Hi all, I have an old Pioneer VSX-D1S receiver and am trying to hunt down the source of hiss.
When using any source input with playback on pause or disconnected, and using Direct Mode, there is no hiss until I crank the volume knob knob past 22. (I'm okay with that)
However, when using non-direct mode (again using any disconnected source input or playback paused), there is audible hiss when I turn the volume past 12. The hiss behavior is the same on Front, Rear, and Center speaker outputs, using none or any of the Dolby modes.
When I disconnect the DSP/DAC boards from the system, both Direct Mode and non-direct Mode have no hiss until I crank the volume past 22. I think this means the problem is in the DSP/DAC boards, or maybe these assemblies' upstream power supplies/regulators?
I re-capped most of the electrolytics on these two boards, and replaced the voltage regulators on these boards, but want to diagnose further before I buy other components.
The other thing I wonder is if the DSP/DAC needs to be adjusted (there are some variable resistors to adjust per the service manual), but I do not completely understand the equipment needs or what output to look for. Instructions in the service manual call for a noise meter, and an oscilliscope. I have an entry level oscilliscope; is that enough to try adjusting? It seems like these are the steps most closely related to minimizing hiss?
Schematics and service manual can be found at https://www.manualslib.com/manual/1123277/Pioneer-Vsx-D1s.html
Any help would be greatly appreciated!
When using any source input with playback on pause or disconnected, and using Direct Mode, there is no hiss until I crank the volume knob knob past 22. (I'm okay with that)
However, when using non-direct mode (again using any disconnected source input or playback paused), there is audible hiss when I turn the volume past 12. The hiss behavior is the same on Front, Rear, and Center speaker outputs, using none or any of the Dolby modes.
When I disconnect the DSP/DAC boards from the system, both Direct Mode and non-direct Mode have no hiss until I crank the volume past 22. I think this means the problem is in the DSP/DAC boards, or maybe these assemblies' upstream power supplies/regulators?
I re-capped most of the electrolytics on these two boards, and replaced the voltage regulators on these boards, but want to diagnose further before I buy other components.
The other thing I wonder is if the DSP/DAC needs to be adjusted (there are some variable resistors to adjust per the service manual), but I do not completely understand the equipment needs or what output to look for. Instructions in the service manual call for a noise meter, and an oscilliscope. I have an entry level oscilliscope; is that enough to try adjusting? It seems like these are the steps most closely related to minimizing hiss?
Schematics and service manual can be found at https://www.manualslib.com/manual/1123277/Pioneer-Vsx-D1s.html
Any help would be greatly appreciated!
I was able to adjust the DSP/DAC and view the frequency response via soundcard input but did not reduce the hiss.
However, I have now observed via the frequency response on the pre-out that perhaps the hiss I am hearing is actually 60 hz hum and harmonics.
Pre-out signal with Direct Mode on:
Pre-out signal with Direct Mode off:
(I think the spike at ~6.5khz is related to the sound card itself)
Thinking that it is power supply related, I replaced as many related electrolytics caps as I could (circled red in the power supply schematic excerpts below)
However, that still does not fix the issue.
The DSP/DAC board uses +5, -5, +15V, -15V for various devices and I see that the +15 and -15 are used for many of the buffers.
DSP/DAC schematics:
The +15 and -15 used for the DSP/DAC board seem to be formed from the "pos27" and "neg27" lines (power supply schematics).
"pos37" and "neg37" I believe is used for the main speaker output, and is therefore used whether Direct Mode is on or off.
To investigate, I built a DC blocking circuit so I could use the sound card input to see if 60hz and harmonics are on the power supply rails.
From the power schematics above, the frequency response for the following points are:
"pos27":
"neg27":
"pos37":
"neg37":
Questions:
1) Does the pre-out signal frequency response difference between Direct Mode on and off exhibit a power supply issue?
2) Can the increased magnitude of the 60 hz harmonics on the "pos27" and "neg27" lines contribute to all noise I am hearing when using the DSP/DAC?
I am definitely not an EE nor any kind of expert on circuits, but am willing to listen to any suggestions! Thanks!
However, I have now observed via the frequency response on the pre-out that perhaps the hiss I am hearing is actually 60 hz hum and harmonics.
Pre-out signal with Direct Mode on:
Pre-out signal with Direct Mode off:
(I think the spike at ~6.5khz is related to the sound card itself)
Thinking that it is power supply related, I replaced as many related electrolytics caps as I could (circled red in the power supply schematic excerpts below)
However, that still does not fix the issue.
The DSP/DAC board uses +5, -5, +15V, -15V for various devices and I see that the +15 and -15 are used for many of the buffers.
DSP/DAC schematics:
The +15 and -15 used for the DSP/DAC board seem to be formed from the "pos27" and "neg27" lines (power supply schematics).
"pos37" and "neg37" I believe is used for the main speaker output, and is therefore used whether Direct Mode is on or off.
To investigate, I built a DC blocking circuit so I could use the sound card input to see if 60hz and harmonics are on the power supply rails.
From the power schematics above, the frequency response for the following points are:
"pos27":
"neg27":
"pos37":
"neg37":
Questions:
1) Does the pre-out signal frequency response difference between Direct Mode on and off exhibit a power supply issue?
2) Can the increased magnitude of the 60 hz harmonics on the "pos27" and "neg27" lines contribute to all noise I am hearing when using the DSP/DAC?
I am definitely not an EE nor any kind of expert on circuits, but am willing to listen to any suggestions! Thanks!
I meant to post the following two power supply schematics with the electrolytics I replaced in red, along with "pos27" "neg27" "pos37" "neg37" labels:
