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How do you make an effects loop?

Started by d4v1d5hu13r, April 27, 2007, 09:08:04 AM

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d4v1d5hu13r

Hey guys, I want to create an effects loop in my amp so I can buy the EHX tube eq pedal and make it a hybrid. How would one go about doing this?

teemuk

#1
Here is one alternative: Cut the signal path at suitable position to form "input" and "output" for the FX loop. Put a unity gain buffer to precede the input so that the loop won't load load the circuit. Connect the output of the buffer to a phono jack that has an internal switching mechanism, which connects one "lug" to the tip while no plug is inserted. This is the send jack. The signal path (from the buffer) should then connect its tip. Sleeve is naturally connected to common. Solder wire from the "switch" lug to the "switch" lug of another switching jack ("return"). Now the signal line is intact while no plugs are inserted to the jacks. The signal path naturally continues from the tip of the return jack. The sleeve (once again) connects common. I suggest you buffer the signal from the return jack as well (again not to load the preceding circuit). The output of the buffer then connects the other side ("output") of the trace you cut.

Buffer:

Switching jack (A jack plug breaks the contact of a normally closed switch):

d4v1d5hu13r

Can you put that in Noob terms please? :D

teemuk

Frankly put, I can't. Electronics is technical, if you are too "noob" to understand it then you have no other choice but to help yourself and do some studying to ascent from the "noob level".  ;) There is no way one can just rush into this stuff without proper technical knowledge. You can take your chances but you have better luck if you know what you are doing...

Take this as a fair warning: If you are not handy with working on printed circuit boards, soldering tools and do not posses at least a decent electronics knowledge, attempts to mod your amp can easily ruin them to a point where they need an expensive repair job. At worst case you will electrocute yourself.

I apologize if my post didn't seem to make sense. English is not my native tongue and sometimes I have problems expressing things clearly. Perhaps someone else can describe the configuration more fluently. However, I don't think my explanation was too technical for anyone that has skills to start working on the amplifier as "severily" as insering an FX loop into it.

You asked how to design an FX loop. I presented one alternative. Naturally, I leave the final design choices and implentation to you (i.e. how to design the buffer stages). You know your amp amp, you know its schematic (likely) - whereas I have no slightest clue about it. The explanation above was all I can give. Unless you want an explanation on how to insert a parallel FX loop. (The described one is in series). I'm not going to design you anything - unless you pay me, of course.  ;D

Here is a picture showing the configuration. I hope this clears things up a bit.

frank2

Hi, i have done a mod on my Orange Tiny Terror, i have found the point between preamp and power amp, did the effect loop mod. Still i have that tone sucking problem when i use my MXR carbon copy. The effect is good, very good compared at when it sit in front of the amp but the tone is dull and overall volume is reduced.

So i have done a lot of research and so far, it seem i need a buffer. I want to add it inside the amp. Very simple on/off buffer. Don't want it to blend or anything.
It is very a impedance issue. The amp give an impedance of 100K and the pedal is not taking it. When the pedal is in bypass, it is perfect.
That plan here seem what i am looking for. But what is the buffer we should use?

joecool85

Any of the buffers here should work just fine for your purpose: http://www.muzique.com/lab/buffers.htm
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

frank2

okay thank you, i will read it tomorrow, i am totally wasted tonight  ;)


J M Fahey

Hi FRank2.
Please post the schematic of what you did, so we all talk about the same.


J M Fahey

I'm cutting and pasting it here for easier viewing:

It's a classical Effects Loop insertion point, but be aware that there are two full gain stages before it, signal voltages must reach real scary values there, maybe some pedal effects will take it, others won't.
The "problem" with the Tiny Terror is that it does not clip the preamp but the power amp tubes driver stage, tens of volts there, so really any Effects Loop is *still* pre-distortion.
The only real (expensive) way to add a Loop is to go the (excellent) Phatt way: hook the Tiny Terror to a load box, tap some of that signal, send it to the loop and reamplify with another amp.

frank2

Okay, i will try to take a voltage there while playing(i will open a jack and put aligator clip there)
Wouldnt a buffer at this place the best solution?

The carbon copy have taking it so far, i won't test too much before next step, i don't want to broke it. Still, the sound is very different in this effect loop than in front of the amp.

J M Fahey

QuoteStill i have that tone sucking problem when i use my MXR carbon copy. The effect is good, very good compared at when it sit in front of the amp but the tone is dull and overall volume is reduced.
Talking specifically about this effect:
1) The "dull tone" may be due to lack of buffering, but you may compensate it by adding a "bright cap" in the second half of the gain control.
Copy what C10 is doing. It should do.
2) I'm afraid you won't be able to solve the loss of volume.
That 12AX7 is fed around 250V DC , and can easily provide from 60 to 90V AC of audio before clipping; any 9V DC powered pedal will clip trying to reach 3 V AC.
The only way to beat that is what Soldano did in the SLO100 (check the schematic): they attenuate 50X the distorted signal, send it to the loop, and then add a full gain stage+cathode follower to recover original level, and even more important: if there is any clipping there, it's *tube* clipping, and not the fuzzy dull SS clipping of a poor pedal being beaten to death.
But then that's why a Soldano is a World class amplifier and most "good" others (including Mesa Boogie) shamelessly copy it.
Oh well.
I think the beauty of the Tiny Terror lies in its being small and simple yet offering excellent sound.
Try to keep it that way.

phatt

Frank2,
           Mr Fahey is trying to tell you in a nice way,,,, I'm a little more direct. :trouble

I know it will fall on deaf ears but EFX loop is about the dumbest thing ever invented.
Half useable in SS Amps but in a tiny Amp such as this it's about as useful as an ashtray on a motorbike.

There is little an efx loop can do that can't be done at the input of a decent well designed amp.

In My Observation it seems the loop thing is more of a fashion statement than a useful tool.
If I could get a dollar for every axe player that askes me to sort out there efx loop issues,, I'd be rich by now.

The few tricks that can be done *only with EFX loops* are like one hit wonder tricks in some songs that may only get used once in a while.
Leave that until you are famous then the big names will fall over themselves to do it for you. 8)


Read again what JM Fahey is trying to suggest.
The signal at that point in the circuit has to be completly re-designed to work.
You need at least one more triode to make it work.

Your Amp was never intended to have efx loops, If you can't live without one then buy an amp that already has one.

A tube Amp is/was designed to work as *one*. The big signal from the triodes makes the power tubes respond in a very dynamic way.
Cut an efx loop in at the point you show you will just kill all the magic of Valve Amps.
(The very symptoms you have stated)

May as well go get a SS Amp and be done with it.

Hint keep the amp stock and soak it,,, worked for EVH ;)
Yes I use a very simple Valve Amp (not unlike yours) which is loaded via a soak and Reamplified into a second Amplifier.  Far more usefull than those efx loops and you have access to a whole list of tricks not just efx.
Cheers, Phil.


frank2

Damn, i have already make hole on the side of my TT  :P
I was wanting a fx loop for acceptable echo/delay/reverb...
Look like a carbon copy will be for sale pretty soon...

frank2

I forgot, thank you very much for your useful info, i should have ask before piercing the amp lol
At least the job is clean...