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Review and Measurements of eXemplar Exception Phono Amp

rebbiputzmaker

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#41
I just spent $80.00 (that's right, eighty dollars--shipping included) on a 9V battery powered MC amp from Ebay. Arrived in 2 days, shrink wrapped, sans batteries. Two gain settings with a line bypass. And an off/on switch. Some guy in California makes them. Made in USA, it says here. I guess it's worth his while to put these together and sell them, mail order. I tried to take the board out of the aluminum case in order to check it out, but the way it was put together didn't allow for an easy pull. My impression is that it's a variation of the 80s Marshall Leach designs. But that's only my guess. I powered it up. Works fine. Subjectively I didn't notice any problems with a Denon DL103. No need to spend a fortune on this stuff.
That is cool, there is allot of decent stuff available for reasonable prices.

The old green Altec 4722 input transformers are very nice MC step-ups. They are a bit expensive now, used to pay around $35 ea for them, but they are an excellent transformer. Cinemags are good also. Transformers are nice imo if one is up to a little diy.
 

JohnBooty

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#43
Actually, from my limited experience, records today are a much better physical product, than they were in their heydey.
I think everything you said is 100% true. However, the maximum theoretical dB of a perfect vinyl record is still only about 70dB. At least that's the commonly-accepted figure I've seen over the years.

https://en.wikipedia.org/wiki/Comparison_of_analog_and_digital_recording#Dynamic_range

That's not necessarily a bad thing. A listening room will have 30-40dB of background noise anyway, so 70dB of dynamic range is just about plenty anyway.

So my question still stands. Does a phono preamp need more than 70dB of headroom?
 

sergeauckland

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#44
I think everything you said is 100% true. However, the maximum theoretical dB of a perfect vinyl record is still only about 70dB. At least that's the commonly-accepted figure I've seen over the years.

https://en.wikipedia.org/wiki/Comparison_of_analog_and_digital_recording#Dynamic_range

That's not necessarily a bad thing. A listening room will have 30-40dB of background noise anyway, so 70dB of dynamic range is just about plenty anyway.

So my question still stands. Does a phono preamp need more than 70dB of headroom?
I take it by 'headroom', you mean S/N ratio relative to operating level. My answer is that you don't, 70dB is quite adequate. However, you also need headroom above operating level, my minimum standard is 20dB, so that means that the maximum S/N ratio between the noise floor and the clipping point has to be 90dB. Quite a few achieve that, but not all.

S
 

SIY

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#45
The other part to consider is the thermal noise from the cartridge, which puts a hard limit on how low your noise floor can be. 70 dB from the rated output is pretty typical.

Of course, by using a low impedance resistive drive for MM phono stage measurement, you not only lose that part of overall noise, you also miss the noise induced by phono stage input noise current. That's generally not a factor with tubes or FETs, but can be significant in bipolar transistor designs. This is a major flaw in both Stereophile's and Amir's measurements.
 
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amirm

amirm

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Thread Starter #46
This is a major flaw in both Stereophile's and Amir's measurements.
Well, it is not like they are doing so well that inclusion of that matters. :)
 

SIY

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#47
Well, it is not like they are doing so well that inclusion of that matters. :)
True this time. :D

At some point, someone will give me a commercial phono stage to measure and I'll try to turn my hot air into actual work and show how I think it should be done.
 

restorer-john

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#48
...and I'll try to turn my hot air into actual work and show how I think it should be done...
I found the perfect balloon for all your hot air!

yoda balloon.jpg


Amir's balloon:

1553754082699.png


Thomas's balloon:

1553754142117.png


And his other one:

1553754696559.png


:)
 

anmpr1

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#49
"The old green Altec 4722 input transformers are very nice MC step-ups. They are a bit expensive now, used to pay around $35 ea for them, but they are an excellent transformer.

You should have invested in Altecs. LOL. Prices are on the move. Looks like singles are going for a couple of Ben Franklins, with assembled duals (wired can and RCA plugs) going for upwards of 800 dollars. New production Jensens/Lundahls are in that ballpark. Homemade is the way to go, if you know how.

Even so, those prices are bargain basement compared to some transformers being advertised, out and about. I remember back in the day, when Mitch Cotter blew the doors off the audio world with his own style of Mark "I never met a preamp that was too expensive" Levinsonesque pricing. That was 40 years ago. But everyone liked his blue box, and, since then, no one has batted an analog eye over through the roof pricing.

I recently checked out a reviewer discussing MC step ups. I've edited out the brands, to protect the innocent. Here are a few quotes, offered just for fun. It's like reading wine reviews. Or even now, beer reviews. I never hear any of this stuff, but I wouldn't mind a beer, or a glass of wine with my music, occasionally:

It lacks the immediacy, transparency, (inner an outer) detail, purity, speed and low sound-floor...

It was clean, smooth, quiet and detailed. It was especially impressive in the high frequencies, with extraordinary extension...

There is a noticeable "drying" ... You hear less definition, natural texture, "air" and "harmonics" developing and decaying. There is also a slight reduction of image size and focus; musicians are a little diffuse sounding.

The "timing" ... is good, but it is not quite as precise as the XXX, so the music isn't quite as intelligible...

The high frequencies are also good, being smooth and clean, but there is a sense of a "rounding" of the tiny details which individualize music. This may be caused by either a roll-off or a subtraction of low-level harmonics (and other musical information) or both. One other problem is that this model doesn't have the dynamic "jump" or "shock"...


PS: I think these subjective reviewers, the one's who can hear all this stuff, out of principle, ought to post their hearing test audiogram, updated once a year, in order to show readers just how golden their hearing really is. Fat chance that will ever happen.
 

SIY

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#50
OK, I'm convinced- my 4722s are going on eBay.
 

Jaimo

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#52
That is cool, there is allot of decent stuff available for reasonable prices.

The old green Altec 4722 input transformers are very nice MC step-ups. They are a bit expensive now, used to pay around $35 ea for them, but they are an excellent transformer. Cinemags are good also. Transformers are nice imo if one is up to a little diy.
DIY is the way to go. A good SUT is the way to go. I use a pair of Softone trannys from Japan with my DL103R. Cost around $130 when I purchased them a few years ago.
 

Panelhead

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#53
I had a Cotter back in the early 90’s. Went to sell it. Received about a 100 offers. Was not even the fabled low impedance version.
I am very familiar with eXemplar Audio. John and Jeff are very old friends. Both are engineers who worked for NASA and these products were a joint venture. The first product was a two way Altec based horn. Extremely dynamic and linear in response.
The price charged for their products is high. Every unit is essentially a custom build. High priced labor and design work. Plus I am sure parts quality is first rate.
The phono may not have good measured performance. Tube gear always measures poorly in comparison to solid state.
The testing of the output into 600 ohms is really not an issue. The 600 ohm units I am familiar with all are balanced. Single ended 600 ohm connections are uncommon. I would be surprised if anymore here uses 600 ohms.
I only know of one tube preamp that can drive 600 ohms with ease. It is in my attic and uses 6080 output tubes and huge value coupling caps. It can output an amp. Will drive anything.
 

Panelhead

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#55
I’ll show my amps noise plot with an AP if you have one of yours.
I will wager a 100.00 your tube amp noise floor is 20 dB higher than my solid state at 1 watt and around 18 watt output. It is only a 40 watt unit. And I built it.
Talk is cheap. Getting beat by 20 dB is beaten bad.
 

SIY

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#56
Wait, isn't this thread about phono stages?
 

Panelhead

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#57
Accept that.
I still would like to see an AP plot of these tube amps that do not compare poorly versus solid state.
This site is all about measurements and double blind comparison. Subjective comparison is weak.
 

SIY

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#58
Accept that.
I still would like to see an AP plot of these tube amps that do not compare poorly versus solid state.
This site is all about measurements and double blind comparison. Subjective comparison is weak.
The measurements for my most recent phono stage were published in Linear Audio, v8. Sorry, that was before I got the AP gracing my current lab bench, but they're still solidly done. I'd say that HD and IMD down -100 dB and noise floor below the thermal noise of the cartridge are pretty respectable.
 

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Panelhead

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#59
That is nice. I only have AP of my amp. Can I send the phono to get measurement performed?
I have a Borbelly, an Pass diy Pearl, and did have an Xono. Currently use a software RIAA and the mic pres of the interface. This is quieter than the phono’s I have.
Getting around -100 dB with tubes is impressive. I have an Audible Illusions, a Croft Epoch, and a Diy also. But no AP to test with.
Have had a VTL ultimate, CAT Reference, and Audio Research SP-11. My tube phono gear was way less than -100 dB. Mid 70’s to low 80’s. From manufacturer specs.
I need to borrow an AP to see what the current phono delivers.
I was thinking solid state versus tubes in general. Noise, stability, longevity, and not having heater circuitry is why I went from all tubes to all solid state a long time ago.
I do not know what your amps are, this phono looks top notch. If you designed it, kudos! Great work.
I retired in 2015, went right back to work. Getting the phono sorted and ripping the 40’ of lp’s is a project for once it is a real retirement. I now work 40 hour weeks instead of 80.
 

SIY

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#60
Yes, my design. And, with all due modesty, it performs well in areas that many other designs neglect.

If you want yours measured, let me know. I don't have a APx555 like Amir, but an APx525 is usually good enough, and I have a lot of phono test fixtures..
 
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