yamaha amp headphone hiss

[Impunity]

I have a Yamaha RX-V670 amp. It sounds well but has quite a hiss through the headphones in both channels but a bit louder in the right. It's the same no matter which input I select and doesn't respond to volume changes. That is with no audio signal and turning up the volume, no difference is heard with the hiss. I don't have speakers to hook up yet so I don't know if the problem exists there or not. Any ideas please?
Regards John L.

 

[PRR]

What headphones? Impedance, sensitivity? Some hot hi-Z phones will take "all the voltage" of the speaker outputs and that may be a lot of normal hiss.

Pull the "couplers" (don't lose them!). Any change of hiss?

Putting 39 Ohms in shunt across the headphones to ground may be a better match for both low and high impedance phones, and be plenty loud into 99% of phones.

 

[stratus46]

How loud is the tuner section? What I'm wondering is if your phones are very sensitive and the volume will
be very loud at a very low setting of the control. When you connect speakers you'll get a much better idea
of what is "normal".

Remember NO amplifier is totally quiet. Kick the gain up high enough and you'll always find noise. Some
models are better than others but ALL do it to some extent.

Schematic is available on HiFi Engine. The headphone jack has a 390 ohm resistor in series for each channel.
That's it. You might need to add a a 'pad' in front of your phones. For test purposes I would add a shunt
resistor to ground but make it with connectors you that you don't alter the phones or the receiver. This pad
circuit will only require you to turn up the volume more. You're increasing the S/N ratio.

You need more info so connect some speakers.

G²

 

[PRR]

> The headphone jack has a 390 ohm resistor in series

You are correct. I mis-read "180".

 

[Mark Tillotson]

That amp has a poor signal to noise ratio of 95dB at best, so you need significant attenuation to drive headphones and push that 0.4mV of noise down to something quiet. That will require power resistors I think.