Can I? Stereo in > parallel out into 1 speaker?

[mfaughn]

Hi,
I have an HK A402 which is by all accounts a dual mono design. FWIW, the pre-amp section is dead (for now) and I just use it as a power amp. Can I put a stereo signal into the power amp and parallel both channel's outputs into a single speaker? Amp can handle a 4 ohm load, speaker is 8 ohm. I'm pretty sure I could do this if both channels were amplifying the same signal but am wondering if having dissimilar signals in each channel would present a problem. I could sum them before going in but if I can get away without it then I will.
Thanks,
Michael

[sofaspud]

The appropriate answer is no.

I'm pretty sure I could do this if both channels were amplifying the same signal but am wondering if having dissimilar signals in each channel would present a problem.

Instead of destroying amplifiers, take this statement of yours, run with it, and learn just how far away you are... and yet so close.

[mfaughn]

Err thanks I think. I haven't destroyed anything. That is why I ask first. Perhaps it is late and I'm extra thick. Are you saying that if the signals were the same I'd be alright but that because they are not it is a no go? If that is the case then I should be able to sum the signals before the power amp and proceed.

[sofaspud]

If the signals are the same then there is no voltage across the speaker. Which means no power. Which means no sound. That basically leaves only shorted amp outputs. What you're asking can be done, but it must be done correctly. IMO it's something best left to more advanced diyers. In your case, aren't you running stereo? What are you trying to achieve?

[VictoriaGuy]

Originally Posted by sofaspud

If the signals are the same then there is no voltage across the speaker. Which means no power. Which means no sound. That basically leaves only shorted amp outputs.

?
I don't understand. Suppose that we have 1kHz sine wave of 10v at each output. If they are connected in-phase how will the resulting voltage be zero v ?

I don't play with solid state stuff much, but I thought the issue with parallel-ing speaker outs had something to do with common ground (or lack thereof..) ?

[sofaspud]

If you have "10v at each output" and you measure across the outputs, that's 0v.
I was really just trying to convince the OP, nothing more. I don't play with this stuff much either. Bridge/parallel is confined to "amps I'll never build".

[mfaughn]

That doesn't make any sense at all. IF the signals are the same (see here) then how exactly do you get zero voltage?
If it won't work then I'm curious as to why. That's how we "inexperienced" diyers get experienced -- not by hearing a simple "no". FWIW, I usually use tube gear and bridging or paralleling tube amps is a doable thing. I just would prefer to use solid state for this particular application. The application is the running of a single mono speaker (not a sub) in the most energy efficient way (because it'll run off battery) using the gear I have on hand TODAY (as in by about 1pm east coast time).

[Nico Ras]

Originally Posted by mfaughn

Hi,
I have an HK A402 which is by all accounts a dual mono design. FWIW, the pre-amp section is dead (for now) and I just use it as a power amp. Can I put a stereo signal into the power amp and parallel both channel's outputs into a single speaker? Amp can handle a 4 ohm load, speaker is 8 ohm. I'm pretty sure I could do this if both channels were amplifying the same signal but am wondering if having dissimilar signals in each channel would present a problem. I could sum them before going in but if I can get away without it then I will.
Thanks,
Michael

If you sum the inputs, i.e. make them mono, then theoretically you can parallel the outputs and it will be capable of driving a lower impedance. But what is the point, you are not gaining anything, your speaker is 8 ohms.

[adason]

this is done all the time, every time you have parallel output transistors, or integrated circuits, to increase current drive capability
if you feed your stereo amp with identical signals and hook it up to one speaker, you double the current
i have seen guts of highly respected amps (jeff rowland) with eight chips in parallel
nothing new

[adason]

Originally Posted by sofaspud

If you have "10v at each output" and you measure across the outputs, that's 0v.

only if you measure between two live wires, but when you parallel the outputs and measure to the ground you get the same voltage as on both outputs, just can get twice the current

you probably misunderstood the whole idea
what you talk about is similar to the bridge, but you have to invert phase into one input, he said nothing about inverting one input, just paralleling two identical channels into one...