Issue with Alto 415 Speaker - Need Help with Diagnosis

[Zap]

Thanks for your response !

I apologize, I think my previous descriptions were not clear. Or maybe I didn't understood well your answer. Let me provide a more detailed summary of my current setup and testing procedures to help clarify the situation :

1. My typical audio source for testing is a laptop dock, but I also have a Samsung A52 smartphone and a wireless microphone receiver (which also plays music) available for testing.
2. This source are connected to a Truemix 500 mixing table using a 3.5mm stereo mini-jack to dual mono jack cable.
3. The mixing table is then connected to an Alto 415 speaker using a dual mono jack to a single stereo jack cable.

I should mention that I no longer have access to the ZMX52 mixing table. This was a borrowed device and I can't use it for testing anymore. If I remember correctly, I used to connect it using an RCA to Jack cable (I can't recall if it was mono or stereo, but given the RCA, I presume it was stereo).

If necessary, I also have a 3.5mm mini-jack to XLR cable at my disposal.

I've noticed that the sound functions correctly only under the following conditions:

1. When I connect my source (e.g. laptop dock) to the Truemix 500 mixer using only one of the mono jacks connected to an "R" input on the mixer;
2. Or, when I split the two mono jacks between two "R" inputs on the mixer.

In both cases, the audio functions as expected.

Thank you for your patience and help in solving this issue. I look forward to your insights.

[Hugh Robjohns]

I apologize, I think my previous descriptions were not clear.

Indeed. Every post reveals brand new, extremely critical, information!

The mixing table is then connected to an Alto 415 speaker using a dual mono jack to a single stereo jack cable.

Aaarrrggghhhh! Why would you do that?!!!

This is the source of all your problems. It is the same issue we suspected originally, but in a location you didn't tell us about!

You are feeding unbalanced stereo (courtesy of the left/right unbalanced plugs) into a mono balanced input on the Alto.

You need to use TWO separate cables — one for the left channel and one for the right — standard TS instrument cables will work, but balanced TRS cables would be better.

The reason it works in the two scenarios you list is because in both cases there is no signal on the left channel, only the right.

If you recall from earlier, the balanced input on the Alto looks for the voltage difference between the hot and cold connections — left and right in your case. With nothing on the left side, the right channel is the whole difference, hence you get your expected signal.

When you feed both left and right, the difference is only the reverbs and anything panned very wise — all central sources like vocals, bass, kick etc, are the same on both channels. No difference means no output!

Use two separate cables to two inputs on the Alto and your problems go away!

[Zap]

Thank you for the clarification ! Your explanation makes a lot of sense and I appreciate your patience with me.

In light of your advice, I plan on purchasing two TRS jack to TRS jack cables (see image below) to connect the Truemix 500 mixer to the Alto 415 speaker. I'll use one cable to connect the mixer's L output to the speaker's INPUT 1, and the second cable to connect the mixer's R output to the speaker's INPUT 2. Then, I'll connect the 3.5mm stereo mini-jack to dual mono jack cable from my source (laptop dock) directly to the L and R inputs of CH2 on the mixer.

Does this sound like a suitable plan to you?

Also, is it impossible to connect the mixer's L and R outputs to a single input on the Alto 415 speaker? And I guess it is not interesting to connect a stereo mini-jack cable to double jack TRS mono jack from my source (laptop dock) to the input of the Truemix 500 mixer if this type of cable exists (I'm not sure that makes sense) ?

Thank you very much again ! I look forward to your response.

[Hugh Robjohns]

Does this sound like a suitable plan to you?

Sounds a good plan to me.

Also, is it impossible to connect the mixer's L and R outputs to a single input on the Alto 415 speaker?

Yes, they are two mono inputs, not stereo inputs.

And I guess it is not interesting to connect a stereo mini-jack cable to double jack TRS mono jack from my source (laptop dock) to the input of the Truemix 500 mixer if this type of cable exists (I'm not sure that makes sense) ?

It doesn't make sense.

The phone and laptop have unbalanced outputs, carried on a stereo minijack plug for convenience. Few if any commercial mixers gave stereo unbalanced inputs. Most have separate connectors for the left-right channels. Hence the need for acsplitter cables — 3.5mm TRS minihack to dual quarter-inch TS.