DIY bluetooth speaker

[SentinelAeon]

I need data on this:

**broken link removed**

What i need is at what voltage i get what wattage. Since i got BMS and charger for 5S, maybe i could use my stepup.

 

[audioguru]

The Chinese amplifier module uses the new TDA7492P Rev6 version and is missing a heatsink on its bottom. The datasheet for this version shows 25W + 25W at 10% horrible clipping distortion into 8 ohms when the supply is 20V. As usual, ebay is wrong.

All the graphs do not show a supply higher than 20V.
At low distortion the power is 18W per channel into 8 ohms. If this power is continuous then the IC might shut down due to overheating.

 

[SentinelAeon]

If i understand this right, my last amp was better ? It was 2x25W with lower distortion ?

 

[audioguru]

This thread is too long, I cannot remember which IC version and which power supply voltage your last amplifier used.

The old Rev5 amplifier IC had its thermal pad on top for a heatsink attachment and with a 25V supply and 8 ohm speakers, produced 2 x 40W with horrible 10% distortion, about 32W per channel at 1% distortion and about 27W per channel at low distortion. With a 22V supply, it could produce 2 x 50W into 4 ohm speakers at 10% horrible distortion and produce about 37W per channel at low distortion.

10 times the power sounds twice as loud. 2 times the power is only a little louder but you will not notice if you do not quickly switch the 1times and 2times powers back and forth quickly.

 

[SentinelAeon]

I have a very simple question, i hope you can give me the answer.

Right now i power the bluetooth amp with 5 batteries in series, which gives me about 21 volts. I use dedicated charger and BMS. Now lets consider for a moment that i replace this with simply 5 batteries in parallel and step-up to produce 21 volts. Step-up is said to be 80%+ effective meaning 20% battery life will be wasted as heat. Apart from that, should i feel any difference in some other area or will speaker play as it did with 5 batteries in series, only that it will play a bit less time due to energy wasted on step-up, and on the positive side i can use a simple usb charger board for battery and can therefor charge the speaker with powerbank.

So, parallel + step-up vs in series. Will i hear/feel the difference ?

 

[audioguru]

You said you will use old laptop batteries that might have trouble producing the current needed by the amplifier.
With the batteries in parallel then you will not notice the 20% loss of power going into making heat in the voltage step-up circuit. 50% of the output power would be a small but noticeable drop in level.

 

[SentinelAeon]

Even the worst batteries put out 10A of power when shorted, the better ones more. So im ok with going parallel Thank you

 

[SentinelAeon]

Oh and if anyone has any other comments bout using step-up i will be glad of opinions. I would hate to use step-up and find out that sound is less loud or crappier

Also, would someone comment on those small bluetooth speakers using passive radiators, how do they manage to get as much bass as they do ? I even saw that little JBL speaker which is the size of a fist andi t has better bass then my big speaker, i just dont get it.

 

[audioguru]

A passive radiator replaces the port in a bass-reflex enclosure. It extends the low frequency response lower but with a doubly sharp drop-off.
I was amazed at the bass produced by a little Bose stereo Bluetooth speaker on demo at Cosco until I saw its very high price.
My son bought a cheap Chinese copy for me but it produces no bass.
I guess you get what you pay for.

 

[rjenkinsgb]

Also, would someone comment on those small bluetooth speakers using passive radiators, how do they manage to get as much bass as they do ? I even saw that little JBL speaker which is the size of a fist andi t has better bass then my big speaker, i just dont get it.

I've got a JBL "Charge 2+". That has amazing low frequency response for the size; bass guitars and bass drums are very clear but still with a good smooth overall frequency response, it's not "boomy" like a far more expensive Bose model one of my friends has.


The end panels on this are more like waterproofing membranes over the ends, which can incidentally be seen to vibrate, than true passive radiators (as my big Goodmans cabs have).
The casing is far too small to be tuned in any way.

The "secret" appears to be some very well designed and somewhat unusual long-travel speakers plus good amps and well matched equalisation.
These are the speakers in the model I have:

(Photo from an ifixit teardown, here: https://www.ifixit.com/Guide/JBL+Charge+2+Plus+full+disassembly/97318 )

 

[SentinelAeon]

I guess i will try to play around with radiators and see if i can produce any bass at all while speaker being compact, being compact is most important cause i dont have much space in my backpack. Loudness is second i guess, quality/bass is less important since we usualy have some beers when we listen to it and its not that important, though if i could improve bass even a little, i wouldnt say no to that.

Would anyone else to confirm that going parallel with stepup will produce the same quality/bass etc. as with 5 batteries in series (ofcourse voltage will be same in both cases)

 

[audioguru]

A cheap little 3" speaker like in a cheap clock radio cannot produce bass. Medium priced 4" speakers are available that produce pretty good bass when they are in an enclosure designed for their detailed spec's. For a more expensive smaller speaker you need an amplifier with a higher output power so that bass boost can be used.

 

[SentinelAeon]

I have a question. Lets say i use this 2x25W amplifier and power it with a DC adapter that is strong enough to power it. And i use killawatt to measure wattage. So i plug killawatt into AC socket, plug my DC adapter into it and power on the speakers. Will this wattage i get the correct one ? Or is here the same problem with Hz as is with measuring with multimeter ? I have no other measuring device apart from cheap multimeter and this killawatt and i would like to get appropriate wattage that my bluetooth speaker is using.

If the problem with Hz is same in using killawatt, would it help to get sound of certain Hz, play it and then measure it ?

 

[rjenkinsgb]

That will show you the total input power to the amp & any other connected electronics.

The output power depends on the amp efficiency.
For a typical analog (Class AB) amp, the efficiency is often around 40%; eg 100W input to give 40W RMS out.

Digital amps (Class D etc) can be somewhere around 80 - 90% efficient, so possibly 50W in for 40W RAM out..

Measuring at the mains input the frequency is just 50 or 60Hz, the audio frequency or range through the amp does not matter.
Subtract the idle power level (with everything working but volume turned to zero) from the full load power, to get the amount used by the actual amplifier.

 

[SentinelAeon]

Great, thank you. I am using this amp:

https://www.st.com/en/audio-ics/tda7492p.html

Ofcourse i ordered it from ebay for 7$ so its obviously fake, but can i belive that if the original has 90% efficiency, this one has at least 80% ? Because i am interested in both total power draw and the actual power going to the speakers. The reasons are obvious, i am interested in total power so i can calculate how long my batteries will hold. And i am interested in actual power going to the speakers to know how powerful my system is

 

[audioguru]

The datasheet shows that with a 20V supply, the output power into 8 ohm speakers is 25W with horrible 10% distortion or 21W with 1% distortion that is still obvious. It is 18W with low distortion. If you are deaf then you will not hear the distortion.

A fake IC might produce an output of only 4W or less.

I doubt that you play a continuous full power tone to calculate how long the battery lasts. Music and voices are at full power only occasionally, maybe you never play at full blast.

 

[rjenkinsgb]

Before you start running your audio module flat out, see how the heatsink is attached - I've bought a couple of batches of 100W modules and all the heatsinks are just stuck with what appears to be silicone rubber bath seal type stuff - and thick globs of it in some case.

All the ICs appear genuine, but I would not like to use them as they were.

I've just posted an item re. that here, with photos:

Ebay TPA3116 50+50 / 100W amp modules - good and the bad features, plus a warning.

Hi all, I'm gradually rebuilding my home automation setup and part of that is updating the audio system, to stereo and a bit more power capability. I've bought a few TPA3116-based amp boards from ebay, costing around £4 to £5 each. I liked the look of the amp IC from the Texas data sheet as...

www.electro-tech-online.com

 

[SentinelAeon]

Ok i will be careful about it. The one in my speaker came without heatsink and as far as i remember i didnt include any heatsink and its been playing ok for quite a while. I guess it would be smart to add a heatsink to prevent overheating. Or at least measure temp.

About distortion i would like to ask how to make sure i get lower distortion. Lets say i use 25V as opossed to 21V i am using now, is this better or worse with 8 ohm speakers ? I hope u can explain to me.

 

[rjenkinsgb]

With conventional analog amps, the distortion generally increases rapidly as you get to teh power limit; at 50 to possibly 70% power it will be far lower than 90 - 100%.
(Though that is very dependant on the amp design).

With digital amps - I'm not sure... The one in that link are the first I've bought and I've not got them set up yet.

I'd expect some increase in distortion as you get near maximum output for a given supply voltage?
I'm planning to only run mine at a fraction of the rated power, and on 24V, so I'm hoping the quality is OK!

 

[audioguru]

About distortion i would like to ask how to make sure i get lower distortion. Lets say i use 25V as opossed to 21V i am using now, is this better or worse with 8 ohm speakers ? I hope u can explain to me.

ANY amplifier produces extreme distortion when its output is clipping. It is clipping when the output voltage swing is trying to be higher than is possible. Therefore with a higher supply voltage then the maximum undistorted output power will be higher.