Yet another transimpedance question

Try it. It’s impossible to damage anything if you try it. It seems you’ve configured the MC inputs for pretty typical MM standards, so why not bypass the JFET?

@lewm 

Sorry, I wasn’t very clear.  Jim H offers two versions of the Trumpet, the MC and the MM.  The mc has a non bipassable jfet front end to allow for the ability to vary impedance and gain.  The jfet also has a 555 chip to increase voltage (internal switching power source).  The mm version has not jfet front end, not sure how the voltage is handled in that one, have not looked at the schematic in detail.  So, would the sound be much different from the Piccolo zero of one used the mm version without the jfet?  Also, if the power source is some how handled in a more direct or non-switched manner, would an external LPS make more of a difference?  As an aside, I find it a little hard to swallow that something like an Sbooster would make much difference with the mc version, since it would feed directly into the internal switching power source.  Sort of defeats the purpose of an LPS.

This is why I am a bit confused, if it matters:

"The mc has a non bipassable jfet front end to allow for the ability to vary impedance and gain."  You don't necessarily need a JFET to allow for the ability to vary impedance or gain.  Phono input impedance is largely determined by the size of the resistor between the hot pin (the grid of the input tube or the gate of the input transistor) and ground.

"The jfet also has a 555 chip to increase voltage (internal switching power source)." I thought that a 555 chip is primarily used as a timer, like when you want an LED to flash on and off, by supplying and then alternately cutting a low voltage to the LED, on and off and on and etc. In the Trumpet, it may be used to switch on the B+ and B- voltages with a time delay after the tube filaments are already powered up; this is good practice with tubes. There is very little detail about the PS on the Hagerman website, but there is a hint that it is a switching type, just a hint.

It seems like your real question is whether you should buy the MM version of the Trumpet in order to sample the Piccolo Zero operating into it. Yes? Until now, I had not understood that you would need to buy an entirely different unit. Anyway, I personally would not spend the bucks to do that. But no one here can tell you whether you would be happier with the MM version using the Piccolo Zero, except maybe someone else who has tried the Zero both ways.

@lewm 

Thanks, yes, you are correct on all counts, the way I read it the 55 chip is for the timing/switching functions as you describe (not actual PS, sorry, that was confusing).  I was trying to explain why external LPS didn't make much sense to me since there is what essentially seems to be an internal switching PS in the Trumpet MC.  And, not the jfet is not actually needed for the variability functions, but it is there as a very quiet way to enable that (hope that makes sense?).  My ability to understand and explain these things is (obviously) limited.

At this point I lean toward not spending the $ unless someone responds that they have tried the Piccolo and the Trumpet MM and have heard a significant improvement or difference.  

I know that @mulveling has a Trumpet reference and he might have something to say...

In all cases I know about where a JFET is the input device in a tube phono, it’s simply to increase overall gain of the circuit while adding very little noise. The Herron MC phono is another example.