LM1875 integrated Chip Amp with external PSU

cuthien said:
Where do you get this type of board (without the copper.) The boards at radioshack and outlet stores in my area all have the copper on one side. For some reason, i like the spider look better :D Thanks.
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ratshak part number 276-1395 a

I used pad-per-hole board for the second one because soldering the lead directly under the component is slightly more stable. Plus the copper pads allow me to run the jumpers at right angles easier. It's basically for visual clarity in photos.
 
It's official

I just got confirmation that a version of this amp will appear as a major project article in Make Magazine #22 in April 2010. I'll probably start another thread to show some of the progress.

With Schottky rectifiers and 4700uf capacitors the power output goes up from 8 Watts to 11W into 8 Ohms and 13.7W into 4 Ohms.

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So... How much did it cost you after any medications and/or trips to the hospital? :D


Many years ago, I did some plumbing. Without going into details, the plumbing fix was $6. Medical bills for separated shoulder was $600. :sigh:
 
cfranz said:
So... How much did it cost you after any medications and/or trips to the hospital? :D


Many years ago, I did some plumbing. Without going into details, the plumbing fix was $6. Medical bills for separated shoulder was $600. :sigh:
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This stuff is therapy for me. I love wiring up circuit boards and testing them. It's like playing the kids' game Operation or defusing a bomb. It's challenging and I like to set difficult goals to test my skills.
Wait until you see this finished. I think it's going to show well.
 
cuthien said:
"ratshak part number 276-1395"

Thanks. I will put in my order.

This thread here at diyaudio showing some improvement that you can do over the standard schematics:
http://www.diyaudio.com/forums/chip...egarding-example-application-datasheet-2.html
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I read through those. I used the standard NatSemi schematic and parts callouts because it's a very stable and repeatable version. Suitable for a wide variety of applications with high reliability.
In my experience building amps with LM1875, TDA2050, 3875, 3876 and 4780, passive component types and values will make some difference, but you're still dealing with a fixed circuit topology and 42 or more transistors in the chip. Looking for sonic nirvana in the right input cap is like looking for better performance from your car by changing the spark plug wires. It's a visible change but the effect is swamped by all of the dominant factors that are unalterable in the chip design.
 
"passive component types and values will make some difference, but you're still dealing with a fixed circuit topology and 42 or more transistors in the chip. Looking for sonic nirvana in the right input cap is like looking for better performance from your car by changing the spark plug wires. It's a visible change but the effect is swamped by all of the dominant factors that are unalterable in the chip design. "

That makes perfect sense. Thanks.
 
Final version

Here's the final version that will appear in the magazine article. I made it 1" longer to make assembly easier. The diodes are now SB540, which are smaller than the 10A 100V ones I first used. The volume pot and switch have been offset to the left to allow better clearance inside to the tops of the PSU caps. I'm shipping it to the magazine photographer today for its closeup.

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Ross, I am still, after 4 days, thinking about how good this amp sounds. It is truely hitting on all 8 cylinders. Anything coming that close, would cost $500 or better. You done good!!!
 
djnagle said:
Ross, I am still, after 4 days, thinking about how good this amp sounds. It is truely hitting on all 8 cylinders. Anything coming that close, would cost $500 or better. You done good!!!
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Thanks, Dennis. I wasn't going for an ultimate fidelity design. Just something simple that anyone can duplicate with common parts. I was really surprised at how good it sounded. makes me want to do another with fancier parts to see what that would sound like.

I really think it helps a lot to follow the most careful grounding practices with these. It's a hassle to run 10 different wires to a star ground, but I'm sure I hear cleaner sound when it's done that way.

As usual, following the manufacturer's recommendations turns out to be right.

Today I shipped the unit in the picture off to the magazine's photographer. I can't wait to see how the article turns out after their editors, photographer nad artists are done with it.
 
No doubt it is CLEAN. The bass really surprised me. It was super tight, and the mids were lush, and the highs did not hurt my ears and I am extremely sensitive in the range.

Can't wait to see the layout of the mag. I'm sure using high end parts would change the sound but I don't know how it would get better than what I heard.
 
Article to appear in about 2 months

I've been corresponding with the editors, photographers, artists and researchers on this project for the last week or so. They're tuning up the article for issue #23 of Make Magazine, to appear in July or August. I can't believe what they've done with this. It's one of the best electronics article layouts I've ever seen. The whole deal is 14 pages long for the description, build, BOM and notes. I donated the prototype to the magazine in thanks for the excellent photography that they did on the article cover shot. I couldn't be happier with the effort and resources that they've put into making my little amp into a big production.
If possible I'll get part of the article from them to post here when it goes to press.

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In print!

The editor just informed me that Make Magazine #23 with my LM1875 amp featured has gone to press. Now all of my errors in the article are set in stone. I'll get a page or two to show off if I can when it's available.
 
Bauhausler said:
The editor just informed me that Make Magazine #23 with my LM1875 amp featured has gone to press. Now all of my errors in the article are set in stone. I'll get a page or two to show off if I can when it's available.
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Ross, thanks for developing this nifty project.
I picked up the magazine last weekend, now to source the parts. It was the article that led me to this thread. I'll be using an unused black anodized case I picked up a couple of years back for another project that I eventually had someone else build for me. This one won't take the same space and equipment resources and looks like an easy one without a ton of electrical calculations.
Anyone in Canada know where I can pick up some LM1875 chips?
 
carbonman said:
Ross, thanks for developing this nifty project.
I picked up the magazine last weekend, now to source the parts. It was the article that led me to this thread. I'll be using an unused black anodized case I picked up a couple of years back for another project that I eventually had someone else build for me. This one won't take the same space and equipment resources and looks like an easy one without a ton of electrical calculations.
Anyone in Canada know where I can pick up some LM1875 chips?
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Thanks! I hope you'll enjoy building it.
I got my chips from Mouser, Digikey or Newark. I can't remember which. You can use TDA2050A also, but you have to add reverse biased diodes from the output to voltage rails because it doesn't have internal protection diodes. The performance is the same.

This weekend is Maker Faire Detroit at The Henry Ford. I'll be there at the Make Magazine table.
 
voltcontrol said:
Conrgats on the great work, not the first chipamp, but very good to see it published in makezine.
Also congrats on the interview, nice to read, :)
http://blog.makezine.com/archive/2010/08/ross_hershberger_interview.html

Looking forward to the 'rocket guidance' amp :)
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Thank you! The folks at Make Magazine have been just great to me. I highly recommend this DIY magazine packed full of wonderful ideas from passionate people.
Chip amps are old hat to DIY audiophiles but haven't had wider exposure. I wanted to take this audio gem, with a very high performance/cost ratio and bring it to a larger audience. I hope a lot of non-audiophiles will build and enjoy amps as a result of my article.
 
Source or Part # for 1 uF Capacitors

I can't find compact enough 1 uF film capacitors to fit locations I8-I13 and AD8-AD13. Does anyone have a part number and source for these? I can't find anything suitable in the Vancouver area. My only option would be to take an axial capacitor and stand it on end. I could insulate the exposed lead but it's not a very elegant solution.
 
carbonman said:
I can't find compact enough 1 uF film capacitors to fit locations I8-I13 and AD8-AD13. Does anyone have a part number and source for these? I can't find anything suitable in the Vancouver area. My only option would be to take an axial capacitor and stand it on end. I could insulate the exposed lead but it's not a very elegant solution.
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The ones I used are 5mm wide and have 13mm lead spacing. Something like this Wima, e**y number 280448082399 should work. A wider cap will fit if you lean it over toward the AG end of the board, away from the A end of the board so it clears the electrolytic cap next to it.
In the article's online discussion section I've added recommended dimensions for all of the components.
 
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