- #1
chaoseverlasting
- 1,051
- 3
Im building an MXR phasor, the thing is I can't find the JFET's 2N5952. What other JFETS can I replace them with?
JFET Replacements for 2N5952 in MXR Phasor
- Thread starter chaoseverlasting
- Start date
Click For Summary
Discussion Overview
The discussion revolves around finding suitable replacements for the JFET 2N5952 in the context of building an MXR phasor, a guitar effect pedal. Participants explore various alternatives and their specifications, as well as the implications of using different JFETs in this application.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
- Experimental/applied
Main Points Raised
- One participant inquires about the application of the JFET in the MXR phasor to recommend appropriate replacements.
- Another suggests the Fairchild J309 or J310 as potential substitutes, noting they are not exact matches but are somewhat similar and readily available.
- A participant mentions the MPF102, highlighting its lower voltage rating compared to the 2N5952 and warns about the differences in pin configuration.
- It is noted that the FETs may be used as switches in the circuit, which could require matching characteristics among multiple units.
- One participant proposes testing methods for the FETs to ensure they are similar, suggesting the use of a multimeter for gain testing and discussing the importance of cutoff voltage.
- Another participant expresses a desire for a more generic and commonly available JFET, likening it to the 741 operational amplifier in terms of ubiquity.
- There is a reiteration of the risks involved in substituting transistors, emphasizing that results may vary.
Areas of Agreement / Disagreement
Participants do not reach a consensus on a single replacement part, and multiple competing views on suitable alternatives remain. There is uncertainty regarding the exact application of the JFETs in the circuit, leading to varied recommendations.
Contextual Notes
Participants discuss the importance of matching characteristics among JFETs and the potential need for testing multiple units to find suitable replacements. There are unresolved questions about the specific requirements for the JFETs in the MXR phasor circuit.
- #2
uart
Science Advisor
- 2,797
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Whats an MXR phasor? It's hard to recommend a good replacement if we don't know that application. Is the jfet being used as an RF amplifier or an analog switch or something else?
Anyway you might give the Fairchild J309 or J310 a try. They're not an exact match for you part but they're readily available and somewhat similar to it.
Anyway you might give the Fairchild J309 or J310 a try. They're not an exact match for you part but they're readily available and somewhat similar to it.
- #3
vk6kro
Science Advisor
- 4,079
- 41
Seems to be just a low powered device but with 30 volt breakdown ratings.
Radio Shack have MPF102 s which have a 25 volt rating while the 2N5932 has a 30 volt rating. If that matters, don't use the MPF102. They are $1.29.
The MPF102 has the G and D wires in opposite places to the 2N5932, so be careful if you use it.
There is always a risk that a substitute transistor may not work, so try at your own risk.
Radio Shack have MPF102 s which have a 25 volt rating while the 2N5932 has a 30 volt rating. If that matters, don't use the MPF102. They are $1.29.
The MPF102 has the G and D wires in opposite places to the 2N5932, so be careful if you use it.
There is always a risk that a substitute transistor may not work, so try at your own risk.
- #4
chaoseverlasting
- 1,051
- 3
Its being used as an RF amplifier I think... An MXR Phasor is a guitar effect pedal. Variable phase shift all pass filter (Im 99% sure that's the exact description)
- #5
vk6kro
Science Advisor
- 4,079
- 41
If you have a circuit, maybe you could post it.
It is unlikely to be an RF amplifier, but if it is, the MPF102 is normally used as an RF amplifier. It is OK at audio, too, of course.
Or, just get one and try it, if you are sure the original type is unavailable.
It is unlikely to be an RF amplifier, but if it is, the MPF102 is normally used as an RF amplifier. It is OK at audio, too, of course.
Or, just get one and try it, if you are sure the original type is unavailable.
- #6
chaoseverlasting
- 1,051
- 3
Here's a pdf of the diagram. I couldn't find a JPEG link, sorry.
- #7
vk6kro
Science Advisor
- 4,079
- 41
The FETs seem to be being used as switches but the description says they have to be matched. This is because they are all being controlled together.
This might mean you would have to buy 10 of them and test them to get similar ones.
They don't say which way they should be tested but one way would be to test them in a multimeter that has a transistor tester in it. This only tests for gain, but it may be enough.
In this circuit, it might be better to test for cutoff voltage, but you would have to set up a bit of equipment to do this.
This is the negative voltage on the gate that just stops the current flowing between the drain and source.
This might mean you would have to buy 10 of them and test them to get similar ones.
They don't say which way they should be tested but one way would be to test them in a multimeter that has a transistor tester in it. This only tests for gain, but it may be enough.
In this circuit, it might be better to test for cutoff voltage, but you would have to set up a bit of equipment to do this.
This is the negative voltage on the gate that just stops the current flowing between the drain and source.
- #8
chaoseverlasting
- 1,051
- 3
How would I go about it? What do I need to do?
- #9
vk6kro
Science Advisor
- 4,079
- 41
You would need some equipment.
TWO 9 volt batteries
one potentiometer, about 10 K total resistance.
TWO multimeters, one on voltage and one on current.
See attachment. Be careful to get it right if you wire it up.
The FET gets negative voltage from the potentiometer across the left battery and it gets its normal positive voltage from the battery on the right.
Current is measured in the drain lead of the FET and voltage is measured across the Gate- source .
You need to check a few FETs for
(1) gate voltage to cut off drain current and
(2) drain current with zero voltage on the gate and
find 4 that are most alike.
Just to remind you of my earlier comment:
There is always a risk that a substitute transistor may not work, so try at your own risk.
TWO 9 volt batteries
one potentiometer, about 10 K total resistance.
TWO multimeters, one on voltage and one on current.
See attachment. Be careful to get it right if you wire it up.
The FET gets negative voltage from the potentiometer across the left battery and it gets its normal positive voltage from the battery on the right.
Current is measured in the drain lead of the FET and voltage is measured across the Gate- source .
You need to check a few FETs for
(1) gate voltage to cut off drain current and
(2) drain current with zero voltage on the gate and
find 4 that are most alike.
Just to remind you of my earlier comment:
There is always a risk that a substitute transistor may not work, so try at your own risk.
Attachments
- #10
chaoseverlasting
- 1,051
- 3
I can't even find those! What would be the most generic, out-dated but commonly available part? Something like the 741 of JFETs?
- #11
vk6kro
Science Advisor
- 4,079
- 41
Try this:
http://www.radioshack.com/product/index.jsp?productId=2062616
The MPF102 is an old FET but still works just fine. Nice to see Radio Shack carry them.
That test setup is ideal for learning about how FETs work, too.
http://www.radioshack.com/product/index.jsp?productId=2062616
The MPF102 is an old FET but still works just fine. Nice to see Radio Shack carry them.
That test setup is ideal for learning about how FETs work, too.
- #12
chaoseverlasting
- 1,051
- 3
Thanks a lot vk6kro, Ill give it a shot. If this works, youre a lifesaver man!
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