DIY Purifi Amp builds

[JimB]

... The smps1200a400 Vaux is 17/22/25, where as the Purifi eval board needs 16.4/18/19.8 for the secondary supply. How does this end Up working out? ...

The Hypex SMPS1200A400 is what Purifi uses for their demonstration amp.
https://www.audiosciencereview.com/...-of-purifi-1et400a-amplifier.7984/post-194274

 

[HLee]

I'm considering multichannel system. How can I put power trigger system into diy amplifier?
Any reference would be appreciated.

 

[KarVi71]

The smps1200a400 Vaux is 17/22/25, where as the Purifi eval board needs 16.4/18/19.8 for the secondary supply. How does this end up working out? Is it because it's regulated on the Purifi side?

Thanks
Tom

I have been planning a build too (for some time). I'll have the money in february, if nothing else goes wrong

I noticed the same thing as you, and asked Purifi pr. e-mail. They answered that it would not pose a problem, as the voltage regulators on the eval board could handle these voltages. They said they would probably change the documentation at some point to reflect this reality.

Seing that they use the smps1200a400 for their demo builds, is another identification that its no problem.

 

[mocenigo]

. If you have an AC 110-220V -> 5V DC supply, than you can do real standby mode.

In other word one can rig a little phone charger?

 

[JimB]

... I noticed the same thing as you, and asked Purifi pr. e-mail. They answered that it would not pose a problem, as the voltage regulators on the eval board could handle these voltages. They said they would probably change the documentation at some point to reflect this reality. ...

Those +VUNREG max rating limits for the EVAL1 do appear to be overly conservative, yet they have not changed them in the latest (v1.11) datasheet.

As of Rev. 1.20, Jan. 6, 2020, they increased the rating spec to 25V.

 

[JimB]

I'm considering multichannel system. How can I put power trigger system into diy amplifier?
Any reference would be appreciated.

I struggled with this for my NC400 amps. In the end, I used a triggered power relay, switched by the 12V trigger output of my AVR. It switches two sockets, which was enough for my case. The power amps go on and off with the AVR - no other power supply running all the time. You just need to wire a trigger cable to its little green plug.

https://dlidirect.com/products/iot-power-relay

EDIT 02/25/2020:
@Zak66 found this nice solution for those in Europe:
https://www.audiophonics.fr/en/powe....html?search_query=12v trigger&fast_search=fs

 

[JimB]

It's just here
https://purifi-audio.com/eigentakt/eval1/
but, it is still Rev 1.00. I got an advance copy of Rev 1.10 by email, today, as a means of answering a few specific questions I had asked them before Christmas. They said Rev 1.10 would be on their website, 'shortly'. I have shared here the aspects that addressed my questions to them. I hesitate to share the whole thing directly, in case they are still revising it before posting. I'll email them and ask if they are okay for me to share it before they post it.

Purifi has just informed me that there is an error in the gain information of Rev 1.10 and asked that I wait for them to correct it before sharing the whole document. I have made the correction in my earlier posts to Rev. 1.11.

 

[JimB]

Right. But retaining the connectors means offsetting the board back from the rear panel and then the XLRs won't fit right. Unless... you mean to have the existing connectors available through the back panel AND add speakONs? Genius! Only those who want spades, or direct wiring will be left wanting. Actually, if there is space to add speakONs on the back panel, there should be space to add binding posts.

FWIW, here is what Purifi themselves did for their demo boxes. Without the DELTRONs in place, they used two of the three available holes for output connections up to the binding post cups. AND, note how they fitted a third lead from the binding post cup back to the forward hole for the DELTRON to get the signal for feedback at the last possible point leaving the box. They did not use the 0R links at R8 and R9. Nor did they do tightly twisted lead pairs.

If you notice the seemingly strange configuration of the (blue) buffer bypass jumpers, that is just in by-pass mode, with the two spare jumpers set on unused pins to keep them with the board.

 

[JimB]

Purifi has just informed me that there is an error in the gain information of Rev 1.10 and asked that I wait for them to correct it before sharing the whole document. I have made the correction in my earlier posts to Rev. 1.11.

The main website page for EVAL1 is now showing Rev 1.20 of the User Guide
https://purifi-audio.com/eigentakt/eval1/
which is also available via a download link:
https://purifi-audio.com/wp-content/uploads/2020/01/EVAL1-Users-Guide-1.20.pdf

It contains a number of updates for us, including the corrected buffer gain details, the feedback sense 0R resistors, the onboard voltage regulator schematic and official increase of |VUNREG Max| to 25V (within the range of the unregulated SMPS1200A400 output).

 

[Julf]

I struggled with this for my NC400 amps. In the end, I used a triggered power relay, switched by the 12V trigger output of my AVR.

Was there a reason you didn't use the standby inputs of the amps or power supplies?

 

[JimB]

In the 1ET400A amp review, @LondonLad asked:

Hello all, I'm new to the DIY amp/speaker world, would like to try out building some of these kits, I am not an electrical engineer but I have soldered on a PCB. I'm just trying out new things whilst in retirement and thought maybe I'd give Purifi a go. I'm learning as quickly as I can, so if my questions annoy the more seasoned of you, well, what can I say, try to keep in mind that you were once where I am knowledge-wise. One nube question that I have is how does the 1et400a board "know" what impedance my speakers are (they are manufacture-rated at 6 ohms, 3 ohms minimum, and are 86dB sensitive)? Second question, how does the board "know" what voltage it's being supplied (230 vs 120)? Or is this independent of the Purifi board and related only to the power supply board? Third, if I buy the Eval-1 kit from Purifi and pair that with a Hypex SMPS1200A400 2x64 VDC 1200 watt switch mode power supply, making sure all connections are correct, that's all I need to do to try out the Purifi "sound" (outside of installing everything in a box), yes? (If so, it almost seems radically too simple for an uninitiated person like me.) Forth, do I need to take into consideration the particular output specs of a preamp (or if no preamp a DAC) in order to fully test (sonically) this kit?

There are already responses in that thread, but I am adding a couple here, in the DIY topic.

1. As @Julf explained there, the amp does not know or care about the speaker impedance as long as it it not too low.
2. This is a parameter for the power supply one uses. The Hypex SMPS600N400 is auto mains switching. The Hypex SMPS1200A400 requires proper application of a jumper (NOT supplied!) for 115 VAC operation.
3. Is that all one needs? Well, a case and proper connections. The Purifi cable set is assembled for the EVAL1 end, but not the SMPS end, though they do provide the plug housings needed for the SMPS end if you use the SMPS1200A400. One needs to insert the individual crimped ends into the corresponding plug body holes. Additional advice about use of this PSU is given in this thread, including here:
https://www.audiosciencereview.com/...iy-purifi-amp-builds.10478/page-6#post-292096
Here is a table showing the wires provided by Purifi (the three power connections), as well as the two control interface connections that can be added:

TABLE CORRECTED Jan 13, 2020
As far as I know, no one has done a nice, complete "how-to" for this project, with all details and options laid out, clearly. Details are still coming out, but people HAVE done complete amp builds already.

 

[JimB]

Was there a reason you didn't use the standby inputs of the amps or power supplies?

A reason? Sure! It was more than I wanted to do to design and create a 12V Trigger interface in the Ghent cases I was using. Also, that meant the power supplies were always going to be on in a low power state (need a high input to be in Standby, right?). The power relay solved my issues, perfectly. If others have a nice implementation of a trigger for this use, I'd love to see it, since I will be doing more amps, soon.

 

[JimB]

Finally, more details are given on the voltage regulators, as well.

I'm liking this FE02A board, more and more. The only thing I really don't like is the "standby" switch. It makes sense for some bench testing, but I just don't see a point to it for us on an everyday amp. It's something to go wrong and requires a panel hole 'breaking' into that of the adjacent output socket. And removing it without damaging the PCB will be a pain for most people. I think that function is best handled by the SMPS1200 through pin 1 of J3 here.

From anyone who has already implemented this, can you confirm the interaction of S1, shunt R3 and J3p1?

Purifi confirmed that the nAMPON pull-down control of S1 and pin1 of J3 are in parallel. If you are using the control from the SMPS (via pin 1 of J3), there is no benefit from S1 ("S1 can be removed").

R3 (referenced in the User Guide regarding nAMPON control) is fitted by default and appears just to link the S1 signal through to the 1ET400A, but not the external control path (pin 1 of S3). (To be confirmed.) If so, removing R3 is electrically equivalent to removing S1.

CORRECTION! Per Purifi Jan. 8, 2020, the User Guide reference to R3 is in error. It should have said R4 (normally not populated). R3 should always be left in place (default) to link the signal for both amp channels.

 

[Julf]

A reason? Sure! It was more than I wanted to do to design and create a 12V Trigger interface in the Ghent cases I was using. Also, that meant the power supplies were always going to be on in a low power state (need a high input to be in Standby, right?). The power relay solved my issues, perfectly. If others have a nice implementation of a trigger for this use, I'd love to see it, since I will be doing more amps, soon.

Sure. Switching mains just seems a bit brute force.

 

[JimB]

Sure. Switching mains just seems a bit brute force.

Old school! From when on-off buttons actually powered things on and off!

Also, I had two such amps (mono blocs), and not enough power sockets, so that also gave me a means of controlling two amps from one mains connection and one trigger signal.

 

[LondonLad]

JimB, thank you.

 

[Massimo]

FWIW, here is what Purifi themselves did for their demo boxes. Without the DELTRONs in place, they used two of the three available holes for output connections up to the binding post cups. AND, note how they fitted a third lead from the binding post cup back to the forward hole for the DELTRON to get the signal for feedback at the last possible point leaving the box. They did not use the 0R links at R8 and R9. Nor did they do tightly twisted lead pairs.

View attachment 44660 View attachment 44661

If you notice the seemingly strange configuration of the (blue) buffer bypass jumpers, that is just in by-pass mode, with the two spare jumpers set on unused pins to keep them with the board.

Did Purifi confirm that they did not install the 0R resistors on the eval amp? I can see solder on the board where R8/R9 are marked. My board is clean copper.

 

[JimB]

JimB, thank you. How does one identify the correct, authentic SMPS1200A400 board? I see one for sale on eBay (https://www.ebay.com/itm/Hypex-SMPS...312905928564?_trksid=p2385738.m4383.l4275.c10 ) but it looks slightly different from the prototype unit displayed here on Page 1 (https://www.audiosciencereview.com/...of-purifi-1et400a-amplifier.7984/#post-194274). The color of the element adjacent to the 230v vs 115v on eBay is red with the identifier "RT314012". The corresponding element on the SMPS board on the prototype is black with the identifier "FRM10NH-1CS2".

It doesn't immediately look 'wrong' to me, but I can't really advise in this case. I have always purchased my Hypex products directly from Hypex. You should ask more about that item from the eBay seller. The colored boxes to which you refer are 12V relays - unlikely to bee a significant difference from version to version.

 

[Massimo]

Purifi confirmed that the nAMPON pull-down control of S1 and pin1 of J3 are in parallel. If you are using the control from the SMPS (via pin 1 of J3), there is no benefit from S1 ("S1 can be removed").

R3 (referenced in the User Guide regarding nAMPON control) is fitted by default and appears just to link the S1 signal through to the 1ET400A, but not the external control path (pin 1 of S3). (To be confirmed.) If so, removing R3 is electrically equivalent to removing S1.

You should be able to just remove S1 and not R3 (which is rather more difficult). I can confirm that once nAmpon is connected, the SMPS1200 will power up the amps and S1 has no effect.

 

[JimB]

Did Purifi confirm that they did not install the 0R resistors? I can see solder on the board where R8/R9 are marked. My board is clean copper.

No. I would not ask what they did on any specific amp that someone had in the field. I see what you see, but it is clear to me. My board (and yours?) is gold plated there. The board in the demo unit is tinned, and, to my eye, there is no component there:

But there is no question to me. The User Guide says be sure to add 0R at those locations to provide a feedback path in case of removing (or not installing) the DELTRON sockets. The DELTRON is, in effect a big, 0R from the main output trace (WIDE) to the feedback trace (tiny). You NEED a feedback path from the output! So, in case there is no DELTRON, the board provides a jumper (as a 0R 0603 resistor) to get the feedback path from the main output trace (you can see all of this in the photos if you look, carefully). The interesting point to me was that they chose to get that feedback connection with a wire to the binding post that is the electrical equivalent of using the DELTRON, rather than use the 0R jumper. This is a tiny bit better than using the jumper for achieving the lowest possible output impedance (includes a bit more of the output path in the feedback loop). Consider it an expert trick or adaptation. Using a 0R jumper AND a feedback wire from the connector would lose much of the value of the added feedback wire.

However, IF I remove my DELTRONs, AND add wires to the output connectors, I've been toying with the idea of putting 1R jumpers in there just to ensure it can never be open loop, accidentally. I'll still have the benefit of a direct connection via the added feedback wire to my output connectors. Belt and suspenders (belt and braces). If I wanted to get perfectionist about it, I'd drill a small hole out through the binding post and solder the insulated feedback wire as close to the speaker wire connection point as possible:

That seems a suitably over-zealous DIY thing to do, no?