[mastertrash]

Hi there,

First post, so please forgive me if I've wound up in the wrong spot...

I've got an old CounterPoint SA-1000 pre-amp which has served me well for the last couple years.  But somewhere during the last 6 months or so, I've noticed that one channel is significantly louder than the other, but only on the phono input (using MM setting).  Switching the connects from the TT doesn't move the problem, and the line level inputs seem to work fine, so I'm reasonably sure it's the phono stage.  I tried swapping the tubes, but this too made no difference...

Does anybody have any thoughts?  I was tempted to play with the gain settings on one or both tubes (there's a screw by the tube for each) to try to balance the level, but then I came to my senses.  This is a bad idea right?  I don't have any gear that would allow me to do any sorts of measurements or anything.  What's my next move?  Do I need to take it in to have someone look at it?  AltaVista Audio says $270 minimum for taking a look at it...   

Any thoughts or suggestions would be most appreciated.

Many thanks!

mastertrash

[*Scotty*]

mastertrash, Maybe this link to Alta Vista Audio will help. Repairs and upgrades to CounterPoint products are available from them.
http://www.altavistaaudio.com/
Scotty

[mastertrash]

Cool -- Thanks, Scotty.  I'm still hoping that there's some way not to incur a $275 charge from them while fixing my phono section, but it's not looking so good at the moment...

[jules]

The pre does have a built in phono I presume?

The simplest option here could be that your source select switch is making poor contact on one channel. Does it crackle if you play with the switch a bit [at low volume  ]

There's a heap of other possibilities but this might be one you could have a look at ... ??? depending on the design of the source select switch.

jules

[mastertrash]

I certainly like that thought.  I haven't noticed any crackle, but I did apply some deoxit to it already just in case.  That said I didn't get the actual knob off, so it wasn't necessarily the best job ever, but I did get some behind it (it stands off the front fascia a quarter inch or so).  After that, my gut is telling me this isn't the issue...

And the preamp does indeed have a mm/mc phono stage.

[jules]

yes  , my gut too but it's the easiest option.

Another "easy" option could be a dry solder joint, though again, these tend to crackle.

Jules

[BobM]

I think you still need to truly isolate the component causing the problem.does it still occur using the other phono stage? If yes, then the problem is uopstream of that, in the TT or cartridge. If it doesn't happen on CD's then it could be a cartridge aloignment problem.

Bob

[richidoo]

You can't clean a pot or switch from outside the case just shooting behind the knob. You shoot the cleaner into the switch body from inside the case while you work the switch. The cleaner must thoroughly wet and flush out the dirty contacts. Good instructions are on the Caig website.  You could measure resistance through the circuit for each channel, looking for marked differences. It could also be a coupling cap that is affecting high frequency of one side making it sound softer.

I like the cart alignment idea. Use Occam's Razor. I've also read that cartridges need periodic maintenence of their own, but I don't know if that could cause signal strength difference L/R. Perhaps your cart needs fixin or replacement?  If you have or can borrow an external phono pre, even a junker then you could verify the cartridge is OK. You could also swap the connections on the back of the cartridge L/R see what changes. Good luck MT.

[mastertrash]

Thanks much for the good thoughts, folks.  I really appreciate it.

I see that you're probably right about the contacts.  I have had deoxit applied from the front clear out controls before, but I recognize that this is suboptimal.  A more thorough cleaning is in the works for this evening then.  It's certainly worth a shot.

I also like the cartridge idea, but I think I've already ruled that out.  If it was any sort of problem with the TT, wouldn't switching the L and R leads into the preamp swap the problem to the other speaker?  This doesn't happen, so I figure it has to be the preamp.  (My amp is obviously fine with direct input from CD, or any other input from the preamp.)

Would I be able to see a dry solder joint?  Google here I come...

One last question...  After I've tried everything else, would it be totally fool-hardy to play with the gain trim on the channel in question?  I figure I could just dial it up a bit and see if that raises the level.  But I don't want to shock myself or fry the pre in some dramatic fashion...

[richidoo]

Do you know it is gain trim??
I don't know if messing with the gain trim is a good idea, but if you do it, get a safe plastic tool
http://www.mouser.com/Search/ProductDetail.aspx?qs=TvmmGzrYY2NGgbx3TRb96A%3d%3d
Remember high voltage DC can kill you.

[*Scotty*]

mastertrash,Don't abandon the common sense you found after isolating the problem to a single channel of the phono stage independent of the tubes used it. Without the service manual and schematics for the preamp you are going to face insurmountable problems in properly repairing the problem. Any mistake you make is going to cost you even more money and may damage the circuit board beyond repair. I think the entire preamp has to be dismantled including removing the transformer to even get at the circuit board to repair it as there is no removable bottom plate on the preamp. Having it properly serviced and restored to as new condition would be the wisest course of action.
Scotty

[mastertrash]

Even though I wanted a different answer, I'm sure you're right, Scotty.  I guess I'm just going to have to bite the bullet and get it looked at.

Anyway, I really appreciate all the help and advice.  You guys are great.

[doug s.]

i have a similar problem w/a wintage tuna i picked up.  all the techs at the yahoo tuna forum said "bad coupling cap..."  i'd try to find a local tech who is capable of looking at it - $275 yust for a look-see sounds excessive - a competent tech should be able to fix it for less than half that amount...

doug s.

[mastertrash]

Agreed -- But $275 is the lowest price for any repair from AltaVista Audio (the guy from CounterPoint's new company).  I don't think I paid much more than $275 for the preamp in the first place...  I could probably just pick up a newer Cambridge Audio or NAD phono section for less and probably wouldn't miss much in terms of sound quality.

I might see if the local shop can do anything more reasonably.