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Old 9th October 2012, 09:59 PM   #21
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Thanks! Mr. donpetru.

Do i need to use one more pair of D11 and D12 if i use two transistors(MJE2955) in parallel? Likewise for 2N3055.

So, Now, here i have the schematic which is more refined then as before.

More comments are welcomed on the schematic by others.

Thanks.
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Old 15th October 2012, 07:02 AM   #22
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The partner to MJE2955 is MJE3055. They are cute little TO220 size devices.

We wouldn't want to run any devices (transistors, chips or diodes) over 43% of max current listed in the datasheet. That's a handy "ballpark" derating figure; however HFE per current datasheet graph tells the devices actual performance at a given level of current, so using the graph would be helpful. When both conditions are true, derating is successful.

A more linear and more sturdy substitute for MJE3055/MJE2955 systems is: MJL21194/MJL21193

You can use the little MJE if doing one regulator per each channel of LM1875 -or- the big MJL if doing one regulator to run 2 channels of LM1875.

I would favor MJE regulator per each channel of LM1875 because that will give you excellent stereo separation.
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Last edited by danielwritesbac; 15th October 2012 at 07:05 AM.
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Old 15th October 2012, 01:15 PM   #23
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Looking better, some of the audio guys might not like this suggestion but I would remove C8, c9, c10 and c14. A good quality smps rated 1000uF electrolytic will have an ESR of less than 50 milliohms at 100 Khz and 100 milliohms at 1Mhz, the impedance of the 0.1 uF capacitor will not even approach this value until over 30 MHz if ever. The 10UF capacitor does nothing.
You can either look up the capacitor manufacturers ESR tables or simulate it with a 100 - 10 MHz frequency sweep applied to the 3 capacitor set. Modern SMPS rated electrolytic capacitors have very low ESL (this shows in their low ESR figure at high frequency) and do not need supplemental bypassing till into the MHz range, after that ceramic capacitors take over.
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Old 30th October 2012, 06:46 PM   #24
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Quote:
I would favor MJE regulator per each channel of LM1875 because that will give you excellent stereo separation.
Does that means the same regulator circuit twice in parallel for stereo with the same single center tap transformer?

Thanks.

Last edited by noddy55; 30th October 2012 at 07:15 PM.
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Old 30th October 2012, 07:12 PM   #25
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Certain questions are comming out of my mind, just out of curosity to understand things better.I will appreciate, all of those who could help me with these questions.

a). What is exaclty R12,C33 and R13,C34 doing? Are they shunting any frequency to the ground? Which frequency(Is it 225.7Mhz)? How we determine the appropriate value for these components?

b). What are all the frequencies that we need to shunt to the ground in a well designed power supply?

c). How do we calculate the appropriate value of R and its wattage, in a CRC filter?

d). Does using a resistance at the output of the power supply, will have the large effect over the sound quality? If yes, then how we determine the proper value of such a resistor?

e). I have heard people saying that the last smoothing capacitor used in the power supply rail, will have the greatest effect over the sound quality. So it should be good quality and large. Is it True? But, i think i am using the last capacitor as 1000uf(C21, C22). Please, throw some light on this.

f). To determine the proper value of resistance used with LED is always being a mystery or confusion with me. Like i still don't understands how 6.8k(R10,R11) is required in my case with LED's(D9 and D10) at 25 volts. An example would clear this easily, forever.

Thanks.
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Old 4th November 2012, 12:52 AM   #26
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Quote:
Originally Posted by noddy55 View Post
To determine the proper value of resistance used with LED is always being a mystery or confusion with me. Like i still don't understands how 6.8k(R10,R11) is required in my case with LED's(D9 and D10) at 25 volts. An example would clear this easily, forever.
Internet search for LED calculator:
LED calculator for single LEDs

The led will light most brightly and die most quickly if run at maximum. To get the brightest light with a reasonably longer life, I multiply the constant current datasheet figure by 0.43. So, I'll end up running a 21ma diode at 9ma or less. Less current = longer life.

P.S.
Running diodes in parallel doesn't double their current tolerance.
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Old 4th November 2012, 12:56 AM   #27
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Stereo separation:
A V+ regulator and a V- regulator for the left channel
A V+ regulator and a V- regulator for the right channel
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