Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Building homemade digital jukebox need amp (Read 7460 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Building homemade digital jukebox need amp

I am currently building a Homemade jukebox with coin acceptor. I am using ubuntu as the base operating system and have built my own software for the interface below is the interface after a couple of days development. It is nearly finished now. It is being controlled from a touchscreen and credits are added from a coin mech attached to a arduino

https://www.youtube.com/watch?v=U6ri5bDWp3I

I need to power some passive speakers and need an amp that will fit in the Cabinet for the jukebox, there are 4 speakers and they are labeled 150 watt. 8/4 ohms.

Would using a car amp be appropriate for this or should I be using something else, I am just thinking of size requirements and the fact that there will be no access to controls on the amp

Building homemade digital jukebox need amp

Reply #1 –
A car amp would require a high-current 12V supply. I would go for one of the class D chip amp designs, maybe based on the TPA3116D2 - ebay has a bunch of ready-yo-use modules.

P.S. cool project - I still have the selector part of an old jukebox that I intended to use as a front-end for my music player...

Building homemade digital jukebox need amp

Reply #2 –
You could use a car amp but it might not drive them to their full potential.

Building homemade digital jukebox need amp

Reply #3 –
could I not use the 12v line on a molex connection?

Building homemade digital jukebox need amp

Reply #4 –
Quote from: tombruton87 on
could I not use the 12v line on a molex connection?

Not unless the car amp is quite small.  A single 12v molex does not have enough current capacity.

If you are using a PC power supply and it has PCIe video card power cables those would probably do.  You would need to figure out the current draw of the amp and likely hook up more than one of the connectors.  It may need a fairly beefy PC power supply.

Building homemade digital jukebox need amp

Reply #5 –
Quote
Would using a car amp be appropriate for this
No.  Just look for a power amplifier.    High-power car amplifiers require LOTS of Current at 12V.  If you want something a little smaller/cheaper, try Parts Express.  If this is for home use, 20W is probably plenty of power.

Quote
I need to power some passive speakers and need an amp that will fit in the Cabinet for the jukebox, there are 4 speakers and they are labeled 150 watt. 8/4 ohms.
This is an older jukebox you are updating?      That's a little confusing...  The only way they can be 4 and 8 Ohms is if they have a dual voice coil (with 3 or 4 terminals).  How many terminals are on the speaker?  If there are only two terminals on the speaker, the "safe" thing to do is to assume they are 4-Ohms.

When you wire impedance/resistance in parallel, the impedance is cut in half.  A pair of 8-Ohm speakers on the left & right is 4-Ohms on each side, and most amps can handle that.    But, a pair of 4-Ohm speakers in parallel is 2-Ohms.    Your options are to look an amp that can handle 2-Ohms, or use a pair of stereo amps.  Or, "cross your fingers" and hope the impedance load is OK....

The power ratings on a speaker are basically the "maximum" rating.  So, 150W doesn't mean you need a 150W amplifier.    You can probably get-away with a smaller amplifier, or you can use a bigger amplifier, unless you "go crazy" with the volume.

Or....  Are all of those speakers the same size, or do you have a woofer and tweeter on both sides?  If it's a woofer & tweeter, you'll need a crossover.   

And if there is no tweeter, you might want to consider adding one (along with a crossover) to improve the high frequencies.

Building homemade digital jukebox need amp

Reply #6 –
Quote from: DVDdoug on
Quote
Would using a car amp be appropriate for this
No.  Just look for a power amplifier.    High-power car amplifiers require LOTS of Current at 12V. 


Have you looked at a PC power supply recently?  $30 gets you 30+ amps @12v from a name brand.  I've used car amplifiers before in projects, they're quite power efficient, and at reasonable volume levels the current load is moderate. 

Building homemade digital jukebox need amp

Reply #7 –
Quote from: tombruton87 on
could I not use the 12v line on a molex connection?


You could. Here are some considerations:

(1) The PC power supply puts out 12 volts but car audio gear is really designed for 14.7 volts which is almost 25% more than 12 volts. Figure on obtaining at least 40% less power than rated. And of course the power ratings on most car audio gear is from outer space. It's not unusual to find car audio amps rated at 100 watts when they can really deliver about 15 watts going downhill with a tailwind.

(2) If you exceed the current limits of the PC power supply for even an instant the whole system will shut down instantly.

(3) It would be wise to put a very large electrolytic cap across the 12 volt supply to forestall (2).  But that cap may keep the PC power supply from starting up because of its heavy instantaneous drain.

(4) Do the math - 240 watts is 20 amps @ 12 volts and that assumes 100% efficiency of your power amps which of course is impossible.

Building homemade digital jukebox need amp

Reply #8 –
Quote
could I not use the 12v line on a molex connection?
I don't see the advantage.  If you are trying to save money, there are cheap power amps that run on AC. 

You could also get noise problems.    Computer power supplies can be noisy and the associated computer-electronics generate more noise.    Once I had some computer speakers but I didn't have the wall wart power supply.  I got the "bright idea" of mounting a 12V power connector in a blank PCI cover on the back of the computer...    There was a horrible noise from the speakers and it was useless...  Plan B:  Stop by the electronics store on the way home from work and pick-up a wall wart.

That's just one experience with one computer and one set of powered speakers, but I'll probably never try that again!

Automotive power tends to be noisy too, so maybe a car amp is more immune to power supply noise than the powered speakers I was using...  But, I'm not going to try that again...  If were ever going to use a car stereo amp for a non-automotive application, it would have it's own power supply.

Building homemade digital jukebox need amp

Reply #9 –
Quote from: DVDdoug on
Quote
could I not use the 12v line on a molex connection?
I don't see the advantage.  If you are trying to save money, there are cheap power amps that run on AC. 


All amps actually run on low voltage DC.  An AC amp is just one built with the power supply on the inside.  Depending on what you are doing one or the other may make more sense, particularly if you already have a DC power supply.

Building homemade digital jukebox need amp

Reply #10 –
Quote from: saratoga on
Quote from: DVDdoug on
Quote
could I not use the 12v line on a molex connection?
I don't see the advantage.  If you are trying to save money, there are cheap power amps that run on AC. 


All amps actually run on low voltage DC.  An AC amp is just one built with the power supply on the inside.  Depending on what you are doing one or the other may make more sense, particularly if you already have a DC power supply.


Car audio amps typically have their own internal switchmode power supply to step 12-14.7 volts up to whatever it takes to make a power amp with the desired rating - often +/- 35 to 80 volts. The maximum power possible with a 12 volt supply all by itself is about 12-15  watts into 4 ohms, achieved by using bridged operation.

I'll bet money that the worst noise source for someone trying to use a computer power supply to replace a wall wart is that the computer power supply has a grounding plug, and most wall warts don't.

Building homemade digital jukebox need amp

Reply #11 –
It is a completetly new jukebox build. However the room has speakers allready installed, yes they do have 4 connections on the back of them. Can anybody recommend any non car amps that would work in this situation

Building homemade digital jukebox need amp

Reply #12 –
Cool concept; can you provide any detail about the speakers that are installed already?
Are these passive home A/V style speakers or something you'd install in commercial spaces?

Four inputs may mean these are optional or obligatorily biamplified speakers.
Can you provide a brand, model number and describe what the inputs look like? Such information will enable proper recommendations.

Building homemade digital jukebox need amp

Reply #14 –
The speakers are wharfedale programme 30D.6

here is a page with the most specs I could find on the speakers http://www.cookies.co.uk/product.aspx?productid=30334

also there is 5 speakers, one is daisy chained by splicing into the wire. Not great practice I know, I might remove this speaker

Building homemade digital jukebox need amp

Reply #15 –
Quote from: tombruton87 on
The speakers are wharfedale programme 30D.6

here is a page with the most specs I could find on the speakers http://www.cookies.co.uk/product.aspx?productid=30334

also there is 5 speakers, one is daisy chained by splicing into the wire. Not great practice I know, I might remove this speaker


Do you want stereo (and how do you want to split up the signal among the 4 or 5 speakers) or mono?

The specs seem to recommend a 50W amp per speaker, but it also depends on how loud you need to go.

You can do stereo by connecting 4 speakers as 2 parallel stereo pairs (of 4 ohm each), preferably with a bridged TPA3132D2 per channel, and a separate one for the 5th speaker, fed through a couple of resistors to produce a mono centre channel, or connect 4 speakers as a 8 ohm "2 parallel pairs of 2 speakers in series"  mono combination driven by one bridged amp - harder to accommodate the 5th speaker in that config.

Building homemade digital jukebox need amp

Reply #17 –
Quote
also there is 5 speakers, one is daisy chained by splicing into the wire. Not great practice I know, I might remove this speaker
Yes you'll probably want to leave-out the 5th one.  I assume this is a stereo setup (left/right)?  A 5th speaker will "unbalance" the system electrically and acoustically.

You can wire the speakers in series or parallel.  Parallel wiring is the most common method.    If two speakers are wired in parallel, you get twice the power (as long as the amp can handle it)  If speaker A was running at 50W, the 2nd speaker also gets 50W.    ....The same as plugging two 50W lamps into the same wall socket.

In series, you get half the total power with speaker A & B getting 25W each.  This puts less of a load on the amp.


Quote
A 30T version is available to order that incorporates a 100V line transformer with taps for 10, 5, 2.5 and 1.25 watts, selected by using a rear panel switch.
Do you have that version?

That's called "constant voltage", and it's used in commercial applications such as supermarkets.    It uses a special commercial amplifier with a 100V output, and the speakers are wired in parallel.    You can used the various wattage taps to make some speakers in the system louder than others (higher wattage in bigger rooms or noisy rooms and lower wattage in quieter rooms such as the office or break room).