Stereo to Mono question

[Jack.Straw]

Hi. I purchased a class-d dual channel audio amplifier on ebay. Specs are:

Features:
This board uses PAM8610 chip, PAM8610 chip is 10W (per channel) D-level stereo audio amplifier.
This board has over current / temperature / short circuit protection.

Specifications:
Work: D Class
Quiescent Current: 20mA
Efficiency: 90%
Rated output power: 10W+10W(8ω)
Frequency response: 20Hz to 50KHz
Operating voltage: DC7.5-15V
Recommended supply voltage: 12V, The center PIN of 12V DC is +.
PCB board size: (40 * 40*20) mm
100% Brand New

NOTE:
it is not acceptable to connect the - outputs of the L & R speakers together.

For my project there will be only one 4" speaker. Is it possible for me to combine the left and right channel into a single speaker? The seller says "it is not acceptable to connect the - outputs of the L & R speakers together."

Also, what kind of speaker should i use with this to achieve the best sound? It is intended for music playing via mp3 player / phone.

Thanks!

 

[crutschow]

I would accept what the seller says.

If you want the best sound you need more than one 4" speaker. A small high quality two or three way bookshelf speaker would give the best sound in a small space.

If you want only one 4" speaker than use a full range unit, such as one of these, in a suitable speaker cabinet.

 

[Jack.Straw]

Ok, let me rephrase, i'm looking for the best possible sound given the confines of my project. There will only be one 4" speaker, there is no way around that. I understand that I need a full range speaker... i'm more interested in specs... Ohms & watts. Is there any benefit or hindrance from using a speaker with a wattage rating significantly higher than what the amp will be pushing?

I went ahead and purchased that amp module because I was almost positive (if naively) that there is a way to combine the L & R output safely into a single channel. Am i wrong?

Thanks for your time and advice,
-Scott

 

[betwixt]

I would suggest only using one amplifier channel (sadly, thay can't be wired in bridge configuaration) and also combining the left and right INPUT signals before feeding them to the amplifiers. You should be able to use a pair of resistors to combine the channel inputs but it is far easier to do this at low signal level than at high power levels.

Brian.

 

[Jack.Straw]

Thanks Brian, that's helpful. I'll mix the signals with a couple resistors when it comes in, then just use one of the channels on the amp. Any input on what Ohm and watt speaker to look for?

 

[crutschow]

One way to possibly use both channels is to add an inversion (op amp unity-gain inverter) to one of the inputs before applying the mono signal to the inputs. Then you connect one terminal of the speaker to each amp output (between the two outputs). That should allow the two amps to act as a bridge amplifier.

 

[Borber]

Correct way to join L and R channels into mono signal is to pass them first through phase shifter circuits which maintain 90° between L and R in all audio spectrum and then join them. This is necessary because average phase angle of audio L and R is not 0° but about 45° and simple joining produces lack of treble which subtracts in this case.

 

[FvM]

Correct way to join L and R channels into mono signal is to pass them first through phase shifter circuits which maintain 90° between L and R in all audio spectrum and then join them. This is necessary because average phase angle of audio L and R is not 0° but about 45° and simple joining produces lack of treble which subtracts in this case.

Which kind of stereo signals do you refer to? I don't see a 45° phase shift with common stereo signals (CD-audio, good old analog disc, FM broadcast).

 

[betwixt]

Woooaaaahhhh!!!

You can't do this with a PAM8610, it is already a bridge output device, both sides of the loudspeaker output are already connected to arms of a bridge inside each channel of the amplifier. IT *may* be possible to parallel them but I would be very cautious in case of phase differences in the class D clocks making the outputs go out of step with each other.

I still suggest nothing more than a pair of resistors (or an active mixer) at the input to combine left and right then use only one channel of the PAM8610.

Brian.

 

[Borber]

FmV, it is standard stereo material. You can play some stereo CD and then press mono button. Difference is obvious.

 

[FvM]

FmV, it is standard stereo material. You can play some stereo CD and then press mono button. Difference is obvious.

I may check this on occasion.

In any case I don't understand yet the 90° suggestion. It only makes sense if high frequencies are phase shifted and low frequencies aren't. But if this is the case, you would generate an even larger difference of the summed treble versus bass magnitudes.

 

[crutschow]

Betwixt is correct. My suggestion to use both channels wouldn't work since the amp has a bridge output already.