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Hoffman Amps Forum image Author Topic: Adding FX loop  (Read 207 times)

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Offline RoadShow

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Adding FX loop
« 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

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.

Offline Auke Jolman

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Re: Adding FX loop
« Reply #1 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.
With Regards,

Auke

Offline Merlin

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Re: Adding FX loop
« Reply #2 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.
« Last Edit: January 23, 2026, 07:58:34 am by Merlin »

Offline Banjan73

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Re: Adding FX loop
« Reply #3 on: January 23, 2026, 01:36:54 pm »
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.

 


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