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DIY Purifi Amp builds

Rottmannash

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Oh, snap!
 

MSL

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First - Thanks for a great forum!
I think I have read all 123 pages to find an alternative to the SMPS1200A400 as it is not in stock anywhere. The only thing I have found is a SMPS1K-PFCR2 from Micro Audio. The problem is just that it is not sent from the EU and it therefore becomes too expensive.
Is there an alternative to the two, which are PnP and which are sent from the EU? (I'm from Denmark)
Thanks in advance :)
 

tomchr

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Personally, I would order the SMPS1200A400 and wait. You could also ask Purifi when they're planning to have a power supply available. A year-or-so ago when I developed the Purifi/Hypex Buffer they said they were working on one.

Tom
 

tomchr

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05 NOV will be here before you know it. :) Many of the components I'm looking at have delivery dates stretching into the second half of 2022.

Tom
 

Foxenfurter

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I finally got around to building my Purifi Eval 1 kit. It was delayed in UK customs for an eternity, so I used the time to go through these pages and suck out all the tips.

I haven't assembled an amp since I was a teenager, however I have built a dozen or more PC's and this is in similar territory - i.e. bolt it together, with a little guesswork along the way.

I used the Ghent Audio case, but modified it slightly by adding in a fuse, following some advice on these pages. I really don't understand why they don't include a fused mains inlet, the cost difference is marginal.

To be honest the biggest pita was getting the wiring tags pushed onto the mains inlet. I was really surprised (and delighted) when everything worked first time. I think going slow and double then triple checking everything really helped.

It replaces a valve amplifier that I sold, so I set it to bypass the gain and the volume at max on my speakers is about the same as the 20 watt valve amp. I am planning to use DSP to EQ my main speakers I think I am going to switch it back to stock gain as I will need a bit of headroom

I am already thinking of some mods, like front volume switch and some case cosmetics - likely I will ruin it!

Anyway I want to say thanks to everyone who posted advice on here - I have wanted to build another amp for ages, and wouldn't have taken the plunge without all this help.
 

Synergy4

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.... I used the Ghent Audio case, but modified it slightly by adding in a fuse, following some advice on these pages. I really don't understand why they don't include a fused mains inlet, the cost difference is marginal....

Technically the Hypex SMPS1200A400 power supply is already fused (12A slow-blow fuse), but since it soldered to the PCB, it not considered replaceable.

Personally I would be tempted to add an external 8A or 10A slo-blow fuse, that is easily replaceable. Most people do not need full power output. If one needs full power, one can always put in a higher current (12A) slo-blow fuse externally .

Fuse.JPG


Example 0977012.MXEP Littlefuse Slow Blow fuse curves: Time vs Current: https://www.mouser.com/datasheet/2/240/Littelfuse_Fuse_977_Datasheet.pdf-1317309.pdf
Slow-Blow-Fuse-Littlefuse.JPG
 

tomchr

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If you use a fused IEC inlet you also get protection in case one of the wires from the inlet to the power supply ever connects to the chassis.

Tom
 

peng

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Technically the Hypex SMPS1200A400 power supply is already fused (12A slow-blow fuse), but since it soldered to the PCB, it not considered replaceable.

Personally I would be tempted to add an external 8A or 10A slo-blow fuse, that is easily replaceable. Most people do not need full power output. If one needs full power, one can always put in a higher current (12A) slo-blow fuse externally .

View attachment 154621

Example 0977012.MXEP Littlefuse Slow Blow fuse curves: Time vs Current: https://www.mouser.com/datasheet/2/240/Littelfuse_Fuse_977_Datasheet.pdf-1317309.pdf
View attachment 154627

Fuses are not for overload protection in this case, but I am sure you know that already, so I assume your goal is to "protect" the onboard fuse. In that case, even using an external 8A slow blow of the same type (as shown on the attached TTC curves) would not be a sure bet. If the fault current is high enough both will still blow. Even if the board 12A one managed to survive it could have been weakened if it started to melt but not blow in the one fault event. No harm doing it though but I would probably just leave it.
 

peng

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I've read this mentioned elsewhere. What is the theoretical and measured impact of using an inlet with a Y cap filter?

From what I can see I doubt it is a real issue, for measured impact I suppose you can compare one of the measured VTV amp and the Eigentakt. The VTV amp had more visible noise (Amir called it "ugly" but that's relative:)) in the FFT but they don't seem high enough to have audible effects. Chance are good that the amp will still be the quietest one in your signal chain.

SINAD may differ by a few dB, that's about it.


index.php


index.php
 

beren777

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From what I can see I doubt it is a real issue, for measured impact I suppose you can compare one of the measured VTV amp and the Eigentakt. The VTV amp had more visible noise (Amir called it "ugly" but that's relative:)) in the FFT but they don't seem high enough to have audible effects. Chance are good that the amp will still be the quietest one in your signal chain.

SINAD may differ by a few dB, that's about it.

Thanks. Even there, we have multiple possibilities for root cause:
  • power filter
  • buffer boards
  • long speaker wire path
  • speaker wires crossing over one of the power supply feeds to a buffer board
  • one of the speaker wires crossing over a power supply
  • trigger next to a buffer board, trigger wires crossing over buffer boards
  • Loose, poorly intertwined inlet power wire from inlet to power supplies across entire width of case
  • Two SMPS instead of one, positioned such that they bracket the buffer boards
  • combination of above factors
With the EVAL1, the banana connectors are directly soldered to the buffer board and no part of the signal path appears to come close to the power supply.

My Purifi is a DIY in a Ghent case so it doesn't have the power inlet filter. My Hypex 252 is a VTV and does have the power filter.

Separate question: some sources I've read suggest that a power line filter is required as much to prevent outbound HF from the device. Do the Hypex power supplies already provide EMC filtering? If not, is it something to consider in selecting components like inlets?



index.php
 

peng

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Thanks. Even there, we have multiple possibilities for root cause:
  • power filter
  • buffer boards
  • long speaker wire path
  • speaker wires crossing over one of the power supply feeds to a buffer board
  • one of the speaker wires crossing over a power supply
  • trigger next to a buffer board, trigger wires crossing over buffer boards
  • Loose, poorly intertwined inlet power wire from inlet to power supplies across entire width of case
  • Two SMPS instead of one, positioned such that they bracket the buffer boards
  • combination of above factors
With the EVAL1, the banana connectors are directly soldered to the buffer board and no part of the signal path appears to come close to the power supply.

My Purifi is a DIY in a Ghent case so it doesn't have the power inlet filter. My Hypex 252 is a VTV and does have the power filter.

Separate question: some sources I've read suggest that a power line filter is required as much to prevent outbound HF from the device. Do the Hypex power supplies already provide EMC filtering? If not, is it something to consider in selecting components like inlets?



index.php

Agreed, that noise of the VTV amp could have been from all of the things you mentioned, but even then the overall results is a few dB difference in SINAD. It was actually even closer if you compared the "reference" unit with the other VTV Amir mentioned, the one with the Weiss buffer if I remember right (and spell the buffer name right). So I think Bruno's comments on the negative effects of the Y-filter was for the worse case scenarios, depending on the specific inlets, for example.

From my hours and hours of going through the Purifi, Hypex amp related threads, it would seem that the so called standalone hypex input buffer board does not have the RF input filter, but the latest OEM version, such as the NC502MP for example, does have the input filter. Regardless, imo again, whether there will be audible effects or not would depend, but I would bet likely not.
 

tomchr

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From what I can see I doubt it is a real issue, for measured impact I suppose you can compare one of the measured VTV amp and the Eigentakt. The VTV amp had more visible noise (Amir called it "ugly" but that's relative:)) in the FFT but they don't seem high enough to have audible effects. Chance are good that the amp will still be the quietest one in your signal chain.
That mains hum may not be due to a Y capacitor. It could just as easily be caused by crappy chassis layout ... or a ground loop.

Tom
 

tomchr

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Fuses are not for overload protection in this case, but I am sure you know that already, so I assume your goal is to "protect" the onboard fuse. In that case, even using an external 8A slow blow of the same type (as shown on the attached TTC curves) would not be a sure bet. If the fault current is high enough both will still blow. Even if the board 12A one managed to survive it could have been weakened if it started to melt but not blow in the one fault event. No harm doing it though but I would probably just leave it.
The only advantage of having a fuse on the chassis wall is that if the wiring from the IEC inlet to the SMPS fails and shorts to ground, the fuse on the chassis wall will blow.

Given that many DIYers (and some manufacturers - see Amir's pictures above) use single-insulated wire that is simply resting within the case I always recommend the fuse on the chassis wall when asked.

Tom
 

peng

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The only advantage of having a fuse on the chassis wall is that if the wiring from the IEC inlet to the SMPS fails and shorts to ground, the fuse on the chassis wall will blow.

Given that many DIYers (and some manufacturers - see Amir's pictures above) use single-insulated wire that is simply resting within the case I always recommend the fuse on the chassis wall when asked.

Tom

It is more a convenience than a safety thing. For safety, the 15A breaker will trip.

A gfi device could help in case of a resistance to ground kind of faults, but for a real short to chassis, the 15A breaker will do the job. Still, i agree an added fuse for the amp is a good feature, just not a must that some (not you) may think it is.

I also wonder if someone replaced that unfused inlet with a fused one, would it still void the warranty, even though it is an improvement.
 
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Meanpeak

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First - Thanks for a great forum!
I think I have read all 123 pages to find an alternative to the SMPS1200A400 as it is not in stock anywhere. The only thing I have found is a SMPS1K-PFCR2 from Micro Audio. The problem is just that it is not sent from the EU and it therefore becomes too expensive.
Is there an alternative to the two, which are PnP and which are sent from the EU? (I'm from Denmark)
Thanks in advance :)
Where to find more info on that microaudio SMPS? my HYPEX SMPS1200 died today and hypex as usual won't help, they ask to send the unit back for repair, which i cannot do because of shipping cost and also bad support.
 

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