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Hi all, I'm buying a used mint condition above amp. Other then it's power output 86watts per channel and it's a hybrid running 4pcs of 6922 at the input stage and amp stage using Mosfet, I dun have much information on it. Please let me know whether it's a class A amp, as it is quite warm after 1/2 hour of running or semi class A. Further info regarding power comsumption will be helpful and frequency response and reviews will be highly appreciated. Thank you in advance. Have a wonderful day.
Follow Ups:
I've had an SA-12 since late '87/early '88. I liked it's ability to give me a good amount of 'tube' magic without the expense of output tube replacements while otherwise being a respectable ampMine was an early version… playing it hard one day arced one of the driver stage tubes and damaged a power supply resistor. Counterpoint got it going with a pair of zener diodes protecting the output tubes and a replacement of that resistor… and they also added some additional bypassing across the output stage bias supply and increased the bias level. That brought it up to the then-current production level, pre-SA-100.
The original SA-12 had a fixed-bias on the input stage which needed an input coupling cap. As reported in the IAR report on the amp, Michael reconfigured the input to use a cathode bias and eliminated that cap. I believe that mod was included in some SA-12's and know it was in the SA-100's, an upgraded version of the SA-12.
The SA-100 also included some changes to the driver stage, the feedback configuration, a slightly up-sized power supply (hence the increase to 100 watts output), and Counterpoint's pretty unique copper-plated steel chassis. BTW, the SA-100 didn't have any additional protection over the SA-12, but the SA-220 had some serious protection upgrades over the SA-20.
Being a tweaker, I extensively modified my SA-12 less than a year after I got it. I added 2 additional power transformers in a box hanging under the original transformer location to power the output stages. In addition, I upgraded all the coupling caps, increased the size of the power-supply caps and bypasses, stiffened the bias supply, rewired the output stages to eliminate the plated-steel TO-3 sockets and directly soldered to the output devices, and wired the output directly from the output devices. This all provided definite improvements in detail, slam, bass extension, and dynamics (as you'd expect).
This and creative tube-rolling kept me very happy for many years with it… BTW, I preferred Amperex Bugle-Boy 7308's in the input stage and JAN Phillips 6922's… of course, this was back when they were only 'mildly overpriced'. Sovtek 6922's were an acceptable alternative… and except for one set, the Counterpoint-labeled tubes were not even close.
I blew it up in the middle '90s experimenting with an upgraded op-amp in the regulator of my phono stage that proved to be conditionally stable… while changing phono connections one day, I heard a sound similar to that of a helicopter in my livingroom (full sized, full sound!). Then smoke arose from my SA-12 and a beloved pair of Spica TC-50's (which worked very well with that amp, but my main ones back in those days were a highly-modified pair of Acoustat 1+1's and I'm glad I didn't blow them up!)
I was a bit disheartened by this (and in the early stages of a divorce), so I creatively ignored my stereo for a couple of years. After my now-ex and I moved into separate places, I wanted to get my tunes going and was a little gunshy at this time about the SA-12, so I picked up a used SA-100. The sound was good… better than my SA-12 originally, not as refined and nowhere near as dynamic and slamming as my modded SA-12, but it kept me in sound.
Later I got a chance to buy an SA-20 used and lived with it for a couple years until Michael Elliot resurfaced as Alta-Vista Audio. I vacillated for several months on his SA-20 upgrade, finally relenting. I started with his original upgrade that kept (but rewired) the SA-20 main board and added a board that provided upgraded drivers and outputs. As he improved it with a new mainboard, I upgraded to that and later upgraded it to his 'Premium' level. It was definitely a more 'robust-sounding' amp with greater resolution and bass detail over the stock SA-20… and as your friend suggested, more neutral with less of that 'tube-magic'. I found it best paired with warm and involving front-end components… an original Ah Tjoeb and a later Njoe Tjoeb CDP worked well, along with a good analog front end. Tube-rolling helped a lot here too, but I don't have any definitive suggestions for these two amps.
I've also repaired my SA-12 and ran it on-and-off for 4-5 years… until it dropped a channel just last fall. This time it did not damage the speakers and I'm not sure if it's even anything more than a blow fuse… I had a replacement set of amps coming the next week and just waited until they were in and haven't really looked at what I need to do to repair the SA-12 again.
So to respond to your inquiries, first, you want to keep it going with the original outputs as long as you can. To do that, you will want to NEVER short the outputs… I'd suggest never changing speaker cable connections while the amp is on. Also as others mentioned, it will run hot (it's class A/B with a fairly high-bias), so keep it well-ventilated.
On the Alta-Vista Audio site, Michael mentions a recent MOSFET made by Exicon that might work as a replacement… and in a recent update on the repair link for the SA-20/220 upgrade, mentions that it'd take some serious rewiring to use them. That's less of an issue in the SA-12 as opposed to an SA-220 as the MOSFETS are point-to-point wired instead of mounted to a circuit board, so rewiring won't be as involved. John Hillig of Musical Concepts (http://www.musicalconcepts.com/) has them for Hafler upgrades and offers them at what I thought was a reasonable price when I last checked. Someone on this board used them (thread here: http://www.audioasylum.com/scripts/t.pl?f=amp&m=112317) and may be able to offer more details on using them.
Michael at Alta-Vista also offers repairs and repair kits using MOSFETs pulled from upgraded units… not a bad source, that's what I used for repairing my SA-12 when I blew it, but there's no guarantee on them.
Michael also offers copies of Service and Owner manuals… but his prices seem a bit dear to me. I can copy an Owners Manual and some reviews for you someday, but it won't be before next winter (right now I'm in the middle of a move and little of my audio info is accessable).
I hope this all helps a bit… please feel free to contact me via this list if you have more questions on the SA-12.
Hi Greg, thank you very much for giving such a lot of info regarding my SA12. I will go through all the info carefully and if I have any more questions I will contact you again. Thanks again and have a wonderful day.
Inspect the interior closely. Make sure you ask about the repair or mod. history.
I owned a Solid 2A and a Solid 1B. Both had major problems and the 2A blew out both of my midranges when both servos failed.
I know that the SA12 had major reliability issues. I don't know much beyond that.
Thank you all for your advices. This unit of mine is practically a NOS, still have all it's stock 6922 tubes marked Counterpoint on them. My friend told me not to mod it, He had his mod and after that that sweet '6922' sound has gone and the whole music presentation was so dry and uninteresting. Anyway, I will keep mine as original. Thanks a lot and have a nice day!
The amps did run hot, and as previously stated, the Mosfets used are no longer manufactured. Tne output devices do not use the traditional emitter resisters and, as a caution, tend to be a bit twitchy under heavy and complex loads. The transistors had to be precisely matched and if they drift, the outputs can blow. The SA 100'a added more protective circuitry, IIRC and the output devices were matched at operating temperatures. The amp has a push-pull configured transistorized output.
After all this negatives, you are probably worried, but I would simply run a computer type fan over the unit. Don't place it in an enclosed cabinet where heat will excessively build up.
Unclestu52 covered it quite well. It has been a long time since I last heard one but I remember them as being very pleasant but not terribly resolving, especially in the lower octaves (unclestu52 please correct me if I'm wrong here). Keep in mind the reliability issues and the fact that if it fails you probably won't be able to get it repaired short of a total Alta Vista rebuild.
I had an SA-12 awhile back, it was a great sounding amp. The big thing these days is the lack of replacement mos-fet output transistors. Mike Eliott from Alta-Vista Audio the original designer, can probably offer an update to the SA-12 but it's not cheap. As I understand the upgraded amp is quite an improvement.
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