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Old 6th April 2008, 09:59 AM   #51
Nordic is offline Nordic  South Africa
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I'm going to limit the gain on my units quite a bit to stay within the clean THD band. a gain of about 16 to a 1V signal looks about right, judgeing from the graphs etc.

I have enough high power stuff here, as welll as the usual low power gear like PC speakers... which is what I want to use mine for. I noticed once that my logitech speakers actualy can sound pretty good coupled to a decent amp...

It gets sad when you have too many amps...
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Old 6th April 2008, 01:25 PM   #52
Nordic is offline Nordic  South Africa
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Click the image to open in full size.

spent some more time on the layout...
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Old 6th April 2008, 02:51 PM   #53
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Hi Daniel:
Thanks for your remarks, I'll try for the 1uF poly-22uF NFB.
The spreadsheet you attach is too complicate to my knowledge (my electronycs knowledge is very, very basic, sorry, but I'll try, I promise).
Have 22uF/63V, seems to be ok.
The PS I choose is 18+18V center tapped to drive 4 LM1875 10ABridge diodes is fine? (i.e. KBU10M? and 20000uF/50v per rail?). With this configurtion I expect to drive 2x 5"mid's and 2 tweeters, all 8ohm.
The source I'll use is active crossover from
http://www.siliconchip.com.au/cms/A_30278/article.html
Thanks again.
Iván
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Old 6th April 2008, 03:38 PM   #54
Nordic is offline Nordic  South Africa
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A little further along in concept now.
These will make some nifty multi channel bricks...
Size about 9.5" x 1.8"

Click the image to open in full size.
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Old 6th April 2008, 07:21 PM   #55
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Quote:
Originally posted by Nordic
A little further along in concept now.
These will make some nifty multi channel bricks...
Size about 9.5" x 1.8"

Click the image to open in full size.
Seeing that pretty picture, I can't help but think: "Parallel, parallel, pant, pant, pant, purr, slobber, bark!" or something like that. Hmm. I may have just made the oddest reference yet to AN1192. Anyway, is parallel an option with that board?
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Old 6th April 2008, 07:36 PM   #56
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Quote:
Originally posted by Iván Francisco
Hi Daniel:
Thanks for your remarks, I'll try for the 1uF poly-22uF NFB.
The spreadsheet you attach is too complicate to my knowledge (my electronycs knowledge is very, very basic, sorry, but I'll try, I promise).
Have 22uF/63V, seems to be ok.
The PS I choose is 18+18V center tapped to drive 4 LM1875 10ABridge diodes is fine? (i.e. KBU10M? and 20000uF/50v per rail?). With this configurtion I expect to drive 2x 5"mid's and 2 tweeters, all 8ohm.
The source I'll use is active crossover from
http://www.siliconchip.com.au/cms/A_30278/article.html
Thanks again.
Iván
Hi Ivan!

My electronic knowledge is also basic; however, my soldering and stubbornness are in excellent condition.

Check out the PDF files at national semiconductor. The lm1875.pdf and lm1876.pdf are quite informative. The spreadsheet works from the variables in lm1876.pdf. It is 2x, LM1875's internally, removes monoblock potential, limits power, and adds spike protector's possible noises; however, the data file is a useful reference because it is more up to date.

I can't answer most of your power supply question because I don't know the amperage or VA for your transformer, and also can't imagine why a triamp system would use a quad amp that almost defeats the purpose, instead of monoblocs which are more suited to the goals of triamp systems.
As far as bridge rectifier units, I only have experience with KBPC, which is quite huge. You might ask Nordic and Ashok about the model code for the mini rectifier.

Here's my guess on your PCB layout. I have made the first component at the chip's input to be a load. The input circuit is now driving a 22k load.
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Old 6th April 2008, 08:05 PM   #57
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Hi Daniel:
A'll check all the data you propose, thanks for encourage me to keep learning about this littles (electronycs) secrets.
I also have a pair of KBPC 25A bridge rectifiers. Just wondering to use only one trafo and one PS for the four units.
Thanks a lot for the pcb correction. I'll make the changes immediately.
Cheers,
Iván
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Old 6th April 2008, 08:59 PM   #58
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Hi Ivan!
On your tri-amp, there's two benefits:

One is that its a crossover style that gives an easier time with driver selection.

The other benefit is great dynamics. To me, that means monoblocs. Otherwise, opportunity is lost.

Although, I can't really answer this for you, here's a guess.
That's mid and tweet for left on one power supply, but mid and tweet for right on the other power supply.

Per each pair LM1875 chips, 70va (2 ampers) and 8800uF (4400uF per rail) is about the minimum. That would also need a pair of 100nF at the rectifier.
See, it doesn't cost more.

Seperate power supplies for left and right, might preserve the intended dynamics of the tri-amp. This is also true of stereo and multi-channel setups, as far as I know.
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Old 6th April 2008, 09:19 PM   #59
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Hi Daniel:

You are right, I was a little confused about the PS's , one for the right channel and the other for the left channel (both driven one tweeter and one mid's).
I have the caps and the diodes, only need to buy the two trafos.
Thanks again.
PS: tomorrow I"ll post the new pcb's picture.
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Old 7th April 2008, 12:03 AM   #60
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Quote:
Originally posted by Iván Francisco
I have the caps and the diodes. . .
Hi Ivan!
My studies of power supplies do suggest that the 1 piece bridge rectifier unit may be especially helpful to amplifiers running from center tap transformers. I suppose that's because the diodes within are perfectly matched?

In the study, fidelity wasn't measured because there are work-arounds in power supply design, but the measure was heat at the heatsink.

In testing several seperate diodes verses several random 1 piece bridge rectifier units, with transformers pushed over their amperage limits, all of the 1 piece did well, while only one of the diodes did well--the Motorola Litespeed series MR.

The remaining seperate diodes did poorly, and the very worst was On-Semi's MUR860, followed closely by their MR and FR series. That indicates some variance by brand as well as the usual advertisments <> applications.

So, it seems that the 1 piece bridge rectifier unit is a good partner for LM1875. Does anyone have some news on specific models that they currently use? That would be greatly appreciated.

P.S. So far, we have documented KPBC2504, which is huge, so it would be great to have news of some smaller options.
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