+- Tube Amp Forum: The Ultimate Tone (https://theultimatetone.com)
+-- Forum: Tube Amp Community (Hi-fi too!) (https://theultimatetone.com/Forum-Tube-Amp-Community-Hi-fi-too)
+--- Forum: Preamp Mods & Design (https://theultimatetone.com/Forum-Preamp-Mods-Design)
+--- Thread: Am I miss something about this FX Loop Design? (/Thread-Am-I-miss-something-about-this-FX-Loop-Design)
Am I miss something about this FX Loop Design? - makinrose - 02-14-2025
Hey everyone! Recently I've seen several amps recently that have serial fx loops that the sends are plate fed with steep attenuation rather than a buffered send. Phaez's Daisycutter (the builder has a video talking about the pre-amp design) and Suhr's Badger both use that type of loop. It all seems like very poor situation for feeding long cables and interfacing with effects. TUT's chapter on FX loops is really clear on that point as are many other sources. Am I missing something? Is there a reason a designer would elect to do it that way? Both of those builders are experienced....
Here's a schematic someone posted for the Badger: suhr_badger_schematic.pdf
RE: Am I miss something about this FX Loop Design? - K O'Connor - 02-14-2025
Hi Makinrose
You are not missing anything
The attenuation is 470k series with 5k6 to ground, cutting the signal by at least 85 or 38dB. The input impedance of the effect is not significant unless it is unusually low to compete with the 5k6.
Following the loop is a free-running gain stage whose output is attenuated through an EQ, and the power amp runs open-loop providing some of the make-up gain needed for the use of pedals in the effects loop.
It is not an ideal arrangement but it is entirely workable.
RE: Am I miss something about this FX Loop Design? - makinrose - 02-14-2025
(02-14-2025, 04:11 PM)K O'Connor Wrote: Hi Makinrose
You are not missing anything
The attenuation is 470k series with 5k6 to ground, cutting the signal by at least 85 or 38dB. The input impedance of the effect is not significant unless it is unusually low to compete with the 5k6.
Following the loop is a free-running gain stage whose output is attenuated through an EQ, and the power amp runs open-loop providing some of the make-up gain needed for the use of pedals in the effects loop.
It is not an ideal arrangement but it is entirely workable.
Cool, thanks for the reply! I just wanted to be sure I understood what was going on.