Keen to get your thoughts on the new buffers, have you had a chance to listen to them? Are you 100% sure the harshness is coming from the amp and not another component in your chain?
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VTV Purifi 1ET400A updates
- Thread starter Rugger
- Start date
The VTV buffers with the Sparkos SS3602's are installed and I have begun my auditions. I have a few more select recordings to listen to but to this point there seems to be an improvement -- i.e. so far no "shriek" at high volumes with brass, violins, et al. I will update if I can't confirm this improvement.
No, I quite sure the problem is with the amp, or more probably the buffer. I have listen with the same up and downstream components with different amps without the weird distortion as above.
I have just got round to re-testing this. Im afraid what you have been told is incorrect, or at least if implemented its ineffective. The MPs certainly do still need RF filtering. I specifically raised this with Hypex last year and was told there was no filtering and that it may be implemented in a new revision. It is possible that this happened without me being aware so I pulled a recently delivered and manufactured NC122MP off the shelf and hooked it up to the scope and FFT analyser.Just to clarify as I checked with Hypex support. The MP family amps do have RF filtering on the audio inputs as does the NC1200.
NC500 does not have filtering either with or without the (supplied) buffer on the eval board.
Its switching frequency is around 400kHz. I input a 406kHz tone into the audio input and it showed the same problems as I have seen before.
On the scope the switching signal goes bananas and on the FFT you see the noise floor go up dramatically and spurious intermodulation tones appear.
Ignore the title on the plots
No audio signal input. Just switching signal is evident.
406kHz audio (Rf really) signal input
This is why we have seen a couple of reports on ASR about "odd noises" with certain dacs. Some dacs output garbage at around 380kHz. Note these noises went away when a filter was implemented.
It will also be a problem at multiples of the switching frequency. So my advice is that an RF filter is still required and what we fit as standard.
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That is very interesting, thank you for posting this.
Given that the DAC's output garbage is interfering with the switching frequency, can we say that this specific DAC-induced problem (separate from non-DAC interference such as a cellphone sitting next to the amp) only really applies to class D amps? And there is no way of knowing which DACs will or will not output this ugly noise?
Given that the DAC's output garbage is interfering with the switching frequency, can we say that this specific DAC-induced problem (separate from non-DAC interference such as a cellphone sitting next to the amp) only really applies to class D amps? And there is no way of knowing which DACs will or will not output this ugly noise?
Its still possible for external RF to get into the amp so not exclusively a dac related issue.
All amps should have RF filters not just class d. Its just good practice. I'm sure we have all heard cell phones .......badup badup badup baaaaaaaaaaa
I'm afraid there is no way without testing what dacs will be an issue. As you never know what RF environment the amp will be used in the simple and obvious solution is to fit a filter into the design as standard.
Alan, thanks again!
Not sure why Hypex response was incorrect.
I specifically asked them about am/fm frequencies.
shal
Active Member
Its still possible for external RF to get into the amp so not exclusively a dac related issue.
All amps should have RF filters not just class d. Its just good practice. I'm sure we have all heard cell phones .......badup badup badup baaaaaaaaaaa
I'm afraid there is no way without testing what dacs will be an issue. As you never know what RF environment the amp will be used in the simple and obvious solution is to fit a filter into the design as standard.
Thank you for your input.
There is one thing that I cannot understand in ampli (or dac) review/test/measurement.
We have a lot of review with SINAD ranking. And people said : "this amp X with 105 SINAD is a way better than this amp Y with only 103 SINAD but of course both are transparent" (yes, audio is full of schizoid people) .
But in reality, sometime the amp X have -65db of distortion due to the RF and the amp Y have not this problem.
What the interest to do this run of better SINAD ?
Can we have review of a amp in his worse conditions case ?
Ok THD+N, IMD, is OK but there is also, RF test, thermal test (cold, warm), speaker with odd impedance/phase , ground test (PIN1 problem for example) , quality component (e.g. capacitor (Sorry March-audio)). Protection against DC, amp failure , too high distortion....
=> Have we a complete list of these characteristics ? I am interested if someone have this list, it can be a good post.
I am more interested by a amp that will be always (very) good that a amp that can be perfect in some inaudible aspect in some case and sometime bad in another case
PS: sorry for the bad english, sometime it is not simple to make a good sentence on a complex situation
The problem is you would have to run a myriad of tests to establish how any amp behaves under different operating conditions. Its not really feasible for Amir to do this.
shal
Active Member
Yes, of course it's not to Amir to do all this test.
But there is a drawback if we only test a part of characteristics of amps and do a ranking. People will look only the ranking....
So constructors should enter in the competition of "who have the best SINAD" and ignore others (and important) characteristics.
Your previous post is a superb example : Bad RF input management of hypex that can bring audbible problem. But it's difficult to find the information about this characteristic on constructor site
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I have a miniDSP SHD Studio -> Matrix X Sabre DAC -> Schiit Freya+ -> NC400 and it's *fantastic*. Just sayin'.
For those who might be interested in a subjective review of VTV's version of the Purifi 1ET400A, see mine available here ... https://www.audioasylum.com/forums/amp/messages/23/238411.html
- Thread Starter
- #53
I got the NC502MP in and spent a while comparing it directly with the purifi amp. It is clear that the purifi is very VERY detailed, the NCore in comparison is more laid back in the upper treble. For some things I like it more, for instance, the crack of the snare drum, crash of the symbols, the felling of the pick on the strings, for me it sounds much more realistic and forward. You are right that heavy brass can get shrieky and for that, I like the MP more. I am going to try them both on the horns once they are together and see which I prefer. Right not I'm leaning toward the NCcore. I think i would like to grab a Freya+ and see how it sounds with some tube in the signal.
Great review @Feanor and very interesting comparison @Rugger . I wonder if there is a difference in sound between the stock Hypex buffer and the buffer used in the EVAL1 Purifi module - surely the stock Purifi EVAL1 unit wouldn't have received so many good reviews and descriptions of sounding dead neutral if the treble was as harsh/shrieky as it is being described here.
@Rugger how are you finding the bass/midrange between the NCore and Purifi?
@Rugger how are you finding the bass/midrange between the NCore and Purifi?
I had an NC252MP, (by VTV), before the Purifi. I agree with your observations about the Purifi and also the the NC is more laid-back while still being quite resolved and dynamic.
I have begun to listen more to my Purifi with my Freya + in 'Tube' mode. My impression after just a few hours is that the 'Tube' mode does moderate the brilliance of the Purifi and I'll probably proceed to use Tube mode routinely. It's too bad in away because in case of the all-too-rare really excellent recording, the advantages of the Purif are realized.
If interested, see my (subjective) review of the Schiit Freya + here ... https://www.audioasylum.com/forums/amp/messages/23/236688.html (I wrote this before receiving my Purifi amp.)
- Thread Starter
- #56
Nice write up!
Do you think Freya is providing enough taming and "tubiness" to justify the $1000 price tag as opposed to say $300 in op amps?
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The ability to tube roll means it has significantly more options for adding euphonic distortion after-the-fact.
This youtube channel did a whole bunch of tube rolling videos with the Freya, so you can see how that goes:
No, but then that wasn't the only reason I bought the Freya +. As TheGhostofEugeneDebs points out, playing with euphonic distortion can be fun, (if not exactly profitable).
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VTV is offering an EVAL1-based amp for $959. I thought the whole idea of the EVAL1 board was for “evaluation” and not incorporation in commercially available products, but I could be wrong. In any event, the $959 price is about $400 less than what a person could DIY it for. This just took me out of the DIY market.
https://vtvamplifier.com/product/vtv-amplifier-purifi-eigentakt-stereo-amplifier-based-on-eval-1/
Other than the EMI/RFI filter on the power mains input and without a front illuminated power button (because the I2C connector is no longer present on the current EVAL1) it looks to be essentially the same as the test units Purifi sent out:
https://vtvamplifier.com/product/vtv-amplifier-purifi-eigentakt-stereo-amplifier-based-on-eval-1/
Other than the EMI/RFI filter on the power mains input and without a front illuminated power button (because the I2C connector is no longer present on the current EVAL1) it looks to be essentially the same as the test units Purifi sent out:
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Just ordered a Freya+.
