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Chip Amps Amplifiers based on integrated circuits

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Old 19th January 2013, 08:41 PM   #51
blu_glo is offline blu_glo  England
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Since the values are so high, they'll need to be electrolytic, would there be any benefit to a poly cap bypass on the electrolytics in the signal path? I built the Millet Starving Student Hybrid headphone amp and used a poly bypass on the output capacitors and did notice a difference, maybe that's a different case though.

Nichicon KZ or FG a fine choice here?

I would still plumb for non-polarised electrolytics and yes, decouple them with your poly bypass caps.....
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Old 19th January 2013, 08:46 PM   #52
blu_glo is offline blu_glo  England
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BTW, here's my MSSH I built last year. Other than a cmoy, this was my first real amp project. I'm pretty happy with how it turned out. I use it on my desk at work most of the time. Funny how many people are somewhat afraid of glowing tubes for some reason...[/QUOTE]

Excellent! I have my own collection of Leak valve gear - 2 off Stereo 60s tuner and preamp, greatr combination and they don't shame themselves with CD or streaming/internet radio!!!!
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Old 20th January 2013, 03:16 AM   #53
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Quote:
Originally Posted by Mooly View Post
That looks nice Excellent job.

The big thing to concentrate on with the chip amp is the layout and grounding of it all.

Did I post a link to this ?
3 stage LIN topology - NFB tappings?

you have to get this right.
Well, much of that was above my understanding, but let me take a stab at implementing this. See attached with grounding scheme. Am i close?

Is it possible to have an individual star ground for each channel, and then bring them together at a single point, or is it just better to bring everything to one common point?

Will the signal and supply ground points need to be isolated from the chassis since the chassis is attached to earth ground (and since they'll all be joined via resistors). Also, what wattage should those resistors be for the grounds?

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Originally Posted by Mooly View Post
Don't be afraid of caps in the signal line

It should look something like this... I've left the bypass as it was.

The 470K's define the DC conditions on the caps when they could otherwise be "floating". It stops load thumps and bangs when switching and connecting.
Thanks, added these resistors and changed values based on your edits.

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Originally Posted by blu_glo View Post
This subject has already been touched apon by Mooley, thanks, although I may repeat and/or exand on it we seem to agree!
the formula you want is if we assume C (in Farads) R (Ohms) and frequency of interest F (in Hz or cycles a second):

C= 1 / (6.284 x R x F) [ 6.284 = 2 x pi (approx) ]

If, as Mooley suggests, you want to include subsonics you would probably use 1Hz as F - it is indeed what I tend to do!

If you use seperate sub or small speakers with no chance of producing subsonics, you can use even higher eg 5 or 20Hz

My suggested values would be C1 10uF; C2 100uF, Ci (power amp feedback) 220 uF all at least 35V non-polarised electrolytics if you can. It's a personal thing but i'm not a fan of using polarised electrolytics in signal paths with no DC (as all these positions are). You can however "get away with" ignoring me on that one!
Updated with your recommendations for C1, C2, C6, and Cin.

But, lets say I really only need a 10hz cut off frequency. This amp won't be used on speakers that can reach near that low, and at some point I'll probably add a sub (or build a totally different amp ). It seems like i should be able to use smaller values for C1, C6 and Cin (and maybe C2 and Ci?)
f = 1/(2 x π x 20,000 x 0.000001) = ~7.96 hz
So a 1uf cap should be sufficient for those 3 positions, no? That would let me use poly caps in those positions instead of electrolytic, which is generally preferable too, right? Then no bypass cap silliness (which i might not do anyway after reading more into it. or maybe I'll get some to experiment with and see how it sounds).
Not sure what that means for C2 and Ci though.

I've also included my plans for the power supply now.

Really, thanks for the help. I'm definitely learning a lot through this process. It's fun.
Attached Images
File Type: png LM3886 wTone V3.png (200.1 KB, 235 views)
File Type: png LM3886 Power Supply.png (74.8 KB, 231 views)
File Type: png Screen Shot 2013-01-19 at 10.20.31 PM.png (143.7 KB, 226 views)

Last edited by mxriddler; 20th January 2013 at 03:21 AM.
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Old 20th January 2013, 07:31 AM   #54
Mooly is offline Mooly  United Kingdom
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That looks OK for grounding. The most important thing is to keep the high current lines (which means the power amp) separate which you have shown. Separate... as in not connecting other components to those lines.
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Old 21st January 2013, 06:57 PM   #55
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Ordering parts in the next day or so. Will post results as I get it built.

Thanks all!
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Old 21st January 2013, 07:16 PM   #56
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Thats good

(When you power it up for the first time I would recommend a bulb tester... 60 or 100 watt filament bulb in series with the mains)
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Old 10th February 2013, 04:34 PM   #57
blu_glo is offline blu_glo  England
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.... all gone quiet....
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Old 10th February 2013, 07:31 PM   #58
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.... all gone quiet....
I've not forgotten about the thread nor given up! It took me a little longer to get the parts together than I expected. But I have everything now, except for a case.

I was going to go with an Antek transformer, but when I went to order one, everything was out of stock. I emailed them and turns out they just had a fire in their offices and warehouse and won't be back in business until April. Ended up going with an Avel transformer from parts express.

I just started building this week. I've got my power supply board together and tested without load and seems to be working fine so far. I'm working on planning/assembling the amp boards now. Once I get both channels of the amp working, I'll move onto the tone section and power supply.
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Old 10th February 2013, 07:34 PM   #59
Mooly is offline Mooly  United Kingdom
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Take it steady checking along the way. And don't forget the bulb tester when you power up for the first time.
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Old 11th February 2013, 07:10 AM   #60
blu_glo is offline blu_glo  England
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- Thats an interesting shape for the power amp pcb??
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