Fairchild FJA4310

jgray · 10th November 2010, 12:08 AM

Hi. I am working on a somewhat low power class A amp, and considering the Fairchild FJA4310 NPN BJT for the output section. Does anyone have experience with this part and its suitability for an application like this? The beta droop looks good in the datasheet.
Thanks,
Joel

jgray · 11th November 2010, 01:19 AM

How about the 2SC5242 instead? That one looks even better.

hitsware · 11th November 2010, 01:53 AM

In what way ?

jgray · 11th November 2010, 02:51 AM

Even more uniform gain as collector current varies.
Joel

CBS240 · 03:55 AM

How much power do you expect from this amplifier and into what load Z? Seems heat dissapation would be the primary concern of a class A OPS, so bigger transistor less worries, eh? How about FJL4315?

Hmmm, it appears that same die comes in diffferent packages,

....for a different price I'm sure.

AKSA · 11th November 2010, 05:28 AM

I've always found mosfets better for Class A; they handle the thermal abuse easily......

Hugh

jgray · 11th November 2010, 05:26 PM

CBS240...The supply is +/- 12.5 V rms and currently the output is biased at 1.0A, and running into 8 ohms. I am currently using two 2N3715 (push pull) in a TO-3 package, and fairly happy with the waveforms, and the sound. I am looking to improve the audio performance, and also switch to a TO-3p package for mechanical mounting reasons.

It looks like the FJL4315 would handle even more power and the gain curve is similarly flat, although as you can tell from my little supply, I don't think I will pushing any of these devices to their limits for temperature and power. I'm sure you're right about the price too!

Thanks,
Joel

jgray · 11th November 2010, 05:29 PM

AKSA...I am sure you are right about the mosfets and thermal abuse. I still have a lot to learn about them before I would try and design them into an amp. That's on my list of things to explore after I finish this amp. Well actually, I have an old tube radio to restore next, but then on to the mosfets!
Thanks,
Joel

10th November 2010, 12:08 AM	#1
jgray diyAudio Member Join Date: Sep 2010 Location: Chicago NW suburbs	Fairchild FJA4310 Hi. I am working on a somewhat low power class A amp, and considering the Fairchild FJA4310 NPN BJT for the output section. Does anyone have experience with this part and its suitability for an application like this? The beta droop looks good in the datasheet. Thanks, Joel

11th November 2010, 03:48 AM	#5
CBS240 diyAudio Member Join Date: Aug 2005 Location: K-town	How much power do you expect from this amplifier and into what load Z? Seems heat dissapation would be the primary concern of a class A OPS, so bigger transistor less worries, eh? How about FJL4315? Hmmm, it appears that same die comes in diffferent packages, ....for a different price I'm sure. __________________ All the trouble I've ever been in started out as fun...... Last edited by CBS240; 11th November 2010 at 03:55 AM.

11th November 2010, 05:28 AM	#6
AKSA diyAudio Member Join Date: Sep 2001 Location: Melbourne, Australia	I've always found mosfets better for Class A; they handle the thermal abuse easily...... Hugh __________________ Aspen Amplifiers P/L (Australia) www.aksaonline.com

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11th November 2010, 01:19 AM	#2
jgray diyAudio Member Join Date: Sep 2010 Location: Chicago NW suburbs	How about the 2SC5242 instead? That one looks even better.

11th November 2010, 01:53 AM	#3
hitsware diyAudio Member Join Date: Mar 2002	In what way ?

11th November 2010, 02:51 AM	#4
jgray diyAudio Member Join Date: Sep 2010 Location: Chicago NW suburbs	Even more uniform gain as collector current varies. Joel

11th November 2010, 05:26 PM	#7
jgray diyAudio Member Join Date: Sep 2010 Location: Chicago NW suburbs	CBS240...The supply is +/- 12.5 V rms and currently the output is biased at 1.0A, and running into 8 ohms. I am currently using two 2N3715 (push pull) in a TO-3 package, and fairly happy with the waveforms, and the sound. I am looking to improve the audio performance, and also switch to a TO-3p package for mechanical mounting reasons. It looks like the FJL4315 would handle even more power and the gain curve is similarly flat, although as you can tell from my little supply, I don't think I will pushing any of these devices to their limits for temperature and power. I'm sure you're right about the price too! Thanks, Joel

11th November 2010, 05:29 PM	#8
jgray diyAudio Member Join Date: Sep 2010 Location: Chicago NW suburbs	AKSA...I am sure you are right about the mosfets and thermal abuse. I still have a lot to learn about them before I would try and design them into an amp. That's on my list of things to explore after I finish this amp. Well actually, I have an old tube radio to restore next, but then on to the mosfets! Thanks, Joel

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