Small and loud guitar amp?

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Hi guys,

Smurfing around on a couple of music 'sites, I've come across the ZT Lunchbox guitar amplifier. They claim 120dB @1m peak output from a single 6" driver.

ZT Amplifiers - Support - Technical Data

Now, I realise there has to be some limiting of lower frequencies to get anywhere near this output from such a small driver - I've done a proof-of-concept that works to limit the bass independantly of the mid/highs.

I'm thinking of using an amplifier of say 200w into a driver like this. I know that such a small driver does have limited power handling and efficiency, but would prefer to use a 6" over an 8" to keep with the idea of a tiny guitar amp that'll keep up with drums and another guitarist.
That particular speaker (running at 200w) will hit 117dB. I've never done anything I'd consider high powered before, so I'd like to know if I'm likely to cook such a driver.

The design criteria is similar to that of ZT's - portable, and able to go really loud.

What do you guys think? Am I insane trying something like this, or is there a chance it'll work?

Cheers,
Chris
 
Power Rating**
Watts 100W
Music Program 200W

Worthy expairment but -- you still have to move air to make a loud noise. Just because a speaker can handle a lot of power without blowing apart, dosen't mean that it can convert that power to acoustic energy. Im trying to not be too much of a doubting thomas but don't get your hopes up that you are going to achieve that SPL.
 
And, you have to dissipate heat which is much harder to do with smaller voice coils, pole pieces, etc. If your plan is to keep up with loud drums, the heat soak from the power dissipation is going to have some negative effects. Aside from the obvious one of cooking the driver, as the voice coil heats up, it's impedance will rise leading to lowered output. What about using two of the 6" drivers? If ultimate size is an issue, you get better packaging efficiency this way.
 
here's some numbers...

if 200W amp and one driver, then using:

dB(Max):=dB(sens) + 10*log (P2/P1)
where dB Max is based on the power available
dB(sens) is the sensitivity at 1W@1m.

Substituting dB(sens) of 93.6, and P1:=1, P2:=200, then the result is 116.6 dB. If you use a stereo amplifier (class D again), and 2 of these drivers, then you can get (close to) the 120 dB(Max) target you are seeking. If you place the drivers as close together as possible (without touching each other), a 3dB gain can be had, so then you could get +3dB (doubling the electrical power) and +3dB (by spacing the 2 drivers as close together as possible). Otherwise I'd look for a driver with something closer to 96-100 dB @ 1W@1M sensitivity. Using the same equation, with a dB(sens) of 97dB would get you to 120 dB(Max) @1W@1m if thermally capable...

Thermal capability is probably one of the limiting factors. You could look at some of the small "Orange" amplifiers, etc. Behringer sells a few efficient combination amps that could fill your needs at a very low cost.

have a look here for a very easy to use calculator
 
Hi guys,

Thanks for the quick replies.

Sounds like multiple 6"s will be the way to do this. I'm heading toward something like this

ztstack.gif


Given 100w per speaker at pretty much 94dB efficiency, that'd be 120dB@1m. Think that'd be enough.

I'm going to buy just one of the drivers, knock up a quick test box and give it a good thrashing - 117dB might be loud enough after all.

Pictures to come when things actually happen.

Chris
 
If you play country twang or screachin blues I bet that little combo works great, but try a down-tuned chugga-chugga riff and I suspect it doesnt do even for bedroom practice levels.
Not that it's a bad idea, just that it probably only suits some styles of playing.
 
is it loud enough?

What's your application (specifically)? Small gig amp? Practice amp?

For this example I am assuming 100 watts "music power"(basically I guess from the driver's lowest available output to it's natural highest), and that SPL (in dB) reduces by 1/r² in a "field". I am not concentrating on peak power as it is for very short durations.

So 117dB@100W@1m becomes 114db@100W@2m and only 110.5 dB@100W@3m. So if playing balls out, and your listeners are more than 4m away, you'll need a lot more power and/or more small drivers and/or larger driver(s).
 
Nanook, my application is, primarily, band practice. That is, unmiked drum kit, other guitarist, bassist, vocalist.
The practise mainly occurs at college, so being able to transport the amplifier room to room easily is priority. Despite my efforts (beefed up PSU & output stage), my 1x10" 40w combo doesn't have enough oomph, and gets annoying to move around when there's other stuff to be carried, too (I tend to be the techie that sets stuff up, so the fewer trips I have to make, the better.).
The 1x10" combo will do 111dB before clipping (calculated - 95dB speaker, 40w input). It won't keep up with a drum kit, even if I run everything wide open and drive it into square waves.

I have no problem with DIing out to a PA system at gigs, so long as I can hear myself onstage: the small size of these amps mean I can put it where I like and still hear it - that could easily be at head height instead of blasting away at my feet.

Cheers,
Chris
 
I'm very dubious about those ZT amps?.

Volume is simply about moving air - you can either move a large cone a small distance, or a small cone a large distance, either will move the same amount of air, and give the same volume.

The problems arise though that cones can only move so far - so small cones are limited in the amount of air they can shift.

I can only imagine that the ZT filters out all low frequencies, which limit the cone movement required, allowing higher powers to be used.

I would suggest getting a 1x12, 60W or 100W - if you can stand the weight (and the cost), get a valve one, which will be far louder because of it's distortion.

I've used a 1x12 Fender 60W transistor keyboard amp for guitar and bass (at the same time - it has two inputs) at a gig, and it coped fine with rock drums played hard.
 
Ex-Moderator R.I.P.
Joined 2005
make it slim and taller
with a couple of wheels it will much easier to pull around
instead of carrying it
but if there are stairs, not so good

but building this stuff is definately not easy

not sure, but with a plateamp mounted in the speaker, maybe you can drive it with a small combo, from headphone out
then you have a small practice amp, and a powered speaker cab
 
The plan is to limit the bass independently (ie, low pass into a compressor-limiter) of the rest of the mix, instead of brickwalling the output at 200Hz as ZT themselves have done.

See last page here http://www.ztamplifiers.com/pdf/ZT_Amplifiers_Lunchbox_Whitepaper.pdf - I'm hoping for better LF performance at moderate levels than this, but for loud low frequencies, more speaker will be required.

Chris
 
Chris: Ok, now "clean" or "dirty"?

One of the things that can eat power is running clean. Dirty is essentially overdriving the output of the guitar? (I think, I am no guitarist). Also what bandwidth is typical of your instrument? (electric? bass? acoustic?). The Eminence Tonkerlite might be something to consider:

Nominal Basket Diameter 12", 304.8mm
Nominal Impedance* 8 ohms
Power Rating**
Watts 125W
Music Program N/A
Resonance 109Hz
Usable Frequency Range 70Hz - 5.5kHz
Sensitivity*** 101dB
Magnet Weight 4 oz.

There may be other candidates, I just chose something that had good sensitivity, that could handle the power ...(the Little Buddy 10" looks pretty good, but rated to 50W ). Don't ask me about tone, because that is an individual thing.

So here's something that should work well for you and is (perhaps) something you should consider. Get a more efficient 8" (or whatever size driver you have or slightly larger), and swap it into your existing practice amp (if good, but power limited). Have a look at some 8" "fullrangers" , they may just be what you need. A pair of Wil Burro "Betsy" drivers in an open backed cabinet or OB could be relatively inexpensive..then add a 100W/ch amp (kits are out there for "gainclones", class D and class T amps. that should be suitable. I have built and love the the 41Hz kits, but there are others out there).



Sub'ing a more efficient loudspeaker driver into your existing combo will allow you to see if 116 dB@1W@1m (40W into a 100 dB driver) is suitable. You can always use the new driver in a project amp if not suitable for installation into your combo, thus still economizing (and benefiting from any "tweaks" that you may have already done). This mod to your combo amp should be able to be done rather inexpensively and should be done so that it is reversible.

Nigel is absolutely correct. There is a fine line to be had regarding size and the ability to move air and efficiency. Surprisingly, a larger driver can be more efficient than a smaller one (and often is). Speakers that I use on my desktop are only 83dB@1W@1m, but they are less than 1m away...what I listen to in my living room are single drivers (usually), but their efficiency is nothing to get exicited about: 85dB, driven by a good, robust (McCormack) 100w/ch stereo amp, and 109 db is plenty loud enough for me.
tinitus has a good idea. If you must make an combo amp, perhaps 2 100db drivers (mounted closely together) driven by a 100W/ch, 2 channel amp in a tall cabinet that can be dragged around with castors (or oversize wheels if going up stairs) on the rear could be an effective solution. Why don't the others help out dragging the stuff more?

Eminence drivers are very good, but get yourself a guitar speaker type from them
 
instead of brickwalling the output at 200Hz as ZT themselves have done.

That agrees with what I suggested, you can get MUCH higher power handling from a driver with mid-range only and no bass content - and of course the small sealed enclosure further limits the bass capability, and helps to 'restrain' cone movement.

It looks a nice little thing, though I suspect it's far too limited for many users - but could be great for some players and styles of playing.

I suspect you're really want to see one 'used in anger' at a gig, and probably do extensive testing before you bought one - I'm presuming they aren't cheap?.
 
Hi Nigel,

The limited bass response doesn't bother me much: the combo I use has a low Q speaker in an open backed cabinet, and the tone controls (set flat) have bass cut and treble boost. The upshot is that the LF output is mostly harmonics.
ZZ Top have reputedly used the ZT Lunchbox at gigs, though they were televised so stage volume was low. There are those (on the forum I was reading) that suspected the little amps couldn't possibly be making all that sound, and others that said the amps were great and nothing more would be needed.
The amplifiers themselves are a little over £250 for the little one, £350 for the bigger one (single 12", reputed to hit 131dB). I could try one at the music shop, but not at its proper volume.


Nanook,
While I appreciate your suggestions, the idea of a larger speaker is going away from the original design intentions somewhat: this is an amplifier that must be small and portable. As a teenager on a budget, the idea of replacing the speaker to see what happens isn't really an option. Eminence (and other) guitar speakers come in around £70 here, which is more than I'd be willing to spend just to try it.
This really is a no expense expended project - I even have a suitable linear PSU here.

Chris
 
small, loud, cheap...and in the UK

Nanook,
While I appreciate your suggestions, the idea of a larger speaker is going away from the original design intentions somewhat: this is an amplifier that must be small and portable. As a teenager on a budget, the idea of replacing the speaker to see what happens isn't really an option. Eminence (and other) guitar speakers come in around £70 here, which is more than I'd be willing to spend just to try it. This really is a no expense expended project - I even have a suitable linear PSU here.
Chris

So finally the complete situation is stated. Thanks. So currently you have a 40 W single channel amp. And all you want is something to play louder, not necessarily better, and with low budget. (I am assuming you can afford a £50) My suggestion was for a good driver that could be loud enough ....

See if you can borrow a friend's amp or one from a music store. Beg, borrow or steal a SPL meter or see if one of the music store guys will come out to a practice with an amp and SPL meter. Then you can find out how loud you really need it and then go from there.

After that help can be had that will address the better defined project parameters and a reasonable budget can be created. It may be that the best alternative is to retrofit a more efficient driver into your existing combination amp.
 
See if you can borrow a friend's amp or one from a music store. Beg, borrow or steal a SPL meter or see if one of the music store guys will come out to a practice with an amp and SPL meter. Then you can find out how loud you really need it and then go from there.

If you need an SPL meter to tell if you're loud enough?, then perhaps music isn't for you? :D
 
So finally the complete situation is stated.

I'm sorry - I wasn't aware I had been vague. Wasn't intentional.

As a loudness reference, we've gone loud enough to make my ears distort. This was in a room of around 6' by 12', with an acoustic drum kit, another guitarist, bassist, and singer.
My amp was clipping square - 111dB plus the additional loudness of all the harmonics. I read somewhere that a square wave of equal peak voltage to a sine wave has twice the power. So could we say 114dB?

I'm still searching for a suitable power amplifier - I've got (for nowt) a 24v SMPS. Weighs next to nothing, so I'd like to continue the switch-mode theme with a similar power amplifier. This would keep weight down and efficiency up (you've heard it all before).

Assuming bridged operation, 48v peak output = 34v RMS = 144w (using V^2/R) into 8ohm.

This would be enough to get over 114dB (just about) clean.
I suspect the difficulty is that I want to keep up with a bigger amplifier that's being used with distortion, while keeping my own sound clean.

Chris
 
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