Problem with Rotel RB850 - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th January 2009, 10:12 AM   #11
Account disabled at member's request
 
Join Date: May 2006
Hi Gavin, I think the pdf file is too large to post here, maybe you could just post the schematic page.
  Reply With Quote
Old 14th January 2009, 10:17 AM   #12
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
Quote:
Originally posted by stoolpigeon
the higher model 870
Ditto, an RB870(BX) is definitely worth a repair.
__________________
The buck stops Here
  Reply With Quote
Old 14th January 2009, 10:24 AM   #13
Account disabled at member's request
 
Join Date: May 2006
Ive heard bad things about the pre amp, most probably uses old type opamps, nothing to do with the amp.

I would suggest rmsmax to replace the output transistors and driver which is most probably the cause of the fault and take the amp to be auditioned against others in its price range. Remember this amp cost a measly 170 euros or so when new, what can you get for that price nowadays. Those slitfoils might still be ok for use, I have some rotels 15 years old now and the caps are still good. The parts could always be used to construct another amp if the results arent good. Couple it to a better preamp for testing.
  Reply With Quote
Old 14th January 2009, 11:30 AM   #14
Evaas is offline Evaas  Canada
diyAudio Member
 
Evaas's Avatar
 
Join Date: Apr 2001
Location: Montreal QC
apparently I was misunderstood. I found the situation amusing as I wasn't sure if rmsmax knew what he was in for when he wrote. but I'm completely in favor of encouraging him with to do some upgrades.

sorry for any confusion.
__________________
-roomatthebottom
  Reply With Quote
Old 14th January 2009, 10:21 PM   #15
rmsmax is offline rmsmax  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
Evaas ...no I probably wasn't prepared for such enthusiastic input as ..."taking a saw to it"..... but good to see an optimistic outlook to what I saw as gloomy!

At the time when I bought the combo they were well rated and they were not cheap. As you say Jacco given replacement parts to repair and balance the output stages may be expensive it may be more economical to get a second hand quality amp.

For interest the schematic is attached (I hope).

Anyway great to have your input guys and thankyou.

Gavin
Attached Images
File Type: gif rb850-schematic.gif (37.1 KB, 296 views)
  Reply With Quote
Old 15th January 2009, 12:43 AM   #16
Account disabled at member's request
 
Join Date: May 2006
Not what I thought but still worth a fix, and easy to upgrade.

For less then 10 pounds you can get get it going again with original parts and if you know how to handle a soldering iron. If you take it for repairs via rotel expect it to be expensive, thats normal, they are dealers and want to make big profits. The ouput trannys cost less than 2 pounds each and the drivers around 80 cents each. Easy to upgrade too, just have to do some work on the compensation. What preamp do you have, here is the weakest link. Have a schematic of that ??

Its up to you what you want to spend. A second hand unit can be had for around 70 dollars off ebay. There are guys selling amps with this topology and some refinements for 300 dollars a channel, complete working amp would cost you over a 1000 dollars. So much for low fi topology.

Going jacco way s would most probably set you back around 70 pounds a channel and the sound quality improvement is debatable. Replacing those power supply caps is what is expensive but this you would have to do even with jacco s suggestion. Maybe they are still ok, because they are high quality slitfoils but its something you will have to do eventually.
  Reply With Quote
Old 18th January 2009, 11:22 AM   #17
rmsmax is offline rmsmax  United Kingdom
diyAudio Member
 
Join Date: Jan 2009
Hi Homemodder. I think I'll have a go at what you suggest. I know you aren't in the UK but where should I look for the bits? (used to be local component shops now long gone.... so out of touch!!)

Probably the pre-amp (RC850) is the weakest link and would need replacing to upgrade. Thought about a Lindsey-Hood but I'm sure there are more modern designs. However I can always use the modded power-amp it for bi-amping.

Thanks for your advice and I look forward to having a play!

Gavin
  Reply With Quote
Old 18th January 2009, 12:38 PM   #18
diyAudio Member
 
jacco vermeulen's Avatar
 
Join Date: Oct 2004
Location: At the sea front, Rotterdam or Curaçao
Send a message via Yahoo to jacco vermeulen
The easiest 3 :

www.dalbani.co.uk
www.grandata.co.uk
www.cricklewoodelectronics.com
__________________
The buck stops Here
  Reply With Quote
Old 18th January 2009, 01:26 PM   #19
jaycee is offline jaycee  United Kingdom
diyAudio Member
 
Join Date: Apr 2004
Location: Norwich, UK
Best to test whats wrong first, although if it was a short on the output, you can bet the output transistors are dead.

The schematic looks typical of most of Rotel's amps of that era. Rotel seem to love the 2SD1047/2SB817 from Sanyo.

Farnell has them, and I'd buy them from there rather than anywhere else, as Japanese transistors are notorious for counterfeiting.

The driver transistors might also be damaged, but I can't make out the part numbers on them to advise. I would guess they are 2SD600/2SB631. Fairchild's KSA1220/KSC2690 would be a good replacement, but Farnell don't stock them (although you could try buying them as samples from Fairchild Direct)
  Reply With Quote
Old 18th January 2009, 07:41 PM   #20
Account disabled at member's request
 
Join Date: May 2006
The suppliers Jacco suggests are good ones, I have purchaced from criclewood and dalbani. Tell them you want original Sanyo parts and not second source, if they have from same batch and group gain its the best bet. I find criclewood to be cheaper in most instances. Test the transistors first, the drivers and outputs, all might not have blown, thats the 2sd1047, 2sb817, 2sd600 and 2sb631. Maybe only one of the output tranies have blown together with its driver, has happened to me many times with rotels.

You could always try get them from rotel, they will sell them to you as well, maybe its cheaper, shop around. Farnell is a safe bet if they have the output transistors. You could also get those equivalent drivers like jaycee has suggested, that might work you out cheaper, depending on shipping charges.

Nothing wrong with linsey hood, I have a preamp of his which is still my reference from 1988. Purchased it as a kit when still teenager, I have upgraded the parts with modern japanese transistors and high quality caps and resistors, it sounds awesome, so far I have only encountered two preamps that to me sound as good or better, both are selling for over 5000 dollars. Linsey hood was a master, I use some of his technics in my own designs, some of them are 30 years old and till today cant still be bettered. A 1969 designed amp of his is still loved, highly regarded and used by thousands around the world.

You could build a simple preamp and put it in the case of your current 850, easy upgrade and wont cost much. Try get the service manual on this preamp, maybe a simple change of opamps will do the trick, as it was an entry level seperate, they might have used cheap low cost opamps on this model.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Rotel RB850 transformer blown? rhiolly rub gt Solid State 5 16th April 2009 02:59 PM
Rotel RB850 Still Current? Schematic Included transducer Solid State 50 20th April 2008 12:36 AM
Rotel rb850 Leisner Solid State 54 4th October 2007 08:28 PM
Rotel RCC-955 Problem sorenj07 Digital Source 0 27th February 2007 01:51 AM
Rotel RA-931 problem njholland Solid State 3 16th July 2006 04:01 PM


New To Site? Need Help?

All times are GMT. The time now is 04:42 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2