temol
Well-known member
Question: what's the J201 substitute for ....? Is there a J201 substitute?
Answer: it depends
I'd like to share my point of view for a J201 replacements, using Son of Ben an an example.
So we're using JFET for amplifying signal (gain stage).
But before I start with measurements, ltspice sim results, etc...
Most schematics do not mention anything about JFET parameters (Vp, Idss) so even if we have the same transistor model, we cannot be sure that the parameters of the transistors we intend to use are similar to those of the original circuit. The use of a substitute complicates the matter even more because since there is no 1:1 substitute for J201, it is to be expected that our circuit will not sound identical to the original. It can be similar, more or less, but not the same. So - if we want to have a faithful copy of the original (soundwise) - we need to use transistors identical to the original. I omit here other issues such as tolerance of other components in the circuit.
Let's start.
I chose 4 JFET models.
J201 (MMBFJ201) - because it's in the original circuit.
2N5457 (MMBF5457) - because it's often listed as J201 replacement.
2SK208-R - because in my opinion it's a good J201 replacement.
2SK117GR - because it was mentioned on the forum as a possible replacement.
I've measured three pieces of each model - Vp and Idss, then I've tried my best to replicate each transistor in ltspice. So I have separate ltspice model for each transistor. Probably an overkill but why not. Especially that in a real life we rarely have identical JFET transistors (unless we select them).
As mentioned before - in my opinion 2SK208R is quite close to J201. Espeially if we take low Vp/Idss J201's. I have many MMBFJ201's with Vp below -0.7V.
Now some ltspice.
Comparison of the frequency response - output of the SoB. Note similar frequency response of the J201 and 2SK208R.
Output signal.
I've tried to keep the drain voltages the same for each circuit. PPCB build doc says - TRIM1 - 2k. So for Q1 (J201) we have total drain resistance of 12k and around 6V. Different JFET models require different drain resistor value to set 6V. Higher or lower than 12k.
Drain resistance values. In red - values below 10k, so in order to set the desired voltage it's necessary to jumper or lower default 10k resistor in series with a trimmer.
Signal on Q1, Q2 and Q3 drains.
And frequency response for the Q1, Q2 and Q3 drains.
To be continued...
Answer: it depends
I'd like to share my point of view for a J201 replacements, using Son of Ben an an example.
So we're using JFET for amplifying signal (gain stage).
But before I start with measurements, ltspice sim results, etc...
Most schematics do not mention anything about JFET parameters (Vp, Idss) so even if we have the same transistor model, we cannot be sure that the parameters of the transistors we intend to use are similar to those of the original circuit. The use of a substitute complicates the matter even more because since there is no 1:1 substitute for J201, it is to be expected that our circuit will not sound identical to the original. It can be similar, more or less, but not the same. So - if we want to have a faithful copy of the original (soundwise) - we need to use transistors identical to the original. I omit here other issues such as tolerance of other components in the circuit.
Let's start.
I chose 4 JFET models.
J201 (MMBFJ201) - because it's in the original circuit.
2N5457 (MMBF5457) - because it's often listed as J201 replacement.
2SK208-R - because in my opinion it's a good J201 replacement.
2SK117GR - because it was mentioned on the forum as a possible replacement.
I've measured three pieces of each model - Vp and Idss, then I've tried my best to replicate each transistor in ltspice. So I have separate ltspice model for each transistor. Probably an overkill but why not. Especially that in a real life we rarely have identical JFET transistors (unless we select them).
As mentioned before - in my opinion 2SK208R is quite close to J201. Espeially if we take low Vp/Idss J201's. I have many MMBFJ201's with Vp below -0.7V.
Now some ltspice.
Comparison of the frequency response - output of the SoB. Note similar frequency response of the J201 and 2SK208R.
Output signal.
I've tried to keep the drain voltages the same for each circuit. PPCB build doc says - TRIM1 - 2k. So for Q1 (J201) we have total drain resistance of 12k and around 6V. Different JFET models require different drain resistor value to set 6V. Higher or lower than 12k.
Drain resistance values. In red - values below 10k, so in order to set the desired voltage it's necessary to jumper or lower default 10k resistor in series with a trimmer.
Signal on Q1, Q2 and Q3 drains.
And frequency response for the Q1, Q2 and Q3 drains.
To be continued...
Last edited:
