G1176 : 2N5952 instead of BF245A ?

[ricothetroll]

Hi,

I have a dual 1176LN working but without matched transistors for the moment. As I want to use it dual or stereo (I have Hairball's stereo link kit installed), I should use a matched quartett of fets. As I have an order to do at Musikding soon, I saw they have a matched quartett of 2N5952 fets, used as variable resistors in phaser circuits :
http://www.musikding.de/product_info.php/info/p759_2N5952---matched-quartett.html

I looked for the datasheet of both 2N5952 and BF245A to compare them and eventually find out whether they are similar enough or not.
Here are the only two datasheet I could find for the 2N5952 :
http://www.datasheetcatalog.com/datasheets_pdf/2/N/5/9/2N5952.shtml
And here are the ones for the BF245A :
http://www.datasheetcatalog.com/datasheets_pdf/B/F/2/4/BF245A.shtml

I can see that for BF245A rds(on) = 200 Ohms (Vgs=0, fig. 20 on Philips datasheet) and for 2N5952 rds(on) = 300 Ohms (Vgs=0, Central Semi datasheet). I guess that, considering the characteristics spread between specimens, can be considered as pretty equivalent. But I don't have the rest of the graphic for the 2N5952, neither Vp to calculate it (1/rds = (2Idss/Vp²)*(0.5Vc-Vp) ).

My question is : is there another way to find out whether those transistors are equivalent enough or not ? Am I missing something here ?

Best regards.

Eric

 

[MeToo2]

Hi,

I have a dual 1176LN working but without matched transistors for the moment. As I want to use it dual or stereo (I have Hairball's stereo link kit installed), I should use a matched quartett of fets. As I have an order to do at Musikding soon, I saw they have a matched quartett of 2N5952 fets, used as variable resistors in phaser circuits :
http://www.musikding.de/product_info.php/info/p759_2N5952---matched-quartett.html

I looked for the datasheet of both 2N5952 and BF245A to compare them and eventually find out whether they are similar enough or not.
Here are the only two datasheet I could find for the 2N5952 :
http://www.datasheetcatalog.com/datasheets_pdf/2/N/5/9/2N5952.shtml
And here are the ones for the BF245A :
http://www.datasheetcatalog.com/datasheets_pdf/B/F/2/4/BF245A.shtml

I can see that for BF245A rds(on) = 200 Ohms (Vgs=0, fig. 20 on Philips datasheet) and for 2N5952 rds(on) = 300 Ohms (Vgs=0, Central Semi datasheet). I guess that, considering the characteristics spread between specimens, can be considered as pretty equivalent. But I don't have the rest of the graphic for the 2N5952, neither Vp to calculate it (1/rds = (2Idss/Vp²)*(0.5Vc-Vp) ).

My question is : is there another way to find out whether those transistors are equivalent enough or not ? Am I missing something here ?

Best regards.

Eric

I think you're missing something pretty fundamental:

How well "matched" is that quartet of 2N5952 to each other? Couldn't see any spec at all on that in the site.

Are they matched specifically for use in a 1176 type GR circuit with 27K resistor? Are they matched at 3dB GR? 6dB GR? 12dB GR? Over the whole curve? At how many points on the curve?

How well matched do you want your quartet to be?

For a stereo 1176 it's much more important to have the two best matched FET's for the gain reduction circuits, especially around the point that you are going to operate the 1176 (is that -3dB GR?, it's your choice). The other two FET's only indicate GR on the meter, so if you can live with slightly wonky metering that's less important.

FYI I bought 100 BF245a for 30 euros. I got two very usable "closely matched" quads out of that (to within 1dB over a very good portion of the operating range) after 2 hours work using an extended version of this procedure http://www.nrgrecording.de/html/fetmachting.html to match at -1dB -3dB and -6dB.

Then the question still remains: does a 2N5952 have the same resistance curve as a BF245a (or the original UREI FET) for a given Vgs?

You could always buy this quad and try them: it ain't that expensive. But I wouldn't want to guarantee the result.

 

[ricothetroll]

Hi !
I finally ordered some, I'll measure the resistance curve and let you guys know if they're how they look ! Else I could still build a phaser

 

[MeToo2]

Hi !
I finally ordered some, I'll measure the resistance curve and let you guys know if they're how they look ! Else I could still build a phaser

Cool. Thanks for the info.

 

[gyraf]

Good post, MT2 - thanks.

Jakob E.