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frank2 19th December 2012 08:56 PM

adding a fxloop to a guitar amp
Hi, i have a ceriatone Straycat and i would like to add a unbuffered FX loop. But i can't find where to cut the signal in the chain. I have made it in a orange amplifier and it was very easy to find the best spot to cut the signal between the preamp and power amp. Here is the Schematic of the Straycat, if someone could help me, it would be much appreciated...

Thank you

Frank Thompson

jjman 20th December 2012 12:54 AM

FX loops provide an advantage only if you intend to sometimes employ clipping in the preamp section. To employ that, the signal would normally be "strong" at some point in the preamp. So some sort of attenuation is normally needed before the "send" assuming a "series" type loop. Otherwise the signal to the loop's effect will be so strong it will overdrive the effects in a bad way. I used a parallel loop in an amp to avoid this issue.

Do you have a schematic? The file you attached is a "layout."

frank2 20th December 2012 01:05 AM

hi, thank you for your reply, i wan't a unbuffered effect loop because i use an external buffer. It is indeed too strong else and it may broke an effect or cause artefact. I am happy i ain't blow my carbon copy pedal when i learn that. I only have the layout unfortunately... the problem i have to determine where to cut the signal is that two separate signal ( at J and K ) enter in each EL34 tube. The signal seem to split right at the beginning at (L and N). When it come to this amp, i don't understand a lot of how it work. I have some knowledge but most of the tube amp i have deal with were much simpler in their design... Hope you can help me..


kevinkr 20th December 2012 04:39 AM

:cop: Please post all guitar amplifier threads to the proper forum which is Instruments & Amplifiers.

At the top of the Tubes / Valves forum is the following statement:

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum
Moved per forum policy.

GeorgK 20th December 2012 09:36 AM


Originally Posted by frank2 (
the problem i have to determine where to cut the signal is that two separate signal ( at J and K ) enter in each EL34 tube. The signal seem to split right at the beginning at (L and N).

Hi Frank,
you have to cut BEFORE the phase inverter of course. You could do this at the input or output of the master volume control. Depending on the buffer you use this might affect tonal characteristics anyway as you are connected directly to the output of the tone stack there. Use good shielded cables to the buffer and keep them as short as possible. The reason that the amp has no loop might be that there is no ideal place for one.

frank2 20th December 2012 02:26 PM

Okay, i will try it there, anyway hole has been made on the back so i prefer having a bad fx loop that i don't use than two hole for nothing :P Thank you very much for your help, i will do as you say.

Forum mod: sorry about posting in the wrong section, i have just read the first sentence.. :P

JMFahey 20th December 2012 05:12 PM

The proper point for a "Preamp Out > Power amp in" is cutting the red wire in the center leg of the Master pot which goes to a .01uF cap on Pin 7 of the PI.
That said, signal level there will be a couple volts RMS and will absolutely clip to death *any* regular "floor" pedal you may have.
It might be used with Studio type Rack Processors designed to work at a +4dBV level. (around 1200mV RMS)
Most floor type pedals or processors expect around -20 dBV (70/80 mV RMS).
Even if you pad the signal down so they can swallow it; then they probably won't be able to supply without clipping the signal needed to drive a tube power amp.
I don't think you want to introduce SS uncontrolled distortion in your sound ;)
The proper way to do this is, for example, the Soldano way, who pads 20X the send signal, and then reamplifies it again 20X with tubes, before resending it to the Power Amp.
And even so, he recommends Studio type stuf there .

frank2 21st December 2012 01:38 AM

i plan to build a Ceriatone "c-lator" witch is based on Dumble "dumbleator", one of the best tube fx loop buffer for that purpose, thank you.

Frank Thompson

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