Could someone tell me all the ways I could damage this amp?

[PortalKeeper]

Hello all. I have an Audiophonics LPA-S400ET power amp and I was wondering if it has any of these so called protection features I've been hearing about. Does anyone know what it cannot protect against?

Main reason I ask is I have this headphone amp (Sterling SHA4) I got awhile ago at a guitar center for a jam. I recently sold my DAC and wanted to try to temporarily power my KEF Q950 tower speakers with my PC's motherboard's line out port which is a stereo TRS unbalanced output. This headphone amp, if you have a moment to look at the manual, supposedly supports a single unbalanced stereo input (one TRS cable) for the two sources 'A' and 'B' that you can switch between. It also has balanced link out ports (which I believe are at line level) to daisy chain to other equipment (this is what I hooked my power amp's left and right channels to). I wasn't expecting tremendous volume from this setup as my power is set to medium gain and line level is 1V which is a quarter of full power (I think?). Well I didn't get any sound from this setup no matter how much I tried to switch between sources on my PC or turned up the input level gain knob on the headphone amp. I concluded that this unbalanced stereo input is broken.

I tried then connecting this unbalanced stereo signal from my PC to the balanced left input for source 'A' and it worked! But the sound was muddy in the midrange and so you could not really hear much singing. The sound was coming out of both left and right speakers thankfully which the manual said would happen, but my theory on why it sounded bad is because of this common mode rejection stuff with balanced inputs. I think maybe the parts of the positive signal is being canceled out by everything panned to the right (as the right channel is now the negative) in the song that you are listening to. Am I thinking about this correctly? Thank you for any of your information on this subject.

 

[radix]

The TRS on your computer is likely: tip = right, ring = left, sleave = gnd. The TRS on the SHA4 is a balanced connection.

Your PC likely has a 3.5mm jack? Your PC output is a "stereo TRS" not a balanced TRS. Get a 3.5mm TRS to 1/4" TRS adapter cable, they are like $8 on amazon. Use the UNBAL input. Do not use the balanced A or B input.

 

[PortalKeeper]

The TRS on your computer is likely: tip = right, ring = left, sleave = gnd. The TRS on the SHA4 is a balanced connection.

Your PC likely has a 3.5mm jack? Your PC output is a "stereo TRS" not a balanced TRS. Get a 3.5mm TRS to 1/4" TRS adapter cable, they are like $8 on amazon. Use the UNBAL input. Do not use the balanced A or B input.

View attachment 345834

I did use that cable but I just use a female 3.5mm TRS to male 1/4" TRS adapter. I am curious as to why you say "do not use the balanced inputs." What can doing this do damage to and how?

 

[radix]

I did use that cable but I just use a female 3.5mm TRS to male 1/4" TRS adapter. I am curious as to why you say "do not use the balanced inputs." What can doing this do damage to and how?

The 3.5mm cable is: TIP = RIGHT, RING = LEFT, SLEAVE = GND. The TRS balanced is: TIP = + phase, RING = - phase, SLEAVE = GND. So you are sending your L/R signals to the +/- inputs. This will cancel out almost all the audio.

The UNBAL inputs are "stereo TRS" not "balanced TRS". The stereo TRS input matches your computer's output configuration.

 

[MaxwellsEq]

I have an Audiophonics LPA-S400ET power amp and I was wondering if it has any of these so called protection features I've been hearing about. Does anyone know what it cannot protect against?

The protection mechanisms are against obvious mistakes or external fault conditions. Such as:

If you accidentally short the outputs or use a speaker with a very challenging impedance

If the amplifier overheats e.g. because ventilation is poor.

If devices plugged in to the inputs have a significant DC offset.

There are things it won't protect against, such as physical damage, water ingress, applying mains voltages to inputs or outputs.