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Channels on AVR have slightly different voltage

nitpicker1

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May 7, 2024
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While taking apart my around 10 year old Pioneer VSX cheapo AVR to create some pre-out RCA connections for Left, Right and Center, I discovered that the left channel has slightly lower voltage than center and right. Center inbetween the two. This is only after preamp and amp stages. The line out from decoder board before pre-out/DSP has equal static values. But I needed/wanted pre-out...

On the speaker output around 60% volume: Left = 5.50-6.00VAC while Right = 5.90-6.50VAC while playing its own testtone to set channel dB. On the pre-outs it was 180-200mV for Left and 190-210mV for right. Center somewhere inbetween. Rough estimations as the test tone made measurements jump around.

Side question: These speaker output voltages generally seems low to me... Wear or manufacturer overstating its 100W RMS per channel?

Main question: is it normal for cheap AVR's to have a slightly different voltage on pre-out and amp channels?

While playing test tone on my living room towers, I've always been able to barely detect a lower volume on left channel. I always thought this was because of room acoustics, but now I'm wondering if it's this...
 
Side question: These speaker output voltages generally seems low to me... Wear or manufacturer overstating its 100W RMS per channel?
Make yourself a 60Hz 0dBFS test tone, or download the one attached below.

Disable all EQ and volume limits on the AVR.

Plug all speakers out of your AVR.

If your AVR can play from a thumb drive, load the tone onto one and play it on repeat.

Otherwise, play the tone from a PC, making sure you use Wasapi Exclusive playback for bit-perfect transmission.

Set the AVR to 100% volume.

Measure the AC voltage across the main speaker output.

This will tell you the theoretical maximum output power of your AVR.

For example, if you measure 20Vrms, then the highest possible output power is 20^2/4=100W at 4Ω or 20^2/8=50W at 8Ω.

This does not guarantee that the AVR can actually output as much when loaded, but it will tell you if the manufacturer's specs are at least feasible.
 

Attachments

  • Sine_60_0_dBFS_44k_PCM16.wav.zip
    39.9 KB · Views: 27
The automated test tone levels are always set rather low, so users don't destroy their loudspeakers. Think about it.

Make sure the balance control is defeated/set to centre.

Does the volume control stop at 0dB or does it go considerably higher?
 
Curious, what is "60 % volume" in terms of the master volume control? On a logarithmic volume scale percentages aren't readily apparent.
 
Thanks for the replies, I'll do more testing and get back.
The automated test tone levels are always set rather low, so users don't destroy their loudspeakers. Think about it.

Make sure the balance control is defeated/set to centre.

Does the volume control stop at 0dB or does it go considerably higher?

Not sure if it stops at 0dB, but I can't imagine I've been above. I've ever stayed below 50 during actual listening. At 40 it starts getting pretty loud. That said, the AVR is rated for 6-8 ohm and I'm using 4 ohm speakers.

Only balance control I have is dB per channel/channel level, and they're set to 0/centered. Setting -1 or +1 adjusts the voltage well beyond the slight difference when they're the same.

I'll get into testing with the 60Hz tone above (thanks!) tomorrow and see what I get. But with the data so far, I expect a slight voltage skew still between left and right. It'll be interesting to see how large the difference is at max theoretical output.
 
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