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Old 2nd October 2005, 06:25 PM   #1
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Question headphone amp similar to Borbely jfet design

Hi guys,
can anyone tell me in short and simple how to determine the current that is flowing through Q4 and Q5. Also I would like to know if this amplifier would theoretically work - it is similar to Borbely headphone amplifier made with jfet on input (Q6 and Q7 are 2sk389).
I would like to make headphone amplifier from Borbely but doesn't have j511 and also no output mosfet's (2sj79, 2sk216) - so this sch is perfect for me - but I am not sure about the quescient current and also if this would work - to complicated for my puny brain ).
Please help and best regards to all of You
sunny
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Old 2nd October 2005, 07:45 PM   #2
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(D5-Vgs)/(R17)

D5, the zener voltage of 1N4733
Vgs = 3-4 V
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Old 2nd October 2005, 08:29 PM   #3
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Thanks - that's what I had in mind.... I was not sure about it since mr. Borbely said in his document no. EB-804-421 and EB602-210 that he uses 100-160ma.... and from this calculation we get arround 8mA. That is strange...... I would like to construct Borbely headphone amplifier but with 160mA quescient current and IRF610/9610 combination - current like in EB602-210 document.

How do You calculate the current in this - original sch that is attached here.... it confuses me... those 2sk216 need smaller Vgs to start conducting - right?




p.s. (schematic for p.s. is in the post after this one - it is the original sch from the EB602-210) it is a bit confusing - since in his original document (EB-602-210) mr. Borbely sais that 6.8ohm or 3.9 ohm for the R12 (o.k. he also uses transistor instead of the zener diode)... i can calculate this - bjt needs 0.6V - so Iq=0.6/3.9ohm...... this is o.k. but how to calculate R10
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Old 2nd October 2005, 08:38 PM   #4
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this is the sch i am talking about in p.s. part of my previous mail.....


i would like to substitute j511 with a transistor and Q2 and Q4 with IRF610 and IRF9610 - easier to find but also I would like to have 10-160mA of quiescient current.........

R11 would be 10k and R12 would be 100ohm. I would say that I would like 3.6V on my Q4 gate so that Vgs is 3V (I loose 0.6V on R13). So, Ic for Q5 is Ic=(24-3.6)/10k=arround 2mA. Is this o.k.? What about R10? And how to calculate transistor that would substitute D1a and D1b like in sch in my first mail??
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Old 2nd October 2005, 08:50 PM   #5
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I think you can manage your calculations by yourself if you only get datasheets for the transistors. If you know which currents your interested in you will also know the Vgs, if you only have the datasheets.

You could also use the freeware LTSpice and fetch the simulations models in mind. I'm sure Netlist can supply you

If you play around with LTSpice you'll also see the working points without too much work. You will also get distortion, bandwidth and step response in the same time.
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Old 2nd October 2005, 08:59 PM   #6
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yes - but i didn't simulate anything at all so it would be a little bit difficult to use LT SPice.... I am on it on Yahoo groups but it is progressing slowly..... oh, well ..... i will look at the sch a little bit .... i think that I will calculate something than draw it and post here for someone to say if it is o.k. or not.... we all learn
thanks for Your help P-A
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Old 3rd October 2005, 10:20 PM   #7
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No one like my cat picture

kidding.... i have done some calculations and tomorrow I will draw an sch and post it here for evaluation and coments.....regards
sunny
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Old 3rd October 2005, 11:12 PM   #8
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Quote:
Originally posted by sunrise
No one like my cat picture
Nice!
Burmese?


Arne K
(Used to have Abbysinian)
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Old 4th October 2005, 03:59 AM   #9
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no - british shorthair..
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Old 4th October 2005, 08:06 AM   #10
Cobra2 is offline Cobra2  Norway
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Default Why not

- just build the circuit, and experiment with bias-settings for the mosfets...they are tough enough...
(stop when you burn your fingers!)

Arne K
(still think your cat looks like what we call "holy birma")
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