Easy envelope follower circuit?

[T-Man]

Is there any good way to make an envelope follower for pedals other than the usual LED photoresistor combo??  Can I just use a diode and some caps or something??

Any help would be great.

Thanks
T-Man

[johngreene]

Depends on what you are using it for.

--john

[Mark Hammer]

An LDR will operate as a resistor under ANY circumstances, so LED/LDR-based envelope followers are the most generic and adaptable of what's available.  At the same time, it is possible to have envelope controlled transistors that do something useful.  The Dr. Q/Quack is an obvious and textbook example of that.  The key thing is that the bipolar transistor serve as a resistance to ground in a particular type of circuit.  If you see the schematic of the Rolls Ducker, they also use a transistor (a 2N5087 to be exact) as an envelope-controlled  resistance to ground.

Alternatively, there are LED/FET-based optoisolators like the H11F1/2/3 that are more consistent and available than some LED/LDR-based devices.  Here, the FET is used in exactly the same way that FETs are used in phasers.

All told, though, the best envelope followers are often LDR-based because: a) the LDRs contribute little or no noise, b) the LDRs can be placed anywhere that a resistor can, c) LDRs can't be distorted (where FETs can), and d) the slight lag of LDRs eliminates some of the envelope ripple.

[T-Man]

Sorry I should have been clearer.  I am looking for alternatives to light-based devices only.  Would a circuit similar to a basic AM demodulator work?

[johngreene]

I think I was confused as well because the term 'envelope follower' usually means 'envelope controlled filter'. I 'think' what you are asking is are there other ways of doing envelope detection. The envelope detection and the 'light' part are actually not connected. The LED/LDR part is one way of using the envelope signal to control 'something'.  For envelope detection, a basic AM demodulator will work. However, you have to take into consideration it's a lot easier to detect an envelope of a RF signal modulated with an audio frequency than it is to detect the dynamics of an audio signal. Probably the most simple envelope detector is the one use on the DOD 440. I don't know if that pedal used it first or not but the same design is reused in a lot of different envelope-controlled pedals.

Hopefully this helps?

--john

[T-Man]

You know what I was trying to say better than I do! 

Yes, I was reffering to envelope detection.  And yes that did help...  I thought that LED/LDRs were used as the control element AND part of the detection process... and I guess they can be... but as in the DOD 440 the detection is done and then fed to the LEDs it looks like.  I will probably do something similar but try FETs as the control element.  Thanks!

T-Man

[johngreene]

np

[Paul Perry (Frostwave)]

Johngreene, I hope that 'np' doesn't mean 'not possible'

[Dave_B]

Just curious, is there a reason you want to avoid LED/LDR's?  And yes, I consider the $6 price tag a valid reason.