Counterpoint SA-3(.1) rebuild/upgrade

[cdfac]

I recently agreed to buy an SA-3 preamp as a project. It actually has a 3.1 board set in it, which is a good thing. Cosmetically it's in great condition, single local owner since new in ~1986, and it sounded wonderful during a brief demo with a Classe amp and Minimus 7 speakers. Initially, I thought it just had a balance control problem which we immediately heard during that demo, but I discovered at home that it was a deeper issue. Two of the four resistors pictured below were blown essentially open, while the other two measured extremely high.

Anyone familiar with this preamp model knows that the power supply voltages generally red-lined some of the power supply components, and with wall voltages frequently near 125+ VAC around here it's extra-hard on everything. Once I get the bad resistors replaced, I'll be checking the upstream components and will also replace them if required. Capacitors in particular will get replaced with higher-rated parts where needed. I'll be running it through a variac to drop the line voltage slightly. I'm hopeful it will be a fairly simple repair, compared to what Counterpoint amps need when they have issues.

I know Counterpoint's reputation for reliability is not very good, but this is simply the best-sounding tube preamp I've heard for the money and I'd like to get it in reasonable working shape again. I believe that part of reason it sounds so good because of the way it pushes the envelope. When it's repaird, I'll decide how much to invest in upgrading the 3uF and .47uF caps in the line and phono stages (mostly because they don't match each other that well between channels). It runs 6922 tubes by design, and these appear to be original Ei tubes @ 32 years old, so I'm thinking of upgrading to Siemens 6922/ECC82 or Amperex gold-pin 7308 -- note there is one tube for the line stage and one tube per channel for MM stage.

If anyone has any experience upgrading or repairing this preamp, I'd be curious to hear what you've discovered in the process.

 

[kward]

No experience with that preamp. Can you make out the colors on those blown resistors? They all look like the same value. Colors to me look like brown, red, violet, black?, brown, red.

32 year old tubes are not that old and may still test as new depending on the bias conditions of the circuit. The EI tubes are no longer manufactured and they are now hard to come by. I have some of these EI 6DJ8 tubes and they sound quite fantastic. I would consider carefully before rolling them out. See of you can find someone with a tube tester.

 

[primosounds]

• The Sprague Atom caps are 'revered' by the geet boys for their reliability. It is pretty hard to blow those up. So, i would guess those resistors maybe balancing the current in the cap lineup. Maybe acting as a fuse to limit PS problems. The yellow coupling caps are not really special and they can be upgraded but those values will be expensive.

 

[arts]

• The yellow coupling caps are not really special and they can be upgraded but those values will be expensive.

Rel-Cap are nothing special? Interesting.......I guess Audio Research Corporation and Conrad-Johnson have been screwing us......Imagine just how good their products could sound with an ''upgraded'' part. Somebody should notify them

 

[primosounds]

Are you kidding me. Have you seen the price of boutique and audiophile caps? I am sure you thought those prices are effing crazy. Rel caps also have various quality levels from economy to top shelf ridiculous. The entry level rel caps are really nothing special, just metallized plastic conductor.

 

[primosounds]

Rel-Cap are nothing special? Interesting.......I guess Audio Research Corporation and Conrad-Johnson have been screwing us......Imagine just how good their products could sound with an ''upgraded'' part. Somebody should notify them

I changed out these same type Rel caps in a MFA Magus preamp. I used the Rel cap RT and there was a noticeable improvement in detail. The RT is polystyrene insulator with tin foil conductor.

 

[cdfac]

As an update, the problem resistors are replaced and the machine is working fine (channel balance is restored). The film caps ended up measuring fairly well matched between channels -- didn't realize I needed to discharge the power supply with the circuit in "operate" mode in order to get good readings. I think I'm going to leave them for now as it sounds good enough for me. With the variac dropping the line voltage, I've got enough voltage headroom on the Atoms to feel OK leaving them for now. I will likely be trying some 7308 tubes in the near future. For now, it's just more of

 

[arts]

The Sprague 39D & the Atom types are generally reliable,and so long as they are used on a regular basis should continue to be ok. This is not a high-heat/high-ripple environment,so they are not being stressed anywhere near to their limits,which is a good way to ensure long life.

Good plan with the variac,those guys really ran the filters close to their limits.Luckily,if you like the unit,there is enough internal space to install an inboard bucking transformer.

Do keep in mind though,the datecodes on those caps is 1984,so ymmv. The pre may have sat for some time,and when powered up smoked those resistors,which are in series with the 200/250's.I would go to 1W with the replacements.

 

[kward]

Glad you got things working. One nagging thing in my head is that usually resistors don't blow on their own, unless the original design was faulty or a tube was faulty or something.

There still might be an underlying problem lurking there. But for now, enjoy!

 

[cdfac]

I've got a few more parts on order to freshen the unit up, when I have free time to work on it. One issue I'm noticing is that the right channel has maybe twice as much background noise as the left (just regular hiss/hash). Swapping tubes didn't help. We'll see if the new PS capacitors and a couple new resistors makes any difference, I guess. I will add a screenshot of the schematic to this post, in case anyone is curious -- I would be happy to have suggestions of things to look at.

 

[KentTeffeteller]

Big issues with Counterpoint gear. Every component in them was ran very hard, often at or past spec. The higher line voltages of today are detrimental to their already problematic reliability. Uprate those power supply components and those electrolytic capacitors by 30% or more to keep them reliable.

 

[kward]

If one channel has more noise than the other, I'd look at either one of the dropping resistors in the power supply (one of R3 thru R6) or one of the plate resistors. If it's noisy on the line source input only, look at R20. If it's quiet on line input but noisy on phono input, look at R11 and R16, but it could be other resistors in the phono circuit as well.

 

[fastguy1955]

Anything New to report? hows the project going?

 

[EdRogers]

I'd like to bring this thread back for some help. I've got the same preamp with issues. I've had it for many years, and would like to get it going again. I've pretty much replaced and upgraded all main power supply parts and ran into heater supply problems.
Without tubes, everything looks great, B+ looking good, heaters holding 6.2, which should be higher. When I put tubes in, everything starts great, then the heater voltage, after about ten seconds starts to drop, really fast to no voltage. I've replaced the lm317 twice, just to make sure.
My question is whether I should be looking upstream or downstream? Maybe just a tip would get me going, a little frustrated right now. I keep looking at the schematic and I think I'm having a brain fart. I know it could be a simple problem, but I'm overthinking it.

Thanks again, Ed

 

[kward]

1. The 317 will go into thermal shutdown if it gets too hot if it's not properly heat sunk.
2. Modern 317 regulators may not be able to handle the current load on start of cold cathodes. An LT1084 will probably be able to handle it. Pin out may be different though. I've used LT1084s before in filament regulators, I know they work. The LT1084 needs a large cap hung off the output though, for stability.
3. To prove if #2 is really a problem you could dummy load the filament circuit with a 20 watt 5.6 ohm wire wound resistor. If the filament circuit holds its voltage with the dummy load, then its either a short in the filament circuit or the modern 317 can't stomach an initial near short as the filaments warm up. I've found through my own testing of all available 317 manufacturers, the STmicro and Texas Instruments are the best. Personally I would avoid the others under a demanding application like this.

 

[Drummerboy2]

I'd like to bring this thread back for some help. I've got the same preamp with issues. I've had it for many years, and would like to get it going again. I've pretty much replaced and upgraded all main power supply parts and ran into heater supply problems.
Without tubes, everything looks great, B+ looking good, heaters holding 6.2, which should be higher. When I put tubes in, everything starts great, then the heater voltage, after about ten seconds starts to drop, really fast to no voltage. I've replaced the lm317 twice, just to make sure.
My question is whether I should be looking upstream or downstream? Maybe just a tip would get me going, a little frustrated right now. I keep looking at the schematic and I think I'm having a brain fart. I know it could be a simple problem, but I'm overthinking it.

Thanks again, Ed

First off, was there an issue with the Heater power supply when you last used the preamp? can you tell us what happened when the preamp originally stopped working? what tubes were being used at the time? Was there any mods done to the preamp in any way or form?

What have you done in the HEATER supply other than change out the LM317? Did you make ANY other changes there that you forgot to tell us? Did you buy the LM317's new or salvaged them from somewhere else? the On Semi or Motorola should be LM317 fine. Don't start changing to different parts until you have fixed this problem first. You may end up making things worse due to addition of a different part and start going in circles.

You said the output of the LM317 is measuring 6.2 Vdc without tubes in it. Did you monitor the in input to the LM317 to see if the voltage drops as well when the output is dropping to no voltage? Please give us actual voltage and places (reference designators) you are taking readings at so we can actually see what voltages you are getting and at what places.

Are you using the proper 6DG8 tubes that are known good? That's what these preamps use.

Look at the schematic above, you only have so many components. I have worked on these and Mike Elliott stretched to the limits on a lot of parts as far a voltages. I would check all the components first to make sure they are ok. Mike used Roderstiens resistors in his audio gear and I have found a lot to go bad in time. Take measurements at different places like right after the transformer input to the Bridge Rect. then go on from there. Write the measurements down. Also, make sure all the ground on the power supply are good. I found bad / cold solder joints on a lot of counterpoint gear as well.

I will try to dig up my SA 3.1 service manual to see the actual voltages at certain points you should have.

 

[EdRogers]

Thank you for the response. I forgot to mention that the heater will run for up to ten seconds with only one tube installed, not three. It won't last more than a second with all three. Looking into the 317, I see that input voltage also shouldn't be too far off output, or else there will be too much stress on it. The input is about 13.7, which might be too much of a drop for it.
There is a 2200uf cap hung off of it, which I upgraded to a 50v. I wonder if I should either try and drop the voltage before it with a large wirewound, or just put a more robust regulator, like you suggest. The amount of heat generated by the 317 is impressive. Thanks for the help. I feel I am getting close though. Ed

 

[EdRogers]

First off, was there an issue with the Heater power supply when you last used the preamp? can you tell us what happened when the preamp originally stopped working? what tubes were being used at the time? Was there any mods done to the preamp in any way or form?

What have you done in the HEATER supply other than change out the LM317? Did you make ANY other changes there that you forgot to tell us? Did you buy the LM317's new or salvaged them from somewhere else? the On Semi or Motorola should be LM317 fine. Don't start changing to different parts until you have fixed this problem first. You may end up making things worse due to addition of a different part and start going in circles.

You said the output of the LM317 is measuring 6.2 Vdc without tubes in it. Did you monitor the in input to the LM317 to see if the voltage drops as well when the output is dropping to no voltage? Please give us actual voltage and places (reference designators) you are taking readings at so we can actually see what voltages you are getting and at what places.

Are you using the proper 6DG8 tubes that are known good? That's what these preamps use.

Look at the schematic above, you only have so many components. I have worked on these and Mike Elliott stretched to the limits on a lot of parts as far a voltages. I would check all the components first to make sure they are ok. Mike used Roderstiens resistors in his audio gear and I have found a lot to go bad in time. Take measurements at different places like right after the transformer input to the Bridge Rect. then go on from there. Write the measurements down. Also, make sure all the ground on the power supply are good. I found bad / cold solder joints on a lot of counterpoint gear as well.

I will try to dig up my SA 3.1 service manual to see the actual voltages at certain points you should have.

Thank you. Here's the story. I've had this unit for fifteen years. I rarely used it, and one day a puff of smoke came out. Resistor 1, the 500ohm 5w burnt. I shelved it. A few years ago I pulled it out and started trying to get it going again. I replaced a electrolytic, the resistor, and the resistor burnt up again. I don't remember what else I did, but everything is stock.
Just recently, I dug into it again. This time I first replaced all electrolytics, diodes, and resistors in the main power supply. Pretty much everything, stock values, but higher rated. The first two electrolytics are 500v,. The highest I could find to fit. The main b+ Supply looks really good now. I have the service manual with voltages.
It's interesting that I have two schematics for the 3.1, but neither are exactly right compared to my unit. Might have been a version in between?
The heater circuit is stock, except for the lm317 and the 2200uf 50v I put in, same value, higher voltage rating. The lm317 input voltage stays at 13.7 even as the heater voltage drops.

 

[Drummerboy2]

Thank you. Here's the story. I've had this unit for fifteen years. I rarely used it, and one day a puff of smoke came out. Resistor 1, the 500ohm 5w burnt. I shelved it. A few years ago I pulled it out and started trying to get it going again. I replaced a electrolytic, the resistor, and the resistor burnt up again. I don't remember what else I did, but everything is stock.
Just recently, I dug into it again. This time I first replaced all electrolytics, diodes, and resistors in the main power supply. Pretty much everything, stock values, but higher rated. The first two electrolytics are 500v,. The highest I could find to fit. The main b+ Supply looks really good now. I have the service manual with voltages.
It's interesting that I have two schematics for the 3.1, but neither are exactly right compared to my unit. Might have been a version in between?
The heater circuit is stock, except for the lm317 and the 2200uf 50v I put in, same value, higher voltage rating. The lm317 input voltage stays at 13.7 even as the heater voltage drops.

Ok, so the issue seems to be on the other side of the LM317. Check R7, R8, C11, and C12 out of circuit. If they measure ok, I would just still replace them just to have new caps and resistors in. Like I said before those resistor go bad and I have seen enough to replace them out. Also make sure there are no cracked traces anywhere between all those connections.

Are you using the exact same tubes you had in the preamp when it burned up R1? You never answered if the tubes you are using now are the same type or if they are known good.

One last question, Did yo spray any type of cleaner or anything in this preamp?

 

[EdRogers]

Thanks again. I have been swapping out different tubes that have been checked on my tube tester. 6dj8's, 6922's, ecc88's,. I have a pretty good stash of them, I have two other preamps that use them. I will swap out r7 and 8, and C10, those are all that are left from the original circuit. I have been really careful with the traces, and they all look pretty good, substantial. Nice and thick, easy to solder to.
The main culprit so far that took a lot of parts down was the transistor Q1, mj12005, not the same as listed in the schematics(s2530), but higher voltage rated, so I just used a same replacement. It's the only change that isn't right on with the schematic that was there prior.