Tin of FETs headphone amplifier

[EUVL]

Your boards are a touch larger than TO92 ?
Ours are 4x5mm.




Patrick

 

[easphyx]

I have found an old article from Vishay in which PN4393 is claimed as low noise JFET. On simulation it's model shows quite good linearity at 1.8 mA. Maybe I should try this one.

 

[NicMac]

There is none.
The closest is LSK170C, but Yfs is lower. Also too expensive.

What about 2SK170-V or maybe 2SK369-V?
There seems to be quite a lot up for sale at a decent price here.

 

[EUVL]

PN4393 has half the Yfs and ~3x the noise as a BF862.

See :

https://groupdiy.com/index.php?topic=2048.0
"....... The closest contender FETs with decent gain are the 2N5566 and 2N4393 with two to three times of the 2SK389 noise. You would have to hook eight of them in parallel to get the voltage noise figure of the 2SK389."

http://www.diyaudio.com/forums/pass-labs/175040-more-fet-noise-measurements-euvl.html
(Noise measurement for BF862)

Measurements Rate SMT Low-Voltage n-JFETs Under Consistent Conditions | Power content from Electronic Design

For this particular circuit, I would not ue anything else.


Patrick

 

[EUVL]

Nic,

Your suggestions are both good.

But for each channel, you need 10 matched JFETs.
How many of 2SK170V and 2SK369V do you think you need to find 2 sets of 10, even if only Idss matched to say 5% or so ?


Patrick

 

[EUVL]

One of the lowest noise 1000x amplifier out there, the Groner LNA, uses 8x BF862 in parallel to achieve ~0.4nV/sqrtHz input noise.
http://www.diyaudio.com/forums/equi...ment-amp-linear-audio-vol-3-spare-boards.html


Patrick

 

[EUVL]

Here you can find some noise figures for PN4393 andPF5102, etc.
http://www.itisravenna.gov.it/sheet/jfet.pdf


Patrick

 

[NicMac]

Nic,

Your suggestions are both good.

But for each channel, you need 10 matched JFETs.
How many of 2SK170V and 2SK369V do you think you need to find 2 sets of 10, even if only Idss matched to say 5% or so ?

Patrick

For the 2SK369V my data tells me that 100 devices would yields about 6 sets of 10 with an average matching of around 3%.
With 50 you would be lucky to find just one set < 5%.
With 500 you would probably find 49 sets < 1%

As you know, I use them for the great SEN I/V converter and there I use 16 FETs matched to <0.5%
If you should have run out I can send you some.

I unfortunately have no data on the 2SK170V

 

[EUVL]

We have none left ourselves, so we'll take all you can offer, as long as reaonably priced.

Send me a email.




P.

 

[xrk971]

Although I do not normally build amps with output coupling caps, I find this a very clever solution for a portable.
So I have taken the liberty to play around a bit with the circuit.
I hope you would not mind.

Here I share with you my simulation results.
I use one type JFET throughout (BF862 SOT23).
This has lower noise than both J112 and ZVN4306.
Even though bias is a touch lower at 50mA, I can still get comparable performance into 32R 1Vrms.
-3dB bandwidth is > 3MHz.
And the use of JFETs simplfies the output White Follower considerably.


Best regards,
Patrick

I built this amp but am having problems getting it to work.

http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp-45.html#post4919251

 

[T117]

schematic
http://www.diyaudio.com/forums/atta...-fets-headphone-amplifier-many_many_jfets.png

I don't know how stable the voltage at the drain of Q2. The amplifier has to have to adjust this voltage trimmer resistors R4 or R5.

 

[ElFishi]

Although I do not normally build amps with output coupling caps,

Is there anything wrong with moving the cap in front of the White follower stage? With clever Idss selection and some tuning of source resistors we can make the remaining output DC go away.

Ah, pls note the typo: the supply voltages should be symmetrical.

 

[xrk971]

Interesting idea. For a portable HA I kind of like the cap output for auto DC protect.

 

[xrk971]

I built this amp but am having problems getting it to work.

http://www.diyaudio.com/forums/pass-labs/146310-bf862-preamp-45.html#post4919251

Amp works! I had a bad wire from PCB to the headphone jack. I am using 33R source resistors on the bottom to get 12mA bias current in each leg for 48mA total bias. Running 17v DC from a XL6009 DC-DC booster module. Has capability of being driven from 5v USB type cell phone battery for a nice portable class A amp.

 

[xrk971]

Amp works! I had a bad wire from PCB to the headphone jack. I am using 33R source resistors on the bottom to get 12mA bias current in each leg for 48mA total bias. Running 17v DC from a XL6009 DC-DC booster module. Has capability of being driven from 5v USB type cell phone battery for a nice portable class A amp.

Sounds great in stereo.

 

[xrk971]

Just wanted to thank Easphyx for the original circuit - works well with the four pair BF862 implementation. I could probably shrink it to fit an Altoids tin but the FETs would be pretty densely packed (20 total). As fitted inside typical small "O2" size box, heat is not an issue at all.

http://www.diyaudio.com/forums/head...f862-based-se-class-headamp-without-heat.html

 

[DontHertzMe]

Would it be worthwhile adding additional pairs of FETs for lower individual dissipation?

 

[xrk971]

10mA to 12mA current ea JFET is not a lot and where thy are designed to work. Adding more I would aim for more power from larger current to the headphones.

 

[DontHertzMe]

10mA to 12mA current ea JFET is not a lot and where thy are designed to work. Adding more I would aim for more power from larger current to the headphones.

More power, captain! Flank speed!

 

[JordiMB]

Would it be a good idea to use depletion mode mosfets for output, like the DN2540? It comes in different packages, including TO-92 (capable of 1 W, 120 mA continuous current, 500mA pulsed current).