Tonedexter Hum???

[TheJackal]

First things first. As one of the early purchasers of the TD, I remain of the view that this one piece of equipment is a positive game changer for amplification of acoustic instruments.

Most of the guitars I use with the TD have K&K pickups. Yesterday, in advance of a gig, I decided to train my Taylor Nylon. It's one of the few guitars that have the Fishman pickup. Training went fine. However, I noticed a very slight hum that disappeared when I touched the frame of the TD. It would probably not have been noticeable for live play with the band but I didn't want to risk it.

My question, have any other TD users had this issue? If so, were you able to diagnose and resolve it? I'm going to check the guitar plugged straight in to my PA to see if the problem might be a problem with the pickup independent of the TD.

Any help or assistance/advice is deeply appreciated.

[SpruceTop]

Originally Posted by TheJackal

First things first. As one of the early purchasers of the TD, I remain of the view that this one piece of equipment is a positive game changer for amplification of acoustic instruments.

Most of the guitars I use with the TD have K&K pickups. Yesterday, in advance of a gig, I decided to train my Taylor Nylon. It's one of the few guitars that have the Fishman pickup. Training went fine. However, I noticed a very slight hum that disappeared when I touched the frame of the TD. It would probably not have been noticeable for live play with the band but I didn't want to risk it.

My question, have any other TD users had this issue? If so, were you able to diagnose and resolve it? I'm going to check the guitar plugged straight in to my PA to see if the problem might be a problem with the pickup independent of the TD.

Any help or assistance/advice is deeply appreciated.

Yes, I've noticed this humming, too. When using my Taylors with ES2 (the real ES2 and not ES1.2 magnetic system) through my ToneDexter, I get a hum in the headphone circuit but it can be reduced with plugging-in the ToneDexter to another downstream device with a three-prong, grounded circuit. This hum doesn't seem to translate to the ToneDexter WaveMap that is generated by the Taylors with ES 2. My Trance products don't seem to have this hum problem in the headphone circuit.

I think usage of wall-warts for powering devices, even though these 2-pronged wall-warts are plugged into a 3-prong, grounded outlet, can result in a greater possibility of hum being introduced into the functions of a device. Perhaps JonFields45 can comment on this to shed some light on why this occurs?

[James May]

Originally Posted by TheJackal

First things first. As one of the early purchasers of the TD, I remain of the view that this one piece of equipment is a positive game changer for amplification of acoustic instruments.

Most of the guitars I use with the TD have K&K pickups. Yesterday, in advance of a gig, I decided to train my Taylor Nylon. It's one of the few guitars that have the Fishman pickup. Training went fine. However, I noticed a very slight hum that disappeared when I touched the frame of the TD. It would probably not have been noticeable for live play with the band but I didn't want to risk it.

My question, have any other TD users had this issue? If so, were you able to diagnose and resolve it? I'm going to check the guitar plugged straight in to my PA to see if the problem might be a problem with the pickup independent of the TD.

Any help or assistance/advice is deeply appreciated.

There is a note in the user guide about this. The power supply for ToneDexter is floating, without a connection to earth ground. Therefore, some higher impedance pickups will act as an antenna and pickup stray power line hum. It all goes away when ToneDexter gets plugged into a mixer or amplifier that is grounded. This is the normal usage case.

This issue is not unique to ToneDexter, BTW. It has been reported by many others with different equipment in a similar configuration.

[jonfields45]

In the early 90s I managed a design group working on chips for VGA cards (that ancient PC standard that still plagues us with VGA cables). I later worked on hard disk drive electronics where the signal off the disk wouldn't count as noise in the music biz. Getting a decent ground is part science and part art.

With the mix of slowly oxidizing contacts on signal and power connectors, two prong power supplies, in-theory properly grounded 3 prong power supplies, it is amazing anything works as well as it does. I've had ground loops and ground noise bite me hard three times in my life and one was solved by throwing what seemed to be a perfectly good power supply out (it worked most of the time, but most does not cut it).

Start by plugging everything into the same grounded power strip. Try reversing all the two prong plugs (for N plugs that makes 2^N combinations). Have a few spare wall warts of different brands to try. And hope for good luck! Also, listen to some old Jimi Hendrix live videos to get your expectations grounded :~).

[TheJackal]

Thanks to all who replied. The hum was through the headphones. I didn't test things through the PA as I was pressed for time. I'll test again with things plugged up as I would use it. Likely will resolve the problem.

As a side note, the Taylor Nylon tonedexterized sounds amazing. Far better than pickup only. Incredible piece of equipment, James et al.

[jonfields45]

Probably restating James May's response a little differently...

The ToneDexter spec says it can handle either power supply polarity, negative tip Ibanez stomp box standard, and rest-of-world positive tip. Something similar to 4 diodes in a full wave bridge configuration isolate the wall wart from ToneDextor. Maybe a good idea if you want to use your Yamaha Keyboard/Mixer positive tip wall wart or your 1Spot in a pinch, but a unique design decision as far as I know for guitar equipment. If you are only using ToneDextor and no other device, it is genuinely floating which is not different than running on batteries. But could put you in trouble inside your house full of stray electrical and magnetic noise with your battery powered or unpowered guitar acting as a great antenna.

Here's a better play; take ToneDextor's headphone output and plug it into your grounded mixer (note my MG06x mixer is not grounded, so it won't necessarily help) or amp, and then plug your headphone into that mixer or amp.

[James May]

Originally Posted by jonfields45

Probably restating James May's response a little differently...

The ToneDexter spec says it can handle either power supply polarity, negative tip Ibanez stomp box standard, and rest-of-world positive tip. Something similar to 4 diodes in a full wave bridge configuration isolate the wall wart from ToneDextor. Maybe a good idea if you want to use your Yamaha Keyboard/Mixer positive tip wall wart or your 1Spot in a pinch, but a unique design decision as far as I know for guitar equipment. If you are only using ToneDextor and no other device, it is genuinely floating which is not different than running on batteries. But could put you in trouble inside your house full of stray electrical and magnetic noise with your battery powered or unpowered guitar acting as a great antenna....

Yes, essentially that is correct. However, one small correction: the full wave diode bridge circuit we use to allow supplies of either polarity is not the cause of the hum. It would do the same without the diode bridge.

The issue is that the power supply is floating, as are most of them these days. The secondary of the the supply, which powers the unit, has no reference to AC power ground. Therefore, as you noted, unless there is a ground connection SOMEWHERE, high z pickups (especially USTs, not so much SBTs) will act as an antenna to power line noise fields.

[jonfields45]

Hi James,

In a situation where you can hear hum through the headphones, the harmonics of the hum would be in the pass band of the system. Does this corrupt the training? It seems that people who report hum don't report a problem with training.

I might quibble with this being limited to high impedance guitars as for at least this thread, active systems such as Taylor ES and Fishman barn doors are being discussed.

While I don't disagree with your analysis of the diode bridge, it is a unique design choice (maybe a good one if you want to use whatever power supply you happen to have on a pedal board) and plenty of toy sized guitar amps work off of floating power supplies with no problem. Getting back to my experience that ground design is part science and part art (knowing what works and doing that over and over); a real Spice simulation of an entire system's ground would be too much work when simple art solves the problem.

As an interesting story... I once lifted the ground of a toy sized Vox amp (to see if I could get away with a smaller power supply I gave a smaller two prong one a try) and when the cable was plugged-in but not attached to a guitar, it was an unbelievable hum (nice high impedance antenna) and once the guitar was attached it was perfectly quiet. The larger grounded power supplies are not completely without utility even if they seem to be a hassle to lug around.

[raduray]

Sorry to resurrect this old thread, but as a new owner of a ToneDexter connected to my Taylor's ES2, I've also experienced this phenomenon. Granted, as stated in the manual and in this and other threads, the hum is eliminated when I connect the output to my Loudbox Mini.

However, there are times that I may want to just listen to headphones and not have to connect to the Loudbox Mini just to eliminate the hum.

To that end, I connected a cheater plug (http://tinyurl.com/yyxdaoa7) to the same outlet strip as the TD's wall wart and then connected the metal tab on the cheater plug to various points on the TD's chassis, but it was to no avail. I had assumed the chassis to be connected to circuit ground, but that seems to not be the case. Are there variations of this approach that I can try, or some other scheme that would not require me to do an audio connection to another piece of grounded gear?

EDIT: Never mind. See Jon and my responses below.

[jonfields45]

Originally Posted by raduray

Sorry to resurrect this old thread, but as a new owner of a ToneDexter connected to my Taylor's ES2, I've also experienced this phenomenon. Granted, as stated in the manual and in this and other threads, the hum is eliminated when I connect the output to my Loudbox Mini.

However, there are times that I may want to just listen to headphones and not have to connect to the Loudbox Mini just to eliminate the hum.

To that end, I connected a cheater plug (http://tinyurl.com/yyxdaoa7) to the same outlet strip as the TD's wall wart and then connected the metal tab on the cheater plug to various points on the TD's chassis, but it was to no avail. I had assumed the chassis to be connected to circuit ground, but that seems to not be the case. Are there variations of this approach that I can try, or some other scheme that would not require me to do an audio connection to another piece of grounded gear?

That tab is not grounded as it is only a two prong plug and won't help. You could connect a wire from a wall outlet cover plate screw (where that "cheater" tab is intended to be screwed in to) to the ToneDexter chassis but it seems simpler just to plug ToneDexter into something with a 3-prong power cable (which is itself plugged in to AC power).

[raduray]

Originally Posted by jonfields45

That tab is not grounded as it is only a two prong plug and won't help. You could connect a wire from a wall outlet cover plate screw (where that "cheater" tab is intended to be screwed in to) to the ToneDexter chassis but it seems simpler just to plug ToneDexter into something with a 3-prong power cable (which is itself plugged in to AC power).

Brain fart on my part. I had the concept of the cheater backwards. Duh!