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DIY Purifi Amp builds

Aardappel said:
What is the reason for the pretty sizeable difference in Purifi output power measurements between their own measurement (top chart) and the soundstagehifi measurement (bottom chart)? In 8 Ohm its about a 100W difference - is it because of the input buffer being bypassed or not? And if so, why would one want to bypass the buffer if power output drops by 100W..?
Click to expand...
Those 8 ohm soundstage measurements are highly suspect. It's not 100W more, it's almost 175W more. This doesn't agree with Purifi, or the review here on ASR. 375W into 8 ohms corresponds to 54.8V RMS, and 77.5 peak. The max power supply rating for the EVAL1 is +70V and +75V for the 1ET400A. Output swing would be somewhat less than that, so it should take >80V supplies to get 375W (assuming the drive circuitry had the range).
 
JimB said:
Those 8 ohm soundstage measurements are highly suspect. They don't agree with Purifi, and they don't agree with the review here on ASR. 375W into 8 ohms corresponds to 54.8V RMS, and 77.5 peak. The max power supply rating for the EVAL1 is +70V and +75V for the 1ET400A. Output swing would be somewhat less than that, so it should take >80V supplies to get 375W.
Click to expand...
@Murray A - how did your Purifi measurements compare?
 
Aardappel said:
@Murray A - how did your Purifi measurements compare?
Click to expand...
Don't know because I didn't measure it yet! Line voltage regulation is important when power measurements are done and I suspect the output regulation of the SMPS1200A400 is partially responsible for the discrepancy. The accuracy of the AP rms converter also may be a contributing factor when presented with a clipped waveform.
 
Murray A said:
Don't know because I didn't measure it yet! Line voltage regulation is important when power measurements are done and I suspect the output regulation of the SMPS1200A400 is partially responsible for the discrepancy. The accuracy of the AP rms converter also may be a contributing factor when presented with a clipped waveform.
Click to expand...
Per the SMPS1200A400 datasheet, output voltage is approximately proportional to input voltage, with 63VDC out being nominal for 230VAC in. Max out is 72VDC for max permitted input of 264VAC. But you only get 49VDC out at the Min of 180VAC in. These will definitely determine the max power from the amp modules, but they cannot get you to 375W into 8 ohms (1% distortion). At the EVAL1 max permitted supply voltage of 70V, the amps should not be able to reach above about 290W. This is significantly more than 200W, but who is running 260+VAC mains?
 
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JimB said:
Per the SMPS1200A400 datasheet, output voltage is approximately proportional to input voltage, with 63VDC out being nominal for 230VAC in. Max out is 72VDC for max permitted input of 264VAC. But you only get 49VDC out at the Min of 180VAC in. These will definitely determine the max power from the amp modules, but they cannot get you to 375W into 8 ohms (1% distortion). At the EVAL1 max permitted supply voltage of 70V, the amps should not be able to reach above about 290W. This is significantly more than 200W, but who is running 260+VAC mains?
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Very interesting. Well here in on the east coast of Australia we have an absolutely appalling grid with Voltages frequently over 250V, especially in summer when there is a lot of solar being injected into the grid. Lots of people are complaining about their solar inverters tripping frequently, which according to AS4777 should only happen at Voltages over 257V.

So I guess this 3rd world grid is good news for the Purifi Amp :) What would happen to the SMPS if the Voltage did briefly tip over 264V though..?
 
Aardappel said:
Very interesting. Well here in on the east coast of Australia we have an absolutely appalling grid with Voltages frequently over 250V, especially in summer when there is a lot of solar being injected into the grid. Lots of people are complaining about their solar inverters tripping frequently, which according to AS4777 should only happen at Voltages over 257V.

So I guess this 3rd world grid is good news for the Purifi Amp :) What would happen to the SMPS if the Voltage did briefly tip over 264V though..?
Click to expand...
Maybe those power supplies with regulated primaries would be good there?
 
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Finally done ...

1606223797297.jpeg
 
Hi folks!

First post here, though have visited often. It was Amir’s review of the Purifi amplifier plus positive word of mouth here that convinced me to order one, as I couldn’t stretch to a Benchmark AHB2. Ordered the EVAL1 ‘kit’ plus the Ghent case. Very pleased with it indeed, but now turning to getting the best out of it.

First question is, should the provided wiring between J1 on the smps and J1 on the EVAL1 board be twisted? I assume not as on pictures of the Purifi demonstration amps I don’t see this done.

Secondly; speaker cable. I’ve ordered some Canare 4S11 Star-quad speaker cable, but am unsure as to the best way to solder it up. Is there likely to be a performance difference between using either the 2 pole or 4 pole speakon connector and plugs?

The Ghent case I have came with the 4 pole Speakon connectors, so I assumed a 4 pole connector would be best, but then I came across this from the Benchmark website (I know the two amps are not the same, but assume if it was needed to use all four poles, Benchmark would have done so):

“The plug used on this cable is a two conductor Neutrik NL2 SpeakON™ connector. It is compatible with the four-conductor NL4 jacks on the back of the AHB2 power amplifier. The NL4 jacks provide two additional contacts (+2 and -2) but these extra contacts are only needed for some bi-amp applications. Use this 2-pole cable for stereo and bridged mono applications.”

Lastly, would I use the clear and clear red Star-quad wires for one banana plug, and the red and white for the other banana plug? Or should it be clear red & red, and clear & white on the other plug... or doesn’t it matter?

Cheers! :)

John
 
JohnM-73 said:
Hi folks!

First post here, though have visited often. It was Amir’s review of the Purifi amplifier plus positive word of mouth here that convinced me to order one, as I couldn’t stretch to a Benchmark AHB2. Ordered the EVAL1 ‘kit’ plus the Ghent case. Very pleased with it indeed, but now turning to getting the best out of it.

First question is, should the provided wiring between J1 on the smps and J1 on the EVAL1 board be twisted? I assume not as on pictures of the Purifi demonstration amps I don’t see this done.

Secondly; speaker cable. I’ve ordered some Canare 4S11 Star-quad speaker cable, but am unsure as to the best way to solder it up. Is there likely to be a performance difference between using either the 2 pole or 4 pole speakon connector and plugs?

The Ghent case I have came with the 4 pole Speakon connectors, so I assumed a 4 pole connector would be best, but then I came across this from the Benchmark website (I know the two amps are not the same, but assume if it was needed to use all four poles, Benchmark would have done so):

“The plug used on this cable is a two conductor Neutrik NL2 SpeakON™ connector. It is compatible with the four-conductor NL4 jacks on the back of the AHB2 power amplifier. The NL4 jacks provide two additional contacts (+2 and -2) but these extra contacts are only needed for some bi-amp applications. Use this 2-pole cable for stereo and bridged mono applications.”

Lastly, would I use the clear and clear red Star-quad wires for one banana plug, and the red and white for the other banana plug? Or should it be clear red & red, and clear & white on the other plug... or doesn’t it matter?

Cheers! :)

John
Click to expand...
1. Not important, but not bad. I would. I did, but I 'wound' the wires together before inserting them into the second plug so there was little stress in the bundle. Ghent cable is (I think). Be careful not to insert the wires in the wrong positions!!!
2. For just a 2-wire cable, conductors on the opposing corners of a square go together, so that should mean the reds go together and the whites go together. As for the speakONs, it depends what you want to do. As noted here recently, there is a common pattern for wiring the 4-poles in the case for these Purifi amps. If you want to use your speaker cables for this amp only, I'd wire the four conductors to the four pins of four-pole plugs to match the wiring to the four poles in the case. That is, on the amp end, each conductor gets its own pin in the plug. Just don't use the cable with other amps without first confirming how they are wired. Otherwise, a more universal cable would be to use 2-pole plugs and double the wires (reds and whites) into the terminations on the speakONs.
 
Thanks very much for your reply Jim. That clears up the wiring. I’ll be using the Neutrik SpeakON at the Purifi end (and only for that amp), and standard pair of banana plugs at each speaker end.

Just curious why the 4-pole version per channel of the Purifi modules seems to be the more popular option here? Is there a slight measured advantage (lower impedance?) over the 2 pole, or is it slightly more mechanically reliable?

I’m using a Quad Artera Play+, which is a combination dac/cd/pre-amp, bought to cut down on the clutter. It can output up to 8Vrms via it’s balanced outputs. I assume therefore it might be advantageous to bypass the input stage on the Purifi for a tad more transparency, by moving the pre-gain jumpers as detailed in the manual?
 
JohnM-73 said:
Thanks very much for your reply Jim. That clears up the wiring. I’ll be using the Neutrik SpeakON at the Purifi end (and only for that amp), and standard pair of banana plugs at each speaker end.

Just curious why the 4-pole version per channel of the Purifi modules seems to be the more popular option here? Is there a slight measured advantage (lower impedance?) over the 2 pole, or is it slightly more mechanically reliable?

I’m using a Quad Artera Play+, which is a combination dac/cd/pre-amp, bought to cut down on the clutter. It can output up to 8Vrms via it’s balanced outputs. I assume therefore it might be advantageous to bypass the input stage on the Purifi for a tad more transparency, by moving the pre-gain jumpers as detailed in the manual?
Click to expand...
The speakON socket in the Ghent case is offered, and is 4-pole, because Purifi chose it for themselves. I'm not aware of any other case kits for the EVAL1 with speakONs, so no other basis for it to be considered popular.

You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
 
JimB said:
You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
Click to expand...

Hi,

How will be required output in Vrms for into 6 ohms (and/or 4 ohms) ?

Also, if one have the source's max output at 5.55Vrms (0.035 ohms) and it will ONLY be used to drive the tweeter, will it be enough to bypass the buffer ?
 
JimB said:
The speakON socket in the Ghent case is offered, and is 4-pole, because Purifi chose it for themselves. I'm not aware of any other case kits for the EVAL1 with speakONs, so no other basis for it to be considered popular.

You will get lightly better performance from the EVAL1 if you by-pass the buffer gain. Total benefit depends on the gain from your source being better than the EVAL1 gain stage. With 8V (rms) output, you'll be slightly short of full output power into 8 ohms. To get full rated output, you'd want at least 9V capability. I'd certainly try bypassing the EVAL1 gain stage.
Click to expand...

Thanks again Jim. My speakers are 6 ohms and I don’t play at particularly loud levels so will give it a try, and report back in due course.
 
Assembled the EVAL1/SMPS1200A400 in the Ghent case with Ghent harness and it was straight forward and easy having followed this thread. The case and harness fit perfectly (provided mains inlet was a bit tight fit) and all screws were provided.

Will leave it running for some time to settle in before giving it some serious listen.

There is one issue, thought, that I would like to consult the forum‘s experience on rather than finding out by trial and error myself. I have a tube pre-amp (Linear Tube Audio Microzotl MZ2, that does double duty as a headphone amp and pre-amp) that will feed the Purifi. I am very careful to switch the tube amp on before the Purifi and then off after it, as I am concerned with DC leakage into the Purifi and speakers. Now I would prefer to keep the Purifi permanently on, while turning the tube preamp on only when I need it. Does anyone already have any experience how sensitive the Purifi is to DC leaks/spikes?
 
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