The hamptone jfet as a line amp

[pucho812]

Going over the hamptone jfet article there is an example of using it as a summing amp.  I'm wondering what would change to use it as a simple Line input/ line trim on a mixer... To refresh people's memory

here is a scan of the article

I am also referencing this as here is a jfp module redesign to work with a bi-polar PSU
http://groupdiy.com/index.php?action=dlattach;topic=40106.0;attach=4285

Since this is a per channel line trim, I am guessing I can eliminate the master volume pot and would only need one gain stage. Add a that 1200 chip to unbalance the signal and add another chip on the back end. hmmmmmm. I am sure there is a lot wrong here and I missing something.

 

[jensenmann]

This circuit has tons of character. I´m not sure if I wanted to have this in my mixer´s line ins. It might be too much to have it on all signals.

 

[pucho812]

This circuit has tons of character. I´m not sure if I wanted to have this in my mixer´s line ins. It might be too much to have it on all signals.

Then your really not going enjoy my idea of the hamptone  mic pre  in a 500 series that also doubles as a variable line in using the same fet module  designs. Obviously the line in would only have one of the fet stages Hmmmm I'm wondering how much character one would have if I am leaving out the  I/O transformers in place of balancing chips. for the line side.

 

[jensenmann]

For 500 series it might be perfectly fine as a "soulful" line-in since you always have the choice to use it or not. It can be tamed, btw, by adding neg. feedback across it. Less gain, less nonlinearities.
Great idea for a 500 series preamp! And the line-in feature surely is a nice to have goodie, not so often seen with other preamps.

 

[pucho812]

Exactly. So yes Hamptone mic pre is set, but still deciding the line stage and what to do. Yes can tame it with resisters if I do the hamptone fet design, I may do something else instead that is still a discrete design, still planning things.

 

[My3gger]

This circuit has tons of character. I´m not sure if I wanted to have this in my mixer´s line ins. It might be too much to have it on all signals.

Then your really not going enjoy my idea of the hamptone  mic pre  in a 500 series that also doubles as a variable line in using the same fet module  designs. Obviously the line in would only have one of the fet stages Hmmmm I'm wondering how much character one would have if I am leaving out the  I/O transformers in place of balancing chips. for the line side.

I built HJFP preamp with two modules and also tested one module as a line in, after some time preferred sound without OT's. Input trafos in mic amp configuration were high quality, didn't notice much change without them, if any at all. Everyone who tested them really liked their tone and interstage pot which makes it easy to drive them. So i think your idea is good and i would work on it. Thanks for reminding us about this flexible, simple and nice sounding design.

 

[pucho812]

O.k. so how did you connect your balanced line in?

 

[My3gger]

From transformer balanced i connected pin 3 to pin 1 at the source, so pin 2 had signal at the module and pin 1 shield. I think pot was 10k. If i wanted balanced input it would be THAT line receiver or something like 10k:10k trafo. Found out it was worth paying a bit more for good 2N5457 (iirc text says which company makes them) because they were very close and easier to bias.

 

[pucho812]

yup. I want to try it with a that chip as a balanced line level input. still working, will build a few up and do some testing. the jfet modules are pretty inexpensive to build...

 

[My3gger]

Yeah, play with it, i really liked changing bias because sound is changing so much with it. I would say this gives much more "sound" than iron, so used it only to have proper mic input. 500 series is great idea, i would add output pad and maybe control for several bias points or something like this.