tinwhiskers
New member
[Edited.]
Hi, gang; I'm hoping someone might be able to help with this one...
I have a Technics SH-8040 Space Dimension Controller with a problem on the Left Channel. It appears whether I use Line Outs or Rec Outs. There's some low level noise on the Left compared to the Right, but the main problem is distortion on sibilant sounds. If I run a vocal through the Line Ins, it distorts on 'S's just in the Left Channel. If the vocal is more strident, there is general distortion on the Left. The same happens if I use the Mic In on the front panel with a microphone. I only encounter the problem if 'Dimension' is enabled. It is present even when the 'Ambience' and 'Echo' potentiometers are set full anti-clockwise.
When dialled up, I believe the effect of the BBD Echo is slightly quieter or less pronounced on the Left too. Indeed, if I test this by 'tutting' into a mic, then the display reads lower on the left side. To confirm, passing a 1kHz test tone through, once the 'Echo' pot pass 12oc, the volume of the effect only increases on the Right channel.
If 'Dimension' (therefore both the 'Ambience' and 'Echo' effects) is disengaged, then signal from both Line Ins and the Mic In passes through fine, without distortion, so I'm guessing the general Output is in fact OK.
Running a 1kHz tone, with 'Dimension' engaged, and viewing the frequency response via DAW, the Right channel passes the tone, whereas the left introduces harmonics at 2kHz, 3kHz, 4kHz, and so on. This occurs even if both 'Ambience' and 'Echo' dials are full anti-clockwise.
I haven't used the unit in a while (bought and ear-tested in June this year), but believe this is potentially a new fault. To complicate matters (or aid in troubleshooting), the Line Outs were plugged into an audio interface's XLR/TRS combo-jacks running global phantom power for a minute or two after I hooked it up. As the unit uses unbalanced phono connectors, I believe this may have over-volted a component or components. I know, idiot alert, right here. That said, on inspection, the top face of the PCB looks OK—and the Right channel seems fine.
*EDIT*
Turns out I'm _not_ an idiot—or at least not over this particular issue—and phantom power was _not_ applied to the Line Outs/Rec Out.
The PCB has sections marked for 'Ambience', 'LPF', and 'Echo'. As the issue is affecting mainly sibilant sounds when 'Dimension' is engaged, I am wondering if the fault lies in the 'LPF' section...
The Service Manual is readily available online, but so far the issue is a little beyond my pay-grade.
Any assistance would be most gratefully received and greatly appreciated.
Thanks again.
*EDIT/UPDATE*
Using an audio probe, and a _lot_ of guidance from a v kind member of an FB Group, I've found the low level noise, or rustling, coming off Pin 1 of IC204, a 4558 op amp. I'm wondering, with this being the 'Mix' chip, if this could be the culprit for all my woes—the Left channel distortion, and the low level of the BBD Echo on the Left channel? In the vicinity, there are a couple of caps and transistors (C211 + C212; Q201 + Q202) which I'm also looking at; I'm trying to determine which element is most likely to be responsible for the deformation of the waveform leading to the 2nd and 3rd harmonic distortion.
Hi, gang; I'm hoping someone might be able to help with this one...
I have a Technics SH-8040 Space Dimension Controller with a problem on the Left Channel. It appears whether I use Line Outs or Rec Outs. There's some low level noise on the Left compared to the Right, but the main problem is distortion on sibilant sounds. If I run a vocal through the Line Ins, it distorts on 'S's just in the Left Channel. If the vocal is more strident, there is general distortion on the Left. The same happens if I use the Mic In on the front panel with a microphone. I only encounter the problem if 'Dimension' is enabled. It is present even when the 'Ambience' and 'Echo' potentiometers are set full anti-clockwise.
When dialled up, I believe the effect of the BBD Echo is slightly quieter or less pronounced on the Left too. Indeed, if I test this by 'tutting' into a mic, then the display reads lower on the left side. To confirm, passing a 1kHz test tone through, once the 'Echo' pot pass 12oc, the volume of the effect only increases on the Right channel.
If 'Dimension' (therefore both the 'Ambience' and 'Echo' effects) is disengaged, then signal from both Line Ins and the Mic In passes through fine, without distortion, so I'm guessing the general Output is in fact OK.
Running a 1kHz tone, with 'Dimension' engaged, and viewing the frequency response via DAW, the Right channel passes the tone, whereas the left introduces harmonics at 2kHz, 3kHz, 4kHz, and so on. This occurs even if both 'Ambience' and 'Echo' dials are full anti-clockwise.
I haven't used the unit in a while (bought and ear-tested in June this year), but believe this is potentially a new fault. To complicate matters (or aid in troubleshooting), the Line Outs were plugged into an audio interface's XLR/TRS combo-jacks running global phantom power for a minute or two after I hooked it up. As the unit uses unbalanced phono connectors, I believe this may have over-volted a component or components. I know, idiot alert, right here. That said, on inspection, the top face of the PCB looks OK—and the Right channel seems fine.
*EDIT*
Turns out I'm _not_ an idiot—or at least not over this particular issue—and phantom power was _not_ applied to the Line Outs/Rec Out.
The PCB has sections marked for 'Ambience', 'LPF', and 'Echo'. As the issue is affecting mainly sibilant sounds when 'Dimension' is engaged, I am wondering if the fault lies in the 'LPF' section...
The Service Manual is readily available online, but so far the issue is a little beyond my pay-grade.
Any assistance would be most gratefully received and greatly appreciated.
Thanks again.
*EDIT/UPDATE*
Using an audio probe, and a _lot_ of guidance from a v kind member of an FB Group, I've found the low level noise, or rustling, coming off Pin 1 of IC204, a 4558 op amp. I'm wondering, with this being the 'Mix' chip, if this could be the culprit for all my woes—the Left channel distortion, and the low level of the BBD Echo on the Left channel? In the vicinity, there are a couple of caps and transistors (C211 + C212; Q201 + Q202) which I'm also looking at; I'm trying to determine which element is most likely to be responsible for the deformation of the waveform leading to the 2nd and 3rd harmonic distortion.
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