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

A.West

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I connected a 5 channel amp based on 2 NC502MP and one NC500MP units to my Marantz 6014 AVR pre-outs. I have no test instruments but my ears. I initially heard a volume-invariant hum, (used monoprice xlr to rca cables), and went away via the 99cent cheater plug, which i also put on a GFCI outlet to hopefully reduce risk. With the more powerful amp it still sounds great. I cannot do a blind test because connecting wires and re-running Audyssey is time consuming. I don't hear any spurious noise except walls shaking. It will play as loud as my speakers and ears can handle without sounding stressed, though i have not moved the volume to above about relative -5.
 

March Audio

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Which is why I was going to stay away from XLR Amps in the first place.
Wrong conclusion. You need to stay away from single ended components. This problem doesnt exist with just RCA to balanced (where you can solve it with the correct cable) it exists with RCA to RCA where you cant solve it.

It doesnt exist at all with balanced to balanced.
 
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boXem

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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?
You still have the issue of imbalanced impedance which I carefully omitted in my simplified explanation and will continue to carefully omit :facepalm:. It's well explained in the first document I linked. If TL;DNR, there will still be assymmetrical currents on the signal lines creating distortion.

The shield trick allows to keep most of these currents outside of the signal line.

So worth a try, mainly with an RCA to RCA connection where there is no way to deviate the pollution outside the signal lines.
 
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patoulol

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uh i am amazed to read this I thought it was recommended the association Denon et purifi ...
 

patoulol

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Hello ... I have a problem with a PUFIRI amp at home. So far I had not tried at home. But yesterday I plugged everything in and I have a ground loop ... I go through RCA - RCA

some are affected here?
 

boXem

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Hello ... I have a problem with a PUFIRI amp at home. So far I had not tried at home. But yesterday I plugged everything in and I have a ground loop ... I go through RCA - RCA

some are affected here?

There are no Purifi amps on the market, only amps with Purifi modules more or less well implemented. So, what is you amplifier?
 

TabCam

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Hello ... I have a problem with a PUFIRI amp at home. So far I had not tried at home. But yesterday I plugged everything in and I have a ground loop ... I go through RCA - RCA

some are affected here?
If I look at your pictures it is the AudioPhonics HPA-S400. I had a ground loop when I moved the Purifi amplifier to the attic but only with XLR adapters. The hum subsided to just ear-next-to-tweeter level as soon as I connected it with RCA. It also seems their grounding in their first (my) version could have be done neater. Yours looks at least better organized without any haphazard copper tape.
 
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patoulol

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an AudioPhonics HPA-S400. Yes.

I fixed the problem by plugging the computer into another electrical network. Without doing that I heard the hard drives in my speakers!
 

iraweiss

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I'm thinking on connecting a Hypex amp with balanced connectors to a new Yamaha receiver, also with a balanced connector for front channels. Should this work?
 

TabCam

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I'm thinking on connecting a Hypex amp with balanced connectors to a new Yamaha receiver, also with a balanced connector for front channels. Should this work?
Yes, but consumer electronics sometimes implement XLR differently, especially with signal ground. If you hear hum, unbalanced can be easier.
 

patoulol

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an AudioPhonics HPA-S400. Yes.

I fixed the problem by plugging the computer into another electrical network. Without doing that I heard the hard drives in my speakers!
The problem came back with ... my video projector plugged in. The ground loop has returned slightly.

Also after 11 days of testing, I haven't heard the slightest difference between the "Denon + purifi "versus the "Denon alone".

I returned the product to the seller.

This is valid in MY situation (no difference), in others person maybe a difference.
 

sg1838

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I have my Yamaha TSR-7850 hooked up to my VTV Stereo Purifi 1ET400A amp via these Monoprice 1.5' XLR to RCA cables (https://www.monoprice.com/product?p_id=4775), and for the most part it sounds great. When I first installed it I heard a lower-frequency "pop" when I switched inputs, but after talking with a bunch of people was told to not worry about it (so I didn't). However, now in the last couple of weeks, twice when I have powered the entire system up I have heard a higher frequency electrical "snap", and am wondering if it might be because of the Monoprice cables. I hear no ground loop hum or anything else out of the ordinary once the system is up and running.

My understanding is that VTV fixed the incorrect pin 1 wiring issue by the time I purchased my amp (a few months ago). I hate hearing my speakers (Tekton Lore Reference) creating that noise, as the only other time I heard it was with my old Paradigm Titans & Phantoms where the foam surrounds had rotted away and I turned up the volume. Any thoughts on whether the Monoprice cables might be causing this, or if I have something else going on? The only thing that has changed in my system is the addition of a new TP-Link 16 port Gigabit switch (which the receiver is connected to via a standard Ethernet cable), but I would find it hard to believe this has caused this issue, and if it did I would think it would happen more than once per week (the devices are plugged into the same wall outlet, but the AVR and amp are going through my Monster Power HTS 3600 MKII, whereas the switch is into a separate plug strip with a bunch of other "non-critical" home theater devices).

To me, it almost seems like a static buildup issue - once the charge gets high enough, it finally dissipates, which is now happening once per week. That's where I could see an incorrectly grounded cable or device causing this to happen. I have no idea what would be causing the static to be created though, particularly now in the summer months when it isn't as dry as it was a few months ago when I first set the system up.

Thoughts?
 

Gyroscopics

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I have my Yamaha TSR-7850 hooked up to my VTV Stereo Purifi 1ET400A amp via these Monoprice 1.5' XLR to RCA cables (https://www.monoprice.com/product?p_id=4775), and for the most part it sounds great.

I have a similar Monoprice RCA to XLR cable but I don't use it on my VTV Hypex amp. I never had issues with that cable and I have used it in many applications such as but not limited to: 1) Sonos Connect ==> JBL 306p MkII, 2) D50 ==> A23 power amp, etc.

I bought a pair of this Neutrik RCA to XLR adapter from Warren along with my mono-blocks. I tested these adapters on the VTV amp they worked flawlessly on my 2-ch setup. No hiss, no ground loop. I kept the adapters as alternative option for the amp if and when I decide to use it on my HT. At present I feed the VTV mono-blocks directly from my DAC via XLR cables.

What is the input sensitivity of Purifi 1ET400A? I searched but couldn't find that information on the Datasheet.

EDIT:
NVM I found the info at Nord website:
• Input Sensitivity 8ohm 2.52Vrms 10.24dBu
• 26.8 dB Gain
• Input Sensitivity 8ohm 2.52Vrm
 
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sg1838

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I was just looking for this myself. OK, now I'm about to show my ignorance. What does this matter?
 

Gyroscopics

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I was just looking for this myself. OK, now I'm about to show my ignorance. What does this matter?

It matters because AVRs have limited pre-out voltage and it varies by manufacturer and model. If the power-amp's input sensitivity is too high compared to the AVR's pre-out voltage, then you end up NOT being able to fully utilize the capability of the power amp in spite of how powerful that power-amp is on paper. In other words if the power-amp's input sensitivity is too high, the AVR would not be able to drive the power-amp to its full capacity without clipping the signal. The worst case is if the power amp's noise floor is higher than the AVR's nominal pre-out voltage, then you end up with a bad combo. I'm not saying that Hypex/Purify have high noise floor. I just cited that hypothetical scenario as an example.
 

sg1838

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The input sensitivity is determined by the input buffer. Each manufacturer using it's own buffer has a different sensitivity.

OK, so did I screw myself by going with the Sparkos Labs SS3602 input buffer?
 

restorer-john

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It matters because AVRs have limited pre-out voltage and it varies by manufacturer and model. If the power-amp's input sensitivity is too high compared to the AVR's pre-out voltage, then you end up NOT being able to fully utilize the capability of the power amp in spite of how powerful that power-amp is on paper. In other words if the power-amp's input sensitivity is too high, the AVR would not be able to drive the power-amp to its full capacity without clipping the signal. The worst case is if the power amp's noise floor is higher than the AVR's nominal pre-out voltage, then you end up with a bad combo. I'm not saying that Hypex/Purify have high noise floor. I just cited that hypothetical scenario as an example.

You have it mixed up.

A high sensitivity power amplifier means higher gain, hence less input voltage required to drive.

A low sensitivity amplifier means lower gain and more voltage needed to drive. Hypex/Purifi are low sensitivity/gain amplifiers, especially without a gain stage up front (buffer). Buffer implementations vary, but most tend to offer just enough gain to keep noise levels as low as they can for advertising purposes.

Typical HiFi power amplifiers have a around 29dB of gain with sensitivities of between 1-1.5V required for rated power output on single ended inputs.
 

Gyroscopics

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It matters because AVRs have limited pre-out voltage and it varies by manufacturer and model. If the power-amp's input sensitivity is too high compared to the AVR's pre-out voltage, then you end up NOT being able to fully utilize the capability of the power amp in spite of how powerful that power-amp is on paper.

You have it mixed up.

A high sensitivity power amplifier means higher gain, hence less input voltage required to drive.

A low sensitivity amplifier means lower gain and more voltage needed to drive.


I mentioned "input sensitivity" and you explained "sensitivity". Those are different.

The input sensitivity is calculated as below (for NC252MP as an example):



Screen Shot 2021-06-14 at 6.36.48 PM.png
 
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