Difference between Bridge & Parallel mode

[Peter Daniel]

Originally posted by slackman

I decided to test the parallel mode ampmodule made by Peter Daniel,
maybe i try the bridged mode module later on (from jackinj).

The main difference between those two is that to use my board in bridged configuration you need a phase splitter, or a source with balanced output. Jackinj board is to be used with a single ended input.

As I can configure that board in all 3 modes of operation (using basically same components), my preference with regards to the sound is as follows:

1 bridged
2 stereo
3 parallel

[john_lenfr]

So I want to know if it is dangerous to have 6 ohm speaker on a LM4780 in bridge mode?

[jaudio]

This may help you.


www.national.com/an/AN/AN-1192.pdf#page=1

Read page 3.

Dont forget lm4780 is 2 lm3886 in one case so pd might be alittle less.

[macboy]

So I want to know if it is dangerous to have 6 ohm speaker on a LM4780 in bridge mode?

Simply, Yes. It is dangerous.
The 4780 cannot safely drive a 3 ohm load, and that is what the effective load will be for the amp on each half of the bridged amp.

6 ohm is a awkward impedance to use... bridging results in a 3 ohm effective load which is too lown to be safe, and paralleling results in a 12 ohm load which is too high (it's perfectly safe, but you will not get as much power out of the chips as you would with 8 ohms, because of the limits on power supply voltages).

The ideal solution for 6 ohm speaker is a bridge-parallel amp. This is contructed as two parallel amps, bridged together. The "parallel amp" parts of this can have as many chips in parallel as you want; you are not limitted to two. If you use 4 chips total (2 in parallel each side) then the effective load to each chip is 6 ohms. You can calculate the approximate output power by figuring out (with the help of the datasheet and/or the Overture Design Guide spreadsheet from National) the output power of the chip into 6 ohms (effective load per chip) and multiplying that by 4 (total number of chips). If you used a three chips in parallel on each side (6 total), then the effective load per chip is (6*3/2) = 9 ohms. To calculate the approximate power of this, find the output power for each chip into 8 ohms and subtract 11% (due to the load being 9 ohms), and multiply by 6 (total number of chips). For more information on bridge-parallel amps, download National's app note AN-1192 and their Overture Design Guide spreadsheet