46 replies to this topic

[Tesla]

Finally getting around to adding SSF to my little cabinet.

 

I got a couple of these ZK-TB21 amps (with the TPA3116D2 chips) to use somewhere. I've only tried one so far, but it ended-up working fine.

 

I guess yall just get your 12v from a 12v-rail on your internal PC-power-supplies? My gaming-pc is external (under cabinet) so for now, I was using a 12v-3amp AC-Adapter (SMPS) from my dead router. Worked fine, but I was wondering how input power can be up to 21volts? Sure enough, when run at only 12v, there are various limitations (to max power-output and speaker types).

 

So, I had this idea to use my old dead HP laptop's AC-Adapter 19volts @ 3.5 amps. Like the smaller 12volt one, it sounded fine in Windows Sound Test (very quiet, chimes, then very quiet again)

... but in PinballY and VPX I was getting some major whirling audio-distortion. 

I then tried a 12v-5amp AC-Adapter from a old Security System. Same "ground loop whirling sounding" distortion. What the heck it going on here? 

 

What it turned-out to be was that the good-sounding and working 12v-3amp AC-Adapter was 2-prong (un-grounded).

Once I used 120v adapters to defeat the ground on the larger ones (basically turning them into 2-prongers) ... they also BOTH worked with no distortion.   

 

So, you would think more grounds would sound better, but was not the case here. Just thought I would pass that on.

Edited by Tesla, 25 October 2025 - 02:56 AM.

[Tesla]

To be clear, my solution of un-grounding them was more of a work-around if anything.

 

What is interesting is that both of the grounded AC-Adapters worked fine in Windows-11 Speaker Test (with all 3 prongs connected), so seems like that pretty much validates my hardware setup.

 

Never-the-less ... I need to run PinballY and VPX, so whatever helps to make that work acceptably is the final-answer.

 

It still might be something on my particular setup (like my APC-UPS, a power-strip, etc)

 

Edit: well probably not since I tried connecting the grounded AC-Adapters directly to the 120v wall-socket and they behaved the same ....

 

but really seemed more like something VPX and/or PinballY was doing to the audio-channels to get ready for VPX to run its emulation and a table. Strange that "whirling sounding distortion" starts when PinballY is loaded, seeing as though I have the videos disabled (and I'm not clicking a flipper button to change the table).

 

So, old-school failings of analog-audio. I see much talk of EMI-noise and use of filters. I'm more interested in where the noise is coming from in the first-place. Back in the day, all PC-audio was analog, and it always seemed acceptable ... without the use of filters. Furthermore, in my situation ...the PC is even outside the pinball-cabinet, still in it's OEM shielded computer case.

Edited by Tesla, 12 September 2025 - 07:12 PM.

[Tesla]

So, now I'm running two of my ZK-TB21 (with a 3.5mm splitter) off the one 19v @ 3.5 amp old-laptop AC-Adapter (un-grounded to prevent whirling-distortion ground-loop).

 

I just used one my from the computer's Center/Sub-jack to run a "sub-woofer" (using a normal TRS 3.5mm cable) . It's really just an old Boston Acoustics full-range bookshelf-speaker from the 90's .  All my real subs are already spoken-for ... the Polk-Audio one is in the Home Theater as usual and I moved my old Infinity-sub to the garage (the neighbors like that) <smile>

 

In Control-Panel/Speakers I made my Surrounds "small" (as they are truthfully) and Turned on Bass-Management in the other place. I'll have to see if that is better than leaving the Surrounds on Full-Range.

 

Anyway, real easy to add a Sub and I like that the ZK-TB21 has a potentiometer for the Frequency (like the panel on a real-sub does). 

Edited by Tesla, 25 October 2025 - 02:57 AM.

[Tesla]

Interesting that all this old stuff worked fine when it was installed on my computer and their desks over the years. But put some of it together here, and it wants to be problematic.

 

I really wanted to utilize my old 12v@5amp Surveillance DVR/Cam Power-Supply so I could split the 3.5mm plug to run my
-  BuyStuffArcades HDMI/LVDS AtGames Backbox 15-in LCD Controller
- My Dell SoundBar (with internal) amp that I just installed

This AC-Adapter works better with the 120v input grounded as designed.

 

That set off this whole cascade of events and the ground-loop hum came back.

TL;DR I got it all working.

Even with the Volume turned-up, my Windows Desktop is now very quiet of background noise or hum (good Noise-Floor). When I start Pinball-Y (as it seizes the 7.1 audio-channels) it gets virtually silent (like perfect). I don't run videos in Pinball-Y (just still-pics of my Tables with no music) so only sound in Selector Wheel is if you press a flipper -button, you get a low-beep.

 

On this gutted ALP, there is very little access inside the cabinet. I think that is why you often see us owners only install inside what we must (using small areas we can easily get to in the back. Most other stuff goes outside the cabinet. 

 

First thing I did was disconnect everything, I removed the old used power-strip (one I grabbed from my closet years ago) and installed a new (good) Tripplite Power-Strip with surge/grounding-light on the back panel of the ALP. 

I'm still using my newish APC-1350-UPS. The Computer is plugged into the APC directly so it never gets accidentally turned-off of Shut-Down improperly. 

 

Then, I more carefully routed the wires in groups
- AC Power
- HDMI, USB, SUB-Power, and any DC-voltage lines

- Line-level analog audio lines 
- High-power or "amped"  speaker wires between amps and speakers themselves

 

The old 19v laptop AC-Adapter for the two ZK-TB21 had to stay un-grounded to prevent (this other major type of) whirling-distortion ground-loop noise. These amps are much more versatile with 19-volts verses just 12v. Maybe I can get some better speakers later.

 

The BuyStuffArcades HDMI/LVDS AtGames Backbox 15-in LCD Controller looks cool mounted on stand-offs inside the Backbox, but I think it really should be in a (shielded) metal case/box to prevent EMI spilling everywhere.

 

Two of my speaker systems have internal Amps, so some long-ish runs outside the cabinet (that need to isolated properly).

 

I installed 2 ferrite cores in key places but none of those "inline filters" I've seen guys use.

 

One other tip to make sure you are not fixing a irrelevant problem. I noticed that when my computer if OFF, the Realtek-7.1 audio jacks are left "floating". This causes internally amplified speaker-sets to hum when their on-board volume-controls are turned up (how I usually keep them) ... until you boot-up the computer. Un-plugging the 3.5mm jack from the back of the PC also silences the hum. 

 

It all helped a little, but not as much as you would think. There was not "one thing" that fixed it all.

Edited by Tesla, 19 September 2025 - 01:04 AM.

[rickh]

Tesla,

 

Have you tried those line level audio isolators?  They use an 1/8" audio jack on both ends.  I don't know what is inside of these cylindrical shaped devices, but it eliminates all ground loop related noise.  

 

https://www.amazon.c...T1zcF9hdGY&th=1

 

Regard,

 

Rick

[Tesla]

Tesla,

 

Have you tried those line level audio isolators?  They use an 1/8" audio jack on both ends.  I don't know what is inside of these cylindrical shaped devices, but it eliminates all ground loop related noise.  

 

https://www.amazon.c...T1zcF9hdGY&th=1

 

Regard,

 

Rick

 

My sound-floor is now acceptable without them. I've been making an effort to combat-it or just not insert the ground-loop noise in the first-place.

 

But I see guys using them, and now your recommendation, so I'm intrigued ... I just ordered a couple from Amazon just to see what they do (along with a metric wing-nut assortment-pack).

Edited by Tesla, 23 September 2025 - 03:52 AM.

[rickh]

Tesla,

 

After I wrote that reply, I searched the internet for a schematic for these isolators.  Briefly, they use audio transformers to eliminate any ground loops.  In short, these transformers might affect sound quality to a small extent (only if you are a audiophile snob).  As you may have read, ground loops cause common mode noise which is challenging to resolve.  First and foremost, do not use the same PSU from your PC to power your amplifier.  Signal ground should be isolated from power ground.  Shielded cable may only need grounding on one end while a seperate wire should be used to connect both chassis between the shielded cable.  If you are old enough to play around with a old stereo phonograph, you may recall attaching RCA shielded cables between the stereo receiver and the turntable.  In most cases the turnable would have a black or green wire with a lug on the end.  This was fastened to the chassis of the stereo.  It was a near perfect setup and the noise was minimal.  Anyway resolving or avoiding common mode noise was part of my career for over 45 years. 

 

Regards,

 

Rick

[Tesla]

Tesla,

 

After I wrote that reply, I searched the internet for a schematic for these isolators.  Briefly, they use audio transformers to eliminate any ground loops. 

 

In short, these transformers might affect sound quality to a small extent (only if you are a audiophile snob).  

 

 

Good to hear they aren't just ferrite-cores in a pretty (and easy to hook-up) box.

 

Yeah, that is what I'm trying to avoid (filtering out the hum ... along with some of the good sound). So, trying to just avoid the cause it in the first place. 

 

I'll have to find some hum and then do a evaluation of them.

 

 

1. As you may have read, ground loops cause common mode noise which is challenging to resolve. 

 

2. First and foremost, do not use the same PSU from your PC to power your amplifier. 

 

3. Signal ground should be isolated from power ground. 

 

4. Shielded cable may only need grounding on one end while a separate wire should be used to connect both chassis between the shielded cable.  

 

1. Yes.

 

2. No problem there. My (dedicated to the cabinet) gaming-PC is still in it's shielded case and under the cabinet. The pinball cabinet is more of a separate peripheral. All it's power-supplies are separate.

 

3. Sounds correct.

 

4. Shielded cables I understand. They help block EMI from your signal-cables. Analog signals seem to be more susceptible to interference than digital ones. As far as chassis of the cabinet, it's all MDF so very little chassis or shielding (likely part of the problem). 

Edited by Tesla, 24 September 2025 - 05:33 AM.

[Tesla]

If you are old enough to play around with a old stereo phonograph, you may recall attaching RCA shielded cables between the stereo receiver and the turntable.  In most cases the turnable would have a black or green wire with a lug on the end.  This was fastened to the chassis of the stereo.  It was a near perfect setup and the noise was minimal. 

 

Anyway resolving or avoiding common mode noise was part of my career for over 45 years. 

 

 

 

I still have my Technics Turntable from the 80's. New belt about 10 years ago, and it's good as new. Plays and sounds fine. My wife still has her vinyl record collection (but we rarely play them, as I prefer CDs). It is connected to my Panasonic Amp here in the pinball room. Yes, I always connect the separate ground wire to the amp's chassis as directed. It's a secondary-system with some nice 10-year old JBL's and other older components and still sounds perfect. I just replaced all the (5.1) speaker wires because they had tarnished inside, also now with new Sewell Banana-Plugs everywhere. The original Boston album is on there now, and side A was played as part of rewire testing.

 

Really? I might need your help in the future.

 

As I said above, one thing I might do soon is put the BuyStuffArcades video (LVDS) controller in a proper metal box. Meaning, not just an easy pop-on cover, but a full box. Something more along the lines of the ZK-TB21 Amps (metal isolation of top-bottom PCB, with a bit of side-cooling). I'm pretty sure it's radiating a good amount of EMI everywhere. I'm thinking De-cased or DIY stuff is really not ideal. I've opened enough CRTs and monitors ... all those thin-metal covers are not there for looks.

Edited by Tesla, 24 September 2025 - 05:36 AM.

[Tesla]

Signal ground should be isolated from power ground.  ... while a separate wire should be used to connect both chassis ...

 

Anyway resolving or avoiding common mode noise was part of my career for over 45 years. 

 

Regards, Rick

 

Rick,

 

When you have a chance, could you please weigh-in on this question?

 

https://www.vpforums...=52387&p=548264

Edited by Tesla, 25 September 2025 - 09:14 PM.

[Tesla]

Tesla,

 

Have you tried those line level audio isolators?  They use an 1/8" audio jack on both ends.  I don't know what is inside of these cylindrical shaped devices, but it eliminates all ground loop related noise.  

 

https://www.amazon.c...T1zcF9hdGY&th=1

 

Regard,

 

Rick

 

This worked perfectly. I chose to use it on my computer's Realtek 7.1 (3.5mm for Front Left/Right Channel) which is Dell powered Soundbar for lower-playfield cabinet mechanicals. An un-grounded 12v-SMPS didn't help because it wasn't the sound-bar or it's SMPS, but rather the gaming-computer itself. The PC itself is one ground I'm NOT willing to shed or bypass. 

 

Previously, the slight ground-loop-hum would mostly go away after all the audio-channels get activated (like when running Pinball-Y and VPX). It's was really only present when it's sitting on Windows-11 Desktop (but was still annoying me). The Besign-device silences it and I don't really hear any effect on the audio from that channel (it's not really dulled or anything). This is in a quiet residence (you might not hear these kinds of things in an Arcade setting or like in a bar with ambient music playing).

 

I notice that the Chinese 2.1 speaker-set I got long-ago from Parts-Express (used on a different channel) ... fairly beefy amped-set and UL-Listed, but no grounded power-plug (and so no ground-loop problems). As I said above, the two ZK-TB21's are running from a (non-ungrounded, ground-loop friendly) 19v laptop SMPS ... now they also have a low noise-floor.

 

Those common 12v@5amp SMPS (for surveillance cams and DVRs) come either way ... with a built-in AC-power cord it is un-grounded (and still UL-Approved). It's only with you get it with the removable Universal Power Cord that it gains a ground.

 

I'm guessing that a lot of high-level audio equipment (or devices used in DAW) is either ground-less or has circuits similar to this Besign-device build-in as required.

Edited by Tesla, 25 October 2025 - 02:54 AM.

[Tesla]

It was a near perfect setup and the noise was minimal.  Anyway resolving or avoiding common mode noise was part of my career for over 45 years. 

 

 

 

So, I've been trying to keep things routed and separated into groups like this:

 

- AC Power lines

- HDMI, USB, SUB-Power, and any DC-voltage lines

- Line-level analog audio lines 

- High-power or "amped"  speaker wires between amps and speakers themselves

 

But it's becoming increasing more difficult in this small space, getting things from front-to-back, but still organized... I think you understand my dilemma. 

 

Back when I was installing networks and Point-of-Sale terminals and touch-screens (often in hospitality environments) as a final step, we often neatly bundled-up and zip-tied all the AC-Power and communication cables together. The equipment and com-lines were overall tolerant (especially as we migrated away from RS-232 to more-digital ethernet and similar-tech at end-point work-stations). However, on my Home-Theater and similar installs ... I still try to at least keep the AC-Power lines a little separate (and especially not long parallel bundlings). It seemed to become less important as we moved away from analog-audio in Home-Theater, but with this pinball-cabinet, seems I'm back to analog-audio again.

 

My question to you is ... is this a real concern? Or, it this now more of an unfounded limitation that I am imposing on myself and my installs (and my little VP-cabinet)? Or maybe it was real in years-gone-by, but not really now-days with APC-UPS units with AVR, filters in power-strips, isolation-transformer technology in various places. My recent experiences tell me the others can all be together (I think even the final lines to speakers/transducers). It's really just the AC-Lines I'm wondering about at this point. 

 

Your thoughts?

Edited by Tesla, 30 October 2025 - 04:08 PM.

[rickh]

 

It was a near perfect setup and the noise was minimal.  Anyway resolving or avoiding common mode noise was part of my career for over 45 years. 

 

 

 

So, I've been trying to keep things routed and separated into groups like this:

 

- AC Power lines

- HDMI, USB, SUB-Power, and any DC-voltage lines

- Line-level analog audio lines 

- High-power or "amped"  speaker wires between amps and speakers themselves

 

But it's becoming increasing more difficult in this small space, getting things from front-to-back, but still organized... I think you understand my dilemma. 

 

Back when I was installing networks and Point-of-Sale terminals and touch-screens (often in hospitality environments) as a final step, we often neatly bundled-up and zip-tied all the AC-Power and communication cables together. The equipment and com-lines were overall tolerant (especially as we migrated away from RS-232 to more-digital ethernet and similar-tech at end-point work-stations). However, on my Home-Theater and similar installs ... I still try to at least keep the AC-Power lines a little separate (and especially not long parallel bundlings). It seemed to become less important as we moved away from analog-audio in Home-Theater, but with this pinball-cabinet, seems I'm back to analog-audio again.

 

My question to you is ... is this a real concern? Or, it this now more of an unfounded limitation that I am imposing on myself and my installs (and my little VP-cabinet)? Or maybe it was real in years-gone-by, but not really now-days with APC-UPS units with AVR, filters in power-strips, isolation-transformer technology in various places. My recent experiences tell me the others can all be together (I think even the final lines to speakers/transducers). It's really just the AC-Lines I'm wondering about at this point. 

 

Your thoughts?

 

Tesla,

 

I understand your concern.  I'm routing some of my speaker zip lines with a power line, but I cannot hear any 60Hz hum.   However, I would be careful routing line level audio close to any power line.   Obviously, if you are using premium quality shielded cable for your audio this would not be an issue.  As for routing cheap line level audio cables with cheap USB cables, I would use a bit of caution.  As mentioned, common mode noise is more of a nuisance than EMI noise. 

 

Rick  

[Tesla]

 

I understand your concern.  I'm routing some of my speaker zip lines with a power line, but I cannot hear any 60Hz hum.   However, I would be careful routing line level audio close to any power line.   Obviously, if you are using premium quality shielded cable for your audio this would not be an issue.  As for routing cheap line level audio cables with cheap USB cables, I would use a bit of caution.  As mentioned, common mode noise is more of a nuisance than EMI noise. 

 

Rick  

 

 

All good info about allowable bundlings (based on your experiences) and reminders of things to avoid. Also that it's often the shielding that is important (not that a cable is on-hand, inexpensive, or thin) and can facilitate the install as a whole to run acceptably. 

 

I will try not to forget about appropriate high quality line-level cables as well (good shielding and of appropriate length).

 

As for interference seeping-in on the originating line-level-cables ... "garbage-in/garbage-out" comes to mind, as well as "your system is only as good as the weakest-link".

 

Thanks, that helps.

Edited by Tesla, 31 October 2025 - 02:32 PM.

[Tesla]

So, one more issue if I may ...

 

Now that everything turns on/off with a single power-strip (which is very handy and even seems appropriate with all these components and separate power-supplies) an unintentional issue remains.

 

When everything powers-up, the computer starts to boot-up and the ZK-TB21's play a little tune. As you likely know, the tune plays lather loudly because the Amps are turned-up to their desired volume level while you play the Tables. That is all fine.

 

But during the power-down sequence, the last thing that happens is the power is turned-off to the amps. When they are finally powered down, there is a loud popping-noise from all-or most of the speakers. Not only is it jarring in a residence, it can't be good for the speakers in the long-run.

 

Can you think of any way to prevent this? Spending a little time, effort, or money on it isn't a problem if you have a viable idea or solution.

 

As I finally document this issue here, I'm wondering if the "after-market car-stereo and amps" guys might have a solution. I'm not sure if this setup is Home-Theater-like or more like theirs.

Edited by Tesla, 31 October 2025 - 02:53 PM.

[rickh]

So, one more issue if I may ...

 

Now that everything turns on/off with a single power-strip (which is very handy and even seems appropriate with all these components and separate power-supplies) an unintentional issue remains.

 

When everything powers-up, the computer starts to boot-up and the ZK-TB21's play a little tune. As you likely know, the tune plays lather loudly because the Amps are turned-up to their desired volume level while you play the Tables. That is all fine.

 

But during the power-down sequence, the last thing that happens is the power is turned-off to the amps. When they are finally powered down, there is a loud popping-noise from all-or most of the speakers. Not only is it jarring in a residence, it can't be good for the speakers in the long-run.

 

Can you think of any way to prevent this? Spending a little time, effort, or money on it isn't a problem if you have a viable idea or solution.

 

As I finally document this issue here, I'm wondering if the "after-market car-stereo and amps" guys might have a solution. I'm not sure if this setup is Home-Theater-like or more like theirs.

I took an unconventional approach for managing cabinet power.  I have a very simple setup, a 24VDC PSU, playfield monitor, and a back box monitor.   I use the PC's USB VBUS to power up a relay.  This relay energizes both monitors and PSU.  When the PC is turned off, the VBUS power extinguishes, thus turning the relay off along with the three peripherals mentioned.   Let me know if you would like a photo and a BOM.

 

Rick

[Tesla]

Well, I have many more AC-Powered devices ... looks like about 8. I use a Energy-Saving Power-Strip with a Master-Outlet (my gaming-computer is the master-power-controller). All that works fine.

 

This is really just a minor cabinet refinement. I'll add it to my ToDo list, but maybe will never get around to it after-all ... I just thought someone might have already.

 

I quickly Googled it, and yes ... I see many people in 12v auto-stereo amp scene combatting this problem, and there are already several inexpensive after-market products available, so I will just use one of those (instead of trying to build something) ... I have enough un-accomplished hardware-mods for my cabinet already.

 

Oh, I also found a guy on YouTube talking specifically about these little Amps, this issue, and his ideas for curing-it. But that is a very narrow solution, and might only apply to these particular amps (so might not be as helpful to this group as a whole).

 

If I accomplish something, I'll let you know.

[Tesla]

So, one more issue if I may ...

 

Now that everything turns on/off with a single power-strip (which is very handy and even seems appropriate with all these components and separate power-supplies) an unintentional issue remains.

 

When everything powers-up, the computer starts to boot-up and the ZK-TB21's play a little tune. As you likely know, the tune plays lather loudly because the Amps are turned-up to their desired volume level while you play the Tables. That is all fine.

 

But during the power-down sequence, the last thing that happens is the power is turned-off to the amps. When they are finally powered down, there is a loud popping-noise from all-or most of the speakers. Not only is it jarring in a residence, it can't be good for the speakers in the long-run.

 

Can you think of any way to prevent this? Spending a little time, effort, or money on it isn't a problem if you have a viable idea or solution.

 

As I finally document this issue here, I'm wondering if the "after-market car-stereo and amps" guys might have a solution. I'm not sure if this setup is Home-Theater-like or more like theirs.

 

So, I have two of these ZK-TB21 Amps. I'm going to try two different solutions.

 

One solution is to replace the ZK-TB21 with a slightly better Amp (and use that ZK-TB21 somewhere else later).

 

I'm going to try one of these instead: 2.0-Amp AK-55 
There is a less expensive AK-45, but it's less powerful and has no SPDIF/optical-output. If allow-to, I'm gonna try to grab some channels over optical. No analog distortion on those.

 

The second solution involves trying to fix one of these ZK-TB21 with a Speaker Protection PCB (12v-24)

The reason I selected this one is because the reviews were OK, it's inexpensive, and:
a. it delays on power ON AND OFF
b. Works between 12-24v (so I can use my existing SMPS-18v_DC that powers my ZK-TB21's) ... remember, ZK-TB21's run better with a bit more voltage over 12v.

c. Reportedly, this PCB can also work with Class-D Amps (non-shared speaker grounds). Just leave the negative speaker-wires connected, and just "relay-switch" the positives.

 

We'll see if it works or I smoke-something. <smile>

Edited by Tesla, 13 December 2025 - 01:02 AM.

[rickh]

One of the disadvantages of many of these class D amplifiers is that they have this noisy pop when they are turned off, especially the TPA3116.  On my cabinets I have been using a simple power switch on the front panel that basically controls the power to the amplifier.  When I turn it on, I do get a thump from the woofer, but it is not an annoyance, when I turn the amplifier off, there is no loud snap.   However, if the PSU de-energized to the amplifier, there is a load snap.  I am suspect that when power is removed from the amplifier, there is a huge EMF surge that is snubbed by the PSU's filter cap and I suspect it is causing the loud snap or pop (There ain't no crackle!).   So if the power wire is opened on the amplifier when it is energized, it does not make a noise. 

So if you want to test my theory, simply remove the power wire from the amplifier.  If it makes a loud pop or crack, then my theory is wrong, it won't hurt my feelings.  However, if it works, try using a huge diode between the power in and the amplifier.  

[mjr]

For what it’s worth, my Theatre of Magic pinball has exactly this same quirk with popping the speakers when you power it off. So if all else fails, look at it as a little bit of real pinball authenticity that the true pinball fanatics would pay extra for!