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Old 7th March 2010, 10:04 PM   #3011
gjfim is offline gjfim  United States
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Zen Mod,
Thanks for your reply.

Voltage across R3 is 71.1mV. Voltage across R4 is 70.5mV.

Gary
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Old 7th March 2010, 10:20 PM   #3012
Zen Mod is offline Zen Mod  Serbia
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in that case everything seems fine - output mosfets are biased fine , current through input Jfets is in ballpark ;

desolder both input jfets , then inject signal at junction of C1 and C2 ;

if you get sound , replace both input jfets ;

if not - we'll see .....
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Old 10th March 2010, 12:44 AM   #3013
gjfim is offline gjfim  United States
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Default Thanks to Zen Mod

Zen Mod- Your suggestion worked. I replaced both JFETs and adjusted DC offset. Sound is back.

Thanks for your help. Now I am ready to try Pumpkin.

Gary
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Old 28th March 2010, 03:54 PM   #3014
Liliya is offline Liliya  Norway
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Default F4 as a headphone amplifier

Hello

I have started building my second pair of F4 on Villers PCB. This time I intend to try out how it will work as a headphone amplifier for my AKG K701.
I do need some adwises form someone with a better electronic understanding than myself about (still running in classe A):


Power voltage (lower than +/- 23 V if possible) and bias per device.

Preamp will be B1


Specifications AKG K 701

Type: Circumaural, open back headphones

Efficiency: 105 dB SPL /V

Maximum input power: 200 mW

Impedance: 62 Ohms

I have a lot of 220uF/16 V cond. Can I use them as C1/C2.
What about C3/C4?

Sincerely

Eivind Stillingen
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Old 28th March 2010, 05:11 PM   #3015
cviller is offline cviller  Denmark
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You can run the amp at lower bias when your load is 62 ohm - but sounds like you already know that.

You can use the 16V caps on C1 and C2, but it might be a good idea to lower the voltage too. C3 and C4 will see a higher voltage, so you need to be careful with those. If you don't plan on using any gain, then you can lower the voltage quite a bit and still have plenty of swing without clipping.
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Old 28th March 2010, 06:40 PM   #3016
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Default MPP from Joachim Gerhard

Quote:
Originally Posted by Liliya View Post
Hello

I have started building my second pair of F4 on Villers PCB. This time I intend to try out how it will work as a headphone amplifier for my AKG K701.
I do need some adwises form someone with a better electronic understanding than myself about (still running in classe A):


Power voltage (lower than +/- 23 V if possible) and bias per device.

Preamp will be B1


Specifications AKG K 701

Type: Circumaural, open back headphones

Efficiency: 105 dB SPL /V

Maximum input power: 200 mW

Impedance: 62 Ohms

I have a lot of 220uF/16 V cond. Can I use them as C1/C2.
What about C3/C4?

Sincerely

Eivind Stillingen
Hi Eivind,

Go to the thread of Joachim and go to the 4 last pages. You'll find all you need to make a good Phone amp for your AKG.

Just my 2 cents,


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Old 29th March 2010, 06:29 PM   #3017
Liliya is offline Liliya  Norway
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Default F4 as a headphone amplifier.

Audiofanatic

"Joachims thread". Can you please be more precise where to find this thread?

Thank you!

So to my question about a suitable power voltage and a corresponding bias for F4 driving my AKG K701 62 ohm imp.

How much can I reduce both and still be in classe A. The reason I ask has influence on how big heatsinks I must use (I already have two that I hope will fit)

Sincerely

Eivind Stillingen
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Old 29th March 2010, 07:11 PM   #3018
generg is offline generg  Germany
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post 1088

on this side i suppose ....
Mpp

good luck!
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Old 29th March 2010, 07:19 PM   #3019
generg is offline generg  Germany
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.... do you know this version of F4?

Could be enough for your headphone .....
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File Type: jpg f4-for-16e.jpg (50.7 KB, 593 views)
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Old 29th March 2010, 11:06 PM   #3020
Liliya is offline Liliya  Norway
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Default F4 as headphone amplifier

generg

You wrote:

".... do you know this version of F4?

Could be enough for your headphone".

Do you mean that this can do the job alone, without B1 as "pre"?
How do I fix a volumecontrol?

The PCB I use is from cviller. Here is the schema he use:

http://www.diyaudio.com/forums/blogs...-f4-guide.html

As you can see, it is a little bit different from the version you show me. If I go for that version, as far as I can see, I have to keep Q3 and Q6 on cvillers PCB board and skip out the rest of IRF240/IRFP 9240? Will it be nessecary take away all 0,47/100 ohm resistors or can they stay (that will be the easiest way)??

D3/D4 out?

What about P2: 500 ohm versus 5 Kohm
R5: 1Kohm versus 3,32 Kohm
R22: 750 ohm versus 1 Kohm

Sincerely

Eivind Stillingen
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