Feedback for Modifications to VTV 3-Channel Amp and Buzz on Trigger Off

[Rick Sykora]

The amp was purchased very recently and arrived just last week.

I see B05 on the NC500MP but can't seem to find any other identifiers of revision.

The NC502MP module says B19.

Is there a specific spot to look if that's not right?

Do not have one handy, but the NC252MP I have has a date code. I thought the latest NC502MP was rev 4ish.

 

[Hov]

threads like this trouble me because my VTV 502MP is dead silent once it's on, however until a recent change I just made it had a pretty bad on/off pop/click noise. A little history- it's a 2 channel and it is apparently an early production board because of how bad the pop noise is, and it does not have a 12v trigger or any other customizations. I initially bought some neutrik adaptors and fed it from an unbalanced source but the pop noise was scary loud so I found a cheap SMSL DAC with balanced outs (M300). This brought the pop down but I was still unhappy so I was disconnecting the speaker wires every time before turning the unit off. Here's where it gets weird. I recently replaced the SMSL with a MiniDSP flex and low and behold - the pop is completely gone! So something that was reported as a problem with the Hypex boards was remedied by a DAC with somehow different balanced output behavior?? And here's someone come along with essentially the same amp and they're chasing ground loop noise and hum that I'm not even getting? Could it still be an input problem? What will happen with my next Hypex amp (probably a 4 channel to drive some "budget" speakers using the MiniDSP as a digital crossover)? Why is the Hypex so sensitive to the balanced nature of the inputs?

Edit- of course I bought the Flex with the balanced outs.

I hear you and can appreciate the concern for sure. I myself am using an unbalanced source, an Anthem MRX 720 AVR, with correctly-wired XLR cables.

Did you use the same cables with the Flex that you did with the SMSL? The pin config is important. Otherwise it would be very curious to see if the DACs did something differently to make the difference. I suppose it's also possible the SMSL unit had some sort of internal/grounding issue perhaps.

It's interesting that a fully balanced setup addressed the pop, I'm not sure if that was mainly affecting unbalanced setups or if that's more the constant low-volume hum that's present.

 

[Hov]

Do not have one handy, but the NC252MP I have has a date code. I thought the latest NC502MP was rev 4ish.

I tried but can only seem to find these markings:

 

[Hov]

Do not have one handy, but the NC252MP I have has a date code. I thought the latest NC502MP was rev 4ish.

Ah I found it! 15th week of 2019!

The NC502MP is much newer, 43rd week of 2022. I suppose the former is less popular. I wonder if this could be the culprit of some of the strangeness, and maybe why the 502 is not the same. I also notice a bit more noise with the constant hum out of the mono module vs either of the 502's channels.

 

[Hov]

After a bit of other things to take care of, I got around to finishing (I think) this up:

-I installed new Neutrik screw-post XLR connectors and ensured to properly bundled the (entire) copper shielding of the input cable and used heatshrink to make it clean
-shortened the input cables and properly bundled the (entire) shielding of the input cables, used heatshrink to keep it all tidy, and wired that into Pin 1 of the XLR connector
-I couldn't find any ring adapters in my "box of stuff" so I temporarily used the ones from the old XLRs and extended them to ground the XLR shield to the chassis
--the one input cable off the NC502MP looks like it's contacting the blue capacitor in the front, but that's just the angle, it is not touching, at least a good half inch away (basically halfway between it and the frontmost LCT5)
-sanded a few intersecting areas of the case to help ensure the back and top panels are properly grounded to/with the whole chassis

Very happy with how they're coming off the connectors now though, and they're very stable in their connection with no wobbling, therefore should have very little risk of coming unseated.

As mentioned before, I swapped the IEC inlet back around to its original position, so back to the hot wire being close to that capacitor on the corner of the NC500MP. Any thoughts on it being worth swapping back so the neutral is the one closer instead? Is this better than the hot line, or does it not matter (for potential noise or interference that is)?

I may add a couple more zip-ties, but soon ready to close it up and reconnect it. I'll update with any changes or new discoveries.

Thank you very much for the help so far!

Side question: I don't mind the 12v trigger approach in this case (for simple/basic builds), and wondering how I may go about sourcing a similar module for another little mono amp I'll be putting together. I'd rather not use a relay. I'm not sure if there are any similar and solderless options, which would be ideal, but open to ideas/suggestions.

 

[Hov]

Edit: connected it up and I can say that the constant low-level buzz from the speakers seem to have been reduced (again, could be placebo) but still not eliminated. I can't imagine it's just a characteristic of the amp modules, but I could be wrong. Also not sure if something else in the setup could be causing it. There is a cable box involved, but unplugging/completely disconnecting it does not affect the buzz.

Thankfully it's only audible fairly close to the speaker and definitely not from the listening position, but perhaps still a bit strange.

 

[thecheapseats]

Ah I found it! 15th week of 2019!
View attachment 277486

The NC502MP is much newer, 43rd week of 2022. I suppose the former is less popular. I wonder if this could be the culprit of some of the strangeness, and maybe why the 502 is not the same. I also notice a bit more noise with the constant hum out of the mono module vs either of the 502's channels.

and this is just one reason why I immediately open everything up I buy before powering it up - take notes and pics - look for stupid stuff (in case it slipped by QC)... a pain doing so after it's installed (usually)...

 

[Hov]

and this is just one reason why I immediately open everything up I buy before powering it up - take notes and pics - look for stupid stuff (in case it slipped by QC)... a pain doing so after it's installed (usually)...

Yeah I'm glad I was able to identify and (mostly) address everything.

Interestingly, I'm noticing that the case is getting quite hot (not skin burning but quite close I think, gonna get a thermometer to check) and when it gets to a certain point, a very high pitched hum/whine comes from just the left channel. Right channel of the same NC502MP and the centre off the NC500MP does not make it. Strange. Doesn't seem like it should be overheating.

 

[thecheapseats]

Yeah I'm glad I was able to identify and (mostly) address everything.

Interestingly, I'm noticing that the case is getting quite hot (not skin burning but quite close I think, gonna get a thermometer to check) and when it gets to a certain point, a very high pitched hum/whine comes from just the left channel. Right channel of the same NC502MP and the centre off the NC500MP does not make it. Strange. Doesn't seem like it should be overheating.

hopefully someone who owns the same unit will speak to what might be normal thermals... as for hums?... whines?... wth? - sounds like it's warranty time to me...

 

[Hov]

hopefully someone who owns the same unit will speak to what might be normal thermals... as for hums?... whines?... wth? - sounds like it's warranty time to me...

I tried swapping the trigger so my second stereo amp for 2 of my channels triggers the VTV after it is triggered by the AVR, let's see how that works. It's strange that it shows up after some time of being on and used.