Plexi PI input level?

jof006 · Post by **jof006** » Thu May 02, 2013 6:55 am

Could someone tell me what a typical peak-to-peak signal level is going into the PI of a brown sounding Plexi?

I've got a 6101LM that does its channel switching with op-amps just before the PI using +/- 15V rails, so obviously I'll never get more than 30V peak-to-peak. Is that enough?

Cheers.

Post by **VelvetGeorge** » Sun May 12, 2013 9:59 am

You can see 90V P-P in a plexi.

Steve's loop, for example, uses FETs and is called "zero loss" specifically because it can deliver full signal into the PI, overcoming that limitation of op amps.

George

jof006 · Post by **jof006** » Fri May 17, 2013 10:37 am

Thanks George.
I thought < 30V pk-pk would not give me the cranked Plexi sound, but it's good to know for sure.
It seems like the PI's clipping is quite important in getting a good brown sound.
Cheers.

vanhalen5150 · Post by **vanhalen5150** » Fri May 17, 2013 10:42 am

What's the voltage FETs can accept? Is there a max?

jof006 · Post by **jof006** » Fri May 17, 2013 2:23 pm

vanhalen5150 wrote:What's the voltage FETs can accept? Is there a max?

MOSFETs can be easily obtained with a drain-source voltage of up to 1.5kV.

vh junkie · Post by **vh junkie** » Fri May 17, 2013 4:18 pm

jof006 wrote:
vanhalen5150 wrote:What's the voltage FETs can accept? Is there a max?
MOSFETs can be easily obtained with a drain-source voltage of up to 1.5kV.

I don't think the devices are quite that robust... but they can essentially operate at the same voltages as preamp tubes (up to 500v)... The input signal that they can handle without distortion would increase with the B+ that they are operating at. You can read the installation instruction for the loop to see that target B+ range that is desired.

demonufo · Post by **demonufo** » Fri May 17, 2013 4:46 pm

vh junkie wrote:
I don't think the devices are quite that robust... but they can essentially operate at the same voltages as preamp tubes (up to 500v)...

You'd be surprised. There certainly are, but not necessarily designed with audio use in mind. MOSFET's have a multitude of different applications.

vh junkie · Post by **vh junkie** » Fri May 17, 2013 5:58 pm

demonufo wrote:
vh junkie wrote:
I don't think the devices are quite that robust... but they can essentially operate at the same voltages as preamp tubes (up to 500v)...
You'd be surprised. There certainly are, but not necessarily designed with audio use in mind. MOSFET's have a multitude of different applications.

I was talking about the the particular mosfet used in the loop... not mosfets in general...

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