# Making a BD139 voltage follower buffer, need a little help



## FallenAngel

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:






 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!


----------



## TzeYang

erm are you sure you can multi loop this? The HEED IIRC uses conventional single set of feedback resistors to control the gain and set feedback. Plus, there is a capacitor to ground at the feedback loop (this method makes sure that DC isnt amplified.)


----------



## FallenAngel

Well, I tried with multiloop and single loop but the offset is exactly the same. I did notice the Heed having a capacitor to ground following the 1K resistor, and noticed the same in the GainClone I'm building, but didn't try that.

 That's probably what it's there for. I'll see what I can do with it. I don't think I have any high quality caps to go there, so I might have to go with a Panasonic FM. Any idea on what size it should be? The Heed (and a similar BD139 buffer) shows 10uF, the GainClone shows 22uF and general GainClone discussion suggest 47uF. I'll have to check what I have.

 I think I have a pair of 470uF BlackGate Standard series, 4.7uF Nichicon Muse ES and a pair of 47uF BlackGate NX but they are only 6.3V.


----------



## majkel

You built too complictaed and DC-uncompensated feedback loop, that's why you get offset voltage.
 1) Remove parts: 1M, 475k, 3.32k
 2) Replace 4.32k for 910 ohm
 3) Replace 200 ohm resistor for wire.
 4) When strange behavior occurs, add capacitor parallel to 10k resistor, starting with 22pF. If still unstable - increase the capacity, if stable - try to lower the capacity as much as possible.


----------



## FallenAngel

Majkel:

 The 1M to ground on input is to set the impedance and I think it might be a good idea to keep it so the source doesn't see 0-50K which changes with volume setting.

 475K and 3.32K are for multiloop - I can definitely remove those and make it single loop.

 I'll change the 4.42K on the input to 1K (I don't have a 910 Ohm handy).

 I'll see how this works, hopefully there won't be much "strange behavior".

 What do you think about adding the capacitor in the feedback loop?


----------



## majkel

You can place 10k parallel to 1k in place of the 910 ohm, and then will be perfect. 1k is probably still OK, just observe the offset voltage. Your explanation for 1M resistor is invalid. The source always gets 50k of load, whatever setting of volume is applied. If it makes you feel better, leave the 1M resistor in it's place. BTW, what op-amp are you using? I guess at such a high gain =11 there won't be any instability and the additional capacitor won't be necessary.
 One more thing: use a pot of lower impedance, for instance 10k, then it will be easier to compensate the offset voltage when you use op-amps with high input current (read: many bipolar).


----------



## TzeYang

ah yes, bipolars. But since this is quite an experiment, would it not be safer to use fet input opamps first? (fallenangel did not specify which opamp but i was just making an assumption lol)


----------



## NelsonVandal

Tori amp with BJT
HeadWize: DIY Workshop > Changing the Tori amp to use a BJT


----------



## TzeYang

the circuit actually works. I did a simulation just to be sure. offset is extremely low. Of course, without jung multiloop and OPA627 as opamp.


----------



## amb

Yup, you can't multiloop this design because the opamp's output needs to be Vbe=~0.6V higher than the BD139 emitter (where you want it to be 0). The inner loop would force the DC offset up.


----------



## ~n00beR

Not of a multi loop design however, after examining the pictures of the amp (google images) I came to the attached schematic.

 It seems to simulate fine in TINA however, im new to using the software.

 Any comments suggestions welcome


----------



## FallenAngel

New schematic following (most of) Majkel's advice






 Opamp in there was an OPA2227 (which might have fried during initial testing since offset was 600mV), but after replacing it with OPA2132 and OPA2134 the offset is 150mV and 200mV respectively. Still definitely not a good thing, but better. Just to test, I tried thowing in a pair of OPA637 - the offset is 300mV with those.

 I don't think the 200 Ohm resistor is the culprit (at least I hope not).

 Any ideas on what else I could try (except for adding resistor parallel to 10K (I don't have a very small one handy, just 0.1uF X7R Ceramic)

 Also, if going with the capacitor to ground after the 1K resistor (I heard this is a bad thing for audio in general), what voltage rating does it need to be?


----------



## ~n00beR

In the canamp, the capacitor to ground in the feedback loop is an electrolytic, 10uF/100V

 I think the main problem is that you are missing the input capacitor.

 I have simulated the effects of with and without the input capacitor, and it needs to be there.

 The use of the capacitor to ground in the feedback does effect the offset, however as far as i can tell the offset will still be low enough for headphones without it.. However if both are not there, as we both now know damage will be done.

 Input cap is 0.47uf non polar.

 Hope this is of some help


----------



## amb

Why do you have that 200R resistor at the output anyway? The reason for the BD139 being there is to serve as a current booster, but all that benefit is lost on that resistor... If you must use a resistor there, it should be very low value, not hundreds of ohms.

 I also suggest adding a series resistor at the base of the BD139, so that the opamp isn't driving the base directly. Something like 47-100 ohms should do. It will help prevent parasitic oscillations. I also suggest a small value capacitor going from the opamp output to its inverting input (see the M³ amp schematic, or the Pimeta's ground channel as example). This should also help with stability.

 Inserting a cap from the bottom of the 1K resistor to ground will give 100% NFB at DC and will surely reduce output DC offset, but you will need a large value electrolytic... 10uF will yield a high-pass -3dB frequency of around 16Hz in this circuit. This cap should normally "see" very little voltage but you should use something that is rated at least the rail voltage just in case. Also, it should be a non-polar cap.


----------



## ~n00beR

ahhh, miss read the begining of the thread 
 Yes, listen to amb


----------



## majkel

Nice too see another advice for 200 ohm resistor removal. If you keep it, then the transistor makes disputable sense in this circuit. I also agree to putting a resistor between the base and the op-amp out, however if the oscillations are about to occur, they will surely do even with the resisitor.
 Another thing - I said remove 1M, you placed 100k. :| Next time I say "stand up" when you are sitting, you will lay down. 
 And the last thing. I HATE OPA2227's sound. Dark, dull, emotionless, boring, annoying, gimme more adjectives...


----------



## ~n00beR

Although the value maybe high, I thought the reason for putting a resistor to ground at the input signal was to prevent DC offset if the pot wiper lifts off the contact surface?


----------



## majkel

Quote:


  Originally Posted by *~n00beR* /img/forum/go_quote.gif 
_Although the value maybe high, I thought the reason for putting a resistor to ground at the input signal was to prevent DC offset if the pot wiper lifts off the contact surface?_

 

This is true but, would it happen? On the other hand, you'd still hear the unpleasant scratch with the 100k resistor. This resistor makes more sense when we build an AC-coupled input, and then AMB's suggestion about the capacitor between 1k and ground is valid. Otherwise - not.


----------



## FallenAngel

New schematic - still a huge offset, but different value, now it's around 300mV 
	

	
	
		
		

		
			










 Going to play around with this thing some more later today


----------



## TzeYang

i'm pretty sure you have to install a cap from the 1K resistor to ground. 
	

	
	
		
		

		
		
	


	




, at least the Heed CanAmp does so.

 And since you're using FET inputs why bother with 910ohm resistors? Wouldn't it be better to use a higher value so to balanced the input bias?


----------



## ~n00beR

As i said before the heed amp has a non polar cap in series witht the input signal.
 I have found that this cap has the most effect on offset.

 Just to test it you could use a polarised cap, and changed to a non polarised cap when you get one.

 Using the input cap should take you into the 10's of milivotlts range (30 ish), using the input cap and the feedback cap should take it even lower.

 Input caps are not all that bad, many people use them as upgrades to "smooth out" the sound.

 Hope this helps 

 n00b


----------



## NelsonVandal

Now it's almost a Tori amp. Why not use the exact values suggested by PRR. It's supposed to be working. Is your opamp healthy? What does the ground look like?


----------



## majkel

Quote:


  Originally Posted by *~n00beR* /img/forum/go_quote.gif 
_As i said before the heed amp has a non polar cap in series witht the input signal._

 

And this is the only case that both caps make sense - .47uF~1uF non-polar instead of 910 ohm resistor, and 10uF in series with 1k. Then the pot can also be of higher resistance with no impact on the circuit.


----------



## FallenAngel

Hey guys,

 Thanks for the generous amount of help here, and as I feared, the problem was not with the circuit, but with my oversight in building it. I accidentally shorted the Output of the chip to the inverting input during construction (I plan on paper and then transfer to perfboard, so changes in circuits are harder to track). When I cut the 475K resistor for the inner loop, I attached the two points.

 After waking up this morning with a vision in my mind of why this doesn't work (yeah, I'm strange that way, I can wake up in the middle of the night and have all sorts of weird realizations about things I was thinking about earlier). Quickly rushing out of bed and cutting that connection, I get a DC offset of 0.0mV, like NONE. As _amb_ said earlier, the output of of the opamp is around 0.6V, but after the transistor, it's 0mV.

 I haven't tested that the amp works yet (no actual input/ouput wired), but I'm think it will.

 So.... any suggestions on how to make it sound better? I'm going to lower the gain to about 4 to make it reasonable.

 EDIT / UPDATE : Well, being the impatient person I am, I wired everything up and it sounds pretty damn good! Nice and clean, no noise at all with 32Ohm Grado SR225 even though the transformer is within 6" of the amp. Thanks a bunch to all who helped out with getting the design up to this point.

 I will be rebuilding this amp to make it smaller and look nicer sometime this weekend, if anybody has suggestions on what to do differently, they would be appreciated. Thanks!


----------



## FallenAngel

Quick question guys, how much heat can these BD139-16's handle? The heatsink gets VERY hot, I've had the amp running about 2 hours (and it sounds wonderful), but the heatsink is too hot to touch. I can't get much info from the datasheet, just that the Maximum Junction Voltage is 150V.


----------



## MisterX

That is way to hot.


----------



## FallenAngel

Thanks, very descriptive 
	

	
	
		
		

		
		
	


	




 It's not exactly too hot to touch, just too hot to keep a finger on for more than 5 seconds without some kind of meditation.


----------



## TzeYang

i had experience with modding the heed can amp. They are in fact operating at temperatures where i cant lay my finger on the heatsinks for more than 5 seconds.






, not to say it's wrong but i would rather switch to a larger heatsink.


----------



## FallenAngel

I've got another somewhat bigger CPU heatsink around, I'll switch to that one and report back if it still gets hot, but with the size of that monster, I'm thinking it'll be fine.


----------



## MisterX

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Thanks, very descriptive 
	

	
	
		
		

		
		
	


	




 It's not exactly too hot to touch, just too hot to keep a finger on for more than 5 seconds without some kind of meditation._

 


 Ironic you mentioned the 5 second rule of thumb because I had actually typed that in my "very descriptive" reply but removed it because I felt it came across as patronizing when I previewed it. 
 Don't go overboard with the heatsink here cause you don't need to.
 (the heatsink for a tread is better suited for this role then a cpu heatsink)


----------



## ~n00beR

Some kind soul allowed me to look under the cover of there canamp.

 The schematics from around the web appear and my own (from pictures) are wrong.

 My schematic shows R4 at the emmiter of the transistor, as amb and majkel have suggested it should be between the opamp and transistor, this is also the correct configuration in the canamp.

 The amp i managed to get a look at has been modified and has had the input capacitors removed, with no measurable problems, as well as having a regulated PSU and upgraded caps and rectifer diodes.
 It sounds very nice indeed.

 However i couldn't figure out what the capacitor that sat at the top of the opamp is for?!?

 Anyway glad to see your amp is working


----------



## majkel

5 seconds with no harm to the finger means the transistor will survive.


----------



## FallenAngel

Thanks for the advice, but being overanxious as I am, I already cut this one to size. Pics soon


----------



## FallenAngel

Hey guys, a question regarding changing the power supply in this amp. If I was to make this amp with a virtual ground off a single secondary 24V AC transformer, which virtual ground scheme would you recommend? Since this amp has a huge output current would the easiest thing be to simply add another opamp + BD139 to drive the ground and would it need to pull double the current?


----------



## amb

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Since this amp has a huge output current would the easiest thing be to simply add another opamp + BD139 to drive the ground_

 

Yes. Better yet, do it M³/Mini³/PPA/Pimeta style. Use a TLE2426 as rail splitter for the nil-current signal ground, and use your 3rd channel to drive the output ground return from the headphone.

  Quote:


 and would it need to pull double the current? 
 

The ground channel will source/sink the combined return current from the left and right channels, and if such signal is in-phase mono, then it would indeed be double. But the BD139 output stage has plenty of current capability so it doesn't really matter.


----------



## FallenAngel

Thanks amb, I'll be making a 3-channel of this soon and will try it using the same ground scheme as those.

 I just noticed something today when I was changing the gain on this amp. I messed up with one connection and locked the gain to about 2.

 This is the schematic as it should be:





 This is what I actually connected:





 Now I'm not sure what this actually did and it does sound great, but the gain is too low and I wanted to raise it. When I "fixed" the amp by making it exactly by the schematic, I got a very nasty buzzing noise in the headphones. Still no offset, just this irritating buzzing noise. Not really a hum, a definite buzz.

 Any ideas on what to do with it?


----------



## amb

The wiring mistake yielded a unity-gain amp. Not gain of 2.

 As for the buzzing, is your amp enclosed in a metal case and properly grounded? How far away is the power supply and its transformer from the amp? By the way, the "fixed" version has a gain of 11. If you have low-Z or sensitive headphones it might be too much gain, and you'd hear noise that might otherwise go undetected in a high-Z phone.


----------



## FallenAngel

Thanks amb, I guess the unity gain buffer was a very nice sounding one as well, 
	

	
	
		
		

		
		
	


	




 It also was completely noise-free.

 I updated the schematic, it was actually with a gain of around 4, but now it's with a gain of 6 using a 4.7K feedback resistor.

 It is in a mesh metal chassis with a toroidal transformer about 4 inches away from the amp module and the power supply between the transformer and amp.

 The thing that I'm curious about is that there was absolutely no noise when it was configured as a unity gain buffer and there is quite a bit of a buzz now. Any ideas how that happened?


----------



## amb

There is a difference of almost 16dB between unity gain and gain of 6. Any amount of inherent noise, as well as interference (most likely from the transformer, but you could also have other sources of RFI and EMI) are amplified by the gain of the amp.

 4 inches between the transformer and the amp is not a lot of distance especially if the transformer is sizable or if it's an EI-core unit. You can try turning the transformer so that the mounting orientation is changed, to see if it makes any difference.

 Also, is your mesh metal case grounded? And how is it grounded?


----------



## FallenAngel

I did a little test today. I took the amp module, rca jacks, pot and headphone jack all out of the case, ran a 3ft power cord to it and had a listen and surprise, surprise, there is exactly the same buzzing noise in the circuit. I then rebuilt the entire thing in a slightly different layout with the same results 
	

	
	
		
		

		
		
	


	




 Now I'm really frustrated and confused to where this noise could be coming from and why I only hear it when the amp has gain.


----------



## amb

You did not describe the grounding scheme. Bad grounding causes noise. Also, some pictures might help.


----------



## MisterX

PICTURES!


----------



## FallenAngel

Photo of basically how it looks when not in pieces.




 PSU is basically 2 TREADS with the a +/- tied together forming a ground.

 All grounds go to this point: headphone jack, pot, RCA input and single point on the amp board (there isn't much grounded, just a pair of 1K resistors).


----------



## FallenAngel

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:


----------



## majkel

Why don't you build a classic symmetric PSU, instead of messing around with all that ground channel and virtual ground stuff? 
 What you need is:
 - center tapped transformer or with two equal secondary windings (better), 12~17V AC output
 - one or two (better, only when you have double secondary winding transformer) Graetz bridges
 - some 'lytics
 - 7812S and 7912S chips
 Sorry for not providing the schematic ATM but I'm in work, away from my EDA software now.


----------



## 00940

majkel.... the ground output too is buffered by a bd139

 edit : you edited your post in the meantime


----------



## majkel

Quote:


  Originally Posted by *00940* /img/forum/go_quote.gif 
_majkel.... the ground output too is buffered by a bd139

 edit : you edited your post in the meantime 
	

	
	
		
		

		
		
	


	


_

 

Yep, I realised the ground buffer later. I was reading in a small IE window, you know...


----------



## bearmann

Ummmm... my I ask, why you have to use a virtual ground power supply, when using a ground channel?
 So you can't use a dual power supply?

 sorry for this dumb question and best regards,
 bearmann


----------



## tyre

.


----------



## FallenAngel

Quote:


  Originally Posted by *majkel* /img/forum/go_quote.gif 
_Why don't you build a classic symmetric PSU, instead of messing around with all that ground channel and virtual ground stuff? 
 What you need is:
 - center tapped transformer or with two equal secondary windings (better), 12~17V AC output
 - one or two (better, only when you have double secondary winding transformer) Graetz bridges
 - some 'lytics
 - 7812S and 7912S chips
 Sorry for not providing the schematic ATM but I'm in work, away from my EDA software now._

 

Basically because I just tried that and is what I had all along. Dual secondary transformer with 2x 12V AC outputs, followed by 2 diode bridges and a 2 LM317 based power supplies (I didn't have an LM337 handy so I used a pair of these and tied the output to form a ground). The power supply is almost exactly Tangent's TREAD. It was outputting exactly +/- 12.5V. I think there was a nice and clear 60Hz buzzing noise and I can't get a very good AC ripple reading from the PSU because my DMM goes all crazy trying to measure it.


----------



## majkel

TREAD is just a positive half of your destination PSU. You have to build a complementary circuit using LM337 (with some changes) and then create the ground from the (-) voltage of the positive supply section and (+) of the negative supply section connecting them together.


----------



## FallenAngel

Quote:


  Originally Posted by *majkel* /img/forum/go_quote.gif 
_TREAD is just a positive half of your destination PSU. You have to build a complementary circuit using LM337 (with some changes) and then create the ground from the (-) voltage of the positive supply section and (+) of the negative supply section connecting them together._

 

But if I make 2 TREADs and connect a V- from one to the V+ from another, it creates an equal ground, no?


----------



## amb

Yes, you could make two TREADs and hook it up as a split supply -- in fact this is a better solution than using a LM337 for the negative rail, because the LM317 performs better than LM337.

 However, using a single TREAD and then splitting it into a dual rail supply with TLE2426 is cheaper than doing two TREADs, and offers a performance advantage in a 3-channel output application (where headphone return ground current isn't dumped into the virtual ground). It gives you the benefit of a _tracking_ dual rail supply because the TLE2426 will self-adjust the split, without the complexity and cost of a real tracking split-rail PSU.


----------



## majkel

Using positive regulators for the negative rail is kind of weird because then you will have the negative voltage regulator referenced to the rail instead of the ground. However, it might work but is suboptimal.
 Regarding the TLE2426, better replace it for a decent op-amp as a buffer + resistor divider. TLE2426 itself has got an unpleasant sonic signature when used that way. You can civilize it's influence by placing a ~100uF capacitor between it's output and either rail (try which, because the choices slightly differ - due to different phase shift at the TLE's output).


----------



## amb

Quote:


  Originally Posted by *majkel* /img/forum/go_quote.gif 
_Using positive regulators for the negative rail is kind of weird because then you will have the negative voltage regulator referenced to the rail instead of the ground. However, it might work but is suboptimal._

 

You might think it's weird, but voltages are simply a difference in potential, and when the two regulators are each referenced individually, neither one "cares" which is positive or negative, as long as it's hooked up appropriately. Using two positive regulators to make a +/- split supply is nothing new and has been done by many designers in many circuits. Even the dynahi PSU does it that way in the pre-regulator stage.

  Quote:


 Regarding the TLE2426, better replace it for a decent op-amp as a buffer + resistor divider. TLE2426 itself has got an unpleasant sonic signature when used that way. You can civilize it's influence by placing a ~100uF capacitor between it's output and either rail (try which, because the choices slightly differ - due to different phase shift at the TLE's output). 
 

Sorry, but that's nonsense. In this circuit the TLE2426 does nothing more than provide a mid-way split in order to serve as the signal ground zero reference, and to provide the sub-microamp current required to bias the opamps' inputs. It swings no voltage nor is it asked to sink/source appreciable current, so what does _phase_ have to do with it? Look at the schematic carefully and see what nodes are actually connected to the virtual ground. The TLE2426, when used in this way, imparts no sonic character to the amp at all.

 Oh and btw, what do you think is inside a TLE2426 anyway? It's a resistor divider and a buffer! And a fairly good one at that.


----------



## FallenAngel

Hey guys,

 I'm about to finish up with the 3-channel version, but have a quick question regarding the input resistor (latest schematic shows 4.32K). I will only be using FET opamps and I know this resistor is used to balance input impedance on FET opamps and trim DC with bipolar opamps. What's a good value, as I'm seeing different values all over the place. Mini3 v2 is 330R, PINT was 1K, majkel suggesting 910R, Pimeta/PPA are 4.32K. What would be a good value for FET-only opamps?

 Thanks in advance


----------



## TzeYang

My personal favourite is 4.7k for non inverting input, and 4.7k for feedback, and the feedback ground resistor 1k~2.2k

 Generally, you don't want too much or too little for the input impedance. Best of all, remind yourself to balance the input bias to minimize error.


----------



## majkel

Where TF is my post sent a couple of days ago in response to AMB's post #55?! When somebody doesn't understand my explanations this doesn't mean I was wrong. 
*To the mods: As a common rule I suggest sending me PM when deleting my posts and include a brief explanation. *
 When comparing the abilities - mine are MSc degree in Electronic Engineering + 6 years of professional experience. Tell me yours. 
	

	
	
		
		

		
		
	


	




 FallenAngel, sorry for the off-topic, that pissed me off.


----------



## amb

FallenAngel, for an FET input opamp, the value of that resistor is not very critical because the input bias current is so low, there is no need to worry about balancing the resistances on both inputs for low DC offset. A few hundred ohms to a couple of Kohms are all ok.


----------



## FallenAngel

So I built this latest 3-channel amp and I get some very strange distortion and symptoms. I can disconnect one channel of the source and I still get sound in both headphones. I have also discovered that it is not a wiring / pot problem.

 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?

 EDIT: Sorry, bad opamp, damn OPA627 burned! Now it's fixed and sound pretty darn good! Photos soon!


----------



## amb

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.


----------



## FallenAngel

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.


----------



## neazoi

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:






 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?


----------



## FallenAngel

I used around +/- 12V.

 What do you mean by "boost signal"? The BD139 is used as a buffer, it does not amplify voltage, only current. If you want to take the opamp out of the picture, yes, I think you would need input and output caps, or a DC servo and an input cap.


----------



## rds

Nice work FallenAngel, I hadn't seen this before. It was a good Sunday "morning" read.


----------



## TzeYang

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.


----------



## Spacehead

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:



_

 

I looked at your schematic and did this:





 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.


----------



## FallenAngel

Very nice build! Perfboard builds are so much more fun to than PCB. 
	

	
	
		
		

		
		
	


	




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


----------



## Spacehead

Quote:


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

	
	
		
		

		
		
	


	




 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 
	

	
	
		
		

		
		
	


	




 ). A moment ago I removed the caps from TLE2426's output, I think the sound improved a bit, maybe 
	

	
	
		
		

		
		
	


	



 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.


----------



## Spacehead

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?


----------



## FallenAngel

7905 is a fixed voltage regulator, I don't think it can be used as a CSS.

 BD140 is a PNP part, I think you still need to stay with NPN.

 That resistor sees a lot of heat, kind of need to keep it that rating.


----------



## amb

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.


----------



## FallenAngel

What do you know, it can be used as a current source.


----------



## diditmyself

Use one of your BD139's as a current sink with a resistor and a LED, zener or two diodes. This is standard procedure, and cheap. Current source - Wikipedia, the free encyclopedia


----------



## Spacehead

Quote:


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

	
	
		
		

		
		
	


	


_

 

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 
	

	
	
		
		

		
		
	


	



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


----------



## diditmyself

A class A amplifier is inefficient by nature and single end is the least inefficient of them all, so these kind of amps will generate some heat. Besides being ininefficient, a single end amp can't operate in class AB, so you'd want some margins which will make it even hotter. Since you don't need that much power driving headphones, this is no major problem in a stationary amp. Just use a proper heatsink.


----------



## diditmyself




----------



## Spacehead

thank you for those schematics, diditmyself

 I forgot to order LM317, but I am getting 12.5 ohm resistors (0.6W) and extra BD139s
 but I don't have 6.8 ohm resistors (at least I don't remember having). 

 Could I use 7905 and 12.5 ohm resistors to create a constant current source for BD139?


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_ 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._

 

How much current you think this whole circuit takes? I am trying to build a small power supply that would be powered from a 6 W DC-DC converter.


----------



## FallenAngel

Well, it's about about 100mA per channel for that BD139 buffer.

 All this talk about this thing made me want to build another one from scrap parts. Waiting for PSU now.


----------



## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Well, it's about about 100mA per channel for that BD139 buffer.

 All this talk about this thing made me want to build another one from scrap parts. Waiting for PSU now._

 

That's pretty cool you are hooked again 
	

	
	
		
		

		
		
	


	




 But 100 mA with that 5 Watt resistor? High voltages? I am wondering if that 6 W DC-DC converter will be enough... It was cheap so I had to buy it for fun!


----------



## diditmyself

The values in the 1st schematic isn't absolute. They should give a constant current of about 100 mA, but the 6.8R resistor might have to be adjusted. I don't know if 100 mA is sufficient for you. It depends on the impedance of your phones and how loud you want to listen. When using LM317 you can calculate the resistor value and be sure that it matches reality.


----------



## Spacehead

I have now learned through experimentation, that only the ground channel is important if better current driving ability is needed. I am now listening to amp that has 2SD612K in ground channel. RMAA says that noise level is -88 dB and dynamic range also -88 dB.
 I am having hard time getting THD low enough. It is now 0.2%. I am using batteries (6x1.5V NiMH). 
 Dual mono cmoy configuration , with OPA1611 x 3

 FallenAngel, did you get that PSU already?



 edit: both amplifiers give some ringing on high frequencies. I don't know what is causing that. Maybe I should use only electrolytics.

 edit2: ringing fixed with proper decoupling of op amps. THD dropped to 0.039%. But now I notice that it doesn't properly give current to my 24 ohm cans. I need to add some power transistors to left and right channel op amps feedback loop. then it rocks, and with batteries!!


----------



## FallenAngel

2x 15V transformer has landed, making an LM317/LM337 split supply now, should have photos up this weekend.


----------



## Spacehead

Cool

 I didn't want to play with AC mains voltages and split the wall wart supply with TLE2426 buffered with NJM4556(bridged). My wall wart gives 17V, so I get about +6.56V and -6.56V with 7805/7915 (made adjustable). Now that I think of it, the rail voltages are pretty low. Bridged NJM4556 is parallel with bridged NJM2068 , so I get about 250-300 mA virtual ground. Parts don't get hot except BD139 and their resistors. 
 Next wall wart that I have, gives 33 Volts at no-load. That is quite a lot , after regulating I should get 14.5V rails. That would be plenty, but some op amps can't stand that high voltages. 
 I have also been modding my Sound Blaster X-FI. But something is wrong as I get bad THD value.


----------



## Spacehead

I had to test the 24V 300 mA wall wart. The regulators output 11V. I couldn't hear any difference in sound. I think it is as good as it can be. 

 One thing I would like to do. I would like to add BD140 so that it would be Push-Pull configuration. How about DC then? And how would the circuit look? Adding another transistor in parallel should decrease distortions and noise.


----------



## Spacehead

Quote:


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







_

 

ok I bought LM317LZ and not LM317T

 Is it ok to use LM317LZ, it handles only 100 mA max ?! 

 I also have LM337T. How can I proceed to do a CCS for BD139s? 

 I also have couple JFETS, 2SK363 and 2SK246 ...


----------



## TzeYang

short answer no. use the LM317T.


----------



## Spacehead

Quote:


  Originally Posted by *TzeYang* /img/forum/go_quote.gif 
_short answer no. use the LM317T._

 

ok, I calculated the power dissipations and came into conclusion that LM317LZ can't take it. 
 Too bad. I guess I need to settle in for wirewound resistor.


----------



## diditmyself

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.


----------



## 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.


----------



## forsakenrider

Quote: 





diditmyself said:


>


 

 I just built this amp based on this schematic with a +/- 15v supply. I was getting 200-300mV offset after building it. I swapped the opamp and it because 2v, so I swapped back and still 2v! DO'h! It's bedtime now but when I get up tomorrow I hope someone has some pointers.


----------



## forsakenrider

Well I Changed R2 to 470k and R11 to 220 ohm, addeda 47uf cap across the +/- voltage point (Power supply is separate), and all seems well!


----------

