AUDIOPHONICS MPA-S250NC Amp Review

[JeremyFife]

I'm having a (what I think is a Grounding) issue with my Audiophonics MPA-S250NC XLR amp, connecting to my active sub's speaker level inputs (RSL Speedwoofer 10s).

Setup: Source = PC > Duok U2 PRO XMOS XU208 Digital Interface > Schiit Modi DAC > Schiit Loki preamp > Schiit Vali2+ headphone/preamp > Audiophonics MPA-S250NX XLR Amp > Speakers (RCA/Banana Plug from Amp's Output)
> RSL Sub, Speaker Level In (Spade Connectors also coming from the Amp's same Output)

• When I make the connection to any of the Sub's Speaker Level Inputs I get a significant, constant humming from the subwoofer. I am reasonably sure this is a grounding issue.
• It occurs even when the amplifier is Audiophonics amp is powered off
• Both the sub and amp are connected to the same outlet (power strip)
  • I tried connecting the sub to an entirely different outlet, issue remained
• I was using a different amp recently that has a dedicated sub out (RSL ia255.1) without any hum, I just tried upgrading to the Audiophonics and from my research this spade connection to sub speaker level in seemed like the simplest way to connect my sub. I don't have any other available connections on my preamps in this setup.

Since discovering the issue and doing some research, I'm reading that some Class D amp's black speaker terminals are not actually grounded, rather both terminals of each output are active. Is this the case with my Audiophonics amp? If so this means I have a grounding issue, is there an easier/cleaner solution than buying a Line Out Converter?

View attachment 357802

View attachment 357801

Thanks in advance!

What happens if you just take a line out to your sub from the pre-amp?

 

[Fahzz]

Recently my MPA-S250NC XPS unit has stopped outputting audio while in use. The power indicator lights up but no sound is produced from the AVR for music or television. The first time I turned the power of and then on, which solved the problem, but last night that didn't work, I tried unplugging etc. but no joy. This afternoon I turned the system on and it worked fine. Any ideas on what might be causing this? Thanks.

 

[Kimbrough Xu]

Recently my MPA-S250NC XPS unit has stopped outputting audio while in use. The power indicator lights up but no sound is produced from the AVR for music or television. The first time I turned the power of and then on, which solved the problem, but last night that didn't work, I tried unplugging etc. but no joy. This afternoon I turned the system on and it worked fine. Any ideas on what might be causing this? Thanks.

Maybe it runs into protection, are you feeding too much power to it and is it too hot?

 

[Doodski]

Recently my MPA-S250NC XPS unit has stopped outputting audio while in use. The power indicator lights up but no sound is produced from the AVR for music or television. The first time I turned the power of and then on, which solved the problem, but last night that didn't work, I tried unplugging etc. but no joy. This afternoon I turned the system on and it worked fine. Any ideas on what might be causing this? Thanks.

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[Fahzz]

I don't run it loud or hot. In fact the case isn't even warm after playing for hours. Is there some kind of reset button or procedure on these things?

 

[Repdetect]

I placed this usb fan on top of my Buckeye Hypex NC502MP 2-Channel amp. Amp was a bit warm before, now stays at room temp while playing. No noise. Figure even with this little need for cooling, components will last longer.... I hope. Only $16

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[Fahzz]

I think I've narrowed this down to a preout problem on my avr. Any ideas how to troubleshoot this?

 

[Chromatischism]

I think I've narrowed this down to a preout problem on my avr. Any ideas how to troubleshoot this?

Use the amp on a different preout?

 

[Sokel]

I think I've narrowed this down to a preout problem on my avr. Any ideas how to troubleshoot this?

Do you have a multimeter?
Just measure the pre-outs (AC scale) at different frequencies with everything unconnected and see if is within specs.

 

[Fahzz]

Yesterday when the sound stopped I connected the pre outs to another amp and still no sound. But somehow It went on again Here's the odd thing: The sound went out again last night, this morning it's fine???? So it's a transient problem. Why would the pre outs just stop working? Time for repair shop?

 

[IamJF]

Yesterday when the sound stopped I connected the pre outs to another amp and still no sound. But somehow It went on again Here's the odd thing: The sound went out again last night, this morning it's fine???? So it's a transient problem. Why would the pre outs just stop working? Time for repair shop?

Can be as easy as a wonky capacitor at the output. Or something crazy nobody ever will find ... hard to say from the other side of a screen ;-)

 

[Fahzz]

Fingers crossed it's going ok right now. I'm going to leave it on an not touch anything until after the NCAA basketball championships which end tomorrow night. LOL

 

[Fahzz]

Use the amp on a different preout?

I missed this the other day - that's a sensible step to rule some things out. Thanks.

 

[Overseas]

If it is sensitive to shaking, then it is some contact, soldering etc

 

[Bernardo_G]

I bought this amp, based on the glowing reviews I've seen here and on some other sites. After several hours of testing I have very mixed feelings about it.

Call me newbie or whatever but I find this amp seriously under-powered for 125W per channel at 8 Ohms; I have it connected to a Ladder Bach preamp and JBL Classic L82 speakers, and it's quieter than my previous integrated amp, a Mission 778X, which is 45W per channel. I also had an old Technics integrated amp from the 80's (don't remember the model, though) which was something like 75W and boy... that thing played LOUD!!

Yes this amp produces very clean and clear sound, very detailed; everything is beautifully presented and you can hear nuances in the music, but honestly I'd like a bit more of muscle. I don't know if I'm doing something wrong with the amp or I just got a dud unit.

Any recommendations are most welcome; thanks!!

 

[mdsimon2]

I bought this amp, based on the glowing reviews I've seen here and on some other sites. After several hours of testing I have very mixed feelings about it.

Call me newbie or whatever but I find this amp seriously under-powered for 125W per channel at 8 Ohms; I have it connected to a Ladder Bach preamp and JBL Classic L82 speakers, and it's quieter than my previous integrated amp, a Mission 778X, which is 45W per channel. I also had an old Technics integrated amp from the 80's (don't remember the model, though) which was something like 75W and boy... that thing played LOUD!!

Yes this amp produces very clean and clear sound, very detailed; everything is beautifully presented and you can hear nuances in the music, but honestly I'd like a bit more of muscle. I don't know if I'm doing something wrong with the amp or I just got a dud unit.

Any recommendations are most welcome; thanks!!

Do not confuse gain with power output. The Mission M778X has 31 dB gain, the Audiophonics has 25.6 dB gain. This means if you feed each the same input, the Mission will be louder. However, the Audiophonics is capable of higher output levels if fed more input voltage.

For example, let's look at feeding each amp 0.54 V which is the input sensitivity of the Mission.

Mission - 0.54 V input
Voltage Out = 0.54 x 10^(31 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W

Audiophonics - 0.54 V input
Voltage Out = 0.54 x 10^(25.6 / 20) = 10.3 V
Power into 8 ohm = 13.2^2 / 8 = 13 W

If you feed the Mission more than 0.54 V it will clip and not produce any more power, however if you feed the Audiophonics more than 0.54 V it will keep producing more power until you reach the input sensitivity of 1.66 V.

For example, at 1.01 V input, the Audiophonics will produce 46 W in to 8 ohm just like the Mission with 0.54 V input.

Audiophonics - 1.01 v input
Voltage Out = 1.01 x 10^(25.6 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W

To get 125 W into 8 ohm out of the Audiophonics you need to feed it 1.66 V.

Audiophonics = 1.66 V input
Voltage Out = 1.66 x 10^(25.6 / 20) = 31.6 V
Power into 8 ohm = 31.6^2 / 8 = 125 W

In case it isn't clear, to increase the input voltage to the amplifier you need to turn the volume on your preamp up.

Also, what are you feeding the preamp with? It looks like it only attenuates and does not provide any gain, so if you have a low voltage source in to the preamp you might not be able to get the full power out of the Audiophonics.

Michael

 

[IamJF]

Any recommendations are most welcome; thanks!!

Just turn that volume knob up!
Power amps with lower gain provide better gain staging and better S/N over your chain. All you have to do is - turn your knob to the right.

It's a total nonsense invented by the HiFi industry that you regulate your SPL in the first quater of the level pot - where it works worst and you loose TONS of dynamic range. Get the gain of the power amps down and turn that knob to at least 50%!
(In pro audio you use faders. And you keep them around 0dB, not in the bottom quater. For a good reason!)

 

[Bernardo_G]

Do not confuse gain with power output. The Mission M778X has 31 dB gain, the Audiophonics has 25.6 dB gain. This means if you feed each the same input, the Mission will be louder. However, the Audiophonics is capable of higher output levels if fed more input voltage.

For example, let's look at feeding each amp 0.54 V which is the input sensitivity of the Mission.

Mission - 0.54 V input
Voltage Out = 0.54 x 10^(31 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W

Audiophonics - 0.54 V input
Voltage Out = 0.54 x 10^(25.6 / 20) = 10.3 V
Power into 8 ohm = 13.2^2 / 8 = 13 W

If you feed the Mission more than 0.54 V it will clip and not produce any more power, however if you feed the Audiophonics more than 0.54 V it will keep producing more power until you reach the input sensitivity of 1.66 V.

For example, at 1.01 V input, the Audiophonics will produce 46 W in to 8 ohm just like the Mission with 0.54 V input.

Audiophonics - 1.01 v input
Voltage Out = 1.01 x 10^(25.6 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W

To get 125 W into 8 ohm out of the Audiophonics you need to feed it 1.66 V.

Audiophonics = 1.66 V input
Voltage Out = 1.66 x 10^(25.6 / 20) = 31.6 V
Power into 8 ohm = 31.6^2 / 8 = 125 W

In case it isn't clear, to increase the input voltage to the amplifier you need to turn the volume on your preamp up.

Also, what are you feeding the preamp with? It looks like it only attenuates and does not provide any gain, so if you have a low voltage source in to the preamp you might not be able to get the full power out of the Audiophonics.

Michael

Great information really!!! I truly appreciate it; now I know what else to look for when buying a power amp in the future. I'll keep this one for now and when funds permit, I'll look for another power amp.

BTW, if there's any recommendation of a solid power amp in the range of $1,000 to $1,600, I'll be very interested. Some people have recommended me the Gallion TS-A75

 

[Bernardo_G]

Just turn that volume knob up!
Power amps with lower gain provide better gain staging and better S/N over your chain. All you have to do is - turn your knob to the right.

It's a total nonsense invented by the HiFi industry that you regulate your SPL in the first quater of the level pot - where it works worst and you loose TONS of dynamic range. Get the gain of the power amps down and turn that knob to at least 50%!
(In pro audio you use faders. And you keep them around 0dB, not in the bottom quater. For a good reason!)

That's what I did; however, when listening to some of my vinyls, the power is just not there, even at near maximum volume. I have to crank the volume pot around 50% to 60% to get to normal listening levels

 

[IamJF]

That's fine. You can turn it around to 100% if needed - it's built to do so . We are just not used to it.
The power IS there for sure! Unleash it properly