Rotel RA-840BX4

[Skorpio]

I am looking for schematic for this amplifier.....

[Lenin]

Contact Rotel direct, they have always supplied me with schematics - at a cost of £5.

I doubt that policy would have changed.

The amplifier you mention (along with all Rotel amps in the 800 - 900 series) are derivative of a design Stan Curtis did for Rotel.

(I suspect later amps are derivative too).

If I can find my schematics (all now in storage following a move) I'l scan and post here.

Lenin

[Skorpio]

Thank you for a fine answer.....Stan Curtis has also made a Class A in the 80'ties?

[Skorpio]

Looking inside the amp, I found some interesting things:

-No output series inductor/resistor
-No zobel network at output (cap and resistor from output to ground)
-Fuse in series with output (4A)
-Very hot driver stage, looking like an single ended emitter follower, with 1K resistor as load..(one for each half)...

[kite_maniacs]

Hi Scorpio,

If you are still looking for the schematics I can send you the scans.

I started this week my own modding project for this great amp. As of today I am quite pleased with the first result. I would be happy to find some one in the forum who likes to share some thoughts or experiences of Rotel 840 BX4.

I will come up with more information soon.

Best

Joerg

[derguteton]

you can download it for free from:


3w.sendspace.com/file/6k4i2y


Michael

[Pingrs]

Michael,

Useful post. Now I can start resurrecting one I've been given.... or is it worth it? Is it a "great amp" or should I rip out the guts and use the case etc. and fit something "better", e.g. Leach, Symasym, FC-100 or DX's?

On second thoughts, maybe I should fix it then listen.

Thanks,

Brian.

[derguteton]

for my opinion Rotels are always very good, soft sounding Amps.

[homemodder]

Had a look at the schematics, its definetly worth to fix, very nice amp and very decent design. Just change the usual, old caps, upgrade the opamps, I would upgrade some transistors too, would be a fine amp.

[kite_maniacs]

There is a lot to improve ;o)

What I did already:

-Killed/bridged the sound tuning (bass /treble) section
-Removed the rubbish multi switches
-Replaced the cheap volume potentiometer by a new one from ALPS
-Changed the speaker wiring (removed remote speaker connectors) and removed the headphone wiring.
-Replaced the NE5532AN with an PMI OPAMP. Maybe will test BurrBrown ones.

What I still want to do:

-Add new high quality cinch adapters
-Restructure/Improve the wiring from cinch->volume->preamp->amp
-Add new speaker connectors

Still not sure if it is worth to replace some electrolytic capacitor or to bridge the big ones with films.

Second I don't like the fuses in the amp speaker output. Any suggestions ?

Cheers
Joerg