Simple buffered effects loop

[jestaudio]

Ok, I know some guys have managed to squeeze a full Dumbleator inside the chassis but I really want to cut this down the minimum literally a send level and return/recovery level, no bright caps or switch's, can someone point me in the appropriate direction of the simplest working solution, the rack effects I use has extensive eq capabilitys
many thanks in advance

[martin manning]

xtian did a version of Blencowe's serial loop here: https://tubeamparchive.com/viewtopic.ph ... highlight=
You can easily add a 1M return level pot in place of the 1M grid leak resistor on the recovery stage.

[jestaudio]

xtian did a version of Blencowe's serial loop here: https://tubeamparchive.com/viewtopic.ph ... highlight=
You can easily add a 1M return level pot in place of the 1M grid leak resistor on the recovery stage.

Tried mocking up that one and couldn't get it to work, I,ll have to have another look see if I screwed up

[10thTx]

There are numerous schematics of FX loops here:

http://el34world.com/Forum/index.php?topic=10208.0

I have used this one in 4 different amps and have liked how it has turned out for me.

With respect, 10thtx

[jestaudio]

Just had to walk away from my bluesmaster for a bit, I have been trying to implement Xtian loop with absolutely zero success , I have rebuilt it at least 4 times, the recovery side works ok but the input just will not work, either I,m totally missing something or just plain mad, any help is appreciated at this point

[martin manning]

Get voltages on the loop's tube pins and post. Also, what's the supply voltage at the top of the plate load resistors? Do you have Merlin's book so you can see the schematic?

[jestaudio]

pin 1 260dc
2 ov
3 1.89 dc
6 257
7 0v
8 3.19 dc

Probing pin 6 gives a loud sound, as does pin 1, signal injected into the return socket works fine so the recovery half should be good,

I don,t have a copy of Merlins excellent publication..............yet

[martin manning]

The 3.19V on pin 8 (that's the send side right?) looks about 1V high. The odd thing is the plate looks right. Are you testing with nothing plugged into the loop jacks?

[jestaudio]

The 3.19V on pin 8 (that's the send side right?) looks about 1V high. The odd thing is the plate looks right. Are you testing with nothing plugged into the loop jacks?

That's the send side, nothing in the loop, looking at a few other loops the whole thing looks wrong to me

The original passive send from the relay is attached to the 1 meg as indicated in the layout Xtian posted

[jestaudio]

This it what I,m working from

[martin manning]

The layout seems to be correct, and the whole thing should just insert between the OD relay and PI input cap, so output from clean or OD (as determined by the relay) to "in" and "out" to the PI input cap.

[jestaudio]

The layout seems to be correct, and the whole thing should just insert between the OD relay and PI input cap, so output from clean or OD (as determined by the relay) to "in" and "out" to the PI input cap.

Yep tell me about it, i have no idea what the hell is wrong with it, i have input into the 1 meg and absolutely nothing out of the send jack, if i connect the send to the return , nothing

[martin manning]

Tried a different tube? I'm bothered by the 3.2V on the cathode of the driver stage. Both sides have the same supply voltage, plate load, and cathode resistor so the voltages on pins 1 and 6, and on 3 and 8 should be very close.

[jestaudio]

Jeez wept to i feel like a asshole, pin 7 and 8 reversed, all sounds good, just need to figure where the return level needs to sit


Many thanks for your input Martin, made me actually look and think

[martin manning]

Great! Do you have a return level pot? Merlin suggests a 100k, but it probably isn't too critical. FWIW, I would make the input divider 910k and 33k to get unity gain through the loop when nothing is plugged in.