It's me again!
My saga continues as I have little time to spend on this.
I CANNOT get a satisfactory DC reading with the inputs shorted.....800mv > 1000mv. Op amp removed.
I tried the headphone test as mentioned by the ever helpful Ian @IDM....seems to work ok on this test mode, albeit was with a pair of ultra cheap ear buds...but no nasty squeal.
What would this point to?
My saga continues as I have little time to spend on this.
I CANNOT get a satisfactory DC reading with the inputs shorted.....800mv > 1000mv. Op amp removed.
I tried the headphone test as mentioned by the ever helpful Ian @IDM....seems to work ok on this test mode, albeit was with a pair of ultra cheap ear buds...but no nasty squeal.
What would this point to?
Grounding.....the heatsink is in contact with the chassis and the board is mounted on brass standoff....I have no separate ground wire.....where should I put one?
No DC at all on the inputs..soon settles to 0mv ...checked just now.
Ian asked me to do a test on the upa.....outer pin to ground and I got 13v
No DC at all on the inputs..soon settles to 0mv ...checked just now.
Ian asked me to do a test on the upa.....outer pin to ground and I got 13v
Added a ground. Re tweaked the trim pots. I turn them one way to lower the DC with no op amp but them if I measure with it in place the DC lowers if i turn the trimmer back the other way.
Anyway....i have good music playing.
Last small issues are still some hiss and when the amp is 'driven' with a peak of music I hear the slight noise of that squealchy sound
Still can't get a low mv DC reading shorted inputs
Anyway....i have good music playing.
Last small issues are still some hiss and when the amp is 'driven' with a peak of music I hear the slight noise of that squealchy sound
Still can't get a low mv DC reading shorted inputs
The trimmers are not to be re-adjusted after the op-amp is inserted no matter if the offset result worsens a bit. Some op-amp samples can have better or worse inherent offset performance in absolute terms but the difference is that they will not let the circuit drift from there with temperature changes in the future because they counteract further offset dynamically. This pre-amp can indeed null very well on its own with just the trimmers but the resultant DC condition is not guaranteed in the long term.
Those small issues seem oscillatory so please check that the actual R1 C1 C2 parts on the board are not different in value than listed in the BOM by any chance. Also if there is a way see what happens when connecting an alternative signal source than the specific mobile phone.
Lastly if the small issues persist after the above checks, add 100 Ohm series resistors on the line outputs. Between the outgoing cable's hot and the output RCA's centre pin will do. Maybe 50 Ohm already installed on the board as line output damping resistor isn't enough with the specific power amp and interconnects.
Those small issues seem oscillatory so please check that the actual R1 C1 C2 parts on the board are not different in value than listed in the BOM by any chance. Also if there is a way see what happens when connecting an alternative signal source than the specific mobile phone.
Lastly if the small issues persist after the above checks, add 100 Ohm series resistors on the line outputs. Between the outgoing cable's hot and the output RCA's centre pin will do. Maybe 50 Ohm already installed on the board as line output damping resistor isn't enough with the specific power amp and interconnects.
Salas you are saying you don't need a resistor between earth and signal ground?
Would 8mm thick 60mm height and 140mm in length aluminium plate work better for each side of UBib? I would place it vertically.
Its the same for quick test purposes having a loop breaker resistor or not i.e. either way still referencing the chassis to signal ground. He may see about that when he will add the mains earth to the chassis. In case a ground loop between finalized components occurs i.e. hum & buzz.
As a matter of fact he will test better and securely with the mains earth connected to that only chassis because his amp is just PCB right now.
It's just a regular aluminium plate, there's no heat dissipation information available. It would be thicker than current one with larger overall area, but without radiator wings. One plate would be shared between both mosfets on one side.
It's quite cheap so I'll give it a try. I don't want to re-soldier mosfets for attachment to baseplate. So vertical sinks are the only way to go. With limited space on the sides flat plate would be best approach for me.
Only thing is that it is a bitt too small, fitting a dual mono will be a problem.