Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: RoadShow on January 22, 2026, 01:29:01 pm

Title: Adding FX loop
Post by: RoadShow on January 22, 2026, 01:29:01 pm

Before I ask my question, I did read this thread and others:
https://el34world.com/Forum/index.php?topic=10208.0 (https://el34world.com/Forum/index.php?topic=10208.0)

and when I built the dual JTM45/2203 amp 3 or so years ago I included the Metropolous FX loop board.

So, here's my question.  The Ceriatone FX loop just has jacks, intercepting the MV output to the PI .022uF cap.  Can that be problematic, or can you get away with it.  See attachment.

Title: Re: Adding FX loop
Post by: Auke Jolman on January 23, 2026, 03:43:05 am

You can get away with it because the tonestack is driven by a cathode follower getting the impedence right. There will be some volume loss depending on the pedals you use in the loop.

Title: Re: Adding FX loop
Post by: Merlin on January 23, 2026, 07:56:25 am

The cathode follower is irrelevant. It's a cheap n dirty way to do it. Output impedance is high and you have no recovery gain, so some pedals won't be able to drive the power stage to full output. It has major shortcomings but it's better than no FX loop at all, I guess.

Title: Re: Adding FX loop
Post by: Banjan73 on January 23, 2026, 01:36:54 pm

Quote from: Merlin on January 23, 2026, 07:56:25 am

The cathode follower is irrelevant. It's a cheap n dirty way to do it. Output impedance is high and you have no recovery gain, so some pedals won't be able to drive the power stage to full output. It has major shortcomings but it's better than no FX loop at all, I guess.

Agreed.
I've built a couple of effects loop now and my experience is that you really need both cathode follower to minimize output impedance on "send"  AND a recovery stage after "return" to make it work properly.