How to add an effects loop to this?

[ncusack]

Hello,

Im looking to add an effects loop to the California Dreamer Lite amp found on ax84. I've posted a few things over there but have yet to really get the answers im looking for.

Ive attached a schematic image of the amp. I also have the .sch file and can send it to anyone willing to show me the edits required to add an effects loop.

[Jazz P Bass]

I would think that an effects loop would have to be driven.
At the least, the send.
Which would you prefer?
Solid state or a tube?
For that matter, where are you going to put it if it is a tube?
And powering an opamp is going to be tricky.
You could look at a Marshall JCM 800 schematic to see how they did it.
Or a newer Fender amp.

[ncusack]

If possible id like to keep things all tube in this build. Maybe the better bet here would be to design a cathode follower tone stack and feed the output of that into an effects loop and into the PI.

[pdf64]

'Maybe the better bet here would be to design a cathode follower tone stack and feed the output of that into an effects loop'
Probably not, as the output of a regular tone stack is high impedance and so you would still need to reduce the impedance and signal level. Then have a gain recovery stage after the loop.
But the important question is, why do you think that an effects loop is needed; what benefits do you think it will bring?
Because unless an amp has a master volume (which is likely to be adjusted such that the power amp isn't getting heavily overdriven) and a pre-amp with adequate gain / overdrive potential, then the rationale for adding a loop isn't usually very strong.

[J M Fahey]

*Very* short answer: nowhere. Nor is it needed.
"Floor" pedals are designed to work with Guitar-level signals (duh!), meaning around 100 mV with 1V peaks.
In that amplifier you'll have 50 (fifty) times that level at the first 12AX7 plate; probably still around 5 to 20 times the guitar signal after the tone stack, depending on settings, and tens of volts after that, because the gain chain goes upwards, so, no "pedal friendly" environement at all, unless you want, say, to use your delay pedal as a farty buzzy horrible fuzz; limiting maximum power to boot.
The "trivial" solution would be to pad that signal to pedal-friendly levels and later re-amplify it ..... which would be the same as hooking the pedals up front.
The main reason for loops is to allow for "clean" effects be added *after* the distortion, which in this amp is generated only in the output stage, after everything else.
That's what PDF64 hinted at with his question.

[ncusack]

That makes a lot more sense now. I never really thought where the distortion would occur in that amp. The main idea would have been to have the loop for reverb and delay effects but it sounds like running those in front will achieve the same thing.

Thanks for setting me straight here.

[J M Fahey]

A *real* spring reverb (as opposed to a digital emulation) may be added between the volume control wiper and the following grid, even if IC driven, because a typical recovery op amp will give *up to* 5V RMS when just clipping, which would be hidden by the power tubes clipping way before that.