Amplifier SS effects loop/reverb circuit questions

[imJonWain]

 I am working on a SS effects loop/reverb project for an amp of mine so I've been reading up a lot and checking out various circuits/ideas.  Most are more or less the same and easily understandable.  However the Laney AOR series II amps have this for an effects loop.

Anyone want to help me better understand what is going on here for the effects loop gain itself? 

what's the jfet switch for?  won't it always be in cutoff with -15v always on the gate?




anyone have any interesting or different circuits for this kinda stuff?  I'll start a thread for my project once it's hashed out better.

[PRR]

> effects loop gain itself?

Need context. There's got to be some series resistors to the left of where you snipped the image. These relative to the 330K set the Send gain. Send level also depends what is to the left of the series resistors left of where you snipped.

The drawing could be clearer. There's two 100K to make a 50:50 Vref divider, but there's other 100K resistors here and there.

The probable point of the JFET is that when the power goes down, the JFET turns "on" and clamps the signal. We all know systems that thump and clunk as they are turned on or off; this may reduce that.

[imJonWain]

gah totally right!  There is jfet switching just before so I just ignored it but there are 1meg resistors on the other side of the switches, makes sense now, standard stuff.

Why are they using -30V in there?  That's the section I am not totally understanding. 


Here's the full schematic
http://www.thetubestore.com/lib/thetubestore/schematics/Laney/Laney-AOR50-Series-2-Schematic.pdf

[PRR]

> Why are they using -30V in there?

Tube amp? (Context!)

Big tube amps have negative supplies to bias the power bottle grids. M-B and many others steal this to run chips. Cheaper than making nice +/-15V rails, and works as good as a +30V supply which is not otherwise readily available in a tube amp.

The 1Meg series also goes with tubes and the (roughly) 1:3 gain in the return. Tube preamp makes big hot signals which must be cut-down to go to external FX. Tube preamps are high impedance and 1Meg is a nice load for them.

[imJonWain]

oh yeah, derp!  Somehow missed the -30V supply, now that completely makes sense.  Thanks for the quick answers!