Stereomour II - Issue with Shunt Regulator?
- Thread starter lskiii
- Start date
I would go ahead and replace the TL431 on the offending side and see if that helps the situation.
You can grab one from Mouser or e-mail replacementparts(at)bottlehead(dot)com about getting a new one. The one we use is the LM431ACZ.
Hello - so I finally got around to trying to replace the LM431. Sadly, I believe I trashed the PC board in the process... I removed the old LM431 but in trying to clean out the old solder to install the new, I must have used too much heat because one of the leads to the whole came loose from the board.
Is it possible for me to purchase a replacement big board and parts or do I need to purchase a whole new upgrade kit? Based on my skills, it's much easier for me to populate a PC board than it is to remove/replace old components - esp. one that has 3 prongs that are close together - so just a new board wouldn't work. I would need the new large board + components...
Thanks.
Is it possible for me to purchase a replacement big board and parts or do I need to purchase a whole new upgrade kit? Based on my skills, it's much easier for me to populate a PC board than it is to remove/replace old components - esp. one that has 3 prongs that are close together - so just a new board wouldn't work. I would need the new large board + components...
Thanks.
Yes, you would just need to e-mail replacementparts(at)bottlehead(dot)com.
Hello
So, today I got the replacement shunt regulator and installed it.
The good news is that the new measurements are all correct - the bad news is that the problem hasn't gone away.
OB 298
OA 298
IB. 392
IA. 392
KREG A 4.0
KREG B 3.7
When I was reassembling the shunt regulator I followed every step and I noticed a problem - I had incorrectly switched the white wire going to C8 and the red wire going to C6. So, correcting that I now I have the white wire from KREG A going to C8. I believe that I messed this up when I was re-soldering all the leads going to "C". I was doing that because I thought that my problem (very weak signal in the left channel) might have been due to an issue there.
So, I suspect that in trying to trouble shoot my issue with the left channel is when I accidentally swapped those 2 wires which led to the messed up shunt regulator readings.
Regardless, I'm kind of back to the original issue. Right channel sounds great. Left channel is weak, has some distortion and gets louder when I power off (and then it fades). I've swapped tubes, source, etc.
Any suggestions?
Thanks,
Louis
So, today I got the replacement shunt regulator and installed it.
The good news is that the new measurements are all correct - the bad news is that the problem hasn't gone away.
OB 298
OA 298
IB. 392
IA. 392
KREG A 4.0
KREG B 3.7
When I was reassembling the shunt regulator I followed every step and I noticed a problem - I had incorrectly switched the white wire going to C8 and the red wire going to C6. So, correcting that I now I have the white wire from KREG A going to C8. I believe that I messed this up when I was re-soldering all the leads going to "C". I was doing that because I thought that my problem (very weak signal in the left channel) might have been due to an issue there.
So, I suspect that in trying to trouble shoot my issue with the left channel is when I accidentally swapped those 2 wires which led to the messed up shunt regulator readings.
Regardless, I'm kind of back to the original issue. Right channel sounds great. Left channel is weak, has some distortion and gets louder when I power off (and then it fades). I've swapped tubes, source, etc.
Any suggestions?
Thanks,
Louis
Are the voltages on the 4 pin socket on that side still solid? If so let me know and I can run you through how to temporarily install some jumpers to narrow things down better.
I will check, but one other thing I wanted to ask - is it possible that the issue could be the tube socket itself? I ask this because:
The left channel has been giving me issues for a while now (I've had the amp for a year). It started with intermittent hum, which over time became intermittent crackling. I swapped out many tubes to try and sort out the source of the issue. Ultimately it became what it is now, which is a weak signal in the left channel that won't go away.
When I was closely looking for any differences between the 2 channels, I noticed that the solder tabs on the left channel socket are much more wobbly than the right channel socket (esp C6 and C8).
I don't know much about how the sockets are internally structured but is it possible that there's a loose internal connection?
Thanks!
Louis
The left channel has been giving me issues for a while now (I've had the amp for a year). It started with intermittent hum, which over time became intermittent crackling. I swapped out many tubes to try and sort out the source of the issue. Ultimately it became what it is now, which is a weak signal in the left channel that won't go away.
When I was closely looking for any differences between the 2 channels, I noticed that the solder tabs on the left channel socket are much more wobbly than the right channel socket (esp C6 and C8).
I don't know much about how the sockets are internally structured but is it possible that there's a loose internal connection?
Thanks!
Louis
On A3 and D3, is that 15mV, or 15V?
If you run a wire temporarily between A3 and D3, does sound now come out properly from both sets of outputs?
If you run a wire temporarily between A3 and D3, does sound now come out properly from both sets of outputs?
Yes, A3 and D3 those were 15mv.
So, I ran a wire between A3 and D3 and played the amp.
I ended up playing some mono tracks to test it. One channel seemed to have more bass than the other, but they seemed at a similar volume. The sound was a little bit distorted and there were some crackling/static at points. When I powered it down there was a big surge in volume and then it faded quickly.
Does that help?
Thanks,
Louis
So, I ran a wire between A3 and D3 and played the amp.
I ended up playing some mono tracks to test it. One channel seemed to have more bass than the other, but they seemed at a similar volume. The sound was a little bit distorted and there were some crackling/static at points. When I powered it down there was a big surge in volume and then it faded quickly.
Does that help?
Thanks,
Louis
Did both channels exhibit the exact same behavior?
Can you describe the distortion you heard?
Is the "more bass" on the channel that was otherwise working normally or the one that was not?
Is the "more bass" on the channel that was otherwise working normally or the one that was not?
OK - spent some time doing much more detailed testing.
The last post I did, when I experienced distortion, I had moved my amp to a different system. This other system has less efficient speakers (86db vs Klipsch Heresy which is what I normally use with the stereomour. So, I wanted to remove that as a variable.
So today I tested w/ the less efficient speakers first, here's what I heard:
Source in all cases was a mono Beatles recording.
With just one channel (RCA from DAC) The right channel on it's own sounded normal to me. Moving the single RCA input to the left channel, I lost all the bass. Essentially could no longer hear the bass guitar lines.
I then plugged in both RCA channels from the DAC. Volume increased dramatically and the sound was badly distorted in both channels. To me, it sounded like a flubby overdriven distortion that you might get in a guitar amp. I turned the volume down 9db on the stepped attenuator and the distortion went away but the sound still sounded off (muddy bass, not alot of treble)
To see if there was still a difference in the bass between the 2 channels, I disconnected the left speaker, and then the right speaker to A/B them. Both speakers sounded the same to me.
Just for the sake of it, I repeated the above steps with inputs 1, 2 and 3 and in all cases the results were the same.
One other thing - when I turn the amp off, there's a sudden and noticeable volume spike. I don't recall that ever happening until this most recent issue (of a very weak L channel) came up.
Then I moved the amp back to the system w/ the Heresy's and repeated the above test.
In this case, the loss of bass when running just the input into the L channel vs R was still there. However, distortion, even with the attenuator completely wide open, went (almost) completely away.
When running both left and right inputs, the overall audio quality still was off. The bass was over emphasized and "flubby" and the treble was muted. I have an A/B amp switcher (on/off/on) and I tested an NAD amp against the Stereomour and the differences were extreme. The NAD sounded correct, the Stereomour was muted/flubby (which is not at all how it normally sounds to me).
I hope that helps?
Thanks
The last post I did, when I experienced distortion, I had moved my amp to a different system. This other system has less efficient speakers (86db vs Klipsch Heresy which is what I normally use with the stereomour. So, I wanted to remove that as a variable.
So today I tested w/ the less efficient speakers first, here's what I heard:
Source in all cases was a mono Beatles recording.
With just one channel (RCA from DAC) The right channel on it's own sounded normal to me. Moving the single RCA input to the left channel, I lost all the bass. Essentially could no longer hear the bass guitar lines.
I then plugged in both RCA channels from the DAC. Volume increased dramatically and the sound was badly distorted in both channels. To me, it sounded like a flubby overdriven distortion that you might get in a guitar amp. I turned the volume down 9db on the stepped attenuator and the distortion went away but the sound still sounded off (muddy bass, not alot of treble)
To see if there was still a difference in the bass between the 2 channels, I disconnected the left speaker, and then the right speaker to A/B them. Both speakers sounded the same to me.
Just for the sake of it, I repeated the above steps with inputs 1, 2 and 3 and in all cases the results were the same.
One other thing - when I turn the amp off, there's a sudden and noticeable volume spike. I don't recall that ever happening until this most recent issue (of a very weak L channel) came up.
Then I moved the amp back to the system w/ the Heresy's and repeated the above test.
In this case, the loss of bass when running just the input into the L channel vs R was still there. However, distortion, even with the attenuator completely wide open, went (almost) completely away.
When running both left and right inputs, the overall audio quality still was off. The bass was over emphasized and "flubby" and the treble was muted. I have an A/B amp switcher (on/off/on) and I tested an NAD amp against the Stereomour and the differences were extreme. The NAD sounded correct, the Stereomour was muted/flubby (which is not at all how it normally sounds to me).
I hope that helps?
Thanks
With the jumper between pins 3 on each 4 pin socket, repeat the test but run the tube with a 12AT7 in one socket and listen, then shut the amp down and move the 12AT7 to the other socket and retest.
