Hi, I leave my Counterpoint SA-2000 line stage to warm up for an hour before use, then when playing music it sounds undynamic for about 20 mins until dynamics return and the volume increases, I purchased the unit used, and wonder if the electrolytic capacitors need replacing on the power PCB board. Thanks for any help.
I would start with the voltages and the bias. Caps don’t typically “kick-in” after time, usually more constant issue
If the volume increases after warm up, it's likely to be more than just the electrolytic capacitors.
Can you post the complete schematic? As I recall this uses fixed bias on the tubes.
Can you post the complete schematic? As I recall this uses fixed bias on the tubes.
Start with measuring the filament and HV voltages. Does the low volume start again
after a turn off of just a couple of minutes, or is the volume normal?
Is the low volume problem in both channels? That would implicate some part of the power supply.
after a turn off of just a couple of minutes, or is the volume normal?
Is the low volume problem in both channels? That would implicate some part of the power supply.
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The low volume problem is in both channels, wouldn't know how to read a schematic or measure filament and HV voltages, I'm not that tech minded apart from able to solder. It's not so much loss of volume, it's loss of dynamics until they kick in after about 20 mins giving the impression of a bit more volume.
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That's different, then it could be old electrolytic capacitors. A local technician could work on it for you.
Not a good first piece to learn electronics on.
Not a good first piece to learn electronics on.
If you can’t read a schematic then you don’t belong inside tube audio equipment. For your own safety take it to someone who knows what their doing - its not the place to learn.
Although you are probably better off finding a tech to resolve the problem, you may be able to narrow down the issue and either help the tech or maybe, just maybe fix the issue yourself.
The SA2000 has a ready/standby switch and a mute/operate switch. So when you say you "leave it to warm up for an hour" - what is the position of those two switches while that is going on? i.e. please clarify the steps that you take with respect to the controls.
I leave it in ready state for an hour in mute. When playing music I have noticed that it doesn't fully mute, some breakthrough is heard, I put this down to the sensitivity of my power amps which require 2volts (26dB gain) for full output.
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The mute function just shorts the output to ground, so it will not be a cause of any sound quality
variation. Have you tried a different preamp in the system?
variation. Have you tried a different preamp in the system?
Is the effect only on LPs, or is it on all sources?
With the fixed bias on the tubes, some drift could occur over time,
especially if some part of the power supply has degraded.
Or the tubes themselves could be showing their ages.
Older electrolytic capacitors can show a similar behavior until they are used
over a period of weeks (or even months). How many hours have you put on it since
buying, including warm up time? Was it in regular use before you bought it?
With the fixed bias on the tubes, some drift could occur over time,
especially if some part of the power supply has degraded.
Or the tubes themselves could be showing their ages.
Older electrolytic capacitors can show a similar behavior until they are used
over a period of weeks (or even months). How many hours have you put on it since
buying, including warm up time? Was it in regular use before you bought it?
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Happens on all sources, tubes are fairly new, It has been in use for about an 2 hours every day for about 1 year now, I think the amp may have had the problem when I purchased it, as I began to notice the problem over time.
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There is also the possibility that this behavior is normal for this preamp.
I have not tested one of these, but all fixed bias circuits can show some short-term
variation with time. If it happens with every use, that could be the case here.
In this power supply, the electrolytic capacitors are relatively isolated from the audio circuits
(by the regulators), so they should not have a large effect on the sound.
I have not tested one of these, but all fixed bias circuits can show some short-term
variation with time. If it happens with every use, that could be the case here.
In this power supply, the electrolytic capacitors are relatively isolated from the audio circuits
(by the regulators), so they should not have a large effect on the sound.
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Film capacitors are very unlikely to vary to a noticeable degree over time.
There may have been a bad connection, etc. The replacement film cap should be
identical and not the source of a problem.
There may have been a bad connection, etc. The replacement film cap should be
identical and not the source of a problem.
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You are looking for 'something' that is common to both L and R channels as it is unliley that both channels would 'fail' in eactly the same way. In the SA2000 that pretty much means everything - the key is to look carefully at the block diagrams on p9/10 of the manual that was attached:
The only piece of crcuitry that is separate is the output buffer.
The B+ and heater supplies are common to both channels.
The valve is common to both channels.
Some things you can check without requiring test equipment - look at these things while the unit control switches are in READY and MUTE positions:
The only piece of crcuitry that is separate is the output buffer.
The B+ and heater supplies are common to both channels.
The valve is common to both channels.
Some things you can check without requiring test equipment - look at these things while the unit control switches are in READY and MUTE positions:
- Check out LED503 (a GREEN LED) - it should be bright adn ON at all times whe the ready/operate switch is the ready position.
- Check out LED501 (a RED LED). It should be OFF and therefore hard to find when the unit is operating.
- Check out LED400 ( a RED LED) - it should be bright red in normal operation
- Check out LED5/105, LED6/106 and LED7/107 (all GREEN LEDs near the valve) - they should all be bright green in normal operation
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One more test. You say that after turning the power on and then running an hour on mute,
after that it takes an hour to sound good after unmuting.
At that point, if you place it on mute again for an hour, does it still sound good only
after an hour unmuted, or does it sound good immediately after unmuting?
Most likely it is just taking about two hours to sound good from a cold start.
after that it takes an hour to sound good after unmuting.
At that point, if you place it on mute again for an hour, does it still sound good only
after an hour unmuted, or does it sound good immediately after unmuting?
Most likely it is just taking about two hours to sound good from a cold start.
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