I recently bought a preamp, however its not working as good as I was expecting.
Returning the preamp would take ages so I decided to fix it instead, or atleast try to.
And in order to do that I need your help. I'm a little unsure where I should start.
Basicly the problem is that its not quiet, there is noise coming from it. Its also producing some DC offset, but I'll add a DC blocking cap on the input of my amp to fix that.
The problem is this noise, its there on every single output, DAC-out, PRE-out and Headphone out.
If I change source to an digital source that's not being used the noise goes away. When I select the analog source the noise is still there (or a digital source that's being used). The noise also goes away when I press mute on the remote.
The noise does not increase with increased volume.
So far I've only secured the connections to earth and cleaned up the PCB (it was full of flux)
Schematics can be found HERE
Maxhax
Returning the preamp would take ages so I decided to fix it instead, or atleast try to.
And in order to do that I need your help. I'm a little unsure where I should start.
Basicly the problem is that its not quiet, there is noise coming from it. Its also producing some DC offset, but I'll add a DC blocking cap on the input of my amp to fix that.
The problem is this noise, its there on every single output, DAC-out, PRE-out and Headphone out.
If I change source to an digital source that's not being used the noise goes away. When I select the analog source the noise is still there (or a digital source that's being used). The noise also goes away when I press mute on the remote.
The noise does not increase with increased volume.
So far I've only secured the connections to earth and cleaned up the PCB (it was full of flux)
Schematics can be found HERE
Maxhax
The noise is probably not coming from the +-15v since it goes away when you press mute. It could be coming from the +5v volume rails. I would try the easy stuff like moving all the power wires away from the signal wires and have all the wires cross at 90's.
The inputs are cap coupled with c514 and c515. You could try bypassing those electrolytics with something better like a mk box cap.
The inputs are cap coupled with c514 and c515. You could try bypassing those electrolytics with something better like a mk box cap.
So what I have done now are:
Soldering Wima MK 330pf to -Vs and +Vs on all of the AD797BR's, both preamp and dac buffer.
Installing Wima MK 330pf in the "additional" slot right next to the AD797 on preamp (C517/C518).
Bypassing the coupling capacitors C514 and C515 with Wima MK 330pf soldered directly to the legs under the PCB.
Shortening and twinning the mains cable.
This reduced the noise by 80% and totally removed the DC offset. I was previously reading about 1.1VDC at the speaker terminals after my power amp, now Its throttling between 3mVDV and 15mVDC.
Thanks alot for the help nightanole!
Soldering Wima MK 330pf to -Vs and +Vs on all of the AD797BR's, both preamp and dac buffer.
Installing Wima MK 330pf in the "additional" slot right next to the AD797 on preamp (C517/C518).
Bypassing the coupling capacitors C514 and C515 with Wima MK 330pf soldered directly to the legs under the PCB.
Shortening and twinning the mains cable.
This reduced the noise by 80% and totally removed the DC offset. I was previously reading about 1.1VDC at the speaker terminals after my power amp, now Its throttling between 3mVDV and 15mVDC.
Thanks alot for the help nightanole!
It doesnt work for me either now, luckily I had it on my HDD.
Uploaded it for you:
A swedish host: http://data.fuskbugg.se/skalman02/DMK-IV-SCH.pdf
Rapidshare: http://rapidshare.com/files/445171173/DMK-IV-SCH.pdf
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