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PostPosted: 28 Oct 2008, 17:20 
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RiGuy wrote:
Actually you are not following the circuit as shown in 1192. You are using monster caps on your chips. These are supposed to be about 4.7uf and polypropylene.

Interesting. I don't know if this would contribute to the problem since it looks like you have snubbers in place, but my preference is to have small caps on the chip and the big caps in the power supply. I don't think it would hurt to remove them.

As for no caps on the chips, I have not tried it, but I would at least have something small there.

I have not tried bridging this chip so I don't have much to add in that regards.

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PostPosted: 28 Oct 2008, 17:37 
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BSGD and I have been PMing about this as well to get exactly what he wants on the boards I will make for him.
He mentioned to me that the caps are actually not noted in the schematic but referred to in another place on AN1192. Its referred to in the BOM as additional components not noted on schematics. The caps in the BOM are 4700uf.
Still, probably not necessary as we get away with 100uf or less on the LM3886 amps but it might not hurt to try without them or with significantly smaller caps in place. Maybe even on just one amp and then if it works try it on two and bridge them.
The DRV134 seems to be what helps people keep these things behaving when they are bridged.
Gio, what do you think of placing the DRV134 and do you think this would address his problem?
I searched DIY Audio for "bridged LM3875" in the chip amp forum and found a lot of references to DRV134 and the AN1192 even refers to using something similar but that they did not want to include it in the schematic because it was not desperately necessary and it would clutter the schematic.
Ri

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PostPosted: 28 Oct 2008, 19:00 
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I think he needs a balanced input.
So you use the DRV134 and it takes a SE input and splits it into a balanced output then you feed one of each of the outputs to one of each of your bridged chips.
DIGIKEY PART http://search.digikey.com/scripts/DkSea ... RV134PA-ND
TI LINK http://focus.ti.com/docs/prod/folders/print/drv134.html
Quote from TI
Description
The DRV134 and DRV135 are differential output amplifiers that convert a single-ended input to a balanced output pair. These balanced audio drivers consist of high performance op amps with on-chip precision resistors. They are fully specified for high performance audio applications and have excellent ac specifications, including low distortion (0.0005% at 1kHz) and high slew rate (15V/µs).

The on-chip resistors are laser-trimmed for accurate gain and optimum output common-mode rejection. Wide output voltage swing and high output drive capability allow use in a wide variety of demanding applications. They easily drive the large capacitive loads associated with long audio cables. Used in combination with the INA134 or INA137 differential receivers, they offer a complete solution for transmitting analog audio signals without degradation.

A good link for building the DRV134 circuit
http://www.diyaudio.com/forums/showthre ... post494571

One poster described using the DRV134 or DRV135 for this purpose:
Well the purpose digi01 built it for is to build a bridged gainclone.
This circuit (using the EXCELLENT drv135 chip) is taking a NON-inverting signal and splitting it evenly to send out a balanced + and - signal to drive the inputs of matching (hopefully paralleled) Gainclones.
Therefore one gainclone amplifies the positive half of the signal, and the other Gainclone amplifies the negative half of the signal.
When the two halves are combined the amplifier develops "roughly" twice the voltage swing and power output.
If the gain of the drv135 can be raised above 1 then it could be used as the pre-amp in the front end of a controller or high gain amplifier.


A website detailing more of the Balanced Line Driver is here:
http://assemblycraft.com/bld.htm

Ri

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PostPosted: 07 Nov 2008, 09:34 
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Bernardo,
How did the testing go that you were going to do?
Ri

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