Which is the most effective decoupling?
1. Rail to GND.
2. Rail to Rail.
3. Cross Rail to Rail with the inverted partner chip.
1. Rail to GND.
2. Rail to Rail.
3. Cross Rail to Rail with the inverted partner chip.
isn't it highly dependent on layout?
examples:
with the shine7 layout, for method #3, lead inductance would be very large and you would be creating a rather large antenna.
given a layout with good symmetry, #2 or #3 might win as a way around the poor negative rail PSRR.
given a layout with a good close by ground point, #1 might win.
examples:
with the shine7 layout, for method #3, lead inductance would be very large and you would be creating a rather large antenna.
given a layout with good symmetry, #2 or #3 might win as a way around the poor negative rail PSRR.
given a layout with a good close by ground point, #1 might win.
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Very nice writeup; Taming the LM3886. Probably the most comprehensive I've seen on this chip.
simplistic of me....but...
Cant you just feed the input signal thru two opamps,one inverting and the other non inverting, and drive the LM3886 (all in the same mode)?
Cant you just feed the input signal thru two opamps,one inverting and the other non inverting, and drive the LM3886 (all in the same mode)?
that's pretty much how a drv-134 bridge adapter works but it has precision resistors built into the chip along with the opamps. if you do decide to roll your own it works better to let the non-inverting opamp drive the inverting one to keep the inverting opamp input loop area confined
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Wouldn't that calculation be for a 2 chip amp? IE PA100? I didn't run the numbers other than in the Overture Design Guide from National. It claims 160W into 8 ohm with 6 paralleled LM3886 with a +/- 24V supply. Maybe that's what Jeff Rowland also did? 😉 I now these numbers can be a bit optimistic and I don't question that. Also, the power was never anything I wanted to discus in this thread anyway.
But, and a big but, after you mentioned it I re-checked photos of the JR amps and I'll be damned, the orange bars seem to has two traces/wires in them. So one bar is + and - for the speaker, and the other bar carries the +/- supply for the chips. So you are right, it is a BPA.
But, yet again but, that doesn't really change anything of what I wanted with this thread. And that was how to parallel multiple LM3886 easy and cheap.
Tom.
Maybe I express my self poorly in English (and I might have been a bit drunk when writing the thread) but my intention was never to reverse-engineer his amps. Neither am I a beginner in this. I have built several LM3886 based amps in all kind of configurations. I have also sold 250 PCBs back in 2008 that had 3 LM3886 paralleled complete with DC-servo, input buffer and on board voltage regulators for the OP-amps. But thanks for the links. (And yes I had all ready seen your material and I have great respect for your knowledge).
I agree with you also that there is room for a lot of improvements on JRs amps. I don't build mine that way, this thread was meant to focus on how to adjust the DC-offset easy and cheap. Now its everything else.
where _exactly_ in the design guide do you see a claim that a PA-600 can deliver 160watts into 8 ohms with a +/-24 v supply and no bridge?
Enter the values in the Excel spreadsheet - chop - chop - magic.
Have you not seen the Excel-file made by National?
the schematic linked to in second paragraph of the following post has several on-the-cheap pots examples for setting offset [specifically they are r4, r14, r55, r69 and r82] the general technique will work with any power opamp.
http://www.diyaudio.com/forums/chip-amps/264015-tda7293-inverting-t-network-fb-point-point.html
http://www.diyaudio.com/forums/chip-amps/264015-tda7293-inverting-t-network-fb-point-point.html
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Enter the values in the Excel spreadsheet - chop - chop - magic.
Have you not seen the Excel-file made by National?
you said it was in the design guide.
where is it in the design guide?
http://www.leetmaa.se/blask/Overture_Design_Guide15.rar
Here. I uploaded it for you. It's an excel file released by National to help people calculate designs in their Overture series. And yes, its legit.
If one chip can supply 22 Volts to a load. What is the maximum voltage that 2, 4 or 6 parallel chips supply?
that spreadsheet is not nearly magical enough to overrule kirchoff's circuit laws and ohm's law 🙂)
The problem with the spreadsheet is that for the multi IC calculation it divides the load impedance by the number of IC.
For 6 parallel IC the load changes to 1.33 ohm and not the 8 ohm as used for the single IC calculation.
So if you want the 6 parallel IC to generate 160 Watts you need a 1.33 ohm speaker.
For 6 parallel IC the load changes to 1.33 ohm and not the 8 ohm as used for the single IC calculation.
So if you want the 6 parallel IC to generate 160 Watts you need a 1.33 ohm speaker.
As usual, one must have sufficient knowledge of the software to be able to check the results, BEFORE one comes to rely on the modelling, or predictions.
If one does not understand what is going on inside the software/model, then one should NOT be relying on the predictions.
If one does not understand what is going on inside the software/model, then one should NOT be relying on the predictions.
With 6 in parallel, one can get within a couple of volts from the supply rail voltage. (see 3886 datasheet)
With Vs at +/-42V max loaded, ~40Vp, ~28.5V continuous, 100W/8
You can check out the 2 plus 4 parallel chips yourself.
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