bordonbert

Thanks for the reply Zolko. I've done that as best I can. It's lucky I'm a Line6 Variax guitar owner and I am already registered with Line6 for that. It does seem you have to have registered a product to request info via a ticket which is logical I suppose. I have raised a ticket but only as an advisory supporter of the original owner, best to be straight with them I find. Whether they will talk to me or not is up for grabs. If they will release info on the output impedances in the Open/Short states, or at least the general configuration of the circuitry on that socket, we could maybe get more amps working with it by trimming values in their own circuitry. I'll let you know how I get on.

I'm having the same problem with a H&K TM18. The problem may not be to do with additional voltages on the output, I strongly suspect it is to do with additional residual resistance in the control line. The switching on many amp models with passive footswitches of a TRS type is done by shorting a line to ground and pulling a current down it which is detected inside the amp in some way. It isn't directly voltage related it is current based. It might run a relay direct or it may trigger other solid state circuitry, both of these happen in the H&K amps. When extra resistance is introduced to the line it reduces that switching current to the point where it does not reliably trigger the amp circuitry any more. Likewise in the open state, when the current should be 0mA due to an infinite resistance open circuit switch, the HX leaves a high resistance still in the line which will of course leave some current flowing which may still partially trigger the amp in the opposite way. The H&K amp shows similar symptoms to those posted here. Its control LEDs can stay on dimly when they should not as they are actually in this control line indicating there is still current flowing when there should be none. The amp tone and noise suffers as only some of the circuit functions are changed and the amp is left in an indeterminate state with stages no longer set up to match each other. This effect can even show itself only after the amp has been on for some time and has presumably heated up components inside changing the switching conditions slightly. I have asked about the impedance conditions on the HX Ext Amp output elsewhere but, as it is able to be configured as an input for Expression Pedal use too, I really suspect this is the reason why you are seeing what you are seeing. To their credit, Line 6 do warn that this is a possibility in the manual. With the flexibility of that socket for use as an input and an output it is not surprising that these problems can arrive. We pay for that flexibility in this way. The only reliable way round it would be to add some sort of circuitry to switch according to the HX command and trigger full switching in the amp line with maybe a relay or lower impedance component. That isn't hard in any way but it is a pain!

I have an enquiry on another forum from someone who is using a HX Effects unit in 4 cable mode with additional switching to control his Hughes & Kettner Tubemeister 18 amp channel and boost settings. As I understand it the Pedal/Ext Amp socket of the HX has been configured to switch channels in the amp by effectively emulating a plain old "FS2" type passive TRS stomp switch. To their credit, in the Helix manual Line 6 does warn that this is not always fully compatible with all amp units but gives no further technical details which might help. The owner found that the amp is not reliable in its switching when controlled by the HX, though it works perfectly with a mechanical switch of course. The reason I know is that the HX is introducing some additional resistance to the H&K control line when it should be a dead short thus decreasing the switching current in the amp presumably to the very edge of reliability, and it also appears to be leaving a residual resistance in the line when it should be open circuit increasing the current which should be 0mA in that state. This effectively runs the simple direct switching circuitry inside the H&K, a mixture of a simple relay and BJT+FET saturation switching units, over too narrow a band whereby not all switching elements activate/deactivate at either extreme. Can anyone give me any info on the output impedance of the HX control circuitry in the On and Off states when it is used in this way? I would guess it must be fairly significant seeing that it can also act as an input for an expression pedal in a different mode. Would it help to approach Helix Tech Support direct rather than using the forum for such a specifically technical enquiry? I'm not underestimating you members' technical ability, only the availability of the information outside of Line 6.

I have to admit to thinking about this last night and wondering if it would be even possible to separate the two. They share aspects like the selector switch and control pots so they are not already set up to be accessed individually. I would have thought there would be no way to rewire so the analogue pups can be used at the same time as the digital signal, it would need at least another set of controls and selector. The idea of bringing both out simultaneously to two amps then selecting which one to use externally seems a bust. And the fact that you have had this warning officially ZB at least sorts out one of my own particular issues. If the passives go through an onboard preamp just as the digital stuff does, that means my worries about cable length capacitive loading are a non-issue. With the guitar actively buffered it will look like a low source impedance so won't matter. Roll on 25m leads! ;)

I think I can maybe see where you are going with that. I use a H&K GM36 which is a fully midi controlled four channel amp with its own effects. I am finding it a new process to change the amp patch and perhaps switch between setups on the JTV59 as well to go from one sound for normal playing and another for solo. Is that your issue? If only the JTV could be controlled by the same midi controller as the amp which has its own dedicated footswitching unit. Don't know if there is a better solution for you but I wouldn't like to have to trail a pair of leads, one for analogus and another for the modelling. I find one enough to trip over and step on occasionally. :P A footswitch kick and a guitar press are still my chosen route and I'll just have to become comfortable with that process when it's needed I guess.

Have you a specific need for this BW, like routing to a separate amp? Or is it because you maybe believe that the analogue signal is being "polluted" by the digital side somehow?

I can second Andertons in Guildford Matt. I just bought my JTV59 a couple of weeks ago and they had the range in then. They also had the XPS-AB footswitch in at £25 too.

Yes, that's the one. You simply plug in the guitar to the footswitch with a TRS (Tip Ring Sleeve - stereo) jack cable, then connect the footswitch output to your amp with a standard TS (Tip Sleeve - mono) guitar lead. There is a power supply supplied with the footswitch which plugs into it, and it routes the power to the guitar using the TRS cable so you become remotely powered and are not using the guitar's internal battery. You also have the option of switching the footswitch over to a second balanced XLR output for inputting direct to your PA. You may not need that, (I don't use it either for the PA), but it is useful if you use the acoustic model at all. I have a second ultra clean amp which I switch to for acoustic numbers, that sounds better than using my normal amp even on its clean channel. Balanced connections are better than unbalanced from the point of view of noise and hum pickup. An unbalanced connection has a signal wire and a ground wire. Any noise and pickup induced into the signal wire remains there at the input of the amp as the ground does not pick it up too and it is the difference between the two wires which counts. A balanced connection has three wires. One is a ground which exists only for screening and to give a common reference at both ends. The other two are both signal wires and they carry a +ve and a -ve version of the signal. That means the -ve is exactly the same as the +ve but is reversed so it goes down as the +ve goes up and vice versa. At the input there is now special circuitry which takes the difference of the two to be the signal. This means that we actually get a bigger voltage by a factor of 2. The clever thing is that any noise picked up will be the same in both wires and in the same direction. When they are subtracted the noise will cancel out. This is similar to humbucking pickups. Sort of like this: If the guitar signal is V, the ideal for us would be: (+V) / (-V) (from guitar) = (+V) - (-V) (at amp) = (+V) + (+V) = 2 x (+V) Now in the real world with noise pickup of N: (+V) / (-V) (from guitar) = (+V + N) - (-V + N) (at amp) = +V + N - (-V) - N = (+V) + (+V) + N - N = 2 x (+V) (the Ns cancel out) I know this is a bit Mathsy if your not keen on algebra but it's not too hard to get just the general idea. This is one reason why balanced connections are used as often as possible in studios and professional installations.

Get the XPS-A/B footswitch which switches between normal unbalanced guitar jack and balanced XLR outputs and also remote powers the guitar. For the price it's a steal, (and I really don't say that too often with musical electronics). When I first got my JTV59 I had a problem with the charger, it would not start charging the battery at all. A replacement was given and it worked for a while but I notice that now the battery never finishes its charging cycle, the charger continues to flash red permanently, and that's after 4 hours during the evening and overnight! There does seem to be some issue with either chargers or batteries or both. I'm sure others will know whether that is true.

I didn't make things very clear in what I wrote originally. When I mentioned using a buffered cable that was of course before getting my JTV59 and with standard type guitars. But it isn't beyond the bounds that I may decide to design another one to match the JTV setup as my original unusual design works so well. In that case, with a high impedance buffer amp about 15" from the plug there was virtually no load capacitance which shifted the pickup resonance way too high and the whole setup sounded very harsh and screechy. After trimming, (I found a 470pF to be the best match for my own setup), it settled down to a beautifully controlled middle and top end which could be adjusted wonderfully with the amp tone controls showing the frequency of the pickup resonance was now in the right ballpark. The issue is that I am worried that the present capacitance of my plain cables could be too high for the magnetics of the JTV59. If the footswitch is straight through then using a slightly longer than usual cable (5m of 56pF per m ≈ 280pF) to the powered A/B footswitch will add to the capacitance of the (generic) cable from footswitch to amp and give me too high a value. And without shortening the cable you can trim up but not down! If the footswitch is buffered, (the signal passes through active electronics usually set as a x1 amplifier), on the way through to the selected output, then the second cable is isolated from the first and it is only the guitar TRS cable which needs to be taken into account in the trimming process. Anyone give me a simple yes or no on this?

I have been used to using my own "long line" guitar cable with a head amp moulded into the cable near the guitar plug. As would be expected I found that trimming the load capacitance on my guitar output via a small cap added into the guitar plug was necessary to keep it down at the top end. I've just made myself a new TSR cable and realised that, if we assume the A/B footswitch is straight through for signal then we have a situation where the cable capacitance is now that of two cables added together, that's the guitar -> footswitch and footswitch -> amp. That could be very dull for the standard magnetics at least. Now I did wonder whether the footswitch may already have a buffer amp added to it in order to get around this problem. Can anyone confirm or deny this? If there is no buffer in the switch unit then how do the rest of you cope with this apart from using 1.5m cables?

Good, thanks for that info GH, I understand what we are dealing with now. It's the better way to go I think, performing calculations of that sort is simpler than manipulating library sounds at the sharp end, and no one can deny the success of the results. So the quality of the models depends on having an accurate impulse response for convolution and a good piezo system to give a responsive and repeatable base signal. And updates to the voices presumably mean loading up more accurate impulse responses. The most noticeable weakness to me is on the lower strings of the acoustic models, in particular the first few frets of the low E. The system seems easily overwhelmed by the signal from that and it picks up the slightest fret buzz and seems to amplify it out of proportion. If the original classic model was measured without any fret buzz and then fret buzz was introduced into the pre-convolved playback signal, and given that the impulse responses for acoustic will lift the higher frequencies, the buzz well may be brought out more than the rest of the signal. If there was any truth in this I would guess that it is a fact of life of applying this method of modelling which would be difficult to eradicate. Any DSP experts out there with info to explain?

Protective shells - Neutrik NE8MC, NE8MC-B. Fitting instructions to existing cable available on download here: http://www.neutrik.co.uk/en-uk/data/ethercon/ethercon-cable-connector-carrier/ne8mc-b Full plug + shell - NE8MX6, NE8MX6-B, instructions in the same general area on that specific page. I used to use these for the cable between my Vox Valvetronix Blueface and its foot pedal unit. The black ones look particularly good.

I've just gone down to look into the clicking issue and I can reproduce it here if I use my palm to gently tap down on the bridge, but only on some occasions. It doesn't go on doing it time after time, but once a note has been sounded it then is more prone to doing it. And all the time the note is still sounding, even slightly, it seems to do it. Once the guitar is effectively silent it generally stops. I have to say I don't think it is at all hardware related, at least on my own guitar. This feels as though the software goes into a more sensitive listening mode once a note is activated to track the tailoff or sense when a different note is picked. Maybe there is an increase in sensitivity in the system under those circumstances. I tried tapping on the piezos with my pick and they each sound different as you would expect, but I think there is an increase in "clickiness" when there is vibration on a string going on. Can anyone tell me if the system works by processing the signal picked up by the piezos to produce its output, or does it just use them as a foundation and put together the output signal in relation to info it reads from the piezo signal from a stored library of captured sounds? If it is the library I would have thought they would maybe have to model the transient attack of the note and the hold and decay separately and if that is the case then the sensitivity of the system may depend on what phase the note is in. If sensitivity drops drastically when there is no need to hear new info in amongst other sounds and rises when a sound could be masking it then it could go towards explaining what I am seeing here. I think there may well be an issue with the bridge on some peoples' models but this goes beyond that, and there is definitely no contact in the grooves of the piezos on my own bridge. And I will say for me, this is not a huge issue under playing conditions, I think it's just a peculiarity of the modelling system which could perhaps be sorted out with development by L6. (Although knowing the software development environment I won't hold my breath for that to happen. ;) )

Just got a new JTV59 and love it. It is genuinely a very different sound to my existing LP Trad, LP Jnr Special DC and Strat but complements them well in its own right. I fell asleep last night after playing it for hours, and then I woke up and found myself here. What an interesting place. It's great to find enthusiasts who are trying to deal with the inevitable eccentricities that a guitar as unusual as the JTV will have. Like minds..... :wacko: I have read the thread quickly and there is a lot of good common sense in it which is good to see. No arguments as to which brand of tape and shrink sleeving sounds best for blues for example :P . And then someone mentioned the VDI cable. Mad? At first glance maybe but it is a good observation. So how many people were using battery and how many external power when you did your testing and modding? I wonder if the power supply source may come into this? I have to be honest, while I admit you guys know the guitar much better than I do so I could easily be totally wrong, it does seem to me that it is at least as likely to be a modelling issue than a structural one. I bought the footswitch power unit even though I was convinced I could have made one myself at a fraction of the cost and spent a lot of time cursing Line6 under my breath as money grabbing corporate pirates. Then I opened it up and looked inside! (I have a couple of pics of the PCB in a dedicated thread.) Barnacles for bollocks, it was worth every penny I paid. Humble apologies L6! The PCB carries a lot of active circuitry; a regulator chip, half a dozen transistors and 4 or 5 SMD chips, even though you would think that it only needed a simple regulator and maybe a handful of sensing/protective/relay control components. I have no idea why there is so much in there but it must do something significant. So I wondered if the pings and clunks you are experiencing could be the result of something sticking artifacts on the power line which kicks in under certain conditions. Another thought I had was, there is no problem with a velcro/felt/foam absorbent strip at the headstock, that floats free and works really well on all guitars if they have a dischordant ringing issue. But at the bridge end, if the velcro/tape/shrinkwrap encloses the string and gives it a firm vibration absorbing bed to lie on, i.e. it gets pinched in the space which should be there under the string, do you find that this affects tuning stability as it can be minutely squashed down under use and slacken the string slightly? Or does it perhaps bed in a little then stay stable? DSP is a funny beast with a few strict laws determining how well the whole thing can work. It isn't unusual to find that there are artifacts in the signal due to bandwidth restrictions caused by sampling/clock rates etc. That may again be a factor in this problem. Is there any info available about the digital setup inside the guitar? And a last simple thought. Looking at the pics in the thread showing the break of the strings over the bridge it is noticeable that there is a significant curve in some of them where they pass over the saddle. I first got this advice from an old amp designer, (being old myself now), who was talking about the speed of bedding in new strings and I found it works. It may make an improvement if you actually push firmly on both sides of the string close to the saddle to put a tighter radius at that point. This prevents the string flexing slightly over the saddle during playing. The string would probably find its way to that point in time but it helps to give it assistance to get there asap. Movement over the bridge saddle during tuning or string bending is of course a reality but it is minimal and doesn't seem to be affected by this tighter bend in my experience.