With that relay circuit and the loss of AC detector, it goes off instantly. There's no way the thump can happen before the AC is lost. I tested it, and if only half the AC cycle disappears, the relays turn off. It's a good circuit!
Truth! 😀 And I have indeed tested it.
Anyway, a better power supply which doesn't cause a thump is first prize.
> And I have indeed tested it.
With the same power supply as donovas, and the same current draw ?
Patrick
With the same power supply as donovas, and the same current draw ?
Patrick
No (and it's an extremely good point), but no power supply (ETA: feasible for audio purposes) can discharge in half an AC cycle.
i put in better transformers in the psu and the thump is now gone. 🙂
i also built another pair of boards (this is fun!) but this time with 9530/530 pairs, hoping for more bass and darker sound from its higher transconductance and capacitance than 9610 but instead got just the opposite.
everything's the same except for the mostfet pairs, same psu, same enclosure, but 9530 pairs have 'thinner' sound and way less bass. biasing is the same also.
why is this?
i also built another pair of boards (this is fun!) but this time with 9530/530 pairs, hoping for more bass and darker sound from its higher transconductance and capacitance than 9610 but instead got just the opposite.
everything's the same except for the mostfet pairs, same psu, same enclosure, but 9530 pairs have 'thinner' sound and way less bass. biasing is the same also.
why is this?
oh also the source resistor on 9530's boards are 2.2ohm, where as 9610 is fed with 3.3ohm. does that make much difference in the bass?
i finally shelled out for sk170 pair and it has been well worth it. best addition to my system so far. however, the bias on mine drifts too much. over an hour of usage it rises from 0.3v to 0.8v. i'm using simplified mr.evil's cap multiplier to power it.
the headamp is built according to the original circuit, except for the feedback resistor being lowered to 200ohm from 500ohm, and the jfet pairs arent thermally coupled.
what's causing so much drift?
the headamp is built according to the original circuit, except for the feedback resistor being lowered to 200ohm from 500ohm, and the jfet pairs arent thermally coupled.
what's causing so much drift?
Why would you have 0.3V in the first place ?
Can't you trim it to <10mV after 30 minutes ?
Did you thermally couple the MOSFETs as well ?
Patrick
Can't you trim it to <10mV after 30 minutes ?
Did you thermally couple the MOSFETs as well ?
Patrick
Sorry. Bias to me is normally measured as current, not as voltage.
So I guess he probably meant voltage across the 3.3R source resistors.
If that is the case, there seems to be insufficient heat sink on the power devices.
On my own (2107 case), heat sink temperature is never over 40°C.
Bias changes maybe from 120mA to 160mA or so after 1 hour.
So never factor of 2.5.
Patrick
So I guess he probably meant voltage across the 3.3R source resistors.
If that is the case, there seems to be insufficient heat sink on the power devices.
On my own (2107 case), heat sink temperature is never over 40°C.
Bias changes maybe from 120mA to 160mA or so after 1 hour.
So never factor of 2.5.
Patrick
hi, yes it is bias. mine goes from 300ma to 800ma. im just using a metal chassis for heatsink.
so the bias is expected to increase with insufficient heatsink?
rather than having anything to do with lowered gain resistor and the fact that the jfets arent thermal coupled?
so the bias is expected to increase with insufficient heatsink?
rather than having anything to do with lowered gain resistor and the fact that the jfets arent thermal coupled?
Poor JFET coupling will result in worsened DC drift.
Bias drift is largely heat sinking problem of the MOSFETs.
Time to use proper heatsinks and Kerafol.
Patrick
Bias drift is largely heat sinking problem of the MOSFETs.
Time to use proper heatsinks and Kerafol.
Patrick