Counterpoint SA-220..got two...time to Mod them!

[KBK]

I went and bought two Counterpoint SA-220 amplifiers. I decided to get two, so I could go stacked for biamp or separate mono-blocks. I am getting the schematic in a week or so, and am wondering if anyone here has ever taken a shot at modifying or upgrading the circuits in these units.

For those that are unfamiliar with the unit, it is a SS-fet based 220WPC output stage, coupled to a input buffer-predriver 6DJ8 based tube stage, that has even got a tube rectifier in it's PS!. It is very much like a tube pre-amp built right into a dual mono (single transformer, dual wound with separate caps and bridge rectification) Fet power amp. The unit weights 69lbs, and is internally strappable to a 600watt monoblock. According to what the manual says, you can upgrade the internal rail fuses to 20 amp, if you should desire to.. for low impedance loads like say.. A pair of Apogee Duettas, or the like. It runs typically blazingly-toaster hot like most fet amps.

Of course, the moment I read that the rail fuses can be upgraded to 20 amp... I spun off to Rat Shack in a cloud of hen $hit and small rocks.... and in they went!

I have to modify and tube-roll both units identically for monoblock/stereo use.

Any ideas?

[Dingaling]

did you ever mod it?

[Dingaling]

also, have you tried other tubes in there?

[KBK]

hmm. Ok. Not much action on this one! I accidentally ended up with a third. Don't ask how. Well, OK. I fixed one of the original two, only after I bid on a third on ebay..because I was PO'd that the fix of my second unit was not advancing at a resonable rate..

I bid high..and now 20 minutes after I bid.. I fixed the second unit. Murphy's law! It looks like I'm going to win that one, so I'll end up with three.

Anyone got a schematic for this puppy at all?

Should I hand them out, like shop class, so we each have one to work on?

[anatech]

Hi KBK,
I just fixed one. I will be working on modifications to make them sound good and be more reliable.
One thing you should know. Those outputs are really matched very tightly, to select a set you may have to buy 50 to get a set that is tight enough. It's not fun. That's why M.E. charges so much for a repair.

You should see where the SA-100 has got to so far. Mind you, it isn't the same circuit anymore. It has the sound people liked, only better.

For tubes, I have had great luck with the Electroharmonix 6922. I would recommend them highly. You will have to mess around with them to get the gains matched between channels.

One last warning, these units don't always match the schematic. Sometimes they don't even come close. You are further ahead to trace it out. Don't worry about the analog computer, it's jumpered at the factory at the minimum sensitivity. As close to off as it gets. I would put the lower rated fuses in if I were you.

-Chris

[KBK]

I was kidding about the fuses, I have 10 amp ones in there right now.

There's these 6 499k resistors in between the Wima caps in the tubed power supply for the 6DJ8 predrivers. One of them was burnt out. I replaced it with something close..and the issue is still there. it seems these resistors need to be exact, or sumpthin'.

Anyway.. I manged to pop the adjacent one during a live voltage test..my dang meter was set to resitance! FUG!

Now both channels are distorted. FUGGIN HECK! Me? I'm short on time these days to 'duke it out' with gear like I used to. Hopefully, If I get some 1 watt 499k resistors, that will fix it. It seems these puppies in some way 'balance' the voltage that goes to the tubes. (B+?, now very low?) I've no idea what the bloody resistors do, and I don't have the energy at this time to take it fully apart and duke it out. Buying the third was the easy way out. Change the silver faeplate to my black one, (to have a black pair) and be done with it. Flip to mono, and leave them alone. Yeah right. That might last a day or two.

The screwy part, is I used 5 100k 1% 1/4 watt resistors to try to hit the 500K the others measured. No go. damn.... I gots to get the schematic..

This amp is also a ba$tard to work on, with the wiring and chassis, etc. Tubes and solid state. A perfect recipie for minor bouts of shocking behaviour. Can you say 'electrocution'? and Screwdrivers stuck in the ceiling? From the reaction of the muscles in the arm....

You see, I lent out the perfect, all original minty one I had first bought. I'm getting it back tomorrow so I can finally do comparative tests. And hopefully get the dead one working..while I await the arrival of the third. Eventually I'll have three working units. By then, i'll likely be out of time to do this sort of thing altogether..but also be in the quandry of having no manufactuer I know of.. make gear to my personal standard of sound quality.

I'm sure most of us here are familiar with that particular sitaution.

In the end, I expect I might get the completed boards for at leat two of them from Alta Vista....and then.. mod from there. I can also then sell the working components. Complete board/trans assembiles. It would drop the price of the upgrade to less than $1k US, each. Each channel board, matched and working/tuned should fetch about $150US, easy, on ebay. A drop in fix, and worth every bloody cent. Then, the main board assembly, in good clean shape, another $150, for sure. The upgrade is $1400, so, deduct about $450-550US from the price...

[sajti]

Originally posted by KBK
hmm. Ok. Not much action on this one! I accidentally ended up with a third. Don't ask how. Well, OK. I fixed one of the original two, only after I bid on a third on ebay..because I was PO'd that the fix of my second unit was not advancing at a resonable rate..

I bid high..and now 20 minutes after I bid.. I fixed the second unit. Murphy's law! It looks like I'm going to win that one, so I'll end up with three.

Anyone got a schematic for this puppy at all?

Should I hand them out, like shop class, so we each have one to work on?

Try to search the web. Due Counterpoint is finished few years before, the founder of the company still keep a new homepage with modification kits, and general help for his amps.
I don't remeber the location, but I saw it, few months before.

sajti

[Elso Kwak]

Originally posted by sajti


Try to search the web. Due Counterpoint is finished few years before, the founder of the company still keep a new homepage with modification kits, and general help for his amps.
I don't remeber the location, but I saw it, few months before.

sajti

www.altavistaaudio.com

[sajti]

Originally posted by Elso Kwak


www.altavistaaudio.com

Thanks!

sajti

[anatech]

Hi KBK,
I was a warranty service center for Counterpoint up until the end. They still owed me $$$. Oh well.

I would think twice about upgrading those amps. I call it the Michael merry go round. Fad central.

Those resistors do not have to be precision parts. Can you say, plate supply decoupling resistor? I think you are looking for 499 ohm parts. 470 to 510 ohm values should work fine. The plate resistor should be 100K ohms.

-Chris