The Verdict Is In! Sort of...

[Zaphod B]

I mentioned a couple of weeks ago that I was going to build a bypass box so that I could judge the Pod XTL's effect on tone.

I got the parts in last week and built the box on Friday. I've had a couple of days to play around with it - toggling between true bypass and keeping the Pod in the loop with no amp models or effects enabled.

I am using a Vox AC30CC 2 X12 amp, and I have not yet experimented with all the guitars - so far, the Les Pauls and my Xaviere Strat-like guitar.

The short answer is that the Pod does affect the tone, but not very much. Not enough that you'd be able to tell in a blind listening test whether you are listening to true bypass or Pod-in-the-loop. I'd characterize the Pod's effect on tone as causing a very slight loss in clarity (upper mids perhaps?) and a very slight increase in bottom end.

The most difficult part of comparing apples to apples is dialing in the Pod's output level so that it matches the line output level of the guitar. Otherwise any tone difference heard from the amp is as likely to be due to a difference in input level as anything else. That said, with output levels matched as closely as my ears would allow, the tone difference is minimal. So minimal, in fact, that since my bypass box does not have an LED indicator, I couldn't tell which was which unless I enabled an effect on the Pod.

So I think the Pod will serve well as a programmable multieffects floor unit, with the amp modeling stuff not being used.

Having said that, I think that the tube amp ameliorates the effects of the Pod's digital signal chain a bit, because when I listen to the Pod directly though headphones, or input directly into my Tascam, it still sounds a bit Piezo-like and artificial.
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Now for something curious and very puzzling, and I would welcome your opinions.

First let me state that the bypass box operates as it should - clearly toggling between the two states. It is well grounded and the box is cast aluminum which means it is well-shielded. I can detect no cross-talk between the two states (for example, with the Pod having a couple of very obvious effects enabled and the box in "bypass," the effects are not audible through the amp).

The Pod has a TAP/TUNE pedal, which doubles as a tap-tempo button, or when held down, invokes an onboard tuner. When the tuner is enabled the output from the Pod is disabled. I was messing around with the setup last night, and to my surprise I found that even when in the "bypass" mode, the Pod is picking up some stray signal - enough for the tuner to work! And, get this - when the Pod is in the loop, with the guitar's volume all the way down, the Pod picks up enough signal for the tuner to work.

I'm really puzzled by this. I can understand that the guitar's volume knob (this happened with the '76 Les Paul Special) might not actually be attenuating all the way, although it seems to be. I can also understand that there may be a little crosstalk occurring in the DPDT switch, but I can't imagine it would be enough to operate a tuner if it's not enough to cause audible crosstalk.

I'm thinking it's a case of a hypersensitive tuner, with a little bit of bypass box crosstalk and a little bit of old volume knob.

Any thoughts?

 

[Jouni]

That's an interesting result to know about Pod... why, I don't know..

Actually, it'd still be interesting.. To know why the outputlevel of Pod is affected when bypassed, and what's the difference when the Pod is at "0db" ..or so. Because if it's weakened at that point, the pod must amplify it to compensate.. Then again, what's the difference if tone remains unchanged.

Mmmm, the tuner... could be it's just sensitive to them telekinetic waves sent by your brains, correlating to heard tune.

 

[Zaphod B]

Actually, it'd still be interesting.. To know why the outputlevel of Pod is affected when bypassed, and what's the difference when the Pod is at "0db" ..or so. Because if it's weakened at that point, the pod must amplify it to compensate.. Then again, what's the difference if tone remains unchanged.

I don't know if the output level of the Pod is changing when bypassed - I don't think so, but I can't hear it. (Because it's bypassed. ) It should just be sitting there idling as if it had no input. The integral tuner automatically shuts off the Pod output.

Mmmm, the tuner... could be it's just sensitive to them telekinetic waves sent by your brains, correlating to heard tune.

Ha! Actually I thought it might actually have a little external mic or something, like chromatic tuners do........but it doesn't.

 

[Zaphod B]

Jouni, what I meant in my original post about the Pod's output is that it is adjustable, both from an overall output pot on the back, and from individual bank volume levels that can be saved with each bank.

So it was just a case of adjusting the Pod's volume to match the dry guitar's volume. There was no interaction occurring.

 

[Bluffboy]

any electronic sound modification will do that. Which is sad, but at least they are improving...

 

[Zaphod B]

any electronic sound modification will do that. Which is sad, but at least they are improving...

Well, you can't expect a completely transparent A/D/A conversion at the Pod's price point. The issue for me wasn't so much "does it affect the sound," as much as "how much?"

 

[ggunn]

I set up a similar test with my Pod, my Strat, and my BF Deluxe Reverb. I noticed enough of a degradation in glassiness in the #2 (quack) position through the Pod that I decided against using the Pod as an effects module.

 

[Zaphod B]

I set up a similar test with my Pod, my Strat, and my BF Deluxe Reverb. I noticed enough of a degradation in glassiness in the #2 (quack) position through the Pod that I decided against using the Pod as an effects module.

Interesting, ggunn - thanks. I haven't spent much time with my Strat copy, no time at all with the real Strat, and no time with the Tele. I'll give a close listen to the #2 and #4 positions on the Strats. But you're right on in the use of the term "glassiness" because that's what the LPs seem to be losing a bit of. In my case it doesn't seem to be much, though.

 

[Whale Bone]

Pod tuner reacting to no signal:
I would guess that when the Pod is bypassed with your box, that it's input cable, particularly the hot, is left open, and not grounded. Input jacks, as far as I've seen, are generally switched so that the hot lead is grounded when nothing's plugged in. If I leave a patch cable in the input of my Boss TU-2 tuner, and leave the tuner on, it registers 60-cycle hum by jumping back and forth between b and b-flat (where 60Hz lives).

Tuner registering when guitar volume is down:
When you turn your volume down, and the tuner still registers input, I believe it is because the signal is not actually being fully shorted to ground, leaving enough for the tuner, but not for your ears. Typically, one end of the pot is grounded to make the volume-off state, but the wiper doesn't short fully to that end even though the pot may be turned all the way down.

One of the volumes on my Gibson EB-3 doesn't even close or short to an inaudible level. Every basss I have will register on the tuner when turned all the way down.

On atleast the basses, I have found that I can't trust the tuning with the volume down. When I suddenly find that all the strings are a little out of tune, it's usually because I forgot the turn the volume up while tuning.

Your bypass:
Did you do anything fancy with the wiring like add a cap or use a special switch to make switching quiet? All the switches I used to make home-brewed boxes always made a real ugly, speaker-wrenching pop.

 

[ggunn]

Your bypass:
Did you do anything fancy with the wiring like add a cap or use a special switch to make switching quiet? All the switches I used to make home-brewed boxes always made a real ugly, speaker-wrenching pop.

You can add a very large resistor (10 Mohm or so) across the terminals of the input and output jacks to dump whatever capacitive charge you have to ground. That will help the pop.

 

[Zaphod B]

I have no fancy wiring in the bypass box - just hardwired connections between the jacks and switch - and there is very little switching noise. The mechanical noise of the switch itself is louder than the electrical switching noise.

Whalebone, you are correct that I am using non-shorting jacks. My reasoning for this was that the jacks should mirror the input and output jacks of the Pod, which I assumed to be just open when nothing is plugged into them. So when the Pod is bypassed the signal path to the Pod is open but the ground path is shared with the other jacks in the box. Is this an incorrect way to do it? Edit: The issue of whether the input jacks are shorting or non-shorting is moot when cables are actually plugged into them, which of course there will be if the box is in use.

By the way, the tuner isn't responding to 60Hz when the Pod is bypassed - it's actually able to tune the guitar but it's accuracy is a little off as you described happens to you when your bass is turned down. Same situation when the Pod is in the loop with my guitar's volume all the way down - it tunes but a little inaccurately.

 

[Whale Bone]

If the tuner's receiving a signal when bypassed by the external bypass, I would think it's not truly bypassed. That's strange. Here's how I would wire it (attached image). The ground on the one terminal of the switch will ground the input of the Pod when bypassed, but it shouldn't really be necessary.

Regarding grounding inputs when not in use, all my amps have always had that feature. I think it's a standard thing to cut down on noise, especially on an unused channel. For the Pod floating, disconnected, it shouldn't matter at all, unless you were taking some other signal out of the Pod at all times and wanted it silent when not in use - not the case for what you've described.

 

[Zaphod B]

Give me a little time to draw up my wiring diagram and I'll show you how I did it. It's a little different from yours, Whale Bone.

 

[Zaphod B]

OK, here we go - not sure how this is going to size....
Edit: corrected Send & Return labels...

 

[Whale Bone]

I think you swapped the send and receive in the drawing, but, yeah that's nice and clean. No reason the Pod should get any signal on bypass, unless there's some connectivity between the end terminals on the switch. Who knows?

 

[Zaphod B]

I think you swapped the send and receive in the drawing, but, yeah that's nice and clean. No reason the Pod should get any signal on bypass, unless there's some connectivity between the end terminals on the switch. Who knows?

Oops! You're right, I was in a hurry and swapped the labels. I'll go back and fix it here in a second.

The only thing I can think of is that there's a little crosstalk within the switch.

 

[ggunn]

Oops! You're right, I was in a hurry and swapped the labels. I'll go back and fix it here in a second.

The only thing I can think of is that there's a little crosstalk within the switch.

It could be that there is a little wiggle on the ground line from the guitar that gives the tuner enough to work with.

 

[Zaphod B]

It could be that there is a little wiggle on the ground line from the guitar that gives the tuner enough to work with.

Yeah, that's possible, too. I'm just surprised that the tuner is sensitive enough to pick it up at all.

 

[DrewPeterson7]

I have nothing to really contribute, but I just wanted to say this is a great thread.