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Making a BD139 voltage follower buffer, need a little help

Apr 15, 2008 at 10:43 PM Post #61 of 107
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
Then, I started thinking - there is only 200 Ohms between ground and each channel because both are connected through V-! Wouldn't this prove a little problem?


No, sound will not "leak" through V- across channels like that. As far as AC signals are concerned, V- "looks" like ground. Of course, there is a possibility of supply rail ripple as a result of current draw that could induce a very small amount of crosstalk, but that's miniscule and not obviously audible.

It's strange that a bad opamp causes crosstalk, though.
 
Apr 15, 2008 at 10:53 PM Post #62 of 107
Quote:

Originally Posted by amb /img/forum/go_quote.gif
No, sound will not "leak" through V- across channels like that. As far as AC signals are concerned, V- "looks" like ground. Of course, there is a possibility of supply rail ripple as a result of current draw that could induce a very small amount of crosstalk, but that's miniscule and not obviously audible.

It's strange that a bad opamp causes crosstalk, though.


Thanks amb, it's weird but replacing that opamp with any other fixed the problem, I'm keeping OPA2107/OPA602 in there now, sounds very sweet actually. Runs hot as hell too, heatsink from an old aftermarket CPU cooler is warming up. The LM317 pulling 300mA+ is getting super hot though, I'm worried it'll go into thermal shutdown. I can't keep my finger on the heatsink for even a part of a second. Thinking of what to do.

Even the 100R resistors are getting super hot, it's like a thermos in there, wow! Can't touch the resistors, can't touch LM317, only output transistors are kept at reasonable temps.
 
Mar 29, 2009 at 8:01 PM Post #63 of 107
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
Hey guys,

I was curious into the Heed CanAmp in the way it uses a single NPN transistor (BD139-16) as a voltage follower as the buffer to an opamp, so I decided to make a much nicer amp but include this buffer.

I have a dual regulated power supply (very similar to 2 of Tangent's TREADs) which to power this thing.

The amp circuit is the same opamp amplifier circuit used by the Pimeta/PPAv2 (implements Jung's multi-loop topology, without CCS on the opamp).

The buffer circuit is a BD139-16 voltage follower biased into Class-A using a 100 Ohm / 5 Watt resistor with a 220 Ohm resistor on output (in the feedback loop of the opamp through a 10K resistor).

The schematic looks like this:
myschematicuu3.jpg


I'm getting an output DC of 600mV which drops to 500mV over 10 seconds or so, but hangs around there afterwards.

Any idea on why this is happening, why the Heed CanAmp uses this buffer without DC offset and what can do to fix it?

Thanks!





What are the +V and -V values?
Could someone use only the bd139 in this into class-A configuration to boost up his signal ?
I think tha the tshould add two caps for the input and the output yes?
 
Mar 30, 2009 at 6:57 AM Post #66 of 107
Quote:

Originally Posted by neazoi /img/forum/go_quote.gif
What are the +V and -V values?
Could someone use only the bd139 in this into class-A configuration to boost up his signal ?
I think tha the tshould add two caps for the input and the output yes?



Don't bother with that circuit. It's a wrong one to begin with. Jung multiloop won't work with this type of output stage.

You should read the later pages for the correct schematic.
 
Jan 12, 2010 at 7:08 PM Post #67 of 107
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
Hey guys,

After banding my head against the wall one too many times, I've decided to skip the 2-channel version with the transformer being very close to the amp and just go ahead with the 3-channel version. I'm also thinking of switching the BD139 to MJE243 because the buffer built above was quite a bright one and these should be a little less bright.

This is what the amp schematic looks like:
myschematic3gf0.jpg



I looked at your schematic and did this:
i357ic.jpg


It is also a 3-channel amplifier. It was A47/Cmoy hybrid, now it is something else.
There is regulator providing good steady 18 volts through couple caps, then TLE2426 splits it and drives virtual ground through two caps. Op amp takes tle2426's output and passes it for D882 power transistor which drives headphone ground channel.

op amps in main amplifier board (a47 configuration) are biased to a class with jfet's then signal goes to BD139s and that's it. That picture is old, I don't have those output caps anymore.

I think it is quite complicated already and I don't know should I keep it or not. I am trying to get most hifi sound possible, now it is very good except balance is a little to the left.

A good dual power supply would do good. Also those wires are bad of course.
This doesn't give any DC to my headphones, or 0.01 V.
 
Jan 12, 2010 at 8:21 PM Post #69 of 107
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
Very nice build! Perfboard builds are so much more fun to than PCB.
smily_headphones1.gif


I don't think you actually need "A47 configuration" if you have a buffer, but it's all fun.


Thanks!
Yeah I have been trying to tweak that for better sound and performance. I noticed quite soon that the other op amp there (A47) is unnecessary and doesn't affect sound at all. It works in a Cmoy config now, but I didn't remove the A47 current sharing resistors yet (they are in the signal
frown.gif
). A moment ago I removed the caps from TLE2426's output, I think the sound improved a bit, maybe
tongue.gif

Some op amps oscillate a little bit even I have added all possible decoupling caps. When I tweak it some wires snap off and I have to solder them back, I guess I need to find out a case for this.


And yes, 5W resistors run very very hot. Transistors aren't so hot at 18V. Do you still have this amplifier? At which voltage have you run it?

I think I have enough bass now, these Sennheiser HD-201s bottom out. Actually I have no ideas how to make a better sound now. It is just lovely!

I would like to do a dual power supply, I think I have one transformer that has dual secondary, but I haven't yet learned how to use AC and how to rectify it. It isn't difficult? I have lot of diodes.
 
Jan 18, 2010 at 7:51 PM Post #70 of 107
Could I use 7905 as a CCS to load the BD139s, as I don't have 317

I have BD140, how about that?

I think the circuit draws too much power and things get too hot. How to get rid of the 5 W resistors?
 
Jan 18, 2010 at 8:53 PM Post #72 of 107
Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif
7905 is a fixed voltage regulator, I don't think it can be used as a CSS.


Actually you can. See the "Typical Applications" section (second figure) of the 7905 datasheet.
wink.gif
 
Jan 19, 2010 at 9:20 AM Post #75 of 107
Quote:

Originally Posted by amb /img/forum/go_quote.gif
Actually you can. See the "Typical Applications" section (second figure) of the 7905 datasheet.
wink.gif



and yet I cannot read that circuit schematic.

what's the meaning of the dashed line? Across that resistor a current gets sourced? Could you explain the schematic on 7905 datasheet, when comparing it to FallenAngel's latest working schematic where is 100 ohm 5 W resistor (as a current source?).

If I understood right, using a CCS I was allowed to get class a biasing and at the same time use less power (higher efficiency). I have only a 15 W AC/DC transformer.

I have some JFETs too. And BC550 + BC560

I have been reading that thread: HeadWize: DIY Workshop > Any unusual or highly touted emitter follower amps out there?

It is easier to copy schematics than do your own guessing
smily_headphones1.gif

FallenAngel's schematics are so simple that I couldn't learn much of them, but thanks it works (at heavy power consumption)
 
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