Rotel Mods..

[rantzmar]

...Hi fellas. Looking for a little advise.

I have an old Rotel amp the RH 1080. Nothing wrong with it, but its a least 10 years old. I've been thinking about taking it in to get a refresher in parts. Has any body done this to any Rotel amps and is it worth it, or should I just get a new amp?

[madmac]

In my opinion, If it works fine then leave it alone. There are too many cheap electronic components floating around the market nowadays with failures resulting. Like they say, they don't makem' like they used to!!.

[Kurtiss]

Hello Rantzmar,

There are a few mods/upgrades which can make a difference. For specifics, you'll want to get a copy of the schematic for your RB-1080 unit. Many of the older tech manuals are available on the B&W support website. The RB-1000 and RB-1010 are available there, but not the 1080:

http://bwgroup-support.com/rotelservicemanuals.html

For good (or bad?) the Rotel power amps are VERY SIMILAR design in the 8xx 9xx and 10xx series. They vary by using single vs. dual power supplies, some have toroidal transformers, etc, some have op-amp buffers for pre-amp, or input selection. But the "core" circuitry is amazingly similar, IMHO.

I am currently doing upgrades to my RB-870 from the mid 1980's. So first, here are some threads which I found useful on the "upgrade" or maintenance topic.

Rotel RB-970BX Upgrade?
http://www.diyaudio.com/forums/solid...x-upgrade.html

Rotel 1072 This is a CD player, but they also (mistakenly) discuss some power amp upgrades also...
http://www.diyaudio.com/forums/digit...el-1072-a.html


A few of the typical upgrades are:
electrolytic capacitors in the power supply

• After many years, the dielectric material looses its capability. Although, they should be fairly good at the 10yr mark.
• Even without a schematic, these are easy to locate inside the case. They are the LARGE caps. They are likely 8200uF or 10,000uF. Rotel often uses fairly good quality (Panasonic or Nichicon) caps in their production.
• consider increasing the value to 10000uF, if it currently has smaller caps
• upgrade to one of the really-good quality brands (Nichicon "muse" series). Plenty of other great choices also
• you can also replace any of the other electrolytic caps. They will all suffer some level of degradation after many years.

input coupling capacitors

• These are currently some type of metal/film capacitor.
• consider upgrading to MKT (Metalized Polyester Film) or better MKP (Metalized Polypropylene Film). the WIMA brand makes fantastic audio coupling caps. Again, plenty of other good choices are available from supply houses like DigiKey or Mouser.
• Some folks suggest using a different value for the input caps. Suit yourself on that. Here is a good discussion on that topic, as well as a calculator to solve for new values:
  http://www.v-cap.com/coupling-capacitor-calculator.php

Now - there will be plenty of discussion on why to upgrade - or not... For me personally: I do it because I like to. I might install chrome valve covers on my car too. Will it go faster? Will it run better? No. But I do it because I enjoy it. So, enjoy the learning as you read articles. I'm interested to see what other upgrades our members have tried, or considered.

Good luck in your adventure!
Kurt

[Kurtiss]

Doing some quick research (since I like the sport) The Technical Manual and schematic are available at:

http://www.hifi-manuals.com/Download/Rotel/RB-1080-schematic

It looks like they used very good caps in the (mostly) dual-mono power supply. It has 1 shared toroidal transformer with separate left/right secondary windings, rectifiers, and filter capacitors. The caps appear to be very good British slit-foil variety, 15,000uF/80v. Those will be fairly expensive to replace. In the schematic, they are identified as C002/C004 (right) and C003/C005 (left).

C601/C602 are the input coupling caps of interest, currently 4.7uF/50V. They service both the balanced and unbalanced inputs. For the calculator I referenced earlier, the input resistance is stated as 33k ohms, and observable via the C603/C604 resistors.

The power output transistors (which you wont need to replace/upgrade) are 5 complimentary pairs of 2sc3856/2sa1492. That is a newer divergence from their older method, which used 2sd1047/2sb817. MANY of their 8xx and 9xx (even some 10-series) models used the 1047/817 combo.

(for a more advanced/adventurous update)
The balanced XLR inputs use the AD711 op amp chip. those do not apply if you are using the unbalanced RCA input jacks. You can read online for sources for really-good op amp replacements. But again, that may be overkill. Still, those chrome valve covers (er, I mean new op amps) will be fun!

As part of your tune-up, you can verify/adjust the bias. That is set using the variable resistors vr601/vr602. They require a small blade screw driver, and are visible (somewhere) mounted to the top of the main circuit board. You can read this discussion for more details on measuring/setting the bias:
http://www.diyaudio.com/forums/solid...s-setting.html

-Kurt

[rantzmar]

Wow Thanks Kurtis....very well appreciated.