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Author Topic: Newbie With a 'Class 'D' Question  (Read 979 times)

Skip Ellis

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Newbie With a 'Class 'D' Question
« on: September 13, 2017, 11:54:19 am »

Greetings all! I recently purchased a little 150 watt class 'd' power amp board from somewhere in China (E-bay) with the intent of adding it to an open back cabinet containing a Peavey 12" Scorpion (8 ohm) speaker. The amp is listed as needing a 12-24 vdc power supply and I plan to use an 18vdc HP printer power supply that I have on hand -is that I want a (very) mini PA to use when I do a solo acoustic act. Input will be from a Yamaha 8 channel board with effects and phantom power to run my condenser mics (hate guitar pickups!!!)

Just wondering if any of you folks see a downside to this scheme - I'm under severe budget restraints and at age 72, I don't want to tote my JBLs, mixer, and power amp every time I go play for an hour in a nursing home. Would love to have one of those nifty little Bose tower things or the Fishman 330 but it's not in the budget and most amps don't provide phantom power.

Thanks!!!
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Chris Hindle

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Re: Newbie With a 'Class 'D' Question
« Reply #1 on: September 13, 2017, 12:28:03 pm »

The amp is listed as needing a 12-24 vdc power supply and I plan to use an 18vdc HP printer power supply that I have on hand -is that I want a (very) mini PA to use when I do a solo acoustic act.

Welcome to the Forums Skip.
This post will be moved to another location soon enough.
Short answer, NO. The HP P/S will not provide the current required to run the amp at any more than a whisper.
Check the Amplifier Board specs. It should list the current required for operation.

Chris.
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

TJ (Tom) Cornish

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Re: Newbie With a 'Class 'D' Question
« Reply #2 on: September 13, 2017, 01:22:35 pm »

Welcome to the Forums Skip.
This post will be moved to another location soon enough.
Short answer, NO. The HP P/S will not provide the current required to run the amp at any more than a whisper.
Check the Amplifier Board specs. It should list the current required for operation.

Chris.
I don't think this is a truism - just a few watts of amplifier output power can get reasonably loud.  A typical speaker would have a output of maybe 92dB with 1 watt of input, which is much more than a whisper.  Whether the HP power supply has enough power to run the amp depends on the idle current specs of the amp and Skip's desired level, but I wouldn't assume it wouldn't work.
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Skip Ellis

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Re: Newbie With a 'Class 'D' Question
« Reply #3 on: September 13, 2017, 01:34:22 pm »

Here's all I have:
Board:
Chip Type: TPA3116D2
with preamplifier NE5532
Supply voltage: dc12-26v
Output Power: 150W MAX
DC 12V 50W
DC 20V 100W
DC26V 150W

Power supply:

HP AC/DC Adapter
HP 0950-3807
Input: 100-240V  1.0A MAx
Output: 18v    2.23A LPS   center hot
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TJ (Tom) Cornish

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Re: Newbie With a 'Class 'D' Question
« Reply #4 on: September 13, 2017, 01:42:16 pm »

Here's all I have:
Board:
Chip Type: TPA3116D2
with preamplifier NE5532
Supply voltage: dc12-26v
Output Power: 150W MAX
DC 12V 50W
DC 20V 100W
DC26V 150W

Power supply:

HP AC/DC Adapter
HP 0950-3807
Input: 100-240V  1.0A MAx
Output: 18v    2.23A LPS   center hot
Skip, your HP power supply puts out around 35-40 watts.  This won't be enough to drive your board amp fully, but as mentioned above, it may be adequate depending on how much output power you need.

Amplifier power does not track linearly with acoustic output, but logarithmically.  Every doubling of amplifier power adds (theoretically) 3dB of acoustic output.  At extreme volumes that means it can be very expensive and heavy to add more output, however at the beginning end of the chain, we actually get a lot of output for our watt.

With a hypothetical speaker with a sensitivity of 92dB/1w@1m, going to 2 watts increases our level to 95dB.  Increasing to 4 watts gives us 98dB, etc.  It's hard to say what exactly would happen, but I think it's worth a shot.
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Chris Hindle

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Re: Newbie With a 'Class 'D' Question
« Reply #5 on: September 13, 2017, 01:48:10 pm »

I don't think this is a truism - just a few watts of amplifier output power can get reasonably loud.  A typical speaker would have a output of maybe 92dB with 1 watt of input, which is much more than a whisper.  Whether the HP power supply has enough power to run the amp depends on the idle current specs of the amp and Skip's desired level, but I wouldn't assume it wouldn't work.

Hi TJ.
I would expect HP to be on the "frugal" side for a Inkjet power supply.
A quick dip to their site shows an inkjet P/S operating on  100-240V, with a MAX consumption of 10 Watts.
Napkin conversion suggests 18 volts at .555 amps.
That ain't a lot of juice, and I'm pretty sure it wouldn't survive max output for very long. Sure, class D is efficient, but...........

** Edit:
OK, specs on the P/S in question posted while I was typing.
Seems there's 5 times the power available than I thought.
It ain't gonne be Rock & Roll, but it may work.
Only one way to know.
Chris.
« Last Edit: September 13, 2017, 01:51:50 pm by Chris Hindle »
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Ya, Whatever. Just throw a '57 on it, and get off my stage.

Craig Hauber

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Re: Newbie With a 'Class 'D' Question
« Reply #6 on: September 13, 2017, 01:52:48 pm »

Greetings all! I recently purchased a little 150 watt class 'd' power amp board from somewhere in China (E-bay) with the intent of adding it to an open back cabinet containing a Peavey 12" Scorpion (8 ohm) speaker. The amp is listed as needing a 12-24 vdc power supply and I plan to use an 18vdc HP printer power supply that I have on hand -is that I want a (very) mini PA to use when I do a solo acoustic act. Input will be from a Yamaha 8 channel board with effects and phantom power to run my condenser mics (hate guitar pickups!!!)

Just wondering if any of you folks see a downside to this scheme - I'm under severe budget restraints and at age 72, I don't want to tote my JBLs, mixer, and power amp every time I go play for an hour in a nursing home. Would love to have one of those nifty little Bose tower things or the Fishman 330 but it's not in the budget and most amps don't provide phantom power.

Thanks!!!
Parts Express sells matching self-contained power supply units for those chip-amp boards with current outputs intended for that use.
https://www.parts-express.com/cat/power-supplies/1474

But you mention you like your mics, assuming for the sound quality. 
However a properly tuned cabinet with an HF device of some kind and raised up on a stand would perform with a higher quality than what to me seems like a guitar-amp backline cab. 
If you are using an existing cabinet I'm sure it could be cheaply modified with a basic amount of woodworking to perform better for PA use.
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Craig Hauber
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Skip Ellis

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Re: Newbie With a 'Class 'D' Question
« Reply #7 on: September 13, 2017, 03:03:27 pm »

Parts Express sells matching self-contained power supply units for those chip-amp boards with current outputs intended for that use.
https://www.parts-express.com/cat/power-supplies/1474

But you mention you like your mics, assuming for the sound quality. 
However a properly tuned cabinet with an HF device of some kind and raised up on a stand would perform with a higher quality than what to me seems like a guitar-amp backline cab. 
If you are using an existing cabinet I'm sure it could be cheaply modified with a basic amount of woodworking to perform better for PA use.

That's my thought - I've built scads of cabinets over the years. Right now, I'm just in the testing stage to see if these little 'toy' amps will even work for what I want. I've got two 12" Scorpions and I figure on putting an amp in each to run off both sides of my board. My venues are small - common areas/foyers of assisted living facilities and not more than 30-40 people. Not a lot of power needed. I guess I should look into one of the acoustic amps on the market but it's more fun to try and do  it on the cheap.
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Chris Grimshaw

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Re: Newbie With a 'Class 'D' Question
« Reply #8 on: September 14, 2017, 03:44:13 am »

A guitar speaker is gonna sound pretty awful. They're designed to add considerable colour to the sound, which is why guitarists can spend ages picking "the one". Mine's an Eminence Man O' War, 16ohm.

Anyway, guitar speakers will tend to have a big ol' peak in the lower kHz range and nothing above that. There'll also be nothing below around 150Hz. Maybe higher, if it's an open-back cabinet. Remember, the peak will be directly on-axis where the sound will be very piercing. Everyone else will get a very muffled sound.

Try connecting music to a clean amplifier and see how the speaker sounds. My bet is you'll switch it off pretty quickly.

If you don't like it, I'd recommend that you replace the speaker with a coaxial unit and crossover, and close the back. It'll sound much more HiFi, and might mean people stick around to listen.

Chris
« Last Edit: September 14, 2017, 07:24:15 am by Chris Grimshaw »
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Stelios Mac

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Re: Newbie With a 'Class 'D' Question
« Reply #9 on: September 14, 2017, 05:05:40 am »

A guitar speaker is gonna sound pretty awful. They're designed to add considerable colour to the sound

This ^
If you hate the sound of guitar pickups, you're gonna hate this even more.

IMHO, a single cheap, lightweight, active cab will be more than enough for what you're looking to do.
If I were you, I'd go for a 12" EV ZLX and call it a day. Very lightweight, and it'll sound ages better than a guitar speaker in an open-back cab ever will - Even a B212D would do the job if the budget is really tight...
Hope this helps :)
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