Crazy idea for a powered sub

Tim Weaver

Tim Weaver

Senior
Feb 2, 2011
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College Station, Texas, United States
www.weaverimaging.com
I've got a pair of 21" drivers looking for a home. I'm thinking about building 2 single 21" cabinets that have a space to mount a regular rack-mount amp in a separate chamber with front and rear venting. The amp would be completely enclosed, untouchable by the crowd. I'm thinking of using a CE4000 since they are cheap and sound really good on subs. It would be bridged into 8 ohms providing 2400 watts to the driver. It also has HP/LP filters built in. The issue I'm having is how to have access to the gain pot.

Would you miss having an accessible gain knob? I would be using these with a pair of HPR153's pretty much all the time so I think that I would be able to gain match the tops to the subs which means that I don't really need a knob on the sub, but I'm just wondering if you might think it would be a problem down the road.


BTW, using these amps bridged into 8, means if one of them lets the smoke out I can open up the other amp and drive the dead cabinet from the good one. Gives me a bit of redundancy which most powered speakers don't have. I plan on having either a door or a vent panel on the back that can be opened up with tools if needed, but the intended SOP for these subs is to plug in power and signal and go.


Any thoughts?
 
Re: Crazy idea for a powered sub

Tim Weaver said:
I've got a pair of 21" drivers looking for a home. I'm thinking about building 2 single 21" cabinets that have a space to mount a regular rack-mount amp in a separate chamber with front and rear venting. The amp would be completely enclosed, untouchable by the crowd. I'm thinking of using a CE4000 since they are cheap and sound really good on subs. It would be bridged into 8 ohms providing 2400 watts to the driver. It also has HP/LP filters built in. The issue I'm having is how to have access to the gain pot.

Would you miss having an accessible gain knob? I would be using these with a pair of HPR153's pretty much all the time so I think that I would be able to gain match the tops to the subs which means that I don't really need a knob on the sub, but I'm just wondering if you might think it would be a problem down the road.


BTW, using these amps bridged into 8, means if one of them lets the smoke out I can open up the other amp and drive the dead cabinet from the good one. Gives me a bit of redundancy which most powered speakers don't have. I plan on having either a door or a vent panel on the back that can be opened up with tools if needed, but the intended SOP for these subs is to plug in power and signal and go.


Any thoughts?
Click to expand...

If you are handy / ambitious, I would re-engineer the CE 4000 into a plate amp format. That should shave a little weight off and make the project look a little more pro. While you're at it, it shouldnt be difficult to desolder the gain controls and relocate it somewhere more accessible.
 
Re: Crazy idea for a powered sub

Tom Manchester said:
If you are handy / ambitious, I would re-engineer the CE 4000 into a plate amp format. That should shave a little weight off and make the project look a little more pro. While you're at it, it shouldnt be difficult to desolder the gain controls and relocate it somewhere more accessible.
Click to expand...

Handy? :)

JR
 
Re: Crazy idea for a powered sub

John Roberts said:
Handy? :)

JR
Click to expand...

Well I suppose if one were going to do it the way I might, they would need to be able to cut a sheet of 1/8" or 3/16" aluminum to size. Then drill all the appropriate holes for powercon and signal in, fan, attenuators, power switch. Mount the PCB and transformer with some threaded PCB standoffs. I'd use a combination of 1/2" Baltic birch and aluminum to create fan ducts to replicate the airflow of the rack mounted CE4000 and possibly add a second fan so you have one for intake and one for exhaust. ASSuming you have access to the tools already, and the amp was cheap enough to begin with, AND you have some spare time, I would figure about $25 in parts to do the conversion if you know where to source them.
 
Re: Crazy idea for a powered sub

Tom Manchester said:
Well I suppose if one were going to do it the way I might, they would need to be able to cut a sheet of 1/8" or 3/16" aluminum to size. Then drill all the appropriate holes for powercon and signal in, fan, attenuators, power switch. Mount the PCB and transformer with some threaded PCB standoffs. I'd use a combination of 1/2" Baltic birch and aluminum to create fan ducts to replicate the airflow of the rack mounted CE4000 and possibly add a second fan so you have one for intake and one for exhaust. ASSuming you have access to the tools already, and the amp was cheap enough to begin with, AND you have some spare time, I would figure about $25 in parts to do the conversion if you know where to source them.
Click to expand...

Power amp design is a little more complicated than just throwing the circuit boards together on a metal plate. While I am not intimately familiar with the inner workings of the CE4k iirc it is class D, which raises the significance of layouts and wire paths even more, not to mention possible RF emission issues without a fully enclosed chassis (so even if it works it could interfere with wireless mics et al). In power amps, because of the high currents involved lots of subtle details matter that don't so much in lower current designs. Big consoles have a similar duality with "simple but difficult to do well" because of noise and crosstalk buildup and...

Not trying to argue that this is high tech rocket science, but it isn't quite gardening either.

JR

PS: I recall back in the very early days of class D amps, when some small company tried to knock off the first generation Peavey class D amp. They copied the schematic verbatim, but still couldn't get it to work right because of PCB layout issue (not that the early Peavey class D worked all that great).
 
Re: Crazy idea for a powered sub

John Roberts said:
Power amp design is a little more complicated than just throwing the circuit boards together on a metal plate. While I am not intimately familiar with the inner workings of the CE4k iirc it is class D, which raises the significance of layouts and wire paths even more, not to mention possible RF emission issues without a fully enclosed chassis (so even if it works it could interfere with wireless mics et al). In power amps, because of the high currents involved lots of subtle details matter that don't so much in lower current designs. Big consoles have a similar duality with "simple but difficult to do well" because of noise and crosstalk buildup and...

Not trying to argue that this is high tech rocket science, but it isn't quite gardening either.

JR

PS: I recall back in the very early days of class D amps, when some small company tried to knock off the first generation Peavey class D amp. They copied the schematic verbatim, but still couldn't get it to work right because of PCB layout issue (not that the early Peavey class D worked all that great).
Click to expand...

Well, hobbyists build formula 1 racing cars and autonomous robots in their basements all the time. I'm sure someone with enough research and knowledge could do it properly.
 
Re: Crazy idea for a powered sub

Tom Manchester said:
Well, hobbyists build formula 1 racing cars and autonomous robots in their basements all the time. I'm sure someone with enough research and knowledge could do it properly.
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I'm sure someone with enough research and knowledge would realize that it's much more economical to just buy an off-the-shelf plate amp as Bennett suggested, or for an even better ROI, buy a 'real' off-the-shelf powered sub.

:lol:
 
Re: Crazy idea for a powered sub

I will not be redesigning the amp for a few reasons.
1} I want this design to be somewhat modular. I would like the ability to move into a dsp-capable amp later on. If I put an itech in there I could run a master-slave pair of subs from this setup
2} The CE4000 is a discontinued amp. If I need to repair/replace it I would not want to deal with any type of custom work. I would like to pull one and install another.
3} The sub cabinet needs to be wide enough to accommodate a 21 inch driver so it will already be wide enough to host rack gear, and I want it tall enough to stack the powered tops on so having extra height doesn't hurt either.

As far as Bennett's suggestion goes, I can't justify putting two 1300 dollar plate amps into a system destined for small club work. For that price I could buy one DSP enabled Lab Gruppen or an Itech. The big plate amp has it's place, but it's place is not here. Not only that, but these subs are 8 ohms each. I would get more power out of the bridged CE4k at a cost of around 500 dollars each. Plus the CE4k is a switch-mode PFC amp. I can feed it 240 volts and get even more performance out of it without the hassle of flipping voltage selectors.
 
Re: Crazy idea for a powered sub

Silas Pradetto said:
I'm sure someone with enough research and knowledge would realize that it's much more economical to just buy an off-the-shelf plate amp as Bennett suggested, or for an even better ROI, buy a 'real' off-the-shelf powered sub.

:lol:
Click to expand...

If this were my project I would wager with you that I could make 2 CE4000 plate amps for the cost of one of the plate amps Bennett linked, but it's a moot point considering the constraints Tim just put on the project. If it were me doing the project, I wouldn't just make a rack inside the sub as Tim proposed because I think it would look kind of cheesy, waste a lot of internal box volume, and give the box an asymmetric weight balance.
 
Re: Crazy idea for a powered sub

Tom Manchester said:
Well, hobbyists build formula 1 racing cars and autonomous robots in their basements all the time. I'm sure someone with enough research and knowledge could do it properly.
Click to expand...

You may be sure, and everyone is entitled to their personal opinions. I base mine on decades of related experience... I built my first DIY power amp from scratch back in the early '70s (4x250W), and have participated in real amp development and production for a couple decades. One of my patents is for an improved amplifier heat sink design.

IMO somebody with enough knowledge would know better and not pursue that path, but you know what they say about opinions.

Amateurs may build things that look like formula 1 race cars, but I don't recall reading about them winning races (I modified my share of street iron too). Building robot's yawn... They should build DIY drones these days, robots are so last century. :)

JR
 
lol,

Actually people are building diy drones using the robotic "brain" provided by lego.

For me, it's a non issue. I'm a decent carpenter but I'm not an electronics tech. Modding the CE4k into a plate amp would take me forever and I would never trust my work to be as reliable as Crown's.

I can put the amp in the cabinet hidden behind the grill in such a way that it is hidden. I'm not worried about the looks. The weight is a bit of an issue, but this sub should be the approximate size/weight of a 218 with similar performance. Plus i DO want it taller in order to stack on it.
 
Re: Crazy idea for a powered sub

John Roberts said:
You may be sure, and everyone is entitled to their personal opinions. I base mine on decades of related experience... I built my first DIY power amp from scratch back in the early '70s (4x250W), and have participated in real amp development and production for a couple decades. One of my patents is for an improved amplifier heat sink design.

IMO somebody with enough knowledge would know better and not pursue that path, but you know what they say about opinions.

Amateurs may build things that look like formula 1 race cars, but I don't recall reading about them winning races (I modified my share of street iron too). Building robot's yawn... They should build DIY drones these days, robots are so last century. :)

JR
Click to expand...

JR I'm not arguing with you on the point of your knowledge, you and I have known each other via the forums for at least 8 years now. My point is that the cost of materials to make my idea happen is quite negligible. In my ideal world, if I were for instance making a plate amp CE4000, I might first propose the idea, buy the amp, take it apart and post pictures. We'd dig up the schematics from the crown website and discuss the shielding and filtering, you might chime in about the proper airflow and cooling, maybe Phil Graham would give his $0.02 about shock mounting the PCB for better reliability, someone else may suggest an inexpensive DSP option to kludge into the design, and in the end we'd all be a little wiser for the experience.

Presumably back in the 70's you decided to build an amp when you could have just gone out and bought a McIntosh or Altec. You opted not to, and in the end you had a job building real amps and several patents to your credit. It's just discouraging to me to see how reluctant people are to get their hands dirty because they are so obsessed with the cost and complexity of the project when realistically you can get some pretty professional results if you talk to the right experts and know the right suppliers.
 
Re: Crazy idea for a powered sub

I am not opposed to DIY... I built my own amp back in the '70s to save money, and because I could. If I needed a new amp today I surely wouldn't do that again (my old amp actually still works). Doing it once was a good experience for me, but i wasn't charging people for sound reinforcement.

I am a moderator on a decent sized DIY forum, where I give advice about how to design and make stuff work (even amps)... GroupDIY - We break stuff...and occasionally make stuff.

OTOH for a forum presumably giving advice to people who work providing sound reinforcement, I am inclined to mix in a little business advice. Cobbling together gear that is not likely to work up to professional standards is not the best use of one's time, effort, and money, unless they have aptitude for doing stuff like that, in which case, maybe they should be doing that as a full time job, instead of trying to join the circus. There is a huge different between making some sawdust to DIY speaker cabinets (been there done that too), and re-arranging the innards of power amps. I recently had a similar exchange over on that other (professional sound reinforcement) sound forum about some guy DIY a microphone adapter... For personal use have fun, for business use, use the stock, already engineered solution.

I still suspect you underestimate the degree of difficulty to break up and reassemble a digital power amp. I have watched and managed engineers designing them as their day job, when it was their actual area of training and expertise, and it wasn't easy for them. Perhaps if you were planning to tear down an old CS800 and repackage that, I'd make less of a stink, but even in the low tech CS800 a great deal of design effort goes into grounding and thermal management. For example the old CS800 used an unbalanced input so the signal was accepted and passed around single ended. Management of ground currents and noise was difficult to deliver the 100dB or so dynamic range. Since several ground paths include the chassis, every screw matters.

Some things about thermal management that may not be readily apparent, it is not a simple matter of just pointing some air flow at a heat sink.. In an optimal design, the amount of cooling airflow delivered to individual devices is managed so the devices reach similar internal temperatures under load. Since some devices are dissipating more or less power, and later devices in the air flow, receive warmer air than the early devices that get cooler air, this is not a trivial engineering feat. If this managed air flow is not replicated precisely, the obvious result is one ore more devices will reach max temperature before the rest of them. If this "hotter" device is on a heat sink with a thermal sensor, it means the amp will probably shut down prematurely before making as much power as a stock design, if the device is not having it's temperature monitored, the device will reach too high of a temperature before the others shut down and likely to fail. Note: Even the heat sink thermal sensor uses only one sensor for multiple devices and will only be accurate if the air flow is properly balanced.

I repeat, this is not rocket science, but more complicated than I believe you appreciate. You may be able to get something to work in some fashion, but it will not likely perform near as well as just leaving the amp stock.

JR

PS If I was going to build an amp today, I like the hypex modules that I think may even be available in kit form. Convert. Control. Amplify.
 
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Re: Crazy idea for a powered sub

Tim Weaver said:
lol,

Actually people are building diy drones using the robotic "brain" provided by lego.

For me, it's a non issue. I'm a decent carpenter but I'm not an electronics tech. Modding the CE4k into a plate amp would take me forever and I would never trust my work to be as reliable as Crown's.

I can put the amp in the cabinet hidden behind the grill in such a way that it is hidden. I'm not worried about the looks. The weight is a bit of an issue, but this sub should be the approximate size/weight of a 218 with similar performance. Plus i DO want it taller in order to stack on it.
Click to expand...

Just because it was brought up, and I think it's super-cool. DIY Drones
 
Re: Crazy idea for a powered sub

Tim Weaver said:
lol,

I can put the amp in the cabinet hidden behind the grill in such a way that it is hidden. I'm not worried about the looks. The weight is a bit of an issue, but this sub should be the approximate size/weight of a 218 with similar performance. Plus i DO want it taller in order to stack on it.
Click to expand...

I see no issue with this, a fairly simple job really. Recess the rack rails in the cabinet section for the amp enough to put the amp behind your front grill, and make it deep enough to fit, and make a rear panel with fan, AC, and signal jacks for convenience, and recess it a bit too. I'd also see about any mounts at the rear of the amp too, just to make it solid.

Best regards,

John
 
Re: Crazy idea for a powered sub

John Halliburton said:
I see no issue with this, a fairly simple job really. Recess the rack rails in the cabinet section for the amp enough to put the amp behind your front grill, and make it deep enough to fit, and make a rear panel with fan, AC, and signal jacks for convenience, and recess it a bit too. I'd also see about any mounts at the rear of the amp too, just to make it solid.

Best regards,

John
Click to expand...

+1 I don't think it's such a big deal either. Build the cabinet with John's suggestions in mind and I'm sure it'll be easier and cost effective. After all, Tim knows that this box is a DIY project and that he may have a hard time selling it if needed.... it's not as if it's a manufactured for sale product. I think it's a great idea... Show some pics after you build this monster ...it'll be cool.

Hammer
 
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