LC, I think I will get those when i get a chance, but i have some bad news of mine.
Maybe is due to poor electricity, when I close one of my house ballast light, the voltage went somewhere else, and my fuse trip. well... i thought it protected my device, but no.... something went burn and I don't know where.... (replaced fuse and still trip, only happen to one channel)
So now i would upgrade my power section first before i proceed.... don't want the same thing happens (I just use unregulated dual supply consist of rectifier and capacitor)
Any suggestion for me regarding this ? Have not much knowledge on power supply.... especially destroy my another amplifier..... (protection against small main voltage fluctuation)
About the amplifier, i can't find the fault so I will desolder it and examine later....
Extra question : I have some spare BD139/BD140 but they are from different manufacturer so their attribute could be very different. So I would ike to know what should do to determine is it "complementary" enough for use in amplifier ?
Maybe is due to poor electricity, when I close one of my house ballast light, the voltage went somewhere else, and my fuse trip. well... i thought it protected my device, but no.... something went burn and I don't know where.... (replaced fuse and still trip, only happen to one channel)
So now i would upgrade my power section first before i proceed.... don't want the same thing happens (I just use unregulated dual supply consist of rectifier and capacitor)
Any suggestion for me regarding this ? Have not much knowledge on power supply.... especially destroy my another amplifier..... (protection against small main voltage fluctuation)
About the amplifier, i can't find the fault so I will desolder it and examine later....
Extra question : I have some spare BD139/BD140 but they are from different manufacturer so their attribute could be very different. So I would ike to know what should do to determine is it "complementary" enough for use in amplifier ?
The multicomp one looks like Philips to me, the ST has a bigger die hence lower Ft. To really know two BJTs are following is curve tracing them but no NPN and PNP are ever perfect mirror images anyway. See to have a pair of near hfe and Cob from the same maker is the practical thing. If you can get the multicomp BD139 also it will be OK. What variety is it? -16? In Philips I got many near hfe ones from both sexes in -16.
The answer had still be given previously in this thread: ~ 150mA per device for FETs, 300 for BJT (but i have less experienced those concerning this point and it depend there more on the open loop bandwidth of the amp).Could you tell us what the current is above which you cannot notice improvement - thx
Of course, assuming you feed them with a GOOD PSU.
The best way is to make (objectively) your own testings.
Concerning temp, the best seems, on my experience, around 40 -> 50°, not less.
LC, regarding VAS, i think i couldn't get those good BJT needed from my dealer. So I think another alternative is using MOSFET, BIBGT, etc. I personally think MOSFET is good for me, since i frequently getting VAS thermal problem, so i think it's thermal property would suitable for me (increase in resistant when heated)
Need alot of advise on this since i don't know them at all...... need information such as criteria of choosing for VAS, modifying circuit connection, precaution using them, etc.
As in 2SA1707/4487, i'm thinking of using them as driver/predriver, is it appropriate ? or excessive ?
Need alot of advise on this since i don't know them at all...... need information such as criteria of choosing for VAS, modifying circuit connection, precaution using them, etc.
As in 2SA1707/4487, i'm thinking of using them as driver/predriver, is it appropriate ? or excessive ?
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Maybe that was not clear enough. Barny Oliver optimum point is 26mV across one emittor resistor(plus re of the transistor) to set quiescent current. If set to high you get more A class power but after that there is more distortion. 300mA is way to much.
dado
Yes that is not so far away, but in most of the schematics I have seen in this thread it was used 0.22ohm and that gives 110mA or close. It will be good when talking about BJT output stage quiescent current to connect it to the emitter resistor used in a case.
dado
Hi Vladimir, actually we have no disagreement here.
For me it is always a must. Even for SS design. For example, find two vanilla amp designs where amp A is preferred by 60% audience and amp B preferred by 40% audience. Then give a good regulated power supply for the front end of amp B (amp A has no dedicated front end supply). I will not surprised if there would be a massive preference switch to amp B.
I was unable to integrate a tube line amp into my system, until I found out that I have to pay critical attention to the heater power supply. Yes, I use chokes for this.
Of course, for cost-no-object design you wont consider the SSA. Neither do I. I pick the SSA for my class-B high power (at least 75W) amp. For smaller wattage amp, who wants an amp with global feedback???
Bias Levels
If you bias up 26mV across the emitter resistor, then re = Re, since the Zout of an emitter follower is 26/Ic.
This halves the transconductance of the output device, and it may be minimising distortion at crossover because it brings the gm doubling issue into line at the crossover event where this problem is greatest.
Your thoughts, Nico?
Hugh
If you bias up 26mV across the emitter resistor, then re = Re, since the Zout of an emitter follower is 26/Ic.
This halves the transconductance of the output device, and it may be minimising distortion at crossover because it brings the gm doubling issue into line at the crossover event where this problem is greatest.
Your thoughts, Nico?
Hugh
According to upper claims, meaning all output transistors in A-class are way out of their optimal operating conditions, producing unavoidable self distortions ...
Are A-class crossover distortions so more beneficial and prevail over transistor's excessive bias current conditions? Where's optimum? Using 30 pairs of outputs at 100 mA each for proper A-class?
Are A-class crossover distortions so more beneficial and prevail over transistor's excessive bias current conditions? Where's optimum? Using 30 pairs of outputs at 100 mA each for proper A-class?
According to upper claims, meaning all output transistors in A-class are way out of their optimal operating conditions, producing unavoidable self distortions ...
Are A-class crossover distortions so more beneficial and prevail over transistor's excessive bias current conditions? Where's optimum? Using 30 pairs of outputs at 100 mA each for proper A-class?
It looks like you do not understand upper claims.
You put it so simply, it must contain some truth. Using mostly lateral MOSFETS I find that the lowest harmonic distortion resulted between 160-190 mA bias current (using 2SK1058/2SJ162 combination). Since reading John Curl's advice I adjusted Rs for the required 25 mV with acceptable and consistent audible results (proportional local negative feedback).
Whether this number is as Hugh says, or from John's experience or just hocus pocus is hard to tell but it seems to have the desired effects.
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