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Old 29th January 2009, 07:45 AM   #1
Dxvideo is offline Dxvideo  Turkey
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Lightbulb TSHA.. A very simple Headphone Amp idea..

Hi all,

I am working on a very simple two stage headphone amplifier (TSHA) for a while..
Its works on simulation very well.. And I will try it in this weekend..
But before trying, I'd like to have your comments on it.
May you say something about the circuit pls?
Thanks in advance.
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Old 29th January 2009, 10:03 AM   #2
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Hi,

what's the purpose of Q1? It provides nearly no voltage gain.

Without Q1 it's a follower with current source; by the way you might be interested in this discussion

MOSFET follower headphone amplifier

If you want to get rid of the output caps, you can use a P-channel current source - just as in the Alephs.

Have fun, Hannes
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Old 29th January 2009, 10:14 AM   #3
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Q1 works as a gain stage. In this configuration it provides ~4.5dB of voltage gain (with 10mA Idss) But it can changeable via changing R2 value..
Concerning the output stage: Yes its based on a design of Mr.Pass (the Zen Amp). I have made different variations of this amp before. But this version has a better CCS. I have tried before with a darlington output transistor and have good results..
Anyway, the main difference between the Zen Amp (and also my older projects) and this amplifier is the input stage..
In fact I am not good at JFET based amplifier stage designing. And need some help to improve it..
Thanks a lot for your comment.
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Old 29th January 2009, 02:49 PM   #4
mjf is offline mjf  Austria
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hello.
i am missing a gate(to ground) res at the input - 10k .......to 100k or so.
inputstage: rs(ource) can be found by trial.....
begin with a bigger res in the lm317 ccs (27 ohm or more),
i think the irf510 and the lm317 need heatsinks.
when using this amp with low impedance headphones (32 ohm or so),let away the 12 ohm res at the output........
there is a basic schematic - perhaps it can help.......
greetings...............
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Old 29th January 2009, 02:59 PM   #5
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sorry-slip of pen: voltage at source irf510 is11volt (and not 9v as shown in the schematic!)
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Old 29th January 2009, 03:00 PM   #6
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In fact I was working on some changes..
I suddenly realised that; there is no gate bias circuit for IRF... So I added a bias circuit and made some calculations on 2SK circuit..
Please have a look the new version..
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Old 29th January 2009, 03:09 PM   #7
h_a is offline h_a  Europe
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Quote:
Q1 works as a gain stage.
Don't worry I knew that

I was hinting that it's not an important part and could be left out. Added distortion for 4.5dB voltage gain?

Don't forget you don't need voltage gain for headphones in general (with regular pre) - just a little current.

Have fun, Hannes

EDIT: I just noticed: why the 12 Ohm resistor in series with the headphones? Just kills output impedance, what is the advantage of that?
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Old 30th January 2009, 06:20 AM   #8
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Hi Hannes,

It will be a general project for our Turkish DIY club.. And a lot of people uses high impedance headphone sets (250 and 600R) so it must provide 100mW into 250R or 600R. I know its a bit hard to drive a 600R headphones and needs more Vcc (may be 30v). But with 24v supply it can easily drive 250R ones and for this it needs a gain stage..
Anyway,
12R is for protection to output devices.. In fact its not 12R, it must be 33 or more. Ok, it adds distortion and noise but if you consider this is a SE project and there is no protection fot the output devices against over current then its a need..
Thanks a lot for your comments again..
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Old 30th January 2009, 07:11 AM   #9
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It is a nice little HPA, head phone amp.

What you can do, is make the JFET have x4 gain, +12dB
Some HP can need some voltage gain.
For example Sennheiser reference, like Sennheiser 600, 650
and the new HD800 http://www.sennheiserusa.com/newsite...transid=500319
This is because they are 300 Ohm impedance.

If you use 32 Ohm phones, like Grado classical series, then you do not need any voltage gain.

But even at gain 1, the NPN JFET input, will buffer the GATE of the MOSFET
and do some good service to drive the IRF510, IRF610.
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Old 30th January 2009, 07:34 AM   #10
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You're right..
In fact I've made some little calculations according to Mr.Mike Martell;
http://www.rason.org/Projects/jfetamp/jfetamp.htm
And this ratio is a natural result of this calculations.. I am not sure but as I understand the gain is not much flexible! I dont want to repeat Mike but these guys (JFETs) have a couple of rules:
- Dont exceed 75% of Idss at Rds On (theorically Zero ohm for Rds)
- Rd and Rs ratio must be 75% - 25%
So;
- If you take consider these
- If you have 7-8mA Idss devices like me
- If your Vcc is 24v (I need some swing on output )
Then 5mA max current is ok. So I need 4800R total, and 3K3/1K2 (E12) meets Rd/Rs rule makes total of 4500R..
I dont know too much gain calculation on this like circuits. But my simulator says it gives 7.7dB @ 1Khz... But with 10mA Idss devices.. So I will see what will happen with 8mA devices..
I will finish and test the amp this weekend. And you will be informed (if I like it of course )

Thank you for the comment.

By the way; as I remember Nico was older than 57.
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