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

[Hov]

Hello and hope everyone is doing well today! Hoping for some feedback on my modifications, and would like to clarify a complete understanding of the XLR Pin 1 situation as well.

Update: now having an issue on power off but only with the NC500MP and when 12v trigger is connected. Tried different combinations of inputs and speakers to be sure, and it's definitely just the NC500MP doing it. Very strange and definitely recent and new. I flipped the IEC socket back around to no avail. I swapped the connectors coming from the 12v board to each module, and the issue remains with the NC500MP so it isn't because of the wiring either. It's fine if it's manually switched off and on. This suggests that something, somehow, is off with the connector on the board that the 12v wiring connects to. I have no idea how or if that's correct, but that seems to be where the process of elimination has led to for now. Without a 12v trigger cable, manually power on/off the NC500MP does not seem to have this issue.

I got a 3-channel VTV amp with 1x NC500MP and 1x NC502MP with the intention of improving it. I'm happy to report that there was a loud buzz (ground loop-ish) that is mostly now gone, which is great. I think the remaining faint buzz (need to be close to speaker to hear it, using Paradigm Monitor 7 v7 and Center 3 v7) is from the XLR connectors.

Originally, the XLR connector had a small wire soldered a small ring adapter from Pin 1 to the bottom screw mount of the XLR connector. T
he shielding from the input cable coming off the Hypex board was soldered to a small ring adapter and connected to the upper screw mount of the same XLR connector. The areas of the mounting holes were not sanded, so I did that, like so (cleaned up the remaining black streaks after this photo so it's fully bare, more like the top one):

I've kept the same XLR connectors as I have not yet been able to source new ones, but working on that as well. I did notice the shielding of the cable coming from the board had some of it still left bundled in with the other cables, so only about half of it was taken out and soldered to the little ring connector. Not sure if that impacts anything, I'll try to add a picture of it soon but hope that's clear.

I'm wondering if the approach was correct. I do still have a faint but constant/consistent buzz coming through the speakers with the AVR (Anthem MRX 720) connected to the amp (used Monoprice RCA to XLR cables with the correct pin configs). And when the cable is not connected, some odd humming that seems inconsistent (not really sure what this part is, it's strange, but there is no "buzz", clearly a different sound, not sure if it still happens along with the buzz when plugged in). I've read many reports of dead quiet amps when connected, so I'm curious to see if I need to make a further modification here or take a different approach with the wiring.

Also, the XLR connectors I've been considering would be this model: https://www.neutrik.com/en/product/nc3fah1

I'd like to avoid soldering, and wondering if the pin design on those can accommodate spades or some sort of other crimp-friendly connector. Open to suggestions for this.

For the changes/upgrades, I did the following:

-sanded down the areas beneath the modules and added 0.5mm thermal pads between them and the case
-sanded the area below the ground nut
-added a 15A in-line fuse and fully replaced the AC wiring using a couple Ghent kits
-extended the 12v cabling with butt connectors and heatshrink to be routed more cleanly, and taped over the exposed solder connections on the little 12v board
-replaced the speaker binding posts with ones that have spade connectors and redid the wiring for that as well

It was a good challenge as I had very limited tools available (old sticky crimpers and small cut-offs of sandpaper are not fun to use). I lent most of my kit to my cousin a while ago and need to get it back!

Notes:
1. the fuse holder I got had black wires, so I added some red heatshrink to help identify it but it's properly wired and working great, purposely had to go right below the blue spade connector because it was making contact with the front-left capacitor of the NC500MP if I covered the bottom of the spade like I would typically
2. the included IEC inlet has built in EMI/RF protection, not sure if that's actually adding to some of the noise issue
3. I was going to use an adhesive tie-down but proceeded to break the clip right after sticking it on, and it's SERIOUSLY stuck on, so the base of it still visible below the left NC500MP module lol -- I'll be sourcing screw-down types if required but I used the holes in the bottom of the case for now and a couple of the module posts instead
4. I used spades to connect the fuse holder to the 2 hot lines for the modules, there is electrical tape wrapped around that connection just for extra precaution of the very slightly exposed spade connection, I wouldn't normally do this but did not want to heatshrink the connection closed just in case but now that is has been tested, I will do that, for a cleaner and more proper solution
5. That one spade connector which is angled, was straightened after I took the pic and before I closed the case back up -- apologies for the OCD trigger!
6. any and all feedback is welcome and very much appreciated

Appreciate the help and support in advance! ASR has been super helpful for many bits of info and buying decisions in the past. Looking forward to becoming more active in the community.

 

[Rick Sykora]

The best explanation I have seen for grounding for Hypex amps is Appendix 2 of the NC400 data sheet. See it here…

https://www.diyclassd.com/img/upload/doc/ncore/nc400/Documentation/NC400_04xx.pdf

 

[restorer-john]

The layout in my opinion could be improved and is quite possibly contributing to the hum and noise.

The input cables (mogami neglex 2549) are sitting right on top of the HF SMPS transformers. I'd move them to the routing in red. You should be able to do that easily.

The mains active input power wire is jammed up against the SMPS secondary side filter caps for the NC500 (back left corner). That is never a good idea for induced noise and hum. Do both amplifiers exhibit similar issues?

 

[Rick Sykora]

Will add that if you find some of the suggested re-routing to be more difficult due to existing wire lengths, since you want to avoid soldering, consider routing the input cabling above the speaker wiring. Getting wiring away from the inductors in any direction may yield improvements. One major problem area for introduced noise is the stiff input wiring flexing the ribbon-style (IDC) connector to the board. Allowing those cables to go more vertical usually puts less strain on the connector.

I highly recommend some hot glue or butyl rubber to keep the male and female IDC connectors together. VTV often uses Tesa tape to try to increase the friction. This might work for the original wiring but re-routing may change the stress points and make it ineffective.

Hope this helps!

 

[Hov]

The layout in my opinion could be improved and is quite possibly contributing to the hum and noise.

The input cables (mogami neglex 2549) are sitting right on top of the HF SMPS transformers. I'd move them to the routing in red. You should be able to do that easily.

View attachment 277145

The mains active input power wire is jammed up against the SMPS secondary side filter caps for the NC500 (back left corner). That is never a good idea for induced noise and hum. Do both amplifiers exhibit similar issues?

Yes, both behave similarly.

Thank you for the tips here, will post some changes tonight!

 

[Hov]

Will add that if you find some of the suggested re-routing to be more difficult due to existing wire lengths. Since you want to avoid soldering, considering routing the input cabling above the speaker wiring. Getting wiring away from the inductors in any direction may yield improvements. One major problem area for introduced noise is the stiff input wiring flexing the ribbon-style (IDC) connector to the board. Allowing those cables to go more vertical usually puts less strain on the connector.

I highly recommend some hot glue or butyl rubber to keep the male and female IDC connectors together. VTV often uses Tesa tape to try to increase the friction. This might work for the original wiring but re-routing may change the stress points and make it ineffective.

Hope this helps!

Makes a lot of sense and I appreciate the explanation. I'll see what I can do about the tightness. The Tesa tape is definitely still helping, but it's noticeably different than the first time I disconnected it for sure. I do have hot glue, maybe I can pull off a small bead in the seem between the connector and the wall of the housing.

I think I can flip the IEC inlet which will make it so the neutral wire is beside that capacitor but also that its entry point is lower into the case. That's the best I can do considering I'm stuck with the layout and screw locations for the module.

As for Pin 1, I think it does match up as long as the areas I sanded haven't combined so the ground is being shared (I was careful not do that) though perhaps not ideal to have both going to the XLR connector. I'll see if there are case holes nearby to move the input wire's shield to, otherwise I may have to wait for new XLR connectors to address that.

Edit: just fixed "toughness" to "tightness"

 

[Rick Sykora]

If you do need to shorten the input cables and rather not solder, these are often supplied with DIY kits…

Neutrik NC3FD-S-1-B​

 

[Hov]

If you do need to shorten the input cables and rather not solder, these are often supplied with DIY kits…

Neutrik NC3FD-S-1-B​

Definitely seems like a great option and I found it in stock at a local shop, thank you!

Here is a quick update, flipped the IEC inlet and used a thinner profile spade connector for the neutral wires:

Also, here is a closer look at the terminations on the XLR side. All are similar.

There is a little spade connector coming off the XLR connector housing. Should I connect that to the Pin 1 grounding position? I can probably wrap the wire around the base of the ring connector and heatshrink it even though it's a bit tight. Would be temporary until I get new XLR connectors.

 

[thecheapseats]

The layout in my opinion could be improved and is quite possibly contributing to the hum and noise.

The input cables (mogami neglex 2549) are sitting right on top of the HF SMPS transformers. I'd move them to the routing in red. You should be able to do that easily.

View attachment 277145

The mains active input power wire is jammed up against the SMPS secondary side filter caps for the NC500 (back left corner). That is never a good idea for induced noise and hum. Do both amplifiers exhibit similar issues?

yep - good catch... first thing I do with any new gear - is take it apart and look inside... just because...

 

[Hov]

Here is what I've been able to do:

The NC500MP input cable gets pushed a little by the top panel, but not much. The NC502MP ones touch right at the corner of the case but are not being pushed down. Wasn't able to make them too vertical and not happy with the bend near the connectors but it's not horrible.

I also replaced the electrical tape with heatshrink for the connection between the fuse and the 2 hot AC lines.

This is the best I can do without bring them closer to power cables or other capacitors on the board.

Unfortunately, the same slight buzz is still present after these changes, thought it seems to be slightly quieter (can't be 100% sure but I think so). I wonder if the spade coming off the XLR needs to be used but I'm not sure that's doing it. Perhaps the proximity of the NC500MP to the IEC inlet as @restorer-john mentioned is just bound to introduce some noise.

Another thing I was thinking - would it be prudent to sand corresponding areas on the panels that meet the base? Such the edges where the rear panel meets the base, as well as the top panel which lowers down onto the base. Not sure if this is worth trying.

 

[Hov]

Just noticed now too that, with the 12v trigger connected, there is a fairly loud buzz for a moment before power down. If I manually power on and off using the switch and no 12v power connected, it's just the expected slight "thud".

I can't imagine what changes could have caused it unless I knocked a wire loose or something but everything seems fine. I suppose something could have come loose within the many butt connectors to extend the 12v wiring, but it was fine after testing when I initially posted this thread.

Very strange. Any ideas?

 

[thecheapseats]

just curious - is this a used unit - or did it ship this way?... not the cable routing (per se) - that's fixable and mild use of a heat gun can help get the cable curves you want (disconnect the cab-assy and do it outside the chassis, however.)... at least it's mog-neglex...

but the various pin 1 shields and having to do your own scraping down to bare metal thru the anodized finish in order to tie chassis to the audio shields?... seems like an odd oversight by the mfg... good job (to my eyes anyway)...

 

[Hov]

just curious - is this a used unit - or did it ship this way?... not the cable routing (per se) - that's fixable and mild use of a heat gun can help get the cable curves you want (disconnect the cab-assy and do it outside the chassis, however.)... at least it's mog-neglex...

but the various pin 1 shields and having to do your own scraping down to bare metal thru the anodized finish in order to tie chassis to the audio shields?... seems like an odd oversight by the mfg... good job (to my eyes anyway)...

Thank you, doing my best with what I've got!

It was a new purchase.

 

[thecheapseats]

Thank you, doing my best with what I've got!

It was a new purchase.

thank goodness you have skills to make right - that's as polite as I can make my comment (not directed at you but at the hum present, new outta' the box)...

 

[Hov]

Just noticed now too that, with the 12v trigger connected, there is a fairly loud buzz for almost a full second before power down. If I manually power on and off using the switch and no 12v power connected, it's just the expected slight "thud".

I can't imagine what changes could have caused it unless I knocked a wire loose or something but everything seems fine. I suppose something could have come loose within the many butt connectors to extend the 12v wiring, but it was fine after testing when I initially posted this thread.

Very strange. Any ideas?

Discovery on this - it's only the NC500MP mono module that is displaying this buzz on shut down. Tried different combinations of inputs and speakers to be sure, and it's definitely just the NC500MP doing it. Very strange and definitely recent and new. I flipped the IEC socket back around to no avail, should have kept it, but not flipping it again for now LOL (this did not seem to affect the buzz).

I swapped the connectors coming from the 12v board to each module, and the issue remains with the NC500MP so it isn't because of the wiring either. It's fine if it's manually switched off and on. This suggests that something, somehow, is off with the connector on the board that the 12v wiring connects to. I have no idea how or if that's correct, but that seems to be where the process of elimination has led to.

I'm going to throw in the towel for tonight and revisit tomorrow evening. Thanks for all the help so far!

Edit: before I actually slept, I re-crimped the neutral wires (it seemed fine but not as good as I'd like using that small gold spade connector, I redid it with a better one and both neutral leads were properly included and connected in the spade), no difference. I also double checked the cables (both XLR and speaker) and everything seems fine. It's odd because if it was something like that, it should be displaying in issue fairly regularly, not just when shutting down. That suggests it's something within the 12v circuit or within the 12v connector on the NC500MP board, which just seems so strange.

 

[Hov]

thank goodness you have skills to make right - that's as polite as I can make my comment (not directed at you but at the hum present, new outta' the box)...

Thank you. I planned to make some improvements knowing what I was going to get, and it seems to be good and rewarding this far. Just can't figure out this new buzz on shut down that seems to have all of a sudden started with the mono module. Hopefully I can solve it somehow, a bum module would be unfortunate for sure.

 

[Hov]

Another update, seems I jumped the gun on the buzzing on shutdown issue. I was always testing it by turning off shortly after turning on. After watching for a couple hours tonight, there was no buzz on shutdown. Still a bit strange that only the NC500MP does it, but it seems like it's fine in that regard at least! I'm guessing there is a certain duration of time that some part of the 12v signal is being sent and turning it off during that time results in the buzz.

I got new XLR connectors and will update with new shots when done. I hope that correctly wiring these up will solve the hum.

 

[cavedriver]

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.

 

[Rick Sykora]

Another update, seems I jumped the gun on the buzzing on shutdown issue. I was always testing it by turning off shortly after turning on. After watching for a couple hours tonight, there was no buzz on shutdown. Still a bit strange that only the NC500MP does it, but it seems like it's fine in that regard at least! I'm guessing there is a certain duration of time that some part of the 12v signal is being sent and turning it off during that time results in the buzz.

I got new XLR connectors and will update with new shots when done. I hope that correctly wiring these up will solve the hum.

How old is this amp? What rev is shown on the module label?

 

[Hov]

How old is this amp? What rev is shown on the module label?

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?