Determining voltage of speaker amp board

[spleenharvester]

http://images.esellerpro.com/2131/I/...mage%20029.JPG

Basically, I have one of the above. It's a HP P/N 5188-6247 speaker board I wish to harness for another use (Xbox 360 through some spare Logitech speakers that would usually be used with a sub).

Pretty simple in theory, L/R input, L/R output, and DC in (red conector). But I don't know the voltage/amperage requirements of the DC input. DC Input was connected to a LCDB-CF board.

Since the computer it was in is no longer around, I have no way of powering it to test.

Anyone know, or know how I can figure out the power needs of this thing? Can take more pictures if need be.

Cheers

[spleenharvester]

Re: Determining voltage of speaker amp board

Just figured something out. Pretty sure, the DC in connects to a block shaped 8 pin connector coming from the PSU. Here are the PSU volts:

http://www.eurotechpcs.co.uk/garages...47505-4288.jpg

Given there's a 16v cap on board there, could the volts be 12V?

http://pdf1.alldatasheet.net/datashe...TPA3008D2.html is the datasheet for the bigger IC.

[spleenharvester]

Re: Determining voltage of speaker amp board

Guys, as per the data sheet, I'm pretty sure it's 8~18V. I've not got the input jacks connected yet, but I used a 12V supply and it was fine (get a sort of low hum from the speaker when ear's up to it so I assume it is, anyway). Then I accidentally shorted the supply so had to use a 15V supply, which also seems fine.

I'm pretty sure, because there's only inputs, outputs and DC, that there's a variable resistor on the LCDB-CF board somewhere, so if one was put in the DC line it should function as a volume control.

Just thought I'd put it out there for anyone who may need the same info.

Also, this amp board can be had for ~£7 off ebay for anyone who also wants to attempt the mod.

[999999999]

Re: Determining voltage of speaker amp board

It's "probably" meant for 12V (regulated) input, no reason for them to reduce output power by making it lower than that with 12V present. For best results you'll want a PSU capable of about 1A current, though the capacitor might be increased for best results.

Ideally it would be powered by a linear regulated supply not a switching PSU, but it was cheaper for HP to do it that way.

A variable resistor on the DC voltage is in no way a volume control. Input DC voltage only determines the peak power limit, volume is a function if input audio signal strength times the gain set by feedback loop resistors acting as a voltage divider (or, it is a fixed gain IC, set internally to a specific multiplier), OR in this case the chip's gain is set by binary signal values on pins GAIN1 and GAIN0 as shown on the following datasheet pg 16, "0" presumably meaning the pin's pulled down to ground and "1" that it's left floating, not connected to ground. The other option is the age old one of putting a potentiometer on the audio input to decrease the signal level prior to further amplification.

The power amp IC is TPA3008d2, you can get the datasheet here:
https://cdn.badcaps-static.com/pdfs/...dd4c0cc6cf.pdf

Check the max voltage spec on the other ICs on the board, it is possible you can increase the peak power a bit by replacing the capacitors with some rated for more than 16V, it is spec'd for up to 18V (absolute max 20V). At 12V PSU input and 1% THD it can do 4W, but at 18V, 9W. However one of the datasheet graphs suggests that you may need to add a heatsink for RMS output above 8W which would be an unusual use for this board but nevertheless, it's an issue. In the datasheet figure 12 on pg 10 shows the relative current to voltage recommended.

In the end if you're happy with it as-is, everything I wrote can be ignored.

[spleenharvester]

Re: Determining voltage of speaker amp board

Funnily enough that just answered quite a few questions I had in mind for something similar lol. Cheers mate!

Just another Q. It's now on a 15V 1.5A supply, and is absolutely deafening, so needs some kind of volume control. Am I right in thinking I need to add a Stereo potentiometer between the speaker outputs and the speakers themselves? Which value would I need, and would it need to be log or linear?

The sound itself is great by my ear, but is way too loud. So needs to just be quieter but untouched as possible.

Ta

[999999999]

Re: Determining voltage of speaker amp board

No, put a dual gang (stereo) log pot between the source and the audio input, something in roughly 10K to 100K Ohm range. A linear pot would work too but you won't like it as much.

[momaka]

Re: Determining voltage of speaker amp board

Just another Q. It's now on a 15V 1.5A supply, and is absolutely deafening, so needs some kind of volume control. Am I right in thinking I need to add a Stereo potentiometer between the speaker outputs and the speakers themselves? Which value would I need, and would it need to be log or linear?

Unless you have a low-ohm potentiometer rated for several watts, putting it between the outputs and the speakers would be a bad idea (and even if you did, it would still be a very inefficient way to control output volume).

It's much better to connect the potentiometer on the board's inputs, instead.
Basically, you connect the signal you're feeding to one side of the potentiometer. The other side of the potentiometer you connect to ground. The variable output of the potentiometer you connect to the board's input.

Use log potentiometer.

[spleenharvester]

Re: Determining voltage of speaker amp board

Ah wonderful, I've worked with potentiometers before in the building of guitars etc but never fully known how to wire them up. Cheers!

So does it get wired up like this? (Just assume it's one side of a stereo pot, would be a needlessly complicated diagram otherwise): http://i.imgur.com/VdFDL.png

Also, can I connect the RCA ground to the back of the pot too? The problem is, the grounding on the PCB is awful and I've had to ground it to the DC15V jack.

[momaka]

Re: Determining voltage of speaker amp board

So does it get wired up like this? (Just assume it's one side of a stereo pot, would be a needlessly complicated diagram otherwise): http://i.imgur.com/VdFDL.png

Yes, exactly.

Also, can I connect the RCA ground to the back of the pot too?

Yes, should be fine (unless you have some special pot that connects its casing to one of the outputs that you don't intend to be ground - but that's very rare).

[spleenharvester]

Re: Determining voltage of speaker amp board

Wonderful, thanks everybody!

[spleenharvester]

Re: Determining voltage of speaker amp board

Bump. Got this all together today and sounds great, thanks all.

Only one problem. You know that sort of buzzy sound a speaker/earphone will get when it's being pushed too hard? I get that at lower volumes. I did have to heatgun some of the heatshrink on in places, is it possible that buggered the cap up somehow? It looks okay physically.

Also, the speakers in the adjacent socket hiss when I'm using it and have to be turned off.