Modushop 4U /300mm for 2sk1058/2sj162 advise


Please advise. I whish to recase my Borbely Audio class A/B Servo 50 amp kit with four pairs of TO-3P 2sk1058/2sj162 per channel output boards.

Heatsinks per channel will be Modushop 4U/300x165x40mm rated at 0,31 C/W

V rails are +/- 32 VDC and bias currente is 200mA per pair, total of 800mA acording to instrutions manual.

I´m considering average room temperature 25C.

I read somewhere an article with pics of an assembled amp with the same Borbely output boards but with five pairs of mosfets, so I believe I´m getting to better heat dissipation with four pairs.

Probably I´m missing something here so please thank you for comments.

Happy New Year all

Ian Finch

Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
The temperature rise above ambient calculates to about 32C for a stereo amplifier with that Modushop case/heatsinks, just idling. As just posted, that means the heatsink would be about 57C if the ambient temperature is a steady 25C and the air flow around the case is unrestricted by a shelf or cabinet etc. Note that specifications and ratings are usually stated under ideal conditions, so you need to consider just how far from ideal, your amplifier location and ambient temperature may be when in use. Also, the heatsink temperature may be safe for the amplifier but too hot to touch for more than a few seconds. In a domestic environment, there needs to be some physical form of barrier to prevent casual contact.

However, just increasing the number of output transistor pairs is only the obvious part of what needs to be done to increase power. You also need to increase rail supply voltages of the power supply and the the component ratings to at least 50V in order to deliver significantly more power output into a given loudspeaker load impedance.

Needless to say, that means a full rebuild with much larger components and costs.