Hi all.
I am new to this forum so bare with me. i am kind of a noob when it comes to audio but i have build a class AB amp based on BD 139/140 transistors.
it amplifies arround 60 watt and plays very good. But i talked with my teacher and he said that it could play even better if i had better effects transistors but i dont know how to see if a transistor is better for the purpose(this is problerly still because i am a noob) so i was hoping that someone could reccomend me some. prefereable would be arround 100-150 watt output per channel.
if you need schematics or any other information about the amplifier please say so. I hope this can be a good start for me making alot of DIY audio projects so it would be nice if my first amp would perform good.
BTW i am building a pre-amp for it atm based on the tda2415A if that can help.
Cheers
Anders "blunt"
I am new to this forum so bare with me. i am kind of a noob when it comes to audio but i have build a class AB amp based on BD 139/140 transistors.
it amplifies arround 60 watt and plays very good. But i talked with my teacher and he said that it could play even better if i had better effects transistors but i dont know how to see if a transistor is better for the purpose(this is problerly still because i am a noob) so i was hoping that someone could reccomend me some. prefereable would be arround 100-150 watt output per channel.
if you need schematics or any other information about the amplifier please say so. I hope this can be a good start for me making alot of DIY audio projects so it would be nice if my first amp would perform good.
BTW i am building a pre-amp for it atm based on the tda2415A if that can help.
Cheers
Anders "blunt"
Anders,
Quick calculation shows that with BD139/BD140 about 20W output will be maximum within the ratings - not sure where the 60W can come from. Presume we are talking per channel?
In a case of my own 80W amplifier I use the BD139/140 to drive my power transistors (TIP35/36). But over where you are quite a larger variety of transistors would be available than here (South Africa). I was restricted to 42V + 42V supply because of the transistor maximum safe ratings (that is for 8 ohm loudpseaker impedance).
I am sure others will reply here.
Quick calculation shows that with BD139/BD140 about 20W output will be maximum within the ratings - not sure where the 60W can come from. Presume we are talking per channel?
In a case of my own 80W amplifier I use the BD139/140 to drive my power transistors (TIP35/36). But over where you are quite a larger variety of transistors would be available than here (South Africa). I was restricted to 42V + 42V supply because of the transistor maximum safe ratings (that is for 8 ohm loudpseaker impedance).
I am sure others will reply here.
ACD said:
Think again, not if you put 20 of them in parallel.
More amusement : a power amp manufacturer overhere even did it for series production.
(not counting 1 diy twit who got as far as 20 per channel)
And a very cheap output stage up to 75 watt at that, 40 of the good pieces could be as little as $10.
I seem to recollect NP mentioned he thought of going as high as 50 low power devices in parallel.
jacco vermeulen said:True, but 20 BD139 in parallel gives an output stage with an;
Ft of nearly 200MHz
hFe of 200
30 amps continuous, 40 amps peak.
A total Pd of 320 watts.
Lower Cob than 1 single big Sumo wrestler.
BD911/912 already were major suck in the previous century.
Ft of 3 Mhz, yikes
Ft of 200Mhz is very usefull in audio ... ;/
Pd = 320 W, i dont' think so, bd139 have very big thermal resistance junction-case, it's 10*C/W, 20 transistor have 0.5*C/W, with 150W of power the junction will have 100*C temp (in 25*C ambient temp) if you have 0*C/W radiator ... in real world it could diffuse maybe 100W ...
what mean Cob ?
jacco vermeulen said:
I thought that was the way non-thinking people used them!
Poor Anders; with all this he is sure to get his output stage exactly right!
As was requested, can we have a circuit, please? You would by now have learnt that you might be able to only add a more powerful complementary pair. Were you thinking of retaining the same power transformer (it it was overrated)? If so, what are the ratings?
Regards
ACD said:
You guys are pretty funny.
If you buy big numbers, 20 BD139 or BD140 devices cost less than a Sanken MT200.
An Rcs of 10 C/W divided 20 = 0.50 C/W, please name me a device with a Rcs of 0.50 C/W.
I've got output devices that have an Ft of 80Mhz and higher and built output stages with them, is 80 Mhz no good for audio either ?
Stax didn't seem to think so, and Nelson Pass had no problem using them for my Forté Audio amp.
Name me a professional audio company that still does BD911/BD912 output stages and i'll name you one that does it with TO126 devices. (and it doesn't come cheap)
BD139/140's work very well as drivers but seem a little underrated as output stage devices. My amp that I built about a month ago uses them as drivers for the 2SC5200/2SA1943 output stage (50 mA bias current). A single pair of 2SC5200/2SA1943 has no problem doing 100w into 8 ohms. Mine get just barely warm playing loud. I had the amp outside playing while I was working in the yard. About six hours of high power playing and the heatsinks were just barely warm to the touch. The transformer was the hottest component of the amp and even it was only warm to the touch (about 110F/40C). Make sure you get them from a reputable dealer. I have heard about some fakes of these transistors.
schematics..
ok i can see one thing from your responses and i need to do some reading in all this amplifying stuff..
and sorry for the late feedback with schematics. but here it is
you talk alot about driver transistors and output transistors ? i only have the bd139/140...
talked with my teacher and he said that they actually kinda stole it from this site... http://www.sound.westhost.com/project3a
ok i can see one thing from your responses and i need to do some reading in all this amplifying stuff..
and sorry for the late feedback with schematics. but here it is
you talk alot about driver transistors and output transistors ? i only have the bd139/140...
talked with my teacher and he said that they actually kinda stole it from this site... http://www.sound.westhost.com/project3a
Attachments
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.