autir Posted September 28, 2005 Report Share Posted September 28, 2005 Hello ppl Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 28, 2005 Report Share Posted September 28, 2005 I used to use BC547B and C and BC557B and C transistors when I worked for Philips, but they are hard to get in Canada.Now I use 2N3904 and 2N3906 transistors that are made by many manufacturers.The BCxxx transistors have the advantage of selected current gain in 3 groups. The 2Nxxx transistors can have just about any amount of gain. ;D Quote Link to comment Share on other sites More sharing options...
walid Posted September 29, 2005 Report Share Posted September 29, 2005 There are many general purpose transistors like what audioguru said and 2n2222, 2n2907i 'll tell you what i do;i get some electronic board from say radio or any other not used device and get all the transistors from it then get their datasheets and put them in boxes for future use. this makes me familiar with many of these transistors. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 29, 2005 Report Share Posted September 29, 2005 I don't use transistors from radios and things. They have too many different types and I can't purchase them if I need more. Quote Link to comment Share on other sites More sharing options...
autir Posted September 29, 2005 Author Report Share Posted September 29, 2005 i get some electronic board from say radio or any other not used device and get all the transistors from it then get their datasheets and put them in boxes for future use. this makes me familiar with many of these transistors.Exactly what I used to do.But if I design a circuit and put it on the Internet, I cannot recommend a possibly cheapo, hard to find transistor type.So, audioguru, I take it as you recommend me to stick just with the BC546-550 family? Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 29, 2005 Report Share Posted September 29, 2005 So, audioguru, I take it as you recommend me to stick just with the BC546-550 family?Yes, and BC557 for PNP. The BC549 NPN and BC559 PNP are especially low-noise types. Quote Link to comment Share on other sites More sharing options...
Guest Alun Posted September 29, 2005 Report Share Posted September 29, 2005 I don't use transistors from radios and things. They have too many different types and I can't purchase them if I need more.I disagree, I encourage using transistors from old appliances providing you can find the datasheets.For most applications the transistor type isn't critical, I typically use BC547, 2N2222A, BC337, 2N2369, BC557 ect.I would be more worried about separating them into groups like NPN and PNP, for the latter I normally use BC560, BC227, 2N2905 ect. Quote Link to comment Share on other sites More sharing options...
audioguru Posted September 29, 2005 Report Share Posted September 29, 2005 I can buy only one 2N3904 for $.08CAN at Newarkinone and they cost less if I buy more.I know it, I like it and I use it. I wouldn't touch a cheap Chinese 2SCxxxx from a radio. :P Quote Link to comment Share on other sites More sharing options...
autir Posted October 1, 2005 Author Report Share Posted October 1, 2005 Hold on a second people!As we know, the flock of characteristic curves in the Vce - Ic level signify the relation between the incoming (Ib) and the outgoing (Ic) signal. In order for the output signal to be an exact replica of the input (though amplified), the curves must be as parallel as possible.I attach two pictures. The first is the flock of the BC548, and the second of 2SA1015 from UTC.As we can clearly see, the cheapo SA1015 I have scavenged from an old radio outperforms the famous BC548. In fact, it makes the perfect amplifier.I know that this seems too good to be true. Especially the fact that the A1015's curves are COMPLETELY parallel to the x axis. I believe that this is mathematically impossible, but I am not certain.Your thoughts? Quote Link to comment Share on other sites More sharing options...
Staigen Posted October 1, 2005 Report Share Posted October 1, 2005 Hi there AutirI think the 2SA1015 curves are a fake! ;DI will check out on the net if i can get something//Staigen Quote Link to comment Share on other sites More sharing options...
Staigen Posted October 1, 2005 Report Share Posted October 1, 2005 Hi againI was right, here is the Toshiba version://Staigen2SA1015.pdf Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 1, 2005 Report Share Posted October 1, 2005 Do you honestly have a pure current source as an input to a transistor? Don't you also feed it voltage swings? Then look what happens to the distortion of any transistor with a pure voltage input and the transistor circuit doesn't use any negative feedback: Quote Link to comment Share on other sites More sharing options...
autir Posted October 2, 2005 Author Report Share Posted October 2, 2005 I think the 2SA1015 curves are a fake!I found the section describing the transistor curves in my theory book.Yes they are fake. Without any doubt. >:(Then look what happens to the distortion of any transistor with a pure voltage input and the transistor circuit doesn't use any negative feedback:What I understand from your reply is that it is impossible to replicate with 100% accuracy the input signal? Even with class A?!? Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 2, 2005 Report Share Posted October 2, 2005 [What I understand from your reply is that it is impossible to replicate with 100% accuracy the input signal? Even with class A?!?Yes, that is why opamps use so many transistors. Class-A transistor stages produce even-harmonics distortion like I showed before with a voltage input.Transistors are non-linear, so push-pull stages are used in opamps to eliminate even-harmonics distortion. Current sources are used instead of collector resistors, or bootstrapping of the collector resistor is used. Of course, plenty of negative feedback is used along with voltage gain of up to one-million in good opamps results in linearity that is just about perfect.Have a look at this duscussion about simple transistor amplifier stages and ways to improve them. Note that they have plenty of negative feedback which reduces their voltage gain to 3. With less negative feedback resulting in more gain, the distortion is much worse.http://www.dself.dsl.pipex.com/ampins/discrete/discrete.htm Quote Link to comment Share on other sites More sharing options...
autir Posted October 2, 2005 Author Report Share Posted October 2, 2005 Yes, that is why opamps use so many transistors. Class-A transistor stages produce even-harmonics distortion like I showed before with a voltage input.For the second time you shock me completely.What about all these people who scorn at op.amps and ICs and design these very expensive class-A amps claiming to be Hi-Fi? Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 2, 2005 Report Share Posted October 2, 2005 Class-A transistor stages produce even-harmonics distortion like I showed before with a voltage input.For the second time you shock me completely.What about all these people who scorn at op.amps and ICs and design these very expensive class-A amps claiming to be Hi-Fi?Then those people are making their own opamps from separate transistors.They use class-A only to warm their homes and to avoid the crossover distortion caused by a poorly designed push-pull circuit.Maybe they are the same people who still use vacuum tubes (valves) in audio amplifiers.Some opamps have a 0.000008% distortion that certainly can't be heard and is extremely difficult to measure. Their output operates in class-AB, not class-A.National Semi and others make excellent class-AB IC audio power amplifiers. Quote Link to comment Share on other sites More sharing options...
autir Posted October 4, 2005 Author Report Share Posted October 4, 2005 I used to use BC547B and C and BC557B and C transistors when I worked for Philips, but they are hard to get in Canada.They cost 0.05 Euros each down here.Want me to send you a hundred or two? ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 5, 2005 Report Share Posted October 5, 2005 Please don't send me any transistors, they distort too much. I have been using low distortion opamps for most of my audio projects.With my FM transmitter project I had a hard time getting any gain from its preamp transistor and still have inaudible distortion. I added negative feedback to a transistor preamp circuit that sounded awful. Quote Link to comment Share on other sites More sharing options...
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