# Building a Powered Cab



## THRobinson (Jun 29, 2014)

Hey guys... was looking to upgrade my amp, but the ones I want are outta budget and/or not finding any used for sale around here. Started to look at the idea of building a nice cab, and adding an amp, preamp and power supply to it. Master volume and nothing else.... just a powered 50w(ish) 12" speaker. I have an old laptop running GuitarRig and figured can run that through it as a modelling amp.

Was on the DIYAUDIO forum, got a LOT of information. I was just gonna get a 60w amp board off eBay, 50w speaker and a power supply and done... but learned a bit more about what all the specs are and such and hopefully will build a better amp as a result.

So basically, looking at a 200w mono amp with either a 24v power supply and 4ohm speaker, or 32v with an 8ohm to get around 45-55w of power with no clipping/distortion.

Looking for some recommendations on speakers. There was a point made about getting a flat speaker (no colour) so it doesn't affect the modelling the software if doing, which makes total sense, but, also the point that you still want a guitar speaker because more efficient and built for guitar.

Initially I looked at the Warehouse G12C 75w, which comes as 4/8/16ohm. Also 25w more than I need so (hopefully) no chance of blowing them. Warehouse sales support was nice enough to email me back and said the ReaperHP is a more flat speaker than the G12C, but 50w... bit close for comfort since be pushing pretty close to that. Someone recommended the Eminence Beta 12-LTA as being a very flat/neutral speaker, but also mentioned not designed for guitar and I think someone said more for bass.

Hoping to stay in around the under $120 range, especially since the cost of this idea keeps going up the more I learn. 

Any suggestions/recommendations?


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## THRobinson (Jun 29, 2014)

What? 0 replies?

Kinda surprised... 

Got a nice cab designed in Sketchup (love that app) though kinda debating if the inside braces may be a bit overkill. 

Down to selecting a speaker... then will have to sort out a few wiring details. 

I'd like to have 

Front: Volume, power indicator light, power toggle switch.

Rear: Power input, 1/4", 3.5mm and RCA input jacks, then probably a 1/4" jack and a switch, so I can switch and bypass the amp/preamp and go direct to the speaker. That way if I ever want to hook up a powered head like a Tiny Terror or something, I'm not plugging a powered head into a preamp and powered amp.


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## greco (Jul 15, 2007)

THRobinson said:


> Someone recommended the Eminence Beta 12-LTA as being a very flat/neutral speaker, but also mentioned not designed for guitar and I think someone said more for bass.


I recently purchased a very solid, homemade 1 x 12" cab with this speaker in it. I think these speakers are mainly for PA use in a sealed or ported cab.
It was "OK" for clean guitar tones ...but sounded a bit too "sterile" to me.
It might be better suited for acoustic guitar (??)
They have a whizzer (sp?) cone


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## THRobinson (Jun 29, 2014)

Ya, my fear was that it's flat response, but also not designed as a guitar speaker... I guess basically looking for a flat response speaker, not PA speaker but designed for guitar.

Figure come the end of the week... Reaper HP 50w wins. 

Downside is the site carries 8/16ohm. I just missed their restock order so if I want the 4ohm it'll be 5-6 weeks. Which I guess is fine. I only get so much time for projects on weekends and by the time the tolex, cloth, and amp arrive... probably be a month anyways.


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## Granny Gremlin (Jun 3, 2016)

Fullrange type PA speakers are very similar to guitar speakers in that they have a similar shapr to the response curve (upper midrange bump; just maybe not quite as big of one, so 'flatter'). Usually also some extended range in both extremes. This is even more true for vintage ones.

As for the amp, my sugg: Tiny Giant Amp (PCB+components kit) (also available PCB only, if that's your jam).

I've used some T class amps from PartsExpress to make a portable battery-powered boom box for my MP3 player, that would be my second suggestion.


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## THRobinson (Jun 29, 2014)

For my design, I'm looking at a 1x200w class D amp because max power supply is 36v. I'm just ignoring the 200w aspect... 32v with an 8ohm speaker should get me about 53w of power with less than 1% distortion. There is a 100w amp as well, an with a 4ohm speaker, could use a 24v power supply and get 55w. 

Downside to both is that ReaperHP which I am leaning towards, is 50w. I'd have to add something (power regulator?) to drop either power supply down 2v to be safe. Kinda where I am right now with those... if the Reaper HP were 75w... I'd be good to go. 

Eminence speaker however, if I recall is 215w 8ohm, so... 0 issues with stepping down the power supply, and either 24v or 32v falls within range of the pre-amp. Also like $40 cheaper I think for that speaker.

But... if a better speaker is out there for the same price... I'd rather get it. Maybe a FANE Triple Cone? I've seen it mentioned a few times... not much for sale in Canada, probably a UK purchase?


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## Hammerhands (Dec 19, 2016)

How about a Peavey Black Widow or Scorpion? The ones meant for PA.


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## THRobinson (Jun 29, 2014)

Just heard back from the guy at NextGen who was nice enough to give me his 2 cents worth on the speakers... said basically all modelling powered cabs are using PA speakers, regardless how they market/label them.

So thinking my decision is swaying over to the Eminence Beta 12LTA.

Which, upside, cheaper than the Warehouse and 215w... so, I don't have to restrict the voltage on whatever power supply I get.

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....

So far that's my setup plan... should put out about 50-55w of clear sound. Amp is rated at

_Output Power
[email protected]Ω 34V DC THD+N 10%
[email protected]Ω 34V DC THD+N 1%_​
So.... 32v @ 8ohm, should be no problem.


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## Granny Gremlin (Jun 3, 2016)

The Fane is considerably flatter than the average guitar speaker, but still has that upper mid bump; much smaller than a typical geetar driver though. So that looks good to me.

https://www.fane-international.com/downloads/FANE-SOVEREIGN-12250TC-DS141117.pdf

The Reaper HP is heavily voiced, British style, so I'm not sure it would be the best fit for this project given the modelling you're planning on doing. That said if you do go that way, don't sweat the power mismatch. Just don't turn the amp up all the way or if you do see how the speaker reacts the first time. It is harder than you'd think to blow a speaker by overpowering it (with clean power) - it's easier to blow a 50 watt driver with a dimed 20 watt solid state amp (it's the square wave clipping that'll do it every time). I say SS, because tube amps have a soft clipping characteristic that doesn't blow speakers as easily. E.G. for my portable boom box project mentioned above - the speakers are 3 watts each (nice vintage alnico fullrange 4" Fosters) but the amp is like 10 watts. Not a problem (the alnico also helps here; has a compression characteristic when pushed to the limit vs ceramic which does not).

RE your chosen amp. Check out the similar options (but cheaper and run off smaller power supplies IIRC) at PartsExpress.com. Many of them also have optional hook up or accessory kits so they're a breeze to integrate into a cabinet (and if not you can get the jacks/connectors you need from the same shop). Sound-wise I'd still recommend the MusicPCB Tiny Giant - class D or T wattage is usually spec'ed pretty high but in the real world this thing is probably louder that a D/T 5 (like 3/4s max - it's log not linear), leaving yourself that headroom. These are not the greatest amps in the world by a long stretch so plan for not pushing them to their limits. If you're worried about accidental diming (or if you lend the amp out, e.g. at a gigi) you can put a (cheap 1/4 watt metal film) resistor of approx 1/4 the value of the manufacturer recommended volume pot (usually 10K, might varry by model) in series with the pot's output to effectively limit the max volume setting - then you can safely dime the volume knob.


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## Granny Gremlin (Jun 3, 2016)

Depending on what the signal source is, I don`t think you need the preamp board. Especially if it has no EQ /tone shaping. Go straight into the amp (guitar Hi Z output is very close to home HiFi line level; even less need for a preamp if coming out yer laptop). Even a basic OD/Distortion pedal will do the job here. Those amp boards have input trim/gain control already (and even if not, just stick a 10k pot out front, wired as a variable resistor).


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## THRobinson (Jun 29, 2014)

Well, from the long thread over at DIYAudio Forum, wattage output of the speaker relies heavily on the voltage of the power supply. So basically, regardless of the amp used... if you want around 50w at 8ohm, you'll need around 32-34v of power.

Initially I was going to grab a 1x50w amp off eBay and use my 19v laptop powersupply for it. But once I started getting into 2ohm rated vs an 8ohm speaker, 10% clip/distortion specs vs 1%, etc... I kinda ended up where I am now.

200w amp isn't because I want 200w... it's because the amp itself can handle a 32v power supply. To hit my goal of about 50w with an 8ohm speaker, I'll need around 32v to make it happen.

It's for home use... so I'm sure 20w would be plenty to be honest... but, futureproofing... in case my nephew every wants it for gigging or practice with a drummer. Honestly, I got 50w in my head, and that's what I've been running with. 

24v PSU is cheaper and more available... by fluke I found the 32v one. Drops me down to about 30w though.

Pre-amp wise... from my understanding, from the Laptop, probably not... but if using just a pedal, or my walkman for music (plan to use this when working on the car as well) the pre-amp may be needed to boost the signal. Cheap part luckily and I think the board has a spot for a preamp.


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## jb welder (Sep 14, 2010)

It's not just the voltage of the supply, but it's current capability. That is what determines how much power you can get out of the supply. You should have it covered with the 5A supply, but it's not something that should be ignored.
That 32V 5A supply can give about 160W, that particular amp is around 80% efficient, so you can get around 130W from amp.
If it were a 32V 1A supply, it could only deliver 32W to the amp and you would get around 80% of that as output. That's why you have to consider the current capability of the supply.


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## THRobinson (Jun 29, 2014)

... Harry? The Guy with the Snake on his Face? 

Ya, power supply, I used an online calculator to see what was needed, then looked for something with a few amps extra. Saw a few laptop type power supplies, which I debated... but half were around 3A I think. From what I recalled I need about 3.5A... done so many calculations and looked at so many things the past 2 weeks, it's all blurring together. 

I really did wish by now (since debated a bit last year on making an amp) that someone would have something similar to GuitarRig on a Raspberry Pi.

Would be really cool to make a modelling amp with a built in touch screen.

Next I guess is making a 3 or 4 button switch pedal. Maybe integrate a removable laptop stand on the cab.


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## ronmac (Sep 22, 2006)

DIY is cool, but if anyone else is wondering if they might want to tackle a project like this, but are a bit reluctant, there are a couple of Tech21 Power Engines for sale on this Forum. Instant gratification.


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## jb welder (Sep 14, 2010)

Came across someone recommending this so I thought I'd pass it on. He said it's real loud, certainly cheap enough:
TPA3116 D2 DA DC 12V 24V 100W Mono Channel Digital Power Audio Amplifier Board | eBay


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## Hammerhands (Dec 19, 2016)

Peavey and some other brands made speakers with rack cabinets in them.

I think Peavey intended them to be used with the SessionBass amp, which combined made something very similar to the DataBass amp, which I desire.

There are a lot of 1 and 2 space rack power amps available with a broad range of power.


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## THRobinson (Jun 29, 2014)

I debated that one... well... about 4 in total I guess were debated. That one maxes at 24v... I'm still debating between 24v/32v. Concern though was if I go 24v, I'd be using the max amount it can handle and I wanted a bit of headroom.


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## rwe333 (Feb 18, 2006)

I would suggest looking at the 200w Eminence EM12 or lighter EM12N for a neutral speaker (EVM12L like).


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## alwaysflat (Feb 14, 2016)

Were you able to find some P/S voltage vs Output power specs for this chip ? I couldn't find reference 
That would be your helping hand to finding ample headroom. I couldn't promise my speakers "no dirt", such that I'd want to have some understanding of where the edge is for reliability consideration. I think for 50 W clean I'd want to consider a 75W RMS minimum speaker. 
I'm just thinking of my wallet tho.


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