[kipman725]

Hello I'm currently fixing a rotell RA-311 Stereo Preamp+Power amp. It has channel imbalance and hum on the attenuated channel. I have narrowed down the problem to the treble control section of the preamp and have in fact found the exact trace where the signal goes in and comes out attenuated. Looks to be some defective 10uF or 100uF capacitors. I don't have any 10uF In my supplies but I replaced the 100uF and the hum is reduced although still there and still have channel imbalance. What I find strange though is looking at the circuit some of the 10uF capacitors appear to be coupling capacitors used without constant DC bias. As I understand it electrolitics are perfectly fine to use as coupling capacitors as long as the DC bias is large in comparison to the AC signal across them is small?

I ask because the coupling capacitors that connect the power amp look prime to replace with polyester or something due to been in this situation.

I quite like this amp it's nice to have treble and bass control and it sounds OK even though its specs are awful compared to the amps usually posted (THD 0.1% 100KHz square wave has some ringing and poor rise time etc). It also has 4 speaker outputs and can drive 4 8ohm speakers or 2 4ohm ones. It apears although I'm not sure how that works to be able with another RA-311 to power a quadraphonic speaker setup aswell although I'm not sure how that would work (speaker 4chn on output selecter).

anyone know where to get the service manual?

 

[pabbi1]

Here

 

[kipman725]

hmm they only have the owners manual that has no schematic and I can get for free from rotells website. Thanks anyway.

 

[Pars]

Rotel will usually give out the service manual (with schematic) for free in a .pdf version. Contact them. More manufacturers should be like this.

 

[kipman725]

Well I emailed Rotel and I now have the service manual! very good service. Makes a nice change from the usual no schematics stuff thats been happening for 30 odd years.

 

[moga95]

hi, I have the same amp as you, and am experiencing the same problems that you have. could you tell me where to get that service manual and maybe tell me what was wrong with your amp.
 
thanks