Rotel RA 930ax mods

I've just come into possesion of one of these........

its a circa 1995 amp

first impressions are pretty good ....sounds fast and lively if a bit lacking in detail. It has the worst speaker connections I've seen since I looked at the back of my A series Nad 3020. They are for spades, but I've got bare wire ....so everytime I tighten them down the cable pops out !

So yesterday I had the lid off ...hoovered out the fluff.

Lots of good quality polystyrene decouple caps and some yellow elna electrolytic caps but not a lot else.

signal is feed from the rear through copper tracks and wire jumpers to the selection and eq stages then on to the vol pot ...a cheap open frame alps[?]50k, the signal is then feed to a TL072 opamp .....

So stage one remove vol pot and fit an alps blue 50k ......straight away more detail but it now sounds a little thin. The vol pot has to be mounted upside down as the pins foul the opamp. The vol pot was hard wired using silver as the hook up to the pcb.

remove the opamp and fit dil socket [ have to remove vol pot grrrrr].

refit TL072 no obvious losses

So swap in an opa2132 [grrrr and double grrrrr have to keep moving the vol pot]. More body and detail but still a little too bright.

So what next.......

Sil bridge in the psu
caps add bypass
resistors in signal path
sockets and signal path to vol pot

I'll have a look at these tomorrow !

 

I remember reading somewhere - possibly diyaudio - that Rotel amps have their PSU tuned to have a punchy sound but that the low bass can suffer a lack of control as a result, but this is a fair trade off for most budget amps.

 

Last rotel amp I bench tested had the bass start rolling off at 100Hz, and was 1.5dB down at 20Hz.

 

That sound very much like this amp ....

The balance is rather bright, I'll have a hunt round and see if there anything obvious placed in the signal path thats causing this..ie a design feature. Though I suspect it could be the limited psu thats not helping.

I was unable to do more than poke around yesterday, so we will see what happens today.

 

Ok....so yes it was a bank holiday and Mrs Z wanted to listen to a cd or two in the conservatory ....so I've had to rush through the mods for the rotel as it now performs its duties in that system.

So bypassed all caps with 1uf film wimas.
replaced all caps in psu [but the largest] with pannasonics FC
replaced the opamp feed caps with pana fc
Swapped jumper links for silver in preamp
fiddled with the speaker cable to make loops [so it stays in the clamps]


So how does it sound ......

gone is the soft laid back lacking bass sound that I first had.

The sound is still clean deailed but with good bass but no longer has the soft presentation. But its not agressive or in your face so Thats a pretty good result for £20 worth of bits......

I keep looking at those cheap rca sockets............still theres always tomorrow.