CE-2 phase prob ? AC coupling?

[jubjub]

Greetings. Have an interesting prob. I use a stereo set-up switching system. In my last stereo loop I have a memory man delay with the delay signal going to one side and the direct signal going to an old CE-2, then to another amp. The problem is that the CE-2 seems to change the phase of the guitar even when the effect isn't on? Does this make sense? Does the buffer cuircut change the phase or do I have gremlins at work?

On a diiferent note, can someone explain the advantages/disadvantages  of A/C coupling a true bypass output to me?
Thanks

[Dman]

Well, lets go for the long answer and then the quick answer.

Long answer- Are both amps in phase with each other when they receive a mono signal? Try that first and see. If so, then its the effects. Have you tried this effects loop on other amps? If so, does it behave the same way?

If your amps are in phase with each other (remember to check the amps first BEFORE DOING THIS), and you are pretty sure you want to keep your effects hooked up the way you discribe, simply take the speaker cable of one amp (assuming a head and cab, not a combo, but it could be done there too) thats out of phase and simply reverse the + and - at one end only. this will  reverse the phase of that amp's speaker and there you go- everything is normal, or in phase.

Quick answer (which ironically will take more work if you have to do it!), is that if you plan to use this effects setup with other amps, you probably won't be able to go around ripping other people's speaker cables apart just for this- to either bring that reversed phase cable with you whenever you know you'll use other people's amps OR you could design and build a buffer circuit that inverts phase of the signal.

Just my two cents here. I'd opt to just make a speaker cable for this use...

[jubjub]

Well, I use a true bypass switching system (the gig rig) so when I bypass the effects the amps are in phase( well, normally there actualy not, but there is a phase switch on the side of the gig rig that lets me correct this prob). Without the chorus in the loop ( remember that the memory man and the chorus are in the same loop, but the chorus is only on one side- direct out of the memory man), the amps are out of phase, but when I take the chorus out completley and just have stereo delay, the amps are back in phase. It just seems to me that phase is such an important thing, so how can an industry standard chorus pedal change your your phase? So my prob is that if I correct the phase for this one loop, all my other presets are out of phase.

[Roberto]

CE-2 seems to change the phase of the guitar even when the effect isn't on?

no, I have a CE-2 too and it not change the phase.

[jubjub]

Hmmmmmmm. Well, I'm confused. I have had this chorus Keeley modded, but I wouldn't think that would do it. I have an old CE-1 that I prefer but it too big for my board. I'll try it and see if I have the same prob.
Thanks for all your help. Will update after some more experiments.

[niftydog]

my 5 cents;

the CE-2 seems to change the phase of the guitar even when the effect isn't on? Does this make sense? Does the buffer cuircut change the phase or do I have gremlins at work?

yes it makes sense. Without knowing the schematic, I would hazard a guess that the buffer is a unity gain inverting op amp.

can someone explain the advantages/disadvantages of A/C coupling a true bypass output to me?

this is by no means comprehensive, but here goes;

AC coupling is supposed to strip any DC component from the signal before passing it to the next stage. Most circuits these days are AC coupled to keep biasing and power supply design simple. AC coupling is however subject to the nasties lurking inside all of your capacitors. In an ideal world, AC coupling works perfectly... in the real world, caps leak small amounts of DC and interaction between them and connected circuitry leads to other problems.

the main problem we often encounter is that caps are designed to store charge, and they do it whether we want them to or not. This means that when they are switched from open circuit to connected or vice versa they suddenly charge or discharge causing a momentary shift in DC conditions… or a pop. To minimise this we try to keep the inputs and outputs of each stage or device as close as possible to zero DC. Usually, a resistor to ground helps, but it’s not always the perfect solution. More info on this can be found by searching these forums.

how can an industry standard chorus pedal change your your phase?

because at the time it was built it was pretty rare to find a stereo guitar rig with lots of pedals.

as you've discovered, you can get pretty messed up with phase switches etc. Seems your only solution would be to individually phase shift the CE2 with your own unity gain inverting buffer.

[cd]

my 5 cents;

the CE-2 seems to change the phase of the guitar even when the effect isn't on? Does this make sense? Does the buffer cuircut change the phase or do I have gremlins at work?

yes it makes sense. Without knowing the schematic, I would hazard a guess that the buffer is a unity gain inverting op amp.

If you go by the schematic, the input transistor buffer is non-inverting (emitter follower), however the pre-emphasis filter is inverting, and so is the de-emphasis filter.  Net result should be non-inverting output with the effect on or off, since the signal still goes through the pre-emphasis and de-emphasis at all times.

[niftydog]

I guess then it's a question of caps in series. Difficult to tell, but maybe it's not an exact phase shift of 180 degrees but a partial shift. Hard to rectify in that case.

[jubjub]

I understand everything except the caps in series. How does a capacitor change phase? How do you have a partial phase shift?

[niftydog]

Phase shift is a fully variable quantity. You can shift the signal by 1 degree or 5,239 degrees, it's totaly variable and not locked into 180 degrees. Although, in the case of speakers and balanced lines etc etc it's very easy to shift the phase by 180 degrees by just swapping some wires over.

caps always have a 90 degree phase shift between voltage and current. That is to say that the current in a cap leads the voltage by 90 degrees. Depending on the circuitry, this phase shift may or may not manifest itself. This is because some devices are voltage driven and others are current driven.

For instance, a transistor is current driven, because the current entering the base dictates the current passing through the collector. However, on the output side, the current passing through the collector induces a voltage in a resistor. Because the current can be phase shifted by a cap, suddenly the input voltage is out of phase with the output voltage - because one of them is derived from the current!

[Roberto]

CE-2 seems to change the phase of the guitar even when the effect isn't on?

no, I have a CE-2 too and it not change the phase.

:roll:

[jubjub]

Sorry it's taken so long to reply roberto. Thank you for taknig the time to post this. I will do the same test on mine and get back to you.