Hello dear people of Tube Town!

First off, I apologise for posting in English instead of German. I'm from the Netherlands and I could attempt to write a bit in German but I fear it would be a mess - and I'd probably cause a laugh or two among you. Anyway, on to the issue at hand.

I would like to integrate the LND150 Seriel FX Loop into the Lummerland Express because I'd like to use time based effects after the amps gain stages, so to speak. I'm not sure where to insert the FX Loop though. I was thinking to integrate it between C6 and R28. Would this work, or would I better be off integrating it elsewhere in the circuit?

Thank you all for reading, I look forward to your replies

Links to the projects/schematics mentioned:
Seriel FX-Loop LND150: https://www.tube-town.net/info/datenblaetter/kits/kit-fxloop150-revc-en.pdf
Lummerland Express: https://www.tube-town.net/cms/userfiles/downloads/kit-lumex.pdf

Best regards,

Kerin

Hi Kerin,

welcome to the board.

I would use a different insert point.

I recommend using the insert point between R10 and the grid of the tube (at R11).

With that you still have a gain stage after the effect loop.

Hi Kerin,

welcome to the board.

I would use a different insert point.

I recommend using the insert point between R10 and the grid of the tube (at R11).

With that you still have a gain stage after the effect loop.

Hi carlitz! Thank you for your answer.
Wouldn't the gain stage after the effect loop potentially distort/overdrive the effected signal though? I'm worried about delay and/or chorus sounding muddy due to distortion/overdrive. The LND150 FX Loop has send and return controls, so I suspect it'll have enough "oomph" to push the cathodyne phase inverter.

The voltage gain of a cathodyne (or split-load) inverter as used in the Lumex is below one.
Means that the PI input sensitivity may be lower by a factor of 30 compared to the LTP inverter shown in the application example of the FX loop.
So you need an extra gain stage before the inverter to compensate.

The voltage gain of a cathodyne (or split-load) inverter as used in the Lumex is below one.
Means that the PI input sensitivity may be lower by a factor of 30 compared to the LTP inverter shown in the application example of the FX loop.
So you need an extra gain stage before the inverter to compensate.

Hello Helmholtz, thank you for your answer!

Ah I see! So if I understand correctly, the gain stage preceding the PI is actually considered part of the PI due to the needed gain compensation. It's unfortunate that the FX Loop documentation does not state what the Return level gain is. Going from your answer though, I assume it's probably not enough to drive the PI sufficiently.

Ah I see! So if I understand correctly, the gain stage preceding the PI is actually considered part of the PI due to the needed gain compensation. It's unfortunate that the FX Loop documentation does not state what the Return level gain is. Going from your answer though, I assume it's probably not enough to drive the PI sufficiently.

To be clear, I have no own experience with the Lumex and the LND loop circuit.
This is the first time I looked at the schematics.
My comment was based on general circuit considerations taking into account the post of carlitz.

Regarding your question, the PI is an essential part of any (tube) push-pull amp.
It's job is to provide opposite phase (or polarity) output signals to drive the output tube(s).
Some PI circuits add gain (like the LTPI  or the paraphase), some don't (like the cathodyne).
I wouldn't call the gain stage before the cathodyne part of the PI.
Rather for a total gain comparable to the LTPI the cathodyne needs a preceding gain stage.

Are you using line level effects?

Also don't forget that very low power amps like the Lumex are typically played with more or less power amp clipping which might muddy up time based effects anyway.
IMO it's best to add such effects in the mix.

To be clear, I have no own experience with the Lumex and the LND loop circuit.
This is the first time I looked at the schematics.
My comment was based on general circuit considerations taking into account the post of carlitz.

Regarding your question, the PI is an essential part of any (tube) push-pull amp.
It's job is to provide opposite phase (or polarity) output signals to drive the output tube(s).
Some PI circuits add gain (like the LTPI  or the paraphase), some don't (like the cathodyne).
I wouldn't call the gain stage before the cathodyne part of the PI.
Rather for a total gain comparable to the LTPI the cathodyne needs a preceding gain stage.

Are you using line level effects?

Also don't forget that very low power amps like the Lumex are typically played with more or less power amp clipping which might muddy up time based effects anyway.
IMO it's best to add such effects in the mix.

Good morning!
I understand, sorry if my earlier post came across brash, it wasn't my intention. I was in a bit of a hurry.

Thank you for your explanation, I did some reading and grasp the differences between the PI's.

I will be using regular stompboxes/pedals for effects - so no line level effects. I plan to use the amp as a living room unit with a low efficiency speaker (the WGS Veteran 10) so I won't be driving the power tube into saturation very often.

When I've got the amp completed I'll try inserting the FX loop at different nodes, can't hurt to experiment right?

I will be using regular stompboxes/pedals for effects - so no line level effects.
When I've got the amp completed I'll try inserting the FX loop at different nodes, can't hurt to experiment right?

Regular pedals expect a guitar level input signal which is typically in the 100mV range.
So here's another good reason to insert the loop before the gain stage where signal levels are lower (but still might be several volts).
Generally line level effects are better suited for amp loops.

As you said, experimenting can't hurt.