OPTO FET issue solved with Negative Feedback!

By applying shunt shunt feedback from the Drain to the Gate of the first JFET stage of my compressor, I reduce VDS across the optofet  by a factor of 5! So with a input of 1 volt, the the VDS of the optofet is about 200mV worst case. Now it performs beautifully. The feedback consists of a 470k ohm resistor in series with a .1uF cap from drain to gate. Now the source must be bypassed with a 10uF cap – where before it was optional. The gain of the stage with this feedback is now about 4. What happens is that the feedback subtracts from the input at the optofet drain node greatly reducing the VDS across the voltage controlled resistor – while still providing gain.

Further Simplification of the Enhanced Orange Squeezer Compressor

It occurred to me that if one is willing to sacrifice some flexibility in the decay length of my compressor design; that it can be simplified by removing the source follower and the Zetex current sensor. What this means is that the control voltage is only half wave rectified instead of full wave, but if you just increase the filter cap – the circuit should still work fine. The trade-off is that you get limited to longer decay times only, but for most guitar applications this is fine. I have not verified this circuit but I will do this soon. I am confident it will work well. Removing these parts may make it more attractive to the DIY builder.

New Schematic:

https://circuitsaladdotcom.files.wordpress.com/2012/09/compressor3.gif

Pedal and Amp demo videos to be posted

I have been building a lot of guitar electronics these days … and more to come I hope! Having said that, I think it is important to show how they can be used in real music and how well DIY designs can perform as compared to commercial products. My first demo is of my portable busking amp and my FET discrete signal chain compressor. This demo  represents a classic jazz sound using the compressor to understate all of elaborate grips on the guitar and make the lines very smooth sounding even with heavy down strokes.

check it out at:

more demos to come shortly!

Enhanced Orange Squeezer type Compressor

This is my twist on the Orange Squeezer compressor. I use an h11M1F optofet instead of a JFET as a current controlled resistor (not voltage controlled). The signal chain is discrete FET and the control signal is generated from a ZETEX  ZXCT1041 current sensor – used for battery chargers. It is configured to act as a full wave precision rectifier. Unlike the Orange Squeezer you can adjust level and compression – it has all sorts of potential for mods. The  ZXCT1041 can be replace by an opamp such as the one I use for the peak detector, configured as a precision full wave diode(see op amp data sheet) – not much difference either way.

Schematic: https://circuitsaladdotcom.files.wordpress.com/2012/09/fet-compressor.gif

Picture: https://circuitsaladdotcom.files.wordpress.com/2012/09/img_4862.jpg

Sound Sample: https://circuitsaladdotcom.files.wordpress.com/2012/09/compressor-blues.mp3

recording starts with no compressor -> compressor on-> off->on->off-> ends with compressor on

UPDATE: 10/14/2012

I have noticed that at very low compression settings with high guitar input levels(>.5Volts) there can be some distortion. The Opto FET  I am using appears to have distortion that looks like crossover distortion with signals greater than 200mV. When compressing the signal across the OPTO FET decreases so that normally eliminates this issue but at low settings – this may be a problem. I am going to explore just using a linearized JFET in its place and or other solutions.

UPDATE:10/17/2012

By applying shunt shunt feedback from the Drain to the Gate of the first JFET stage of my compressor, I reduce VDS across the optofet  by a factor of 5! So with a input of 1 volt, the the VDS of the optofet is about 200mV worst case. Now it performs beautifully. The feedback consists of a 470k ohm resistor in series with a .1uF cap from drain to gate. Now the source must be bypassed with a 10uF cap – where before it was optional. The gain of the stage with this feedback is now about 4. What happens is that the feedback subtracts from the input at the optofet drain node greatly reducing the VDS across the voltage controlled resistor – while still providing gain.