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TVOR-Ceasar
(@tvor-ceasar)
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20/02/2020 1:44 am  

Here's a small tip that is very inexpensive. You can capacitively combine left and right into mono. Check out this board for an example. It is a small mono amp that uses headphone inputs. Follow the Ring and Tip traces to the lower left corner. There are 2 - 1uF capacitors that combine to the input of the chip. If you do similarly, and the caps are polarized, put the positive leg on the amp input side, and the negative leg is where the 1/8" (3.5mm) wires connect. So phone to negative, and positive to amp input.

Might be nice to get the both channels in one point source speaker for practically nothing.

-Charlie


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ImCoKeMaN
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20/02/2020 7:59 am  

So for this if I did as a 3.5mm extension cable it would be a 1uf cap between each output and the mono out.

There are some summing discussions and cables that talk about using resistors here's one I was looking into earlier, but never built: http://silentsky.net/wordpress/archives/624  

Are there any pros/cons between the two methods Caps vs Resistors? 


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DIYAudiphileElliottBridge
(@diyaudiphileelliottbridge)
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20/02/2020 9:56 am  

@imcokeman

Summing cables are different from turning a stereo amp into a mono amp which I think Charlie was on about. I think Charlie was talking about bridging a stereo amp to deal with a mono load giving it the ability to play loudspeakers with lower impedances and much louder (this would also sum the stereo signal into the mono output). However, if you are using a mono amp and want to convert the stereo signal into mono, you can use a computer app like equaliser APO or the resistor + wire joining method you mentioned (I think this will work you will just want low impedance resistors when using to stop your high end from being reduced). I hope this is what you were asking about. 😉

 


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TVOR-Ceasar
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20/02/2020 10:26 am  

I should add a caveat: If you do the method shown in the linked pic above, you need to connect the summed junction to the trace directly to the input into the amp, bypassing any factory installed DC blocking capacitor. Reason being that if you just connect to the standard input jack, you'll put the caps in series and the total capacitance will be less than the smallest cap in the chain. That will attenuate the bass levels even more than the smallest cap. Here's a page that explains how Series and Parallel caps work.

Pros:

Resistors do not affect the sound contour of the signal. No real modification to the input connection, except in certain cases.

Capacitors do not affect the level of the signal. No additional preamp needed in most cases.

Cons:

Resistors attenuate the signal, resulting in lower output overall. If high enough resistors are used, an active preamp may be needed, adding cost and complexity.

Capacitor values may need to be adjusted to allow the best range of audio, so there may be some trial and error involved. Also, the input should be modified so that the summed junction of the new input caps bypass any factory input caps.

Ultimately, it depends on how hands on you are and how comfortable you are in your skills at slight circuit modification. If you want plug and play, go with resistors. If you want the most volume from the stock electronics, go with caps.

-Charlie


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TVOR-Ceasar
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20/02/2020 10:52 am  
Posted by: @diyaudiphileelliottbridge

@imcokeman

Summing cables are different from turning a stereo amp into a mono amp which I think Charlie was on about. I think Charlie was talking about bridging a stereo amp to deal with a mono load giving it the ability to play loudspeakers with lower impedances and much louder (this would also sum the stereo signal into the mono output). However, if you are using a mono amp and want to convert the stereo signal into mono, you can use a computer app like equaliser APO or the resistor + wire joining method you mentioned (I think this will work you will just want low impedance resistors when using to stop your high end from being reduced). I hope this is what you were asking about. 😉

 

I'm actually talking about summing the input. The board shown is a mono design where the low power chip is bridged for higher mono power. I can't say as to what the amp @imcokeman has as outputs, single ended or bridged already, so that was not even a thought. Though, yes, you can parallel them to drive lower impedance loads than original design, BUT, you'd want to drive both channels with the same exact signal to prevent any weird interactions (drop-outs, combing, etc.). Plus the fact that he is only driving one speaker at the moment...

Anyway, if you go to this New Record Day video and look down in the comments, you'll see a convo I had with Jeremy, the Guru of the Chip-amp referenced in the video. We discuss just such things as those brought up above (minus the weird interactions stuff). TVOR = True Voice Of Reason

Elliot, patiently waiting to see how your "school project" comes out. I'll get back to you on that thread.

-Charlie


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ImCoKeMaN
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20/02/2020 4:42 pm  

@tvor-ceasar Thanks for the info, I'll see what I can do when I get some time to dig in with a soldering iron.  I'm thinking the summing cable could be useful for other devices as well, but it might be nice to sum the inputs in the amp that's pretty well single purpose at this point.  It's low power so it would be preferable to not lose volume with the resistor method.  

 

 

 


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