I am already regretting a recent purchase of a Counterpoint SA20. All the FETs are blown and probably more based on the old posts I've been reading. That said, I would like to get it going and need referrals to older posts and/or a troubleshooting order of march and plenty of recommendations on what to look out for!
I'm familiar and have restored a number of Haflers and have seen a couple of posts suggesting that lateral FETS make good replacements (with bias changes?) for the obsolete RFM10N15 & IR9241. I've seen strong pro & con posts--any winners? Other FETs mentioned: IRFP240 / 9240, IRF243/9241, 2SJ56/2SK176 and possibly others.
Also, claims of fanatical matching required, as adding Source resistors is considered a heresy that ruins the quality of the sound. Sorry if this opens old wounds, but I'd really like to restore this amp and stay as true as practical to the original design. Yes, I'm waffling, but need to understand my options / time required / cost.
Thanks in advance to those Counterpoint experts out there that are willing to coach a Counterpoint newbie through his first repair!
Regards,
Ivan
I'm familiar and have restored a number of Haflers and have seen a couple of posts suggesting that lateral FETS make good replacements (with bias changes?) for the obsolete RFM10N15 & IR9241. I've seen strong pro & con posts--any winners? Other FETs mentioned: IRFP240 / 9240, IRF243/9241, 2SJ56/2SK176 and possibly others.
Also, claims of fanatical matching required, as adding Source resistors is considered a heresy that ruins the quality of the sound. Sorry if this opens old wounds, but I'd really like to restore this amp and stay as true as practical to the original design. Yes, I'm waffling, but need to understand my options / time required / cost.
Thanks in advance to those Counterpoint experts out there that are willing to coach a Counterpoint newbie through his first repair!
Regards,
Ivan
I have rebuilt a SA12 and 2 SA220 with IRFP240/9240, and had them running for quite some time now, they sound amazing and are really really powerful.
There are people here who have also been successful and a few who claim to have repaired many of the originals who would advise you against repairing them with anything but the original fet's. Some will even PM you and tell you that you are going to burn your house down if you dare replace the fet's with anything but the matched originals. You will have to make your own decision on the path you want to take, good luck.
PM me if you want the service manual, they are definintely worth putting the time in to fix.
Search the forum and you will find alot of information on this subject.
There are people here who have also been successful and a few who claim to have repaired many of the originals who would advise you against repairing them with anything but the original fet's. Some will even PM you and tell you that you are going to burn your house down if you dare replace the fet's with anything but the matched originals. You will have to make your own decision on the path you want to take, good luck.
PM me if you want the service manual, they are definintely worth putting the time in to fix.
Search the forum and you will find alot of information on this subject.
I'm about to rebuild a working (I was surprised also!) SA-12. It will be getting, first and foremost, source resistors. 0.1 Ohms isn't going to add any noise to the circuit, much less Johnson-Nyquist noise (Well, audible or measurable anyway). If you want non-inductive types, I'll be adding Caddock MP930 resistors in these positions. They are rated, when heatsink-mounted, for 30 Watts. I'll be using a strip of aluminum channel for heat sinking, with 2 resistors mounted to each. The resistors come in a TO-220 transistor package, and are ceramic-backed for insulation. When you see one, you'll think, "No way is that rated for 30 Watts", but the data sheet confirms.
As for MOSFETs, I'm told the originals used HEXFET technology, of which Mouser has 323 different ones of the thru-hole variety in stock. Happy Hunting! FWIW, the SA-12 used IRF130 (N-channel) and IRF9130 (P-channel). These are not available, but I would be willing to bet you Infineon has an updated part that matches or exceeds the specs. You'll have to use a TO-247 package instead of TO-3, but I've done this before repairing an Arcam Alpha, and it worked well. Just make sure you put heat shrink around the pin that goes through the heatsink!
Now, there has also been released instructions for using BJTs instead, at least in the SA-100. Your choice whether or not to go that route:
http://woodman1200.com/Counterpoint_SA-100_BJT_output.html
Same guy also came up with a MOSFET replacement option as well:
http://woodman1200.com/Counterpoint_SA-100_output_stage.html
A quick search shows the MOSFET in the link above is unavailable, but the company that makes them makes that series of MOSFETs specifically for audio purposes. Exicon is the maker, I'm guessing they have an updated part as well.
Either way, since your outputs blew, I'd put new of everything inside the dotted line on the schematic posted above.
Good luck!
As for MOSFETs, I'm told the originals used HEXFET technology, of which Mouser has 323 different ones of the thru-hole variety in stock. Happy Hunting! FWIW, the SA-12 used IRF130 (N-channel) and IRF9130 (P-channel). These are not available, but I would be willing to bet you Infineon has an updated part that matches or exceeds the specs. You'll have to use a TO-247 package instead of TO-3, but I've done this before repairing an Arcam Alpha, and it worked well. Just make sure you put heat shrink around the pin that goes through the heatsink!
Now, there has also been released instructions for using BJTs instead, at least in the SA-100. Your choice whether or not to go that route:
http://woodman1200.com/Counterpoint_SA-100_BJT_output.html
Same guy also came up with a MOSFET replacement option as well:
http://woodman1200.com/Counterpoint_SA-100_output_stage.html
A quick search shows the MOSFET in the link above is unavailable, but the company that makes them makes that series of MOSFETs specifically for audio purposes. Exicon is the maker, I'm guessing they have an updated part as well.
Either way, since your outputs blew, I'd put new of everything inside the dotted line on the schematic posted above.
Good luck!
Thanks, Konst, 3 questions for you: Did you go the matching route, or did you add ballast resistors? Also, how painful was it mounting TO-247 parts where the TO3 holes are? I did find the service manual on the web, but thanks anyway.
Regards,
Ivan
Regards,
Ivan
Hey there, mounting was easy, I actually got soome To3's, cut off the legs and used them as dummies to preserve the look- then just used one of the bolts to mount the IRF"s to the heatsink.
I did match them using Nelson Pass method, I used quite high voltage so they heated up to around 65deg and then I left them for around 12 hours to "burn in", but honestly there really wasn't much deviation after about 15 minutes. I used only ones from the same batch.
Check this post for pix of how I mounted them https://www.diyaudio.com/community/threads/counterpoint-sa-100-mosfets-source.389736/post-7111932
I did match them using Nelson Pass method, I used quite high voltage so they heated up to around 65deg and then I left them for around 12 hours to "burn in", but honestly there really wasn't much deviation after about 15 minutes. I used only ones from the same batch.
Check this post for pix of how I mounted them https://www.diyaudio.com/community/threads/counterpoint-sa-100-mosfets-source.389736/post-7111932
Hi Konst, a great solution and very nicely implemented! I can't tell from the photo, but you probably used a thermal insulating pad for the TO247s, not a Mica type (fragile, although they have better heat transfer). Did you happen to check the temperature of each FET, into a dummy load at say, 100W, a couple of minutes after turn-on and before the heatsink (more or less) equalized the overall temp? I'm curious how well the Pass matching actually worked out in practice.
Also, did you use the 2 different gate drive resistor values (20R for N-ch & 50R for P-ch) to compensate for the different gains?
Thanks,
Ivan
Also, did you use the 2 different gate drive resistor values (20R for N-ch & 50R for P-ch) to compensate for the different gains?
Thanks,
Ivan
Hey there, no I didnt check it into a dummy load, just the NP method. After installing and ruinning I did get the laster thermometer on the individiual trannies, to see if there was anything running hotter than expected though.
I used the same resistor values that were in the original and silicone pads as they are just so much nicer than the messy ones with paste.
I used the same resistor values that were in the original and silicone pads as they are just so much nicer than the messy ones with paste.
How many FETs did you have to buy to get enough to match each polarity? I'll buy, match and install the FETS in my SA20, and let you know. It will be a few weeks as I have some travel plans.
Thanks for your help!
Ivan
Thanks for your help!
Ivan
To quote from the original Counterpoint matching procedure:
"This is a very difficult procedure and it generally requires a few thousand devices to come up with a few dozen sets"
"This is a very difficult procedure and it generally requires a few thousand devices to come up with a few dozen sets"
Hi Konst, You mentioned having a Service manual for the SA20. Does it have the power supply schematic? It turns out that the transformer has shorts in the secondary windings. I'm getting sub-ohm resistances on all the windings. I forgot to check this first thing.
I'm looking for a transformer for my Counterpoint SA-20 Does anyone have a suggested custom manufacturer, or even better, an original that they would be willing to sell? A dead SA-20 would do the trick if the Trannie is OK.
Thanks!!!
Thanks!!!
