subs, vial a dbx graphic and a fairly long cable run, and bass is very clear and again, has that present quality.

For the few hundred quid Arek is currently charging these must be one of the great hi fi bargains of the moment. Pre's determine the sound of a system more than power amps, and here is something quite stellar and transforming, well built - yes HAND built - and attractively designed that will in most cases bring a new level to your system.

I'll just finally say that I think I've undersold the dynamics aspect. The way that it reproduces dynamics is a little different, but when someone really steps up in recording, the instrument's size and power is conveyed without squash or edginess.

 

George 47

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I can only agree.

If people are put off by the well made but basic product then they can 'upgrade' to the Hattors also made by Arek. For the Hattor you get a fancy case with LED display, more resolution/steps in the volume control, dual mono and remote control, with it all controllable from the remote. There are more/better resistors that can be used as well as phonos and XLRs inputs and outputs. Oh and a nice aluminium carry case. I have to admit being a bit lazy and I might be tempted by one, although as soon as you mention fancy cases the prices go up with the lowest price model being about £800 and the top model £1400. Still great value. 

I know what you mean about dynamics as active amps sound as though they have a 'smiley face' response with boosted bass and top end. Very entertaining but could you listen to it for hours on end? All the details are there in the passives it just is not shouted at you. But for the price....??.

 

pgarrish

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Thems some purdy expensive little boxes.... £9k for a couple of transformers and 2 switches in a nice box... £400 for most of the same sounds more like it to me

 

George 47

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I guess the interest in passives has triggered some expensive TVCs with the top Townsend being £9K, the Music First Audio Reference £9K and the Acoustic Imagery passive TVC £8.5K. 

I read the Critic review and saw there was some correlation in reviews with the resistor passives being slightly softer and easier on the ear and the TVCs brighter and slightly more dynamic. I also agree with Critic that these were differences, with both being very high quality preamps. 

I hope to get a chance to hear the Hattor passive with dual stereo, remote control, better resistors and an active buffer amp to get rid of impedance issues. The Hattor prices start at under £1K which is not cheap, but based on what I have heard so far it will take an exceptional active preamp to do better. Certainly Critic found the passive Hattor was as good as the active Gamut at £6.5K (if not better?). If you can live with a less well endowed preamp then the Khozmo is a bit of a bargain. If you must have a passive preamp and very fancy cases then open the wallet and try to find £9K. Good luck with that...... 

 

Lee Henley

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I've heard the £9k passive pre amp and to be honest was a bit underwhelmed, I actually preferred the Hator which was the one I brought in the end.

 

ssfas

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I use the Hattor dual mono with remote. Bought one of the first ones and got a nice deal. Fully balanced from MDAC+ to Quad QMP power amps into Harbeth. Delighted with it. Sonically neutral. What more can one ask for?

Untitled

 

astrostar59

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Hi Guys

I have the Khozmo Passive with RCA's. My Audio Note DAC 5 has transformers on the output so that may help things along? The classic trap most passives fall into is frequency shift at lower volumes (more attenuation). You really need 25 times at least impedance difference from out impedance to input impedance on the power amp. A tubed DAC has more chance of driving a passive IMO. Interesting the thoughts on the Music First Passive. If it is brighter than the Khozmo then I wouldn't be after that aspect, not in my system anyway. 

I am pretty happy with my Khozmo, the only thing is it does frequency shift a bit a really low volumes (late at night levels). I am sat really close to my speakers which probably doesn't help that, the horns fire up quicker at low levels than the big 12 inch mid/bass driver.

Still, it is very fast, transparent and big soundstage, dead quiet (derr!) and when wound up the bass is superb, so maybe the impedance is not so far off?

The Khozmo has a bad rep for getting scratchy after some use. Mine started at 6 months. But I found a fix. When your system is off, manically flick the volume pot from zero to 12 o'clock a few times (polish the contacts). Then all good for a months or so.

ccs.jpg

 
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Swann36

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Really interesting thread as i'm learning about passive pre-amps....or attenuators as they perhaps should be called ....many thanks all contributors and especially George for the review

 

uzzy

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Great review George - did you do a review of the Nord amp you use ?  I am getting this itch to try a new power amp .. but so far have not had to scratch it.

 

Nearly bewildered

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I thought my passive pre amp would be the bees knees..but I find the sound so transparent and the minute detail in the recording ( as mentioned in the fine review above)  quite tiring on the ear! I always thought if i could hear everything on the recording then that must be the pinnacle of hifi? It isn't...i much prefer my quad cdp2 digital pre amp to my passive pre amp...as it's a warmer more inclusive sound where your just listening to music as opposed to having every facet of the recording laid out in front of you to choose which bit you like the best or maybe so much information you can't choose anything but endure the noise!   A good hifi plays music which you want to listen to..and not  be so analytical that you lose the reason your listening to it in the first place!  In my opinion..

 

George 47

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Great review George - did you do a review of the Nord amp you use ?  I am getting this itch to try a new power amp .. but so far have not had to scratch it.
Keeping up to date our Alex 54 reviewed the latest Nord amplifier at:

https://www.hifiwigwam.com/forum/topic/131659-nord-one-up-se-nc500dm-mk-ii-power-amplifier/

And I reviewed my updated Nord a little while later:



And not giving too much away Alex is currently listening to the latest Nord's Purifi amplifier. Should be an interesting comparison.

 
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