Matching transistors

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Disabled Account
Joined 2012
Hi all,

I'm wondering, how important is it to match each transistor pair?

I mean, how much HFE difference is accepted between a PNP and NPN pair?

Per amp I have:
Pairs 1 & 2:
2 x Hitachi 2SA872 HFE 525
2 x Hitachi 2SC1775 HFE 615

Pair 3:
1 x NEC 2SA634 HFE 166
1 x NEC 2SC 1096 HFE 157

Pair 4:
1 x Toshiba 2SA1943 HFE 98
1 x Toshiba 2SC5200 HFE 93

Any help is valued.....

Kind Regards,
Sjoerd Smits
 
For transistors of opposite polarity close Hfe matching often is difficult to obtain.

If you match the hfe within 10% the most is good.
If You in addition match the Vb-e at the same time within 20mV You are even better.

I always match mine within just a couple of millivolts.
As for Hfe matching I am very careful to match transistors in differential configuration.

The numbers You are having there looks fine+
 
Disabled Account
Joined 2012
Schematic

Here's the schematic as I used it.....
 

Attachments

  • Hiraga Super A 30W.png
    Hiraga Super A 30W.png
    37.1 KB · Views: 399
No.:eek:
Been out for a while.

The Q2 and Q 4 should be matched, and the Q1 and Q3 should be matched.
When theese are done, the whole input is in balance.
Quite nifty way to obtain it. No need to match between the NPN and PNP.

I would have ensured good thermical contact between Q3, Q4 and the heatsink. Seems as theese are all involved in the bias cirquit for this amp.
The drivers and the output transistors is difficult to get within the same Hfe-range, wich isn't too critical either.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.