Replacing LA90/LA90D power supply ?

[bud947]

I asked this on the newly released PA7 plus thread but got no answers. I’m putting it here if anyone has a clue.

The PA7 plus power brick is specified at 52V/6.5A while LA90/LA90D were released with 64V/4A power brick. I have 2 LA90 in mono with a Polk r700 (89db but not exactly 8ohms) and I’ll rather have more current in such configuration than voltage as 52V is more than enough in my opinion.

Would the LA90/LA90D work with a different power brick than the one originally supplied?

 

[rationaltime]

I asked this on the newly released PA7 plus thread but got no answers. I’m putting it here if anyone has a clue.

The PA7 plus power brick is specified at 52V/6.5A while LA90/LA90D where released with 64V/4A power brick. I have 2 LA90 in mono with a Polk r700 (89db but not exactly 8ohms) and I’ll rather have more current in such configuration than voltage as 52V is more than enough in my opinion.

I appreciate you are asking about the power supply not the amplifier. Changing the power
will not change the amplifier output impedance. Running in bridge mode will. Are you
connected to the speakers in bridge mode?

Are you hearing an issue? Or is this rather an exercise in optimization?

Would the LA90/LA90D work with a different power brick than the one originally supplied?

While I don't have one I think it would work with the 52V power supply.
Head room would be reduced, but you seem convinced that doesn't
matter in your set up.

 

[bud947]

Are you hearing an issue? Or is this rather an exercise in optimization?

Not hearing an issue, at least not at the level I’m usually listening, but I tried to crank things up (85db average) and I felt a bit of compression. At 75db average, the song I was listening to had a peak +12db and therefore I was expecting peak of 97db at 85db. It was clearly not the case (peak was 92db)

I’m running the amps in bridge mode. Here is the speakers measured impedance curve (not EPDR so may be a bit lower under 100hz)

My understanding (but I might be wrong as my physics years are far behind me) is that when they’re bridged the amplifiers somewhat fail to provide enough current for less than 8R load. Voltage (either 52v or 64v) is more than sufficient in such case because the output wattage would first be limited by current.

 

[rationaltime]

Your experience seems inconsistent with Amir's review of the LA90.
Topping LA90 Review (Integrated Amplifier) amirm Apr 25, 2022

Now let's switch to Bridged mode (both amplifiers driven in differential mono) and run our power sweep again:

I read that Amir used the standard power supply and a non
reactive load. Though he labeled "impedance" I think he could
have written "resistance". Of course, as you showed your
speakers are different.

I guess you are using a calibrated measurement microphone.
What if you take a few more level measurements. You could
measure average audio power at 70 dB, 80 dB, and 90 dB levels
and also measure the peak power. Together with your first two
measurements this might show the level where the peak power
stops tracking the average power. I would also measure the
average AC voltage across the speaker terminals at those levels.
Maybe you did already, but I would turn off the channel not
under test.

That is my suggestion.

 

[restorer-john]

@bud947 Don't go messing with power supplies with the LA-90s. All the internal circuitry, including protection, various regulated rails, time outs etc will be tied to the supplied SMPS voltages.

If you think you are hitting the wall with the LA-90 in bridged mode, and you may well be, it's time to audition/borrow a more powerful power amplifier. I suggest 200wpc@8R/350wpc@4R continuous, with a significant dynamic ability 2-3dB above that. The difference may shock you.

Cheers.

 

[bud947]

@bud947 Don't go messing with power supplies with the LA-90s. All the internal circuitry, including protection, various regulated rails, time outs etc will be tied to the supplied SMPS voltages.

If you think you are hitting the wall with the LA-90 in bridged mode, and you may well be, it's time to audition/borrow a more powerful power amplifier. I suggest 200wpc@8R/350wpc@4R continuous, with a significant dynamic ability 2-3dB above that. The difference may shock you.

Cheers.

@restorer-john internal circuitry is exactly the reason I was asking (and hoping to have @JohnYang1997 providing a hint). aiyima a07 can be used with differents power switch and it would be nice if it was also the case for topping amplifiers sharing the same connectors.

Actually before the LA90 I had a dual mono hypex ucd400oem. While the bottom spectrum was very satisfying, there is a night and day difference in the high frequencies. Honestly, I prefer to give up a bit of dynamic range rather than high frequency clarity. Benchmark AHB2 is twice the price and other comparable alternatives (Nilai, NC500x…) are not widely available.

 

[Ziofrenko]

At 75db average, the song I was listening to had a peak +12db and therefore I was expecting peak of 97db at 85db. It was clearly not the case (peak was 92db).

Have you ever heard of power compression of transducers?!

 

[AdamFrandsen]

Can anyone tell me the aviation plug type/size used on the LA90D, I am in the process of building my own linear power supply. Is it GX12/GX16… Thanks in advance