Power amplifier gain change sound?

[smok333]

Hello, i'm a noob with audio electronics, i'm reading on this forum and there's alot of info and graphs that i don't really understand , so can please someone explain in noob terms the folowing :
1. i have an xtz edge a2-300 power amplifier ( 2 x icepower 300 , with 150w/ch@8ohm) connected to Dynaudio excite x14 speaker 83db sens ( bought higher powerd amp because everyone says dynaudio needs more power) , i have a gain knob on the back of the amp ... does lowering the gain change the quality of the music? like dynamic range / soundstage etc? .. or it's just like a "volume" knob and just change the power output of the amp.
2. if i buy to use as a preamp a dac with no volume control , or a sabaj d5 / topping d70 ... will the volume control affect the sound in preamp mode ? from what i've read on this forum you need to set it up at max or -12db to sound the best.
3. https://www.amazon.com/Nobsound-Precision-Passive-Controller-Preamplifier/dp/B07GRMM9XT will something like this help or it will change the sound quality?

i am scared that if i need to set the power amp gain to max and buy something like a topping d3xpro which with a wrong press of a button can change to 100% volume can blow my speakers
p.s. sorry for my bad english

 

[solderdude]

does lowering the gain change the quality of the music? like dynamic range / soundstage etc? .. or it's just like a "volume" knob and just change the power output of the amp.

Neither, the volume control changes the input sensitivity of the amp.

When using a DAC as pre-amp you just need to adjust the XTZ just once.

Set the XTZ to minimum. Set your DAC to max output level.
Play some music that you know has been recorded a bit quietly.
Turn up the volume on the XTZ as loud as you ever want it to go and turn it slightly louder.
Make sure the sound is not distorted. When the sound starts to distort turn down the volume on the XTZ a bit till it sounds good.

Voila... From now on use the DAC volume control.

 

[smok333]

@solderdude thanks

 

[arisholm]

Neither, the volume control changes the input sensitivity of the amp.
When using a DAC as pre-amp you just need to adjust the XTZ just once.
Set the XTZ to minimum. Set your DAC to max output level.

I also wonder about this when I see DACs with 6V RMS or even higher output voltages...In that case, is there no risk that you may over drive the input stage of the power amp? Or is that input sensitivity adjustment provided in some power amps essentially the same as any other volume control (but on the input), thus reducing the input voltage before the input buffer, and robust enough to handle even such large input voltages? I see that some pre-amps specify a max input voltage but I have not seen such specifications for power amps with gain adjustments..
Thanks!

 

[solderdude]

That would depend on the design of the amp.

When the amp in question has a volume control on it there are 2 possibilities.
A: it has an input stage (buffer most likely), then volume control, then amplifier with fixed amount of gain.
B: volume control followed by amplifier with fixed gain.

Then there is just a plain power amplifier without volume/gain control let's call it design C.
C: fixed gain amplifier.

Suppose all of them are rated for 1V input (with the volume control at max. position). All of them are 50W 8 Ohm = 20V output.
The amplifiers in this case all have a 20x gain (26dB).

When connected to a 6V DAC and amp A and B are dialed down in volume (or gain) it is theoretically possible amp A could be distorting with 6V input and the sound coming out on low volume is distorted in the peaks. (example JDS Labs Atom and O2 on high gain)
It is unlikely you will damage the amplifier input. You would probably have to put a lot higher input voltage on it to do that.

Amp B would not distort at higher input peaks because nothing overloads until you reach the max output power of the amp.

Design C would clip (and thus deliver more than 50W into 8 Ohm. Chances are you won't damage the amplifier but your tweeters will be toast and maybe the mid/range and woofer might also be.
You would have to use digital volume control. This can be done safely till the amp reached max. output power (clipping level).

The specified input voltage of amps usually means the input voltage needed to get near clipping level of the amplifier with the volume/gain control fully open.

 

[arisholm]

Thank you!

 

[wwenze]

I had a Sure TK2050 with digital volume control that changes the sound as the volume is adjusted...

Class D amps have an input impedance that changes with frequency. If the volume control is carelessly designed (or, just high source impedance in general), and throw in some coupling and decoupling capacitors for extra effect, and you get an unpredictable tone control.

The gain knob is usually just the volume control. If you are thinking of the gain as in the resistors in the feedback loop, usually we don't change that at the user level because it affects the stability of the amp.

 

[solderdude]

Class D amps have an input impedance that changes with frequency

That may depend on the circuit used and not specifically for class D in general.

If you are thinking of the gain as in the resistors in the feedback loop, usually we don't change that at the user level because it affects the stability of the amp.

That too depends on the design. Some amplifiers actually change the gain. In most cases though it is just an 'ordinary' volpot for the reason you mentioned, certainly in the case of power amps.

Examples of actual gains being changed (not power amps admittedly): O2, Atom, a lot of Schiit gear, Geshelli and quite a few other designs that show better performance (wider bandwidth and or lower distortion) in low gain mode.

 

[arisholm]

Examples of actual gains being changed (not power amps admittedly): O2, Atom, a lot of Schiit gear, Geshelli and quite a few other designs that show better performance (wider bandwidth and or lower distortion) in low gain mode.

ASR too (I am the proud owner of an Emitter II) has an interesting combination of resistor-ladder based "attenuation" below a certain threshold and "added gain" above the same threshold, and even changing the voltages supplied in "power save" vs "full" mode... so as they say, the optimal volume is "51" (= no attenuation in the input stage and no "added" amp gain afterwards) ... but the details are all a bit above my pay-grade. I just know I love that 135kg piece of engineering thing (even if 2kg of class D perhaps has better SINAD ;-)

 

[mmichii]

That may depend on the circuit used and not specifically for class D in general.



That too depends on the design. Some amplifiers actually change the gain. In most cases though it is just an 'ordinary' volpot for the reason you mentioned, certainly in the case of power amps.

Examples of actual gains being changed (not power amps admittedly): O2, Atom, a lot of Schiit gear, Geshelli and quite a few other designs that show better performance (wider bandwidth and or lower distortion) in low gain mode.

I have an drop thx 789 that definitely sounds better on lower gain. I thought it sounded less crisp on higher gain settings. This was on the balanced outputs. I have not the greatest hearing and even i could tell. Further confirmed by my 13 year old nephew.

 

[solderdude]

How did you switch from high to low gain and at the exact same time increase the volume the exact same amount to properly test this ?

 

[SIY]

Further confirmed by my 13 year old nephew.

Please tell me his name is Hans!

In all seriousness, precise level matching and DOUBLE blinding is necessary for any validity when doing this sort of comparison. These days, with high quality interfaces and editing software, it's easy to make comparison files and run a software-driven ABX. That assumes you're interested in know what's actually true rather than what's entertaining to believe.