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-   -   TDA 7293 vs STK4192 + newbie questions (https://www.diyaudio.com/forums/chip-amps/329017-tda-7293-vs-stk4192-newbie-questions.html)

pompouspompei 22nd October 2018 01:40 PM

TDA 7293 vs STK4192 + newbie questions
 
Hello ,


Im new to audio systems as well as this forum. I hope this thread is in its appropriate forum , if not kindly relocate it to wherever it is deemed appropriate.

I have an old bunch of speakers and amplifiers ( both working ) from my grandfather. Unfortunately , due to the amplifier being : mono , discreet transistor based ( 2n3055 and sort) ,a cassette player input, lost schematics , im planning on building a new amp.

Getting to the point , I have :

1. 2 towers , each consisting of ( 1x Tweeter - 50W(max) 8ohm , 1x Mid- 20W 4 Ohm , and 1x Woofer - unknown wattage, 9 inch dia , 8 ohms). Now my grandpa claims that the system was 80W , so i would say that the woofer can handle a min of 40W. In addition , the tweeters 50W is its peak i guess , so its RMS would be lower . (Pics attached)

2. 1 x 30-0-30 Transformer , 4A ( I guess, it used 6A diodes in its bridge rectifier)

3. 1x 15- 0 -15 Transformer , I guess 500mA

I have a few questions , hope they arnt too noobish :

1. Any opinion on the STK4192 vs the TDA7293 in terms of audio quality , stability , heating and component quality) ? I also have alternate low powered options like the tda2030/40/50

2. Isnt i better to set a constant gain in the IC while modulating the voltage via a potential divider or op amp amplifier in the input to prevent oscillations?

3. By Power = V^2/R , the max power 2x 8 ohm speakers in series can draw if i use my 30 -0 - 30 is approx 500W. But neither the amp nor the speakers can handle it. So , am I supposed to control the Wattage via the output voltage( setting the peak voltage via the gain or some IC function)?

4. If the above is true , then the efficiency with supply of -45 to 45 V and a peak output of just 40V would see a lot of heat since at leat the tda7293 is a class AB

5. Is it worth it to keep the 30 -0 30 around? or should i replace it with a 12 -0 -12 5 Amp ? Im trying to minimze the budget by reusing the old stuff.

6. Is a 80+80W system too loud for a 300 sq feet room?




Thanks! hope these questions are clear and not too noobish!


PS : I have attached the pics of the speakers . If anyone can guesstimate or identify them , it would be great.



https://www.diyaudio.com/forums/data...xC/PEL5Paf/9k=https://www.diyaudio.com/forums/data...BYN9J67nAZ/9k=

nigelwright7557 27th October 2018 01:31 AM

Rather than buy a new power supply just don't turn the amp up full.

A living room doesn't need many watts.
I get by on a couple of watts from a USB DAC into a Fane 12-50WRMS speaker.

danielwritesbac 26th November 2018 10:08 PM

Combine your TDA2030/40/50 idea with your 12-0-12 5a transformer idea for a doable project. The voltage is 'less lethal' that way and the expense is small.

It is probably necessary to have that bit of practice, and a considerable amount more caution before using that 30-0-30 transformer! But, if you wanted to know, a chip amp that can use that, was probably made by STK. There's some pre-built boards pop up on ebay every so often.
Or, over in the discrete amplifier forum and diyaudio store, the Honey Badger can work with the 30-0-30 transformer. That's overkill for 300 sq ft.

This link contains some answers to the voltage vs parts questions: Building a Gainclone chip amp power supply.

Mooly 27th November 2018 08:24 PM

Quote:

Originally Posted by pompouspompei (https://www.diyaudio.com/forums/chip-amps/329017-tda-7293-vs-stk4192-newbie-questions-post5579774.html#post5579774)
I have a few questions , hope they arnt too noobish :

1. Any opinion on the STK4192 vs the TDA7293 in terms of audio quality , stability , heating and component quality) ? I also have alternate low powered options like the tda2030/40/50

STK's have a larger footprint and so will be more amenable to keeping cool.

Quote:


2. Isnt i better to set a constant gain in the IC while modulating the voltage via a potential divider or op amp amplifier in the input to prevent oscillations?
All normal power amplifiers (such as these) run at constant gain, the gain being determined by the feedback network values.

Quote:

3. By Power = V^2/R , the max power 2x 8 ohm speakers in series can draw if i use my 30 -0 - 30 is approx 500W. But neither the amp nor the speakers can handle it. So , am I supposed to control the Wattage via the output voltage( setting the peak voltage via the gain or some IC function)?
It doesn't work quite like that. Your 30-0-30 transformer will create -/+ 42 volt DC rails (approx.). 42 volts would be the maximum voltage the load could see, in practice the amp wont swing that far. Lets say 37 volts peak.

37 volts peak is 26 volts RMS which if applied across 8 ohms would dissipate 84 watts. So a 70 to 80 watt amp is feasible given a suitable 30-0-30 transformer.

Quote:

4. If the above is true , then the efficiency with supply of -45 to 45 V and a peak output of just 40V would see a lot of heat since at leat the tda7293 is a class AB
Explained above.

Quote:

5. Is it worth it to keep the 30 -0 30 around? or should i replace it with a 12 -0 -12 5 Amp ? Im trying to minimze the budget by reusing the old stuff.
Its a bit on the high side for a beginner to put together an amp based on the voltage rating, even the LM3886 would be at its limits. Far better to get something like an 18-0-18 which would make a nice 'chip amp'

Quote:

6. Is a 80+80W system too loud for a 300 sq feet room?
If you turned the volume up and had efficient speakers then yes, to loud... so don't turn it up to much ;)


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