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Old 29th December 2005, 02:16 PM   #11
AR2 is offline AR2  United States
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Quote:
Originally posted by -_nando-_
84v total, it's 42+42v.

I don't have other transformer, and I'll cut the low frequency, so I don't think the 3886 will stress so much heh !

If your transformer is 42 + 42 V, after unregulated PS (diodes and caps) you will have roughly 58 V +58 V. Please read National spec sheet because you will burn your chip. Your Voltage is exceding maximum allowed for the chip. You will have 116 - 119 V between rails.
http://www.national.com/pf/LM/LM3886.html
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Old 1st January 2006, 12:14 PM   #12
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No no no no ! I'm not crazy heheheheh !

42+42 AFTER retification !


I found LM 338 to regulate this 42v to 30v.... But I need the negative voltage equivalent (like LM78XX / 79XX) to regulate -42 to -30v....
What's the part number please?
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Old 1st January 2006, 02:04 PM   #13
lineup is offline lineup  Sweden
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Quote:
Originally posted by -_nando-_
I found LM 338 to regulate this 42v to 30v.... But I need the negative voltage equivalent (like LM78XX / 79XX) to regulate -42 to -30v....
What's the part number please?
Pedja Rogic regulated Gainclone supply - LM388

You should use two LM388 to get +-30 VDC.
This supply is very wellknown at this forum.
If you search "Pedja LM388"
you will find several threads on how using LM388 for gainclone.

You need trafo with two separate windings.
Such a trafo has 4 wires on secondary.

Not a trafo with one winding with 0V tap at half/middle (3 wires).
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Old 1st January 2006, 03:34 PM   #14
venki is offline venki  India
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Hello nando,

If you already have a centre tap transformer. Better option i think will be to use the normal 78xx and 79xx with a power transistor 3055, 2955. To achieve the required voltage eg 30v (assuming you have only 7824) you can lift the groung of 7824 to +6v by a 7806. Likewise for the negative voltage. The output of the regulator is connected to the base of transistor, collector to unregulated supply(42v) and emitter as output. Not sure if there is some other problem in using this. But i have being using this circuit for quiet some time.

Venki.
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Old 1st January 2006, 07:43 PM   #15
Mick_F is offline Mick_F  Germany
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Consult the datasheet! If you want to drive 4 Ohm speakers, your rail voltage should not exceed 30 V

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Old 1st January 2006, 09:24 PM   #16
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Quote:
Originally posted by venki
Hello nando,

If you already have a centre tap transformer. Better option i think will be to use the normal 78xx and 79xx with a power transistor 3055, 2955. To achieve the required voltage eg 30v (assuming you have only 7824) you can lift the groung of 7824 to +6v by a 7806. Likewise for the negative voltage. The output of the regulator is connected to the base of transistor, collector to unregulated supply(42v) and emitter as output. Not sure if there is some other problem in using this. But i have being using this circuit for quiet some time.

Venki.
GREAT ideia !

But power transistors have a little loss, like ~0,6v... If I play music loud, will the transistor have more loss?


Quote:
Originally posted by Mick_F
Consult the datasheet! If you want to drive 4 Ohm speakers, your rail voltage should not exceed 30 V

Mick
So ! I'll drive an 8 Ohm 40W speaker !

In the datasheet says that the MAX voltage is 94v (47+47), when there's NO SIGNAL in... So, this is the peak voltage when the PSU is not heavy loaded, like when we play music loud. My PSU give 84v (42+42) when it's not loaded ! So, playing music this voltage will fall down. The same PSU is shared with an c200 driving a 4 Ohm 125W subwoofer, so when I push it to LOUD the voltage of supply will realy fall, then the 3886 will not suffer so much. The heatsink is big too !

With all this, still dangerous use 3886's this way ? Will be two 3886's and a c200 in the same supply... It will be used every day, but not too loud
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Old 1st January 2006, 10:08 PM   #17
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Hell... I was reading the LM78XX datasheet and it only support 35v of input ! My psu is 42+42
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Old 1st January 2006, 11:06 PM   #18
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Quote:
Originally posted by -_nando-_
Wow

But I"m thinking in use 50v 47uF capacitors between the amp and the speakers. These amps (3886) and speakers are not going to play bass, just mids and high... Bass will be an c200 with 12" 125W subwoofer.

With these capacitors connected between the amp and speakers, will the speakers go away if the supply connection fail?

If the answer is yes or no, doesn't matter, this is not gonna fail


Any crossovers project ?



47uf and 8ohm(two 4ohm series connected) = 400hz crossover frequency. This is too high for crossing over to a sub.
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Old 2nd January 2006, 12:10 AM   #19
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For sure, I tested and I hated the sound.

But, I'll not use crossover for 3886's anymore, I'll use a 7way equalizer, then I reduce the bass.

I'll just use a crossover for SUB, but I want cut the frequency about 150Hz, and I can't find any crossover over the internet with this frequency cut...


About the SUPPLY, I think I found the solution, designing the attached supply.

The logical is the following:

+- 30VAC -> Retification -> +- 42VDC --> Fuse* --> Zenner 24v Regulator** -- LM7812 and LM7912 regulators*** --> 7824 and 7924 regulators **** --> TIP3055 and 2955 power transistors



* After the fuse, the C200 Amplifier will be connected.
** I'll use zener 24v regulator, because 78/9XX only suports max 35v
*** It's to lift the ground of the 7924 and 7824 regulators, because they only suports 40v. So they will work with + - 30V
**** They will drive the power transistors, because of the current that the system will drain

The output voltage to LM3886s will be +-35v, not 36, because the power transistors are not 100% efficient.

35v is a very good voltage, they will drive 8 Ohms speakers.



What you think?

FEEDBACK WELCOME !

edit: I used Multsim7 only to DRAW the schematic... I don't know use this software enough to simulate and etc... I used paint too heh
Attached Images
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Old 2nd January 2006, 04:56 AM   #20
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