c/m labs 35d - 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 16th May 2008, 05:51 AM   #1
sfalt is offline sfalt  United States
diyAudio Member
 
Join Date: Mar 2008
Default c/m labs 35d

was trying to reach wayne chou,or any one with a schematic for he 35d,and more knowledge than myself.I know my way around a soldering gun and very basic electronics.I followed a previous thread about bringing these amps back to life.I replaced all the small caps,and the pair of carbon resistors.The amp worked great untill it was inadvertently unpluged and repowered while under load.The 3 amp fuse blew,and upon replacing,the result was the melting of the solder connection on the250 ohm 20 watt resistor.
a friend thought that it might be the diodes on the power supply.Can any one help me get this baby running again?
  Reply With Quote
Old 18th May 2008, 04:18 AM   #2
diyAudio Member
 
Join Date: Oct 2007
Hi -

Doesn't sound good. Not the typical problem. The resistor that is heating up is supposed to be a soft start which allows power capacitor to charge slowly until sufficient voltage pulls in the relay and shorts out the resistor for full power. Once that is done, no power should be flowing through that resistor. So somewhere there is a short. BTW, the two carbon resistors (3.3k, 2 watts) should be replaced by a single 1.5k 5watt square cement type wire wound. The carbons become negative coefficent when heated after a period of time and they fry themselves as well as the board (the resistor should be spaced off the board).

Back to the problem - check the two large rectifiers. You can unbolt them, rather than unsolder, and using an ohmmeter check for diode operation by connecting the two leads of the meter one way and then with the leads reversed. You should get very different readings. Check both diodes in the same way. If that checks, the sudden power surge could have taken out one of the channels. This is a more difficult and time consuming problem. You could disconnect the power plus lead (red) from one channel at a time. If the amp powers up with one of them disconnected then more than likely a power transistor went on the channel that prevented power up. If both channels are disconnected, and you still have a problem, then you will have to look for a short somewhere else. If you have a Variac, bring the voltage up slowly while monitoring the voltage on the power supply capacitor. If there is no increase, it might help find the defect. You can also wire a lamp in series with the line cord of the amp. With no load on the output of the amp, it should draw very little power, so the lamp should be dim. You can also substitute different wattage lamps to judge the power going into the amp, which essentially is low including the bias current for the output. If a 60 or 100 w lamp burns brightly, and you don't get anywhere near 50 to 100 volts dc at the power cap, there is a serious short somewhere.

However, it is strange that a momentary disconnect from the power line would have destroyed a portion of the amp. I feel it is more likely that a spike could have destroyed one of the rectifiers.

Let me know what you find, and we can go from there.

Wayne
  Reply With Quote
Old 19th May 2008, 12:58 PM   #3
sfalt is offline sfalt  United States
diyAudio Member
 
Join Date: Mar 2008
Default c/m labs 35d

Wayne,
Thanks for the reply,great to be talking to the master of the 35d! First off, I aquired this amp as a memory of a friend of mine who passed away recently(only 50 years old),He collected lots of stuff.I had never heard of CM labs,or Bozak.Well the rest is history,as now I own the 35d,a Bozak CMA- 2 -80,and a Bozak 919 preamp!As I mentioned I followed the DIY thread and re-caped the 35d,(and I followed the instructions for the wirewound resistor upgrade also),I also recapped the CMA-2-80.
Back to the 35d,even before your reply I talked with some folks with more knowledge than myself,and we did determine that one of the diodes off the power supply was shorted.I ordered two from Digikey,and they should arrive any day.I'm confidant that the only problem was a current spike that took one out,and that the amp will be restored to it's glory.I will post to let you know the outcome.
Any chance of finding schematics for any of the amps or the pre-amp?,and any other recommendations for work on the pre-amp( I haven't touched that one yet),or the CMA-2-80 other than the re-capping?
Again thanks for the reply,I'm really new to internet message boards,but what a tool!
Stephen
  Reply With Quote
Old 19th May 2008, 07:12 PM   #4
diyAudio Member
 
Join Date: Oct 2007
Hi Stephen,

Good you found the problem. As I recall, the diodes have a "R" designation which means that the internal diode is reversed in the package. This is was chosen so that the mounting screw would be the common. Just make sure you compare what is left to the ones you get from Digikey, so they are the same polarity.

The only schematic I have is a sketch I made some time ago, reverse engineering, and what I remember, of the 35D. The original schematics went with the new owners of C/M. If you don't have exactly the same values that is on the schematic, don't worry. It would be close enough, and not significantly alter the performance. The unmarked resistor under the relay contacts is the 1.5k 5w resistor we had been talking about.

While I designed the initial mixers and power amps for Rudy Bozak, when my company sold, I could no longer support his needs. He eventually re-engineered/developed a more in depth line of his own, by other engineers. On the mixer-amps models you emailed, I do not have a good feel of what in fact was in them. However, Robert Betts frequents the forum, Bozak_speakers@yahoo.com. I am sure he could help you with some details and what was in them.

Currently I am completing testing and design on an all solid state, all class A, 100 watt mono bloc power amp. Aside from being low distortion, it will have other properties that will make it have very unusual capabilities which can influence whether it sounds more like a transistor amp, or a tube amp, or anywhere in between. Patents are pending.

Good luck on the fix, and enjoy.

Wayne
Attached Images
File Type: jpg 35d.jpg (77.0 KB, 393 views)
  Reply With Quote
Old 19th May 2008, 07:18 PM   #5
diyAudio Member
 
Join Date: Oct 2007
PS >

Robert was chief engineer for Bozak in those years. Just to be sure I got the link right, I repeat it:

Bozak_speakers@yahoogroups.com.

Now that I see it, I know the last link I sent you was wrong.

Sorry about that,

Wayne
  Reply With Quote
Old 22nd May 2008, 02:15 PM   #6
sfalt is offline sfalt  United States
diyAudio Member
 
Join Date: Mar 2008
Wayne,
Easy fix,she's up and running!Thanks for your replys,the wonderful previous threads on bringing the amp up to date,but mostly for the creativity in designing such a wonderful amp, so many years ago.I'm sure it will bring me many years of joyful listening,and will channel the spirit of the man who knew about this gem.
Stephen
  Reply With Quote
Old 22nd May 2008, 03:05 PM   #7
diyAudio Member
 
Join Date: Oct 2007
Stephen,

Glad you got it up and running without too much sweat. Hopefully, good for another 40 years. Enjoy!

Wayne
  Reply With Quote
Old 6th March 2009, 07:53 PM   #8
sfalt is offline sfalt  United States
diyAudio Member
 
Join Date: Mar 2008
Default Cm labs 911/reaching Wayne Chou

Just bought a CM Labs 911 and would like to know Wayne Chou's recomendations on bringing it up to 2009 specs,schematics,etc.Still very new to forum and need administrators OK to do anythingas far as contact.thanks Stephen
  Reply With Quote
Old 6th March 2009, 09:44 PM   #9
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
If no one has a schematic handy I can if needed scan mine.

I have a CM Labs 911, it was my first "high power" amp. I bought mine used about 1973 or so.

It has blown up a few times...

Imho there is no way to bring this amp up to modern standards.

It has several problems in that regard. First, it is a single rail supply, and so has a monster cap at the output. Second it is a design that is relatively crude by today's standards.

Otoh, it does sound relatively nice, smooth and has mostly even order harmonic distortion, lots of second.

I'd bypass the output cap with some good film, as large as will fit in the space and leave it at that. Oh maybe improve or bypass any "bypass caps" or other electrolytics on the board as well.

That's my take on it.

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 10th March 2009, 07:07 AM   #10
dangus is offline dangus  Canada
diyAudio Member
 
Join Date: May 2004
Location: Vancouver Island
How about the CM 920? I've done a hand-drawn schematic by tracing the PC boards, but a _real_ schematic (or service manual?) with voltages and real part designations would allow me to make my drawings and board layouts consistent with the originals.

By the way, I started an entry on C/M & CM Labs in the vintage audio wiki. If anyone can add to it, please do, since information on C/M is hard to come by.
  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
What are people using in JE Labs OB? davidallancole Full Range 4 26th December 2006 02:47 PM
J.E. Labs 2A3 PTSOUNDLAB Tubes / Valves 14 5th September 2003 02:45 PM


New To Site? Need Help?

All times are GMT. The time now is 12:29 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