Quick question about OP Amp power supply

Thread Starter

Dean Rantala

Joined Sep 27, 2018
29
I got some cheap-o plate power amps from Aliexpress. They are getting mounted in some old Bose Acoustimass sub modules in order to "convert" these bass modules into active units.

Yeah, I know these are not true "subwoofers", etc.. But for my application, they are all I need.

I am interfacing these plate amplifiers to my Bose S1 Pro speakers - which have balances (TRS) outputs. In order to reduce noise, I wanted to KEEP the balanced connection all the way to the sub's, sooooo...

I built 2 small "balanced-to-unbalanced" circuits (thanks to ESP Sound) using the NE5532 op-amps.

As you all know, these op-amps prefer +/- 15vdc.

Here is the catch... the plate amps DO HAVE a split-power supply already there - as the built-in crossover already uses NE5532 op-amps. But I noticed, when measuring the actual voltage (out of curiosity) that the actual voltage is +12.5vdc and -15.2vdc.

The two voltages are not perfectly equal.

Would this affect performance any? If so, what might I need to look out for?

Obviously, this works since.. the factory op-amps on the crossover are already dealing with this.

But just curious?
 

Papabravo

Joined Feb 24, 2006
18,786
I got some cheap-o plate power amps from Aliexpress. They are getting mounted in some old Bose Acoustimass sub modules in order to "convert" these bass modules into active units.

Yeah, I know these are not true "subwoofers", etc.. But for my application, they are all I need.

I am interfacing these plate amplifiers to my Bose S1 Pro speakers - which have balances (TRS) outputs. In order to reduce noise, I wanted to KEEP the balanced connection all the way to the sub's, sooooo...

I built 2 small "balanced-to-unbalanced" circuits (thanks to ESP Sound) using the NE5532 op-amps.

As you all know, these op-amps prefer +/- 15vdc.

Here is the catch... the plate amps DO HAVE a split-power supply already there - as the built-in crossover already uses NE5532 op-amps. But I noticed, when measuring the actual voltage (out of curiosity) that the actual voltage is +12.5vdc and -15.2vdc.

The two voltages are not perfectly equal.

Would this affect performance any? If so, what might I need to look out for?

Obviously, this works since.. the factory op-amps on the crossover are already dealing with this.

But just curious?
The opamps do not necessarily require equal supply voltages as long as the maximum allowable difference between the two supply voltages is not exceeded. On reason for doing this might be allowing the maximum positive and negative output voltages to be the same. Some older design opamps had trouble getting as close to the negative rail as the positive rail. The difference should have little or no effect on the output characteristics as long as there is no clipping.
 

MisterBill2

Joined Jan 23, 2018
12,399
The unequal voltages will not be noticed if you are running the opamps within the range. Originally +- 15 was used to assure lreadnear operation in the +- ten volt spread. So the output swing should stay less than the supply spread to avoid severe distortion.
 

crutschow

Joined Mar 14, 2008
30,100
I am interfacing these plate amplifiers to my Bose S1 Pro speakers - which have balances (TRS) outputs. In order to reduce noise, I wanted to KEEP the balanced connection all the way to the sub's,
It would be better (and easier) if you just tapped the audio source and send that to the sub amp.
Is the audio source output available for this or is it Bluetooth only?
 
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