stereo to mono problem

[SentinelAeon]

Hello, i am trying to convert stereo into mono on my bluetooth amplifier/receiver, since i am using a woofer + tweeter setup. I included a picture of how i solder the pins together. Right now the pot is up to a maximum, which means the pins are effectively shorted together. I know ur supposed to use a resistor but i am looking for a max SPL, even if the amplifier dies after a few months. The amplifier chip itself is TPA3116D2. The amplifier board is ZK-502C hifi.

Problem 1: Even when the pins are shorted together, i get on average about 4-5dB less SPL than i would otherwise and i dont understand why since i am not using any resistors and pot doesnt offer any resistance.

Problem 2: When pins are shorted together, the speaker amplifier will shut down and restart if the pot is over 80% volume. This happens even if the speakers are not connected ! I am really wondering why.

Question: Is there any way to get around this since i need every single last dB i can get, so i cant lose even 1dB, let alone 3dB.

 

[SentinelAeon]

Tony Stewart Thread is to long to read all of it, so yes, 6S battery pack with 10A cells, plus about 4000uF worth of capacitors on the battery pack. Was thinking of going to 10000uF but didnt find good data whether that would do any good since 2x50W is not really that much.

 

[audioguru]

An older style Lithium battery cell is 4.2V fully charged. Then your six in series produce 25.2V then slowly drops and the battery discharges.
I assume that the IC is made by Texas Instruments and is not a Chinese copy with lower specs. The datasheet for the TPA3116 IC says that with a 25.2V supply it produces 70W into 4 ohms per channel with 1% of distortion. With your 25.2V supply, it produces 60W per channel and the distortion is very low at 0.05% or 80W per channel and the distortion is very high at 10%.

The IC protects itself and shuts down if it is overloaded or if it gets too hot.

Like almost all power amplifiers, it produces "clipping distortion" when input signal level and its gain are too high and try forcing the output peak-to-peak level higher than is limited by the power supply voltage and come voltage losses. 70W into 4 ohms is a signal that is 16.8V RMS or 47.5Vp-p. Your 25.2V battery is effectively doubled to 50.4V since the amplifier is BTL (it drives both speaker wires).

I think your "power meter" measures only 50Hz or 60Hz electricity, not the higher frequencies produced by the amplifier when it produces many sounds.

 

[Tony Stewart]

When your batteries decline from 10 thousand Farads in series and in charge level they rise in ESR from 25 mohms * 6 rapidly. That's when low ESR caps may help. Otherwise 4 mF vs 10 mF does not store energy for very long into 2 ohms (milliseconds) so it requires testing to verify supply stability.

You can boost your bass 10 dB by putting the speaker on the inside corner of a building by reducing the wave beam angle. That is like tripling your battery voltage.

1 dB won't make any difference even if sober.

 

[christinescoms]

Just wanted to say i put the project on hold for now, not enough time, no way to get needed materials, will use my usual speaker which should be ok since its a privat barbeque. But it would be cool if we keep the thread open to throw around some ideas.

christinescoms: feel free to post a question

audioguru: I know, maybe i was to harsh cause i was under extreme time pressure. I want quality ofcourse, but SPL and bass are first and second, quality is third. The problem is also that i simply fail to notice the difference a lot of the time. And while my hearing at lower frequencies is perfect (i have perfect pitch xD), i have very bad hearing of higher frequencies, above 10.000Hz i barely hear anything. Was like this ever since i was a child. Thats why in the beginning i didnt understand why i even need a tweeter.

To answer my stereo - mono question i posted a schematic i drew a while ago for someone else. Where there is R written, thats a resistor. Value depends. Remember even without resistor i lose 3-5dB and i can hear that a LOT (3dB is about 24% SPL, very clearly heard by me). I tried 10 ohms which is to low to protect the channels. I tried 1000 ohms which might be ok, and someone here said i might even try 100 ohms cause the bluetooth receiver might be for the headphones.
Andrew Tate Life
You said something about me being able to get 80W into the woofer when i use 2 separate mono channels. But wouldn't that blow the amplifier ? I thought amplifier is able to suply just 50W per channel.
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A bonus question about the boost. We talked before that i can replace 2 resistors on the amplifier board to get a +4dB boost which is very welcome. But would that mean i would also use double the power ? Wouldnt that just blow the amp ? And another funny thing. When i mix stereo into mono i lose 3-5dB, dB meter says that and i can very clearly notice the difference. But there doesn't seem to be any difference in power consumption. Its still like 65W combined. Shouldn't it be like 35W if its 3-5dB more quiet ? Its like i am using the same power but getting 3-5dB less out, which doesn't make any sense.

also thank you for your suggestion

 

[carenzop]

it is much better to use one channel playing the woofer and use the other channel playing the tweeter so that when the woofer channel is clipping then the tweeter channel dos not play the woofer channel's distortion harmonics, resulting in louder sounds which is wanted.
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[audioguru]

Yes, it is good to have separate amplifiers for a tweeter and a woofer so that woofer clipping distortion can be reduced.

Elliot Sound Products.com shows bi-amplifying creates a good increase in output level when the sounds are symmetrical (sinewaves) but many sounds in music and speech are not symmetrical:

 

[SentinelAeon]

Been a long time since i posted here, mainly because the speaker i made for my birthday party was a success. But just a few things to clarify here:

1) I used that TPA3116 chip on board. I bridged the channels but this time used a higher resistors to protect receiver lines. Dont remember what it was, maybe 1000 ohms ? Because as it turns out, it wasnt the resistors that were stealing the 3-5dB SPL - it was only the fact that i bridged the channels. You bridge channels even without a resistor, you lose 3-5dB, depending on the song (mostly hard rock and metal, barely noticable in electro music). So including resistors solved the issue with amplifier disconecting at max volume. Remember, the amplifier would disconect even if i didnt connect any speakers. Just turning it on, setting volume at 100% and playing a song would restart the amp. Even with no load. Thats solved now.

2) For those moments when i want those extra 3-5dB, i made 3 little switches that i turn on when i want to switch to stereo mode. Scheme is on previous page. Basicaly 1 of the switches either bridges or unbridges the channels. And the other 2 switches either connect or bypass the resistors protecting the receiver lines.

3) Using Dayton audio TCP115-4 and this amplifier, i dont think i need to waste time on additional boost of the amplifier by changing its settings (like we talked, in manual of the amp you can replace some resistors or caps to get some extra boost). Because i am pretty sure i am driving the TCP115-4 to and over its limits as it is. At 100% volume it will slightly distort and the cone is moving pretty wildly. Now unless there is something i am missing, like that if i somehow eliminate distortion and add clean boost, i think that in my hunt for more SPL i will either need to choose a higher sensitivity speaker (and lose like 10-30Mhz F3) or try to find a bigger speaker (TCP115-4 is 4", maybe go for 4.5" or 5") that will work well in only slightly bigger enclosure to give me same bass level and some more SPL.

But overall i have to say i am extremely impressed with the speaker and with the response of my friends and others who saw it. We really had a good time. Considering i have zero previous knowledge about this things so i was learning as i went and choose basicaly the cheapest materials i could, it brought a lot of pleasure to me and people partying with us. I do want to dive deeper into this in the future though and make a speaker that someone could use for the quality of the sound. Its great for less quality music like rock and electro, but i wouldn't feel comfortable giving such speaker to my dad to listen to classical music.

 

[audioguru]

The TPA3116 amplifier IC already has each of its channels bridged so that its output voltage and current are almost double a single output. Then the output power is 3.5 times to 4 times higher. Maybe you paralleled its outputs instead so that there is a little less output power loss when it is heavily loaded with a 4 ohms speaker.

The Texas instruments TPA3116 is rated to produce 50W into 4 ohms with horrible 10% distortion or 25W at low distortion with a 21V supply.
Maybe your IC is a Chinese poor copy or an American factory reject. The heatsink is probably too small and maybe thermal compound to pass the heating is missing.
Your higher supply voltage and higher rock noises distortion probably overloads and overheats the IC which caused it to shutdown until you paralleled the outputs.

 

[pako202]

Hello, first of all forgive my English, I use the translator.
I am building a speaker without a battery, it is a copy of the marshall woburn.
I have read all the messages and now I am wondering how it would be better...
1 mono amplifier for 2 5.15" 8ohm wofers and another mono amplifier for 2 tweeters 4ohm

or a mono amplifier for 1 wofer and 1 tweeter and another mono amplifier for the other wofer and the other tweeter?

both for one way and for another with crossover.

I have a mono amplifier and another stereo but if it is better to buy another mono instead of modifying the stereo, I ask for one

 

[audioguru]

Pako, your single speaker has two little 8 ohms woofers and two 4 ohms tweeters.
The speakers should all be 8 ohms so that they are 4 ohms when parallel for the woofer amplifier and 4 ohms when parallel for the tweeter amplifier and both amplifiers will produce the same power output.
You need a hidden attenuator to match the loudness from the tweeters to the lower loudness of the woofers.
You need a crossover circuit designed for the specs of the speakers.

Use a stereo amplifier that can drive 4 ohms per channel. It should have one volume control that controls the volume of both channels at the same time.

 

[pako202]

My intention is to put a preamp with tone control before the amp and a crossover after it. Those are the components that I had planned to mount, a low-pass filter for a mono amplifier with 2 8ohm wofers in parallel so that the result is 4ohm, and a stereo amplifier for the two 4ohm tweeters.

https://es.aliexpress.com/item/4001339349273.html?spm=a2g0o.order_list.order_list_main.22.21ef194djIyTzy&gatewayAdapt=glo2esp

https://es.aliexpress.com/item/1005001702682661.html?spm=a2g0o.order_list.order_list_main.46.21ef194d5ZWnvL&gatewayAdapt=glo2esp

https://es.aliexpress.com/item/1005004442927589.html?spm=a2g0o.order_list.order_list_main.35.21ef194d5ZWnvL&gatewayAdapt=glo2esp

https://es.aliexpress.com/item/1005004187992732.html?spm=a2g0o.order_list.order_list_main.16.21ef194d5ZWnvL&gatewayAdapt=glo2esp

 

[audioguru]

Pako:
1) The mono amplifier feeds 100W into 2 ohms or 60W into 4 ohms when the supply is 24V. 30W for each 8 ohms woofer. Will your little woofers survive 30W each?
2) The IC in the tone controls circuit is obsolete and AliExpress says no audio specs like gain and distortion.
3) The stereo amplifier produces 60W into 4 ohms per channel when the supply is 24V. 30W for each 4 ohms tweeter.

You have no important crossover network (3kHz highpass to prevent the tweeters from blowing up when fed lower frequencies and a 3kHz lowpass to prevent the woofers from shrieking).
The 300Hz lowpass filter is for a sub-woofer that you do not have and do not need.

 

[pako202]

thanks for the help. the wofers are 50w rms sony. and what tone controller do you recommend?

 

[audioguru]

A 5" woofer is too small to play many low frequencies. They play only mid-bass. Will your speaker play only a guitar?
A tone controls circuit is usually made with a modern dual audio opamp.

 

[pako202]

The speaker is to play music of all kinds, to listen at home

 

[audioguru]

Mono for a home audio system?
I use stereo for many years, some people use surround sound with 5 channels.

I modified my my clock radio to play 1W wideband mono into a 6.5" woofer in a ported enclosure and 3rd-order crossover network with a 3/4" tweeter.

My 2 TVs and pc have stereo sound systems.

 

[Nigel Goodwin]

thanks for the help. the wofers are 50w rms sony. and what tone controller do you recommend?

As an ex-Sony service engineer I've seen a lot of Sony speakers. They might say 50W RMS on the back, but when you break in to them (they aren't made to come apart) you find a little speaker that says "10W made in China"

This isn't exclusive to Sony, all lower cost manufacturers are the same - you have to buy specialist mid/high end speaker systems to get decent honest specifications.

 

[audioguru]

I found a pair of large Sony speakers thrown out onto the curb. The labels said SONY in large letters then its said, "made in Canada". The enclosures were high quality.
The 10" woofers were the cheapest I have ever seen and produced only mid-bass. The tweeters were ordinary 3" clock radio speakers and were burnt out. The crossover network was only a single capacitor.

The cost was kept down because there was no expensive shipping from Japan. The manager here knew nothing about sound systems.

 

[pako202]

I remind you that a portable speaker

https://www.amazon.com/-/es/Marshall-Altavoz-Bluetooth-inal%C3%A1mbrico-Woburn/dp/B07HPM264C?th=1

NIGEL el sony que tengo tiene esta referencia 1-505-235-13
I have measured the sony and they are 6ohm

 

[pako202]

This is what I had planned to mount and these crossovers