Noob question
I have a HD650, and have no headphone amps, the sound quality is good when plugged on my PC and I never had a comparison. Until I found a old Pioneer SX316 in our garage, plugged it in the front headphone plug, and found the sound to be slightly different (in a good way).
So I want to use this as the “amp”, but someone I know that knows more about headphones than me, said this can damage the headphones. Because these old receivers might have unstable voltages or something. I was skeptical and try to look online for answers but didn’t find anything relevant
It won’t damage it. If it has high output impedance (/u/Bingturong says 330Ω) it will tend to boost the bass a bit on the HD650 as it has an impedance curve that peaks in the bass. This is not necessarily a bad thing, and the HD650 is itself high impedance and one of the headphones likely to sound best out of a high impedance source.
You can see the effect here (scroll to/search for “Amplifier output resistance effect”):
That’s at 120Ω and it is very subtle. It will be a bit more at 330Ω but maybe still reasonable.