2 channels to one (not bridged)

[Dan2]

hey guys, this might be a stupid question, but at least it will clear up some confusion for me.

I have a stereo amp and inverted one channel so it can be bridged. it works well with a 8ohm speaker, but gets really hot with a 4 ohm driver (not much distortion though)

is there any way to "parallel" both channels to one speaker so that both channels share the current.

basically one channel is loud enough, but i only want to run one subwoofer off it and i don't want to waste the other channel (and i want to try preserve the transisters a bit)

[poynton]

Use a dual-coil speaker with the amp as dual mono


Andy

[Dan2]

well i already have the speaker so im not going to buy anouther one. i was thinking that if i have the same signal on both inputs (mono) and link the 2 positive outputs ('cause there should be no voltage drop between the two) and have 1 speaker terminal connected to the link and the other terminal to ground output.

could this actually work?

[djk]

In theory, yes.

In practice, no.

The AC gains and DC off-set would have to match perfectly, and even then I would want to sum the output currents through a pair of 0R5 resistors.

[AndrewT]

Forget your paralleling proposal.
The single amplifier running off the stereo power supply will perform better than having two amplifiers running from a common PSU.
Most cheaper commercial gear is strangled by undersized power supplies. The reason being that a good PSU is more expensive than a good amplifier, so the good PSU goes out the window to save money and weight and volume and case size and distribution costs etc.

[Nordic]

Hi Dan, nice to see the sun again, what bass driver are you useing? Maybe the members can recommend something that can drive it more appropriately.

[Dan2]

well i want to run a car sub with it, i already have the driver so i don't want to get another.

the reason why i wanted to parallel the amp is because it is a cheap amp - its pretty loud but the output transisters are a bit on the weak side.

i got this idea from a friend who wants to build a chip amp - and he was talking about running the chips in parallel to increase the current.

[Dan2]

this is where i got the idea for paralleling the amps. this is from a chip amp data sheet and it shows 2 chips connected to each other.

although i can understand the statement of one amp running better off a stereo PSU, in the case of my amp im not too sure, it has a really nice big toroidal transformer in it, and crappy little output transistors.

so how come you can parallel chip amps but not solid state amps??? (just curious)

[djk]

"The AC gains and DC off-set would have to match perfectly, and even then I would want to sum the output currents through a pair of 0R5 resistors."

[wg_ski]

As others have mentioned, paralleling entire amplifiers can have unpredictable results. But you only really need to parallel the output transistors (and maybe the drivers). Disconnect the rest of the other channel and just parallel the "extra" output transistors. Leave in the emitter resistors and base stoppers (if any). All four outputs must be on a common heat sink or this won't work. If they're not, pull them from the disabled channel and add them to the heat sink of the one you're using.

The reason you can parallel chip amps is because the gains and DC offsets are matched, and the protection circuits have almost no lag time if something does go haywire.