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dgnyberg

External Battery for the Variax 300/500/700

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I have a battery powered Busking rig and I'd like to add one of my Variax guitars to the rig. 

I'm looking at using a battery pack that has 9VDC and 12VDC outputs.
I think I can use the 9VDC output to power the Variax. 
My idea is to make a box with a TSR connector to go to the variax with these connections:
Sleeve - Ground(Power and Guitar Signal)
Ring - 9VDC
Tip - Guitar signal

A TS connector for the output of the circuit
Sleeve - Guitar Signal Ground
Tip - Guitar Signal

A connector for the 9V Battery pack connected to both grounds and the ring of the TRS connector for the guitar.

Has anyone done this before? I'd rather check the feasibility before I just go for it. I'd hate to jack up one of my Variax guitars.

I'm attaching a schematic I worked up

Thanks for any assistance!!

Dave Nyberg

Variax power block.jpg

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I've done some similar experiments, powering a Variax 600 from a 5-volt power bank with an adjustable DC buck that gives me the correct supply voltage. In my case, the DC buck has a 9V battery clip that plugs into the guitar replacing the 6-AA cell battery pack. Works just fine.

 

Your solution is conceptionally-similar, simulating power on the ring of a TRS plug on an XPS footswitch. I have one concern, which may or may not represent an actual problem. Psarkissian may weigh-in with an official position,  which would  probably be a 'Don't do it', but here's my concern:

 

When you connect the TRS plug from your Variax to J1, the tip - which carries the output signal from the guitar electronics - will be briefly connected to the 9V battery voltage from J3 as the plug is inserted into the jack. The output electronics of the Variax may be such that this isn't a problem. For example, if it's a capacitor-coupled connection, the brief DC voltage connection to this pin would be blocked. An output buffer could also provide similar protection. The bottom line is, I don't know what's connected on the Variax innards to the Tip of the TRS plug, so I'd be careful. 

 

If I were to proceed with a connection like this, I would assure that the 1/4" TRS guitar connector to the Variax was fully inserted before any connection was made to the battery at J3. 

 

Just one guy's opinion...

 

 

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On 11/24/2020 at 8:19 AM, cbrillow said:

I've done some similar experiments, powering a Variax 600 from a 5-volt power bank with an adjustable DC buck that gives me the correct supply voltage. In my case, the DC buck has a 9V battery clip that plugs into the guitar replacing the 6-AA cell battery pack. Works just fine.

 

Your solution is conceptionally-similar, simulating power on the ring of a TRS plug on an XPS footswitch. I have one concern, which may or may not represent an actual problem. Psarkissian may weigh-in with an official position,  which would  probably be a 'Don't do it', but here's my concern:

 

When you connect the TRS plug from your Variax to J1, the tip - which carries the output signal from the guitar electronics - will be briefly connected to the 9V battery voltage from J3 as the plug is inserted into the jack. The output electronics of the Variax may be such that this isn't a problem. For example, if it's a capacitor-coupled connection, the brief DC voltage connection to this pin would be blocked. An output buffer could also provide similar protection. The bottom line is, I don't know what's connected on the Variax innards to the Tip of the TRS plug, so I'd be careful. 

 

If I were to proceed with a connection like this, I would assure that the 1/4" TRS guitar connector to the Variax was fully inserted before any connection was made to the battery at J3. 

 

Just one guy's opinion...

 

 

Thank You for your response.

I can see your point and protecting the guitar is the biggest concern.

It might be best if I were to add a power switch to ensure not voltage is present. 

I can use a "Lighted Switch" that way I know the power is off before plugging in the guitar.

I have thought about using the battery pack in the same way you have and just put the battery pack in a pouch on the strap.

But, this pack is pretty heavy and the weight would be a concern.

 

Thanks again!
Dave

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Hi Dave,

 

Happy to try to help. Sounds like you have a good handle on this -- a switch is a good idea. Now all you have to do is remember to check the switch position before plugging it in!

 

The power bank that I experimented with was a low-cost, relatively low capacity unit, and my initial thought was also to attach it to the strap. But I really don't play the 600 much, so I just wound up sticking it on the guitar body with a loop of removable Scotch tape whenever I wanted to use it. That was easy to apply and take off, and left no damaging residue on the finish. I would've come up with a more suitable solution if I were to be playing out somewhere, but this was good enough for fiddling around in the basement.

 

Good luck to ya!

 

 

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