Elan Z660 bridging questions.

[tomman888]

Hello to my friends at DIYAudio.

I was given an Elan six-channel audio amplifier model Z660.

It has 3x LM3886 devices per physical side of the case.

Since it claims to be bridgeable for 120W x3 channels, I have decided to try it as my shop amplifier which is used to test loudspeakers which I often restore.

I have no schematic to analyze, but was curious about the signal path through the amplifier.

When bridged and using 2 channel outputs only, How many LM3886s are utilized, and is it in parallel mode?

My questions are due to my uneasiness about using 6- or 4- ohm loads on this unit while it is bridged.

Also, should the gain controls be run wide open if I am using a passive preamp, in the interest of signal purity?

Just looking for opinions because I have never used an amplifier bridged before, and have never owned a chip-amp.
Thanks.

 

[rayma]

Bridging uses two amplifier channels. One channel drives the positive terminal of the speaker with a positive signal.
The other channel drives the negative terminal of the speaker with a negative (inverted) signal. The amplifier channels
are in series, so the current is the same, but the voltage is doubled. The minimum impedance for the bridged connection
is twice the minimum impedance for one channel. There is a switch to select the bridged mode. It appears that
the minimum rated speaker impedance in bridged mode for your amplifier is 8 ohms. With a passive preamp,
you may need to run the input pots at maximum regardless, but it won't hurt anything.

 

[tomman888]

Thanks. Does it seem like the claimed 120W rating is a bit optimistic for a pair of these chips in bridged mode?

Basically, I am attempting to figure out if this is a cheap way to derive high power but maintain quality for testing purposes.

The clipping indicators do not light unless pushed to ridiculous SPLs on a pair of Boston Acoustics A150s, for example. However, prolonged use of the bridged mode makes the unit exceptionally hot to the touch.

 

[rayma]

Does it seem like the claimed 120W rating is a bit optimistic for a pair of these chips in bridged mode? I am attempting to figure out if this is a cheap way to derive high power but maintain quality for testing purposes.

Here's the power rating:

POWER RATING - RMS
Output Power (6 Channel Stereo) . .. . 60W x 6 @ 8 ohms per channel
Output Power (3 Channel Bridged) . . 120W x 3 @ 8 ohms per channel

Ideally a bridged amplifier should be capable of four times the power of one channel (since the voltage is doubled).
Here it appears that the unit is thermally limited. Probably it meets its specs, and maybe a fan would help. It should
be fine for your purposes, but don't use this on low impedance speakers, since the output current will be excessive.
This may be why it is running hot in bridged mode. It is not rated for four ohms in either configuration.

 

[tomman888]

Thanks again.
I'm going to put this amplifier aside for now, as it is cutting out presumably on temperature during periods of loud playback in the bridged mode, and just runs uncomfortably hot. I have read about these ICs and their inherent "spike" protect modes, and I suppose this is what Elan is relying on for temperature protection. Admittedly, it does keep the chips from failing in these amps.

Learn something new everyday. Regards!