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Review and Measurements of eXemplar Exception Phono Amp

amirm

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#1
This is a review and detailed measurements and listening tests of eXemplar eXception Phono stage (amplifier). It is on kind loan from a member. The cost as listed on eXemplar website is USD $6,950.

For a piece of equipment listed at such a high price, the eXception comes in pretty ordinary boxes, one holding the tube amplifier, and the other the power supply:

eXemplar Audio eXception Phono Amplifier Audio Review.jpg

If the front is ordinary, the back panel is utilitarian at best:

eXemplar Audio eXception Phono Amplifier Back Panel Audio Review.jpg

The boxes look like chassis you buy from ebay and in your garage drill and put jacks and such in. At $7,000, I expect far better.

The two inputs are Moving Coil and Moving Magnet even though neither is identified such. I did not play with the loading but a couple of RCA plugs with a trim pot is supplied for I assume varying the input impedance? I looked online but could not find a manual for it. So I left this alone.

There is no power supply in the this enclosure and all the goods are on one side. I wonder if there is a version with a power supply? Or was this borrowed from another product? Anyway, the 8 pin connector mates with the power supply unit which is quite hefty:

eXemplar Audio eXception Phono Amplifier Power Supply Audio Review.jpg

Sadly there are no safety and regulatory certifications which scares me good bit given the likely very high voltages running around to drive the tubes. Touching the back jack brings your skin within a millimeter of potentially lethal voltages. I sure hope someone has done their homework and this is a safe design inside.

The unit is quite microphonic. Tapping the rack that is under it gently produces a "bing" sound. So better budget for a good isolation platform unless you like every bass note to translate into a delayed bell sound to mix with your music.

Phono Stage Measurements
Let's set the output level to 1 volt by adjusting the input with moving magnet input and see what we get:
eXemplar Audio eXception Phono MM Audio Measurements.png


The gain is pretty close to the spec. Starting from top left, we have nearly 1 dB channel mismatch. I don't know about you but if I pay this kind of money, I want dead on matching for the two channels. This is going to cause a shift in soundstage.

No specs are provided for distortion so we have to go by what we are getting which is 63 dB. Second harmonic is at -70 dB with enough noise added to it to bring the SINAD to 63 dB. Sure, we can buy into tubes having second harmonics but what is up with that all garbage around 6 to 20 kHz? We will dig into this more in a bit.

As a way of reference, our recently reviewed $299 Cambridge Duo Phono stage produces 90 dB SINAD. That is 37 dB better! Not 5, not 10, not 20, but 37 dB better!

Moving Coil with its much higher gain naturally worsens performance:
eXemplar Audio eXception Phono MC Audio Measurements.png


The higher gain exaggerates the switching noise from the power supply rectifier at 120 hz and harmonics of mains thereof.

One channel is a lot worse than the other with a SINAD of just 51 dB versus 57 in the other channel. The red channel has those extra spikes at 7, 11 and 15+ kHz. What do we pay thousands of dollars for if it is two channels that perform similarly? Is there some goodness in one channel distorting more than the other?

Let's look at our noise floor spectrum without the generator playing (but connected and hence loading down the input):

eXemplar Audio eXception Phono Noise Spectrum Audio Measurements.png


How do you defend this? Idle noise spikes going up to nearly -50 dB? Thank heavens our hearing is poor in low frequencies. Again, the worst case spike in Cambridge Duo was -90 dB. Again, did I miss school the day they taught these things to be musical?

The only performance spec in the marketing bullet list from eXemplar is "noise -75 dBu." This is what I get:

eXemplar Audio eXception Phono Signal to Noise Ratio Audio Measurements.png


OK, it is close with MM input but nowhere near with MC. Likely a-weighting was used to reduce the low frequency noise.

Let's sweep the input level and see what kind of distortion+noise we get relative to output voltage. First, moving magnet:
eXemplar Audio eXception Phono MM Level vs Distortion Audio Measurements.png


It is obvious how noisy the eXception is compared to solid state Cambridge Duo. It does have one benefit though in that there is no real clipping. Indeed, by accident I drove the input to higher voltages and saw output as high as 30 volts!!! Hope you have a high voltage tolerant input on your pre-amp as I do in my Audio Precision analyzer or it will cook it good. Not how much cleaner output the Cambridge provides (nearly 8 volts) prior to clipping. The gap in performance is enormous.

Can you guess what happens with higher gain moving coil input? I knew you could:

eXemplar Audio eXception Phono MC Level vs Distortion Audio Measurements.png



Let's look at frequency response at two load impedances: a very high 100 k ohm and a low 600 ohm (inverse RIAA EQ applied to audio generator):

eXemplar Audio eXception Phono MM Frequency Response Audio Measurements.png


100 k Ohm doesn't load the unit at all and hence, provides essentially flat response. There is a tiny rise in low frequencies but it is probably not an issue. Channel imbalance is there of course. The issue becomes when we change the load to 600 ohm and the response drops like a rock below 500 Hz. What is going on there? Yup, output impedance rises rapidly at low frequencies:

eXemplar Audio eXception Phono MM output impedance Audio Measurements.png


At 20 Hz, the output impedance of the eXemplar rises to whopping 3.8K ohm! You better use a pre-amp with very high input impedance or you will surely lose bass response this way. This would be a good thing to mention in the product spec, don't you think?

Listening Test
Yes, there is a listening test. Didn't want to keep dealing with, "measures bad but sounds good." But how do you do that? Driving the unit with a turntable doesn't provide any reference point to compare. So I decided on a different path.

I loaded up one of my audio tracks into the Audio Precision analyzer and told it to act like a DAC. And while it was at it, told it to EQ it with inverse RIAA and set the level to what a cartridge would produce. The output of the analyzer went to eXception phono amp and out to a leg of an AB switcher. I loaded up the same track into Roon player and fed my Topping DX3 Pro. The output of DX3 Pro went to the other leg of the AB switcher. With me so far? Good. We are almost to the end. The output of the AB switcher went to a headphone amplifier. This way, I could start playing the track through a DAC as the sound originally is, and through the AP and then phono amp.

I went all fancy and hooked up my Stax dual differential tube headphone amp and Omega earphones. This was a fail as the combo of Stax and eXception hummed like crazy and no amount of messing with grounding helped it. I switched to Atom headphone amp and that completely cured the problem. And gave me lots more performance too.

The weapon of choice for headphones was my cheap AKG K92. It is closed ear and very efficient so I could get pretty high levels of sound without stressing the data path much.

Matching levels electronically proved futile due to variable impedance of the eXception phono stage. So I had to once again resort to matching levels by ear.

Casual listening showed that the ear was highly forgiving of all the ills of eXception Phono stage. Careful listening however, showed the highs to becoming a bit "tizzy" (trademark: amir) and when track got busy, everything mashed up together. The digital path through Topping was clean and authoritative. The channel mismatch in eXception caused a shift in soundstage.

There was nothing euphonic here. Second harmonic at -70 dB is not going to add "warmth" or whatever to the main tone it is distorting. Instead, the spray of harmonics from each tone in the music is liable for the increased energy in high frequencies. This is the same thing I have found in testing tube headphone amplifiers with similar distortion profiles.

Conclusions
I don't know where you hang your hat on when it comes to eXemplar eXception Phono stage. It doesn't look pretty or expensive. It is massive. It is sensitive to vibrations. It doesn't have any safety ratings. And brings boatload of distortion and noise which does nothing good to my ears. Heck, the tubes are hidden so you don't even get biased into thinking there is warm sound here!

The vagaries of LP playback is such that people probably don't know what they are getting here. I am here to say you are paying more, but getting far less.

------------
As always, questions, comments, recommendations, etc. are welcome.

Going to visit a few local folks to get gear from them. They live 150 miles away round trip so I need gas money. Please consider donating money using:
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#2
The moment I saw the 6 kilobuck price and the tubes, I knew this thing was doomed. And ... ahyup.

Along those same lines, what do you think would happen if you hooked this thing up to the awful Behringer ADC you measured a while back, then fed the ADC's output through your favorite Audio-gd R2R DAC and a Darkvoice headphone amp? Any LP you played would come out sounding like the Chipmunks Christmas album.
 

M00ndancer

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#3
Ouch...
 

graz_lag

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#5
The Dark Side of the Made in USA ...
 
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#6
from the Website:

Quote:
"eXception Phono:
The Oppo 105 For true music lovers, nothing equals the warmth, dynamic range and fidelity of vinyl records. Therefore, a critical component of every audiophile’s vinyl playback system is the phono preamp.

Due to the extremely small signal produced by a phono cartridge a good phono preamp is one of the most difficult pieces of audio equipment to produce. We’ve spent 10 years developing and refining our Exception Phono preamp to meet our standards of performance.

Words are inadequate to explain the Exception Phono. Like the rest of our equipment, you have to hear the Exception Phono to fully appreciate what it does.

Key Features:
...A low noise level of -75dBu allows the quietest passages of your music to be heard
The low impedance output circuit is designed to drive your cables and isolates the output from the influence of the
next stage."
 

restorer-john

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#7
The issue becomes when we change the load to 600 ohm and the response drops like a rock below 500 Hz. What is going on there? Yup, output impedance rises rapidly at low frequencies:
Whilst the performance is clearly lacking in virtually every parameter you chose to test, who on earth loads any domestic active phono stage, pre-amplifier, or D/A converter line stage with a 600ohm load and then calls it out for a rising impedance at LF?

20,000 ohms (20K) is pretty much the de facto standard. How many RIAA stages have you seen that do not have coupling capacitors? There are some, but most (with or without caps) do their job correctly and roll-off everything that may extend into the rumble and cart/arm resonance area. Load it with a representative input impedance for a line input of a proper preamplifier before condemning its FR.

This is not a headphone amplifier needing a Zout of zero or a D/A converter with a response to DC.

What, incidentally, was the overload in mV and uV for the MM and MC respectively?
 

M00ndancer

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#8

Shadrach

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#9
I have a feeling there is a lot of stuff like this around.:(
I did measure my WAD 83 valve headphone amp many years ago and it wasn't a pretty picture.:p
The strange thing is I find it quite okay to listen to, but it didn't cost $7000.:facepalm::D
 

M00ndancer

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#10
@Shadrach We all know by now that there is no correlation between performance and price.
 

anmpr1

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#13
7 K? This is slumming in the world of analog phono. An eponymous company in Boulder CO makes a phono stage selling for fifty large. In truth, these things have nothing to do with measurements. It's all about 'front to back depth", "mid-range bloom", and made up stuff like "pace". That is, stuff no one can pin down. Audio neurosis at its finest. The only thing more idiotic is the world of high end audio cables. Phono science used to be respectable: analysis of the geometry of tracking error, mechanical resonances, and stylus shapes. But all that's been figured out, long ago. As near as I can tell, it all started to go south when Yoshiaki Sugano figured out that he could sell high priced jewelry to men, by enclosing his hand built cartridges in semi-precious stones and exotic wood.
 

SIY

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#15
My question is the same as John's: why a 600 ohm load? Totally unrealistic.

Input impedance for MM and overload voltage and recovery measurements are vital.

One can design an excellent tube-based phono stage, bringing the headroom and voltage swing capabilities of tubes into the picture. Apparently they haven't, but don't blame the tubes, blame the design engineer.
 

sergeauckland

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#17
I once measured a very expensive italian valve phono stage and was similarly surprised. It had a very low frequency instability that caused the cones in a reflex loudspeaker to flap alarmingly with no signal, had high distortion and no precise overload point, the distortion started out high and going higher. Similar to to the eXception, it had no detailed spec, and had a very utilitarian box, stuffed with huge and expensive 'audiophile' capacitors.

I have to say that it did sound good, and I suppose products of this nature are intended to be sold by exclusive dealers who set up suitable demos, not sold on-line with money back guarantees. High price but scruffy build is all part of the marketing schtick.

S.
 

RayDunzl

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#19
Ray: But you didn't test it with muuuuuuuuusic!

Amir: Yes, I did.

Ray: Oh...
 

FrantzM

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#20
Hi

Everyone knows you can't use digital anything to measure a purely analog product. Multimeter and analyzer must be purely analog. Tube laboratory equipment you always can find NOS on eBay are preferred for this kind of testing/review ...

We could have forgotten about his so-called measurements then he goes on his listening test, he eschews the Stax with tube claiming hum ... and go for a digital chain with a cheap <$100 AKG headphones !!! The heresy!!
This is a flawed review
NOT!!!!

:p
 
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