Author Topic: MXR Phase 90 and transistors  (Read 2940 times)


MXR Phase 90 and transistors
« on: January 23, 2017, 08:10:34 AM »
Can I use the J113 as a substitute for 2N5457 and 2N5952 and 2N5485
in my country this transistors is only in the form of SMD or cost 10 times more expensive J113 and delivery a few months
which models you recommend to replace?
The main thing that the body was TO-92 I am not yet ready to work with smd

Rob Strand

Re: MXR Phase 90 and transistors
« Reply #1 on: January 23, 2017, 08:00:37 PM »
I haven't tried the J113.

The issue I see is the 2N5952 is about 230ohms typical whereas the J113 is 100ohms *max*  (probably 50ohms or so typical).   That means the JFET resistance is over 4 times lower.

Now you can compensate for this by increasing the 4x caps by a factor of 4 and see how you go.  What that does is it makes the all-pass filters operate at the same frequency as the MXR.     You should also reduce the 22k resistors by the same factor.
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Re: MXR Phase 90 and transistors
« Reply #2 on: January 24, 2017, 04:00:36 AM »
devices having Vgs(off) lying between -0.3v and -3.6v are bias-able in this circuit, the lower the voltage the stronger the phasing ... the range for J113's is -0.5v to -3.0v // so, would be a good alternate choice for this circuit ... for best results measure Vgs(off) and select four devices with the closest values // all you need is a 9v battery and DMM to approximate it with good degree of accuracy ... connect the battery between Drain (+) and Gate (-), and volt meter between Gate and Source to read directly (typo corrected)
« Last Edit: January 25, 2017, 04:52:08 AM by Eb7+9 »
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Re: MXR Phase 90 and transistors
« Reply #3 on: October 31, 2017, 10:27:16 PM »
I decided to take up a pending project, the problem with transistors has not gone anywhere
I once again flipped through the forum and realized that j201 is not the best option (although it is also available from my supplier).
my supplier can offer me one
2N5485 (in brackets, why is BF245C indicated)
this description introduces me into a stupor, since the specifications of these transistors are different(i mean 5485/245C)&
these transistors are able to work in this circuit or is it worth searching for the sacred 2N5952?
« Last Edit: October 31, 2017, 10:31:08 PM by POTL »


Re: MXR Phase 90 and transistors
« Reply #4 on: November 01, 2017, 09:28:37 AM »
5485 is good replacement. J113 works too

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Re: MXR Phase 90 and transistors
« Reply #5 on: November 01, 2017, 06:33:35 PM »
what do you think about BF245C
Transistors are supplied in smd version and it is difficult to read what kind of model (if it is generally indicated)
I will remind you the whole problem in the marking on the website:
MMBF5485, Transistor, RF, N-channel, 25V, 0.01A [SOT23] (BF245C)
in the data about the BF245C nothing is said, it completely corresponds to 5485, either it is a typo, or the transistors are identical
I'm confused  :icon_eek:


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Re: MXR Phase 90 and transistors
« Reply #6 on: November 01, 2017, 07:31:03 PM »
I recently built a Phase 90 with 2N5485s with no problems and it sounds wonderful.  No circuit changes were required.  I matched the JFETs with the Geofex method and wound up with 6 nice quads out of a lot of 50 NOS (through hole) transistors.  I don't know what country you're in or what your budget is like, but I've been planning on selling a few of these quads, on Ebay or here.  You can PM me if you're interested in a set, but there are also retailers such as Small Bear that sell matched JFET quads for phasers.