The Crescendo woes again - 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 10th January 2008, 01:19 PM   #1
RaviRao is offline RaviRao  India
diyAudio Member
 
Join Date: Jan 2008
Red face The Crescendo woes again

Hi Everyone, Great to be part of this forum at last... I have a request to anyone that can shed some light on the current issue with my Crescendo amp.
1. The amp was constructed by me way back in 1989!!
2. Has been working till last month!! Dec 2007
3. Now I get a heavily distorted sound with a lot of DC on the output --around 20 Volts without the LS connected of course.
4. I have already blown one channel of my Klipsh horns and do not dare connect these back till i fix the problem.

I know this is really insufficient info to suggest anything ...but is there anybody out there who might have some suggestions to go about fixing this.... Ive looked for the scematics and alas they are nowhere to be found. The MOSFETs are already history I beleive and so Iam really open to suggestion on the next set of actions to take.......HELPjavascript:smilie('')
  Reply With Quote
Old 10th January 2008, 03:59 PM   #2
EC8010 is offline EC8010  United Kingdom
diyAudio Moderator Emeritus
 
EC8010's Avatar
 
Join Date: Jan 2003
Location: Near London. UK
I've moved your post because it might get more replies here. I expect you've blown up one half of you output stage at the very least.
__________________
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
  Reply With Quote
Old 15th January 2008, 12:12 PM   #3
RaviRao is offline RaviRao  India
diyAudio Member
 
Join Date: Jan 2008
How did you guess!! I have since started looking for MOSFETS to replace them with. Any ideas ? I have also dug up some mods people have done to this amp over the years and the one with the opamp to correct for the imput offset looks very neat.

Where do I go from here........
  Reply With Quote
Old 15th January 2008, 12:37 PM   #4
diyAudio Member
 
Join Date: Sep 2007
Send a message via Yahoo to linuxguru
The Crescendo was prone to a lot of instability even when it worked - it was prone to oscillate under a lot of conditions, including reactive loads. Your FET(s) may have blown as a result, or for other reasons including output shorts, electrostatic damage to the gate oxide, etc.

The original (Hitachi?) FETs are probably going to be hard to find, so you may have to modify it to use commodity FETs like the IRF540/9640 instead. Search the forums for info on how to go about this.

Just BTW, just about any entry-level gainclone/chipamp today works more reliably, has better specs, sounds better than a Crescendo, and costs a small fraction of the Crescendo. You may want to take a look at the TDA7294 or the LM3886.
  Reply With Quote
Old 16th January 2008, 06:02 PM   #5
pjp is offline pjp  India
diyAudio Member
 
pjp's Avatar
 
Join Date: Nov 2006
Location: under the rainclouds
If you are near bombay, visha/vega sell the 2SK1058/2SJ162 for around 350 rupees.

linuxguru, you have any objective evidence that a TDA7294 is better than a crescendo ? I'm in the process of building one ...
  Reply With Quote
Old 17th January 2008, 12:37 AM   #6
Leolabs is offline Leolabs  Malaysia
diyAudio Member
 
Leolabs's Avatar
 
Join Date: Dec 2004
Location: Bukit Mertajam
Send a message via MSN to Leolabs
Sounds like a thermal drift to me due to heat problem and all the DC operating points starting to drift and cause all the stupid problems.
  Reply With Quote
Old 17th January 2008, 06:38 AM   #7
RaviRao is offline RaviRao  India
diyAudio Member
 
Join Date: Jan 2008
Thanks for your inputs linuxguru. Just for your info the Crescendo once stabilized worked like a charm for around 19 years without any instability problems whatsoever. I think that goes to say something. Any how I have spent some time on the amp and have seen the following .....DC drift was one of the reasons as the zener diode D1 was showing around 4.7 volts and the damping cap across it C8 looks completely open( tested with a DMM). The result was a blown MOSFET and the worst part is it took my 12" woofer( Klipshhorn) with it...amazingly my tweeters survived!!!

Now I am looking at Lateral Mosfet of the type pip has suggested!! Thanks pip I shall check these guys out and try to procure the devices.

I am currently looking to see what mods ,if any,will allow me to ressurect the Crescendo's again. Currrently my thinking is to gut the internals and make a brand new MOSFET if I get the time!!!!
  Reply With Quote
Old 21st January 2008, 07:30 PM   #8
dobias is offline dobias  United States
diyAudio Member
 
Join Date: Jun 2007
Default Crescendo

Gentlemen,
I hope you aren't discussing the Audire Crescendo amplifier I just purchased on eBay.
Please describe what amplifier design you're talking about.
dobias
  Reply With Quote
Old 22nd January 2008, 10:35 AM   #9
RaviRao is offline RaviRao  India
diyAudio Member
 
Join Date: Jan 2008
Dear Dobias,

We are talking about the Crescendo /Mini Crescendo MOS Fet amp described in the Elector Magazine way back in 1984 or thereabouts. I can send you the schematics if you would like to see them to be sure. Just let me know you want them.
Regards
Ravi Rao
  Reply With Quote
Old 22nd January 2008, 02:55 PM   #10
dobias is offline dobias  United States
diyAudio Member
 
Join Date: Jun 2007
Default Crescendo

RaviRao,
Thanks a lot for your response. I'm relieved to know you weren't referring to my Audire Crescendo. No, I don't need any info on the component... I wouldn't know what to do with it. While I can troubleshoot electrical, I am a raw beginner when it comes to SS electronics. My last contact with electronics was over 50 years ago with tube circuits.
dobias
  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
crescendo amp neeraj Solid State 10 22nd April 2012 11:13 AM
Seas Crescendo Jonasz Swap Meet 4 10th September 2008 02:31 PM
Anyone know Opus 3 Crescendo ? lurer Multi-Way 0 18th July 2007 09:38 AM
Help for the Crescendo ME!! FeFe Solid State 11 14th June 2005 01:56 PM


New To Site? Need Help?

All times are GMT. The time now is 11:20 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