VTV Purifi Amplifier Teardown(SIL 994EnH-Ticha Pro Opamp)

[TimoJ]

Yes, did not use the Hypex wording specifically enough. The data sheet refers to "standby" as Aux(ilary) power. Note there are also 2 standby inputs. I was referring to the Amp Standby.

View attachment 140495

I still don't understand how you are going to put Hypex PSU to standby without an external power supply, like VTV has done. Amp standby is possible to do, but SMPS standby is the preferred method. I personally use trigger to drive 12V relay and cut AC power.

 

[MakeMineVinyl]

How? Doesn't it need external voltage (3.3-12V) to go to standby?

The SMPS has low voltage aux outputs which are energized as long as it is receiving AC power from the mains, so in a sense it is functioning as an 'external' supply. In this sense, a power switch on the back of the amp is more of a circuit breaker to cut all power.

 

[TimoJ]

The SMPS has low voltage aux outputs which are energized as long as it is receiving AC power from the mains, so in a sense it is functioning as an 'external' supply. In this sense, a power switch on the back of the amp is more of a circuit breaker to cut all power.

But also aux voltages are cut in standby so you can't use those as an external supply, it needs to be a real separate power supply.

 

[Rick Sykora]

I still don't understand how you are going to put Hypex PSU to standby without an external power supply, like VTV has done. Amp standby is possible to do, but SMPS standby is the preferred method. I personally use trigger to drive 12V relay and cut AC power.

Wish Hypex supplied a state diagram for the power sequence...

Had to go back and re-read the SMPS data sheet after was questioned earlier. I mainly use MP series amps and simply assert Amp Enable to take the amplifier from standby to full power. This is from the NC252MP data sheet:

As stated, standby SMPS is active once main AC power is ON. Would expect that you get better behavior this way than powering (or removing) AC power entirely. Am fairly sure you can replicate this behavior with the separate SMPS, but you clearly have to power it to have power available for a trigger (or other circuits).

 

[amirm]

I updated the review title and description to correct version of the op-amp (994EnH, not 990).

 

[phoenixdogfan]

There's so much room in that case, things could have been arranged with much shorter internal wiring.
e.g. rotate the top psu 180 degrees, rotate both amps 90 degrees, the amp-psu cables would then be quite short.
Put one channel at the top, one at the bottom, mains comes in the centre, then the speaker/signal cables are short.
This is just off the top of my head at first glance - I'm sure the pro's here could do even better.

I see that even in the VTV Eval 1 clone, the SMPS heat shield is oriented toward the back of the box, necessitating running those super thin mains around the side and front perimeter of the case. Placing the Smps with the heat shield toward the front of the box, the way Ghent proposes in all his drawing of these DIY builds. would create a much shorter and more direct path for the mains wiring to the SMPS input which could easily be managed with tie downs. In fact, if I ordered the VTV, I would get out the screwdriver and turn the SMPS around and find a shorter IEC to SMPS mains cable.

 

[wineds]

The Hypex SMPS 1200 12A fuses (1 per PSU), are heatshrunk M205s, pigtailed and soldered to the PCB. Hypex regard the fuses as "non replaceable".

View attachment 140388

Yes indeed. Quite dangerous especially if running on 220/240vac mains.

 

[boXem]

Yes indeed. Quite dangerous especially if running on 220/240vac mains.

Care to elaborate?

 

[KSTR]

I would think the onboard emercency fuse is meant only a last-resort safe-guard when everthing else fails. It is rated at 12A (which means it will pass 12A for some considerable time) to allow for enough current even on low mains (like 100Vac in Japan). At 230V it will allow almost 3kW to be disspated until it blows.

The implementer should use a preceding fuse with proper rating for the application and mains voltage, but that poses the problem of inrush current (Spec says "In-rush current 10Ω In-rush NTC, worst-case, 37A". Using two SMPS's makes this even more severe...

 

[boXem]

I would think the onboard emercency fuse is meant only a last-resort safe-guard when everthing else fails. It is rated at 12A (which means it will pass 12A for some considerable time) to allow for enough current even on low mains (like 100Vac in Japan). At 230V it will allow almost 3kW to be disspated until it blows.

The implementer should use a preceding fuse with proper rating for the application and mains voltage, but that poses the problem of inrush current (Spec says "In-rush current 10Ω In-rush NTC, worst-case, 37A". Using two SMPS's makes this even more severe...

My understanding of the function from such an embedded fuse is more for thermal than electrical reasons. If the SMPS goes mad, better burn the fuse than catch fire.

 

[jimijoeb]

My understanding of the function from such an embedded fuse is more for thermal than electrical reasons. If the SMPS goes mad, better burn the fuse than catch fire.

It is short current protection, it will probably survive more heat than rest of the PSU.

 

[restorer-john]

The fuse is not a thermal fuse, it's a conventional pigtailed M205 or equivalent. Sure 12A is a fair bit of current, but it's a 1200W rated supply that works across 120-240V. They've used a slow blow fuse which means nuisance failures should be virtually non-existant. That said, whats wrong with a user replaceable fuse with a clip on cover like so many other manufacturers use? Board real estate?

They take the view that if the fuse blows, the PSU is a write off anyway. I just hate that line of thinking because as we all know, sometimes a fuse just fails for no good reason. But it is what it is- all Hypex psu/amps (except for a few of the DSP plate amps) have non-replaceable (for the average punter) fuses.

 

[wineds]

Yes indeed. Quite dangerous especially if running on 220/240vac mains.

Not sure about Europe but standard mains power outlets here are 10 amp which is less than the soldered SMPS onboard fuse rating (12amp slow blow). So without an additional (say IEC inlet based) fuse you are relying on possible upstream protection at the electrical switchboard to prevent house fires. Obviously the VTV is not compliant with local electrical safety regulations here and as a consequence insurance would be void in the event of an incident.

 

[boXem]

Since it looks like I am the only one to understand myself, maybe some clarification is needed .

There are several risks taken into account in electrical safety. The one everybody thinks about is electrocution. But avoiding the user to be burnt by overheat or fire is another major function of electrical safety. Installing a fuse at the input of an SMPS is not done to avoid user electrocution, it is to avoid overheat/fire in case of major SMPS failure. Is this situation, since the SMPS is anyhow dead, having a replaceable fuse is of no interest.
Another interest of installing a fuse is to protect the electronics from external stress. In this case, I agree that a replaceable one would be much better.

 

[Rick Sykora]

The fuse is not a thermal fuse, it's a conventional pigtailed M205 or equivalent. Sure 12A is a fair bit of current, but it's a 1200W rated supply that works across 120-240V. They've used a slow blow fuse which means nuisance failures should be virtually non-existant. That said, whats wrong with a user replaceable fuse with a clip on cover like so many other manufacturers use? Board real estate?

They take the view that if the fuse blows, the PSU is a write off anyway. I just hate that line of thinking because as we all know, sometimes a fuse just fails for no good reason. But it is what it is- all Hypex psu/amps (except for a few of the DSP plate amps) have non-replaceable (for the average punter) fuses.

Since researching this a bit more, some of the Hypex SMPS do have replaceable fuses.

Seems they reserved those for DIY customers. For example, see the SMPS600N400 below from diyclassd.com...

 

[Rick Sykora]

So here is a pic of one of my (refurbished) VTV amps…

AFAIK, it is a little over a year old, but you can see some commonality with the one at the start of the thread. Rather than Purifi modules, it is a stock Hypex NC500. I have marked it with 3 areas that I will be addressing. The red X is marking the IEC connector that lacks a case fuse. The yellow oval on the left is exposed AC on the trigger module that is a shock hazard. The upper one is exposed contacts for the amp power mains - also a potential shock hazard.

I plan to add a small inline fuse to address the lack of a case fuse. The trigger board will get a piece of Flexseal tape for insulating and some strain relief. Finally, will add heat shrink tubing over each of the exposed mains quick connects. Otherwise, the amp works well and has already been checked with my QA401 audio analyzer and shows no sign of major hum or noise.

EDIT:

Now with the mods…

 

[Rottmannash]

That's a clear explanation. I like your approach. I plan on shipping it Saturday morning.

 

[jjnvdm]

It looks like EVS has already jumped on the opportunity to mod the stock VTV amps:

http://tweakaudio.com/EVS-2/Purifi_amp_mods.html

And here is a review of the result:

http://www.10audio.com/evs-vtv.htm

 

[Rottmannash]

Interesting but which, if any of these mods will make an audible difference?

 

[tmtomh]

Lost me immediately with "cryoed and demagnetized outlet."