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wrl 21st June 2003 09:29 PM

very simple gainclone questions
Ok, so I am about to get started building my hybrid/esl speakers and I was thinking of using the bridged schematic straight out of national's info sheet here for the woofers. Ok, here come the questions (please bear with me as many of these may sound silly)

First, the notes state a seperate power supply for each channel is necessary. Is this only for the BPA version, or will this also be necessary for the bridged version if so, I was thinking of getting similar transformers from plitron as the ones they reccomemd in the parts list are a little expensive. Also, doesn't +- 42 V seem high for these chips?

Second, I assume that the servo circuits are only necessary for the BPA version right?

Third, (please, I'm new) I see that chips on the schematic only have 3 leads, but the actual chips come with ten. I know that the power supply will go to 3 more in the 3886, but that still leaves 4 pins. I will probably bypass the mute (I assume by shunting to ground?) for the rest of the pins... should I just follow something similar to what national shows in their application note for the lm3886?

I have read Nuuk's Beginner's Gainclone guide and it was very helpful, but I am confused how different a bridged circuit would be (other than the obvious i.e. more power consumption etc.)

Other background details. This amp will power 2 eight ohm woofers to be decided. I will be using ~4X2 panels powered by a leach amp in conjunction with the woofers in a tl line. I would like this circuit to put out around 100W per channel.

Thanks in advance


wrl 22nd June 2003 05:42 PM

oops, nc== not connected:rolleyes: Alright forget the # of pins question.

my bad.

But I still need help on the other questions. + Any feedback on the differences I will need to take into account from nuuk's sight into building a bridged version (other than they are different circuits).

Please guys, I've been looking at this like 4 months and am ready to get started.


VictorG 23rd June 2003 02:42 AM

I guess I am just a little disturbed at your lack of knowledge on what the "NC" would mean in a circuit diagram... should you really be working with high voltage at this point? electicity is serious stuff kid, it could kill you. try taking an Electrical Engineering class when you get to college. Should give you the basics on circuiting. Until then, why don't you try radioshack, they have some pretty safe kits which should teach you the basics. If you need help with some of the nuancies of these basics (soldering, capacitor polarity, voltage vs. current) let me know. Good luck.

leadbelly 23rd June 2003 05:00 AM

I'll take a stab at answering because I just *hate* reading posts of discouragement (on DIYAUDIO for pete's sake!!!).

1) You don't *need* separate PS for each channel. It is recommended to do so because if there is a big power tug on one channel, it doesn't impact the other channel as much.

42VDC is high. The load you plan to drive affects this.

Just do what best you can in your budget re transformers.

2) Yes, and there are threads on bridged designs avoiding servos.

3) Mute bypass is not to ground.

wrl 23rd June 2003 07:01 AM

haha, its all good, victor is my buddy from back home. The discouragment is in jest. (As we try not to kill eachother with our projects) :) No prb, thanks for your reply. I am reasonably familiar with circuits, although I am new to audio circuits. I can swing seperate transformers for the amp on my budget, I just didn't know if 42V was too much for the chips, I guess not considering it is in national's app notes. I'll be driving an 8 ohm load.

I know, I have read many of the posts on bridged gainclones, I just didn't know if there were drastic differences between their circuits and the one in the app notes. From what I understand, they all seem pretty similar. I'll keep researching.


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