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Old 4th August 2017, 02:53 AM   #1
prasi is offline prasi  India
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ESP HPA
Default ESP HPA

Hi,
I am planning to layout the simple HPA by ESP. I have modified the sch a bit by including thiele ckt and some other refinements based on some reading here.
I would like to know if I am on the right track and if some thing else is required to be added/optimized. gain could be around 8-12 by adjusting R4.
would it be a good idea to place the inductor on the PCB itself or somewhere else.?

regards
Prasi
pl feel free to remove sch /delete the post if it violates copyright.
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Old 4th August 2017, 03:06 AM   #2
miro1360 is offline miro1360  Europe
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check my thread with TPA .... it is the best what I built yet, you can try layout own PCB (I can also ship you pair of PCBs without no charge (I am not profiting in this and I never will be) - if you will, they left me for 3 amps) ... you can build it only with one pair laterals - two pair was only my sound test, but I have not noticed difference in sound ...
edit: ok, now I see you have this for headphones and my amp is for speakers ... but anyway ...

Last edited by miro1360; 4th August 2017 at 03:09 AM.
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Old 4th August 2017, 09:21 PM   #3
jaycee is offline jaycee  United Kingdom
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I've built this design on stripboard and it works quite well - however depending on the source and the headphones you are using, you will definitely want to reduce the gain!!

I used this first time with my PC, and with 32 ohm headphones it is capable of blowing your eardrums to pieces with the default gain. I found a gain of two was plenty, and 9V rails were plenty.
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Old 5th August 2017, 04:45 AM   #4
prasi is offline prasi  India
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Quote:
Originally Posted by jaycee View Post
I've built this design on stripboard and it works quite well - however depending on the source and the headphones you are using, you will definitely want to reduce the gain!!

I used this first time with my PC, and with 32 ohm headphones it is capable of blowing your eardrums to pieces with the default gain. I found a gain of two was plenty, and 9V rails were plenty.
OK thank you Jaycee. I would keep that in mind.
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Prasi
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Old 5th August 2017, 06:56 PM   #5
xrk971 is offline xrk971  United States
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I think this will sound very good and neutral. It will have very low THD but sound uninspiring. There are so many ways to power headphones and headphones is the perfect place for Single Ended Class A with cap coupled output.

On this ESP amp, it's already cap coupled input, why not add a couple of caps for output coupling? Try 1000uF Panasonic FR bypassed with 10uF Silmic II. You will avoid need for DC protect and passively prevent headphones from ever getting destroyed should one side of the push pull circuit go bad.

That 22pF on C5 needs to be determined empirically in small increments, make large enough to prevent oscillation but a few pF too much and sound can become lifeless. Specify NP0/C0G SMT here as close to pins on opamp as possible.
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Old 6th August 2017, 09:24 AM   #6
prasi is offline prasi  India
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Thanks x,
Here is what I will do, I will keep provision for o/ p coupling cap.
Is there a way it can be made musical? . Or slightly boost the bass for classical music?
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Old 6th August 2017, 10:27 AM   #7
xrk971 is offline xrk971  United States
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Add three BF862's in a single Ended preamp (Juma's deign) and it will sound more musical.

You could power it from 15v to 18v single rail and it will work fine.

Click the image to open in full size.

Here was my hand made layout:
Click the image to open in full size.


But maybe this is straying too far from the intended purpose of the ESP HPA?
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Last edited by xrk971; 6th August 2017 at 10:36 AM.
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Old 6th August 2017, 07:37 PM   #8
Bonsai is offline Bonsai  Europe
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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
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Old 6th August 2017, 07:43 PM   #9
thimios is online now thimios  Greece
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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
Prasi,it seems that you have to draw another pcb!
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Old 6th August 2017, 09:25 PM   #10
delange is offline delange  Belgium
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Many, many, many years ago I build this one from Elektor.
I remember it worked really well considering the very simple design with only a few components.
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