• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Bruno Strikes Again. Purifi 1ET7040SA VTV Amplifier.

kchap

Addicted to Fun and Learning
Forum Donor
Joined
Jun 10, 2021
Messages
579
Likes
566
Location
Melbourne, Oz
After going through this thread, I have a couple of questions:

1. Does the higher current and possibly damping factor only benefit certain speakers and not all speakers? From what little I've read on it, damping factor helps with the amp's "grip" on the speakers, to better control the drivers. And as for current, certain speakers like Maggies seem to thrive on higher current amps, right? But would there be a general, across the board benefit for all speakers? Trying to determine if the differences between the original and new, more powerful Purifi would be worth the move to the newer modules. I have a pair of original purifi module based monoblocks. From what boXem | audio posted earlier, it would seem that only after going lower than 3ohms would there be a benefit.
I don't why but your comments put the following thought in my head: Assuming a voice coil has a resistance of 1Ω what is the point of a amplifier impedance < 0.1Ω?
 

dlaloum

Major Contributor
Joined
Oct 4, 2021
Messages
3,092
Likes
2,353
After going through this thread, I have a couple of questions:

1. Does the higher current and possibly damping factor only benefit certain speakers and not all speakers? From what little I've read on it, damping factor helps with the amp's "grip" on the speakers, to better control the drivers. And as for current, certain speakers like Maggies seem to thrive on higher current amps, right? But would there be a general, across the board benefit for all speakers? Trying to determine if the differences between the original and new, more powerful Purifi would be worth the move to the newer modules. I have a pair of original purifi module based monoblocks. From what boXem | audio posted earlier, it would seem that only after going lower than 3ohms would there be a benefit.

@Stephen Bayley & others:
2. For those who have the March P501 or P421 (formerly P451 monoblocks, what is the difference you notice with the front power switch vs the original used on P451? It's supposedly not as finicky on the P501/P421?
Yes - an amp with high current capability is only required when you have speakers with low impedance...

Having the additional current capability does no "harm" - but does increase the cost of the amp substantially in many cases... (some Class D designs are the exception).
 
Joined
Jun 17, 2019
Messages
29
Likes
57
Location
Melbourne, Australia
After going through this thread, I have a couple of questions:

1. Does the higher current and possibly damping factor only benefit certain speakers and not all speakers? From what little I've read on it, damping factor helps with the amp's "grip" on the speakers, to better control the drivers. And as for current, certain speakers like Maggies seem to thrive on higher current amps, right? But would there be a general, across the board benefit for all speakers? Trying to determine if the differences between the original and new, more powerful Purifi would be worth the move to the newer modules. I have a pair of original purifi module based monoblocks. From what boXem | audio posted earlier, it would seem that only after going lower than 3ohms would there be a benefit.

@Stephen Bayley & others:
2. For those who have the March P501 or P421 (formerly P451 monoblocks, what is the difference you notice with the front power switch vs the original used on P451? It's supposedly not as finicky on the P501/P421?
The front power switch on the P501 operates as expected, fast and confident action and no finicky operation experienced in the last two weeks.
 

RustyGates

Active Member
Joined
Mar 25, 2019
Messages
116
Likes
85
Location
Melbourne, Australia
1ET400A:
1653639322822.png


1ET7040SA:
1653639364412.png


Both deliver just over 100W@8Ohm, 250W@4Ohm and about 350W-400W@2ohm before they lose their cool, with the 1ET400A measuring slightly better...

The 7040 really should be pulling those numbers up... the only thing it has over the 400 is a higher total current capacity at the cost of measurements; by the time you get to use that additional current on the 7040, SINAD takes a massive plunge.
 

darkless

Member
Joined
Feb 17, 2020
Messages
13
Likes
6
Location
Denmark
Agreed, you only get an additional +3 dB of headroom on a 2 Ohm setup for (almost) the same SINAD.
 

boXem

Major Contributor
Audio Company
Joined
Jun 19, 2019
Messages
2,014
Likes
4,852
Location
Europe
1ET400A:
View attachment 209208

1ET7040SA:
View attachment 209209

Both deliver just over 100W@8Ohm, 250W@4Ohm and about 350W-400W@2ohm before they lose their cool, with the 1ET400A measuring slightly better...

The 7040 really should be pulling those numbers up... the only thing it has over the 400 is a higher total current capacity at the cost of measurements; by the time you get to use that additional current on the 7040, SINAD takes a massive plunge.
7040 gives you -100 dB SINAD for 600W in 2 Ohms. At 700W it is still better than 16 bits resolution. It starts clipping at 750W but I bet you do not yet hear it clipping at 1000 W (-40 dB = 1%)
Compared to a 1ET400A, it doesn't bring a lot for loads impedance staying above 3.3 Ohm, this is true. But below this, it is a completely different animal.
Acording to Purifi, the slight performance degradation is due to the bigger FETs that are quite tricky to drive.
 

dlaloum

Major Contributor
Joined
Oct 4, 2021
Messages
3,092
Likes
2,353
1ET400A:
View attachment 209208

1ET7040SA:
View attachment 209209

Both deliver just over 100W@8Ohm, 250W@4Ohm and about 350W-400W@2ohm before they lose their cool, with the 1ET400A measuring slightly better...

The 7040 really should be pulling those numbers up... the only thing it has over the 400 is a higher total current capacity at the cost of measurements; by the time you get to use that additional current on the 7040, SINAD takes a massive plunge.
Do we know how these were measured? Continuous? Peak?

The power is very good for both, even at 2ohm - but that may reflect a peak measurement which is dependent only on the capacitors, and not the full power supply...

Still this indicates that either should handle low impedance speakers without too much trouble.

It would be of value knowing the time constraints around these measures though.
 

RustyGates

Active Member
Joined
Mar 25, 2019
Messages
116
Likes
85
Location
Melbourne, Australia
7040 gives you -100 dB SINAD for 600W in 2 Ohms. At 700W it is still better than 16 bits resolution. It starts clipping at 750W but I bet you do not yet hear it clipping at 1000 W (-40 dB = 1%)
Compared to a 1ET400A, it doesn't bring a lot for loads impedance staying above 3.3 Ohm, this is true. But below this, it is a completely different animal.
Acording to Purifi, the slight performance degradation is due to the bigger FETs that are quite tricky to drive.

So, I intend to get the KEF Reference 1 Meta at release and looking into the Purifi monoblock amps. Would the 1ET400A suffice given the Ref 1 meta is 4Ohm nominal and dips to an EPDR of 1.8ohm?

The suggested amp power from KEF is 200W (assuming @4ohm). This is a case where I don't think the extra headroom >500W into 2ohm (i.e. up to 700-750W) is needed...
 

KMO

Addicted to Fun and Learning
Joined
Aug 9, 2021
Messages
629
Likes
901
So, I intend to get the KEF Reference 1 Meta at release and looking into the Purifi monoblock amps. Would the 1ET400A suffice given the Ref 1 meta is 4Ohm nominal and dips to an EPDR of 1.8ohm?

The suggested amp power from KEF is 200W (assuming @4ohm). This is a case where I don't think the extra headroom >500W into 2ohm (i.e. up to 700-750W) is needed...
I would say it's absolutely fine.

Is EPDR actually relevant for class D? I was under the impression class D didn't suffer from the effect that EPDR models for, so you want to look just at the basic impedance.

Correct me if I'm wrong, anyone.
 

EdW

Senior Member
Joined
Jul 5, 2020
Messages
329
Likes
413
Location
Cambridge, UK
I would say it's absolutely fine.

Is EPDR actually relevant for class D? I was under the impression class D didn't suffer from the effect that EPDR models for, so you want to look just at the basic impedance.

Correct me if I'm wrong, anyone.
You are correct. EPDR (equivalent peak dissipation resistance) refers to the thermal load thrown onto a linear amplifier which will be worse when terminated with a reactive load rather than a resistive load of the same magnitude. With a class D amplifier this dissipation doesn’t occur in the amplifier, so all that the amplifier needs to be capable of supplying is the peak current into the reactive load. The Purifi 1ET400 amplifier has a current limit which cuts in around 25A peak but with continuous sine drive into a low impedance load thermal constraints may kick in a little lower. So we see a peak output of 450W into 2 Ohms corresponding to just 15A rms or 21A peak. I have discussed with Purifi the best amplifier for driving KEF Reference 5 speakers and their reply was the 1ET400 since it would be operating below the current limiter and has marginally lower distortion than the 1ET7040SA.

For the vast majority of 4-8 ohm loudspeakers the 1ET400 makes most sense when their impedance doesn’t fall below 3 ohms in the lower frequencies.
I’m rather surprised that a lower voltage 1ET7040SA hasn’t been developed for bridged operation or a much higher voltage version for single ended operation since this would be the only real reason to have the 40A peak capability of this amp.
 

HarmonicTHD

Major Contributor
Forum Donor
Joined
Mar 18, 2022
Messages
3,326
Likes
4,829
So, I intend to get the KEF Reference 1 Meta at release and looking into the Purifi monoblock amps. Would the 1ET400A suffice given the Ref 1 meta is 4Ohm nominal and dips to an EPDR of 1.8ohm?

The suggested amp power from KEF is 200W (assuming @4ohm). This is a case where I don't think the extra headroom >500W into 2ohm (i.e. up to 700-750W) is needed...
You are easily fine with 200W.

If you want to verify for yourself, you can use this for example.
 

boXem

Major Contributor
Audio Company
Joined
Jun 19, 2019
Messages
2,014
Likes
4,852
Location
Europe
So, I intend to get the KEF Reference 1 Meta at release and looking into the Purifi monoblock amps. Would the 1ET400A suffice given the Ref 1 meta is 4Ohm nominal and dips to an EPDR of 1.8ohm?

The suggested amp power from KEF is 200W (assuming @4ohm). This is a case where I don't think the extra headroom >500W into 2ohm (i.e. up to 700-750W) is needed...
Depends how loud you listen, the music genre you listen, how far from the speakers you listen, how damped your room is ...
With my personal listening habits, I think that a 1ET400A based amplifier is good enough for such speakers. I know some people (not the majority) for whom the 1ET7040SA is a better fit.
To make a car analogy that anybody right in his mind should avoid, there is nothing like too much horsepower :D
 

HarmonicTHD

Major Contributor
Forum Donor
Joined
Mar 18, 2022
Messages
3,326
Likes
4,829
Depends how loud you listen, the music genre you listen, how far from the speakers you listen, how damped your room is ...
With my personal listening habits, I think that a 1ET400A based amplifier is good enough for such speakers. I know some people (not the majority) for whom the 1ET7040SA is a better fit.
To make a car analogy that anybody right in his mind should avoid, there is nothing like too much horsepower :D
He is talking about some KEF Ref 1. Throwing more power (>200W) at them won’t make them play louder. If you want louder, get larger speakers (and then of course the bigger amp to fit).
 

EdW

Senior Member
Joined
Jul 5, 2020
Messages
329
Likes
413
Location
Cambridge, UK
Depends how loud you listen, the music genre you listen, how far from the speakers you listen, how damped your room is ...
With my personal listening habits, I think that a 1ET400A based amplifier is good enough for such speakers. I know some people (not the majority) for whom the 1ET7040SA is a better fit.
To make a car analogy that anybody right in his mind should avoid, there is nothing like too much horsepower :D
The KEF Ref 1 is a relatively benign load at 3.2 ohm minimum. So the 1ET400 based amplifier would always be operating under voltage clip limitation - never hitting the current limiter. To increase the power we would need a larger supply voltage which in principle the 1ET7040SA could take but only an uplift from 64V to 70V - so about 1dB more power which is hardly noticeable. That is of course if the Hypex SMPS1200A400 is changed for a higher voltage power unit - is the forthcoming Hypex PS500 DIY suitable?
 

Meanpeak

Member
Joined
Oct 5, 2021
Messages
17
Likes
5
I have an interesting comparison of the two Purifi cards side-by-side. The 7040SA is noticeably larger and it also has 6 power supply capacitors per rail rather than the 400A's 4 capacitors, so a lift in the on-board current reservoir, which coupled with the March Audio claimed increase in power supply filter capacitance, may be the origin of the improved transient performance I am experiencing.

I also have a higher res image of the new March Audio power supply partial view found on their website, the PCB is branded with the March Audio logo, so it doesn't seem to be an off the shelf purchase but rather a special build.

Both images came from Alan March while I was discussing ordering of the P501's.

View attachment 205759View attachment 205760
I really like the build quality of that supply.

Also, Marchadio is well known for his quality builds.

Will buy one soon!
 

RustyGates

Active Member
Joined
Mar 25, 2019
Messages
116
Likes
85
Location
Melbourne, Australia
Thanks all, I'll be going with a 1ET400A amp.

@boXem | audio, you mention the 1ET400A is current protection limited to loads below 3.3ohm and with the 7040 its lower than 2ohm, where is that from?

If the 400 can deliver up to 25A peak, then it should technically be able to sink current into loads as low as 1.6ohm before over-current protection kicks in (500W limit)?

Note the Ref 1 Meta can dip down to 2.8ohm as tested by @thewas.
 

boXem

Major Contributor
Audio Company
Joined
Jun 19, 2019
Messages
2,014
Likes
4,852
Location
Europe
He is talking about some KEF Ref 1. Throwing more power (>200W) at them won’t make them play louder. If you want louder, get larger speakers (and then of course the bigger amp to fit).
Throwing more power into a speaker makes it play louder ;). If larger speakers play louder it is because they are more efficient. Then why would they need a bigger amplifier?
Speakers manufacturers are extremely unclear when specifying adequate amplifier power. I always consider they specify power in 8 Ohm, in this case both modules fit the bill.
The KEF Ref 1 is a relatively benign load at 3.2 ohm minimum. So the 1ET400 based amplifier would always be operating under voltage clip limitation - never hitting the current limiter. To increase the power we would need a larger supply voltage which in principle the 1ET7040SA could take but only an uplift from 64V to 70V - so about 1dB more power which is hardly noticeable. That is of course if the Hypex SMPS1200A400 is changed for a higher voltage power unit - is the forthcoming Hypex PS500 DIY suitable?
Changing the power supply from 63 V to 70 V will bring less than 1 dB more at speaker output. Not worth the effort.
The 500 in PS500 is for 500W. Completely inadequate for the more than 1 kW needed by a 1ET7040SA :)
Thanks all, I'll be going with a 1ET400A amp.

@boXem | audio, you mention the 1ET400A is current protection limited to loads below 3.3ohm and with the 7040 its lower than 2ohm, where is that from?

If the 400 can deliver up to 25A peak, then it should technically be able to sink current into loads as low as 1.6ohm before over-current protection kicks in (500W limit)?

Note the Ref 1 Meta can dip down to 2.8ohm as tested by @thewas.
3.3 Ohm is the value I found when testing the modules.
The 25 A from the 1ET400A is for a very short time. I am more interested by what happens after this very short time. 450 W in 2 Ohm means 15 A.
The 1ET7040SA allows 40 A short term, then limits to 28 A.
 

SamR

Member
Joined
Jul 5, 2022
Messages
33
Likes
63
@RustyGates You are fine with 200W if you sit no more than 6’ away. You need to hit 105dB peaks cleanly. It’s amazing how many people forget or ignore this.
 
Top Bottom