Lunchbox Junior Speaker Impedance?

[Belva]

Anybody play around with one of these little critters?

http://www.musiciansfriend.com/amplifiers-effects/zt-lunchbox-junior-guitar-combo-amp

More specifically anybody use this to power an external cab? I'd really like to know what the impedance of the stock speaker is. I haz visions of a custom cab to go with my 1058.............

[DeepEnd]

Here's what their FAQ page (http://www.ztamplifiers.com/support/faq.html) says:

First, the rule for running ZT amps into an external cabinet is the cabinet load must be 8 ohms or greater. 6 ohms, 4 ohms, 2 ohms, all of these are not going to work. 16 ohms, no problem.

However, since the Junior doesn't have an external speaker jack you'll need to open it up and install one. Naturally, that will void the warranty.

[WRGKMC]

I second what deep end says. It has no external speaker jack. You'd have to add a switching jack that disconnects the internal speaker when you plug into it. You'd then be just using the head.

 

You may be able to convert the headphone jack to power an external speaker. Headphone jacks often have some resistors to step the voltage down to headphone level. Removing the resistors and applying the full speaker power to the jack might be possible. You can then use a 1/8 connector to your external speaker. The switch would then toggle between the internal and external speakers.

 

Personally, I'd use the aux out and just plug another amp into it. The Lunchbox would then be the master preamp for the second amp and drive both.

[Belva]

The Junior does have an on/off switch for the speaker. The ZT FAQ is a bit strange as I've never seen a 6 ohm speaker. We all know an 8 ohm is usually somewhere between 6 and about 7.5 measured DC resistance. I'm presuming any 8 ohm speaker would work as impedance and resistance ain't the same thang. The speaker cabs they sell for the Lunchbox are rated at 8 ohms. So unless they're doing something strange, the speaker would show typical DC resistance of any 8 ohm speaker. My vision is making a pine cab to put it in with an Eminence 1058. Decent speaker, fairly efficient and able to handle the 35 WRMS these little buggers put out. And I gotz one. So I'd use the existing speaker wires. If I'm lucky I can pull it off without voiding the warranty, just depends on what hardware gets a drop of paint.

The biggest detractor I've read on these is that the small speaker, well, it's a small speaker. 'Nuff said

[WRGKMC]

The on off switch just toggles between your headphones and internal speaker.

The headphones are still connected when the switch is toggled off and provides a load to the amp.

 

The right way to do it would be to install a switched jack that disconnects the internal speaker when you plug an external speaker cable in.

A Switchcraft 12A will do this for you. http://www.alliedelec.com/switchcraf...FQemaQodQIEJrg

 

 

With no plug connected the tip makes contact with another plate which acts like a closed switch and is in series with the hot wire to the internal speaker. When you plug in, the tip connector bends and opens the connection to the internal speaker.

 

This way you have no possibility of running both speakers in parallel and blowing the head. If the internal speaker is 6 ohms and you connect an 8 ohm external speaker the load drops to like 3.5ohms which will likely overheat the circuit.

 

You may be able to run the internal and an external in series. A 6 ohm and say a 4 ohm will total 10 ohms. But the 6 ohm speaker will see more of the wattage cause its a higher resistance drop.

 

Total Impedance = 10 Ω 4+6 in series

Speaker 6 ohm Power = 21 Watts

Speaker 4 ohms Power = 14 Watts

 

You can counter balance that by getting a higher efficient external speaker (something Id do anyway. Make no sense to use an external speaker if the volume goes down.

 

If you do go for the external, get a highly efficient speaker with a High SPL in any case. You do want te hear a difference or it makes no sense at all. If you just use a budget speaker it can wind up sounding lower in volume. Something with an SPL of 100 or more would be my advice.

 

I don't think 8 ohms would hurt the amp however. Its only two ohms and that's DC resistance not AC impedance which is based on frequency response. Many 8 ohm speakers read 6 ohms DC resistance. The DC resistance is often a ohm or two lower then the speakers actual ac impedance. Unless the manufacturer says they use a 6 ohm or its stamped on the speaker frame, the speakers likely 8 ohms and whatever you came across on the net may not be factual.