Wampler Plexi Drive issues

[Vivek]

Open question :


Does the Wampler Plexi design use some special feature of the FETs and therefore can only work with FETs, 

Or it is possible to redesign the circuitry with Opamps in such a way that no person will be able to tell the difference between the FET version and the Opamp version in a blind test ?


or even more stringent conditions :
Is it possible to design an Opamp version of the FET design such that no person with an Oscilloscope and Audio precision measurement gear will be able to tell the difference ?

[percyhornickel]

There are some others plexi or "marshall in a box" circuit types that uses opamps like Lovepedal Purple Plexi (LM386D), Lovepedal Jubilee (LM386D), Rocket Animal (4558), etc. They all of them wanted to replicate marshall sound and they all has different character...   ...even if they sounds pretty similar like plexi drive and purple plexi (jfet/opamp).

At least for me in a blind test would be really difficult to difference between them.

Jfets has many parameters that make each one to work and sound different too (Vgs / Idss.... ) and opamp some other parameters like slew rate, THD, bandwith, etc. Some opamp circuits uses old style diodes like BAT46 too.

The Vgs will help to set the bias in each jfet and it deppends on how much difference between gate and source (more negative  or minor voltage value) this will allow current to flow between drain and source. Even, jfets could work in ohmnic or saturated zones according this.

Same with opamps, it is not the same to use a LM741 than OP07 or LM308 in a rat circuit for example. Same pinout but so different slew rate and you can easily note the sound difference.