Help! I've got an excess gain problem!

[MartinHyde]

Hi all,

I have a problem with excess gain in my system, which means that the volume is already too high at only 9 o'clock.

I've been playing around with attenuators and have found that I need more than 20 db attenuation to improve the situation.

Using a 10k resistor in series with the signal and 750 ohm across to the ground gives me -23 db (I think). I've put these inside the RCA connectors (neutrik metal) and its much better but not completely perfect. Could do with a bit more i think.

My speakers are sensitive at 90 db and marantz don't publish a gain figure.

I think -23 db attenuation sounds a bit much, don't you? And I'm worried about sound quality and overloading outputs and inputs.

Any ideas?

Martin

Here's my system:

Sources: Apple TV2, Virgin media V+ box, Sony DVD/HDD recorder, Marantz ST4000 tuner

DAC: Dacmagic

Amplifier: Marantz PM6004 integrated

Speakers: Monitor Audio Bronze BX5 and REL Q150E subwoofer

Control: Logitech harmony remote.

 

[jaycee]

Apparently the inputs have 200mV sensitivity, which is very sensitive as most amps now expect line input to be 2V.

 

[forr]

I think -23 db attenuation sounds a bit much, don't you?

Quite normal to me. Many configurations work ok with peak levels of 3 V across the loudspeakers. A CD drive output is about 2.8 Vpk. And most amplifiers have a voltage gain of 26 dB (20 times) or more, which means they can output much more voltage than really needed. I suggest you insert a 20 dB attenuator at the amp input, with lower values for the resistors than those you used : 2700 and 300 Ohm. It won't overload anything and does not degrade the sound.

 

[MartinHyde]

Quite normal to me. Many configurations work ok with peak levels of 3 V across the loudspeakers. A CD drive output is about 2.8 Vpk. And most amplifiers have a voltage gain of 26 dB (20 times) or more, which means they can output much more voltage than really needed. I suggest you insert a 20 dB attenuator at the amp input, with lower values for the resistors than those you used : 2700 and 300 Ohm. It won't overload anything and does not degrade the sound.

Thanks for the info - I am keen to learn and was wondering how you come to these resistor values and what is the benefit of using lower resistances?

I am also contemplating opening up the marantz and fitting the resistors between input selectors and volume control (if accessible). That way, all inputs would use the same attenuators and I'd purchase some really good quality resistors. What do you think?

Cheers, martin

 

[AndrewT]

I wonder if the amplifier has a gain stage before the Power Amplifier section?

It may be possible to bypass that internal gain stage.

It's better to remove excessive gain, than to attenuate before amplifying back up again.