Making a BD139 voltage follower buffer, need a little help

[Spacehead]

Quote:

Originally Posted by diditmyself /img/forum/go_quote.gif You can use your LM337T. Connect IN to negative rail, ADJ to the emitter of BD139 and OUT via a resistor to the emitter of BD139. BTW, when looking at the schematics I posted: I hope you understand that R9 is just there to illustrate the load of a headphone and not a resistor that should be soldered in the amp.

ok thanks, i'll try it

ok, I didn't think R9 too much, I thought it was just a series resistor for protecting the transistor

 

[Spacehead]

Quote:

Originally Posted by diditmyself /img/forum/go_quote.gif You can use your LM337T. Connect IN to negative rail, ADJ to the emitter of BD139 and OUT via a resistor to the emitter of BD139. BTW, when looking at the schematics I posted: I hope you understand that R9 is just there to illustrate the load of a headphone and not a resistor that should be soldered in the amp.

ok, this works! I guess it is better than a resistor.
My first impression was "Oh, is it a little tighter sound than before?!"

LM337Ts are heatsinked, about 1 watt of power to be dissipated? My rail voltages are 14.5V.

With BD139 and LM337T in op amps feedback loop, there is negligible amount of DC offset in output.



BD139 will burn easily if the headphone plug is pulled right when music is playing? For that reason I have a 5 ohm resistor in series with the circuit, shouldn't it protect transistors? To make sure I don't have to replace them, I always power off when I unplug headphones.

 

[FallenAngel]

I don't think the BD139 is as easy to burn up, not like a high-powered MOSFET.

 

[Spacehead]

FallenAngel , have you gathered the scrap parts together already?

 

[Nemo de Monet]

The BD139/BD140 can withstand a fair bit of abuse. I have an amp I use for testing buffer designs, which has a discrete virtual ground made from BD139s and BD140s. I ran the thing for about three months with one of the BD140s installed backwards, before I one day started to wonder why one transistor was so much hotter than all the others.

I've also been using the BD139/BD140 buffers from the tail end of this thread without any sort of output resistor or capacitor or anything for several months without issue, so I'd say don't worry about them burning up or anything...

 

[FallenAngel]

I "finished" the power supply and amp last night but didn't wire the transformer to test the PSU or the amp at all yet. Tonight.

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif I "finished" the power supply and amp last night but didn't wire the transformer to test the PSU or the amp at all yet. Tonight.

Did you do any modifications to the circuit?

I have some hiss now, it is possibly my ground channel which consist of three op amps

It is
TLE2426 -> LM4562 -> CAPS -> Regulators -> caps -> headphone input ground -> NJM4556+NJM2068 -> Headphone output ground


I could modify it to use 1 op amp and BD139+resistor


The hiss is so small that I don't care about it... The sound is absolutely juicy now! Very detailed and still punchy.

 

[FallenAngel]

I'm using passive ground. Haven't tested yet, will see.

 

[Spacehead]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif I could modify it to use 1 op amp and BD139+resistor

Did that today. I had some problems with dc offset but I got it solved. It took again some hours. I learned that if there is capacitors in front of TLE2426 the op amp after those caps doesn't understand anything about that signal. I tried first voltage divider resistors, but they couldn't supply enough power any there was huge shift in virtual ground. Finally I used second TLE2426 and offset is now gone.

Now I have 3 BD139 in that amplifier. Very powerful sound. I could increase the bias a little to get even smoother sound. Op amps are also biased with JFET current sources, 2SK246 5 mA .

 

[FallenAngel]

Got mine up and running, some noise issues, likely because it's uncased and I have some power lines close to signal lines, also tested without pot. Will play with this weekend and see what I can come up with.

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Got mine up and running, some noise issues, likely because it's uncased and I have some power lines close to signal lines, also tested without pot. Will play with this weekend and see what I can come up with.

My noise issues got solved when I added 5 ohm series resistors to outputs. Those shouldn't affect sound too much.

 

[Spacehead]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Got mine up and running, some noise issues, likely because it's uncased and I have some power lines close to signal lines, also tested without pot. Will play with this weekend and see what I can come up with.

Do you have any pictures of it? What kind of solutions and resistor values did you use? My op amp core is cmoy style, but highly tweaked.

I have now biased ground channel to 200 mA with 68 ohm resistor that is cooled by protoboard.

ps. I have some oscillation problems.

 

[Spacehead]

Quote:

Originally Posted by diditmyself /img/forum/go_quote.gif

hmm is there an error? There is no connection point for -V in the current source circuit?

EDIT: ok didn't use that current source, I used 79M05 instead with 22.5 ohm resistor, which gives me 223 mA constant current, that should be plenty. 79M05 heatsink isn't too warm.

 

[Spacehead]

****, I cannot tweak it anymore. It is complete. But probably I could do it on a perfboard and minimize wire and trace lengths.

 

[FallenAngel]

Yay, got mine finally finished and tested - no hiss in background after installing pot with source connected at max volume, slight hiss with no source but that's expected. Now just have to case it. Simple passive ground. Photos when I'm done.

Now I'm off to building a Sijosae Class-AB style amp running off 2x 9V with CFB opamps ground channel ala Larocco PRII.