This current is dependent on thermal equilibrium, so it will settle, implying that fans are not the answer to this on its own.
Do you have a link, or some measurements to explain this a little better?
Thermal energy raises the vibrational velocity. Power and bandwidth are inversely related. Low bandwidth causes distortion and instability. It is better to set the bias current to a reasonable level.
This indicates a problem or possible oscillations, otherwise this is normal for JLH69, but not at Le Monstre. Maybe your drivers are overheating.
I think you need to go lower with those 300R and that some more resistors should be corrected for that supply voltage.
Hiraga update.
Hi All,
Here is an update on my hiraga instability.
- changing feedback R and adding a feedback cap all ended up increasing instability believe it or not. Sound was not bad at all but not stability and it nearly caught fire. When it melted a cap’s outer plastic I called enough. That build had gone through so many mods in a box that was difficult to access, that I decided to re do the whole build.
- I also tried caps on base/collectors of driver transistors which did improve stability but ruined the sound.
- I also “think”, I started to hear instability in the other channel also, leading me to think there wasn’t really a fault with just one board.
- inspecting the circuit of the higher power hiraga shows quite a few differences required when boosting the power of the amp , as I have done.
So I rebuilt it from scratch. In a much bigger box to seperate the amp boards from the supply. All joints solder cleaned and re done.
The result was pleasing. The amp is much more stable now. Even as a Low power amp upped in power. Feedback is stock circuit.
Regards,
Paul.
Hi All,
Here is an update on my hiraga instability.
- changing feedback R and adding a feedback cap all ended up increasing instability believe it or not. Sound was not bad at all but not stability and it nearly caught fire. When it melted a cap’s outer plastic I called enough. That build had gone through so many mods in a box that was difficult to access, that I decided to re do the whole build.
- I also tried caps on base/collectors of driver transistors which did improve stability but ruined the sound.
- I also “think”, I started to hear instability in the other channel also, leading me to think there wasn’t really a fault with just one board.
- inspecting the circuit of the higher power hiraga shows quite a few differences required when boosting the power of the amp , as I have done.
So I rebuilt it from scratch. In a much bigger box to seperate the amp boards from the supply. All joints solder cleaned and re done.
The result was pleasing. The amp is much more stable now. Even as a Low power amp upped in power. Feedback is stock circuit.
Regards,
Paul.
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Just adding a note here that the hiraga has been totally stable since the re build. Use it every day. So it is possible to up the power supply ( tranny VA ) , the rail voltages and the quiescent current, get more power and increase the shear capability of good sound in this standard Jim’s audio 15W hiraga. It’s been a stable 25W amp for about 5 months now. This note is in case someone finds this thread and it is relevant to them in the goodness knows when future. The mods take a good amp and make it super. Enjoy.