Rotel 820 schematics

[pete.a]

Anyone got one, im trying to fix an 820..and it's difficult.

[hollow_man]

Hi pete.a,
I used to own an RA-820, which I have given to my brother. I have tweaked it a lot, and know the circuit quite well. What state is yours in?

[pete.a]

Hi,

The main tx went bang..oh err..as i think someone played with it.
Can you remember what the secondary voltage should be, i got around 44v ? I was going to put a toroidial tx in but not so sure now. Just brought it for an easy repair ,and to go in the work shop until i get time to build a new chip amp. But i would be greatfull for any suggestions.

[hollow_man]

The voltage at the secondary measures 2x25.4V ac (idle). If you want to replace it by a toroidal, 2x24V would do but it is not a bad trany anyway. If the output transistors are dead, you can go directly for the low beta-droop 2SA1302/2SC3281s, which I have tried successfully.
BTW, greetings to Nottingham, Sherwood Rise, Mansfield Road etc!

[pete.a]

Hi,

Im not sure what Va to go for..160 seems to be the best size if using a toroidial..

Guess what..the chap i got this amp from lives on mansfield Rd , small world.

[hollow_man]

Yeap, 160 will do nice. Bleeding small world, too.

[pete.a]

Thank's for that one. Im not sure what state this amp will be in , as it got 44v per rail through it . Dont know the threshold voltage of the components, but i did get a schematic from Rotel. It could be written in Arabic as im not that to hot on electronics, just the basics, sparky by trade..if you get my drift..but im learning fast.
Just one thing to add the protection fuses never blew, so there's something hopefull start with.

[pete.a]

Hey iv'e finally got round to putting in the Tx you recommended , and it worked first time . Whats worth tweaking , though i might change the opamp buffers from those NE5532 to well that im not so sure yet.

[hollow_man]

What I've done is I bypassed the line-stage. No NE5534, no nothing. This will then give you a passive preamp. The power amp's gain was still plenty, at least in my system.
In addition, there is a lot of going backwards and forwards with the signal on its way to the power amp. You can take the output from the volume pot wiper pad and feed it directly to the input of the PA. This way you will bypass the tone-defeat wiring and switch and the balance pot.
Get rid of coupling capacitors too, if your sources have no dc offsets.

Happy tweaking!

[pete.a]

Thanks for the promt reply, i guess you had a good Xmas break.

Yeh i might try those suggestions at some point in time, but for now i'll leave it alone ..if it aint broke and all that...just had a few to many things go wrong . Call it a lack of electronic knowledge/experience. Mind you it sound's damned good in my shed now , i'll post a picture tommorow.