Issue with Alto 415 Speaker - Need Help with Diagnosis

[Zap]

Hello everyone,

I'm experiencing an issue with my Alto Professional 415 speaker and am seeking advice for troubleshooting. Here's a summary of the situation:

1. I bought this speaker about four weeks ago. Initially, I used the speaker with an Alto Professional ZMX52 mixer for three days with no issues. Then, I didn't use it for about four weeks.
2. Recently, I tried connecting my phone to the speaker using a jack cable. The sound is very low and poor quality. To hear anything, I need to crank up the gain and the volume to the max on my phone. Even then, the sound is very muffled, with excessive treble, and I can barely hear the lyrics of the songs.
3. I tried connecting the speaker to an Alto Professional Truemix 500 mixer, but this did not change anything.
4. I've tested different cables (XLR, Mono Jack, Stereo Jack) and several audio sources (computer, phone, a device for wireless microphones), with or without a mixer. The issue persists in all cases.
5. The equalization settings are default on all devices, and I've also tried modifying them with no success.
6. The speaker has a Bluetooth connection, and the speaker works perfectly well if I use it. Sound clear and powerfull, no distorsion.

I have some hypotheses about the source of the problem:

1. There could be an issue with the preamplifier or the circuit that processes input signals.
2. There could be a poor connection or a short circuit in one of the inputs.

However, I find it strange that the issue has appeared when I haven't used the speaker for several weeks, and that both inputs stopped working simultaneously.

Would you have any suggestions on what might be causing this issue and how to resolve it? Any help would be greatly appreciated.

Thank you in advance for your responses.

[Hugh Robjohns]

The good news is the the speaker drivers and amps are okay since it sounds fine when using Bluetooth.

So there's either a problem with the analogue input section, or a connecting cable problem, or some form of user error. ... and I'd bet on it being the last two!

You mention connecting your phone via a (single) jack cable. This will not work and give exactly the symptoms you describe.

Phone jack socket outputs are stereo and unbalanced. The TRS mixer channel input on the Alto is mono and balanced.

A balanced input works by detecting the voltage difference between the tip and ring connections. But if you feed it with unbalanced left-right stereo anything panned centrally — typically main vocals, kick drum, bass guitar, etc — will have the same voltage on tip and ring, and thus be rejected. All you'd be left with is any instruments panned hard left/right and reverb... which sounds very much like your description:

To hear anything, I need to crank up the gain and the volume to the max on my phone. Even then, the sound is very muffled, with excessive treble, and I can barely hear the lyrics of the songs.

I don't know why the mixer output didn't work — it is a balanced output — but you don't say what you were using as a source to the mixer. If it was the phone again the mixer would have behaved in the same way as the speaker.

To connect your phone to the speaker or mixer you need a cable with a 3.5mm mini-trs plug at the phone end breaking out to TWO mono TS quarter-inch plugs for the speaker/mixer ( one for the left channel and the other for the right.

[Wonks]

Is this all with the phone? What were you using before as a sound source with the ZMX52?

The phone output was presumably the headphone output? Did you use a 1/8" TRS to 1/4" TRS lead and you fed it to one of the two combi input sockets?

If so, you were feeding a unbalanced stereo output into a balanced line input. Balanced inputs are designed to work with a balanced output (or a single unbalanced output) as they work on the difference between the two input signal. Your thin, very trebbly sound would then be the difference between the left and right stereo channels.

You'd need a 1/8" (3.5mm) TRS jack to two 1/4" TS (mono) jack cable, with one going into each of the two inputs to get the full sound output. e.g. this sort of cable https://www.amazon.co.uk/Bynccea-Splitt ... C88&sr=8-3

[Zap]

Thank you for all these explanations!

Indeed it seems quite logical that it comes from the incompatibility between my unbalanced stereo source and the balanced mono input of the speaker.

To test, I put the pan completely on Right on the mixer and the sound is indeed immediately perfect, so your explanations seem completely coherent.

Thank you very much, it makes me very happy!

I don't know why it worked with the first mixer, but I also had other audio cables, and in view of your answers it should come from there.

I will carefully read your explanations of the different cables in order to make the good connections.

Again, thanks !

[Hugh Robjohns]

[Wonks]

Not all line inputs are balanced. If your original mixer had unbalanced line inputs, then it will have ignored one side of the stereo input, so you’d be hearing either the left or right side (I forget which) in all its glory.

[Hugh Robjohns]

Tip contact is left channel, ring is right.

[Wonks]

So the left channel then!

[Zap]

Thank you for your previous responses, they were really helpful.

I conducted further testing based on your advice. Here's what I found:

I have the exact cable you mentioned for connecting my phone to the mixer: a 3.5mm mini-trs plug that breaks out to two mono TS quarter-inch plugs. However, I still encounter the same issue when I use it.

I also have a 3.5mm mini-trs to XLR cable, which exhibits the same problem.

The only setup that seems to work is when I plug one of the mono TS jacks into the "R" input of the mixer. The sound is good, but this leaves one of the jacks unused and hanging. Logically, the "main out level" LEDs indicate sound on the right but nothing on the left.

The sound improves when I distribute my two mono TS jacks across two different "R" inputs. I assume this is because I'm not losing one side of the stereo signal.

What do you make of these connections and tests? I'm wondering if I need to somehow "unbalance the signal" so that I can still keep the left and right signals and send them both unbalanced to the speaker. Or maybe my way of plugging into two different R inputs is the right approach?

Thank you again for your help.

[pk.roberts]

I'm wondering if the balanced/unbalanced issue might be a red-herring in this instance and whether an additional issue could be that the phone has a 4-pole (combined headphone/mic) jack fitted? There are (at least) two standards of wiring for these and it's possible for the physical connections to 'miss' the ground connection with some combinations. What model phone are you using?
E2A - Some phones (notably some iPhones) will not output to high impedance destinations (they think they have nothing connected), but they can be 'fooled' by adding resistors to the circuit to simulate headphones.

[Zap]

Thank you for your response !

For the last tests I'm using the audio output from a laptop dock (which is indicated with a headphone symbol only).

And yes, the phone model I'm using does indeed have a combined headphone/mic jack.
The phone seems to detect the headset, an icon indicates that a headset is connected. It's a Samsung A52.

However, I've tried some different audio sources. These include the output from a wireless mic receiver that also has an audio input for connecting other audio sources.

I found no noticeable differences between these sources, they all seemed to produce the same problem. I'd be interested to hear your thoughts on this.

Thank you again for your insights.

[Hugh Robjohns]

I have the exact cable you mentioned for connecting my phone to the mixer: a 3.5mm mini-trs plug that breaks out to two mono TS quarter-inch plugs. However, I still encounter the same issue when I use it.

Okay... this fault-finding is getting pretty chaotic now. We gave three potential problem sources: the Alto speaker input stage, the phone output connections, and the source music material.

We can probably discount the last as you said it sounded fine via Bluetooth.... but it wouldn't be the first time I've traced a problem to a faulty recording!

You have established that using one input on the Alto is fine, but the problem emerges when using both.

To check the Alto separately from the phone I suggest you try the following:

Connect one output (the Right since you say that works?) from the phone (using the minijack to dual TS cable) to ONE mono channel line input of your separate mixer.

Pan that channel to the CENTRE and adjust the channel level appropriately. Both mixer meters should be reading the same.

Connect the left AND right mixer outputs to the TWO Alto inputs, again setting Alto input levels appropriately. (Use balanced cables if you have them).

You should hear the signal normally from the speaker and if you unplug either of the Alto inputs it should just get a little quieter, but not change character in any other way.

If this works then the problem is with the phone output connections. If it doesn't, you either have faulty balanced cables between the mixer and speaker, or a broken speaker.

I also have a 3.5mm mini-trs to XLR cable, which exhibits the same problem.

It would, for the reasons explained above — unbalanced stereo signal feeding balanced mono input).

[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.