P801 Power Amp

Alan March said:
@SmartOne_2000 I have very quickly thrown a P482 (Purifi 1ET6525SA) on the bench and performed some tests to demonstrate the things mentioned above. Our high power dummy load is being used on other work so with these tests I was limited to 10 watts, but this is well into the "hump" range shown in the plot you provided. It was quick and dirty so please dont take this as any difinitive indication of the amps performance.

So we have 5 FFT plots at 100Hz, 1kHz, 5kHz, 10kHz and 15kHz at 10 watts.

View attachment 220

1kHz
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5kHz
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10kHz
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15kHz
View attachment 219

Firstly, noise. You can see it has a small rise towards 45kHz, but is exceptionally low and remains constant regardless of the test signal frequency.

Secondly, the number of harmonics. As discussed, the number of harmonics included in the THD reduces as frequency increases.

Thirdly, harmonic amplitudes. Yes they increase with increasing frequency, but no where near as much as seen in the example you provided. The THD went from -125dB to -103dB.

So to conclude, yes the additional bandwidth of measuring to 48kHz has made the measurement indicate a rise in THD. However, this rise is misleading from a subjective point of view because the harmonics which cause the rise are well above the audible range. They are also still very low in level. They could never be heard. So again, limiting THD+N measurements to 20kHz is the correct thing to do.

Another thing to consider is that due to the spectral nature of music, i.e. there is very little content at high frequencies, you would never actually be making the amp produce 10 watts at 20kHz. Possibly 2 watts tops. Testing at 5 watts at 20kHz more than covers any real world situation.
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This is more than definitive proof Alan. Your modules are definitely designed differently! Thank you so much for making the time and effort to produce these read-them-and-weep graphs. Your are correct to state that limiting the bandwidth to 20kHz is best, not only because ultra-sonics are inaudible but the loudspeaker itself is also a huge low pass filter, starting to fall off at 10kHz and beyond, depending on the design of the speaker.

Pander to guess why so many other class D designs have the original hump? Its not the first time I've seen it, so I assumed it was normal behavior.
 
It will be a lot noisier. Basically OK fo the old 1ET400, but wont get the most out of the new 1et6525. Plus it only has gains suitable for 10 volt and 2 volt inputs. Nothing best suited for XLR 4 volt so sub optimal for noise again.

Not saying it is a problem in this implementation, but the LM4562 he uses can be sensitive to RF and cause lots of issues and spurious signals in the noise floor.
 
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He has RF filters on his inputs, if you look at the circuit topology tab. My main impression were the IMD and noise floor plots, which look impressive.
 
SmartOne_2000 said:
He has RF filters on his inputs, if you look at the circuit topology tab. My main impression were the IMD and noise floor plots, which look impressive.
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Yeah, not that simple depends on layout also. RF doesn't just come in through the signal cable. The buffer is sat in a hostile RF environment (smps and switching amp module).

I haven't seen any data, do you have a link?
 
Alan March said:
Yeah, not that simple depends on layout also. RF doesn't just come in through the signal cable. The buffer is sat in a hostile RF environment (smps and switching amp module).

I haven't seen any data, do you have a link?
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Just the "Specifications" and "Performance Graphs" tabs.

neurochrome.com

Universal Buffer

Fully differential buffer which provides a differential (balanced) and a single-ended (unbalanced) output with extremely low distortion. Great building block for a DIY preamp.
neurochrome.com neurochrome.com
 
SmartOne_2000 said:
Also, is a dual mono version P802 in the works? Maybe with two AC power inlets?
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No. As you allude to, the current requirements for the mains supply are beyond the capability of a single socket in 110v territories (circa 29 amps), and beyond or right at the limit in many other 230v territories. The much larger single case would probably be more expensive than two of the standard monoblock cases we use for multiple products. Performance would not be as good as the monoblock.

Its just not a worthwhile or practical proposition.
 
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SmartOne_2000 said:
Just the "Specifications" and "Performance Graphs" tabs.

neurochrome.com

Universal Buffer

Fully differential buffer which provides a differential (balanced) and a single-ended (unbalanced) output with extremely low distortion. Great building block for a DIY preamp.
neurochrome.com neurochrome.com
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Its not bad :). Still, no load was mentioned, probably open circuit improving performance. Remember a 9040 module input impedance is very low at 1.5k. The topology wont make the most of the 9040. Too noisy. Those plots dont inform you of the noise level due to FFT gain. You need a 20Hz to 20kHz overall measurement.
 
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Alan March said:
Its not bad :). Still, no load was mentioned, probably open circuit improving performance. Remember a 9040 module input impedance is very low at 1.5k. The topology wont make the most of the 9040. Too noisy. Those plots dont inform you of the noise level due to FFT gain. You need a 20Hz to 20kHz overall measurement.
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1737120520390.png

Yes, I guess you get best distortion specs at minimal output current draw? The 100K load is a far cry from the 1.5K load input impedance of the 9040 module.
 
SmartOne_2000 said:
View attachment 228

Yes, I guess you get best distortion specs at minimal output current draw? The 100K load is a far cry from the 1.5K load input impedance of the 9040 module.
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Well it's only the slew rate we have specified at 100k load. No idea what it is for the rest of the measurements. It is critical to know output voltage and load impedance when assessing distortion. Lower load (higher impedance) will be lower distortion.

Another thing to note us that gain is specefied as 0dB. What is the noise and distortion at the +8.6dB and 14.6dB gains required to drive a 9040 module to full power with a standard 4volt xlr and 2volt RCA source? Hint, it will be higher.

Noise at 2.1uV is too high. You need about 0.4uV to take full advantage of the 9040 ( not that anyone has acheived that).

So at+8.6dB gain probably more like 4uV.


Edit: just noticed the note at the bottom saying all measurements at 100k load. This is not representative of real world use with Purifi or Hypex amplifier modules which are all below 5k load. Distortion will be higher as a result.
 
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Alan March said:
Well it's only the slew rate we have specified at 100k load. No idea what it is for the rest of the measurements. It is critical to know output voltage and load impedance when assessing distortion. Lower load (higher impedance) will be lower distortion.

Another thing to note us that gain is specefied as 0dB. What is the noise and distortion at the +8.6dB and 14.6dB gains required to drive a 9040 module to full power with a standard 4volt xlr and 2volt RCA source? Hint, it will be higher.
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So true...thank you for highlighting these points.
 
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SmartOne_2000 said:
So true...thank for highlighting these points.
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And why just 2 volts output? Rather arbitrary. For a 9040 with the usual ASR testing at 5 watts, it needs 4.475v applied to the load. With 14.4dB gain from the 9040, this is an output of about 850mV from the buffer. This lower level will make noise performance far bigger contributing factor to THD+N (SINAD). SNR will be much lower than at 2 volts.

In the other direction, what's the distortion at 10.5 volts into a 1.5k load?

Really these numbers are all a bit meaningless unless you have numbers from another buffer to compare, or even more relevant, if you have the data for a full amp, I.e. it driving a 9040, 6525 etc.

Doing a few calcs I would estimate this buffer would be below 109dB THD+N (SINAD) at 5watts when used with a 9040 or 6525 module. OK for the older 1et400 module, but not these new higher performing variants.
 
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Looking casually at the LMExxxxx and OPA1612 opamps datasheets, they have their lowest distortion at 10 or more volts into a 2K load, just before clipping. These two opamps have fairly similar specs. Shouldn't they perform similarly in the new amps?
 
SmartOne_2000 said:
Looking casually at the LMExxxxx and OPA1612 opamps datasheets, they have their lowest distortion at 10 or more volts into a 2K load, just before clipping. These two opamps have fairly similar specs. Shouldn't they perform similarly in the new amps?
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The LM is a great part but has issues with RFI susceptibility. 1612 is lower noise and distortion. It's the topology, pcb layout and passive components that have to change to obtain the additional performance required for these new modules. Its not just about the op amp itself.

No I'm not going to go into further detail on how 😉.
 
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Alan March said:
The LM is a great part but has issues with RFI susceptibility. 1612 is lower noise and distortion. It's the topology, pcb layout and passive components that have to change to obtain the additional performance required for these new modules. Its not just about the op amp itself.

No I'm not going to go into further detail 😉.
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A conflict you might want to resolve... the gain selection silk screen on the back end (9040ba) says the two gain options are 20.5dB and 26.5dB. But the specs list the options as 23 dB and 29dB respectively? Which is correct? The other mono amps are within 0.5dB agreement between silk screen and listed specs (20.5dB vs 21dB and 26.5dB vs 27dB). I think that's ok. Can't speak for the rest of the amps.
 
SmartOne_2000 said:
A conflict you might want to resolve... the gain selection silk screen on the back end (9040ba) says the two gain options are 20.5dB and 26.5dB. But the specs list the options as 23 dB and 29dB respectively? Which is correct? The other mono amps are within 0.5dB agreement between silk screen and listed specs (20.5dB vs 21dB and 26.5dB vs 27dB). I think that's ok. Can't speak for the rest of the amps.
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That's actually an old picture. It will be updated at some point. All current amps just have "low" and "high" marked on the gain switch.
 
@james dyson I'm sorry but I have to ask, are you the same "james dyson" who was just banned from ASR, moderators & members bizarrely thinking you were Alan for some strange reason?
 
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