Simplistic NJFET RIAA

[Salas]

Of course we can, but told you what I did since you asked.

 

[RCruz]

So finally the trick is to choose a high Vp for the top fet.... I did not care the first time and got into trouble... now I can rest... there is always a solution

 

[massimo]

What's the new toy Salas? A curve tracer?

 

[Joachim Gerhard]

I have no problems with humor.
Quite the contrary.
The Vds of the cascode Fet ( J310 ) develops a voltage over the 2SK170 buffer Fet.
If that voltage is too low we get more distortion. Therefore the J310 was chosen, it has high Vds at the idle of the 2SK170 ( around 8mA ).
You can simply measure from drain to source over the 2SK170, how much voltage you have there.

 

[Joachim Gerhard]

The higher, the better, and both channels should ideally match.

 

[Salas]

What's the new toy Salas? A curve tracer?

Yes a small signal one in a semis checker.

 

[vgeorge]

What's the new toy Salas? A curve tracer?

Peak Electronic Design Limited - Atlas DCA Pro - Advanced Semiconductor Analyser - Model DCA75

Got one too!

 

[massimo]

Ela!

If only I could find one in my Easter egg this year.... A bit too pricey for me at the moment

 

[Salas]

I sold the previous model on Ebay and got the new one. Previous was faster, but this one is richer.

 

[Joachim Gerhard]

This traces is actually very good.
The only problem i found is that it can not measure power transistors.
The voltage is limited to 12V and so is the current.
No chance to measure a power transistor at 1A and 50V for example.

 

[Salas]

If they follow in the lower regions, we can only hope that modern transistors usually follow in the higher regions too, that is for matching. But to surely know, confirm, or fully characterize, then its pro gear territory. But there are some kits of interesting tracers too.

 

[Joachim Gerhard]

What is very interesting is to measure BJTs in the saturation zone.
I found pairs that matched great ones they where full on but did not match in saturation.
I am still figuring out what parameters have to match.
For example in a common base stage high Hfe is not that important because that stage makes an I/U conversion. It has basically no current gain.
In mirrors i think it is important that the BJTs match in the saturation region.
Many medium power devices showed problems here.

 

[AndrewT]

...........
Some of the cascode J-Fets had too low Vgs.
..........

............. Are you talking about Vp ?

........... the trick is to choose a high Vp for the top fet.................

...............
The Vds of the cascode Fet ( J310 ) develops a voltage over the 2SK170 buffer Fet.
If that voltage is too low we get more distortion. Therefore the J310 was chosen, it has high Vds at the idle of the 2SK170 ( around 8mA ).
You can simply measure from drain to source over the 2SK170, how much voltage you have there.

http://www.diyaudio.com/forums/powe...-voltage-shunt-regulator-213.html#post2124715

and confirmed in numerous other posts if you search Vp and/or cascode.

 

[merlin el mago]

Yes a small signal one in a semis checker.

It's the same like told you, right Salas? How much money did you sold the DCA55?

 

[Salas]

$66 free shipping so I ended up with $50 after tracked shipping and Ebay substantial fee. But its $100+ new the 55 model in USA so it went too fast. The 75 model is $200 territory! Its the EU revenge time to US sold Fluke huge price benefit via UK Peak.

 

[merlin el mago]

Thanks. I see on ebay the low price for DCA55 63€+shipping.

 

[Salas]

Its the $ to UKP that promotes the discrepancies in this case but the US products being so salty in EU it must be just policy.

 

[Salas]

What is very interesting is to measure BJTs in the saturation zone.
I found pairs that matched great ones they where full on but did not match in saturation.
I am still figuring out what parameters have to match.
For example in a common base stage high Hfe is not that important because that stage makes an I/U conversion. It has basically no current gain.
In mirrors i think it is important that the BJTs match in the saturation region.
Many medium power devices showed problems here.

Looking for the "kinkless" BJT match. Golden Lion of semis.

 

[buzzforb]

Hi buzz

Look for cannon golden inserts.... the small ones in the picture.
192900-0633 - ITT CANNON - STIFT, LOET GOLD 13A | Farnell Schweiz

THanks RCruz.

 

[RCruz]

http://www.diyaudio.com/forums/powe...-voltage-shunt-regulator-213.html#post2124715

and confirmed in numerous other posts if you search Vp and/or cascode.

Thank you very much Andrew.
Now I have a really clear picture about this.