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Class D Switching Power Amplifiers and Power D/A conversion

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Old 4th August 2010, 12:14 PM   #681
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Quote:
Originally Posted by jimtegel View Post
Sorry for late feedback. But here it goes:
I left the HP-100:s running with pink noise for at least 40h before heading of to Roskilde. My conclusion is that they definitely changed character to the better, sounding more "natural". However, I still think that they are to "soft" and lacking that last "hi-end" treble (that might be impossible to achieve with piezos though...).

Field test report:
I'm really happy with the performance of the Boominator @ this years Roskilde festival! It sounded great and was fairly easy to carry around late nights. Thanks to the aluminum edges and the round metal corners it also became virtually indestructible.
I also added a uC-controlled giant LED VU-meter (using audio as input) on the backside which attracted even more people to the dance parties at the camp

YouTube - Boombox with built in VU-meter

Battery life was excellent. I used two 7.2Ah SLA:s (not at the same time though) and charged them during the day with a 20W solarpanel from solarlab.se.
Thanks for the feedback. Didn't see your at Roskilde this year though. Saw many other Boominators.

It's a definite sign of quality that a piezo can sound "soft" and "natural", that is the usual caveat against them that they tend to be "hard" and "fatigueing".

Great job on the build. I'm actually a little inspired by it. I might put a large LED light show on the bottom of mine as well since they won't be used during daylight hours when the solar panels would be used, so you'd just turn them over. But it requires moving the handle/port in middle of the ends.
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Old 4th August 2010, 03:05 PM   #682
Pano is offline Pano  United States
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Now that's a VU meter! Very cool.
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Old 14th August 2010, 12:22 AM   #683
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I agree panomanic, those VU meters are great!

I've been thinking about building some sort of Boominator type system for a while now, as I have been using an amp 6 to power some old Aiwa speakers and I think with some high efficiency drivers I could get a far more SPL.

Now I've had a look and I can't find anyone in the selling P.audio HP-10W drivers or the Goldwood equivalent in the UK which is a bit of a shame. I did have my eye on the Eminence Delta 10 though, it looks to be a little better in terms of efficiency (99db) but the FS is higher also (66Hz) so I guess it would not give the same bass extension that the P.audio drivers would.

Overall, would the Eminence drivers be a good choice here or are there any better alternatives that may be available in the UK?
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Old 23rd August 2010, 03:28 PM   #684
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Hi there,

This thread has been so interesting and informative that I have to make myself a small efficient boombox now for camping. I want to replace my JVC tube style boombox as the battery life is horrible and I'm tired of buying D batteries like crazy. I have looked at different parts and was just wondering if the ones I have selected will be acceptable and work well together. I need this thing to last about 60 hours or so (If it can be recharged by a vehicle that would be fine as we have vehicles about 200m away from our camping area). My priorities are

1. Battery life (may add solar charger if is necessary)
2. Loudness (battery life is still much more important as the stereo only needs to be loud enough for about 10-15 people)
3. Durablility (lots of drunk people!)
4. Ease of build (I'm not really an expert carpenter or anything but can make a rectangular box I'm sure)
5. Sound quality (we are not very picky about sound quality as most of my friends wouldn't know the difference between high quality audio or a cheap ghettoblaster)
6. Portablilty (not really important, just needs to be small enough to fit in my car)

Please correct me if I'm wrong but the parts I am looking at consist of:

*An amplifier
*2 8" or 10" woofers
*2 piezzo tweeters
*18AH SLA Battery
*Various wiring
*Various plywood and hardware

Here are the parts I have selected so far (I am kind of limited to speakers from a single dealer as I can't seem to find anywhere near Toronto, Canada with reasonable shipping to my house, the site I will be using is Q-Components loudspeakers & audio products)

Amplifier: Dayton DTA-2

Class-T architecture
0.03% THD+N @ 9W, 4Ω
0.10% IHF-IM @ 1W, 4Ω
11W @ 4Ω, 0.1% THD+N
6W @ 8Ω, 0.1% THD+N
High Power
15W @ 4Ω, 10% THD+N
10W @ 8Ω, 10% THD+N
High Efficiency
81% @ 15W, 4Ω
90% @ 10W, 8Ω
Dynamic Range = 98 dB
Over-current protection
Over-temperature protection

Woofers: Pioneer 8" Woofers B20FU20-54F or Pioneer 10" Woofers A25FU20-53F
I'm not sure if 2x10" or 2x8" woofers would be better. Here are the specs for the two woofers.

8"

Outside Dia...........................205 mm
Impedance...............................8 ohm
Power ........................................80 W
Freq. Resp ...............40 Hz - 2.5 KHz
Magnet Wt ................................20 oz
Fs .............................................40 Hz
Re.........................................6.9 ohm
Qts ..............................................0.26
Qes .............................................0.29
Qms............................................2.5 0
Vas .....................................56.6 litres
Xmax .....................................0.1 mm
Voice Coil Dia .........................38 mm
SPL...........................................93 db
Depth ......................................91 mm
Baffle Opening......................185 mm
Mtg. Cntr...................195 mm BC x 4

10"

Outside Dia...........................256 mm
Impedance...............................8 ohm
Power ........................................70 W
Freq. Resp ...............35 Hz - 3.5 KHz
Magnet Wt ................................20 oz
Fs .............................................35 Hz
Re.........................................7.0 ohm
Qts ..............................................0.27
Qes .............................................0.30
Qms............................................2.8 0
Vas ...................................124.9 litres
Xmax .....................................2.4 mm
Voice Coil Dia .........................38 mm
SPL...........................................94 db
Depth ....................................109 mm
Baffle Opening......................236 mm
Mtg. Cntr...................248 mm BC x 4

Tweeters: piezo horn tweeter Goldwood GT-1016

Outside Dim...............67.5 x 145 mm
Impedance.......high at low frequency
Power..............50W RMS / 75W max
Freq. Resp.............3.5 KHz - 40 KHz
Voice Coil................ceramic bimorph
SPL...........................................94 db
Depth ......................................53 mm
Baffle Opening..............51 x 109 mm
Mtg. Cntr.................54 x 132 mm x 4

Battery: 18AH SLA Battery
12180HR-1.jpg

If there is anymore information I can provide please let me know. One of the biggest problems I am having is designing the box, If someone knowledgeable could help me with the measurements or the volume required I would be very grateful! I really don't need it to look fancy at all just regular rectangular box.

Few more questions (sorry!)

1. I assume I would need to add ports as well, anyone with any recommendations for port size?

2. Also do I need any sort of fuses, capacitors, resistors, crossovers? Any extra electronics other than just wiring the amp to the battery and to the speakers.

3. What would the battery life be like? (I tried to calculate it but ended up with some very large numbers and I'm sure I screwed up somewhere!)

Once again thanks for all the information this thread has provided me and I'm very excited to start my build!

-Craig
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Old 24th August 2010, 09:12 AM   #685
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For what it's worth I ran some test tones through my setup with 4 ohm HP-10W and round Jaycar piezos with 150 ohm resistors.
All volume levels equal down to 80Hz.
Half volume at 60Hz
Audible at 40Hz.
All volume equal up to 5kHz
Half volume at 6kHz
Inaudible at 8kHz
The setup sounds good but what happened to the higher frequencies?
Paul
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Old 24th August 2010, 01:32 PM   #686
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Carseneau,

Lots of questions, which is what makes this hobby so fun.

On the speaker box sizer, just Google "speaker box calculator" and you'll find some sites that will let you plug in your speaker specs and box type (Bass reflex, etc.) and get a size in volume. You will have to work out dimensions from that. Unless you go for extreme thinness or length, volume is volume, so you can shape it as needed. Port length can be adjusted to fine-tune your design; you can use cardboard tube for the trials if you want.

Look over the discussions in this thread for info on the minimal crossovers for the piezo tweeters.

You will need some kind of battery charger. That's a huge SLA. You should easily get a whole weekend's sound out of that, probably more. A provision on running the things off of AC isn't a bad idea, as there seems to me unlimited uses for a portable system.

FYI, there is a Class-T amp with a bit more power on 12v: the ones based on the 2020 chip. IMO, if you haven't ordered the amp yet, this is a better choice.

As far as durability, parts express sells metal corners, etc., so you can finish it up in the manner of a guitar amp.

--Buckapound
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Old 24th August 2010, 01:40 PM   #687
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Quote:
Originally Posted by coit View Post
For what it's worth I ran some test tones through my setup with 4 ohm HP-10W and round Jaycar piezos with 150 ohm resistors.
All volume levels equal down to 80Hz.
Half volume at 60Hz
Audible at 40Hz.
All volume equal up to 5kHz
Half volume at 6kHz
Inaudible at 8kHz
The setup sounds good but what happened to the higher frequencies?
Paul
I'm guessing you're using power resistors? In that case the parasitic inductance in those form a low-pass filter. In normal power resistors this cut-off will start inthe 4-6KHz range. In "non-inductive" types it will be in a more acceptable 12-18KHz range.

I always recommend using old fashioned solid carbon resistors, or multiple parallelled metal film resistors when used with piezo tweeters because of their very nature they are extremely sensitive to even miniscule amounts of parasitic inductance in the resistors.
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Old 24th August 2010, 11:10 PM   #688
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Buckapound,

Thank you for your reply, I don't see that parts express carries an amplifier with the 2020 chip. Am I missing something? Would the Sure 2x25W @ 4 Ohm TPA3123 Class-D Audio Amplifier Board be acceptable or would the Sure 2x100W @ 4 Ohm be better? I'm really having a hard time locating a supplier for these type of amps here near Toronto. As Parts-Express offers pretty quick shipment I think I'll probably order from them. If there is a reason I wouldn't want one of these Sure Electronics amplifiers please let me know.

2x25W

Sure 2x25W @ 4 Ohm TPA3123 Class-D Audio Amplifier Board | Parts-Express.com

2x100W

Sure 2x100W @ 4 Ohm TK2050 Class-D Audio Amplifier Board | Parts-Express.com

Thanks again for your help!
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Old 25th August 2010, 07:32 AM   #689
coit is offline coit  Australia
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Quote:
Originally Posted by Saturnus View Post
I'm guessing you're using power resistors? In that case the parasitic inductance in those form a low-pass filter. In normal power resistors this cut-off will start inthe 4-6KHz range. In "non-inductive" types it will be in a more acceptable 12-18KHz range.

I always recommend using old fashioned solid carbon resistors, or multiple parallelled metal film resistors when used with piezo tweeters because of their very nature they are extremely sensitive to even miniscule amounts of parasitic inductance in the resistors.
They're 1W carbon film paralleled to give 3W as I couldn't find 3W resistors.
thanks
Paul
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Old 25th August 2010, 09:31 AM   #690
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Quote:
Originally Posted by coit View Post
They're 1W carbon film paralleled to give 3W as I couldn't find 3W resistors.
thanks
Paul
Hmmm, strange. I have no problem reaching 13Khz flat with my zomax HP100 piezos. 3dB at about 16Khz and falling from there is no problem as the maximum frequency range of mp3s is about 13KHz anyways.
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