Counterpoint SA100 one channel doesn´t work - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

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 4th January 2007, 11:53 AM   #1
diyAudio Member
 
Join Date: Oct 2001
Unhappy Counterpoint SA100 one channel doesn´t work

Want to change Fet Outputstage to Mosfet (IRF 240/9240).

I found a schematic from an italien guy, who mention that it could
be changed to IRF Devices. But after reading the schematic, i saw
that the tube driving stage worked only with 1 or 2 mA.
Way to low for driving these Mosfets.

Has anybody have expirience with these Amp´s?

Maybe adding a fet follower to drive the mosfet?

It does´t seem to be a good design, or am i wrong?

Sorry for the bad english but it isn´t my native language.

Thanks, Andreas
  Reply With Quote
Old 6th January 2007, 07:13 PM   #2
diyAudio Member
 
stokessd's Avatar
 
Join Date: Nov 2002
Location: Grantham, NH
Yeah, I have experience with that amp. I used to use one to almost drive a pair of Eminent Technology LFT-VI's. The output stage melted down on me after a couple years. I sent it to counterpoint, $200 later, I got it back and within 3 minutes it melted down again (different speakers cables etc). I sent it back and they fixed it again (free) and it worked when I got it back. As soon as I realized it worked again I sold it. It was a good sounding amp, but didn't have a particularly good damping factor and couldn't control tough loads like a solid state amp can. I've got the service manual if you want it (I'd have to xerox it and mail it).

The output transistor power rails have fuses, but the FET's are a faster fuse than the fuses, and they melt, then the fuses pop. Handy huh?


If memory serves me right, the output stage used insanely tightly matched transistors due to not having much thermal compensation and no feedback to speak of.

Alta Vista Audio (http://www.altavistaaudio.com/) still repairs and rebuilds these units, although not to original form.

I really like the build quality and the sound quality of these units. I still use a modified SA-1000 pre-amp in my system.


Sheldon
  Reply With Quote
Old 14th January 2007, 03:58 PM   #3
diyAudio Member
 
Join Date: Nov 2004
Location: sequim washington
Default counterpoint sa100 one channel out

i also have a counterpoint sa100 with a channel out. if i can find an easy way to remove the circuit board, i will change the electrolytic caps on the board. there is a heat problem with d60, in5365 36v 5w zenerdiode causing 10 mfd cap to get hot. my unit is 15 years old.
any help appreciated
thank you
pothound
  Reply With Quote
Old 14th January 2007, 04:21 PM   #4
anatech is offline anatech  Canada
diyAudio Moderator
 
anatech's Avatar
 
Join Date: Jun 2004
Location: Georgetown, On
Hi Andreas, pothound,
Now there is an amp I know extremely well.

The outputs are made by IR. You must match them extremely tightly as there is zero sharing between devices. I normally takes me 20 ~ 30 devices of each to get a matched set. Set the bias a little low and the transformer will last longer. Check the darn relay. The heater supply will have a bad first filter cap. Gate resistors and zeners are shot as well. It takes the better part of a day to get the bias set correctly.

The 10 uF caps are dead, the board is crispy. New zeners and resistors of the top as well. Bad design. If you buy a matched set from M.E. (not me), make sure they are in fact good. You are getting "pulls" from amps he has worked on. He will tell you this.

His upgrades sound worse, just know this if you send it in.

-Chris
  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
Put amp in chassis, then, right channel doesn't work! ambience exists Tubes / Valves 11 4th August 2008 10:30 PM
counterpoint sa100 headaches pothound Solid State 46 26th October 2007 10:05 PM
want dead counterpoint SA100 SA-100 in good cosmetics jlw Tubes / Valves 0 4th October 2007 08:52 PM
Right Channel on my amp doesn't work?? nicku1302 Solid State 2 29th November 2005 03:58 PM


New To Site? Need Help?

All times are GMT. The time now is 12:00 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