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Old 6th February 2007, 11:04 PM   #1
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Default LM3886 power supply suggestions?

Looking for recommendations on what specs I will want in a power supply based on the following criteria.

I'm hoping to go 60 volts DC but am unsure how much wattage output I should be looking for. The data sheet says 125 watts draw @60 volts which seems low to me because I also came up with the figure that the gaincard will be outputting 144 watts RMS into 4 ohms with 60 volts DC. I do most things by guestimation as I'm too lazy to go through the math and like to run with my ideas.
That's also because I'm not in the habit of building projects where I have to worry so much about said elements.

All input will be greatly appreciated.

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Old 6th February 2007, 11:34 PM   #2
sek is offline sek  Germany
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Doctor!

125W and 60V are beyond the point of destruction. The numbers given on the title page of the datasheet are ratings the device can barely survive.

The datasheet states 20V - 94V as the supply range. That's +-10V to +-47V. Considering your 60V as +-30V, the datasheet gives a nominal 75W peak on page 10. Even for +-47V it would just be above 100W peak (limited for survival).

If you want to estimate total power consumption including dissipated power and output power, consult the 'Power Dissipation vs. Output Power' graphs on page 11. A summed maximum is in the order of 150W total (again, limited for survival).

You don't need to prepare your power supply to withstand a sustained chipamp explosion.
Simply use fuses, like everyone else...

Please explain...

Cheers,
Sebastian.
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Old 7th February 2007, 01:24 AM   #3
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Ahhhhh ok.
My assumption was based on page 3 of the data sheet. I'm new to power amp stages and have mostly been glancing over specs as I work on other elements of my design which are in the physical development stage rather than still on the drawing board. I now see factors such as 94 volts being a result of the |V+| + |V-| with no input signal. Had I not started asking questions, I may have been a casualty of skimming!

I did however find a very well priced switching power supply that outputs at 43 +/- volts but here's the spec I overlooked when I thought it was too high after taking notice of the power rating more accurately, it can be reduced by 10% via trimpot. Puts me just below the survival ratings
It's rated 2 amp continuous with a 3 amp peak and capable of delivering up to 200 watts..

$24.50 USD with shipping and marketed for use with all the gainclone cards, sound good?
The maker is Lambada

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Old 7th February 2007, 03:03 AM   #4
sek is offline sek  Germany
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Yeah. Those Absolute Maximum Ratings are really exactly only that...

A +-40V supply with only 2A current is a little weak. Again, take a look at the Power Dissipation vs. Output Power graph on page 11. We see a maximum just short of 160W peak.

What is Mr. James Watt requesting? P = U*I.

Thus, with P = 160Wpeak and U = 40V current resolves to I = 4Apeak.
Seen the other way round, your 3Apeak allow for a supply voltage of about 30V.

But for the price it can't be beaten. Just take care of power dissipation safety and heat sinking!

Cheers.
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Old 7th February 2007, 03:40 AM   #5
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Thanks for the input.
For a first run, it'll do. The cab it will be driving has four 10's, 2 horn tweeters and is currently being driven by a 30 watt Behringer amp which has it screaming. I'm sure with this driving my gaincard I won't be lacking in volume or oomph. I can always swap up the power supply when I'm not on such a tight budget. I'd be spending twice this much if I built my own from the ground up.
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Old 7th February 2007, 06:49 PM   #6
Minion is offline Minion  Canada
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Well the Power supplies that I build for my Gainclone chips is really cheap and easy to make....

It supplies +/-26v Unregulated for the Power amp stage and a Regulated +/-15v to +/-24 for the Preamp stages and not counting the Power transformer cost me only about maybe $10 to build, and most of my Power transformers are Salvaged from other equipment so for my the whole PSU costs much less than $20 but it does take me a bit of time to etch the PCB and to stuff the Parts but I have more time than Money so it is OK.....The PSU can also be built to accomidate as much or as little PSU Filtering as you need, it can also be modofied to be regulated for the Power amp by replaceing the Preamp regulators for higher Current regulators....


I can post a PCB design and Stuffing guide if you want....


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Old 7th February 2007, 07:08 PM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by DrFrankenstein
Thanks for the input.
For a first run, it'll do. The cab it will be driving has four 10's, 2 horn tweeters and is currently being driven by a 30 watt Behringer amp which has it screaming. I'm sure with this driving my gaincard I won't be lacking in volume or oomph. I can always swap up the power supply when I'm not on such a tight budget. I'd be spending twice this much if I built my own from the ground up.
I don't know the recommended power rating (nor peak voltage) of your drivers but 4drivers on one side of a crossover sounds like robust discrete amplifier technology. Not fodder for destroying chipamps when you turn the wick up.
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Old 7th February 2007, 09:16 PM   #8
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I'm using a Behringer V-Tone 1x10 combo with 30 watts RMS@ 4 ohms to drive the custom cabinet I designed and built.
It's loaded with two Jensen MOD's and 2 Legacy car subs wired in both series and parallel to achieve a 4 ohm resistance as one channel. It also has two of my favorite piezos It runs as either 2 channels @ 8 ohms each or a mono channel at 4 ohms. Having both wire terminals and 1/4 jacks.
Both RMS and peak wattage is something ridiculous, I believe close to 900 watts RMS and twice that for the peak.
I have a passive notch filter boosting several specific frequencies to all speakers that can be switched in or out. This side of the rig is all my own design. There is also a limiter on the tweeters which is open just the slightest bit to give sparkle and more defined pinch harmonics. The cabinet is sealed back for the woofers which have wood baffles chambering them and the Jensen MOD's are basically open back with a rear wood panel enclosing maybe 15% of the speakers.

I'm willing to bet the Behringer amp is a chip amp and so far it's done just excellent, been running this setup for probably 6-8 months and play it quite regularly for long periods of time.

Overall it's one of my best projects to date. The cabinet being a good quality plywood with nice grain patterns which were stained with a light chocolate brown then poly gloss coated. It looks pretty medieval with the corners and miniture fantasy weapon designed by Kit Rae stuck dead center to the top of the front panel only it's a pin instead of full sized, functioning weapon.

The next step is building my own head to drive it and free up my Behringer practice amp.
It's been slow going but I'm really happy with the distortions my circuits have produced. I have some very heavy duty diamond plate I may use as the head enclosure and just paint it black so it will match rather than rebuffing it to chrome which would likely clash.

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