HFE matched tolerance

[oran.outan]

Hi,

What will be the tolerance or the maximum HFE interval for matched transistor ?
I'd like to match (pair) some NOS Philips BC549c but with 10 of them, no one have the same HFE value.
I only have one close pair = x1: 553 / x2: 551 . Will that be acceptable ? or does it need to be exactly the same values ?

thanks for your feedback.
Best
0-0

 

[gyraf]

question does not compute - entirely depends on what your intended circuit needs, what you're trying to do

 

[JohnRoberts]

What is the particular circuit's sensitivity to beta (HFE)? If the circuit is very sensitive to beta, test the devices in a similar circuit.

JR

 

[Walrus]

Surely 0.4% difference will be good enough??

 

[oran.outan]

question does not compute - entirely depends on what your intended circuit needs, what you're trying to do

so, will that work for a 2520 style DOA like a Gar or similar ?
I also have a schoeps style LdC whose I will start soon… I already have 2x onsemi bc550 matched but maybe give a try with Them !?

Thanks
0-0

 

[Walrus]

The 2520 i was making I matched the input pair to within 10 of each other.
They work perfectly.

 

[Voyager10]

so, will that work for a 2520 style DOA like a Gar or similar ?
I also have a schoeps style LdC whose I will start soon… I already have 2x onsemi bc550 matched but maybe give a try with Them !?

Thanks
0-0

Yes, 1% or so matching is good enough for both applications.

For a DOA, matching of transistors can affect the input offset voltage and current (and therefore the DC offset at the output), and the common-mode distortion (i.e. how that offset changes as the inputs swing up and down).

For the Schoeps circuit, matching will affect the DC offset between XLR pins 2 and 3. This is only a worry if feeding a transformer-coupled preamp, where it causes a DC current to flow in the primary. Too much DC will cause distortion (although I can't find figures for 'how much' for typical transformers).

 

[oran.outan]

@Voyager10 , thanks for the explanations ! good to know...

best
0-0