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PostPosted: 20 Sep 2008, 17:53 
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gmilitano wrote:
It is mainly the Szekeres headphone amplifier http://headwize.com/projects/showproj.p ... dd_prj.htm with a CCS. I decided to go with this one since I have been wanting to try something Class A for a while now and because I had all the parts for this project on hand.
Gio
Anyone building a discrete component headphone driver/amp of the type we have both just built would be foolish not to read this article or at least look at the schematic. There is some great ideas here. WoodyII may well have direct coupling to the phones with no output caps. A differential PS would have to be a starting point for this to occur. I currently am using 5600uf caps snubbed by 10uf polies for the OP caps. The prototype used 4700uf caps but the 5600uf have a smaller form factor and thus easier to get into the small case. Over-kill some might say! I'm not aware of the word "over-kill".

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PostPosted: 20 Sep 2008, 18:22 
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gmilitano wrote:
Any regulated wall wart should be fine. 750mA should be fine. While I have not tried this one from Radio Shack 273-029, it says it will go up to 12V and 1A. That should do the trick. I would try find one that is closer to 15V.
Gio
Though our builds differ in a number of ways I found my bi-polar based emitter-follower Woody worked best at 33V. What I did find when the PS voltage got below 18V lots of distortion crept in on heavy dynamic tracks played at higher sound levels. The more voltage the more power has to dissipated in the cct. but also greater dynamic head room. So it is a real juggling act. PS volts/heat Vs dynamic head room and drive capability. Your constant current source may well work better when the PS voltage gets down.

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PostPosted: 21 Sep 2008, 09:47 
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Hi Mark,

My variable supply only goes up to 20V, so I did not try it beyond that point. The current draw on mine is much higher so I imagine temperature would rise quickly at higher voltage. Mine sounded better with more than 12V.

Cheers,
Gio

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PostPosted: 21 Sep 2008, 23:23 
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Gio

I got some more timber just in case I make another. What should the smallest the OP cap be? I see you used 680uf I went for 5600uf.

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PostPosted: 22 Sep 2008, 01:15 
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Hi Mark,

The corner frequency (fc) is calculated fc=1/(2*pi*R*C) where R is the load in ohms and C is the capacitor in Farads. To go from F to uF divide by 1 million.

For 680uF and 32 ohm Grado Headphones fc=7.3Hz. So you could even go down to 470uF (corner frequency 10.5Hz).

With 300 ohm headphones you could get away with 60 uF. 68uF Metallized Polyester Capacitors are big but manageable.

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PostPosted: 15 Feb 2009, 16:03 
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Hello. I followed this sheme and tried to make my first solid amp :)

I can't get IRF 610, so i used IRF510.

Also used Rg 130R instead of 150R. What regulates this R?

For this "test" sample I used 9V regulated PSU (0.8A). It gives 9.13 Volts

In your article, You wrote:
Quote:
The bias is set by varying the 100k variable resistor until the output side of the MOSFET is at half the supply voltage.
Where is "Output"? I tryed measure different places and found somethng similar to this "output", and set this to 4.3V
I noticed, that if make this voltage lower, for example to 4V, then sound baecame noticable distorted. With 4.3 it's a bit harsh. Making output voltage higher (5V) make sound a bit clearer. So the question is: if it's mportant to set output at half of supply voltage or it can be slightly more?

Btw, I measured voltage between the output caps leads, and it was about 1.35 and 1.39 Volts. If it's ok? Can I use here 6.3V cap?

Thanks.


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PostPosted: 15 Feb 2009, 19:30 
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Hi Stream, welcome to the forum.

Stream wrote:
I can't get IRF 610, so i used IRF510. Also used Rg 130R instead of 150R. What regulates this R?

For this "test" sample I used 9V regulated PSU (0.8A). It gives 9.13 Volts
Those should all be fine.

Quote:
The bias is set by varying the 100k variable resistor until the output side of the MOSFET is at half the supply voltage.

Stream wrote:
Where is "Output"? I tryed measure different places and found somethng similar to this "output", and set this to 4.3V
I noticed, that if make this voltage lower, for example to 4V, then sound baecame noticable distorted. With 4.3 it's a bit harsh. Making output voltage higher (5V) make sound a bit clearer. So the question is: if it's mportant to set output at half of supply voltage or it can be slightly more?
OK, that is written poorly and I will make a clarification on the article page. What you want to do is adjust the 100k pot until the voltage on the Source (S) is one-half the voltage on the Drain (D).

Stream wrote:
Btw, I measured voltage between the output caps leads, and it was about 1.35 and 1.39 Volts. If it's ok? Can I use here 6.3V cap?
The DC voltage before the capacitor should half of your supply voltage, so it should be close to 5V. With a 9V supply, a 6.3V cap would be ok, but my suggestion would be to use a capacitor a bit larger than the supply voltage just in case something ever goes wrong.

PS - I found the amp worked better with more voltage. I did not like it too much with less than 13V.

Cheers,
Gio

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PostPosted: 21 Feb 2009, 04:23 
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Hello, Gio.

Quote:
What you want to do is adjust the 100k pot until the voltage on the Source (S) is one-half the voltage on the Drain (D).

Hmm. Please explain this:
"Voltage on source " - is it Source to Gnd DC voltage?
"Voltage on the Drain - " It should be = Supply Voltage, isn't it ?

I tried adjustng 100k pot from one end to other, but Source Voltage changes ~ from 1.5V to 2.7V...
And At 5V From Gate to Gnd, it sounds better, and Mosfets and LM has ambient temperature. Lowering Gate to Gnd voltage to 4V-4.5V make sound more distorted and mosfets became hot, and supply voltage lovering to ~8V...

Here are some measurments, whis I get with best sounding (but bot good at all)
Image

Quote:
PS - I found the amp worked better with more voltage. I did not like it too much with less than 13V.

Yes, I know, but can 9V supply be the reason, why i have distorted Bass? It sounds like BRRR instead of Boom :)
My PS consist of 9V 1A voltage Regulator. 2*1000uF before Vreg and 680uF after.
Image
Image
Image
Image

P.s. Maybe You can mark measurement points on your sheme? Please...

Thanks.


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PostPosted: 21 Feb 2009, 15:40 
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Quote:
What you want to do is adjust the 100k pot until the voltage on the Source (S) is one-half the voltage on the Drain (D).

Stream wrote:
"Voltage on source " - is it Source to Gnd DC voltage?
"Voltage on the Drain - " It should be = Supply Voltage, isn't it ?

The voltage on the "Source" leg of the mosfet should be 1/2 of the voltage on the "Drain" leg which should be the same as the supply voltage. You measurements will be relative to ground.

See the attached schematic and the measurement points are in red.
Attachment:
IRF610-Class-A-Headphone-Amp-Schematic.png

Stream wrote:
can 9V supply be the reason, why i have distorted Bass?

I never tried less than 10V but I don't recall it distorting. Sound was pretty good at 12V. Too low of a voltage could be the problem, but others have used 9V. Can you try something closer to 12V to eliminate voltage as a potential problem?


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PostPosted: 22 Feb 2009, 12:51 
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Just finished testing my amp, connected to computer PS (+12V).
Low frequency was okey, and it sounded not bad at all. Mosfet were very hot. So, I don't know if 9V were just so low for this sheme, or my 9V PS works wrong...

P.s. Tryed to adjust sheme (100k pot), but failed once again :|
If it should be 1/2 Vs DC or AC? Just to be sure, that I'm searching in right direction :)

Btw tell me please what will changes if I'll increase\descrease gate resistor?


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