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Old 20th August 2011, 03:42 AM   #1
mfaughn is offline mfaughn  United States
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Default Stereo to mono by paralleling outputs?

Hi,
Can I put a stereo signal into a tube power amp and parallel both channel's outputs into a single speaker? Amp I'm considering doing this with at the moment is a Magnavox 9303. OPT have 4 ohm taps, 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

PS- Yes I asked a very similar question about a solid state amp in the SS forum.
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Old 20th August 2011, 08:46 AM   #2
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The usual way of bridging is inverting one input channel and connecting the - on secondary together. connecting speakers to the positive speaker conection one channel inverted now acting as -

Putting two channels in paralell isnŽt a good idea if the signal is a little out of "phase" it will work against each other.
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Old 20th August 2011, 09:39 AM   #3
DF96 is online now DF96  England
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Depends on output impedance. If low, due to NFB, then you would need some series resistance in each output to reduce the amount of one driving the other. If it already has a high output impedance then no need to add any resistance.

Note that putting an 8ohm speaker on two paralleled 4ohm outputs is daft. You should use bridged mode as suggested in post 2.
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Old 20th August 2011, 11:03 AM   #4
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Why don't you build the proper adapter to mono your source? It think it would be safer and easier and you only need one channel.

Read "Why not Wye" by Dennis Bohn

Last edited by Original Burnedfingers; 20th August 2011 at 11:19 AM.
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Old 20th August 2011, 11:28 AM   #5
mfaughn is offline mfaughn  United States
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OK, lets say I sum the signals before input then bridge the amp (no parallel it). But in order to properly bridge the amp I have to invert on side.

FWIW, I tried "naive" paralleling for just a few seconds and there was no smoke but I don't want to tempt fate. I have some some references that suggest it might be alright but I would like to understand why or why not it is or isn't OK.
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Old 20th August 2011, 11:41 AM   #6
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here is a simple bridge adapter.

I do not see your logic in wanting to bridge the amplifier. Properly mono summed it will provide for your needs without the hassles of bridge operation.
In bridge mode the power increases but also so does distortion and wear and tear on parts. My suggestion is mono it on one channel and leave the other channel alone.
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Old 20th August 2011, 11:52 AM   #7
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When you say that you sum the signal are you trying to use both stereo channels to drive one mono channel?

Only use for that iŽm familiar with is in 3 speaker systems with a single subwoofer.

To properly do that will take a few more pieces of sand.
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Old 20th August 2011, 12:59 PM   #8
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Hi,
Can I put a stereo signal into a tube power amp and parallel both channel's outputs into a single speaker?
No you can not do this! The different signals from the stereo inputs will cause the linked outputs to see a very low impedance load, which would probably damage the stereo amp.
Best way to get optimum power for your mono 8 ohm speaker is to sum the 2 stereo signals to mono, then invert one signal and run the amp in bridge with the 4 ohm taps.
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Old 14th November 2011, 02:20 AM   #9
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if i were to parallel 2 stereo channels into one to match two 4ohm subs wired together(in a fullrange 3-way cabinet) down to 2ohms, using this amplifier module from 41hz.com 41Hz Audio:AMP9-BASIC which can easily take that load when paralleled, does this make my output mono? or should i use two right or two left channels to do this?
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Old 14th November 2011, 10:48 AM   #10
DF96 is online now DF96  England
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A power amplifier should not be used in parallel with another unless the designer specifically recommends this. Even then it would require identical input signals, not left and right.
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