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2SA798 dual transitor
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spitfire



Joined: Jan 06, 2011
Posts: 18
Location: Lithuania

PostPosted: Thu Feb 24, 2011 12:54 am    Post subject: 2SA798 dual transitor Reply with quote  Mark this post and the followings unread

Hi,

I'm going to build this filter:

http://yusynth.net/Modular/EN/ARPVCF/index.html

There's 2SA798 transistor in a circuit, and it cost more than 20$... and there's 5 of them in schematic. That's too much for me Smile Is there a cheaper replacement ?

There's also pcb's with BC557 or 2N3906 transistors, they are really cheap, but i need to match a pair of them, and i have no instruments to do that...

How it will work if transistors will not be matched in pairs ?
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andrewF



Joined: Dec 29, 2006
Posts: 1176
Location: australia
Audio files: 4

PostPosted: Thu Feb 24, 2011 5:38 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi there are a lot of threads here on matching transistors

to save you hunting:
here is Ian Fritz's method, for NPN & PNP
Use this and you won't need 2SA798

http://electro-music.com/forum/download.php?id=24386
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frijitz



Joined: May 04, 2007
Posts: 1734
Location: NM USA
Audio files: 54

PostPosted: Thu Feb 24, 2011 5:56 am    Post subject: Re: 2SA798 dual transitor Reply with quote  Mark this post and the followings unread

spitfire wrote:
There's 2SA798 transistor in a circuit, and it cost more than 20$...

Should still be easy to find.
$0.61 here:
http://www.electronicsurplus.com/item/28742/
$1.29 here:
https://www.addison-electronique.com/catalog/advanced_search_result.php?keywords=2sa798&osCsid=f4a438210359152b869f6ba7bac2a0ef&x=2&y=6


Very Happy

Ian
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spitfire



Joined: Jan 06, 2011
Posts: 18
Location: Lithuania

PostPosted: Thu Feb 24, 2011 7:13 am    Post subject: Reply with quote  Mark this post and the followings unread

ok, but if I'm not matching them. whats happening to circuit ?
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yusynth



Joined: Nov 24, 2005
Posts: 1314
Location: France

PostPosted: Thu Feb 24, 2011 2:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

spitfire wrote:
ok, but if I'm not matching them. whats happening to circuit ?


If you don't pay attention at matching the BC557 or 2N39.. chances are that (i) you will have a very high bleedhrough of the CV creating thumps in the audio out for fast varying CVs and (ii) the filter won't behave like a 24dB/octave filter because the poles will not track as expected.

Matching transistor is quite simple, it takes 15 minutes to find 5 matched pairs.
Otherwise 2SA798 are quite cheap and still sourceable.

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Yves
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Strazdas



Joined: Apr 21, 2010
Posts: 42
Location: Kaunas, Lithuania

PostPosted: Sat Mar 19, 2011 5:51 am    Post subject: Re: 2SA798 dual transitor Reply with quote  Mark this post and the followings unread

spitfire wrote:

There's 2SA798 transistor in a circuit, and it cost more than 20$... and there's 5 of them in schematic. That's too much for me Smile Is there a cheaper replacement ?


Gal pabandyk čia: http://www.megaomas.lt/shop/elektronika/elektronines-dalys/tranzistoriai/tranzistorius-2sa798-pnp-50v-01a-400mw-100mhz-5-sip-5201/ tik 3,90LT Už paslaugą galėtum ir man vieną plokštę atspausti.

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