Rotel RB-970BX Upgrade?

[bug2k11]

I've had one RB-970BX power amp for many years and recently acquired another two, which I am using to power a surround system.

I realise these are getting a bit old these days but has served me well over the years, can you guys offer any suggestions as to whether it's worth upgrading any components in them to gain some better performance and give them a new lease of life.

I recently upgraded the caps in my Castle Chester speakers have been impressed with how much better they sound.

The schematics for this amp are in PDF format here.

Any advice would be appreciated.

[bug2k11]

Anyone?

[jaycee]

The standard treatment would be to replace all of the electrolytic capacitors, especially the four big ones in the power supply. Those seem to be 8,200uF 50V. You might be able to get 10,000uF 63V in a size that will fit.

If you can replace C601/C602 with some good quality polyester caps such as Wima MKS2 that may help, likewise C607/C608 with some good quality non-polarised electrolytics.

I'm not going to recommend some "magic" brand of capacitors, just use good quality ones. Panasonic have a good range of parts which are good quality and reliable, and won't break the bank.

[bug2k11]

Thanks for that Jaycee, I'll get some ordered and see what difference they make.

[Toolie]

Hi all,

I'm in a similar position. I have a ROTEL RB970 MKII power amp that needs some life injected into it.
I have noticed that the "big" Electrolyte capacitors on the PS have leaked, so I intend to replace:

* Four PS electrolyte capacitors (from 8200 [uF] 50 [V]) to something a bit bigger.
* Fuses (burnt out)
* Any other suggestions?

Does anyone have the MKII schematics? It seems that the two versions differ in electronic parts naming (naturally).

Thanks,
Toolie

[Toolie]

Anyone?
Do you know the difference between RotelRB970 and the 970MkII ?
Any suggestion to as where can I find the schematics of the MKII ?

Thanks,
Toolie

[homemodder]

Hi Toolie

The difference is usually in the parts quality, From what I have seen on older Rotels the MKII sometimes uses black gate caps instead of regular panasonic caps and they also also change from common opamps to usually ad827. Very small changes, sometimes just a small change in compensation cap value. These small changes do usually bring inprovements in sound.

I have a couple of Rotels, they are reliable, quite good sounding amps for their price range. They use conventional design with high quality parts to achieve good sound. Last year a Rotel won an award as the best amp under 500 pounds. Its price stood at around 380 pounds.

If you want to get it good and up and running I just suggest you change the power supply caps and maybe the input caps depending on what your amp has inside. I strongly recommend that the supply caps be of the same manufaturer as supplied by Rotel. Ableit their markings they are manufactured by BHC in the UK and are what is termed as slit foils. I rate them very highly and are amongst the best caps one can buy at any price, if you want to go one better get from the same manufacturer so called T network caps which is what I use in all my diy amps and for upgrading commercial designs. They are expensive though and youd have to make some changes to the PCB, note this is in the case of the T network caps. Try 4 10 000uf slitfoils as a usefull start.

You could have a look at RB971 and RB971 mkII schematics and see they are essentially the same amp, compared to your RB970 it is also esentially the same.

The burnt fuses should worry you though, is the amp in working condition ??

[gabanyayaya]

my RA-970BX is full with Black Gates STND and this is what I got from the first time.

I did change all LCR poyester caps to silver micas and FKP and made some noticeable improvement...

[homemodder]

Originally Posted by gabanyayaya

my RA-970BX is full with Black Gates STND and this is what I got from the first time.

I did change all LCR poyester caps to silver micas and FKP and made some noticeable improvement...

The LCR s are only used in the tone controls so Im not really sure how that could improve things except if you do use tone controls. The RB970 has no preamp.

BTW try polystyrene caps as used on the the feedback and filter caps of the opamps, better than the micas.

[gabanyayaya]

Originally Posted by homemodder

The LCR s are only used in the tone controls so Im not really sure how that could improve things except if you do use tone controls. The RB970 has no preamp.

BTW try polystyrene caps as used on the the feedback and filter caps of the opamps, better than the micas.

RB970 is a power amp, RA970 i integrated version.

LCR is the polystyrene type replaced by micas in the feedback give me a much more 'vivid and dynamic' character from my observation...

BTW the AD827JN opamp replaced with some discrete type like the burson and it didn't change anything....