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Any issues when pairing Purifi or Hypex class D amps with home cinema AVR?

ririt

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#1
I have asked to Amir what would be the ending SINAD when pairing the new Denon 3700H with a purifi amp.
Please find below its disappointing answer:
Well, I tried to test this scenario but failed completely. :(
Hooking up the output of 3700 to Purifi using RCA to XLR adapter generated worse results than the internal amps! Some of this I traced to increased ground loop. But even when I filtered this out, the Purifi still performed worse.
I then tested the Purifi using my Audio Precision unbalanced (RCA) outputs. To my surprise, its performance was worse than it was with balanced input. It was still much better than what I could do with 3700H though.
After an hour of messing with it, I gave up. It is possible there is ultrasonic noise from the 3700H DAC that is disturbing the Purifi amplifier (wild guess).
In abstract, you need to have the amp be 10 dB better to have it almost be transparent (0.5 dB loss in SINAD). In your scenario we don't have that so the SINAD will drop to around 96 to 97 dB (my guess).

Since I am envisaging such set-up, I would like to know if anyone has already successfully associated an AVR (especially a Denon) with either hypex-based or purifi amps?
I am looking forward reading your feedbacks!
 
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#2
Personnaly, it's a big mistake to mix high fedifity, "audiophylitic" or "multi-channel" home cinema. When some people think a new theater cinema have the new equiment avaible a the moment. You think is "realtity"?!. I'm also sure many people in the world and or this forum has some particular configuration of audio engine's at the moment is superior to "the commun audio feature". In some years, new technologies, class D or something else have great "avenir" but with the "great" mondialisation of electronic's part and assembly, we have to test and confirm ?!
 
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#3
I have asked to Amir what would be the ending SINAD when pairing the new Denon 3700H with a purifi amp.
Please find below its disappointing answer:
Well, I tried to test this scenario but failed completely. :(
Hooking up the output of 3700 to Purifi using RCA to XLR adapter generated worse results than the internal amps! Some of this I traced to increased ground loop. But even when I filtered this out, the Purifi still performed worse.
I then tested the Purifi using my Audio Precision unbalanced (RCA) outputs. To my surprise, its performance was worse than it was with balanced input. It was still much better than what I could do with 3700H though.
After an hour of messing with it, I gave up. It is possible there is ultrasonic noise from the 3700H DAC that is disturbing the Purifi amplifier (wild guess).
In abstract, you need to have the amp be 10 dB better to have it almost be transparent (0.5 dB loss in SINAD). In your scenario we don't have that so the SINAD will drop to around 96 to 97 dB (my guess).

Since I am envisaging such set-up, I would like to know if anyone has already successfully associated an AVR (especially a Denon) with either hypex-based or purifi amps?
I am looking forward reading your feedbacks!
I’m surprised to read that. I had a ground loop issue when I hooked up my Marantz 6012 to a balanced class A amp (BAT VK500) via RCA to XLR cables. Now I have the Marantz AVR feeding a Benchmark DAC3 via its unbalanced input. The Benchmark is hooked up to NC1200 monoblocks (March Audio P701) via XLRs. No ground loop issues.

For me, home theater is less about critical listening and more about explosions. When I want to listen to music only, I have Roon software from a PC feeding the Benchmark via USB, and the Marantz AVR is off.
 

Fred Jacquot

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#4
It would be interesting to know how @amirm's RCA to XLR adapter is cabled.
Many of these adapters leave the shield open on RCA side, opening at the same time the door to ground loops.
 

CDMC

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#5
It would be interesting to know how @amirm's RCA to XLR adapter is cabled.
Many of these adapters leave the shield open on RCA side, opening at the same time the door to ground loops.
When I bought mine, the only two companies I could identify that definitely did it correctly were Benchmark and March Audio.
 
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#6
I have an Arcam AVR550 with an AudioPhonics HPA-S400ET with no problems. In stereo I play with a Chord Hugo and in HT with the Arcam. Arcam output is less detailed but it works for HT, as I am probably less critical but still like good (enough) sound with series and movies.
 
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ririt

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Thread Starter #7
It would be interesting to know how @amirm's RCA to XLR adapter is cabled.
Many of these adapters leave the shield open on RCA side, opening at the same time the door to ground loops.
Thanks for your first feedbacks. Meanwhile, I have been in touch through email with Alan from March Audio. He raised the same point as Fred Jacquot and CDMC: the issue should be related to the RCA to XLR connector.
this will definitively be a point of attention in my future system. Tabcam, which cable are you using to connect your Arcam AVR with the Purifi amp?
 

Vasr

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#8
Don't input filters on reputable brand Class D amps solve this problem? At least for the UHF noise. Ground loop hum in the audible range can be a cabling solution.
 
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#9
It is possible that Amir used the Purifi evaluation kit. That one has no protection for UHF as far as I know.

I use both a normal RCA cable and an el cheapo "pro audio" RCA->XLR cable. Both seem to be functioning fine, but I did not measure it. At least no ground loops, no humming, no noise from tweeters, even up close.

I recently switched to a Swissonic ADC for convenience reasons as that allows me to use the Chord Hugo to switch between inputs. I probably loose quality for HT but stereo is most important, as well as convenience.
 

Grandzoltar

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#10
What about unbalanced to balanced converters. Which could increase 4 dbu to 26 dbu. Rdl ez-afc2, Art cleanbox pro
 
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#11
Would rather buy an input buffer which does have that functionality. I just used it to connect two unbalanced devices.
 
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#12
Personnaly, it's a big mistake to mix high fedifity, "audiophylitic" or "multi-channel" home cinema. When some people think a new theater cinema have the new equiment avaible a the moment. You think is "realtity"?!. I'm also sure many people in the world and or this forum has some particular configuration of audio engine's at the moment is superior to "the commun audio feature". In some years, new technologies, class D or something else have great "avenir" but with the "great" mondialisation of electronic's part and assembly, we have to test and confirm ?!
Is... is this a bot-generated comment?
 

Fred Jacquot

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#13
When I bought mine, the only two companies I could identify that definitely did it correctly were Benchmark and March Audio.
Thanks for your first feedbacks. Meanwhile, I have been in touch through email with Alan from March Audio. He raised the same point as Fred Jacquot and CDMC: the issue should be related to the RCA to XLR connector.
this will definitively be a point of attention in my future system. Tabcam, which cable are you using to connect your Arcam AVR with the Purifi amp?
If you look at pro audio stuff, they usually do this correctly, at a reasonable price.
Some properly wired RCA to XLR cables
Some others
 

March Audio

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#14
I have had a few emails and questions regarding this result today :)

Some general comments, you shouldnt use a RCA to XLR adaptor like this.

1596532271877.png


Any noise currents flowing in the RCA screen will be seen by the amp. This is why we dont fit RCA inputs on our amps. You have to use a cable wired as below.

1596532720106.png

Fig 3 from Hypex guidence notes

With this configuration the XLR screen is terminated at the far RCA source end. Noise currents flow in the shield wire and not the signal conductors eliminating ground loop based noise issues. Our RCA to XLR cables are configured this way as are the aforementioned Benchmark ones.

Secondly it should be noted the Hypex/Purifi speaker outputs are ground referenced. As such from a measurement perspective it is possible to get noise problems and the AP balanced input should have the same cable config as shown above to again make sure ground currents flow in the shield and not the signal conductors. Using the single ended input could also lead to noise issues for the same ground loop issues.

We often use (as do our customers) RCA single ended sources with our Hypex and Purifi amps and dont hear or measure any noise issues.
.
 
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March Audio

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#15
Don't input filters on reputable brand Class D amps solve this problem? At least for the UHF noise. Ground loop hum in the audible range can be a cabling solution.
RF getting into an amp (any amp not just class d) can cause issues, demodulation or dc offsets. There is a specific further potential issue (unlikely but possible) with class d where RF noise (external or from say a dac) can intermodulate with the switching signal and create in band noise. So any amp should have an appropriate input filter. AFAIK we are the only one of the oem Hypex/Purifi manufacturers that pays attention to this and fit a filter at the xlr socket.
 
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#16
Is... is this a bot-generated comment?
No, I'm a "real" live person. Perharps Artificial Intelligence can at the moment say "some ironic" comments but a true one comment from "me" !?
 

Fred Jacquot

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#18
I would say just the opposite.
Yes, it can be a bit counter-intuitive.

When we connect two parts together (a DAC/preamp and an amplifier in example), each of them has a reference potential (ground) at a different level. Connecting them will create current flowing between the two grounds. Since there is not a lot we can do against this, the game is to keep these current outside of the signal path.

On an XLR to XLR connection, the shield is connected to pins 1 on each side, themselves connected to the ground of each side, ground currents are flowing through the shield, signal is carried through pins 2 and 3, end of the story.

In an RCA connection, there is one wire and one shield. Physics being physics, a voltage is a difference of potential between two points. If one wants to carry a signal using voltage, he needs two wires. In the case of the RCA, these are the wire and the shield.
In the case of the XLR, we use pins 2 and 3 to carry the signal.
So for carrying signal from RCA to XLR, we connect RCA wire to XLR pin 2, RCA shield to XLR pin 3.
All this would be perfect if the RCA shield was not also connected to the ground. If we keep the connection like this, ground currents will search for a path, and the only one they will find is through XLR pin 3, i.e. a signal pin. Then the signal is corrupted.
To avoid this, we need to find another path for the ground currents. Since pin 3 has a high input impedance to ground, if we connect the cable shield to the RCA shield, the huge majority of ground current will flow through the shield instead of pin 3. Problem is not completely solved, but seriously minimized.

I frankly oversimplified the thing, master Bruno P. explains it much better than I do here and here but he needs lots of pages to do it :).
 
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Vasr

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#20
All this would be perfect if the RCA shield was not also connected to the ground. .
Some receivers and pre-amps provide a switch to "lift the ground" (disconnect from power ground) for RCA outputs or make it the default. Wouldn't this solve the problem?
 
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