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Review and Measurements of eXemplar Exception Phono Amp

rebbiputzmaker

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#24
Even the choice of tubes is not the greatest, The 6c45p and the 6bz7 is not the way to do a proper high gain MC amp IMO. 3 stages, something like the Loesch with a modified GenRad power supply is much better IMO, I build several over the years. Working with 417As can be a bit tricky though, you need allot to select them. I liked 437As much better,great amp driver, plus had more than 100 of them, a great tube but they are now pretty much extinct like $300 each.

http://www.tempoelectric.com/phono.htm#circuit

https://www.teresaudio.com/haven/preamp/preamp.html

A variation.
 
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gvl

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#25
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#26
Maybe someone has been working on their undergrad for more than 10 years and has some serious student loans to pay off. If they could just sell 30 of these ... :)
 

sergeauckland

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#27
Even the choice of tubes is not the greatest, The 6c45p and the 6bz7 is not the way to do a proper high gain MC amp IMO. 3 stages, something like the Loesch with a modified GenRad power supply is much better IMO, I build several over the years. Working with 417As can be a bit tricky though, you need allot to select them. I liked 437As much better,great amp driver, plus had more than 100 of them, a great tube but they are now pretty much extinct like $300 each.

http://www.tempoelectric.com/phono.htm#circuit

https://www.teresaudio.com/haven/preamp/preamp.html

A variation.
Not impressed with that design. Firstly, the output has a high impedance, it would have been better if the output had been taken from the cathode as a cathode follower. It then wouldn't have had any gain, but that's probably not a bad thing.

Secondly, what happens to the valves when the bias batteries go flat?
 

rebbiputzmaker

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#29
Not impressed with that design. Firstly, the output has a high impedance, it would have been better if the output had been taken from the cathode as a cathode follower. It then wouldn't have had any gain, but that's probably not a bad thing.

Secondly, what happens to the valves when the bias batteries go flat?
Good points.


There are many variations, the one I put up was different from Arthur's. There are many variations.

The battery charges in circuit. There are many ways to build a good MC front end. I also like using transformer.

It is amazing though how much people can charge for junk, like the one Amir just tested.
 

SIY

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#30
Not impressed with that design. Firstly, the output has a high impedance, it would have been better if the output had been taken from the cathode as a cathode follower. It then wouldn't have had any gain, but that's probably not a bad thing.

Secondly, what happens to the valves when the bias batteries go flat?
All good points. I'll add in that this is likely to be quite microphonic as well. Very poor power supply rejection. AL did a couple of nice tricks in there, but there's too much emphasis on parts brands and not enough on optimizing the circuit.
 

JohnBooty

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#32
Noob question.

The maximum theoretical dynamic range of a vinyl record is only ~70dB.

So does it matter if a phono preamp has SINAD that's not much better than that?

I'm sure there's a fairly simple answer and I'm probably missing something obvious. School away!
 

rebbiputzmaker

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#33
All good points. I'll add in that this is likely to be quite microphonic as well. Very poor power supply rejection. AL did a couple of nice tricks in there, but there's too much emphasis on parts brands and not enough on optimizing the circuit.
Yes the parts branding is not necessary. I liked to shock mount some sockets when needed to help reduce microphonics.
 

anmpr1

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#35
At Exemplar, we’ve learned not to depend on the numbers. In the electronics world, they measure the speed of circuits in microseconds and our ears hear harmonic structure in nanoseconds. In the end, it’s not about charts and numbers…..it’s about bodily sensations and emotions.

So you see, according the company, no valid measurements are even possible. Although I don't know what hearing an "harmonic structure" at a billionth of a second could mean, I'm sure it's a very emotional experience. I also wonder what sorts of bodily sensations arise from swapping out your standard wall plug for their 1.5 meter, two thousand dollar power cord? Maybe it's not insulated well, and you get a mild shock.
 

anmpr1

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#36
The maximum theoretical dynamic range of a vinyl record is only ~70dB. So does it matter if a phono preamp has SINAD that's not much better than that? I'm sure there's a fairly simple answer and I'm probably missing something obvious. School away!
Actually, from my limited experience, records today are a much better physical product, than they were in their heydey. I think it's because they are not mass-market, and pressing plants care more about overall quality. From the 60s through the 70s, up until the digit age, stereo magazine letter forums often complained about the poor quality of records. Very common complaint. I've a large collection, and most are average at best, from a quality standpoint. The big change came with small, cottage industry, direct to disk recordings, like Doug Sax's operation. But these had program limitations; the content was not always very good (i.e., musically compelling).

I think lack of noise was one of the problems people had with early digital recordings. I mean the ones that were mastered and equalized correctly. Even with the quietest record, you can still hear vinyl noise artifacts in low level passages (or tape hiss, if you were using open reel). I think some folks were shocked at the zero noise floor in CDs. It was a strange encounter. I remember one of my first CDs: an analog (AAD) recording of a pop song. On one particular passage in the mix, the left channel dropped out, and only the right channel had music. With headphones, I could distinctly hear tape hiss on the channel with no music. I never heard that before. I then put on the record, and could not hear any hiss, due to vinyl noise. It was then that I realized that digital was the future in high quality recording and reproduction. So much more revealing than plastic.
 

sergeauckland

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#37
At Exemplar, we’ve learned not to depend on the numbers. In the electronics world, they measure the speed of circuits in microseconds and our ears hear harmonic structure in nanoseconds. In the end, it’s not about charts and numbers…..it’s about bodily sensations and emotions.

So you see, according the company, no valid measurements are even possible. Although I don't know what hearing an "harmonic structure" at a billionth of a second could mean, I'm sure it's a very emotional experience. I also wonder what sorts of bodily sensations arise from swapping out your standard wall plug for their 1.5 meter, two thousand dollar power cord? Maybe it's not insulated well, and you get a mild shock.
That has so often been the response of the Foo merchants and purveyors of massively overpriced junk. Measurements can't measure emotion, there's no number for 'musicality', our ears are far more sensitive than instruments etc etc etc. Pushed by the manufacturers, propagated firstly by magazines and now by HiFi forums where all opinions, no matter how crackpot and misguided, are equally valid. I'm very glad I found this place where opinions, especially the more outre, have to be justified.

S.
 
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amirm

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Thread Starter #38
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?
600 Ohm testing is more or less standard at stereophile. JA runs it on the output of DACs, phono pre-amps, etc. It was requested that I start showing the same data because some gear has far lower input impedance than the 100k I use for testing. Unfortunately the analyzer only has 100k, 600 and 300 ohm. So nothing in between. Like you, I pushed back that 600 ohm testing is not useful for distortion, etc. as it is too harsh.

In this case though, I am not measuring distortion. Instead, it is a simple way to show the effect of high output impedance in a way that is simpler to understand than pure impedance graph. People understand frequency response. Impedance is harder to grasp.

In this regard, I am not seeing an issue with showing that graph with 600 ohm load.
 

sergeauckland

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#39
600 Ohm testing is more or less standard at stereophile. JA runs it on the output of DACs, phono pre-amps, etc. It was requested that I start showing the same data because some gear has far lower input impedance than the 100k I use for testing. Unfortunately the analyzer only has 100k, 600 and 300 ohm. So nothing in between. Like you, I pushed back that 600 ohm testing is not useful for distortion, etc. as it is too harsh.

In this case though, I am not measuring distortion. Instead, it is a simple way to show the effect of high output impedance in a way that is simpler to understand than pure impedance graph. People understand frequency response. Impedance is harder to grasp.

In this regard, I am not seeing an issue with showing that graph with 600 ohm load.
I like to see 600ohm used as a load on equipment designed to drive line levels. I know that these days it's not common to see anything with a 600ohm input, but if a phono stage or whatever will drive 600 ohm satisfactorily, then there's a good chance it'll drive any length of cable, and won't be troubled if the load is 20k, 10k or even lower. With anything I use in my own system, I test at 10k and 600 ohm and expect no significant difference in performance except for a small voltage difference.

S
 

anmpr1

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#40
There are many variations, the one I put up was different from Arthur's. There are many variations. The battery charges in circuit. There are many ways to build a good MC front end. I also like using transformer. It is amazing though how much people can charge for junk, like the one Amir just tested.
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.
 
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