Transistor sounds

[lumanauw]

I believe that these amps are asymetrical. In this case the thermaldrift creates only a DC-offset that can be nearly eliminated by the feedback.

This does not apply to symetrical design. Here the thermal drift can be "symetrical". Let's say thermal drift moves the current to the "left" side, DC does not change, but the bias in the vas explodes. -> Smoke !

Yes, you are right. Both examples are single differential design. So, you are saying, if the design is single differential, it is OK not to use RE degeneration in differential?

 

[sajti]

Hi sajti !

How does speedup-caps at the drivers help if they operate ClassA ?
I thought these caps help reducing on/off-times ?

Mike

This speed up not only the on/of times. But gives more current to increase the speed of charge/discharge the internal capacitors. I didn't test the drivers current, because it much lower than the current on the output stage..

sajti

 

[MikeB]

Yes, you are right. Both examples are single differential design. So, you are saying, if the design is single differential, it is OK not to use RE degeneration in differential?

Principally, Yes. But i think at least small values are good for
stabilizing biasing/DC.

This speed up not only the on/of times. But gives more current to increase the speed of charge/discharge the internal capacitors. I didn't test the drivers current, because it much lower than the current on the output stage..

sajti

I will make some experiments...

Mike

 

[Cortez]

BD139/140

> I don't think that the speed is so important in this case. 30MHz,
> or 50Mhz doesn't make any difference. But MJE has better SOA.

They are much faster ! and at 24V i guess the SOA is not
so an important aspect, isnt ? So please try out the BD-s
too, but only with mark phillips ! Thx !

Check this for the speed, and other datas: http://home.planet.nl/~midde639/specs/BD135_137_139.PDF

 

[MikeB]

hmm, but i only have original onsemi...

 

[MikeB]

according to the philips-datasheet, the bd139 is better then some
wannabe smallsignaltransistor !
What do you think, are the ON-devices of same speed and beta ?
The ON-Sheet is crap...

Mike

 

[Cortez]

Then try to find a place, where you can buy phillips bd-s !
And after all did you tried with onsemis BD ?

 

[sajti]

according to the philips-datasheet, the bd139 is better then some
wannabe smallsignaltransistor !
What do you think, are the ON-devices of same speed and beta ?
The ON-Sheet is crap...

Mike

The chip inside the BD139 is same as in the BC639. So practically this is a small signal transistor in power package...

sajti

 

[MikeB]

Ah, then i will try this this evening with the ON-devices !

Mike

 

[Cortez]

And where are the results ?

 

[MikeB]

And where are the results ?

Hmm, had no time yet to heat up the iron...
It's not a simple replacement, the to220 are screwed to the heatsink,
for the smaller bd140 this hole is too far up, and the pinout is different.
So i need a separate heatsink for those. As i use bias of 40ma, i can't
drive them without heatsink.

Mike

 

[Cortez]

Ok ! I'am just curious about the result...

 

[lumanauw]

Hi, Mike,

Got a question. Is there any difference if we built a CCS with MOSFET or Bipolar? What the SIM tells? Which is better audibly?

 

[Cortez]

Try it ! I'am affraid that's the only way to know it !
The simus maybe can help in simple electronic situations,
but the sound is a much more complex thing...
The listening tests are good to get real (!) information !

 

[MikeB]

Hi, Mike,

Got a question. Is there any difference if we built a CCS with MOSFET or Bipolar? What the SIM tells? Which is better audibly?

hi lumanauw !

I made some sims, ccs for diffamp and vas.
Output was 30v,20khz into 4ohm

The results: (2nd,3rd harmonic)

normal bjt
531uV
298uV

normal mosfet
640uV
271uV

cascoded mosfet
523uV
303uV

cascoded bjt
534uV
306uV

cascoded jfet
528uV
301uV

There's no big difference in harmonics, i would say use the normal
ccs with 2 bjts. The mosfet-ccs in the vas might not be the best
choice because of big Vgs. You will get asymetrical clipping.
I did not test the 2diodes version, in recent simulations it was
outperformed by the 2bjt version. I will never use it again...
I did the mosfet-ccs with 1bjt+1mosfet.
The jfetversion is one jfet+1resistor+cascode.
"normal jfet" is missing because jfets don't withstand that high voltages.

Of course this does not say much about the sounding.

Mike

 

[lumanauw]

Hi, Mike,
Thanks for exploring. If there's no big difference, I will go with bipolars, since it has small VBE and small drop, and the VBE is much-much predictable than mosfets.
I usually made this bipolar CCS with LED drop for reference. How is this compared with 2 bipolars like you used?

 

[Cortez]

That interest me too ! And what about the cascoded CCS ?
A lot of people have a good opinion about this solution !

 

[MikeB]

Hi, Mike,
Thanks for exploring. If there's no big difference, I will go with bipolars, since it has small VBE and small drop, and the VBE is much-much predictable than mosfets.
I usually made this bipolar CCS with LED drop for reference. How is this compared with 2 bipolars like you used?

Hmm, can't say, have no sim-model of LEDs...

That interest me too ! And what about the cascoded CCS ?
A lot of people have a good opinion about this solution !

I don't know, in sims it didn't make a big difference, it might be much
bigger if you work with diodes or leds. But like always, sims don't tell
you about the sound...

Mike