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Old 24th January 2004, 08:23 PM   #1
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Default Best possible 10W from chip amp

Hi,

Some weeks after having found this forum I have become curious of chip amps. Now I want to build my one ones.
I have also for the last years been thinking of building a pair of TL or horn speakers with fullrange drivers.
Consequently I now want to build those as active speakers with chip amps.
Currently I have a small collection of Quad amplifiers (33,34,303, 405-II, QC-2 and Quad-II:s)
Since I have used my 15W Quad II tube amps with my speakers with only 88dB efficiency I'm quite confident that 10W into a speaker with well above 90dB will be enough for me.
It doesn't matter to me if there is 50W instead of 10W as long as the first 10W is delivered with best possible sound quality.
And If there is not more than 10W thats fine with me - I don't need more.

My local component dealer www.elfa.se offers:
TDA2005, TDA2030, TDA2040, TDA2050, LM3875, LM3886, LM4700 and som others which I don't think will be my choice anyway. There Is offcausse different prices on these, but I think all of them are cheap enough and I will buy the ones from which I can expect the best sound quality.

Now to my question:
In what way will the supply voltage on e.g LM3886 affect the sound quality. Will It benefit to not have more supply voltage than needed or is it better to build an +-48V 68W LM3886 with low gain setting ? ......Or will e.g the TDA2030 perform as good as LM3886 if 10W is all you need?

I have 2pcs of 12-0-12V 20VA torid transformers in my scrap box. Will it be enough with one of these for each channel?

Robert
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Old 25th January 2004, 08:44 AM   #2
Nuuk is offline Nuuk  United Kingdom
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Robert, there are no definitive answers to your questions and you will have to sift through the numerous opinions on this forum and draw your own conclusions.

If you only want a small amount of power, try the LM1875 with your 12v transformers ad see what it sounds like with your speakers.
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Old 30th January 2004, 06:24 PM   #3
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Thank you for the advice Nuuk!

Even if The supplier i planned to buy from doesn't have LM1875 I did find this chip interesting for my purposes.
I asked an TV-repair man if he could order a pair of them for me and it was no problem. It become also very cheap this way.

I have spent some more hours reading this forum and have got some more useful information.
Still I haven't found any posts with any general ideas about the relation between soundquality vs supplyvoltage.
Maby there are hints to read out from the diagrams in the datasheets, but I'm not capable to do it.
However, if no one knows I have to accept this and try to find out for my self.

I have also made my 1st chip amp. It's very low budget with a TDA2003 I bought years ago and with cheap standard components. It sounds but it's offcausse far from good hifi.
see the picture, note the heatsink
Wonder whats the worst of the design? Components too narrow? poor pcb? cheap components?
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Old 30th January 2004, 06:44 PM   #4
sss is offline sss  Israel
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keep the coke inside
that way the amp will be water cooled
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Old 30th January 2004, 06:56 PM   #5
GregGC is offline GregGC  Canada
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Quote:
Originally posted by Robert_66
Thank you for the advice Nuuk!

Even if The supplier i planned to buy from doesn't have LM1875 I did find this chip interesting for my purposes.
I asked an TV-repair man if he could order a pair of them for me and it was no problem. It become also very cheap this way.

I have spent some more hours reading this forum and have got some more useful information.
Still I haven't found any posts with any general ideas about the relation between soundquality vs supplyvoltage.
Maby there are hints to read out from the diagrams in the datasheets, but I'm not capable to do it.
However, if no one knows I have to accept this and try to find out for my self.

I have also made my 1st chip amp. It's very low budget with a TDA2003 I bought years ago and with cheap standard components. It sounds but it's offcausse far from good hifi.
see the picture, note the heatsink
Wonder whats the worst of the design? Components too narrow? poor pcb? cheap components?

What is the sch. that you use? I think it may has to do with the IC and the specific sch. and PS. Parts too, but I'd start with the speciffic sch. Use LM1875 and 18-0-18VAC with Pnasonic FC caps and normal resistors. If you can avoid the el. caps at the input and the NFB that's the best IMHO. How sensitive are your speakers? You may need more power than 12V can provide.
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Old 30th January 2004, 07:51 PM   #6
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Hi Greg GC,

For this quick-and-dirty-allways-learn-something project on the picture I used the "typical configuration" scheme on the TDA2003 datasheet. At this point I regret I did the layout so narrow. It makes it difficult to rebuild and test different modifications.
If I understand it right your opinion is that significant improvements can be made by using an other scheme.
Since my preamp have capacitors on the outputs I think it will be no problem to skip the caps at the input.

I have not yet decided which scheme I will use on my more serious attempt with the LM1875:s, but it will be with some kind of plastic caps in the NFB.

The speakers I'm planning to build will be with 6" Fostex or possibly Lowther fullrange drivers and I think they will be very sensitive - maby 94dB ?!

I'm also afraid that 12V-0-12V AC will be a bit to low. After the rectifier and PS caps It will be approx 16V. This is the minimum supply voltage specified for LM1875.
I think your advice 18V-0-18V AC may be good. It will give approx. 25V DC. This is somewhere between the min and max specified. Most of the ratings specified on the datasheet is valid at 25V. It gives me the feeling that this can't be wrong.
But I will test with the transformers I already got to start with.
It will be easy to make the upgrade later on.

Robert
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Old 30th January 2004, 09:34 PM   #7
GregGC is offline GregGC  Canada
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Robert,

After looking at the TDA2003 data sheet I can promise you that you'll get much better results from LM1875, 18-0-18VAC. Pick a IGC or NIGC (I build a NIGC no signal caps. LM3875) and enjoy the music. It's worth the effort.

http://www.diyaudio.com/forums/showt...481#post309481

Another GC project

Greg
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Old 30th January 2004, 10:26 PM   #8
Morse is offline Morse  United States
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Hi Robert 66;

If the LM1875's not available, you might try the TDA2050; I recently built a TDA2030A and it's sound is significantly better than I thought it would be. I'd still rate my 2A3 as sounding better (given the disparity in costs, I'd be crushed if the reverse was the case!) but I can listen to my TDA2030A all day long without fatigue and better yet I can even enjoy the music through it (not possible on some systems!).

The reason I suggest the 2050 over the 2030A is that the specs look better on it and the blocking diodes are integral to the chip. Personally I'd love to try one but I can't find a supplier on this side of the pond.

The 20VA rating will be a REAL limit to be sure, but it should work - just do NOT hook it up to a 4 ohm load and DO fuse the secondary. Also, as with all new electronics, keep an eye on the temperature of that PS trafo during high power operation to get an idea of how close to it's real capacity you are.

FWIW, I'm running my 2030A into 8 ohms and even runs at max power have not heated the 50VA 25VCT trafo to levels I would regard as dicey. Frankly though, I don't think you can have too much current capacity in a PS, so I'd put in an inexpensive EI core 25VCT rated a bit higher. 50 VA is fine here, but I'd like to go up to something with 2 or 3 times the capacity....

Good luck and all the best!
Morse
PS. Love the heatsink! I wish I would've thought of it!
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Old 29th October 2004, 08:23 AM   #9
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I hear many good things of the LM4700 ic, and so i think my next gc will be based on that. it will be interesting to test it up against my lm3886 gc.
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Old 29th October 2004, 11:22 AM   #10
mcs is offline mcs  Denmark
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I think a standard LM3875 amp would be a good choice also. The voltage range specified in the datasheet is 20-84V, so a 2*12V transformer will work fine. I think the 20VA rating is a bit low though, but it may be OK for a monoblock...

Best regards,

Mikkel C. Simonsen
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