Guitar Cabinet / Amp

[THRobinson]

Had some fun designing the box in Sketchup this weekend... been a year since I used the app, luckily it was a simple project.

Basically down to speaker... had some good points towards the Eminence Beta 12LTA, also some good points about a guitar speaker being used. Posted over on the Ultimate Guitar forum and Canadian Guitar Forum asking what speaker people use when upgrading a modelling amp speaker, or what would they use... 0 response. Usually decent forums for that stuff but got zilch.

Other forums, not much either... question gets asked, but no specific speakers mentioned apart from the Celestion G12H30, which I believe the Warehouse Reaper 30 is a clone of. Reaper HP 50 is just a more powerful version of that.

Electrical questions I posted in the All About Circuits forum... also got zilch.

My goal, for buttons and knobs etc... is to have the power switch, power light, and master volume on the front. On the rear, power input, 1/4", 3.5mm and RCA inputs through the preamp, and either a switch on the 1/4", or a separate 1/4" with a switch to bypass the amp/preamp and go direct to speaker. That way, if I ever get something like a Micro Terror I can hook it up, since I assume (never used one) the heads power the speaker and running a powered head through a powered amp won't be a great idea.

I plan to make the box from 3/4" plywood, inside the straps/braces will be probably 1/2" strips. The back panels and strip on the front for the volume/power will be mahogany if I can find some around here. Then brown leather tolex, gold piping, black hardware, and 'brown basket' grill cloth.

Otherwise I think I'm good to go... really just need to figure out which speaker to use before I order anything because if only comes as 8ohm it affects which PSU I get, and possible which AMP board I get as well.

Pretty much between the Reaper and the Eminence.

Reaper wise, the 30w and 50w are the same price... makes more sense to go 50w because of the extra 'overhead'... maybe the Reaper HP 50w 4ohm, plus a 24v PSU, and some aorta voltage regulator to drop it to a safer 22v. 45w would be pretty much spot on for my goal. Plus 100w amp is $10 cheaper.

 

[THRobinson]

Allowing for 3 volts loss due to output device saturation, and power supply droop, I estimate more like 70 watts RMS. (But what's a decibel between friends?)

Was mentioned a few pages back... does that mean, if I got a 24v PSU and 4ohm speaker, or the 32v PSU and 8ohm... instead of needing to knock the PSU down 2v in either case for the 50w Reaper... I'd probably be safe?

Plus... if I don't knock the voltage down a few volts, I'd only really be running the risk of blowing the speaker if I went full volume, correct? At volume level 5 and under, I'd be fine?

 

[THRobinson]

Nevermind... guy from the speaker site messaged back.

Said for a modelling amp, all the powered modelling cabs use PA speakers, regardless how they label it or hype it up, they're PA speakers.

So... 215w Eminence Beta 12LTA it is. Only an 8ohm, so, will get the 200w amp, with the 32v power supply (150W@3Ω 34V DC THD+N 1%). Max is 36v so, 32v is less which is good, and a bit less than the 1% distortion spec'd PSU as well.

So... final build, should be around 50-55w and under the 1% clip/distortion....

Sure 1x200w Class D Amp
Eminence Beta 12LTA 12" 8oh 215w speaker
32v5A160W Power Supply
Pre-amplifier Board 12-35V

Plus a few knobs, lights, jacks, etc....

Any foreseeable issues?

I was also looking at pre-amp boards with volume... but not sure how they work. Audio in/out but no power so, how's it boosting the signal? I guess passive means just throughput no boost?

 

[29285]

according to JM Faheys posting it is foreseeable that you will get less audible power than some 50W guitar amp with a typical guitar speaker. This may be sufficient or not, depending on your requirements (loud drummer etc).
Personally I am hit with a loud drummer. My setup is TPA3118 supplied with 24V which yields about 25Watts into 8Ohms. Speaker is one 12inch high efficient low weight Celestion Century.
This gives me just enough power with little headroom:
It could be more, but I refuse adding to the total loudness level.

 

[Gnobuddy]

Said for a modelling amp, all the powered modelling cabs use PA speakers, regardless how they label it or hype it up, they're PA speakers.

Interesting! I wouldn't have thought it would be so hard to pin down something as basic as this - and yet, we've seen entirely contrary opinions on this thread.

Any foreseeable issues?

I didn't spot any obvious ones this time around...hope I didn't miss anything!

You are going to add your own volume knob at the input to your powered speaker, yes? In principle you don't need one (turn on the powered speaker last, turn it off first, and there shouldn't be any damaging pops and thumps from the preamp.) But in practice, having a volume knob and leaving it set to zero until you are ready to start making music, is a nice bit of insurance. Otherwise sooner or later you will meet one of those guitarists who leaves the amp powered on and unplugs his guitar cable, creating an almighty "pop!" which tries to blast your speaker cone across your living room.

I guess passive means just throughput no boost?

Exactly. Some audio sources (such as CD / DVD / Blu Ray players) put out signals more than big enough to drive any reasonable power amp to full output. No preamp needed, just a volume control.


-Gnobuddy

 

[Gnobuddy]

It could be more, but I refuse adding to the total loudness level.

I agree with you entirely.

This is a no-win game, the usual "Everybody wants to be louder than everybody else!" situation. All it does is drive away your audience, and cause hearing loss to the musicians. Not good.

There are several things one can do to make acoustic drums a little less obnoxiously loud: 7 Ways To Make Drums Quieter - Andertons Blog

-Gnobuddy

 

[THRobinson]

I play by myself... so I always win the who's loudest battle.

 

[Gnobuddy]

I play by myself... so I always win the who's loudest battle.

That would be the perfect solution, except for the fact that it's a lot of fun to play with other people.

I spent a lot of years playing by myself, eventually the fun went out of it, and I put down the guitar for many years. Eventually I read Victor Wooten's book ("The Music Lesson"), where he talks about music being a form of communication. No wonder music had stopped being fun for me - I'd been talking to myself for a decade!

Since then, I found that many evolutionary biologists as well as cultural anthropologists agree with Wooten. It seems likely that music evolved in our ancestral pre-human species before speech did, served as a way to communicate and bond the members of the pack, and was a precursor to the evolution of speech itself.

No wonder music has such a powerful emotional hold on almost all of us humans!

-Gnobuddy

 

[THRobinson]

Sadly, only other person i know that plays is my nephew who lives a fair distance away. He owes me a jam though, given i built him a guitar.

Gotta say, after converting to CAD funds plus shiping, $38 amp becomes $60 pretty quick, PSU as well.

As well, on eBay looking for cheaper boards... Now that know what the specs mean, I'm annoyed when they don't list them.

Went from a 2x12, to 1x12, then 75w, to 50w and now pondering 30w.

Saw this one on eBay.... 100w amp up to 26v and has a volume onboard, which i could i assume desolder and run to a larger pot.

DC 12V 24V 100W TPA3116 D2 DA Mono Channel Digital Power Audio Amplifier Board | eBay

TPA3116D2 100W Digital Amplifier Board Subwoofer NE5532 AMP 8-25V Audio Module | eBay


DC 12V 24V 100W TPA3116 D2 DA Mono Channel Digital Power Audio Amplifier Board | eBay

DC 12V 24V 150W TPA3116DA Mono Channel digital Power audio amplifier board | eBay

TDA7498 D Class 20mA Subwoofer Amplifier Board 150w 4-8ohm | eBay

Last one especially looks good, low on specs but if goes 18-32v then I assume 32v is with 10% distortion so probably around 24v I'd be safe. Has a vol pot already, plus led light so can wire that to the power light at the front. Also $13CAD vs $60. PSU also drop from $30 down to $15. Found these chip specs though and i see where mentions distortion 1% and 10% but didnt seem to show at which voltage... For 1% anyways...

https://www.google.ca/url?sa=t&sour...FjAAegQIBhAB&usg=AOvVaw3fjFj5013b0fOn4NvUoQ-I

 

[Gnobuddy]

Sadly, only other person i know that plays is my nephew who lives a fair distance away.

Around here, the trick is to find one regular jam group and get to know a few of the members. Usually someone knows about at least one other jam, and if you go to that one and make some more friends, they know about yet another one, and so on...

I don't know Zurich (been to Mississauga, Oakville, Hamilton, etc, though). But from a glance at Google Maps, it looks like there is enough of a population within, say, 30 minutes driving, to sustain a few jams? In London, maybe?

Most likely not all jams will be a good fit, but with a little luck and persistence, hopefully you can find one you like.

Personally, I've run away from bluegrass nazis (it's not music if it's not bluegrass, and it's not a guitar if it's not a Martin steel-string acoustic), I've run away from cowboy jams (play anything other than G-C-D chord progressions and you get looks that could kill), and I run as fast as I can away from all blues-only jams (I could die happy without ever hearing yet another badly played 12-bar blues shuffle in E major or A minor!)

Gotta say, after converting to CAD funds plus shiping, $38 amp becomes $60 pretty quick, PSU as well.

Yeah, I know what you mean. The Yeeco amp I bought was around $25, with free shipping on orders over $35...I bought two amp boards for two planned projects, and got the free shipping.

I got lucky with one PSU, $4 at Value Village for a 1.8 amp, 24V SMPS with a Kodak label on it. A 2.5A power supply would have been better, but I've never driven this amp hard enough for the $4 PSU to object...

Now that I know what the specs mean, I'm annoyed when they don't list them.

If the ad names the chip used, try Googling "chip name + datasheet". Usually that will turn up a factory datasheet with more specs than you can shake a stick at. Example: http://www.st.com/content/ccc/resou...df/jcr:content/translations/en.CD00244535.pdf

Went from a 2x12, to 1x12, then 75w, to 50w and now pondering 30w.

If you're like me, it will be more than enough...as long as you don't try to play bass guitar through it, or compete with a loud set of acoustic drums.

I use an Acoustic AG30 as a P.A. system. It has an 8" woofer with a post-mounted coaxial Mylar dome tweeter, no nasty-sounding cheap horns; only 30 watts RMS, but that is more than enough volume for me - I once used it for vocals and acoustic guitar for a crowd of about 75 people enjoying a free dinner courtesy of a local church, without running it to its limits. And that was in a fairly large room, probably around 1500 square feet.

Now everyone thinks they need 1000 watts to play a coffee shop gig, but that is just the power of decades of misleading advertising...

For the projects I've built using this sort of cheap class-D board, I just find two identical cheap speakers - then you can do 2 x 30W with a fairly inexpensive amp board and power supply.

TDA7498 D Class 20mA Subwoofer Amplifier Board 150w 4-8ohm | eBay

Last one especially looks good,

I used that one in a previous project. Beware the weird input (audio) connector - I believe it's a "JST-XH", which has 3 pins spaced 2.5 mm apart, and it doesn't come with the amp board, so you have to source it separately. Guess how I found that out.

Also, the heatsink was loose when I bought that board - in fact, the heatsink was not tightened down on three out of three class-D boards I bought. Don't go overboard, but you do want the heatsink in good contact with the thermal pad on the chip to keep it from overheating.

..but if goes 18-32v then I assume 32v is with 10% distortion so probably around 24v I'd be safe.

Not sure I understand that.

The datasheet I linked earlier in this post is for the TDA7498, the chip in this particular amp board.

-Gnobuddy

 

[THRobinson]

Ya... I moved here from Guelph, big change, such a small... country music lovin'... area. Bleck. I'm more into 70/80's rock. Never learned blues and don't really listen to it much but always liked how it sounded with the acoustic. May start learning some of that.

PSU's... I do have a few laptop power supplies, I think ranging from 18-24v, not sure the wattage/amps though off-hand. Had one set aside for a $6 eBay board, 19v but ended up not using the board for the project. Still plan to do a cap swap and probably use it for something else. Quality was meh... heatsink also barely on, holes were off a bit as well so sat crooked, volume control could have been mounted a bit better as well.

I did find the spec sheet for that chip actually, I guess 2 versions, a stereo one and a mono one under TDA7498MV

Features
• 100 W output power at THD = 10% with RL = 6 Ω and VCC = 36 V
• 80 W output power at THD = 10% with RL = 8 Ω and VCC = 34 V
• Wide-range single-supply operation (14 - 39 V)
• High efficiency (η = 90%)

Lower down it has a spot in a chart for 10%/1%... but no mention of power supply, ohms or anything. I guess 100w with 10% THD with 36v and 78w with 1% with 36V both with 6ohm?

I've seen some amps listed where they've listed 10% THD at Xvolts, and 1% THD at Yvolts... so think I got my math mixed up reading too many eBay China mis-specs.

So I guess with 8ohm... 80w with 10% THD using 34v. From your chart before, I guess 10% 80w, around 60w 1%? Hmm... maybe go cheaper on the amp, and pay the $30 for the 32v PSU.

Though I will admit... I'm fine with cheap eBay China parts like the amp, power supply however is a bit more of a fire hazard. If I go 24v, may be better to go to DigiKey and get a 24v Mean Well brand one for $10 more.

LRS-100-24 Mean Well USA Inc. | Power Supplies - External/Internal (Off-Board) | DigiKey

Going from computer power supply horror stories, it has me debating.

I used that one in a previous project. Beware the weird input (audio) connector - I believe it's a "JST-XH", which has 3 pins spaced 2.5 mm apart, and it doesn't come with the amp board, so you have to source it separately. Guess how I found that out.

Luckily I'm not too worried about desoldering stuff. Likely desolder it and solder the wires direct to the board. Desolder the pot as well, solder in a foot of wire and run to the front of the cab same as the LED. Though may upgrade the pot to something bigger, or, a slide pot. Kinda like the idea of a sliding volume control.

So, that board should work and a few with 0 bids for $13CAD. Also saves me the trouble of sorting out where/how to add a volume pot which is a bonus.

I guess now it's 24v or 32v PSU. Brand name or no-name.

So, when picking out this stuff... how do you know which chips are better than others? for example.. the TPA3116DA I linked, could it be a better choice than the TDA7498?

 

[29285]

I do not know what is "better".
All I can say that 36V is louder than 24V
And TPA3118 is limited to 24V

 

[THRobinson]

so... here's an onion in the ointment...

NextGen did mention the best for the modelling is a PA speaker cab, woofer+tweeter/horn.

In a guitar forum I was also asking for advice on speakers to see what they'd recommend and was mentioned as well, better to have a woofer+tweeter.

That Eminence is a PA speaker so I assume will handle what it needs for mids/lows. Would it make sense to add in a dome tweeter and a crossover?

Which kinda messes up things a wee bit.... 2 speakers and such.

 

[THRobinson]

I do not know what is "better".
All I can say that 36V is louder than 24V
And TPA3118 is limited to 24V

Simple and straight forward... I'm good with that.

Quality wise though I guess so long as within the parameters (ohm, volt, etc) they're all about the same.

 

[Gnobuddy]

Quality wise though I guess so long as within the parameters (ohm, volt, etc) they're all about the same.

You know how discussion of religion and politics is banned on this forum because people tend to get very emotionally engaged on those topics?

Discussions of audio amplifier distortion aren't banned, but it seems to stir up equally crazy levels of emotion for some true believers.

The science is pretty simple: at least five decades ago, it had been thoroughly demonstrated in well-conducted double blind listening tests that few if any people could detect 1% THD in music, though some could detect it when added to a pure sine wave test tone. Drop that to 0.5% THD or less, and nobody could detect it on any kind of signal (music or test tones) with any statistical significance.

All the chips we've discussed on this thread dip down to around 0.1% THD over much of their output power range, and stay there until they get close to clipping, at which point the distortion curves switch from being nearly horizontal, to nearly vertical.

To get bigger power numbers, the manufacturers push these chips far into clipping (10% THD). But IMO this is marketing at its dumbest, ignoring an important spec (inaudibly low levels of distortion) for an unimportant one (how loud it can get if you clip the heck out of it.)

The important point being: as long as you keep them out of clipping, all these chips have distortion levels too low for the human ear to detect. Distortion-wise, they are all essentially perfect as far as our ears are concerned.

This applies to almost every home Hi-Fi amp sold in the last four decades, too. I used to be interested in Hi-Fi audio amp design, until I realized that any old $40 thrift-store receiver from the 1990's (in good working condition) is audibly perfect as far as distortion goes; keep it out of clipping, and you can't improve on its sound with any amount of money.

Since the science of audio / audio perception was 95% settled by 1970, most actual researchers and scientists had left the field by then. The resulting vacuum was filled mostly by audiophiles - which usually translates as "a person with deep emotional involvement with audio electronics and hardware, who rejects the scientific method completely, and may not have any real technical knowledge."

These people continue to believe that you can hear 0.0005% distortion, that red plastic insulation makes a wire sound different than black plastic insulation, that wooden discs made out of mpingo have magic properties ( The Magic of Mpingo ), and so on.

But if you don't belong to their crazy-making world, Voltwide's approach makes complete sense. All modern audio amps have perfect distortion levels (too low to hear.) So choose by price, power output, and reliability, if you have any information on that. Maybe signal-to-noise ratio, if you happen to find an amp noisy enough to not be perfect in that department as well.

Amps are essentially audibly perfect, but speakers - and their interaction with rooms - are very far from perfect. One of the things that is a head-scratcher for me is that some people obsess about 0.01% THD in their power amplifier - while ignoring the 10% THD from their woofer!

-Gnobuddy

 

[chris661]

so... here's an onion in the ointment...

NextGen did mention the best for the modelling is a PA speaker cab, woofer+tweeter/horn.

In a guitar forum I was also asking for advice on speakers to see what they'd recommend and was mentioned as well, better to have a woofer+tweeter.

That Eminence is a PA speaker so I assume will handle what it needs for mids/lows. Would it make sense to add in a dome tweeter and a crossover?

Which kinda messes up things a wee bit.... 2 speakers and such.

You don't need a tweeter. The reason I recommended the LT version is because it has a whizzer cone which extends the high-frequency response high enough for your purposes.

Chris

 

[THRobinson]

That's right... I knew there was a reason for the LT over the other model... and I was certain it was in this forum that I read it but, couldn't for the life of me find it.

 

[29285]

From my point of view a two-way guitar cab with passive x-over is quite a bad idea, because:
When the amp is driven into clipping by frequencies of let us say some 300Hz, this tweeter will reproduce all nasty harmonics up to 20kHz - and this is exactly what gnobuddy called the "cazoo" sound.
A real guitar speaker has a very sharp roll of above 3..5kHz - so this will never happen with a guitar speaker.
And this is an audible difference you CANNOT equalize with any DSP in the signal chain.
So, if a tweeter is on your wishlist, you should consider bi-amping as well.
Or a very good limiter that avoids clipping of the power stage.

 

[dotneck335]

You might have some benefit of a Hi-Fi type of approach for an acoustic guitar; but NEVER for an electric guitar. I have never heard an electric guitar sound good through a Hi-Fi speaker, no matter what processing is put in the preamp.

 

[THRobinson]

I think I am good to go... few tweeks in the Sketchup design, make sure everything fits nice and tidy... speaker size a tad different, but internal volume of the cab is within specs of what that speaker recommends. Then order some parts this weekend.

Down to the debate of 30w or 50w...

Plan to make the cab from 3/4" Plywood (birch probably). Inside, I'll use 1/2" strapping. Hoping for some 3/4" thick accenting wood on the front for the volume/light/power switch, like mahogany, but small cheap bits are hard to find, being exotic/endangered woods and such.

I think overall (not at my home PC) the design is 22"Wx18"Hx14"D... with 1/3 of the back being open.

Sadly, no 1 place has everything I need... trying to find a cheap amp board in N.America else given my usual experience with eBay China (or Amazon China nowadays) I may not have this built until August.