Assistance please with rs-232 controlled power amp

[froop]

Hi All,

It's been many moons since I studied electronics, and I was always better with digital than analog, so I'm hoping for some help with this project of mine. I don't really want to design and build from the ground up, but preferably find suitable kits that I can plug together to see my idea come into fruition.

So to that end, here's my idea along with some kits and components which I believe should work, but I'm pretty sure there are better choices out there. Hopefully someone can help me identify those!

What I want to do is build a power amp suitable for home audio, to drive ceiling speakers for ambient music. I'm looking at 30-50W per channel, 6 channels. And I need to control it via a PC, most likely RS-232 (or USB via a USB-RS232 convertor)

Here are some of the components I've identified. Forgive the invalid URLs, I'm not allowed to post links until I've made 3 posts on this forum;

Power amp (www_kitsrus_com/pdf/k106.pdf). Not the cheapest, and that's a pretty big heatsink, especially if I'm going to have 6 of them!

Volume control (para_maxim-ic_com/results.mvp?fam=dig_pot). Seems pretty straight forward to use something off that list or similar, either using a pushbutton or SPI control

At first I saw this (www_oceancontrols_com_au/controllers/phaed/som96.htm) which looks like it could simplify some control, but its works out pretty expensive at $25 per channel.

So first off, an easy question. If I use the Kit106 power amp as described above, according to the kit notes I'll need 150VA for two channels. That seems to a pretty big power draw if I'm running 6 channels. Or is that to be expected?
In building a bridge rectifier, what are some suitable diodes for the recommended 5A load? And what capacitor and resistor should I use for a reservoir capacitor and bleeder resistor?

So now I guess the more tricky part, what are my options for using something as off-the-shelf as possible to control something like a DS1802 via its contact closure mechanism, or preferrably using the 3-wire serial as this gives discrete control over volume rather than just up/down. Or the DS1807 provides an addressable 2-wire interface which may be more suitable for control multiple channels.

Are there any nifty off-the-shelf devices that will fairly easily allow me to interface to such a bus via RS-232 control? At this stage I'm thinking something along the lines of an Arduino.

Thanks in advance to anyone who can offer their opinions, advice or alternatives.

Mark.

 

[blueroomelectronics]

What are you hoping the RS232 will control? Just amp power & volume?

 

[froop]

What are you hoping the RS232 will control? Just amp power & volume?

Correct. Want to be able to switch individual channels into standby when not being used, switch the whole unit (except for rs-232 controller!) into standby, and control volume and mute for each channel (or in pairs of channels for stereo)

 

[blueroomelectronics]

How many amps are you looking to control, how far from the host PC will they be. RS232 is end to end (one device per port)
RS485 might be more practical as its long range and multidrop, even RS422 can be hooked up to 10 nodes.
The microcontroller, ganged digital pot and relay for power should work.

 

[froop]

I intend on having all amp channels housed in the same case which will be withing a couple of metres of the host PC. So current thinking is to use an Arduino to convert rs-232 to the addressable 2-wire bus on a DS1807.

I'm just concerned about the power requirements, especially putting 6 (was hoping for 8 originally) of these into one casing will require a lot of heat sink, and 3 (or 4) 150VA transformers, plus an additional low voltage supply for the microcontroller.

Hence my question about whether this particular amp kit is suitable, or if I'll find similar power requirements for any amp of similar output.

 

[blueroomelectronics]

I'm not familiar with the K106, but for 50W RMS per channel x 6 amps (3 stereo channels) yes you're going to get warm.
The DS1807 I2C device looks like an excellent volume control and it's addressable so you'll only need the one microcontroller.

 

[Gayan Soyza]

I'm working on a project called remote volume control project.

I used PGA2311 digital volume IC by texas instruments & for the protocol I'm using SIRC infrared.

But my one is a stereo system.

 

[froop]

Thanks for your feedback Bill. I've ordered a couple of the DS1807's to see how well they work. Now I just gotta brush the cobwebs off - it's been a while since coding for any comms interface lower level than RS-232

I guess if I'm that concerned about power, I could drop down to 20W amps, but I'd rather too much than not enough. Or maybe even 4 50W channels for the largest room and outside, and then 4 20W channels for the smaller rooms.

 

[mneary]

If this is truly background music, then the 50W is for rare peaks and not for continuous operation. Comfortable listening is probably closer to 1W per channel average audio, probably a DC load of 5Wpc. Loud but undistorted listening is no more than 10Wpc RMS (assuming 50W amplifiers), with DC needs of 25Wpc. So your 8 channels of 50Wrms needs 200VA with pretty large filter caps. You need enough cooling to dispose of 150W if necessary.

Warning, eight 50W amplifiers, with only 200VA available, will overheat if someone does decide to run it heavily distorted (clipped) for extended periods.

 

[froop]

I've decided to dial down my specs a bit, and instead opted for 2x25W RMS amps (https://www.electro-tech-online.com/custompdfs/2008/09/k50.pdf) along with suitable power supply (https://www.electro-tech-online.com/custompdfs/2008/09/k114.pdf). I'll build just the two channels to check the power output in my various rooms (and outdoor entertaining area as well, which may require more oomph)

 

[froop]

Hi again all,

I've made a start with 2 of the www.kitsrus.com K50 amps and 1 K114 power supply. Thought I'd try just the two channels first. I built the power supply and drove one amp firstly from my laptop headphone out, and then direct from my CD player. Sound was good and clean.

Now I've build it into a casing, and there's some nasty hum going on. Can someone please offer some suggestions? I've included below some pics if that helps. There is still no preamp - just input straight from my CD player.

Some things to note;
I've added a 50k log pot on the input as volume control (neg and pos of the input signal to each end of the pot, and the signal to the amp on the middle).

There's a lot of crackle when I handle the pot.

I've used cat6 for the run from the RCA in at the rear, to the pot at the front, and then back to the amp. Purely because I had it handy, and there's enough wires to carry a stereo signal. Will I be better off with lengths of centre core shielded, or shouldn't it matter?

The cat6 run is close to the toroidal transformer on the right, but the hum doesn't change if I unmount the pot and keep the wire well away from the AC.

The mains input is also closer than I would like, but again unmounting that and keeping mains away from the input signal has not effect.

I've also removed the pot out of the circuit, and I get the same hum.

I have not connected mains earth. Not sure where to connect it to. Ground it to the chassis, obviously, but should it also be connected to the 0V line of the power supply?

Power train for the circuit is 240V down to 18-0-18 (AC) through the transformer, and then 25-0-25 (DC) into the amps.


Any assistance, suggestions or advise are much appreciated!

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