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VTV Purifi EVAL1 teardown and rebuild

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Rick Sykora

Rick Sykora

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Twisting the wire is probably sufficient (notably for short runs).

Fuse sizing is discussed earlier. My thinking is to size based on how hard you will push your amp. If it will see light duty use, a 3A fuse may be fine. If you expect to drive harder or drive multiple modules, would size closer to the power supply fuse's value (for Hypex A400 would be 12A). There are more experienced folks on ASR that may have more specific advice. A very specific sizing requires specifically measuring the amp and I do not have any Purifi amps on hand.
 

SCG

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Believe me I read the entire thread so I wasn't inquiring about sizing recommendations, I was asking if you could provide the make and model of the fuse you installed on the VTV Purifi EVAL1?

So on the AC wiring did you just twist them and encase in a PET cable protector?

Looking to learn from others like you who have made changes with documented measurements instead of reinventing the wheel and hoping it makes a positive difference or causes no harm. As your thread here is a great service to the community!
 
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Rick Sykora

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Believe me I read the entire thread so I wasn't inquiring about sizing recommendations, I was asking if you could provide the make and model of the fuse you installed on the VTV Purifi EVAL1?
Was a fuse assortment I bought quite a while ago, so will check and let you know.
So on the AC wiring did you just twist them and encase in a PET cable protector?
Yes
Looking to learn others like you who have made changes with documented measurements instead of reinventing the wheel and hoping it makes a difference. As your thread here is a great service to the community!
Thanks, but have had some good role models in the past and here on ASR. Still learning too!
 

rebbiputzmaker

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In the original orientation, does the heat sink act as a shield to reduce power supply noise from coupling into the amplifier boards? No idea, curious...
Of course it does.
 
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Rick Sykora

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Speaking of still learning what are your thoughts of adding this to the internal signal wires, overkill/useless or can't hurt so why not?

Tinned-Copper-PET-Braided-Sleeving
If you are asking about the internal wiring for the audio inputs, I recently tested the Mogami cables vs ribbon cable and did not find any major SINAD measurement between them on a Hypex NC252MP.

The Purifi wiring options are different with the XLR connectors mounted to the board in the EVAL-1. Would not change that arrangement. Otherwise, replacing other wiring would need to be evaluated on a case by case basis. If being shipped or moved constantly, mechanical resilience becomes more of a concern. IMO, all connectors should be interlocking or otherwise secured for good reliability.

I did not mention originally, but for the VTV Purifi amp in this post, it seems marginal to run ribbon cable into a JST connector IMO. However, for most folks who are not constantly poking about amp internals, it seems acceptable.
 

SCG

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The Purifi wiring options are different with the XLR connectors mounted to the board in the EVAL-1. Would not change that arrangement. Otherwise, replacing other wiring would need to be evaluated on a case by case basis.

Just to be clear the above post wasn't about replacing any existing wiring, that was a link to PET/Copper sleeving that would go over the signal wires vs just strictly using PET sleeving.
 
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Rick Sykora

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Just to be clear the above post wasn't about replacing any existing wiring, that was a link to PET/Copper sleeving that would go over the signal wires vs just strictly using PET sleeving.

ok, gotcha. Answers are comparable though as have no experience with it and would need to measure. Would seem to be like adding an additional shield around already shielded conductors. Seems like overkill unless you had some really noisy environment to consider. There is certainly a point of diminishing returns for most applications. Otherwise, save your time and money and save your money for other fun or potential problems that may arise.
 

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It appears that the main difference in SINAD measurements between the testing Amir did on the Purifi "Prototype" unit and the testing you and Amir did on production VTV amps is generally PS induced noise (with harmonics) so this sleeving has EMI protection but the noise might not be entering thru any cabling.

Yea definitely on the overkill side, like using a belt and suspenders but at $0.50/foot and already opening up the amp to rotate the PS and adding sleeving to the AC line, not much time or money to add plus might be fun to get some clean aesthetics for the "after" photo pics with all matching sleeving :)
 
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SCG

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Like the BoXem Arthur units
 

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xkommando

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It has been years since I dug into specs and standards for fuses and breakers. I know back when I was looking at this that it was common to use 1.5x~2x or higher fast-blow current ratings when replacing a slow-blow fuse with a fast-blow fuse. Fuses, and breakers, will easily handle 2x to 10x their design rating for a short spike (few ms to maybe 100 ms), since the design rating is for long-term (seconds or more) current flow. Breakers more so than fuses IIRC. With high in-rush current a fast-blow fuse would not last as long for me as a slow-blow of about half the amperage rating, based upon foggy memory. Of course it is very application- and circuit-dependent... And even if it is a series of short high-current pulses you have to watch average heating (duty cycle) and all that jazz. I remember discovering a fuse was a complicated beast when I dug deep into how they worked and blew.

So based upon no research save that of a vague old memory, I would stick a series 20 A or even 25 A fast fuse in series with a 12-A slow-blow fuse with the expectation that it would last a good long while (whatever that means ;) ).

But here is the big caveat: in this situation, you probably want the new easily-replaceable fuse to blow first, so maybe sticking on the low side is a reasonable choice.

Blah, glad I have no dog in this hunt - Don
Hi Donh56,
Thanks for sharing your experience.
I'm planning to add a fuse or breaker before my diy hypex stereo amp (nc252mp), since I'm not confident that I can replace the onboard fuse. Do you have any suggestions if I should use a fuse or breaker? and do you think the impedance of the fuse or break will make any audiable difference on the amp?
And last question (pardon me if it is dumb) should I get a breaker/fuse that is just above the amp settings? The main smps is rated 650w and has in-rush current of 75a. Is a 6a fuse a good choice?
 

DonH56

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Hi Donh56,
Thanks for sharing your experience.
I'm planning to add a fuse or breaker before my diy hypex stereo amp (nc252mp), since I'm not confident that I can replace the onboard fuse. Do you have any suggestions if I should use a fuse or breaker? and do you think the impedance of the fuse or break will make any audiable difference on the amp?
And last question (pardon me if it is dumb) should I get a breaker/fuse that is just above the amp settings? The main smps is rated 650w and has in-rush current of 75a. Is a 6a fuse a good choice?
I would go with the suggestion of @Rick Sykora, @Buckeye Amps, @orchardaudio, or one of the other people who have more experience with this amp. In general, I would stick with the manufacturer's rating, on the assumption they designed it and thus know the best value to use. In this case, the fuse would be in the power supply for the two modules, so you may want to go with that.

If you are adding an external fuse (or breaker) because you do not want to have to replace the internal fuse, then I would use one rated a little below the internal fuse so that it would blow first. That is, you want the easiest-to-replace fuse to be the one that goes.

A breaker is resettable but responds much more slowly than a fuse, even a slow-blow fuse. I do not know the type of fuse in the amp's power supply but would use one of the same type (slow- or fast-blow) and a little under the power supply fuse. Given the high in-rush current I imagine it is a slow-blow fuse. At 120 V line voltage, 650 W is 5.4 A, so 6 A seems not unreasonable, but again I would look at the actual power supply fuse and/or what Hypex recommends for a line fuse rather than guessing.

As an aside, most SMPS have built-in slow-start circuitry to control in-rush current. I am surprised it is that high.

HTH - Don
 
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Rick Sykora

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Was a fuse assortment I bought quite a while ago, so will check and let you know.

Yes

Thanks, but have had some good role models in the past and here on ASR. Still learning too!

Sorry, forgot about this. The brand is Bojack.
I would go with the suggestion of @Rick Sykora, @Buckeye Amps, @orchardaudio, or one of the other people who have more experience with this amp. In general, I would stick with the manufacturer's rating, on the assumption they designed it and thus know the best value to use. In this case, the fuse would be in the power supply for the two modules, so you may want to go with that.

If you are adding an external fuse (or breaker) because you do not want to have to replace the internal fuse, then I would use one rated a little below the internal fuse so that it would blow first. That is, you want the easiest-to-replace fuse to be the one that goes.

A breaker is resettable but responds much more slowly than a fuse, even a slow-blow fuse. I do not know the type of fuse in the amp's power supply but would use one of the same type (slow- or fast-blow) and a little under the power supply fuse. Given the high in-rush current I imagine it is a slow-blow fuse. At 120 V line voltage, 650 W is 5.4 A, so 6 A seems not unreasonable, but again I would look at the actual power supply fuse and/or what Hypex recommends for a line fuse rather than guessing.

As an aside, most SMPS have built-in slow-start circuitry to control in-rush current. I am surprised it is that high.

HTH - Don
From NC252 datasheet, would be a 6.3A, slow-blow fuse...
1653251957293.png
 

Hov

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Awesome thread and info in it. Will be ordering a 3-channel VTV (I'm in Canada and it seems to be the best option by far for cost and availability for me). I'm interested in making some changes but don't have any soldering experience. I'm wondering if there are things that can be done without the need for that, like with spade connectors or other tips/tricks. Specifically the fuse I'd say is the priority, and wondering if thicker-gauge speaker wire from the terminals to the molex connectors are worth the trouble. Also, I did get a 12v trigger, so we'll see how that looks. I'm thinking of maybe starting a thread with pics when I get it, but wanted to chime in here first (though I know it's been a while since the last post).

Thanks in advance!
 

AdamG

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Thread notification: This is a “VTV teardown and rebuild” Thread. Please keep your posting relevant to the Teardown and rebuild subject matter.

Please and thank you for your cooperation and understanding.
 
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