Denon PMA800NE volume increases too fast when turning the potentiometer.

[Tonke]

L.S.

My PMA800 works fine, except that the volume increases so fast, that if at the 7 o'clock postition of the potentiometer everything is fine, but at 9 o'çlock postion the music is very loud and starts to distort the sound of my Infinity reference 80 mk2 speakers.

I searched for a not properly soldered potentiometer, I removed the board itself, but everything seems fine.
I checked both analog and digital input. No differences.

I found a schematic digram, if anyone has the service manual it will be appreciated.

 

[swechsler]

Is the volume actually an analog pot, or is it a rotary encoder?

 

[Tonke]

An analog pot.

 

[Olle]

Did someone replace a logarithmic potentiometer with a linear one?

 

[rothwellaudio]

Specs say the line input sensitivity is 105mV. Looks like that is the problem, but since its a design fault there's not a lot you can do about it (other than use attenuators on the input, but I have to declare an interest there).

 

[Tonke]

Did someone replace a logarithmic potentiometer with a linear one?

This makes sense. I checked the printed-on type number on the potentiometer and it says 833M-50KBX2. According to Google an "A" potentiometer is a logarithmic one and a "B" potentiometer is a lineair one. Bur having this said, there is no link between this number and Alps (the logo is Alps according to me) partnumbers who start with RK for potentiometers.
Any clues will be highly appreciated.

 

[Olle]

I assume finding an open dual logarithmic (audio taper) potentiometer may be difficult. If you can't find one, maybe you could use one of the sealed PCB mount ones.
Or you can fudge an audio taper using a resistor.

Using linear potentiometers for pseudo-logarithmic volume control

Note: This text assumes knowledge of Ohm’s Law, series and parallel resistances, and voltage dividers

kennypeng.com

 

[whoaru99]

... double comments removed ...

 

[whoaru99]

Any clues will be highly appreciated

Most likely is not technically broken or subject of parts tampering.

Rather, the most likely problem is the high input sensitivity mentioned back in post #5, and/or overall high gain.

 

[RVT1K]

It does seem to have very high input sensitivity.

What are you using as a source? Can you lower the output of the source?

 

[Tonke]

I use a Hifidelio as the source.

the service manual: https://www.swisstransfer.com/d/5c647dd1-3fe2-4068-8ba5-5bd9d797e7c5