Can't explain clipping when I use a split the DAC into multiple sources.

[KTN46]

I have a Schiit Modius connected to a Magni Heresy and a random speaker amp via a little splitter thingy that looks like this:

Splitter goes into DAC, which splits the left and right channels into 2. One interconnect goes to the Heresy, the other goes to the Amp.

I've noticed however that doing this introduces distortion/clipping into the Heresy. Turning the volume down from 100 to 70 fixed the problem, any higher and you can start to hear clipping. This has happened with 2 separate speaker amps.

I'm trying to understand why this would be, but I'm honestly stumped. The volume doesn't change, so the DAC isn't magically outputting a higher voltage. Furthermore, this only happens when the speaker amp is off. When the speaker amp is on at the same time as the Heresy, there is no clipping/distortion. I've even cracked open the splitter to check the wiring, and it checks out in there too.

Would you guys be able to help explain this phenomena to me?

 

[raindance]

When the speaker amp is off you're driving an unpowered device, likely a transistor, and it's behaving like a diode, thus clipping the signal. You need both amps to be on for this to work cleanly. Just use a switch instead of a splitter. Alternatively, use an active splitter, although that could reduce sound quality.

 

[Kal Rubinson]

Just use a switch instead of a splitter. Alternatively, use an active splitter, although that could reduce sound quality.

This is correct! The two amps need to be isolated from each other.

 

[Noodles]

You can use a thing like this:
https://www.sweetwater.com/store/de...ig-knob-passive-2x2-studio-monitor-controller

That will eliminate the issue.

 

[KTN46]

When the speaker amp is off you're driving an unpowered device, likely a transistor, and it's behaving like a diode, thus clipping the signal. You need both amps to be on for this to work cleanly. Just use a switch instead of a splitter. Alternatively, use an active splitter, although that could reduce sound quality.

Thankyou for this! I guess what I don't understand now is how it physically impacts the signal, since the splitter is in parallel. My basic understanding of electronics tells me Diodes only let current through in one direction, but I can't understand how that can clip a signal. In parallel the voltage isn't split, and the amplifier cares mostly about the voltage... Right?

 

[KTN46]

https://www.aliexpress.com/item/4001244625871.html

I found this switcher thingy on Aliexpress. Would I be able to reverse it by plugging my DAC output into the "OUT" and then plugging the devices I want to switch between into the "IN"?

I was reading up on the specs, but I'm not sure what they mean when they talk about resistance. Shouldn't there be zero resistance in this circuit?

 

[solderdude]

Thankyou for this! I guess what I don't understand now is how it physically impacts the signal, since the splitter is in parallel. My basic understanding of electronics tells me Diodes only let current through in one direction, but I can't understand how that can clip a signal. In parallel the voltage isn't split, and the amplifier cares mostly about the voltage... Right?

The previous responses are correct.
When you switch off the amp what the input of it basically becomes is some resistance + diodes to ground. It will do that above 0.6V and depending on the circuit maybe -0.6V or even +/- 0.6V
It probably won't clip 'hard' but becomes a soft limiter, this depends on the series resistance used in the amp circuit. Most have some resistance there.
The actual effect is caused by the output resistance of the DAC (which is 75Ohm and is the reason for this effect) combined with the 'clipping circuit' in series with the output R.
Assuming the DAC is 2V out = 2.8V peak.
Lowering the digital volume so it stays below the onset of the 'softclip' circuit you created by switching off the amp will of-course give the proper not distorted sound.

I would suggest to use either a switch or use an XLR to RCA cable to the amp and the RCA out for the Heresy.
Schiit claims the outputs have independent buffer circuits so should solve the problem.

 

[KTN46]

The previous responses are correct.
When you switch off the amp what the input of it basically becomes is some resistance + diodes to ground. It will do that above 0.6V and depending on the circuit maybe -0.6V or even +/- 0.6V
It probably won't clip 'hard' but becomes a soft limiter, this depends on the series resistance used in the amp circuit. Most have some resistance there.
The actual effect is caused by the output resistance of the DAC (which is 75Ohm and is the reason for this effect) combined with the 'clipping circuit' in series with the output R.
Assuming the DAC is 2V out = 2.8V peak.
Lowering the digital volume so it stays below the onset of the 'softclip' circuit you created by switching off the amp will of-course give the proper not distorted sound.

I would suggest to use either a switch or use an XLR to RCA cable to the amp and the RCA out for the Heresy.
Schiit claims the outputs have independent buffer circuits so should solve the problem.

Thankyou for your explanation! I feel like a bit of a scrub here but I'm still a little confused. How can the combination of the resistor + diode add more voltage into side of the splitter going into the headphone amp? My understanding was that voltages in parallel circuits remain constant. In this case, the splitter creates a parallel circuit with the Speaker Amp and the Heresy. Is anything I said there incorrect?

Sorry for being so dense, my knowledge of electronics is still only at a high school level.

 

[solderdude]

Thankyou for your explanation! I feel like a bit of a scrub here but I'm still a little confused. How can the combination of the resistor + diode add more voltage into side of the splitter going into the headphone amp?

It doesn't. when the amp is switched off it actually lowers the voltage (soft clips/limits) the output of the DAC at the RCA outs (part of the voltage will fall across the output resistor.

The dac out is NOT in parallel to both inputs. Only the inputs are in parallel. The DAC out and amp inputs are connected via a 75 Ohm resistor inside the DAC.

As mentioned when you use the XLR out for one amp and the RCA out for the other amp it will work without problems providing the buffer circuits indeed are separate.

 

[KTN46]

It doesn't. when the amp is switched off it actually lowers the voltage (soft clips/limits) the output of the DAC at the RCA outs (part of the voltage will fall across the output resistor.

The dac out is NOT in parallel to both inputs. Only the inputs are in parallel. The DAC out and amp inputs are connected via a 75 Ohm resistor inside the DAC.

As mentioned when you use the XLR out for one amp and the RCA out for the other amp it will work without problems providing the buffer circuits indeed are separate.

I think I get it now! Your clarification on parallel circuit cleared things up. Thankyou! I've just ordered an XLR to RCA cable.

If I wanted to get more outputs, would the Aliexpress switch above add any noise/distortion to the circuit if I were to use it in reverse?

 

[solderdude]

Make sure the cable is XLR out TO RCA.
There are also RCA to XLR cables (so XLR in, sometimes even with female connectors !) that will short one of the DAC outputs when this one is used.

would the Aliexpress switch above add any noise/distortion to the circuit if I were to use it in reverse?

No.

 

[KTN46]

Make sure the cable is XLR out TO RCA.
There are also RCA to XLR cables (so XLR in, sometimes even with female connectors !) that will short one of the DAC outputs when this one is used.

Ah, you have just saved me a lot of fuss!

...I have now actually ordered an XLA to RCA cable.