#1
I'm trying to see if I can mod in an fx loop on my cube. However, I can't find any schematics on it, nor do I know what to look for myself.

If I'm correct, you add the loop in between the end of the preamp and the start of the poweramp. That's relatively easy to find with tube amps, but with a digital modelling amp I'm having trouble.

Any tips? c:
#3
Warning! the amp can kill you even when plugged off. Some components store enough charge to kill a person. Also, if it is done incorrectly, it can damage the amp permanently. I am not a qualified electronics technician, I am a mechanical tech. So I may be mistaken on the following information. I also do not know about the reliability of the following source for the amp schematic.

http://www.freeinfosociety.com/electronics/schemview.php?id=1325

I believe that R22 (15k ohm) is in parallel with the reverb. So I believe that the effects loop shall be in series to that resitor/reverb circuit. place it between this circuit and the preamp where there is the 1.1V label either in series or parallel to the clean signal.

I would not do this to my amp. Also, do not mod you amp yourself due to the danger of dying and to avoid damaging the amp. Take it to a qualified technician to carry out the modification. Note that you will need to add a buffer circuit to compensate to the resistance of the cables that shall be used in the effects loop.
#4
I am fairly certain that schematic is not correct. The 20X does not have a reverb breakaway like the one listed. Just a pot. There does seem to be some sort of 3-lead cable run from the EQ/effects section to the later part of the amp. I'm curious if that would essentially let me run effects after the on-board effects section..

I tried checking the circuitry before I started poking around, I didn't find any charges (but was careful nonetheless).
Last edited by Will Lane at Mar 26, 2015,
#5
I'm pretty sure a solid state amp that small isn't going to throw any super dangerous charges around. Solid states usually don't store as much current as tube amps. Added the fact it's so small (20W at that) I wouldn't be so concerned poking around. You may just get a few jolts that'll make you twitch at most

That being said I have no idea about modding this thing beyond that.
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#6
Quote by Gab_Azz
Warning! the amp can kill you even when plugged off. Some components store enough charge to kill a person. Also, if it is done incorrectly, it can damage the amp permanently. I am not a qualified electronics technician, I am a mechanical tech. So I may be mistaken on the following information.



Not true in a solid state amp. Tube amps can have a couple hundred volts sitting on a capacitor, even though it's not plugged in. If you happen to get a shock from a tube amp and your heart is in the path, you could find yourself dead.

Solid state amps still use capacitors in the power supply section, but you're not dealing with the hundreds of volts, like with a tube amp. Better designs will use bleeder resistors to get rid of any remaining charge in a capacitor after the amp is turned off - however, bleeder resistors can fail and they're not always used. In a solid state amp, I'd be more worried about zapping CMOS or MOSFET circuits with static electricity, which might be used in modeling amps.

Someone with adequate electronics knowledge should be able to pull off a mod like this with no problem. You just have to know what you're looking for and where to apply the soldering iron. If you don't know what you're doing, stay out of the amp.
#7
I added an effects loop to my Vox AD30VT.
And it didn't require adding a buffer.
While not the same amp, if it can be done with the Vox, there probably is a way to do it with the cube.
I haven't looked for the cube, but there is a forum dedicated to the Valvetronix amps, which is where I found the info for doing the effects loop mod for my AD30VT.
Perhaps there is a forum dedicated to the cube.
IMO, that would be your best source of info for what you want to do.
#8
No it would not kill to a healthy adult but, I do not know to whom I am talking to. Still it may hurt or having children around while opening the amp.

Installing an effects loop with no buffer would work if you use pedals with a level control. The level control would act as the buffer. Also, on solid state amps they do not sound as great, thus, you are less likely to notice the signal degradation of a passive effects loop.
#9
^Just to be clear, I did probe around a lot and I could only get a few volts in charge, probes direct on the leads. And I am also the youngest in my household :p The board on the Cube is much less straightforward from what I've seen in my small amount of experience. It's very difficult to follow.

I've kept trying to find where I could put the loop, but without a schematic or a professional opinion I'm not sure where it could go. A bit too much effort for my uses, but I might try again in the future. If anyone does know where it could go, I would love to know. I had wanted this so I could have a back-up amp, but I think I'll either just work towards a VT80+ or just use a cab sim to direct input.
Last edited by Will Lane at Mar 28, 2015,