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Old 7th February 2013, 10:03 PM   #161
prezden is offline prezden  Canada
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Hey guys- sorry if I seem snarkey. I'm just an old man trying to learn something new.
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Old 7th February 2013, 10:42 PM   #162
JMFahey is offline JMFahey  Argentina
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Ok.
In your list of materials you mentioned "a TO220 heatsink", and if you ask a sales guy for that, he will go to a drawer marked "TO220 heatsinks" and give you one ... like the first one I posted.
Which is usually enough for a TO220 transistor, sometimes even for a voltage regulator .... but the LM1875 , although *housed* in a TO220 case, is a real 20W RMS amplifier and with the "regular" one, it will live a hot but short life
It needs something better, like the 2nd example.
As of the other parts, you mentioned "cut and copy " apparently from different schematics, I suggested picking one and sticking to it.
In fact, and specially if you are beginning with this (fine ), it's useful and safe to follow the "learn to walk before you try to run", meaning try to follow the most classic , tried and true path, before trying "improvements" of any sort.
Boring? Maybe so for he who already built a couple dozen projects ... I bet you'll find it quite exciting.
Building a kit is good: it saves many parts sourcing problems, normally uses a classic schematic, many offer PCBs and a few PSU, up to the transformer (or suggest a very specific one).
Some even offer heatsinks !!!
I'd start with something standard, "by the book", and enjoy it.
And later, the Sky is the limit
As a reference, google the LM1875 datasheet, they offer examples and even suggest a PCB.
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Old 7th February 2013, 11:08 PM   #163
prezden is offline prezden  Canada
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Thank you Fahey
I thought the above list was for the same project. First part the basic components and optional components in the last couple posts. After reading your last post I have decided to start with the basic components Daniel listed and forget about the options.
I have built and modified a few D class amps and wanted to move on to a project that would help me learn more about how these things actually work. I am rambling on here
Again- thanks for your help. I'm going to get the order into DigiKey and get going on it
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Old 8th February 2013, 05:31 AM   #164
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Quote:
Originally Posted by lausar View Post
Thanks again. This will be in my office system using Panadora for tunes thru our iPod. Found some 50k pots here...so just add it before the 1st resistor? Can I or should I eliminate any resistors? I want something down and dirty...build once and forget about it...let her play.
That's what the post1 design is for. Put together and play. A lot of component variances have been controlled in that design so that the typical "fine tuning" effort are reduced from weeks to about 10 minutes.

Much smaller component count is possible but might be regrettable by taking a lot more time to get good sound.
Quote:
Originally Posted by JMFahey View Post
I don't find much logic either in avoiding a cap in the feedback loop (so it amplifies DC) and then adding huge (unneeded) caps in the output. ??
If someone wants a design that's ready to go the moment it is built, that is at Post#1. I know its funny looking. But did you try it?

I have many other designs, but that one is arranged for very short timeframe from start to finish. It bypasses much of the fine tuning by not putting 34X gain on an RC. Most of the caveats of that omission are patched by adding output caps to restore some protection, some dynamics and some headroom. Those output caps go at the speaker output jack so the amp is driving a bit of cable first. Its really easy to put them on and they do still cost less than speakers. Again, protection utility is only a small portion of their benefits.
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Originally Posted by prezden View Post
Were my questions above to dumb to warrant a response from anyone
The question wasn't dumb. I did answer. See schematic at Post#1.
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Old 8th February 2013, 11:21 AM   #165
JMFahey is offline JMFahey  Argentina
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If you want the solutions "all together in a single page", take a hard long look at this:
ELECTRONICA / components | projects | applications
Good circuit implementation, "by the book", layout, PCB, finished product pictures, transformer suggestions, even an auxiliary (optional) +/-15V PSU to feed your preamp, if so needed.
The finished PCBs looks like this:
Click the image to open in full size.

EDIT: If you don't want to mess with making your own PCB, this one looks very good:
Click the image to open in full size.
seems to be available at:
http://diyhifishop.com/lm1875-tda203...-pcb-p-18.html
It's for two LM1875/TDA2030 (I guess TDA2050 should fit there too) and includes the PSU PCB.
All for a claimed $9.90 which sounds reasonable.

Last edited by JMFahey; 8th February 2013 at 11:28 AM.
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Old 8th February 2013, 04:32 PM   #166
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Thanks for the information!
Two-chip boards can be transformed into Parallel LM1875 amplifiers which are more sturdy and more elegant. Also, one could choose to upgrade to an offboard power supply.

P.S.
For parallel amplifier on a stereo board, it is possible to jumper the NFB (feedback shunt) caps together at the point where feedback-shunt resistor meets capacitor, so that the capacitor differences (which have gain on them) don't cause excess heat. What I'm saying results in only 1 feedback-shunt cap (it is two caps parallel) so that results are same for both chips. Likewise the input caps can be jumpered together. Parallel amplifiers share all of the caps, none of the resistors. That's easy to remember. Lastly, we'd just add ballast of 0.33R (or similar value) 5w to each + speaker output as is customary for parallel amplifiers.
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Last edited by danielwritesbac; 8th February 2013 at 04:40 PM.
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Old 8th February 2013, 05:07 PM   #167
prezden is offline prezden  Canada
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Thanks Daniel and Fahey. I really appreciate your help and your suggestions I've been reading so much and looking at so many options it's starting to make my head spin. I was dreaming about caps last knight and that can't be good
The one at DiyHiFi looks interesting. I just read the thread that Daniel mentioned somewhere along the way about dual parallel 3886 boards. I have also been considering ChipAmp's 1875 which is quite inexpensive. I wish he provided more info on his site. Click on manual or photos and there is nothing there O well

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Old 9th February 2013, 12:53 AM   #168
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One thing. When comparing LM3886, with LM1875, you'll see LM3886's with onboard power supply and large caps right at the chip to muffle their shout, but if you do exactly the same circuit with LM1875, that would be as dull as any cheap ebay amp kit. The LM1875 favors some 220u~470u caps at the amplifier board, and an offboard power supply.

If it was going to be as easy as using an onboard power supply I would have done it--pair of big caps and a KBU6D would be so easy, and sound dreadful. Hi-fi is not that easy.
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Last edited by danielwritesbac; 9th February 2013 at 01:02 AM.
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Old 9th February 2013, 10:47 AM   #169
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Quote:
Originally Posted by danielwritesbac View Post
One thing. When comparing LM3886, with LM1875, you'll see LM3886's with onboard power supply and large caps right at the chip to muffle their shout, but if you do exactly the same circuit with LM1875, that would be as dull as any cheap ebay amp kit. The LM1875 favors some 220u~470u caps at the amplifier board, and an offboard power supply.

If it was going to be as easy as using an onboard power supply I would have done it--pair of big caps and a KBU6D would be so easy, and sound dreadful. Hi-fi is not that easy.
I actually disagree with this. I've built two 1875s just in the last few weeks. One had 470u caps at chip, the other 2200u. Same off board psu. There wasn't much in it but the 2200u had the edge at volume: purer, more lifelike. They were both going into nominally 4 ohm, which may have made the difference.

If I had some 8 ohm speakers in my workshop I would be interested to hear any difference there.
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Old 9th February 2013, 11:51 AM   #170
JMFahey is offline JMFahey  Argentina
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I don't find a reason why having higher filter capacitance (= less ripple - stiffer voltage - softer current delivery - higher power reserve - etc. etc. etc.), even better stsying close by, connected with thick tracks ..... might "muffle" ??????????? the sound ???
Now the amplifier will be *dull* ????
No logic to it.
It's quite the other way around.

PS: there's a reason for typical 0.1uF decoupling caps being applied "as close as possible to power pins, ideally on the same pads".
Same here.

Last edited by JMFahey; 9th February 2013 at 11:54 AM.
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