New P482 Stereo Power Amplifier

james dyson said:
Hey Alan
On ASR there was a question regarding the validity of your corrected SINAD figure. The poster said it wasn't valid because the noise floor increases with increasing power output. Therefore just taking the shorted input noise figure doesn't account for the increased noise at higher power output. Whats your response to that?
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Hi @james dyson

Thanks for your question. If I understand the question correctly, the poster makes a valid point. An amplifiers noise floor does indeed increase at higher output levels compared to low or no signal output.

However, at the test point in question that of ASRs favourite 5 watts into 4 ohms :) , the noise increase on the P482 is barely visible. We are talking 0.1 to 0.2 dB. This is easily in the area of measurement repeatability/error.

So at this test point, it is a far more accurate method to measure THD+N than not taking the signal generator inherent noise into account (circa 3dB error).

If I get time I will publish some measurements of how the noise floor changes with output level.

Hope that helps.

Alan
 
I received the New P482 Stereo Power Amplifier
And It works awesome.

Without any colouration, quiet, and It played The assault/entering sequence at the beginning of the movie Sicario (2015) silky smooth. Which has rush of low frequencies and high dynamic range quite challenging to drive.

It may take some time, but I'll post the objective review after I do some test including really interesting measurements. I'm very excited to be able to use the newest Purifi amplifier on the market so quickly.
 
Alan March said:
Hi @james dyson

Thanks for your question. If I understand the question correctly, the poster makes a valid point. An amplifiers noise floor does indeed increase at higher output levels compared to low or no signal output.

However, at the test point in question that of ASRs favourite 5 watts into 4 ohms :) , the noise increase on the P482 is barely visible. We are talking 0.1 to 0.2 dB. This is easily in the area of measurement repeatability/error.

So at this test point, it is a far more accurate method to measure THD+N than not taking the signal generator inherent noise into account (circa 3dB error).

If I get time I will publish some measurements of how the noise floor changes with output level.

Hope that helps.

Alan
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Hey Alan,

I was wondering if you have had some free time to publish some of those measurements of how the P482's noise floor changes with the output level?

It would be really great to see whilst I await delivery :)
 
Alan March said:
Hi @james dyson

Thanks for your question. If I understand the question correctly, the poster makes a valid point. An amplifiers noise floor does indeed increase at higher output levels compared to low or no signal output.

However, at the test point in question that of ASRs favourite 5 watts into 4 ohms :) , the noise increase on the P482 is barely visible. We are talking 0.1 to 0.2 dB. This is easily in the area of measurement repeatability/error.

So at this test point, it is a far more accurate method to measure THD+N than not taking the signal generator inherent noise into account (circa 3dB error).

If I get time I will publish some measurements of how the noise floor changes with output level.

Hope that helps.

Alan
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Hey @Alan March

I'm curious to see those measurements of how the noise floor changes with the output level on the P482, you had mentioned it about a month or so ago :)
 
Hey @Alan March

I was wondering if you would know the reason as to why Purifi has released a revision to the 1ET6525SA module, there is the 1ET6525SA01B & 1ET6525SA01C, seems strange to implement some component changes upon release, the 1ET6525SA01B is pictured in Purifi's 1ET6525SA datasheet below,
Purifi 1ET6525SA01B.png

I believe you have the 1ET6525SA01C which I assume is the latest revision of the module on your P482, P282, P481 product pages as pictured below,
Purifi 1ET6525SA01C.png
 
@Alan March A P482 customer recently posted over at StereoNet the following,

"Received a P482 today from March. 8hrs into things and I like what I'm hearing. Using a Supratek Cab 6SN7 pre with Harbeth SHL5 30th Annaversary's.

Great impact, good bass resolve, clean mids, highs are just a tad soft compared to Krell class A but nothing interconnects can't address and who knows how thing pan out 100hrs further down the road. It has nice textures and an ear to ear 180deg stage that images beautifully. It's front to back placement of vocals in my book are bang on! Job very well done March.

These things draw very little at idle so while its in the system it's staying on."

The same P482 customer from another post "I have the P482 and can vouch its a good little amp. I bought one as a summer amp instead of running class A which is now reserved for winter.

Was it worth their asking price, yes. I have absolutely no issue with its highs. Man, its quiet, quietest amp I've heard

For me it doesnt have the last bit of resolve in its stage.. it doesn't have the depth of a Krell KSA150 which was 3x the P482s price ($10k) in the 1980s.. bit unfair.

I'm driving the P482 with 6SN7 tubes... it does a pretty good job."

I was just curious how can interconnects improve the clarity in the treble region? I have no complaints really with the P482's "sound signature", I thought the whole point of Purifi was to be fairly neutral & not colour the sound in any particular way?

I haven't had any issues with my P482 & P481 amps except for the one time when I hooked up my P482 & it exhibited an extremely loud thump upon powering on when I first received it, it wasn't a very nice Christmas day surprise, I thought it had done damage to my Klipsch RF-7 IIIs' Compression Drivers but thankfully that doesn't appear to be the case.
 
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If interconnect cables are significantly changing the sound then they will have "unusual" technical parameters. Most of the time its simply expectation bias when people are hearing more than the most subtle of differences.

I would suggest the most likely culprit for highs sounding soft will be the Harbeths. They have a slightly low HF response. It doesnt look like a lot but spread over that wide range it has an impact. Especially with that bass boost.

1749119558303.png

Also, the tube pre may well be impacting the sound.

We have a lot of customers that have dumped their uber expensive class A behemoth amps for our amps and not missed the former one bit.
 
@Alan March Hi Alan, I came across this BobWire XLR1 automatic XLR Balanced selector/switcher product https://www.bobwireaudio.com/xlr1, it was reviewed favourably over at ASR & was wondering if you're familiar with such a product?
BobWire XLR1.png

I was thinking of utilising it in between my Denon X8500H AVR & P482 amp, it helps get around the inherent limitations when going with RCA to XLR adapter cables concerning the 6dB loss with Single Ended RCA outputs to XLR inputs.

The BobWire manufacturer (who is a former senior engineer for Parasound) had this to say about the ineffectiveness of RCA to XLR adapter cables,

"An RCA to XLR cable (adapter) will only be using a single "leg"(signal) of the balanced XLR cable. The XLR cable is intended to carry 2 "legs"(signals), each out of phase from each other. The use of 2 out of phase audio signals allows the noise picked up along the cable to be removed(rejected) at the end, inside the amplifier. This is called CMR (common mode rejection) and is the primary reason XLR/balanced connections are used.

If you used the RCA to XLR cable it would produce sound but you would be throwing away any advantage of a balanced cable. The BobWire XLR1 will take the RCA signal and convert it to balanced, using active phase inverters. This means the output of the XLR1 will be fully balanced and you can enjoy the advantage this brings as the signal travels to you amplifier.

The 2nd reason is just as drodgers suggests, you will not get the 6dB of gain that the balanced XLR connection provides. This means, if you are using an RCA to XLR cable, the audio level would drop 6dB when you try and listen to the source with othe RCA outputs.

As you mention, Amir found the SINAD was higher using the RCA input. This would be expected because the RCA input is going through the phase inverts to produce the true balanced signal. What you perhaps are not taking into account, is that if you use RCA to XLR cable, your amp is only "seeing" half the balanced signal. This totally removes the advantages of the balanced inputs on your amp. You will also need to turn your preamp/source up more to compensate for the 6dB lower signal(adding to the SINAD). So there is a give an take here but I believe the end result will be better using the phase inverters of the XLR1 rather than a RCA to XLR cable."
 
Sorry but this is pointless in the context of use with our amplifiers. You are still converting single ended to balanced, as we do if the input is single ended into our amps. Our buffer already has gain selections suitable for RCA.

It doesnt solve the fundamental limitations of RCA sources any more than using the amps input directly. It just adds another amplifier stage which I can guarantee will add more noise and distortion than our input buffer.
 
Oniiz86 said:
The BobWire XLR1 will take the RCA signal and convert it to balanced, using active phase inverters. This means the output of the XLR1 will be fully balanced and you can enjoy the advantage this brings as the signal travels to you amplifier.
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Thanks for that Alan, so what I've quoted above is moot & will not make a lick of difference, I was particularly interested in the use of "active phase inverters"?
 
Oniiz86 said:
Thanks for that Alan, so what I've quoted above is moot & will not make a lick of difference, I was particularly interested in the use of "active phase inverters"?
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"Active phase inverters" is just a fancy marketing term to let you know that they take a single-ended (single-phase) RCA signal and convert it to a differential signal (two phases, 180 degrees out of phase with each other). The "active" part means they use chips or transistors in their circuitry, as opposed to passive converters that use transformers to perform the same task.

As Alan said, going through another (very unnecessary) active stage is going to add more noise and distortion to the signal path into your amp. He already does this task you are concerned about inside his amps. In short, what this box supposedly does is already done in his amplifiers, making this box moot. Hope that makes it clear.
 
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