Good Class D amps ??

[mocenigo]

27 minutes ago, Ralf11 said:

my point (as crazy-audiophiliac as it sounds) is that if burn-in exists for a Class D design, maybe - just maybe - a purely resistive load will not accomplish burn-in

 

Uh, why? It just has to run.

[Ralf11]

if it just had to run you would need resistors either

 

 

 

[audio.bill]

At least having a simple resistive load allows output current to flow, which operating with no speaker connection does not permit.

 

[Ralf11]

sure, but is it enough?

 

what would a true audiophile do?

[audio.bill]

48 minutes ago, Ralf11 said:

sure, but is it enough?

 

what would a true audiophile do?

Buy a pure Class A amp! 

[AudioDoctor]

We need GUTB to answer this for us...

[Matias]

March Audio just introduced their NC1200 based monos for $1,395 usd each. Great price for the nCore flagship!

https://www.marchaudio.net.au/product-page/p701-flagship-mono-block-power-amplifier

 

[firedog]

Burn in- I think if you just play them continuously, and put them at very low volume when no actually listening. Easiest, fastest way to get there. 

[firedog]

1 hour ago, Matias said:

March Audio just introduced their NC1200 based monos for $1,395 usd each. Great price for the nCore flagship!

https://www.marchaudio.net.au/product-page/p701-flagship-mono-block-power-amplifier

 

Looks interesting, but the site doesn't give much info. What's the input section and the PS? I'm assuming standard NCore, but it would be good to know. What's the layout look like inside?That picture of the layout isn't the most helpful in seeing how the cables are setup, etc. 
Just having the 1200 board doesn't mean it is necessarily better than a really well done NC500 unit. 

[mocenigo]

On 6/17/2019 at 4:06 PM, Matias said:

March Audio just introduced their NC1200 based monos for $1,395 usd each. Great price for the nCore flagship!

https://www.marchaudio.net.au/product-page/p701-flagship-mono-block-power-amplifier

 

 

For that price I doubt they bypassed the integrated opamp based buffer with a better one, not to speak provided separated power supplies for opamp and comparator. 

 

 Roberto 

[Matias]

No, it uses the standard opamps and regulators that Hypex provides.

 

More info and pics here

 

https://www.audiosciencereview.com/forum/index.php?threads/march-audio-p701-mono-block-power-amp.6862/post-185443

[Matias]

For what I can see the March Audio P701 ($1.9k full price) is pretty similar to the Mola Mola Kaluga ($16k). The former has the standby auxiliary power supply attached to the main SMSP heatsink, while the latter has it in the front of the chassis. 

 

 

 

Nord's NC1200 mono (£ 2k) uses the same large pro opamp options as their NC500 based offerings: Sonic Imagery and Sparkos.

 

 

While Apollon's new NC1200 based monos (€ 1.75k ?) use fancier Weiss OP2-BP op amps for the input buffer and a linear power supply for the input buffer stage and modulator stage.

 

 

[Matias]

Plus the ICEpower 1200AS is also competitive. And my bet is that Purifi will announce a 1200W module soon enough. Market is on fire. 🔥

[Matias]

Kaluga is $8k each btw, no edit button.

[March Audio]

On 6/19/2019 at 1:34 PM, mocenigo said:

 

For that price I doubt they bypassed the integrated opamp based buffer with a better one, not to speak provided separated power supplies for opamp and comparator. 

 

 Roberto 

 

Just stumbled across this.

 

When you say "better" what do you mean or like to see?  The LM4652 is an exceptionally good buffer.  If you feel that a component with 0.00003% THD + Noise (-130dB), IMD of 0.00005%, voltage noise density of 2.7nV etc is somehow lacking, then you need to explain why.

 

http://www.ti.com/lit/ds/symlink/lm4562.pdf

 

My advice would be to always ask for the measurements of alternative buffer options to check how they actually perform in comparison - and at the output voltage they will be used at not excessively high output levels.  Its all well and good saying you have put in a fancy discrete op amp or whatever, but that in itself counts for little.  Some are good, some are absolute dogs.

 

The buffer and modulator are supplied from a separate PSU output from the main amp and drive circuit.  This is regulated by the very low noise HNR12 units.   Note the HF performance.

 

 

Hope that helps

 

 

[opus101]

20 minutes ago, March Audio said:

 

When you say "better" what do you mean or like to see?  The LM4652 is an exceptionally good buffer.  If you feel that a component with 0.00003% THD + Noise (-130dB), IMD of 0.00005%, voltage noise density of 2.7nV etc is somehow lacking, then you need to explain why.

 

 

Of course the measurements of the LM4562 aren't in doubt, what makes it a questionable choice subjectively for an input stage is its susceptibility to RF. Check out the thread(s) on DIYA where the device is shown to rectify DECT (home portable phone) transmissions.

[March Audio]

10 minutes ago, opus101 said:

 

Of course the measurements of the LM4562 aren't in doubt, what makes it a questionable choice subjectively for an input stage is its susceptibility to RF. Check out the thread(s) on DIYA where the device is shown to rectify DECT (home portable phone) transmissions.

 

Any amp should have an input RF filter which makes the point moot.  Mine do.  Unless you choose an opamp that has built in input RF filtering (a few do) then it will always be a requirement.

 

Designs that are DC to daylight are not a good idea.

 

Also, if we are talking subjectively, the evidence needs to be better than just "I think it sounds better".  Unsighted and controlled is an absolute requirement.

[opus101]

10 minutes ago, March Audio said:

 

Any amp should have an input RF filter which makes the point moot.  Mine do.

 

The point is only moot if the FR of the RF filter demonstrates the received energy is truly negligible at the frequency of interest. Do you have the measured FR of your filter up to (say) 2.5GHz ?

[March Audio]

 

Not measured to 2 Ghz but SPICE shows the following.

 

 

If someones design of amp is showing susceptibility to DECT signals which are limited to 10mWatts RF output from the handsets, then they need to take a second look at what they are doing.  So frankly, even taking into account that the real world performance wont be as good as the model, I have zero concerns about DECT signals.

 

 

[opus101]

10 minutes ago, March Audio said:

 

Not measured to 2 Ghz but SPICE shows the following.

 

 

If you're wanting to rely on SPICE rather than measurements then you'll need to show the circuit you modelled to be at all convincing. What parasitics did you take into account? How did your model account for the particular layout config on your PCB?

[March Audio]

49 minutes ago, opus101 said:

 

If you're wanting to rely on SPICE rather than measurements then you'll need to show the circuit you modelled to be at all convincing. What parasitics did you take into account? How did your model account for the particular layout config on your PCB?

Im not relying on it, it was a quick example to hand.

 

One far more convincing real world test was to use a mobile phone near the amp.  No DC offset or measured spuria on its output was seen. No audible consequences were heard. Far more challenging than a DECT phone. The RF levels could be a watt or more (yes it was tested in a poor reception area).

 

BTW I have access to a Keysight Fieldfox and other spec ans, but not right at the moment.

 

I havent seen the thread you refer to but seriously, an amp getting upset by no more than 10 mW of RF from a dect handset?  As I said, they need to take a look at what they are doing with the design.

 

Basically your point is totally unconvincing.  *ANY* non RF hardened op amp can suffer from problems with RF and I have taken measures to minimise the potential for problems. A good question for other vendors perhaps?

[opus101]

Just now, March Audio said:

I havent seen the thread you refer to but seriously, an amp getting upset by no more than 10 mW of RF from a dect handset?  As I said, they need to take a look at what they are doing with the design.

 

Basically your point is unconvincing.  Any non RF hardened op amp can suffer from problems with RF and I have taken measures to minimise the potential for problems. A good question for other vendors perhaps?

 

If you're at all curious then you'll go look at the thread (I think there's more than one where this particular issue comes up) and no, its not an 'amp getting upset by no more than 10mW'. That's just caricaturing - I am fairly sure some those involved (Pavel Macura was one I remember) were already more knowledgeable than you, but happy to be shown to be wrong.

 

I wasn't intending to convince you, hopefully potential customers will be educated to ask more pertinent questions when they're presented with graphs and numbers set out to dazzle.

[March Audio]

11 minutes ago, opus101 said:

 

If you're at all curious then you'll go look at the thread (I think there's more than one where this particular issue comes up) and no, its not an 'amp getting upset by no more than 10mW'. That's just caricaturing - I am fairly sure some those involved (Pavel Macura was one I remember) were already more knowledgeable than you, but happy to be shown to be wrong.

 

I wasn't intending to convince you, hopefully potential customers will be educated to ask more pertinent questions when they're presented with graphs and numbers set out to dazzle.

Caricaturing?

 

More like characterising.

 

How much RF does a DECT phone put out - Tiny.  10mW max.

 

How much does that small field strength reduce with distance? - Significantly.

 

Why didnt a simple and standard RF input filter stop the alleged issue (whatever it was)? - No idea.

 

Just take a look through some op amp datasheets and you will find recommended designs for RF filters from the people who designed the devices.  This really isnt unknown territory.

 

I fully encourage people to ask pertinent questions.  Its precisely why I pointed out the technical performance of the buffer and power supplies above.  It was to challenge the assumption that what was there was somehow inadequate, or that an alternative will always be better.

[opus101]

1 minute ago, March Audio said:

 

How much RF does a DECT phone put out - Tiny.  10mW max.

 

Quite. So the fact that the DECT 'signature' was visible at the output is itself quite remarkable. How could an opamp be designed to be so incredibly sensitive to such low levels of RF? Inquiring minds want to know.

[March Audio]

1 minute ago, opus101 said:

 

Quite. So the fact that the DECT 'signature' was visible at the output is itself quite remarkable. How could an opamp be designed to be so incredibly sensitive to such low levels of RF? Inquiring minds want to know.

 

Considering it is not a problem I have seen with this op amp, even with specific RF testing, then my conclusion is that it isnt sensitive to RF in the way you are claiming when normal design considerations are made.