Rotel RA-980BX

Improving the sound of my Rotel RA-980BX

So, ever since I was a kid I was fascinated by hifi equipment. I loved drooling over the fancy hifi brochures with modern, minimalist villas showing the amplifiers, tapedecks and cd players in the best way possible. I guess the Rotel stereo from my parents with KEF speakers also added up to the allure of decent equipment.

Hifi history

At the age of 16, when I was old enough to start working in the holidays, I was finally able to start buying my own stuff. The first serious buy were my B&W V201 speakers (which are still active at the office I work!). 
I recall hooking it up to an old Akai amplifier I bought at a garagesale. After that, and after saving a lot of money, and I ended up buying my Yamaha AX-380 Amplifier, Denon DCD-855 CD Player, Kenwood tapedeck and a cheap Technics tuner to complete my setup.

Years later, when the surround hype was peaking, I bought the famous KEF KHT2005.2 “eggs” and a Marantz SR4200 to drive them. Upgraded my CD Player to the Rotel RCD-02, which I later modified with upgraded OpAmps and caps.

Although I loved the eggs, I wanted something better for listening to music. That’s when I bought some DALI Floorstanding speakers, which where later upgraded to B&W CM7's.

B&W CM7

These CM7 speakers are great, but need a good amp to drive them. The Yamaha came back in. However, as years progressed and I recently stumbled upon a topic online that raved about the Rotel amplifiers I used to want so bad back in the 90’s. Things started itching.

First I bought a broken RA-970BX which I fixed, cleaned and upgraded. Total cost: €60,- It’s a nice amp, but as soon as the big brother, the infamous RA-980BX showed up on marktplaats (dutch craigslist) cheap, I bought one!


Let’s dive right in!

First thing when buying stuff secondhand is opening it up!

First look after opening her up…Not bad!

So, there it was. the Rotel I always dreamed of. The insides all looked fine. That toroidal transformer is huge… and the two 8A(!) fuses give an idea of the power this beauty has.

Cleaned it up a bit, and sprayed the Alps volume and all the switches to get rid of small crackling noises. Cleaned the gold plated cinch connectors at the back and downloaded the servicemanual.

As mentioned earlier, I upgraded my Rotel CD Player with new OpAmps and better caps. That plan worked out great, so why not do the same for the amp.

These AD712 OpAmps are replaced. On top of this image C501, C502, C513 & C514, which I removed.

I desoldered the AD712 opamps, and replaced them with LM4562’s. Also, the preamp stage has black gate caps before and after the non-inverting amplifying stage. Caps are always the greatest (or should I say worst) influencer in sound quality. So I decided to remove the caps before and after the opamp, because later on in the signal path is another to block out any dc voltages. (And hey, there are output caps in all my source equipment, right?)

The remaining caps, also black gates, 4,7uF, where replaced with huge MKP parts (28x44x38mm) I salvaged from a SolarEdge converter. They where so big, I had to glue them to the case and use short twisted lead wires to connect them on the PCB.

HUGE caps

As you can see just top right in the image is some bulky silver solder and wire on the pre-out cinches which are used to bridge it directly. No more signal degradation through these clunky external bridges.

I also replaced the dinky speaker terminals with some high-end terminals. Because I reused the old terminal holes and the new terminals where pretty bulky, I had to sacrifice the “remote speaker” terminals, but who cares :)

Decent terminals for all that power

Conclusion

Boy, does that make a difference. I’m really awful at explaining sound quality, but stuff just cleared up and I just loved the “ease” the Rotel has in driving the large B&W’s. Just by replacing some OpAmps and 2 caps. 
The amp I always dreamed of when I was a teenager is now in my possession, and for about 20% of it’s original price. I’m happy!

For people interested; here are parts of the service manual with the edited schematic:

The PreAmp schematic with modifications

Any more plans?

Not yet. Feel free to comment if you have more diy upgrades I should do!