30-0-30vac 150VA chipamp suggestion - diyAudio
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Old 7th April 2015, 01:06 PM   #1
wertz is offline wertz  Philippines
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Default 30-0-30vac 150VA chipamp suggestion

hi, im new so let me start. i have an existing sound system(chinese clone amp thingie) which has separate tuner, tone control and power amp boxes. im planning to change the amp into chipamp and reuse things i can from the amp-box and the transformer. the transformer is a toroid with 150va 30-0-30vac(42v when rectrified). so i was wondering what chipamp would be ideal to replace the old solid-state(based on C4468/A1695 pair).

i have the old speaker @ 4 ohms rated 50 watts, but i am planning to re-used a speaker system(model L90VH from sony) for the new amp.

i was planning to go with LM3886 but @ 42v i am at limit. thanks for the suggestions.
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Old 7th April 2015, 04:16 PM   #2
vodka is offline vodka  Argentina
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TDA7294 states the absolute maximum voltage as ±50v. It recommends ±40v as the sane maximum, so you should be just fine. The problem is that chipamps hate high voltage and low impedance loads like the original speakers... Thankfully that sony speaker system states 8 ohms in its manual. Have some beefy heatsinks doing the job, maybe even helped with a 80mm computer fan at 5-7v which equals silent.



edit: reading further into the datasheet

Quote:
The TDA7294 is a monolithic MOS power amplifier which can be operated at 80V supply voltage (100V with no signal applied) while delivering output currents up to ±10 A.
It's the same situation as the LM3886... my bad.


I think there are some LME series chips that can withstand the voltage, but then require discrete output transistors to do the job and complete the amplifier.

Last edited by vodka; 7th April 2015 at 04:33 PM.
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Old 7th April 2015, 05:34 PM   #3
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Hello altogether, i am new here to.
Last month i finished a small Stereoamp with the TDA 7293- each one wih a 30 - 0 -30 V / 80VA torodial transformer. they each drive a 4 ohms Visaton WS 17 E - Speaker. The System works fine. In the Datasheet the absolute Voltage Maximum is described as 120V ! Of course you Need a big Heatsink cause the Chip gets rerally HOT. The Circuit Diagram of this Amp is in the Datasheet or you can find it on sound-westhost.com (Rod Elliot).

Please excuse my English, i am in Germany...

Regards, Jörg
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Old 8th April 2015, 02:45 AM   #4
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Parallel 7294's is about the same complexity as something like a lm49811 + Sanken STD03's. The latter is liable to be a higher performing setup.
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Old 8th April 2015, 05:50 AM   #5
wertz is offline wertz  Philippines
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thanks for the replies guys.

@vodka; your right, most chipamps suggests at +/- 35v for continuous operations. my sony l90vh speakers are indeed 8 ohms as specified at its back cover. based on service manual this speaker is rated at 100-120 watts. im doubtful to use th eold speaker coz its just too small (4" woofer cone) and dont do good high freq.

Basslastig67 - im looking at TDA7293's datasheet and it indeed falls to my requirements but datasheet shows about THD @ 10% when running 8 ohms at 38+ volts.

Derfnofred - yes, probably bridging might do but still needs voltage to be just about 35-38volts which would mean i will change my toroid(they are hard to find where i am and costs 2-3 times more of the cost of building 2 lm3886;s w/o power caps). but bridging will cost me more space unless i place amp boards sideways or facing upside-down each other. the box is just 12"x8.5"x4.5"(LxWxH) and the toroid is 4.5" at its outer diameter.

thanks all.
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Old 8th April 2015, 02:41 PM   #6
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Wertz--not bridging, parallel 7294's. You're sitting close to the edge SOA of these devices, so paralleling chips will help minimize risks with power handling (since each chip is ultimately running at ~1/2 the global current). The 7294's can handle 42V, but not at any sort of low impedance. You'll want to have a input buffer (unity gain) sitting in front of these two chips in order to present a nice, high, input impedance.
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Old 8th April 2015, 05:29 PM   #7
Spuds is offline Spuds  South Africa
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Regulated PSU?
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Old 9th April 2015, 11:19 AM   #8
AndrewT is offline AndrewT  Scotland
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30-0-30Vac will almost certainly blow a 3886, if not immediately, then eventually.

The internal protections will probably not work properly/effectively when the supplies are higher than that absolute 84V limit.

Do you have the transformer?
Have you measured the capacitor voltage?
Have you calculated/predicted the maximum worst case supply rail voltage?
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Old 10th April 2015, 09:47 PM   #9
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the supply is allmost good for paralell tda7293/7294.
You can even afford to use regulators.
then the rails will be just right for the stuff.
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Old 12th April 2015, 05:45 PM   #10
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Hi Werts,
i think that you are afraid of the THD 10% is at every listening Level bui it is not ! in my Datasheet is the THD of 10% while it is running at +-40V rails and delivers 100 Watts at a 8 ohms load. That is quite clear because clipping starts at this Voltage by driving 100 Watts at 8 ohms.
just a Little below 100 Watts the THD will less than 1%.
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