The RA-02 is a decent sounding amplifier, nothing special circuit wise though. First of all to Mikeks WHile I see part of your reasoning for the designers to go back to school it is quite obvious the the amplifier section has been designed around a very old and well proven emitter follower design and a single differential front end. Two transistors and one resistor form the vas current source which is not the most stahdard fare, while many other designs typically share the same voltage drop diode between differential and vas, with a low collector capacitance transistor c1951 as the vas stage, low capacitance being the same thing the hugh dean has sought out with the 2sc3423 in his lifeforce..I personally loved the pre-amp voltage regulator (simple, quiet, damn effective and low impedence),. I still own an RA-02 but have had it out of service for while after my diy project sounded much better. It is not the end all be all obviously, but for an integrated at 499 or less it is a darn good deal while it was offered. Ironically though it had the exact same design as the rb850 amp section..There are any tweaks that can make this amplifier perform better but most require extreme handiness with a solder iron. The first being the opa2604 as input buffer before the volume control, and the gain stage after the volume control opa2604, i replaced both with class-a biased opa627 browndogged single to dual adaptors, this led to better overall sound from top to botoom than stock. Secondly replacing the stockpolarized electrolytic Panasonic fc coupling caps with 7.5-8.2uf solen mkp makes a huge difference iin clearing up some high end grain and resolves more distinct bass. Bypassing the op amp caps with small value 100nf films. There will inevitably be a limitation being that by the time you tweak the crap out of it with all of the information on the internet you will come to realize you can build something better, and quite possible cheaper with some research and alot of pouring over available schematics from well known and respected "audiophile" brands...
Colin
Colin
I wish to resurrect this four-year-old thread. I have an RA-02, and I like to tinker. (I converted its AUX 2 input into a "main in," so I can use an external crossover.) I do not know beans about amplifiers though. What can a naive owner do to tweak the RA-02's performance?
The service manual with schematics is available here: Rotel RA-02 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
The service manual with schematics is available here: Rotel RA-02 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine
I know it's very old, old topic.... But by chance maybe someone could advice me. I am doing standard cleaning of my old RA-02 amp, changing old electrolytics caps and I would like to change Panasonic fc coupling caps (10uF/25V) with some PP caps and I am looking for an advice of the capacity. I've read some topics that 2,2 uF is ok, here is written 7.5-8.2 uF. Could anyone advice me? ANd I will change only last pair (C601, C602) because there is place. Previous 2 pairs (C501, C502 and C515, C516) I will change for Elna cerafine 10uF 25V. Thanks, Peter