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

[jimijoeb]

Radiations are mainly done by the cables, and by a few components that happen to be on the other side from the heat sink.
I tested both positions of the SMPS1200 for my amplifiers. Measurements were exactly the same but one of the 2 positions was allowing both better cable management and better air flow.

Ok, make sense for your decision. I saw design, nice short and sleeved cables and lot of orange. It reminds me trend in PC builds with cable sleeving.

I used to think that but I found out that the aluminum used in heatsinks is weak for magnetic shielding, almost like air.
https://en.wikipedia.org/wiki/Permeability_(electromagnetism)#Values_for_some_common_materials

Steel is a cheap solution, just like Apollon did with the Purifi Mini.
View attachment 140460

That was exatly my thought for best design. Al is good for statics, but not for magnetics. That piece of steel probably coud help a lot and add few $ to BOM, only downside is weight. I would also avoid stainless steel, as not all of them are magnetic.
Edit: Also noticed that it seems like they used short wires from PCB to XLR connectors to prevent mechanical issues.

 

[tomtoo]

The problem with the super thin wires is that in assembly it can easily get caught and present a shock hazard. There is no excuse for mains wiring that thin going to the back panel relay board.

It would not be allowed in germany. A wire hast to stand the tripping current of the upstream fuse permanently.
A shortcut is not allways a 0Ohm shortcut. Contac could be oxydised and you could end up with a current thats perfectly ok for the fuse, but not for the cable. Thats why its forbidden.

 

[Francis Vaughan]

That piece of steel probably coud help a lot and add few $ to BOM, only downside is weight. I would also avoid stainless steel, as not all of them are magnetic.

Magnetic shielding is a black art, and just messing about with steel, no matter what composition, is not going to provide much joy. To provide useful magnetic shielding requires the use of mu-metal, and very careful design and construction. You must design in a manner that controls the magnetic circuit, which means you must fully enclose the shielded device, or leave gaps in very carefully managed ways. Worse, mu-metal work hardens, is terrible to work with, and if it work hardens it losses its shielding capabilities. Typically enclosures are folded and punched as needed, and then annealed in a reducing (hydrogen) atmosphere. There are mu-metal foils and tapes that can be used as well, but these still require very careful use. You can't shield a magnetic field (not without a superconductor), but you can redirect one. Just adding lumps of steel will also redirect, but invariably not where you hoped.

Overall, magnetic shielding isn't something you see a lot of. Mostly because it is hard and expensive.

Most shielding is for the electric field. For that you just need appropriate electrical conductors.

You see the common fallacy that a Faraday Cage provides magnetic shielding. It doesn't.

Managing interference is best done in two places, at the source and at the receiver. The rules are the same. Control your return paths and get loop areas down. After that, distance is your best friend. Excessive bandwidth is never a good idea.

 

[Francis Vaughan]

So, it appears that there is no input fuse. But if you add the trigger option they add the trigger board that connects directly to the power inlet. So, not only is this a potential shock hazard, it is a very clear fire danger. Another safety fail, and a big one. As I wrote above, this is unacceptable. Indeed so much so that VTV should recall any product they have sold and fix this. They have a serious issue here. Loss of livelihood and lose house level of serious.

 

[KSTR]

I think even though the module placement is not optimal and the wiring is a mess the real problem of this construction (besides the safety stuff) is horrible GND wiring. I'm pretty sure with a proper ground concept we'd see top-notch noise & hum/buzz performance.
At the moment, for example, the PSU leakage current return path goes right through the buffer boards. Ony tiny little routing inconsistency on that board and the current may find a common path with the local "reference" ground only to develop an error voltage on the order of a microvolt which is enough to spoil performance the amp module.

 

[Rottmannash]

Is the wiring on my VTV Eval 1 amp as bad? I posted pics earlier in the thread.

 

[MakeMineVinyl]

Is the wiring on my VTV Eval 1 amp as bad? I posted pics earlier in the thread.

It looks a lot better to me from what I can see, but is that safety ground a stud or a screw?.

 

[Francis Vaughan]

Is the wiring on my VTV Eval 1 amp as bad? I posted pics earlier in the thread.

For the most part no. The wiring is very simple using the eval buffer board.
However you have the trigger option, and that is a safety issue. The mains connection isn't fused, and the wiring is not really up to safe spec. Although not urgent, I would be thinking about fixing that.

Some proper fixing of the mains cable wouldn't go astry either. Not with self adhesive tie-down points however.

 

[MakeMineVinyl]

However you have the trigger option, and that is a safety issue.

I'm not familiar with how the trigger is handled in this case, as I've never seen a schematic. What is the safety issue?

In the case of our amps, the trigger inputs and outputs are all opto-isolated and managed by a microcontroller on a separate PSU.

 

[jimijoeb]

I'm not familiar with how the trigger is handled in this case, as I've never seen a schematic. What is the safety issue?

In the case of our amps, the trigger inputs and outputs are all opto-isolated and managed by a microcontroller on a separate PSU.

Trigger module is directly connected to main AC with thin wires soldered to PCB and not fused on chassis input. It look better on his VTV Eval 1 as wires look bit sturdier and they are short.

 

[Rottmannash]

Thanks for the reassurance.

 

[Rick Sykora]

Trigger module is directly connected to main AC with thin wires soldered to PCB and not fused on chassis input. It look better on his VTV Eval 1 as wires look bit sturdier and they are short.

This is arguable as the shorter wire may put more stress on the solder joint. In any case, this is just one potential for a short. The exposed solder pads on the trigger board are also a shock hazard.

The bigger safety issue is the lack of a AC input fuse.

 

[BlackTalon]

I have an Eval-1 w/ trigger in transit that was built late last week. I'll get some pictures after it arrives for comparison with earlier ones.

 

[jimijoeb]

This is arguable as the shorter wire may put more stress on the solder joint. In any case, this is just one potential for a short. The exposed solder pads on the trigger board are also a shock hazard.

The bigger safety issue is the lack of a AC input fuse.

It is lower chance it get somewhere damaged eg. during cover assembly.

 

[Rick Sykora]

It is lower chance it get somewhere damaged eg. during cover assembly.

Welcome to ASR btw!

You may be right, but not going to split hairs as it is just one of the potential sources for a short. The bigger issue is the lack of short circuit protection overall.

Also, the Hypex supply has standby power that can be used for a trigger circuit. VTV chose to use AC power.

 

[TimoJ]

Also, the Hypex supply has standby power that can be used for a trigger circuit.

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

 

[simbloke]

I think it's the opposite. I've built a remote for my Audiophonics amps that turns them on by sending 5v to the trigger inputs.

 

[Rick Sykora]

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

As long as the SMPS has AC supplied, it is in standby, Typically, the trigger circuit (or a simple switch). transitions the supply from standby to full power. EDIT: Aux power is not available in SMPS standby, I confused AMP enable and SMPS standby in an earlier edit.

For more discussion on the trigger, click this link.

 

[jimijoeb]

Welcome to ASR btw!

You may be right, but not going to split hairs as it is just one of the potential sources for a short. The bigger issue is the lack of short circuit protection overall.

Also, the Hypex supply has standby power that can be used for a trigger circuit. VTV chose to use AC power.

Thank you.

Unfortunetly, I didn't see anything about Standby power suply in SMPS datasheet. Only stanby IO are Inputs for standby control, but no voltage outputs.

 

[Rick Sykora]

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.