Rotel RB850 Still Current? Schematic Included - 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 8th October 2002, 06:58 PM   #1
diyAudio Member
 
Join Date: Mar 2002
Location: Toronto, Canada
Default Rotel RB850 Still Current? Schematic Included

I've got a Rotel RB850 amplifier, to which I made some small mods years ago (new Audioquest power cord, real binding posts and RCA jacks). The amp uses dual transformers and rectifiers. I have the schematic, what do the experts think, is this amp a good design or not? Is it worth upgrading some of the parts (I was thinking of input cap, feedback resistor, and 0.22 ohm emitter resistors in the output stage, and perhaps Schottky rectifiers if I can find the proper rating of what is in there now). Or is the design so old that it should be tossed into the basement system?

Thanks,
RonS
Attached Images
File Type: jpg rb850.jpg (86.8 KB, 3494 views)
  Reply With Quote
Old 8th October 2002, 08:50 PM   #2
raul_77 is offline raul_77  Europe
diyAudio Member
 
Join Date: May 2001
Location: Spain
Hi,

Besides the usual changes of compnents for better ones, you can add a 100uF capacitor across D602 (+) and R608 (GROUND).

I think than read R608 in the source current for the differential input.

This down the noise floor in the input, generated for the output in the supply, and the ressult are tath are show new information, and appear a 3D image. Almost magic.

But you need made before the other improvements for apreciate all this.

Happy days,

Raśl Couto
  Reply With Quote
Old 8th October 2002, 08:59 PM   #3
diyAudio Member
 
Join Date: Mar 2002
Location: Toronto, Canada
Hi Raul,

Yes, D602+ is followed by D604 then R608 to ground, in the current source for the input differential pair. So I should bypass the entire string of D602 to R608 with on cap, 100uF, about 100V to be safe? And this will lower the noise floor? That's what I want, lower noise, more 3D magic

Anything else besides parts upgrades, and what parts would you upgrade? I was told that maybe C616, 5pF should be improved. What about a seperate regulated power supply for the input diff. pair, like the Ryan Adcom upgrade?

Thanks again,
RonS
  Reply With Quote
Old 8th October 2002, 11:12 PM   #4
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Default Regulator

The Adcom's Kit Ryan upgrade was for the whole amp, a high current regulator, not just for the first stages.


Carlos
  Reply With Quote
Old 9th October 2002, 09:04 PM   #5
raul_77 is offline raul_77  Europe
diyAudio Member
 
Join Date: May 2001
Location: Spain
Hi RonS

The usual parts for upgrade are the capacitors.

For small values, less than 10nF, the best election are the Styroflex, or the Ceramic NPO.

For up to 1uF use polipropilene, or any film and foil: MkC, MKT. The series 470 from BC componennts (Philips) are a good election.

For higer values use low Z electrolitics. The minimun can be the Panasonic FO.

If you can, please, read the series of articles about "Sound of Capacitors" tath Mr Cyril Bateman have publised from this June, perhaps are the best work about capacitors tath have never writen.

The other upgrades: Schottkys, etc. are also a good idea.

Happy days,

Raśl Couto
  Reply With Quote
Old 9th October 2002, 09:17 PM   #6
raul_77 is offline raul_77  Europe
diyAudio Member
 
Join Date: May 2001
Location: Spain
Sorry,

"Sound of Capacitors" are pubished in Electronics World & Wireless World.

Happy days,

Raśl Couto
  Reply With Quote
Old 10th October 2002, 12:19 AM   #7
diyAudio Member
 
Join Date: Mar 2001
Location: Brazil
Default Rotel circuit

Am I wrong or there should be a connection point between Q612's collector and the trace that goes to Q618's base?

What does that star close to C616 mean? What do they say on the diagram?


Carlos
  Reply With Quote
Old 10th October 2002, 01:07 AM   #8
diyAudio Member
 
Join Date: Mar 2002
Location: Toronto, Canada
Carlos,

I can't comment on the connection between Q612 and Q18, that's beyond my comprehension

As to C616, the star indicates that this part should be used everywhere in the world except for the UK. It's a 5pF cap. Any ideas about this one?

What do you think of the circuit in general, and the quality of the transistors themselves?

Cheers,
RonS
  Reply With Quote
Old 10th October 2002, 01:13 AM   #9
diyAudio Member
 
Tube_Dude's Avatar
 
Join Date: Mar 2002
Location: Aveiro-Portugal
Default carlmart

Hei Carlmart!!

You are right, there should be a connection point between Q612's collector and the trace that goes to Q618's base...of course!!!

Regards

Jorge Santos
  Reply With Quote
Old 11th October 2002, 06:18 AM   #10
diyAudio Member
 
Morello's Avatar
 
Join Date: Jan 2002
Location: Sweden
Send a message via ICQ to Morello
Default Re: carlmart

Quote:
Originally posted by Tube_Dude
Hei Carlmart!!

You are right, there should be a connection point between Q612's collector and the trace that goes to Q618's base...of course!!!

Regards

Jorge Santos
Thers should not! The 5p-cap is HF-feedback.
__________________
"It was never supposed to be a hit, it was supposed to be a Joe Morello drum solo"- Paul Desmond
  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 03:59 PM
Problem with Rotel RB850 rmsmax Solid State 21 27th January 2009 01:42 AM
Rotel rb850 Leisner Solid State 54 4th October 2007 09:28 PM
Current feedback amp, pcb files included Mark Hathaway Solid State 1 14th December 2003 07:42 AM


New To Site? Need Help?

All times are GMT. The time now is 01:06 AM.


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