Beginner's Gainclone, HiFi LM1875, The Amplifier Board

I found the ebay seller who had the OCL/BTL modes for the board I use. Also available from Oddwires if you want it quicker. Below is 2 grabs, magnify 300% and the print nicely, if I wasn't so computer illiterate I would put these on 1 piece of paper.

An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
 
I understand the 18-0-18 1 or 2 amp transformers (I prefer 2 amps) Amps is what creates the heat and when you push chips if you can't keep them cool they let the magic blue smoke out.

I just ordered one of these today for my build. Hope it is the right one.

https://www.antekinc.com/details.php?p=676

bummer out of stock till late december so I cancelled
 
My lm1875 has a dark voice,not very energic,what could i try to do?

I bet that Daniel will have some ideas.

What schematic did you use?

Check that you haven't accidentally made any low-pass filters, either at the input or with the feedback.

Make sure that you have some smaller electrolytics very close to each of the chips' power pins, with short paths to ground. At least 470 uF for each power rail is recommended by National. You might have bigger ones, already. But also having some smaller ones, closer to the power pins of the chips, could help the highs, and the transient response, and the imaging. Two or more smaller ones, in parallel, should also be slightly better than one larger one.

Also make sure that you have a very physically-small 0.1 uF (probably X7R ceramic) cap right AT each power pin, directly to a very close ground. Otherwise, you could get ringing or oscillation at RF frequencies, which could also change the character of the sound. (You should also have RF protection on the input. Just make sure that the low-pass filter for the RF is not accidentally set TOO low.)

If you have all of that, then the problem would probably be in the feedback network or the input network, with something making a low-pass filter, somehow.
 
Two or more smaller ones, in parallel, should also be slightly better than one larger one.
Yes, I agree with that!

372655d1379884576-beginners-gainclone-hifi-lm1875-amplifier-board-lm1875_turbo-ii_color.gif
 
I bet that Daniel will have some ideas.

What schematic did you use?

Check that you haven't accidentally made any low-pass filters, either at the input or with the feedback.

Make sure that you have some smaller electrolytics very close to each of the chips' power pins, with short paths to ground. At least 470 uF for each power rail is recommended by National. You might have bigger ones, already. But also having some smaller ones, closer to the power pins of the chips, could help the highs, and the transient response, and the imaging. Two or more smaller ones, in parallel, should also be slightly better than one larger one.

Also make sure that you have a very physically-small 0.1 uF (probably X7R ceramic) cap right AT each power pin, directly to a very close ground. Otherwise, you could get ringing or oscillation at RF frequencies, which could also change the character of the sound. (You should also have RF protection on the input. Just make sure that the low-pass filter for the RF is not accidentally set TOO low.)

If you have all of that, then the problem would probably be in the feedback network or the input network, with something making a low-pass filter, somehow.
Highs are ok,decoupling is right at pins,could it be because i didint use feedback cap?. i have what i think is 250va transformer,14700 filtering,voltage sags 1 volt on max power .
Implementation is simplest possible,with zobel
 
That cap is too big for a 4" woofer. With that speaker, the cap size would be about 1000uF although that suggestion may be off the mark by either half or double. With split rail amp, the cap can go series to woofer negative. The cap size can be determined practically--I suggest to give the amp a shove with a bass boosted source and loud playback to get that woofer moving and then experiment to find the smallest size series cap that reduces voiceband distortion without reducing the useful bass output.

Without pointlessly shaking the woofer for pitches it won't reproduce while it is also attempting to play voiceband, you'll get less clipping and less distortion from the speaker. Basically, don't shake the vocalists. Now, that is how the series cap could really help a small size 2-way speaker.

If sealed box cabinets, the right size cap can also be determined by bass extension, since a just right current drive will make the speaker able to replay lower pitches than it could before. It does not make the bass louder, it can make the bass slightly clearer, and a right-sized cap really can make the system much better able to withstand a bass boost at input.

See also, Bob Cordell EQSS: CordellAudio.com - The Athena Active Loudspeaker
 
Thanks. I'll experiment with 2200uF since I have two of them at hand. I'll do some checking on the board as you suggested.

That cap is too big for a 4" woofer. With that speaker, the cap size would be about 1000uF although that suggestion may be off the mark by either half or double. With split rail amp, the cap can go series to woofer negative. The cap size can be determined practically--I suggest to give the amp a shove with a bass boosted source and loud playback to get that woofer moving and then experiment to find the smallest size series cap that reduces voiceband distortion without reducing the useful bass output.
 
I must agree to this advice. I've tried both 4700uF and 2200uF as the output cap, which I think 4700uF gives better bass performance than 2200uF.

try two in series for effective 1m1F and compare to two in parallel for an effective 4m4F.

I think you will prefer the parallel arrangement.
If this is the case, then buy a pair of 10mF, one for each channel.

What I haven't tried is changing the feedback-shunt capacitor value, it is currently 22uF which Daniel suggests it's waaay too small value and results in poor bass performance.
 
Comments on PCB design for TDA2030a

Dear All,

I have designed a PCB for a stereo TDA2030a chip. This PCB is already made & I have built one prototype...it is not working as expected! (made this long time back before knowing about this forum :))The chips get heated too much & i get 60-70 KHz on output on my DMM.:confused: I have gathered that this chip is very similar to LM1875!

Can all of you please comment & help me improve this?
 

Attachments

  • 1.pdf
    160.1 KB · Views: 163
  • 2.pdf
    156.2 KB · Views: 123
Last edited: