I need an example part # of a couple of low threshold voltage n-channel mosfets in enhancement mode. A threshold voltage of 50 millivolts or less would be nice. I want to build an audio compressor with a power supply of 10 to 20 volts. I would prefer to-92 case. I don't want surface mount. Please consider low cost and where I could buy it from. I need at least six.

 

The Si2302CDS has a Vgs max threshold of 0.85V which is the lowest I know of.

 

A threshold voltage of 50 millivolts or less would be nice.

You're not going to find any discrete devices with that low of a threshold voltage.

I want to build an audio compressor with a power supply of 10 to 20 volts.

It would be helpful if you gave us more information on your project.

I would prefer to-92 case. I don't want surface mount. Please consider low cost and where I could buy it from. I need at least six.

Low threshold devices aren't readily available in TO-92; at least not at a reasonable price. I've been using AO3400 0.65-1.45V in SOT-23. I use these adapters:

The MOSFETs are a $0.02 each and the adapters are $0.04 each on Ali Express. I wouldn't normally buy bare semiconductors from them, but I took a chance and haven't had any issues yet.

EDIT: The leads in the bottom of the picture are around $0.10 each in quantity 100+, if you can find them. Price is better if you buy reels of 25-40k pieces. You can use right angle male header pins instead.

 

A threshold voltage of 50 millivolts or less would be nice.

0.05V no not going to find any.
Post your schematic. Why 50mV?
Years ago I built some audio compressor with MOSFETs that have 7V Gate turn threshold voltage.

 

I attach my test schematic. I am thinking that R5 would set the threshold and R3 would turn the transistor on or off at the threshold. This would allow the signal to pass or not to the output. The input to Output is never attenuated. the threshold of the transistor is 0.8v to 3 volts I think.

 

All the many audio compressor circuits in Google Images show an ordinary transistor or Jfet doing the compression.
Of course a compressor attenuates the signal when it gets too loud.
Here is a Wien Bridge sinewave oscillator that uses a Jfet for compression:

 

My compressor doesn't test correctly. The input signal is not limited by the circuit. I was wondering if I have to send back the audio output to the input of the mosfet gate rectified? How is the compression level point determined with respect to threshold level at the source of the mosfet? Stupid me.

 

A compressor circuit senses the input signal voltage and rectifies it. Yours does not.
Then the compressor circuit uses that rectified signal voltage to adjust the Vgs of the Mosfet. Yours does not.
Your circuit is a simple trimmer adjusted variable attenuator.

 

A compressor circuit senses the input signal voltage and rectifies it. Yours does not.
Then the compressor circuit uses that rectified signal voltage to adjust the Vgs of the Mosfet. Yours does not.
Your circuit is a simple trimmer adjusted variable attenuator.

Got it. What gate voltage do I set R3 for to affect the 100 milli volt input signal

 

The amount of conduction for a Mosfet is a range of voltages. Each one is different even if they all have the same part number.
For a 2N7000 fed the 100mV signal from the 220k resistor the Vgs will be so low that leakage current will affect it. Use a Jfet instead and maybe reduce the 220k to 47k. You will need an opamp amplifier to make the active rectifier circuit.

 

Are you trying to build a guitar effect box? If no, why are the signal levels so low? Line livel audio is around 1V.

Bob

 

Are you trying to build a guitar effect box? If no, why are the signal levels so low? Line livel audio is around 1V.

Bob

I eventually want to build a microphone amp and the compressor is to limit loud voice passages

 

Have a look at 2SK1825 and FDN327N.

You can always amplify the signal before processing it.

 

I repeat. Your circuit is not a compressor. Instead it is a simple DC volume control.

 

Have a look at 2SK1825 and FDN327N.

You can always amplify the signal before processing it.

Thanks Dick, I appreciate your selections.

 

I need an example part # of a couple of low threshold voltage n-channel mosfets in enhancement mode. A threshold voltage of 50 millivolts or less would be nice. I want to build an audio compressor with a power supply of 10 to 20 volts. I would prefer to-92 case. I don't want surface mount. Please consider low cost and where I could buy it from. I need at least six.

Petkan: There are no known devices with so low threshold, but why would you need one? Schematic design should work with components limitations and part to part variations. You may find some devices fitting your expectations...but you cannot rely on re-produce able performance. When you use a device beyond what the datasheet guarantees - you cannot manufacture in volume and you cannot repair. Think how to use widely available components

 

https://ez.analog.com/audio/f/q-a/3998/audio-compression-chip

https://www.electroschematics.com/tag/audio-compressor-circuits/

https://circuitszone.com/audio-compressor-circuit-based-lf357/


Regards, Dana.

 

Look ALD212900PAL

 

I have never seen a Mosfet used for Automatic Gain Control (compression) but instead a Jfet was always used. It produces severe distortion if the signal at its drain is more than only 100mV but produces much less distortion if a voltage divider made with 2 resistors feeds half the drain signal to its gate.

 

I have never seen a Mosfet used for Automatic Gain Control (compression) but instead a Jfet was always used. It produces severe distortion if the signal at its drain is more than only 100mV but produces much less distortion if a voltage divider made with 2 resistors feeds half the drain signal to its gate.

I used an MOS transistor in the attenuator to stabilize the sine amplitude in the resonant voltage converter. I needed a low-noise source 12V--> 45V. So I made a transducer based on serial resonance (330 kHz). But I agree that the MOS transistor is not a very suitable element for an attenuator.