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Bluetooth speaker build

G

GreenMax

New Member
I don't want any hate for being a novice I'm new to this sorry

I am converting a bookshelf speaker into a Bluetooth speaker, and I was wondering if this amp "TDA7492P" with 50w on both channels could power one "Technics SB-CS50".

All I know about the speaker is that it says this:
Music 60W
Input 120W
Impedance 8ohms

Will the amp provide enough power? Im unsure
 
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Yes, that should be enough power. But if you plan on putting the amp in the speaker cabinet, you may want to try it external first. Make sure you like the sound before you cut or drill into the speaker cabinet.
 
With such minimal cooling, I doubt that amp is capable of putting out anywhere near 50 watts/channel. Probably 1/10th of that, max. Plus you'll only be able to use one channel, as it doesn't appear to support bridging - you can't just send both outputs to one speaker (I'm assuming you're talking about just a single speaker here) as it will either not work or possibly fry the board. Using a single channel isn't necessarily a bad thing, but you'll have to convert your signal to mono before feeding to the amp (there are inexpensive converters to do this).

Are you attempting to create a portable system? If not, there are better ways to create a bluetooth system.
 
swechsler said:
With such minimal cooling, I doubt that amp is capable of putting out anywhere near 50 watts/channel. Probably 1/10th of that, max. Plus you'll only be able to use one channel, as it doesn't appear to support bridging - you can't just send both outputs to one speaker (I'm assuming you're talking about just a single speaker here) as it will either not work or possibly fry the board. Using a single channel isn't necessarily a bad thing, but you'll have to convert your signal to mono before feeding to the amp (there are inexpensive converters to do this).

Are you attempting to create a portable system? If not, there are better ways to create a bluetooth system.
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I am thinking of making it portable, plug and play sort of thing.

I want both channels through one speaker if that's possible, if I send mono from my phone and plug the speaker into only one channel will that work?

Also can you think of any amps that would suit my needs to play through one speaker? One that supports bridging what not
 
Ttech said:
Yes, that should be enough power. But if you plan on putting the amp in the speaker cabinet, you may want to try it external first. Make sure you like the sound before you cut or drill into the speaker cabinet.
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Someone said it won't be enough your saying it will be enough power? Confused
 
GreenMax said:
I am thinking of making it portable, plug and play sort of thing.
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If you're going to try to run it off batteries, IMO you're better off purchasing one of the Bluetooth speakers on the market. They'll be optimized for battery power, with high efficiency speakers and amplifier. It's likely that this amp is not optimized in that way. I also couldn't find any info on these speakers to find out their sensitivity (efficiency) rating.

BTW, is there any reason you don't want to use a packaged Bluetooth speaker instead?
GreenMax said:
I want both channels through one speaker if that's possible, if I send mono from my phone and plug the speaker into only one channel will that work?
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Yes, the other channel won't consume much power if it's idle.
GreenMax said:
Also can you think of any amps that would suit my needs to play through one speaker? One that supports bridging what not
Click to expand...
Not anywhere near this price range.
 
swechsler said:
If you're going to try to run it off batteries, IMO you're better off purchasing one of the Bluetooth speakers on the market. They'll be optimized for battery power, with high efficiency speakers and amplifier. It's likely that this amp is not optimized in that way. I also couldn't find any info on these speakers to find out their sensitivity (efficiency) rating.

BTW, is there any reason you don't want to use a packaged Bluetooth speaker instead?

Yes, the other channel won't consume much power if it's idle.

Not anywhere near this price range.
Click to expand...

The main aim was to get the loudness and quality of that bookshelf speaker into a portable package.
I've seen it done before by DIYPerks on YouTube (search
swechsler said:
If you're going to try to run it off batteries, IMO you're better off purchasing one of the Bluetooth speakers on the market. They'll be optimized for battery power, with high efficiency speakers and amplifier. It's likely that this amp is not optimized in that way. I also couldn't find any info on these speakers to find out their sensitivity (efficiency) rating.

BTW, is there any reason you don't want to use a packaged Bluetooth speaker instead?

Yes, the other channel won't consume much power if it's idle.

Not anywhere near this price range.
Click to expand...

I just wanted a retro boom box kind of setup.

Anyway Ive seen it done before with that amp by DIYperks on YouTube. Www.youtube.com/watch?v=N3k9lWz48rw

Would this work with one speaker? How can I make it work
 
Well you do notice in the video that he doesn't say how long it will play before the battery dies (for max playing time, go with D cells instead of AA). However, the speakers in the video look like Tannoy Mercury F1s, which are rated at 87dB sensitivity, which is probably pretty close to the Technics (I couldn't find any info online about those speakers, although this thread didn't speak highly of them). So yes, I think it will work (I still stand by my estimate of the actual power output, though); I'd just leave the other channel disconnected. Also, I'd probably test it out with a 12V power supply first, before purchasing the cells and holders, using an ammeter. With that, combined with the mAh spec for the battery cells, you should be able to calculate how long the battery will last. Here's a thread on an electronics forum discussing this exact subject.

I'm still concerned, however, about the lack of cooling for the amplifier IC*, and that's not addressed in the video (even an amp that puts out only a couple of watts would normally have some sort of heat sink).

*ETA: Answered, to some extent: The manual states that the amp is >= 90% efficient. Presumably (I assumed 90% for calculations) this means that with a power output of 5 watts, the chip would only need to dissipate .56 watts (I do note that a higher power version does include a heat sink and fan). If we further extrapolate, we can calculate the power consumption at 5W output and 12V input (NiMH cells are only 1.2 volts, compared to 1.5 volts for non-rechargeable) to be about 475 mA. With good quality, fully-charged NiMH AA cells, you should be able to get 4-5 hours of playing time.
 
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swechsler said:
Well you do notice in the video that he doesn't say how long it will play before the battery dies (for max playing time, go with D cells instead of AA). However, the speakers in the video look like Tannoy Mercury F1s, which are rated at 87dB sensitivity, which is probably pretty close to the Technics (I couldn't find any info online about those speakers, although this thread didn't speak highly of them). So yes, I think it will work (I still stand by my estimate of the actual power output, though); I'd just leave the other channel disconnected. Also, I'd probably test it out with a 12V power supply first, before purchasing the cells and holders, using an ammeter. With that, combined with the mAh spec for the battery cells, you should be able to calculate how long the battery will last. Here's a thread on an electronics forum discussing this exact subject.

I'm still concerned, however, about the lack of cooling for the amplifier IC*, and that's not addressed in the video (even an amp that puts out only a couple of watts would normally have some sort of heat sink).

*ETA: Answered, to some extent: The manual states that the amp is >= 90% efficient. Presumably (I assumed 90% for calculations) this means that with a power output of 5 watts, the chip would only need to dissipate .56 watts (I do note that a higher power version does include a heat sink and fan). If we further extrapolate, we can calculate the power consumption at 5W output and 12V input (NiMH cells are only 1.2 volts, compared to 1.5 volts for non-rechargeable) to be about 475 mA. With good quality, fully-charged NiMH AA cells, you should be able to get 4-5 hours of playing time.
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Surely if I leave one channel disconnected I will only get one channel from the speaker? Any way to get both channels into the Technics speaker?
 
GreenMax said:
Do you know how to send a mono signal into the amp by Bluetooth?
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Sorry, completely forgot that this was Bluetooth. It's certainly possibly, and probably not difficult, because Bluetooth functionality is on a separate module that's added on to the amplifier board. It would require connecting together the L+R pins on the Bluetooth module (they're probably adjacent, so it could be done with a solder bridge). Unfortunately, figuring out what pins they are might be a little difficult without a little electronics knowledge. The way I'd do it would be to send a signal to the Bluetooth amp without speakers attached, then I'd connect a cable to an input on a separate amp with a speaker attached, connect the shield of the cable to the ground of the amp board, then connect the signal wire of the cable to each pin, one by one, until
I got sound out of the speaker (the sound being played, not a buzz or hum). If you're lucky, you'll only get two pins with a viable signal, and those would be the pins that needed to be connected together.

ETA: Found the pinout.

HT1UiWAFNFbXXagOFbXH.jpg


Looks like you'd have to connect pin 39 to 37 and 38 to 36. I assume that would work without blowing anything up, but don't blame me if it doesn't work. They're balanced speaker outputs which I notice are sent to a capacitor and resistor on the main board before being sent to the amp IC, so it would probably be a better bet to connect the L/R terminals together after that (I've outlined the area in green in the pic below).

itblFNX.jpg
 
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swechsler said:
Sorry, completely forgot that this was Bluetooth. It's certainly possibly, and probably not difficult, because Bluetooth functionality is on a separate module that's added on to the amplifier board. It would require connecting together the L+R pins on the Bluetooth module (they're probably adjacent, so it could be done with a solder bridge). Unfortunately, figuring out what pins they are might be a little difficult without a little electronics knowledge. The way I'd do it would be to send a signal to the Bluetooth amp without speakers attached, then I'd connect a cable to an input on a separate amp with a speaker attached, connect the shield of the cable to the ground of the amp board, then connect the signal wire of the cable to each pin, one by one, until
I got sound out of the speaker (the sound being played, not a buzz or hum). If you're lucky, you'll only get two pins with a viable signal, and those would be the pins that needed to be connected together.

ETA: Found the pinout.

HT1UiWAFNFbXXagOFbXH.jpg


Looks like you'd have to connect pin 39 to 37 and 38 to 36. I assume that would work without blowing anything up, but don't blame me if it doesn't work. They're balanced speaker outputs which I notice are sent to a capacitor and resistor on the main board before being sent to the amp IC, so it would probably be a better bet to connect the L/R terminals together after that (I've outlined the area in green in the pic below).

itblFNX.jpg
Click to expand...
So solder together the pins you have outlined in green?
 
Well, not exactly. You'll see that those pins are connect to C1, C3, C8 and C9, which are further connected to R1, R2, R5 and R6. I'd connect the output of R5 to that of R1, and the output of R6 to that of R2.

Actually, what I'd really do is wait for someone who's more versed in electronics to come along and comment, to make sure I'm not just full of hot air.
 
swechsler said:
Well, not exactly. You'll see that those pins are connect to C1, C3, C8 and C9, which are further connected to R1, R2, R5 and R6. I'd connect the output of R5 to that of R1, and the output of R6 to that of R2.

Actually, what I'd really do is wait for someone who's more versed in electronics to come along and comment, to make sure I'm not just full of hot air.
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Hmmm not sure someone with that kind of know how will come along very quickly but okay, even if I could do that connecting those alternate pins (R6-R2 etc) would mean I would have to solder over R1 and so on? Surely that wouldn't work
 
kirkendoll said:
You can build a stereo to mono summoning box and just tie the two channels together to make mono, directions are on this website
http://www.rane.com/note109.html
I plan on building close to the same myself, I hope this helps.
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Thanks for your input I'm sure that would work if I had the knowledge, however I don't and all that terminology seems alien to me.
Is there no basic way to use a convert stereo to mono either Via a prebuilt transformer or a easy to build mixer maybe?
 
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Again the problem here is that you're working with speaker-level signals, there's really no good way to do that, as far as I know. If the link that kirkendoll pointed to is correct, simply connecting the two outputs of the bluetooth module is not the way to do it (although I've done it with line-level signals). If you wanted to do that anyway, you'd need to use insulated jumpers to avoid them shorting each other out. If you wanted to use the Rane method, I'd recommend the balanced summing box.

Theoretically you could do it with a transformer, but finding the correct one would be difficult, not to mention expensive. Also one site I found said that transformer-based summing went out in the 1950s.
 
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You could use apps such as BTmono, Blue Mono Sound, and Just One Ear to convert stereo to mono before being sent to the amplifier. These are for android devices, but I am sure Apple has similar apps.
 
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