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Old 14th November 2006, 09:26 PM   #1
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Thumbs up Best sounding headphone amp from Wavebourn to Kubeek :)

Quote:
Originally posted by kubeek
Wavebourn, are referring to the schema posted by lineup? Could you post your altered version?
Here you go:

Click the image to open in full size.
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Old 14th November 2006, 10:10 PM   #2
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Let it be V1: BC550BP
V2,V3: BC237
V4,V6: BC135
V5: IRF610

For the same voltage gain R5=680, R6=220

But since the generic output follower is loaded by a current source, for maximum output voltage swing we should apply 8V to the gate, it means 4V on output.

It means emitter of V1 will see approximately 2V, base will see approximately 2.5V

For standard 47K input impedance let R1,R2 will be 100K each, R3=160K.

R4=5.1K

If to assume that idle current is 200 mA, beta of V9 is 100, R7=3.9K
R8 is preventing oscillations of the FET, let it be 1 KOhm, R9 let's take also 1K, R10=200 Ohm.

Maximal output swing will be about 4V if powered from 12V source, it is enough for forte-fortissimo with almost any headphones.
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Old 14th November 2006, 10:15 PM   #3
lineup is offline lineup  Sweden
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hey Wavebourn

I think I know what you were after in my headphones amplifier topic.

The attachment here, I posted already in December 2005
right after joining diyaudio as lineup.

I guess you mean like the first voltage stage in my schematic below.

Yes, this is one of my favourite voltage gain stages, all categories!
Simple - fast and very good!
This stage is often found in older discrete video amplifiers applications ......

I might put together and make some comparing simulation tests
using this topology for a second headphone amplifier.
I am not sure this 'your suggestion' would be the loser


-----------------------------------------------
The first time I posted this Eagle schematic was in

diyAudio Forums > Top >Amplifiers >Solid State >simplest amplifier possible with BJT's
See this post #90
http://www.diyaudio.com/forums/showt...165#post797165


regards
lineup
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Old 14th November 2006, 10:21 PM   #4
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Lineup, this stage reflects K.I.S.S. principle that may be properly applied to audio design as well. When people run for symmetrical distortions they run against Mother - Nature that generates symmetrical distortions only when mechanical oscillating systems are abused. Also, designs that show higher THD on lower powers are again go against Mother Nature: the louder is the sound in reality, the reacher it is with harmonics.

People who run for symmetrical distorting amplifiers that distort symmetrically and the more distort the less is loudness, hawe to feed the sound to some Matrix robot, instead of to real human ears and bodies.
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Old 14th November 2006, 11:27 PM   #5
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by Wavebourn
Let it be V1: BC550BP
V2,V3: BC237
V4,V6: BC135
V5: IRF610
Too bad the transistors are not marked in your schematic, but fortunately we can make educated guesses . BTW shouldn't V4, V6 be BD135 (not BC135)?
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Old 14th November 2006, 11:35 PM   #6
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Quote:
Originally posted by ilimzn


Too bad the transistors are not marked in your schematic, but fortunately we can make educated guesses . BTW shouldn't V4, V6 be BD135 (not BC135)?
Oops... Sure, BD135 - the same as in lineup's version!

Probably, a current mirror instead of R9 containing a diode and resistor in series will improve current source's linearity, but anyway it has much higher dynamic resistance than resistors in Lineup's design, so let's leave it as is and try this way.
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Old 16th November 2006, 05:46 PM   #7
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Hi Kubeek, any success?
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Old 16th November 2006, 05:53 PM   #8
kubeek is offline kubeek  Czech Republic
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No success, I yesterday tried to simulate your circuit, and I wasnīt able to get it working, I couldnīt achieve the output stage to have some reasonable current through it, the mosfet doesnīt open enough.

I am not sure if I didnīt make any mistakes when redraving the picture, the output stage is quite complicated.

BTW you forgot to nuber the transistors, so I canīt tell vhere the stated voltages should be. Also the mosfet is a little bit ambigious, but as it is IRF610, it should be N-type with source pointing down, right?
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Old 16th November 2006, 06:07 PM   #9
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Quote:
Originally posted by kubeek
No success, I yesterday tried to simulate your circuit, and I wasnīt able to get it working, I couldnīt achieve the output stage to have some reasonable current through it, the mosfet doesnīt open enough.

I am not sure if I didnīt make any mistakes when redraving the picture, the output stage is quite complicated.

The output stage is actually very simple, though uncommon:

At top: FET and BJT followers in parallel. When "MOSFET does not open enough" BJT emitter follower does the job.

At bottom: current source, current depends on input voltage, R7 and beta of right bottom BJT transistor.


What load did you try it on?

Idle current depends on R7. 3.9K on 4v gives approximately 1 mA.
If beta of current amplifier (bottom right transistor) is 100, idle current will be 100 mA. Maximum peak current will be (8V/3.9K)*100 = 200 mA. It means, 6/0.2=12 Ohm minimal load impedance. Good enough for 32 Ohm headphones.

However, if you are going to drive speaker, or lower impedance headphones, or beta of transistor is much smaller than 100, you will need to adjust R7 value.
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Old 16th November 2006, 06:19 PM   #10
kubeek is offline kubeek  Czech Republic
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I have 0.125V on the output. The amp looks like this:
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