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Old 7th August 2017, 02:47 AM   #11
prasi is online now prasi  India
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ESP HPA
Thank you Bonsai, for the link. I will have a look.
Delange, the elektor circuit look very similar to the ESP.
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Old 7th August 2017, 03:03 AM   #12
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Quote:
Originally Posted by Bonsai View Post
if you are connecting a pair of low impedance headphones to the output of the JFET circuit above you will have bass roll off starting at about 500 Hz - the 10uF coupling cap needs to be about 470uF. However, for decent sound, I think the earlier design would be better - greater drive.

For a headphone amplifier, assuming c. 2V input from a CD player, you will need a gain of 5x. If the output is from a phono stage, typically 300mV or so, a gain of 10-15 will suffice.

Here is another option for you - class A headphone amp: http://hifisonix.com/wordpress/wp-co...uffer-V1.0.pdf
This was just going to be a preamp to feed the ESP in order to imbue it with SE Class A liveliness. As a direct headamp, I replaced the output JFET with a MOSFET to get my pocket Class A headphone amp.
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Old 7th August 2017, 06:44 AM   #13
delange is offline delange  Belgium
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Quote:
Originally Posted by prasi View Post
Delange, the elektor circuit look very similar to the ESP.
Yes it does. I posted my experiences because of that.
The value of the feedback resistor is a bit high to my taste on the Elektor circuit but you could easily recalculate the gain (R3 and R4) and use a lower value. The LF356 opamp has slightly better noise specs than the TL072. And the Elektor version uses a higher bias.

It shows you could have fun trying to tweak the designs
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Old 7th August 2017, 09:00 AM   #14
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by xrk971 View Post
This was just going to be a preamp to feed the ESP in order to imbue it with SE Class A liveliness. As a direct headamp, I replaced the output JFET with a MOSFET to get my pocket Class A headphone amp.
What value coupling cap did you use?
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Old 7th August 2017, 10:24 AM   #15
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Hi Prasi, I designed this amp some time ago, but with OPA134 (single opamp).I tested it with different headphones - IMHO: it sound better with Gain x 23 and 120 Ohm output resistor (better bass).
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Old 7th August 2017, 11:12 AM   #16
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Bonsai View Post
What value coupling cap did you use?
On the mosfet headphone amp, I started with 390uF, which works well for 250ohm headphones, but lately have gone as high as 2000uF for low impedance but high sensitivity IEMs. The amp seems to work well with a wide range of headphones as feedback on thread has been very positive. Surprisingly, many people have said it drives LCD-2's better than their desktop amps.

More here:
xrk971 Pocket Class A Headamp GB

There's about 150 PCBs out all over the world at this point and most everyone loves the sound. It's a simple amp so and easy first project for diy, even though SMT based.
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Old 7th August 2017, 04:04 PM   #17
prasi is online now prasi  India
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Quote:
Originally Posted by thimios View Post
Prasi,it seems that you have to draw another pcb!
Sure thimios, I will do it.
but let this be project for near future for me.
I am getting involved in ESP HPA ( as its making me learn a lot of things), and I am trying to make it stable against any load/ headphones, with thiele ckt and a cap from 'out' to 'in-'. Plus an input filter so that DAC noises do not get through to o/p stages. + like Xrk suggested, o/p cap so as not to worry about headphone DC protection.

The ckt suggested/designed by bonsai will be put to service here on DIYA if I may have the permission from him.

regards
Prasi
edit: somewhat complicated english in above post, I hope the meaning is conveyed.
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Old 7th August 2017, 04:09 PM   #18
prasi is online now prasi  India
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Quote:
Originally Posted by syr View Post
Hi Prasi, I designed this amp some time ago, but with OPA134 (single opamp).I tested it with different headphones - IMHO: it sound better with Gain x 23 and 120 Ohm output resistor (better bass).
I do not know how I missed your post, but thanks a lot for posting your experience.

Now, could you or some one answer this question.

Would the inline resistor be better off after the thiele circuit (consisting of zobel and inductor // 10 ohm resistor) or before it?
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Old 7th August 2017, 05:07 PM   #19
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by xrk971 View Post
On the mosfet headphone amp, I started with 390uF, which works well for 250ohm headphones, but lately have gone as high as 2000uF for low impedance but high sensitivity IEMs. The amp seems to work well with a wide range of headphones as feedback on thread has been very positive. Surprisingly, many people have said it drives LCD-2's better than their desktop amps.

More here:
xrk971 Pocket Class A Headamp GB

There's about 150 PCBs out all over the world at this point and most everyone loves the sound. It's a simple amp so and easy first project for diy, even though SMT based.

Very nice!

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Old 7th August 2017, 05:08 PM   #20
Bonsai is offline Bonsai  Europe
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Quote:
Originally Posted by prasi View Post
Sure thimios, I will do it.
but let this be project for near future for me.
I am getting involved in ESP HPA ( as its making me learn a lot of things), and I am trying to make it stable against any load/ headphones, with thiele ckt and a cap from 'out' to 'in-'. Plus an input filter so that DAC noises do not get through to o/p stages. + like Xrk suggested, o/p cap so as not to worry about headphone DC protection.

The ckt suggested/designed by bonsai will be put to service here on DIYA if I may have the permission from him.

regards
Prasi
edit: somewhat complicated english in above post, I hope the meaning is conveyed.
No problem Prasi - please go ahead.
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