Hi Guys, advice please from all Hiraga or Hiraga DIY users. I have found a factory Hiraga 20 watt to buy, original transistors and caps, nice condition, but am put off by stories i read about transistor failure putting DC through and frying my expensive speaker drive units. Is this a a genuine concern or a one-off for a poor unfortunate user. Thanks for your help, i have fancied this amp for 20 years, now so close, but i could not justify threatening my speakers. Are there any mods that can be done if this is a real concern?
DC faults are a hazard of any direct coupled design, protection circuits not always providing the safety they should.
I can't comment on the reliability of this amp (I know nothing about it tbh) but can suggest that using two back to back large electrolytics (say 10,000uf each) of a voltage at least equal to the total rail voltage of the amp per channel to connect in series with the speaker will offer essentially total protection whatever happens.
I can't comment on the reliability of this amp (I know nothing about it tbh) but can suggest that using two back to back large electrolytics (say 10,000uf each) of a voltage at least equal to the total rail voltage of the amp per channel to connect in series with the speaker will offer essentially total protection whatever happens.
I guess i showed how poor my electrical knowledge is!!! My concern is how hot the transistors must be operating at must surely lead to failure at some point??
with regards to heat dissipation it should be safe if you can keep your hand on top of the heatsinks
I dont think the 20watt Hiraga runs exstremely very hot
I dont think the 20watt Hiraga runs exstremely very hot
Not necessarily. Junction temperatures of silicon transistors are happy running at well over 100C. That translates to case/heatsink temperatures to hot to touch. A big reliability issue on hot running components is fatigue of the solder joints and that can cause just as destructive conditions as actual failure of a part. Its always worth checking and running an iron over such components for long term reliability.
🙂 Posted together... yes, if you can touch a heatink for four or five seconds before it starts to burn then its quite OK.
Maybe i shouldn't worry too much then?
I was recommended First Watt F5 or J2 as modern 'equivalents', do i assume correctly that they have some sort of protection from this happening?
I was recommended First Watt F5 or J2 as modern 'equivalents', do i assume correctly that they have some sort of protection from this happening?
Heat concern
Hiraga 20W and F5 amps are not worse than other class A amp for temperature management (big degeneration resistor value in the output stage in this case). I also use the 5-10 seconds touch to set the maximum bias for an heatsink.
However, by precaution I also install a 70 degree C thermal cut-off on each heatsink of all my class A amps to cover for possible failure and prevent heat burn. The normally closed Thermal cut-off is on the power supply line of the amp.
Fab
Hiraga 20W and F5 amps are not worse than other class A amp for temperature management (big degeneration resistor value in the output stage in this case). I also use the 5-10 seconds touch to set the maximum bias for an heatsink.
However, by precaution I also install a 70 degree C thermal cut-off on each heatsink of all my class A amps to cover for possible failure and prevent heat burn. The normally closed Thermal cut-off is on the power supply line of the amp.
Fab
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