Addicted to music Posted June 24, 2015 Posted June 24, 2015 Hi Guys, I havent done this for a while because there's no reason for me to do it unless I was putting another amplifier project together. I've had a discussion with some commercial manufacturers, and some have informed me that matching the HFE and Vbe is no longer required because when they leave the production line they are so close that it's not worth doing. I know that with designs like ME it's critical to match them within 1% as Zaph keeps ear bashing me with! . This is because ME amps do not employ GFB and component tolerances are critical and I fully understand that due to its implementations, but even if they leave the production line in the same batch is it really that close that it doesn't need matching? Or is it absolute critical that they must be within acceptable tolerances? Also for those who do it on a regular basis does the batch you receive is so close that you an safely assume that it's matched within a few %
mwhouston Posted June 24, 2015 Posted June 24, 2015 Testing a FET or transistors can be very simple. Let's see what the others come up with.
Zaphod Beeblebrox Posted June 24, 2015 Posted June 24, 2015 (edited) Look at the specs of a typical power transistor: http://pdf1.alldatasheet.com/datasheet-pdf/view/2667/MOSPEC/MJ15003.html Note the hFE spread: 25 ~ 150. Not a problem for amplifiers using plenty of global NFB. BIG problems for some amps. Batch matching is not a substitute for proper matching. Each device needs to be individually tested and graded, AT realistic currents. I should add that Peter Stein goes much further with his amps than just matching output devices. Every single device is matched to it's opposite device AND to the preceding device/s. So, when outputs are selected, then drivers can be selected to match them and so on. Edited June 24, 2015 by Zaphod Beeblebrox 2
andyr Posted June 24, 2015 Posted June 24, 2015 Agree with what ZB said above ... but IME, JFETs are much more of a problem. For best sound, you need to match Idss to 2dp. Not difficult to do but: tedious, and you need to buy a whole lot of them. Andy 1
Equaliser Posted June 30, 2015 Posted June 30, 2015 (edited) Or just buy from specialist diy'ers that pre-match it for you. I know for 2SJ74's, diyaudio offers matched pairs if need last time I checked. Bit O/T @@Zaphod Beeblebrox would you happen to have any W10M 1000v/1.5a rectifier bridge diodes, or know any cheap places to get them from? Element & RS don't have it. Ebay so far looks like my only option. Edited June 30, 2015 by DefQon
Zaphod Beeblebrox Posted July 1, 2015 Posted July 1, 2015 Or just buy from specialist diy'ers that pre-match it for you. I know for 2SJ74's, diyaudio offers matched pairs if need last time I checked. Bit O/T @@Zaphod Beeblebrox would you happen to have any W10M 1000v/1.5a rectifier bridge diodes, or know any cheap places to get them from? Element & RS don't have it. Ebay so far looks like my only option. PM sent.
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