HiFI OP-AMPs, BJTs, and FETs how do I choose them?

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777funk

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Joined 2007
I'm fairly inexperienced in Semiconductor Electronics. I am a young degreed E.E. but that doesn't mean much in terms of experience in Audio electronics. The little experience I do have mis mostly in Tubes.

I'm looking to upgrade the audio equipment I have as well as recording gear.

How do I choose parts? I've read there are some popular opamps by burr brown (now TI) etc. But How in the world do I know what is good?


ALSO, when I'm replacing a transistor (I am now on a blown driver section on an old pioneer amplifier) how do I know what to get? I have two power transistors (D525 and B595) that are shorted. I need new ones. I'd like to get better ones if I can since this is an OLD piece of gear. But I have no idea where to start. I can't even find the originals at any place I've looked (part D525 and B595) which would be at mouser and digikey. Are there brands that I should look for/avoid?

thanks!!
Nick
 
7

777funk

Member
Joined 2007
AndrewT said:
Hi,
can you find the datasheet for the 2sb595 and 2sd525?

Download it and compare specs to currently available drivers.
Click to expand...

Ok got the data sheet from NTE
http://www.nteinc.com/specs/10to99/pdf/nte54.pdf



Forgive me for ignorance here but how do I use those specs. Obviously I will want an NPN and PNP and to the Voltage and Current ratings. But here are my questions on that:
-If I go over the voltage and current ratings will that be ok? I'm assuming so
-What else should I look for?
-Can I tell from the Datasheet that the transistor will sound better or worse than the originals?
 
B

B Cullingford

Member
Joined 2005
Maybe 2SD525 and 2SB595 are obsolete and hence will be difficult to find.

I would not trust NTE replacement specs to be valid, try to find an original data sheet, or data book

you know you could just search - you might find for example:
http://www.jmnic.com/pdf/2sd/2SD525.pdf

Besides the obvious V, I and power ratings you may need to consider beta, and ft; newer, possibly faster transistors could require modifying the circuit to prevent oscillation.

I could help more but my data books and stash of old transistors are thousands of miles away!!
 
7

777funk

Member
Joined 2007
B Cullingford said:
Maybe 2SD525 and 2SB595 are obsolete and hence will be difficult to find.

I would not trust NTE replacement specs to be valid, try to find an original data sheet, or data book

you know you could just search - you might find for example:
http://www.jmnic.com/pdf/2sd/2SD525.pdf

Besides the obvious V, I and power ratings you may need to consider beta, and ft; newer, possibly faster transistors could require modifying the circuit to prevent oscillation.

I could help more but my data books and stash of old transistors are thousands of miles away!!
Click to expand...

OK faster... there's a hifi term I was looking for. How do I find the speed of a transistor. Bandwidth seems to be another hifi term I hear on semiconductors. Can I tell from data sheets which parts will sound better?

I'm not so much worried about replacing them with the originals. I'd like to upgrade if possible.

pacificblue said:
http://www.datasheetcatalog.com/
Click to expand...


Thanks!!
 
7

777funk

Member
Joined 2007
Ok, I have some answers on how to find the parts for this amp... but still my original question:

HiFI OP-AMPs, BJTs, and FETs how do I choose them?


Is it something where I look at data sheets and find the numbers and specs.

How do I know how fast the component is?

Also, I hear the word Bandwidth thrown around all the time. What does that mean in the world of audio and transistors/opamps?

thanks,
 
ostripper

ostripper

Member
Joined 2008
How do I know how fast the component is?
Also, I hear the word Bandwidth thrown around all the time. What does that mean in the world of audio and transistors/opamps
Click to expand...


As far as a replacement for your devices , TIP41/42c
http://www.fairchildsemi.com/ds/TI/TIP41.pdf
are the best bet.
How did I choose these ?
1. Ft (bandwidth) is lower. BUT , this is an audio amp (not RF).
2sd/b's are 12mhz -=TIP' s are 3mhz. If the sub was 20-30 Mhz,
I might be worried that my amp would oscillate. (it was compensated for 12mhz devices.)

2. Pc (collector dissipation) the tip's are 65W and the 2sd/b's
are 40W. a Little more is better for a good repair. :)
SOA of the tip's is also better .

3. Hfe (dc current gain) 2sd/b's is 40 @ 300mA and the TIP's
are 44 @ 300ma , Close. One might have to re-adjust bias
just a little.. look at first typical characteristics plot in the tip41 datasheet.
4. Vceo - voltage rating tip41c = 2sd525 = 100v... right on.

And most important , experiance. 5. my first childhood amp
had these devices (2sd525/2sb595 / kenwood 20w int. amp)
and the tip's worked out like a charm.
OS
 
P

pacificblue

Member
Joined 2008
777funk said:
Is it something where I look at data sheets and find the numbers and specs.
Click to expand...
No, because not all relevant data is in the datasheets, and more important, not all is known about what makes good sound.

An example is the discussion about THD. Usually we strife for lowest THD, but there are many examples of audio gear, where THD is high and the sound is still perceived as good. Some say, that is because the THD distribution is important, others say, because THD is only one of many factors and that others are more important. And then there is taste. What is good sound for you? Natural voices or punchy bass? Pinpoint spatial accuracy or extreme dynamics? Some demands exclude each other and you have to find the best compromise for your taste and application.

One option is to read through the forum and look, what others use. You will find that certain components are used again and again for certain tasks. You will also find that sometimes the schematic and layout play a bigger role than a certain component.

Another option is to determine the exact goal. That will narrow down the choice, e. g. because the supply voltage or current rating forces you to use certain components.
 
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