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Old 14th June 2006, 11:09 PM   #1
mr.duck is offline mr.duck  United Kingdom
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Default What are some "good" transistors?

Hello, i'm trying to find suitable transistors to build this class A headphone amp

The problem is the parts listed are now discontinued (i think), I should still be able to get hold of the PNP and NPN transistors but the JFETs are difficault to find and/or are expensive. Toshiba 2SJ109 in particular. They are dual matched JFETs i believe, and i dont know of any replacements.

So i thought of just getting individual JFETs and matching them myself. Will that work do you think? What do you look for when buying JFETs? i.e. which are best?

And while i'm at it, i thought about using "better" trasistors for driving the headphones with. Again, what do you look for?

Its class A but doesnt require heatsinking.

This is the amplifier...
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Old 15th June 2006, 12:40 AM   #2
EC8010 is offline EC8010  United Kingdom
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The only good transistor is a dead transistor.

Sorry, couldn't help it.
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Old 15th June 2006, 01:03 AM   #3
paulb is offline paulb  Canada
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Have you tried to contact the author of the article?
Do a search here for the FET part numbers and you'll find some information on possible replacements. For the outputs, well...I would bet they are not that critical.

p.s. Most tubes are already dead.
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Old 15th June 2006, 01:26 AM   #4
rpapps is offline rpapps  Antarctica
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Hi Mr.Duck

2SA1015 $0.52
2SC1815 $0.52
2SJ109 $5.60
2SK389 $2.75

enquiries@wescomponents.com

At around 48p to the Aussie Dollar, these prices arn't too bad.
Cheers
Rob
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Old 15th June 2006, 01:27 AM   #5
ostie01 is offline ostie01  Canada
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Hi, 2sk389 and 2sj109 are available at:

http://www.mainelectronics.com/bulksemi.htm from Vancouver Canada

2sj109= $4.27
2sk389=$4.89

Good luck
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Old 15th June 2006, 08:26 AM   #6
MikeB is offline MikeB  Germany
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Hi, try this:

http://www.schuro.de/preisl-jap-trans.htm

sk389: 1.72€
sj109: 2.52€

It should be no problem to ship from germany to england...
You have to order by email, i have good experience with this shop.

Mike
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Old 15th June 2006, 08:45 AM   #7
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Quote:
Originally posted by MikeB
i have good experience with this shop
Make that 2, me for the last 15 years. The option to transfer over the web makes it a lot easier to order than the Klang&Ton add days. THE source to get affordable OPA627/637s and AD797s in the 90s after Thel. The Schuro owner, Mr Rother, is a very pleasant guy.(My g/f had to drag me out of the shop in Kassel after 2 1/2 hours. She seemed to be pretty P..O.. )
You can get all of the items from Nikko Dalbani in Surrey, but the charge for the jfets is over 4 quid the piece, the 2SA/2SCs only cost 10 to 15p.

I would not bother to match JFETs, more pain than pleasure. Matching all the 2SA and 2SC devices on the other hand...
Spend the time on doing a proper layout for the amplifier with Eagle or the likes, Mr Duck.

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Old 15th June 2006, 02:00 PM   #8
mr.duck is offline mr.duck  United Kingdom
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£4 from Nikko Dalbani? Thats half the price i've seen elsewhere in the UK. Some of the other prices from germany and canada look good. But with shipping costs and the credit card people charging me fees (and probably giving me a poor exchange rate), it might end up being quite expensive.

I've contacted the author so hopfully i will get a reply soon.

As for matching components..

"The 500 ohm resistors, 1.6V LEDs, bias transistors and second stage transistors must be matched to within 0.5% or even 0.25% for optimal operation of the servo"

Have you ever seen an amp that required you to had match LED's to 0.25%?? Its a bad circuit really, but thats why I like it audio design without compramise.

I think 2N5462 would make a good replacement for 2SJ109 from what i can work out. They are much cheaper at £0.38. I'd have to buy a few if i was going to match them though. What exactly would i be trying to match? hFe??
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Old 15th June 2006, 02:01 PM   #9
sunsvc is offline sunsvc  Hong Kong
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Any suggestion of a compatible replacement of 2sd799 transistor for power regulation?
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Old 15th June 2006, 03:06 PM   #10
Leolabs is offline Leolabs  Malaysia
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2SC3579,BU810 or any darlington with a few hundred volts,6A,30W.
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