ZT Amplifiers "Lunchbox" - Comprehensive Evaluation

[randyc]

This product has generated a lot of recent interest, some of you may have followed the original thread where an evaluation by forum members was first proposed. The evaluation has been ongoing since that time ... some fifty pages of data and measurements were documented, much of it discussed with ZT. You'll get a better idea of the level of effort when you start reading.

In an effort to condense our thoughts, we produced a summary. I tried to insert the summary here but all formatting was lost and it would have taken hours to edit the document again. So the backup option is required which is to download the evaluation from an "Adobe" site. (Adobe has virus-checked the document and reported it to to be safe.)

I hope that those who are considering this amplifier or are interested in the technology will enjoy reading our work (the document will take a few moments to download):

https://acrobat.com/#d=kXaIRekofFroxu9LQnyYoA

We think that this evaluation went well and we're now conducting a similar one on the ZT "Club".

[NSJ]

Downloaded and will be read tomorrow, when I have time. I have a Lunchbox already, and I can tell the #1 issue---way too much HISS! Other than that, a good amp for the size. Loud! I guess to get the loudness, you have to accept some excessive hiss....

[BigDaddyLoveHandles]

Randy, I hope doing the evaluation itself was rewarding because I don't see how forum members can repay you for all the work you must have put in!

A question: you rate the LB at 60W RMS; the manual calls it 130W RMS. Why the difference?

[randyc]

Good question, BDLH -

At the very beginning of our evaluation, a "Wikipedia" article described several ways that manufacturers describe product capabilities. These descriptions have been flexible since I first had vague comprehension of their meaning. Fender used to advertise their amplifier capabilities as watts - like all other manufacturers - but expressed in "music power".

Most other manufacturers, in order to be competitive, started using that definition which, to an engineer, might be better described as "peak power" rather than the Federal Trade Commission ruling for "RMS power" specification. (The FTC ruling applied to home theater, stereo equipment and the like, not to guitar amplifiers.)

I'm covering ground already included in our report, BTW. Also, I'm no advocate of any particular manufacturer. I advocate a standard measurement of output power, that's also mentioned in our report.

As I've frequently stated here, all other parameters considered equal, a guitarist will ALWAYS choose the product with highest rated output power (the rationale is not always sensible). That was the initial stimulus to this evaluation. I've also stated frequently that power level - RMS, average, peak or otherwise - isn't meaningful unless loudspeaker efficiency is considered.

(BDLH I'm assuming that you're "straight guy" because I KNOW that you are very knowledgeable and non-confrontational about these issues. Thanks for bringing the topic to forum attention as a teaching point.)

I'm hopeful that musicians will pay attention to details like output power conventions while remaining aware that some amplifier technologies aren't directly comparable to tradional ones. That was where I'd hoped this evaluation would conclude.

It didn't end up that way - conclusively - my apologies. I think that further work may provide better means of comparison.

Here's a suggestion: referring to our evaluation, take a look at the final footnote of the concluding summary. The footnote is suggestive of the differences between definitions of output power.

Some further work is required so that the average guitarist (having little or no interest in electronic metrology) can make rational comparisons between combo amplifiers.

cheers,
randyc

PS: Although my profession stresses the importance of physical definitions and measurements, the comments provided by the Team are those that are most relative to most musicians!

[goshawk]

Randy (and Jeff and John and Tom and John), thanks very much for a very valuable piece of work.

[Will Chen]

Thanks for the article, excellent work!

Originally Posted by BigDaddyLoveHandles

Randy, I hope doing the evaluation itself was rewarding because I don't see how forum members can repay you for all the work you must have put in!

A question: you rate the LB at 60W RMS; the manual calls it 130W RMS. Why the difference?

As the article mentions, there is no uniform standard for measuring wattage and companies will post the most flattering specs. Just note that ZT's measurements are as valid as any other amp manufacturer and they're plenty loud for most performance situations. This isn't a case like some old Crates and Peaveys which rated amps at 100w which could never be used in a live situation...

[ken kantor]

Originally Posted by NSJ

Downloaded and will be read tomorrow, when I have time. I have a Lunchbox already, and I can tell the #1 issue---way too much HISS! Other than that, a good amp for the size. Loud! I guess to get the loudness, you have to accept some excessive hiss....

NSJ... please email me the serial # of your amp. If you have a very old unit, there have been some improvements that I can set you up with. They address hiss, among other things.

-k


ken.kantor@ztamplifiers.com

[ken kantor]

Originally Posted by randyc

This product has generated a lot of recent interest, some of you may have followed the original thread where an evaluation by forum members was first proposed. The evaluation has been ongoing since that time ... some fifty pages of data and measurements were documented, much of it discussed with ZT. You'll get a better idea of the level of effort when you start reading.

In an effort to condense our thoughts, we produced a summary. I tried to insert the summary here but all formatting was lost and it would have taken hours to edit the document again. So the backup option is required which is to download the evaluation from an "Adobe" site. (Adobe has virus-checked the document and reported it to to be safe.)

I hope that those who are considering this amplifier or are interested in the technology will enjoy reading our work (the document will take a few moments to download):

https://acrobat.com/#d=kXaIRekofFroxu9LQnyYoA

We think that this evaluation went well and we're now conducting a similar one on the ZT "Club".

Randy, I can't thank you enough for this. It has been a pleasure working with you. (Well, not every email or result was fun or easy, but I think you know what I mean....)

Folks, this guy >knows his stuff< and has done a lot of excellent work that is already finding its way into ZT's product planning.

-k

ken.kantor@ztamplifiers.com

"Nice to know I am not too old to learn new things. It's just that remembering them is tougher."

[derek]

Originally Posted by ken kantor

Randy, I can't thank you enough for this. It has been a pleasure working with you. (Well, not every email or result was fun or easy, but I think you know what I mean....)

Folks, this guy >knows his stuff< and has done a lot of excellent work that is already finding its way into ZT's product planning.

-k

ken.kantor@ztamplifiers.com

"Nice to know I am not too old to learn new things. It's just that remembering them is tougher."

Agreed. In addition to being an all around swell guy, Randy has more knowledge about technical aspects of amps than just about anyone else I have run across. He is a real asset to the group.

[Little Jay]

Thanx Randy and the rest of the test team for this great evaluation of the LB! We are so lucky to have you guys here on the forum!
You make the quest to find the right equipment so much easier and also more pleasurable!

Keep on the good work!

[randyc]

Originally Posted by Little Jay

Thanx Randy and the rest of the test team for this great evaluation of the LB! We are so lucky to have you guys here on the forum!
You make the quest to find the right equipment so much easier and also more pleasurable!

Keep on the good work!

Thank YOU! I'm certain that Tom Karol, John W (LPDeluxe), Jeff (Mr. Beaumont) and John Rosett feel the same as I do: it's rewarding to be of service to such a great bunch of guys. This is the most knowledgeable (and civil) forum with which I've been associated.

Which suggests that we owe Dirk some thanks too, he's a fine moderator!

[mr. beaumont]

agreed, this is a mighty fine corner of the internet.

the whole process was fun, and i'm looking forward to reviewing the club. glad i could help out.

[BigDaddyLoveHandles]

Makes me wonder what's next in the ZT pipeline. A bass amp? How could you go small and still thump?

[Gibson L4CES]

My Lunchbox just arrived this afternoon. It is an amazing little amp... I can see using it both in rehearsal and on some small gigs. I do have a question... Has anyone tried the LB with a Raezer's Edge speaker cab?

[woyvel]

Question regarding wattage specs: Why hasn't anyone ever specified the decibel level achieved at a certain distance with a particular guitar? For example: a Les Paul, bridge pickup volume 10, measured 15' from the amp with settings for volume/gain set at xyz. It seems if a standard was set that this would be a good way to set a level playing field to measure amp output.

[mr. beaumont]

Originally Posted by Gibson L4CES

My Lunchbox just arrived this afternoon. It is an amazing little amp... I can see using it both in rehearsal and on some small gigs. I do have a question... Has anyone tried the LB with a Raezer's Edge speaker cab?

not an RE, but i've played mine many a time with a redstone RS-8, and that little bit of extra speaker plus the cab's construction brought back some bass.

but it still sounded better with a little reverb and outboard EQ though, so the lunchbox gets played on it's own mostly with an effects unit, and the redstone pairs with my heinreksen jazzamp head. I still think the external speaker isn't a bad thing to try with the LB, but i've kinda gone back on my idea earlier that it was necessary...now i just like the LB for what it is--small, clean, loud.

[NSJ]

Originally Posted by ken kantor

Randy, I can't thank you enough for this. It has been a pleasure working with you. (Well, not every email or result was fun or easy, but I think you know what I mean....)

Folks, this guy >knows his stuff< and has done a lot of excellent work that is already finding its way into ZT's product planning.

-k

ken.kantor@ztamplifiers.com

"Nice to know I am not too old to learn new things. It's just that remembering them is tougher."

Ken,
Just sent you an email. Thanks!

[BigDaddyLoveHandles]

Originally Posted by woyvel

Question regarding wattage specs: Why hasn't anyone ever specified the decibel level achieved at a certain distance with a particular guitar? For example: a Les Paul, bridge pickup volume 10, measured 15' from the amp with settings for volume/gain set at xyz. It seems if a standard was set that this would be a good way to set a level playing field to measure amp output.

At the start of the metric system didn't they have a "canonical metre" stick housed in Paris? You'd have to keep this one Les Paul somewhere, too! And have the same person play it with the same pick!

What they do do is play a standard signal, like a sine wave of a certain frequency and amplitude.

[randyc]

Originally Posted by woyvel

Question regarding wattage specs: Why hasn't anyone ever specified the decibel level achieved at a certain distance with a particular guitar? For example: a Les Paul, bridge pickup volume 10, measured 15' from the amp with settings for volume/gain set at xyz. It seems if a standard was set that this would be a good way to set a level playing field to measure amp output.

You're playing my favorite song (sort of). That's what SPL (sound pressure level) measurements are supposed to accomplish. But most manufacturers still won't use them, for numbers of reasons (not the least is that SPL is mostly determined by loudspeaker and many manufacturers use the cheapest loudspeakers they can buy).

This has been discussed numerous times, in fact each time the merits of a specific speaker comes up and the loudspeaker manufacturer refuses to provide SPL curves. Many folks take advantage of the fact that musicians aren't particularly technically aware and that we are trusting, as a rule.

The industry has taken advantage of those two facts for half a century.

FWIW, ZT does provide a SPL description on their website. I'm not sure that it is the same measurement that loudspeaker manufacturers use, however.

The usual definition is sound pressure measurement one meter from the loudspeaker with 2.828 volts RMS applied to the speaker terminals and at frequencies from about 20 Hz t0 10 kHz (less if the speaker obviously hasn't the response). The microphone must have certain characteristics and be calibrated to a specified SPL in millibars.

[randyc]

The topic of the headphone output somehow got panned in the original review except for one reviewer who noted that he uses this output to drive a PA system in larger venues. I've frequently mentioned that this configuration is my favorite: small and lightweight amplifier with a "real" line impedance output should sound reinforcement be required. In fact, I've modified all of my smaller amplifiers to include this feature.

Recently, I made some measurements of the headphone output (line out) characteristics on the "Lunchbox" and found them to be better than I'd initially thought. As we know, line outputs are useful for connecting the amplifier to any device that requires good fidelity and minimum amplitude loss over fairly long cable runs. A typical line impedance is 600 ohms (it's a telephone standard, not a musical standard) but generally anything around 1k or less is regarded as "line impedance". Sometimes even 600 ohms is too high for driving long cable runs.

I measured the headphone output impedance at less than 40 ohms. Because of this very low output impedance the output is capable of driving either high impedance or low impedance loads over substantial distances. Note also that the headphone output has the same EQ characteristics as the main output. This means that the line output requires no special EQ at the other end of the cable run - a PA input with flat EQ is perfectly acceptable. The overall response can then be controlled by the amplifier EQ. (Intentional distortion is also reproduced at the line output.)

This is a plot of the frequency response from the line output at the end of 35 feet of coaxial cable (Radio Shack, impedance and loss characteristics unknown) into a high impedance load, which is the worst case for frequency response.


"Spikes" and "ripples" in the response can be ignored - they are due to group delay (phase shift) variations in the long cable length and the short cable used to establish the reference level. The loss of the unknown cable is about 3 dB and a simple adjustment of the line out (headphone volume) control can easily compensate for the loss. The bandwidth is about 8 kHz - far greater than what is required to reproduce guitar frequencies and significant harmonics. When driving a line impedance input, no frequency degradation would occur.

Although these measurements were made for inclusion into the "Club" review, it's appropriate to add the comments, as an afterthought, to the "Lunchbox" evaluation.

[ES125er]

I've been very curious about the Lunchbox for a while, so I read this thread and the pdf document with a great interest. Thank you all for your time and energy.

One frustration, though: so much time spent, so many testers, so many pages written, technical discussions... and no one considered recording a clip or a video so that everyone could hear the amp's voice?

The only samples of archtop/jazz on a Lunchbox that I could find are the Bill Pettaway video on youtube, and a video of a gypsy-jazzer testing the Acoustic Lunchbox (either the amp is off or it is impressively transparent). Are you guys aware of any other cool clips/videos?

Thanks.

[randyc]

Actually I believe that there may be some sound clips through the Lunchbox on this forum - I'll inquire from the guitarist who may have posted them and let you know.

cheers,
randyc

[amusiathread]

I'm going to spring on the ZT lunchbox acoustic next week. I can't promise anything nearly as informative or technical as the reviews you guys provided for the lunchbox, but I'll gladly share my thoughts with anyone who wants to hear them. Randy, do you have any info (inside or otherwise) on these new amps?

[randyc]

I'll write this morning and see if we can get more than an ad blurb - will report as soon as I hear something.

[randyc]

Originally Posted by randyc

Actually I believe that there may be some sound clips through the Lunchbox on this forum - I'll inquire from the guitarist who may have posted them and let you know.

cheers,
randyc

No sound clips through the Lunchbox to date although that may change soon ...

[ken kantor]

Originally Posted by amusiathread

I'm going to spring on the ZT lunchbox acoustic next week. I can't promise anything nearly as informative or technical as the reviews you guys provided for the lunchbox, but I'll gladly share my thoughts with anyone who wants to hear them. Randy, do you have any info (inside or otherwise) on these new amps?

Hi... Ken from ZT here, thanks to a heads up from Randy. The Acoustic amps are available, and I would be happy to answer questions about them.

ZT Amplifiers Lunchbox Acoustic

Ken Kantor

ken.kantor@ztamplifiers.com

[Mr Bo]

Originally Posted by randyc

This product has generated a lot of recent interest, some of you may have followed the original thread where an evaluation by forum members was first proposed. The evaluation has been ongoing since that time ... some fifty pages of data and measurements were documented, much of it discussed with ZT. You'll get a better idea of the level of effort when you start reading.

In an effort to condense our thoughts, we produced a summary. I tried to insert the summary here but all formatting was lost and it would have taken hours to edit the document again. So the backup option is required which is to download the evaluation from an "Adobe" site. (Adobe has virus-checked the document and reported it to to be safe.)

I hope that those who are considering this amplifier or are interested in the technology will enjoy reading our work (the document will take a few moments to download):

https://acrobat.com/#d=kXaIRekofFroxu9LQnyYoA

We think that this evaluation went well and we're now conducting a similar one on the ZT "Club".

I couldn´t download. Just got the message: "The document can't be found, or you don't have access to it." How can I get grip of it?

[brad4d8]

Originally Posted by Mr Bo

I couldn´t download. Just got the message: "The document can't be found, or you don't have access to it." How can I get grip of it?

Likewise.
Brad

[HotClubBrampton]

Thanks a lot for your work on this analysis. I was on the fence about the Lunchbox, but after reading your review I found out who had the dealership here in Toronto, went over there and got the Lunchbox yesterday...! today, I went back for the cabinet too...I have been using them with my Heritage archtop and the sound/tone are really good for it. Next week I should be receiving a DjangoBucker pickup from Krivo/Djangobooks and I plan to use it with my Gypsy Jazz guitar and the Lunchboxes, will post my findings

[dbbliss]

Same; "The document can't be found, or you don't have access to it."

Bump.

Any chance there's a mirror or does someone know another link or copy?

Thanks!