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Old 23rd July 2005, 02:09 PM   #1
Duo is offline Duo  Canada
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Default STK4274 as audio amplifier.

Well this should be interesting.

This chip is a dual convergence amplifier for projection monitors.

Upon perusal of the datasheets, these look quite feasible as audio amplifiers. The only limit I don't like is that the output transistors can only handle two amps. But that's not stopping me from making something small.

I plan to design a six channel system (being color TV uses three colors, and hence three chips, thus six channels for convergence.)
This will drive speakers for a computer.

I calculate that as a limit that I can deliver up to sixteen watts for a four ohm load (2A with 4ohms, 8Vrms).

Being that these operate on 15.75KHz(NTSC) with a sawtooth waveform and with good linearity, they should be quite capable of performing in the audio spectrum.

The only other thing more weird than this was my using an LM339 quad comparator as op-amps to drive darlington output stages as an audio amplifier. The result was pleasing and it sounded very good; though my other friends in electronics could see no reason why I got a comparator to operate linearly in the analog world.

Anyway, I'll get back to this thread with the results of using convergence amplifiers for audio power amps.

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Old 24th July 2005, 12:40 PM   #2
Duo is offline Duo  Canada
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Well, it looks like no one seems to know what to say.

I have built the amplifier. Did a four channel one for now and I've decided to give it to my friend.

The results are very pleasing actually. It sounds quite transparent and accurate. I'm happy with what it does.

It's very stable and sounds good to my ears.

Another unusual project pulled off!

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Old 24th July 2005, 01:20 PM   #3
tlf9999 is offline tlf9999  United States
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Default Re: STK4274 as audio amplifier.

Quote:
Originally posted by Duo
The only other thing more weird than this was my using an LM339 quad comparator as op-amps to drive darlington output stages as an audio amplifier. The result was pleasing and it sounded very good; though my other friends in electronics could see no reason why I got a comparator to operate linearly in the analog world.
In the "weird and weirder" department, I have used 74-series CMOS NOT gates as op amp in the 1970s with good results (mostly as microphone amps). 74-series TTL gates work as well.

a comparator is nothing but an high gain open loop opamp. so it should work once you wire negative feedback in.

Quote:
Originally posted by Duo
The results are very pleasing actually. It sounds quite transparent and accurate. I'm happy with what it does.
this is another example where as long as you get the foundamental electronics right, you get good results, no matter if the original parts are for audio or not (actually, audio signals are probably the easilst to amplify, aside from digital signals).

As to unusal projects, I have used lm317 as power amplifiers, adsl transmitters / line drivers as headphone amps, and paralleled small signal transistors (over 20 2n5401/5551) in power amp output stages.
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Old 24th July 2005, 01:38 PM   #4
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I dug up a couple TDA8172 / 8177's and talked a friend into trying them out as amps.I was looking at the datasheet,and thought they just might work...sure enough,he got them working!
I think he got ~30 watts from one of them (+24V supply)
The output wasn't the cleanest,but not bad at all for a quick hack-up.
With a little more tweaking they might make great little guitar amps or something!
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