I have refined this design somewhat including the use of the more common LM358 op amp. I also changed the closed loop peak detector to an open loop compensated one with good results. I have attached the schematic. Here is a link to a youtube demo of the compressor in action.http://www.youtube.com/watch?feature=player_detailpage&v=iEcPEYB0Wao

Yes - nice observation - there the JFET is being linearized by feeding back some of the drain voltage to the gate of the voltage controlled resisitor(VCR). This improves the drain to source voltage limitation but primarily makes the change in resistance more linearly proportional to the control voltage. In my circuit, the feedback is not to the VCR but to the input of the amplifier. It is what is called shunt feedback because it lowers the impedance of the amplifier input, thereby reducing the signal across VCR substantially.  However, in your example circuit, the voltage across the VCR is also reduced by the ratio of the feedback resistors across the op amp - so the same idea applies.

I have cooked up a compressor design that uses 3 2N7000 NMOS FETS and one op amp. Its very easy to build and uses a LED as a peak detector and compression level indicator, as it lights up with varying intensity proportional to compression level.

Using a MOSFET as a voltage controlled resistor requires very small signal levels or it will cause distortion. To solve this, I employed negative shunt feedback to buck the input signal at the input node. This results in signals in the range of ten mV across the voltage controlled resistor.

LINK to Schematic:

http://circuitsaladdotcom.files.wordpress.com/2012/10/simple-compressor.gif

yes over all its a pretty simple circuit and you can breadboard in a couple of hours. I think you will be very pleased with the performance. I found having the regulator output pin as close as you possibly can to to VCC pin of the chip helps tame it. This probably will alos be the case with a 7805.

Yes all those symbols are for me - I probably should have posted a more generic schematic. All those references are for the 2.1mm jack sw to disconnect the battery when an adaptor is used, the other jack switch is from a streo input jack, where one connection isused to only connect the ground circuit when pluged in, ect - this is all the making it a "standard pedal" connections and I was trying to keep them straight when I built the damn thing! So point taken. All my wires go to the board - (from the pots, switches, etc) so you are seeing all of my inter-switch and jack to jack wiring take place on the board. I have reflected this on my schematic. So every symbol is a wire connection on my board. You can ignore everything but the input, out put B+ to the regulator and the switch for the tails fet switch, etc. Not sure what you mean about the op amp? Yes there is an op amp in the chip, but functionally you only need to connect to the pins as shown. I imagine you want see what the topology the op amp circuit in isolation and not just connections to pins for informational purposes?

here is a simplified schematic  - maybe this will help - you don't need the PMOS - just use a diode if even that. This further reduction may clarify some of your questions

http://circuitsaladdotcom.files.wordpress.com/2012/10/analog-delay_simple.gif

Hey There

I think you could be a little more diplomatic with your post

You could just say your having some trouble reading my schematic and ask me to clarify. I am smart enough to refine my formatting and style- when someone gives defacto feedback by asking questions.  Lots of people have emailed or posted with questions and I have happily answered them. It difficult to tell where to draw the line with detail so I figure anyone who actually wants to try to build or experiment with the circuit - will put forth the effort to reach out. All of the symbols are referenced to the various jacks and switches at the pedal level. You can just mark them out - if they confuse you?

A number of people have built this "unintelligble" circuit with no problem and have conveyed to me excellent performance - so I am sure you and your professors can figure it out too

seriously though if you have questions I will answer them and lets leave it at that.
A number of parts are arbitrary choices based on what I had floating around others matter. The regulator for example draws less  standby current, allows for a smaller drop for regulation and I beleive has a better transient response than a 7805. Sure the diode could be anything.

I have posted on www.circuitsalad.com, an alternate filter design, if the thought of spending $7.00 of the MAX7401 makes you ill  To me the simplicity and adjustability of the filter makes it well worth it.

I hope at least a few builders will like this circuit, if nothing else as a point of departure for a tweaked, custom tailored design. The reverb circuit may be overkill for many; getting a spring tank to work would not be hard at all.  I can tell you that the TDA7360 is a winner and easy to work with.  Basically anything in front of a tone stack and the final driver/feedback/TDA7360 sub circuit should sound good. I power it with my 14.4V NiMH makita battery and its loud as hell. I blew my original 6" MOD speaker apart! If anyone has suggestions - I'd love to make it better.

Yes they become expensive. Sometimes I break down and pay for them myself but I am fortunate in that I do circuit design for a living and I can often piggy back my experiments and home brew on to other boards I am prototyping for my work. I can just cut them up into the appropriate sub sections. I really try to make my hobby designs as simple  as possible so they can be perf built for someone who does not want to invest in a PCB.

Here are some pictures.... I mainly build with surface mount because the parts end up being cheaper most of the time and I can get the boards really dense. I find smt easy enough to hand solder but you need a good set of tweezers and a nice soldering station!

I added a coupling cap and replaced the schematic with the error.

I'm glad its useful to someone! I used the part for its original purpose and saw an app note describing alternate applications. The part could be used for all sorts of envelope filters or even a high side octave. The only drag is its only availabe as a sot23-5 surface mount part. So for those who feel more comfortable with through-hole parts, may not want to use it.

Here is a compressor demo: Its recorded on a DR1 portable recorder about 3 feet away from my battery amp from an earlier post. It starts with no compressor, then compressor, alternating a couple more times and ending with the compressor. The effect is subtle and the compression level is set about 1/2  of max.

I am posting a schematic of my approach to using the PT2399 for a delay. I can get long .7sec repeats with little noise and I don't need a compander! I did some different things than the standard circuits out there. The trick in my design is using a much larger cap (.47 uF instead of .1 uF) between pins 9 and 10. This gives an increase in signal output but the noise stays the same. Then I reduce the output at the wet dry mixer and the noise goes way down. Also the wet/dry mixer is the op amp between pins 13 and 14.  Instead of using this Opamp as a filter, I used a switch cap filter IC, but all kinds of other low pass filters could be used. I must say that it really does the job and only uses 1 cap to set the cutoff freq from 1Hz up to 5KHz. Check out the audio sample.

I am glad someone likes it (besides me)!

I had some basic goals, discrete signal chain, low noise and nice compression control and not very complicated.
the first problem.. what to use for voltage controlled resistor? The led/photoresistor works fine but you have little control of attack and decay. So I chose the optofet which is linear with respect to current(not voltage) that is why the driver to the optofet is current feedback. It is a current controlled resistor. This part works great with signal swings less than 1 volt, so fortunately here the signal swing across it is  low.

The next issue was generating the control signal. Here you could just used a diode like the Orange Squeezer, but it has offset error and ripple because it is half wave. This creates distortion and limits how fast the decay can be. I chose to use this nifty zetex current monitor IC. It senses difference between the two top terminals(positve or negative) but always give the difference as a positive voltage. This allows it to act like a perfect fullwave recitfier- with very few parts. This IC would be great for any kind of envelope sensing in the audio range.

The op amp I use is special in that it is rail to rail input and output but also can have the input swing way above and below the rails without
phase shifting or slew overloading, originally per its data sheet, I used it as the fullwave recifier and it worked fine. Ultimately, I used the ZXCT1041. Other op amps could be used. In this circuit, it is used as a diode drop compensated buffer for my diode peak detector and as the volage/current converter for the the optofet.

I will post some sound samples this evening.