BARACUDA-Legend-1

[porkluvr]

Hello,

Yes.. there is real improvement ! I think that between a bad and good selection, from those 2 fets, is more then 5 cm differents..(if not more) The sound from a good combination is much 'cleaner' no 50 Hz ?? ( can enybody explain?)
If the offset form the Ne5534 is zero and then looking at the output from the lm358 /1 (lf412) you see much differents in out put if selecting different fets .....

Best regards.

Ap

I won't (or can't) get real technical here but U4A is a differential amplifier and...

When you select FETs for matched Vgs(OFF) you are also narrowing the difference between Rds(ON). That difference can be pretty significant and is effectively in series with the 1k input resistors and will affect the comparative gain between the U4A + and - channels.

CMR (common mode rejection) can suffer as a result and that can be why you see differing levels of AC mains hum at U4-1 with different FETs.

I really hadn't thought of that before you got the idea for matching pinchoff voltages. Good idea, Ap.

[6666]

Hi AP
wow 5cm, thanks, I better get out the soldering iron
on my bara I do not get any 50hz, but it is a little unstable for about 1-2 minutes
after switch on
but then settles down.

[ApBerg]

Ap did you notice much difference in the sensitivity of your MD
when using matched and non matched fets ?

How many cm's ?

Hello,

Yes.. there is real improvement ! I think that between a bad and good selection, from those 2 fets, is more then 5 cm differents..(if not more) The sound from a good combination is much 'cleaner' no 50 Hz ?? ( can enybody explain?)
If the offset form the Ne5534 is zero and then looking at the output from the lm358 /1 (lf412) you see much differents in out put if selecting different fets .....

Best regards.

Ap

[6666]

Ap did you notice much difference in the sensitivity of your MD
when using matched and non matched fets ?

How many cm's ?

[ApBerg]

Hi Ap,

thanks for the Tip, works fine.

Hello Miata.

Wowww... that was fast made !

Yes always nice when a small thing works so nice ... thanks also to R.G Keen

Best regards.

Ap

[Miata]

Hi Ap,

thanks for the Tip, works fine.

[6666]

Thanks Apberg for your information
very interesting for us.

[ApBerg]

Hello Friends

Found http://www.geofex.com/article_folder...h/fetmatch.htm this is the origin for the Fet tester I think..
In the zip is the sprint layout file and also some info from a other electronic hobbyist that has done some fet-testing

Best regards.

Ap

[ApBerg]

Hello Friends

Made some test … checking fets.. marking them with Typex and a number on top.
( fist I used nail paint in a sort code.. little paint dots on top .. not good !)

First conclusion :
It is not important if you use the MPF102 or the 2N5485 both work..
What is important that they are matched..
If I insert fets that have a mismatch .. a MPF 102 that has a 3 volts switching point and a 2n5485 that has a switching point from 2 volts there is less sensitivity and a there is lot 50 Hz noise !?
Best is 2 fets that have the same switching point , for example both 2 volts or both 3 volt.. this gave (indoors) the best results… no 50 Hz ?? and best sensitivity.

Of course this is my opinion…
The term switching point if perhaps not o.k...but it is a indication that can be used ?
Best regards
In short time I mail the litlle pcb that I used for the fet selection.. first have to sears on Internet where I found the info to make it..

Ap

[Cesar]

Hello Friends,

Made a new pcb, I do not like those large standing caps...
In the zip is the sprint layout file, hope there are no errors...

Best regards.

Ap

Hi ApBerg, just want to ask you how many strands (wires) has your Litz wire, i could find some on the net but i need to know exactly the nr. strands/thickness of the wire .

thanks in advance

[6666]

Hi all
got my Baracuda working on the bench tonight
had a faulty 79l05 -5 volt reg only giving .5 of a volt
replaced it and away she went,
now for tune up and a proper coil and real testing
just used a small choke for the coil to get going
thanks Silverdog and all others

[Janou]

I just check all components... and finally find the problem

I use wrong value for R30, normaly 150 Ohms, but 150 kOhms

I recheck with a coin and results are very good ! Thanks for the help, i add more datas, pictures ASAP

[6666]

We are using this cct by Alex 2011, for the silverdog BARACUDA-Legend-1 project, as listed in post number 4 of this thread
see post 4 for all ccts. There are a few changes from the old REV D cct to make it work.

http://www.geotech1.com/forums/attachment.php?attachmentid=14368&stc=1&d=1296185337

[Janou]

My coil former come from a laboratory apparatus

I add somes informations about primary testing with a simple voltmeter if somebody have a problem. ( I use the Rev .D schematic with 20k delay trim and 8 NiMh battery )

Vbat = 9.92V ( pin 8 of U7 )
Vdd = 4,97V( pin 8 of U4 )
Vss = - 4,94V ( pin 7 of U1, pin 4 of U4 )
Vout = 9,86V ( pin 5 of U7 )
Vcc+ = 4,67V ( pin 7 of U7 )
Vcc- = -4,94V ( pin 4 of U7 )

Pin 13 of U1, between 0 and 130 mV ( min/max of delay trim )
180 mV accross coil ( probably not the real value )

Actually i already change U7 ( instability at Vout ) and change U1 but change sound little different but nothing else. I find 2€ coin at 10 cm when i try several setting with "Delay trim", so poor results because i don't understand the right method to set correclty "delay trim" with a mono trace scope.

[smity]

7660CPAZ = 10 V
7660SCPAZ = 12 V