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Chip Amps Amplifiers based on integrated circuits

Another TDA2050 amp built and tested..............
Another TDA2050 amp built and tested..............
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Old 5th July 2007, 11:07 AM   #11
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by ashok
I've attached the circuit I've used with the component values shown on it.
The supply and supply fuse is shared between both channels.
I used 5 A slow blow because I had it . I've just changed it to 3A slow blow and it's working fine. I've used it about 4 hours now with the 3 A fuse and playing it pretty loud ( ocassional clipping).
This is a non inverting scheme and gain is +48 ( +33.6dB ).

So assuming a maximum theoretical 35 watts into 4 ohms , the input required would be just under 0.25 Volts.

Output is at pin 4 . The small +/- supply indicators near the opamp is part of the software package. You can ignore that.

Pin 5 is the +ve supply and pin 3 is the -ve supply.

Cheers.
Hi,
what gain? 1+[47/2k]=24.5 (+27.8db)
Why the decision to set NFB to F-3db=1.7Hz and then filter the input using C3 to F-3db= 7.2Hz?

Where is the T fuse?
If, in the supply, then maximum continuous peak current into your 4ohm load is about 4.2Apk (35W). I have found that a supply fuse (after the main smoothing) of about half this value will allow the amp to run reliably. You could therefore try F2.5A or even F2A and see which does not suffer nuisance blowing.
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Old 5th July 2007, 12:12 PM   #12
ashok is offline ashok
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Another TDA2050 amp built and tested..............
I just lost a long reply. So here is a gist of it.
1. Sorry I made a mistake. The first amp had again of 48. The next one was as shown in the diagram = 28 .
2. The capacitors are so because that's what I had. I had only that value Solen to use and it sounded better than others I had.

3. The fuse should have been between the 4700uF and the rest of the circuit.

4. I have only 3A nd 5 A slow blow fuses at hand at the moment!

Thanks for pointing out the errors.
As it's shown the amp sounds good.
Cheers.
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Old 7th July 2007, 03:02 AM   #13
ashok is offline ashok
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Another TDA2050 amp built and tested..............
A note on the Zobel network and stability.
I used the second design ( Gain 28dB ) for 2 days before realising that the zobel was missing . There were no instability problems . This might of course change with a difficult load.

I later added the zobel and there was of course no audible change in performance.
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Old 12th July 2007, 10:16 AM   #14
ashok is offline ashok
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Another TDA2050 amp built and tested..............
Default Interesting tweaks.

I added some LED's to indicate the presence of power , both before and after fusing !

More interesting was my test with different input capacitors. I went round looking for a 1uF boxed MKP cap to fit my board but couldn't find any that were suitable. So I bought some brown unmarked 1uF film caps .These are most likely Chinese but could be Taiwanese too. Since it has absolutely no marking except the value it most likely is a Chinese brand.

Surprise surprise ! It sounds better than my Solen film cap !! Now that has stumped me. This film cap costs about 5 cents.
Basically it sounds cleaner between different sounds . So different instruments and voices have some air around them making them easier to follow. Overall it sounds easier on the ear on complex sounds but nothing seems to be sacrificed. No loss of low end or high end. It also appears to have more PRAT ! THAT is a very desireable quality.
Other similar cheap 1uF film caps , including Philips, do not sound the same. I tried them earlier.
This unit is much fatter than the Philips caps.

I plan to try these out in other circuits too to see if they work as well. Will surely help with my budget ! An opamp based headphone amp is in the offing . Will see what it does there.
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Old 12th July 2007, 06:59 PM   #15
meepers is offline meepers  United States
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Nice write up. Looks like a good amp to be my first build. How difficult was it to get a good board layout?
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Old 13th July 2007, 02:15 AM   #16
ashok is offline ashok
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Another TDA2050 amp built and tested..............
My boards are not a great design. Some chopped tracks and jumper wires above and below board. I hand painted the tracks.

I think you should stick to the board layout shown in the application note and you should be fine. I was planning on getting some boards made eventually but it hasn't reached that stage yet. Need to improve the layout or possibly redo the full layout again. I want to try out some experiments first.

Unfortunately I do not have enough free time to do all this quickly.
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Old 8th October 2007, 01:33 PM   #17
ashok is offline ashok
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Another TDA2050 amp built and tested..............
meepers , want a pcb ?

Today I did some measurements. The HF on this amp has a peak of about 1db or so at just beyond 20Khz ! I can only assume it's inherent to the chip. If I add a 39pf cap to the NFB resistor ( 47K ) it flattens it out and starts to roll off beyond 20Khz.

The peak is dependent on the speaker load . 4 ohm showing slightly less peaking. However the amp sounds fine and not 'bright ' because of this. I'll post some response plots later.

Distortion is poorer than an LM3886 but still quite low. I pulled out my LM3886 board to make some comparisons. The LM3886 is slightly better but not apparent on casual listening. The Lm3886 however has far more power ( with a dedicated 220 VA torroid ).

So that still means that the 2050 is an incredible bargain . The chip is one fifth the cost of a LM3886 chip . Today I measured the power output using a low quality 15-0-15 transformer . The output was only 12 watts into 8 ohms before the amp clipped due to a sagging power supply. However in listening tests the amp went pretty loud even with that.
Good tight bass too. Since my speakers are 8 ohm ( 88db/watt) rated they might be a comfortable load for the amp.
With less efficient speakers (86 db/watt ) the amp does lack a bit of steam if you want to play it loud. My 86db/watt speakers are also 4 ohms and so it adds to the power problem.

I'll post some measurements later.
Cheers.
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Old 8th October 2007, 03:48 PM   #18
ashok is offline ashok
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Another TDA2050 amp built and tested..............
Default Frequency response

Here is the response of the amp in stock mode.
Unloaded the HF peak was almost 1.5db and rising. With a 8 ohm load its still about 0.5db at 20Khz. With a 4 ohm load it is a bit less .
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File Type: jpg 2050-freq resp-8 ohms.jpg (21.9 KB, 1430 views)
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Old 8th October 2007, 03:49 PM   #19
ashok is offline ashok
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Another TDA2050 amp built and tested..............
Default with compensation

Here is the response with a 39pF disc cap across the 47K NFB resistor.( not 47pF as stated on the picture).
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File Type: jpg 2050 with 47pf across nfb resistor.jpg (21.3 KB, 1386 views)
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Old 8th October 2007, 03:53 PM   #20
ashok is offline ashok
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Another TDA2050 amp built and tested..............
Default Distortion

Distortion at 1 watt with a 4 ohm load.

The picture gets clearer when you see the FFT . The 2050 has more harmonics visible than the LM3886 . That's probably why the LM3886 sounds cleaner . Not really too noticeable if you do not make a comparison side by side. By that I mean you listen to the amp without looking for differences.
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File Type: jpg 2050-4ohm 1watt dist.jpg (27.5 KB, 1392 views)
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