Hi,
I finished my first gainclone yesterday and everything seems fine when no input is connected. DC offset is 12mv/60mv for other channel and 39mv/77mv for other channel. The amp is dead silent when no input is connected.
When connecting input and playing music I hear music from both channels but there is crackling sound on music. The music kind of distorts. I play music through computer and PCM2702 powered AlienDAC. The DAC works fine with my commercial amp. Amp has star ground where are ground connections are connected separately. Also wall socket ground connects to same grounding point. PSU is regulated LM338 based on decibel dungeon design. Amplifier circuit is audiosector LM3875 circuit with pot added. PSu measures 29.6V rail voltage on positive side and -29.4 on negative side. No snubbers or any kind of RF filtering. DAC has coupling on output.
1. When input is connected and music is played through amp, the dc offset fluctuates constantly. Is this normal?
2. Any advices on input signal cabling? My inputs are isolated from chassis. The input return pin connects to star ground. Input signal goes to pot and from pot to LM3875. Pot is grounded in star ground. I used single strands of CAT6 cable for input cabling. Should I use coax?
Below attached two pics from my amp. Any help is appreciated!
https://dl.dropboxusercontent.com/u/19192008/2013-07-24%2007.24.47.jpg
https://dl.dropboxusercontent.com/u/19192008/2013-07-24%2007.24.36.jpg
I finished my first gainclone yesterday and everything seems fine when no input is connected. DC offset is 12mv/60mv for other channel and 39mv/77mv for other channel. The amp is dead silent when no input is connected.
When connecting input and playing music I hear music from both channels but there is crackling sound on music. The music kind of distorts. I play music through computer and PCM2702 powered AlienDAC. The DAC works fine with my commercial amp. Amp has star ground where are ground connections are connected separately. Also wall socket ground connects to same grounding point. PSU is regulated LM338 based on decibel dungeon design. Amplifier circuit is audiosector LM3875 circuit with pot added. PSu measures 29.6V rail voltage on positive side and -29.4 on negative side. No snubbers or any kind of RF filtering. DAC has coupling on output.
1. When input is connected and music is played through amp, the dc offset fluctuates constantly. Is this normal?
2. Any advices on input signal cabling? My inputs are isolated from chassis. The input return pin connects to star ground. Input signal goes to pot and from pot to LM3875. Pot is grounded in star ground. I used single strands of CAT6 cable for input cabling. Should I use coax?
Below attached two pics from my amp. Any help is appreciated!
https://dl.dropboxusercontent.com/u/19192008/2013-07-24%2007.24.47.jpg
https://dl.dropboxusercontent.com/u/19192008/2013-07-24%2007.24.36.jpg
Last edited:
So you mean that star ground should be closer to regulator board and the leads should be shorter?
Or do you mean that the ground lug should be closer to big capacitors at the circuit board, so the ground should not travel across the board long distance.
Problem solved!
Problem solved!
Moving the ground lug did not make a difference in crackling. Intuitively I tried different speaker cables and with different cables everything is awesome!
I tested the amp with diy venhaus braided cat5(15 pairs per cable) and crackling seems to be caused by high capasitance.
With normal shoelace cable amp plays without disturbances.
I will make new cables from quality speaker wire without braiding
Problem solved!
Moving the ground lug did not make a difference in crackling. Intuitively I tried different speaker cables and with different cables everything is awesome!
I tested the amp with diy venhaus braided cat5(15 pairs per cable) and crackling seems to be caused by high capasitance.
With normal shoelace cable amp plays without disturbances.
I will make new cables from quality speaker wire without braiding
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