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Anyone know the details of the ZT Amplifiers Lunchbox???

Started by armstrom, September 08, 2009, 03:21:40 PM

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armstrom

I saw one of these the other day in my local Sam Ash store and was a bit surprised by the size. They claim it's a 200W SS amp and it's quite small. The enclosure is sealed so it's hard to poke around and figure out what's going on inside. The box is pretty heavy (9lbs) so I'm assuming there's a beefy power transformer contributing most of that weight.. Maybe the heat sink as well (although I didn't notice any vents on the back!?!?!?!)

So, does anyone know anything about these amps? What kind of power amp do they use? (discrete? some chip?) I'm assuming they have some kind of digital reverb... Also, any idea where they could come up with a 200W 6" speaker??

It's an odd beast, that's for sure.. but the reviews seem positive so far. Looks like a good amp design to try and emulate/improve upon.

teemuk

It's not a 200W amp. The designer posted on some forum stating that 200W is only a peak figure and that the proper continuous average power is only about 60 watts.

There was some documentation at their site, which implied that it's a linear class AB power amp with ordinary linear supply. Some digital signal processing in the preamp. The reverb is digital and reputedly kind of subtle because they supposedly couldn't add more computing power to make up a longer decay effect without sacrificing other DSP routines.

I see if I can dig up the document, though I think it's still downloadable from their website.

Yes. The amp reputedly has overheating problems. Due to obvious reasons (sealed construction, no ventilation, heatsink is just a plate which is very inefficent in convection cooling, 60W power supply and class AB amp crammed insight a small, sealed space etc.).

Still, I think it's a rather interesting design. I would love to see gut shots and find out more about this.

teemuk

Here's a quote from the Music Electronics Forum:
QuoteI contacted Ken Kantor and asked him how they got the 200 Watt number and he answered:
The 200W number is based on peak voltage. Other numbers we list, for more sustained signals, are based on a THD of under 10%. Just FYI, the >minimum< THD you will find on the LB, at any power level, is about 1%.

200 Watts is the equivalent RMS power available for 100mS tone bursts from 250Hz to 2500Hz. The actual driver impedance is used in the calculation.
I also asked about continuous power and got this answer

The answer is that it depends:there are sophisticated thermal limiting/SOA mechanisms built into the amp, that make testing it the way you suggest [using a 1kHz sine wave into a dummy load]not very straight forward. The longer the signal is applied, the lower the apparent "RMS" power will be. If you measure it within 0.5 seconds, you will see an unclipped RMS power approaching 130W. At the other end of things, the RMS will tend downward towards about 60W, steady-state.

And here's a link to the ZT whitepaper:
http://www.ztamplifiers.com/pdf/ZT_Amplifiers_Lunchbox_Whitepaper.pdf


Edit: ...I strongly suspect the power amp is a chip amp given that the whitepaper states it being bridged and powered by a rather low rail voltage. But I could be wrong on that one as well.

joecool85

Very interesting little fella.  I had never heard of these before.



http://www.ztamplifiers.com/products/lunchbox.html


As for a 6" speaker that can handle 200w peak, I'm sure it's not hard to come across.  There are lots of high end automotive speakers that will handle that type of power.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

J M Fahey

QuoteVery interesting little fella
Indeed.
For what he says , given the +/-24V supply, and he talking about bridged output, it might just be a couple TDA2050s bridged.
They would easily supply 60W RMS (120 peak).
The 200W (for 1 microsecond on a sunny day in the middle of a snowstorm) are close to the PMPO "spec" or "equivalent power" or any similar marketing BS.
A 6" car speaker will stand that power and more, and be flat to 60 Hz, etc., but will be about 82 dB efficient, unusable.
I guess this guy made a *very* efficient 6" "guitar"/midrange speaker , he cuts *everything* below 200hZ, at a steep 24 dB/oct or more, and gets a usable combo. That's why he expressly forbids changing/"upgrading" the driver. Of course, you can drive any regular external box with it.

ponchojuan

Based on his comment about power dissipation under continuous signal, and rail swing, I would SWAG that this is a Class G/H amp design, likely an IC with some cap muscle.

But the enclosure does look pretty sweet...some of the new small drivers  can take some very large intermittent power.

ponch

teemuk

If I remember right, the guy who designed the amp (Kenneth Kantor) used to work for plenty of companies that made speakers. He even has a few patents for them. I guess speakers are his forte so it likely was a lesser issue for him to find an efficient, high quality speaker that has a small size.

I haven't tested the amp so I can't comment on its low frequency response but usually it's lacking in these sort of design because the small driver begins to fart very easily at low freqs.