46 replies to this topic

[Tesla]

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.  

 

So, my "real Amps" and AVRs ... a (pre-HDMI) Panasonic, a Onkyo, and two new Denons ... no popping or thumping during On-cycle or Off.

 

But you can hear the relays inside (even the $2400 Denon). I always thought the Relays were to save the Amp if it detects a shorted wire or shorted driver-cone-coil. Maybe they are but I think for my issue as much as anything else. I think that is what issue this board fixes or combats. If fact, one guy installed one inside his vintage amp (and ran it off internal power). Fixed it right up.

 

It doesn't help that we have to keep hard-controls for power-on and volume turned-up (that is max and we meter-them down from sound-card) ... but many application are like that. 

 

And as for these little Amps ... we are installing in Pinball Machines but some others are installing inside antique radios and what not.

Edited by Tesla, 13 December 2025 - 01:15 AM.

[Tesla]

 

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.  

 

No, it still pops. Even with no input cable connected it pops. It pops on power-down if the speakers are still connected.

 

And it's not just these ZK-TB21's and/or TPA3116 based-amps.

 

I have a fairly nice 2.1 combo unit (the Amp is in the sub-woofer box) that does the same thing (although not as loud or bad). What I'm pretty much seeing here ... any amp like this that does NOT have relays near output-stage, is gonna pop the speakers on power-down (and some even do it on power-up). The (after-market) auto-stereo guys run into this alot I read.

Edited by Tesla, 13 December 2025 - 01:11 AM.

[rickh]

I have both the ZX-TB21 and TPA3116 and I do not have a popping issue when powering either of them off through the PSU.  However, I do have a cheap version of the TPA3116 that does pop when I turn it off through the PSU.  I went through the circuitry and I discovered that the expensive TPA3116 has a Schottky Diode on the power input that prevents the user from applying reverse power.   BTW- the ZX-TB21 sounds excellent, but sometimes when I recycle power to the amp, it refuses to initialize.  It only happens rarely, but it is an issue.  Have you seen this? 

 

Last, although adding a timed relay will eliminate this anomaly, switching three channels through three relays is expensive.  If you must, try these products from Amazon https://www.amazon.c...in_title_6&th=1 and https://www.amazon.com/dp/B0CLYF9RY2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_7.  The later has only a delay on and no off.  I have experimented with both with limited success, but I can't justify spending $30 on relays with a product that is already too expensive for most consumers, especially when I have to compete with a Chinese made ATGames.  Let me know if you need any other information. 

 

 

Rick

[Tesla]

1. However, I do have a cheap version of the TPA3116 that does pop when I turn it off through the PSU.  I went through the circuitry and I discovered that the expensive TPA3116 has a Schottky Diode on the power input that prevents the user from applying reverse power.   

 

2. BTW- the ZX-TB21 sounds excellent, but sometimes when I recycle power to the amp, it refuses to initialize.  It only happens rarely, but it is an issue.  Have you seen this? 

 

3. Last, although adding a timed relay will eliminate this anomaly, switching three channels through three relays is expensive.  If you must, try these products from Amazon https://www.amazon.c...in_title_6&th=1 and 

 

4. The later has only a delay on and no off.  I have experimented with both with limited success,

 

5. but I can't justify spending $30 on relays with a product that is already too expensive for most consumers, especially when I have to compete with a Chinese made ATGames.  Let me know if you need any other information. 

 

 

Rick

 

1. Yes, that sounds like the same issue I'm trying to resolve. Yes, while my two ZK-TB21 were purchased on Amazon about a year apart, they are basically the same and supposedly contain TPA3116 chips.

 

2. No, I have not. You mean it doesn't play the power-up chime or the blue-led power light doesn't even start flashing?

 

3. I think we are not understanding each other. I can simulate delayed power-on/off and I already verified that is NOT a fix. Also, 12v automotive devices won't work for me because I'm using 18v. 

 

4. Finally, if you ARE using 12v, there are nice/cheap/programmable after-market version for car-audio. But these are for combating a different issue (that delayed power on/off fixes).

 

You know me ... I'll certainly let yall know if I find something that works.

 

5. Well, the device I linked to above is only $10. 

 

And then you lost me. Who's competing with AtGames? I'm building and refining a custom virtual pinball cabinet and learning electronics and yet more programming skills in the process. 

 

But yeah, I do run a mostly-gutted ALP. I can tell you all about AtGames. While I got it on-sale for $400 at Sam's-Club (I'm sure they barely broke-even) ... I certainly would not steer anyone to my route. Have you seen AtGames' suggested list (buy direct) prices? Go read my build-thread if you want to know about the quality and long-term durability of their parts. I'm cheap ... it didn't get to be gutted because it was working fine for (OTG) VPX.

Edited by Tesla, 13 December 2025 - 07:40 PM.

[rickh]

 

1. However, I do have a cheap version of the TPA3116 that does pop when I turn it off through the PSU.  I went through the circuitry and I discovered that the expensive TPA3116 has a Schottky Diode on the power input that prevents the user from applying reverse power.   

 

2. BTW- the ZX-TB21 sounds excellent, but sometimes when I recycle power to the amp, it refuses to initialize.  It only happens rarely, but it is an issue.  Have you seen this? 

 

3. Last, although adding a timed relay will eliminate this anomaly, switching three channels through three relays is expensive.  If you must, try these products from Amazon https://www.amazon.c...in_title_6&th=1 and 

 

4. The later has only a delay on and no off.  I have experimented with both with limited success,

 

5. but I can't justify spending $30 on relays with a product that is already too expensive for most consumers, especially when I have to compete with a Chinese made ATGames.  Let me know if you need any other information. 

 

 

Rick

 

1. Yes, that sounds like the same issue I'm trying to resolve. Yes, while my two ZK-TB21 were purchased on Amazon about a year apart, they are basically the same and supposedly contain TPA3116 chips.

 

2. No, I have not. You mean it doesn't play the power-up chime or the blue-led power light doesn't even start flashing?

 

3. I think we are not understanding each other. I can simulate delayed power-on/off and I already verified that is NOT a fix. Also, 12v automotive devices won't work for me because I'm using 18v. 

 

4. Finally, if you ARE using 12v, there are nice/cheap/programmable after-market version for car-audio. But these are for combating a different issue (that delayed power on/off fixes).

 

You know me ... I'll certainly let yall know if I find something that works.

 

5. Well, the device I linked to above is only $10. 

 

And then you lost me. Who's competing with AtGames? I'm building and refining a custom virtual pinball cabinet and learning electronics and yet more programming skills in the process. 

 

But yeah, I do run a mostly-gutted ALP. I can tell you all about AtGames. While I got it on-sale for $400 at Sam's-Club (I'm sure they barely broke-even) ... I certainly would not steer anyone to my route. Have you seen AtGames' suggested list (buy direct) prices? Go read my build-thread if you want to know about the quality and long-term durability of their parts. I'm cheap ... it didn't get to be gutted because it was working fine for (OTG) VPX.

 

1. The ZK-TB21 got a TPA3116 inside? I did not know that. 

2.  No chime, but the LED Illuminates.

3. Okay, I understand, the first link I gave you supports up to 24V

4. Yes, I have seen those relays before.  However, I need to get my test bench back and do some experimenting on how to reduce this popping sound when the amp is powered off. 

5. I don't see the link on this page for that $10 part. Does it switch all three speakers?

ATgames has spoiled the game room industry with cheap, Chinese made virtual pinball machines that wear out like a dollar store pair of sandals.  Six years ago, I was selling my mini machines on Ebay for $1350, they would not last more than 3 days before they were sold.  Sadly, Ebay has increased their fees by 5% since 2019 and inflation has increased by 25%.  In the meantime, I added several more features and enhancements to my product, hence offering better value at $1575, but they are moving slower than a glacier.  Meanwhile, there was a vendor on Ebay that sold five ATgames virtual pinball machines at a price less than what I paid for materials and overhead for my machines.  It's a tougher market today, than it was 6 years ago.

 

 

Regards,

 

Rick 

[Tesla]

1. The ZK-TB21 got a TPA3116 inside? I did not know that. 

2.  No chime, but the LED Illuminates.

3. Okay, I understand, the first link I gave you supports up to 24V

4. Yes, I have seen those relays before.  However, I need to get my test bench back and do some experimenting on how to reduce this popping sound when the amp is powered off. 

5. I don't see the link on this page for that $10 part.

6. Does it switch all three speakers?

 

 

1. The ZK-TB21 I bought has dual TPA3116D2 chips.

 

2. Interesting. No, never had either one of mine do that. I never use the Bluetooth feature, but I wonder if it's interfering (with basic wired analog-audio operation on yours) ? 

 

3. OK

 

4-5. Yeah, I'm eval and testing. It should be here tomorrow. This one.

 

6. It's really only for 2.0 speakers. However, with Class-D amps (where speaker negatives are NOT shared/common ... we don't "switch" the negatives). Since this set of "switching for negative wires" goes unused ... YOU MIGHT be able to use it for the positive wire of a third speaker. Ya follow me? Definite smoke-test there. <smile>

 

And if you REALLY WANT TO switch all 4 wires of a 2.0 stereo pair, we might be able to cut the traces joining the negatives. AFAIK, all this would do is remove "amp failure protections" from one of the speakers.

 

The circuit is very simple. It could be cloned and expanded to 5.1 (or this unusual analog-audio 7.1 we use).

[Tesla]

Well, the AK-55 was a no-go.

 

It's loaded with features, drives some old Boston bookshelf speakers fair (distortion increases with volume-level), and mainly ... doesn't pop/thump on power On or Off.

 

But get this ... the (analog audio stereo input) AUX has some weird signal detection/over-signal protection built-into it. If the computer input (or even little-baby MP3 player) is too loud (or MP3 itself is sampled at too high a volume) it just mutes the speakers for a while.

 

It won't even reliably always pass the Windows Speaker Test (which I've never really seen fail when just messing with analog video).

 

Front (3.5mm) and Back (RCA) AUX ports behave the same. Also tested with baby Sansa MP3 player (uses TRS headphones) and it fails there also. It mostly fails when MP3 starts, but sometimes it cuts-out in the middle. It's acting like a low-line-level input but it's a common AUX input-jack. It's detecting normal audio (low to medium on little ear-buds) as overload-condition instead of actual high-voltage.

 

The FM-radio and SPDIF input both sorta work (with conditions). Only a few features work anywhere near 100% properly. Never got to testing the Bluetooth as the lack of pain-jane analog-audio input was a deal-breaker for me.

 

So, for $45 ... it's being returned to Amazon.

 

It's like a mini-Receiver that barely works. I sorta hate-it-now (as I don't normally really "do returns").

Edited by Tesla, 15 December 2025 - 02:34 AM.

[rickh]

>Well, the AK-55 was a no-go.

 

>It's loaded with features, drives some old Boston bookshelf speakers fair (distortion increases with volume-level), and mainly ... doesn't pop/thump on power On or Off.

 

>But get this ... the (analog audio stereo input) AUX has some weird signal detection/over-signal protection built-into it. If the computer input (or even little-baby MP3 player) is too loud (or MP3 itself is sampled at too high a >volume) it just mutes the speakers for a while.

 

>It won't even reliably always pass the Windows Speaker Test (which I've never really seen fail when just messing with analog video).

 

That is really odd.  The unit must have some type of signal processing circuitry in the front end.  So if the input signal exceeds a certain level, it shuts down and mutes?  Hell, they could have done the same using a couple of zeners or transorbs on the front end. 

 

Rick

[Tesla]

 

 

That is really odd.  The unit must have some type of signal processing circuitry in the front end.  So if the input signal exceeds a certain level, it shuts down and mutes?  

 

 

Correct.

 

I think it might be the result of their poorly designed (solid-state or software-based) solution to not "Don't Pop/Thump on Power On/Off" ... which actually seems to work.

 

Or, it might just be related to a failure in how the Amp detects which physical AUX-port (front or back) since there is really only one. 

 

However you slice it, they missed something somewhere. No trackable firmware levels or ability at this level of inexpensive asian product.

 

----------------

 

My $10 Speaker-Protection-Relay PCB will be here later today, and I might even have time to start on it.

 

I was thinking of my usual "modular design in plastic box" ... using RCA jacks on both Input side, and Output.

[Tesla]

1. The ZK-TB21 I bought has dual TPA3116D2 chips.

 

4-5. Yeah, I'm eval and testing. It should be here tomorrow. This one.

 

6. It's really only for 2.0 speakers. However, with Class-D amps (where speaker negatives are NOT shared/common ... we don't "switch" the negatives). 

 

 

So, I hooked-up the new $10 "Speaker Protection by Relays" PCB with simple-direct wires to the terminals and speakers.

 

The good-news is that is works as designed. It delays the connection of the speakers to the ZK-TB21 Amp after power-On, and ALSO after power-Off. 

 

The bad-news is that delaying the disconnection of the speakers at power-Off is the opposite of I what I needed. I needed the speakers disconnected slightly before the Amp so it's can't pop/thump them. Also, the ZK-TB21 Amp already provides a delayed connection to the input source at startup (so that feature of the board is redundant in my setup). The ZK-TB21 has never had a power-On pop/thump problem. 

 

It does seem to work at 19v (as well as more normal 12v). I did notice some quirks, but since it doesn't suit my needs, no use taking the time to document them here (you can just read Amazon reviews).

 

I've kinda given-up on this issue. I suppose I'll just "live with it" like everyone else that has it. I was looking for an inexpensive automated solution. If it turns-into a real problem I suppose I'll just leave the Amps on most of the time or get a cheap manual Speaker Switch Box(s) and have to "press another button" during startup and shut-down. 

 

A word of advice. Don't do like I initially did and tear-apart your pinball-cabinet. Just test on bench with a pair of speakers and a little (self contained) MP3-Player for the stereo source material. I eventually figured it out for myself. Not sure why I did that as I know better. <smile>

 

Luckily, the ZK-TB21 amps are fairly bullet-proof, so my cabinet is now all back together as before. Actually, I'm now only using one of these for my 3-inch AtGames speakers (which are surprisingly pretty fair). My other 2 amps are integrated in combo-units ... a 2.0 Dell and a good-sounding 2.1 asian from Parts-Express. I un-installed the second ZK-TB21, as it wasn't a real discrete (2nd) Sub-Woofer anyway (just had a single old Bookshelf-Speaker connected). Plus now, I have a physical DOF Relay-Knocker.

 

The above (Hybrid 7.1) is pretty nice compared to what I had before (plain 2.0). If I was to upgrade it later to a more high-end conventional SSF-7.1 (with Transducers and Shakers) instead of buying more ZK-TB21's, I think it might be wise to just go ahead and invest in this nicely-designed pinball-cabinet amp, and use that as a better foundation to build and expand on. There is really nothing like it on Amazon.

 

https://www.clevelan...extra-amplifier

Edited by Tesla, 16 December 2025 - 02:39 PM.

[rickh]

Tesla, I would need to do a couple of experiments before I would have something concrete to say, but using past experience I have the following:

• Placing a relay between the Amp output and speakers requires that there be no DC offset from the amp during relay switching, as this would cause the speakers to pop.
• Adding a large filter cap to the amplifier might allow time for the relay to open before the amp shuts down.  This might prevent popping. 

  As for that Cleveland Amplifier, it looks very nice and it doesn't appear to be a rebranding.  The price also looks attractive.  However, I suspect that it is a class D amplifier too.  It appears to have two 2.1 amplifiers with a parametric equalizer similar if not identical to the ZK-TB21 and a two channel stereo amplifier.  If you purchase one, it would be awesome if you could do a full review.

 

Regards.

 

Rick

[rickh]

I found this $13 USD 2.1 relay system that goes up to 16VDC.  You can use a buck cut regulator to bring your 19V down to 16V.   https://www.aliexpre..._p_origin_prod:

[Tesla]

I found this $13 USD 2.1 relay system that goes up to 16VDC.  You can use a buck cut regulator to bring your 19V down to 16V.   https://www.aliexpre..._p_origin_prod:

 

Nice find. Here is a clone at Amazon.

 

This one is better than the one I tried before:
- 2.1 (3 channel) instead of just 2.0
- Full Opto isolation
- Works without more complex UPC1237 (I think simpler might be better here).
- Specifically supports Class-D Amps with isolated speaker negatives
- Specifically supports using the same power-supply for this PCB and amp.

- Delayed relay-engage on Amp turn-On, but Instant Relay DISENGAGE on Amp turn-Off (what I need in my scenario with ZK-TB21's ).

 

Since you took the time to find it for me, for another $10, I'll try it. Thanks.

 

Over at Amazon, can you please link me to a "good but inexpensive" buck-cut-regulator (I've heard of them but I've never purchased or used one before). Adjustable output (if that is a common feature). No display is required as I can just use my DMM to adjust (even under load).

Edited by Tesla, 22 December 2025 - 09:01 PM.

[rickh]

Tesla,

 

Here is the link https://www.amazon.c...in_title_6&th=1

 

As for those relays, they are not DPDT (They are SRD 12VDC SL C relays, SPDT) so I doubt they are switching both positive and negative legs on the output.  However, the negatives are isolated. 

Edited by rickh, 16 December 2025 - 05:29 PM.

[Tesla]

Tesla,

 

Here is the link https://www.amazon.c...in_title_6&th=1

 

As for those relays, they are not DPDT (They are SRD 12VDC SL C relays, SPDT) so I doubt they are switching both positive and negative legs on the output.  However, the negatives are isolated. 

 

Good enough at $2 a piece huh? Excellent.

 

If you look at the backside of the PCB, you see that the traces for the negatives go straight across to the other side (so definitely NOT switched). But isolated and not all shorted together in a common speaker ground like the other one. It was a good find on your part. I'm not sure why it was not appearing in my previous searches (well, it appears to incorrectly classified).

[Tesla]

Tesla,

 

Here is the link https://www.amazon.c...in_title_6&th=1

 

As for those relays, they are not DPDT (They are SRD 12VDC SL C relays, SPDT) so I doubt they are switching both positive and negative legs on the output.  However, the negatives are isolated. 

 

On the PCBs I used to support and repair, they often had circuits like these but we just called them "DC-to-DC Converters". Difference is they were usually fixed to a certain voltage. Is that the difference? Those were fixed, but when they are modular like this and adjustable, they are called "Buck Converters"?

 

On Ali-Express and Amazon, they all seem very similarly built. I also find it interesting than none of these Buck Converters seem to have fuses (not even slow-blow ones). Not that I'm going to try to push the limits, but I wonder how over-voltage or over-amping is handled on these?

Edited by Tesla, 16 December 2025 - 07:42 PM.

[Tesla]

Nice find. Here is a clone at Amazon.

 

This one is better than the one I tried before:
- 2.1 (3 channel) instead of just 2.0
- Full Opto isolation
- Works without more complex UPC1237 (I think simpler might be better here).
- Specifically supports Class-D Amps with isolated speaker negatives
- Specifically supports using the same power-supply for this PCB and amp.

- Delayed relay-engage on Amp turn-On, but Instant Relay DISENGAGE on Amp turn-Off (what I need in my scenario with ZK-TB21's ).

 

Since you took the time to find it for me, for another $10, I'll try it. Thanks.

 

 

So, I got a chance to bench test this.

TL:DR I finally got it to work (seems like just barely, but passes).

 

My bench-testing setup (thorough, but as simple as possible for now).

 

a ZK-TB21
3 bookshelf speakers
300W 2.1-Ch Class-D Amp & Speaker Protection 3-Relay PCB-Module

a single 12v DC @ 3amps SMPS

MP3-Player for stereo analog-audio input (the music) over 3.5mm TRS-cable

simple dedicated power-strip

 

Sounds fine. No issues with speakers or having it all powered by a single SMPS. This ALMOST works at power-off time also (the new PCB really tries). It's just that when you cut the power (at the power-strip ... as we do with the cabinets) the ZK-TB21 does the pop/thump instantly (like within 200ms). It's still just barely faster than the new 3-relay-PCB (so sound is still transmitted to speakers).

 

The only way I could get it to work consistently-quiet was to connect a second little 12v-DC@1amp power-supply to the 3-relay-pcb separately. And it has to be one that the output-power drops instantly when power is cut to it (like it can't keep outputting 12v for even 1 extra-second).

Edited by Tesla, 22 December 2025 - 09:21 PM.

[rickh]

Tesla,

 

I would call that a win.  So, are you going to buy me a Christmas beer?

[Tesla]

Tesla,

 

I would call that a win.  

 

Yes, me too. It's definitely the correct module for this purpose.

I still might add a Shelly Gen4 Switch to turn off the 3-Relay-Module a little earlier with a Windows batch file on ShutDown.

 

And not sure if I mentioned it before, but I would like ultimate solution to be expandable (with more ZK-TB21 amps or similar) by just adding another of these 3-Relay-Modules. 

So, are you going to buy me a Christmas beer?

 

Sure. How?

Edited by Tesla, 24 December 2025 - 12:41 AM.

[Tesla]

So, I ordered those inexpensive ($2 each) Buck-Converters linked above, but also some of these with a display. Other than that, they look about the same. One button switches between Input and Output voltage (very handy), and the other button turns the display on/off. Pretty cool for $5 each.

 

I also ordered (my first) Shelly-1 (Gen-4) Relay Switch. They say is also works offline/locally and you can control it with a Windows batch-file. The switch-contacts are "dry" or potential-free ... meaning they can switch AC or DC voltage and it doesn't have to match the voltage you are running it with.

 

I plan to switch the 12-volts going to the 3-Relay Speaker Protection PCB(s) ... ON during Windows-Startup and OFF during Windows-ShutDown (well before the ZK-TB21 turns-off and does its pop/thump noise). I use a power-sensing Smart Power-Strip with the computer as the control. If all goes as planned, the Speakers will be disconnected well before the Amp(s) finally lose power (at the very end of power-down sequence), so no way for the speakers to pop/thump any more.

Edited by Tesla, 24 December 2025 - 05:31 AM.