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Review and Measurements of Purifi 1ET400A Amplifier

JimB

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Depends on one's exact design approach - what they are housing. It could be something like this with a specially optimized input board, but not significantly less:
https://ghentaudio.com/kit/ncore-se-200w.html
1579761051787.png


Otherwise, with a shared power supply, like that used by Purifi for their demo build, it can be made to fit in that size case with existing parts, as shown here in a mock-up with a Purifi EVAL1 I/O board (or other available I/O boards):
1579761260669.png
 

mocenigo

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With a DIY-friendly adapter board one may save a couple of cm in depth, if the board is small enough it could even be mounted vertically (!). I am going to test Tom Christensens's boards, but I do not know the full feature set yet.
 

mocenigo

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This. Is. Weird.

But I understand it. if you like the sound (and distortion profile) of a single ended triode, but you wanted to have that exact sound with 500W of power... well.

It is not wrong. It is just not high fidelity. Will an audiophile buy it? Maybe if you add one or two zeros at the end of the price...

Roberto
 

maty

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Weeks ago I made some emulations with the new soft DISTORT (by pkane) to verify what Nelson Pass defends. For acoustic recordings and natural voices, with few musicians, H2 at -73 dB was more pleasant. Orchestral mass sounded better with a cleaner harmonic profile, with all below -90 dB -> verified.

-> https://www.audiosciencereview.com/...test-distort-audibility-of-distortions.10163/

Maybe the commitment is with H2 at -84 dB.

These days, after listening to the superb recordings of PlayClassics I have very clear that I opt for a clean profile. And maybe, in the future, pkane be encouraged to develop a VSTplugin that allows us to add harmonics without anything else in some acoustic / electrified recordings.

-> https://www.audiosciencereview.com/...lassics-album-premiere-for-asr-members.11224/

-> -> http://www.playclassics.com/streaming

But there are many others who like profiles with many harmonics and high level. At least they are dominant H2 and monotonously decreasing as SET topology. For them it is the post.

What I have very clear is that I do not want to see dominant H3.
 
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Billy Budapest

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This. Is. Weird.

But I understand it. if you like the sound (and distortion profile) of a single ended triode, but you wanted to have that exact sound with 500W of power... well.

It is not wrong. It is just not high fidelity. Will an audiophile buy it? Maybe if you add one or two zeros at the end of the price...

Roberto

Not sure why you would do that to a Purifi board! A full tube implementation would make more sense. No pristine measurements to screw up!
 

mocenigo

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Not sure why you would do that to a Purifi board! A full tube implementation would make more sense. No pristine measurements to screw up!

I would never do that, but a 400W tube amp would probably be much more expensive and also use much more power. So it would make sense, to those that need that power and want that type of sound.
 

jalejos

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I have designed this buffer as an option for the Hypex NC500 and 1ET400A modules of Purifi Audio. Everyone knows that these modules have a very low distortion and that many manufacturers have designed different buffers for use with different operational amplifiers (I myself have a buffer for NC500 and 1ET400A that uses the Sonic Imagery SIL994 Enh Ticha operational amplifiers)
Why not design a valve buffer with the advantages and disadvantages it has and that it is the user who has the option to choose?
I have based on the double triode Korg Nutube that can work with low voltage. The circuit is ready to work with the Hypex power supply model SMPS1200A400. The voltage present in the IDC connector is sent, via a CRC filter, to the Korg Nutube and to the low noise regulators Sparkoslabs to power the rest of the circuit.
The circuit operates in differential mode and, by means of the two adjustable resistors, the polarization voltage of the Nutube grilles can be varied, modifying the distortion of the second harmonic. Values of the second harmonic can be adjusted from 0.039% to 1.5% at the output of the buffer. I enclose measures.
This circuit does not seek the perfection of sound, but has the advantages of an amplifier in class D (damping factor and dynamic) and a sound similar to the valves.
Nutube 177mV (+) L.jpg

Nutube 100mV R.jpg




FFT Spectrum Monitor 1KHz V3 994.jpg

This is the measurement with the buffer using the SIL994 Enh Ticha operational amplifier.

FFT Spectrum Monitor 1KHz V3 Burson.jpg

And here using the operational amplifier Burson Audio V5

IMG_2353.JPG


IMG_2352.JPG
 

Billy Budapest

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I get it. At first I did not but now I understand it is basically a way to manufacture a 400 watt amp with the distortion characteristics of tubes.
 
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DonH56

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Stick a 2-8 ohm resistor in series with the output.
 

JimB

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Tube front ends with class D power amps are quite common for bass guitar. Never wanted to run my HiFi stereo through my bass amp, though.
I did a hybrid design back in about 1978 for a boutique audio electronics company using a tube front-end and a "special" solid state output. Infinity had a BIG one. Mine never went to market. Bad market timing and I made it sound too solid-state for the tube crowd by reducing the distortion of the tube front end too much. The output stage design was inspired by what I thought Nelson Pass was going to do in his pending "Stasis" amp at Threshold, but once I read his patent, it turned out my design approach was a different topology. I still have the prototype (though I don't use it). I have to take it to Burning Amp some year. Nelson should get kick out of it. So, tube input and solid state output has a long history and class D solid state output makes sense in that tradition.
 

jsy

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Took me a while tonight but I got through this whole thread. Quite a ride! :) If anyone gets around to a DIY build of one of these amps with a Christensen buffer, I'd love to hear about your results.

If anyone gives poor Thomas those post numbers and a new thread is born, I'd love to see that too. I've been a bit surprised at the ferocity towards subjectivity. From a post in this thread: "if someone says they can hear a difference, it is meaningless unless they demonstrated it in a controlled experiment". I can reliably hear the difference between an amplifier that's on or off, sighted. I can hear the difference between mono and stereo. Sure, these are extreme examples, but I'm willing to at least entertain that it doesn't always take golden ears for someone to meaningfully hear if a reproduction is poor, even absent controls.
 

maty

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@jalejos

I read that a few complained about an excess of microphone microphonic noise with the Nutube vs traditional tubes. How have you solved / minimized it?
 
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Julf

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I've been a bit surprised at the ferocity towards subjectivity.

Maybe the "Science" in the forum name is a hint?

I can reliably hear the difference between an amplifier that's on or off, sighted. I can hear the difference between mono and stereo. Sure, these are extreme examples, but I'm willing to at least entertain that it doesn't always take golden ears for someone to meaningfully hear if a reproduction is poor, even absent controls.

I guess it all depends on the definition of "meaningfully"...
 

0bs3rv3r

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@jalejos

I read that a few complained about an excess of microphone noise with the Nutube vs traditional tubes. How have you solved / minimized it?

I heard that as well. I guess you'd have to mount the whole circuit board on damped mountings and maybe layer some damping material over and around the nutube package.

Personally, I have never heard one, but I get the impression Nutube's are not anywhere near as good as proper tubes working on high voltages. The classic dual-triodes, 6DJ8, 12A*7, 6SN7 etc, still win IMHO. If I had one of these new class D power amps, THAT's what I would put in front of them - despite the giggling in the background around here :)
 
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