My denon amplifer was playing okay then the trebel

Look around for a subwoofer which has speaker level inputs.
Something like this;
https://www.parts-express.com/dayton-audio-sub-1000-10-100-watt-powered-subwoofer--300-628

The only safe way to do this us to connect the sub to one of the other speaker outputs using a "speaker selector" switch. For example, you would go out of the receivers left speaker output, into the selector switch then out of the selector switch into the sub and the left speaker. There really is no other way.

Denon PMA 250SE does not have a RIAA phono preamp.

for some info about these preamp and details here;

Phonopreamps.com Home Page

Note: Choose a better quality regulated power supply,

for these preamps.






Although an updated turntable with USB can be used

without the need of such RIAA phono preamp.

Sounds like you have output transistor problems. Does it have a red protection light that comes on when it shuts down? If it does it will need serviced.

Why? Are you contemplating connection of something OTHER THAN A PHONO CARTRIDGE to it?

Be advised, only a phono cartridge should be connected to a Phono input. There's more going on behind it than just voltage step-up.

Well, it seems you have your finger on the source of the problem. If accessible, try some tuner cleaner inside the potentiometer.

try abeltronics.co.uk

Hi there
You can download one from here Select the FREE download button and you will get a PDF copy of the manual. Let me know if you have any problems getting it. Cheers
regards robotek

If you can follow the circuit from the input of the cd play socket inside the amp itself you might come accross a Memory Retention Capacitor that supplies an IC. If you do. I can't for certain say one will be there, I would replace it, it might be the cause of the lost memory of your device.
If you don't know what a M R C looks like, they are like electrolytic types, but haven the appearance of being squashed. The value will be low only 0.22uf etc and the volts very low say 5.5. The PC board marking will be different to a normal capictor.