Alto TS subwoofer amplifier

[x-pro]

Is this too much noise for such supply lines or it is normal ?

This is not good for analog circuits.
This is probably a normal noise level for a power supply like this.
It is not clear to me what frequencies are shown in the picture.
I don't exclude that the PCB tracing also determines a lot of things here.
On the other hand, this amplifier is not a microphone amplifier to pay attention to dealing with power supply noise. The stabilizer circuitry is trivial. Conventional integrated stabilizers are used.

[x-pro]

"But at power up and at power down crazy things happen."
Which is what?

[JP-Stereo]

Hi, please look at the bottom of the post #15, i add a few pictures.
First there is a strong spark noise followed by strange bass wobbling with some white noise.
This sometime come back when playing normal program for testing.

Shouldn't both rails act the same way in term of tension at power down ?
The unballance in tension is a main suspect for the wobbling and noise in my mind...

[x-pro]

Shouldn't both rails act the same way in term of tension at power down ?
The unballance in tension is a main suspect for the wobbling and noise in my mind...

they may have different discharge times after they've been disconnected.

[x-pro]

But at power up and at power down crazy things happen.
This is the VCC-VEE bus at power off:

You are looking at the wrong thing. There will always be a forest of horrors out there with PWM generation working and not working. That's why they put chokes and capacitors at the input of the device (the AC input before the diode bridge). They protect the AC mains from interference and of the conversion frequency of that power supply.

[JP-Stereo]

OK if i have to put the turnoff behavior of these Vcc Vee lines beside.
But i still ear these snaping sound and the bass woobling anyway, what is supposed to cancel them.
The ON noise are intermittent not symetrical and the lines are comming near perfectly clear at some point.

Are the +/-15 volts and/or +/- 5 volts regulators may be deffectives ?

[x-pro]

Unfortunately, the schematic is not complete. There are no connections between some connectors. For example, where is the connector CN104 connected with the signal "PROTECT" (diagram.2)?
The control command "SD" for muting the low-frequency amplifier depends on this signal.
It is necessary to measure the level change at the point of connection of anodes D100, D101, at the moment of switching the module on and off. Try to trace this level. You may need an oscilloscope with a small sweep, but you can also use a voltmeter.

[x-pro]

But i still ear these snaping sound and the bass woobling anyway, what is supposed to cancel them.

when the device is turned on, or a reaction to the control knobs?

[x-pro]

Are the +/-15 volts and/or +/- 5 volts regulators may be deffectives ?

I think they're fine. Especially since you checked.

[JP-Stereo]

About the schematic, here are the relations between the pages.
Do not forget that this unit is for a sub only, so it didn't have the components for the high-mid range analog circuitry.

For Page 1: ____________________________________For page 2:_____________________________For page 3

[x-pro]

These pictures do not explain what connects to CN104.
The "PROTECT" should have a positive voltage.
Otherwise, there will be no signal at "SD" point (R109).
These elements are mandatory for the whole amplifier.

[JP-Stereo]

I double check and there was nothing plugged in this CN104.
There is only a preamp beside the amplificator module.
No corresponding connector on the preamp, schematic include.

All existing connectors were glued, it's a sub...
And no glue on CN104.

I will check if there is a potential at R109.

[x-pro]

The voltage at pin SD U2 appears to come out of the chip itself. In order to provide MUTE, it is necessary to spend time to charge capacitor C11, which must be blocked by a signal through R109 by nodes on U3 or U4 at the moment of switching on.

[x-pro]

https://manualmachine.com/alto/ts212...ervice-manual/
maybe this scheme is more appropriate?

[JP-Stereo]

I provided what i found that was the nearest, to the point of having the same part numbers.
But they can always improve their design and we are no more exactly up to date.
The entire circuit is the same, exept this 300 ohm resistor i found in serie with D615...

The Protect line is used only by full range speakers that have a more complex preamp from what i found.
I made a move to confirm all this with someone that have the same model anyway.

The SD signal from U2 make sense, i will confirm by testing early next week.
Is there an equivalent delay at power off ?