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Old 12th April 2006, 09:12 AM   #1
swagboy is offline swagboy  United States
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Default Starting a High Power Design. . .

Hi everybody,

I have been reading up on audio power amplifiers for a while and have just
successfully built a two channel 80watt amplifier (Randy Slone's Design from
his high power book). Thus far I have only burned up two resistors for unknown
reasons, but both channels now work.

I am interested in building a high quality concert audio amplifier around about
600 Watts per channel into 8 ohms, with close to 1200 watts into 4 ohms (in
an ideal world).

Thus far the plan included a torrodial power transformer (raw DC supply) and
a class B topology. possibly mirror image. . . Slone says it is cleaner.

So I have the following Questions:

1) Would you recommend BJT's or Mosfets? and which ones (I can't find 2sk1058's
in stock anywhere)? I can find MJ15003/4's fairly easily. . . Slone recommends lateral
mosfets for very high power designs, but I'm not sure its worth doing with mosfets price
wise. I would like to use TO-220's because it seems to be easier to find heatsinks for
these dudes.

2) Is class B a good design for this kind of application or is it just a waste (as compared
to class G or others)? Note: I am more comfortable with building a class B (since I have
built one successfully).

3) How can I prepare the amp for the possibility of a 2 ohm load (God forbid)?

Thank you very much for any and all help and assistance.
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Old 12th April 2006, 09:59 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
there is absolutely no way to use MJ15003/4 at the voltages you need to produce 1200W into 4ohm speakers.

However you could build a pair of bridged amps using 15003/4 but the spec becomes 600W into 2ohms and able to drive 1ohm to achieve your 4ohm target. 6pairs in each half bridge would manage 45degree phase angle. This adds up to 24pairs for a stereo amp.

If you want to drive at a higher phase angle then more pairs are required. 8+8pairs manage 60degree phase angle at Tc=45degC, using 1800VA 4%regulation transformer and +-54mF per amp channel =432000uF for stereo. To keep Tc at or below 45degC will require quite big sinks (64 To3s need a lot of sink space). Costs are mounting. Oh, and forget 2ohm speakers, everthing just doubles. YES, EVERYTHING.

To reduce costs, a design similar to the quasi designs, that have been discussed at length, would be a good starting point.

BTW, I would build a ClassA/B design but of much lower power.
What are your real power needs?
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Old 12th April 2006, 10:02 AM   #3
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Hi Boy,

If you want BJT's then go for MJL21195/96 complementary pairs..
If you want Mosfets then go for atleast Vertical types as lateral types are hard to find and also laterals are very costly ones...
vertical Mosfets as follows IRFP260, IRFP350, IRFP360, APT20m22LVR, APT30M85BVR....

Class-G/H requires somwhat more experience..if you had then go for it only then because they invlove Rail Switching topologies..
otherwise Class-AB would do the job nicely with suitable heatsinking and fan cooling....

2 ohms load require paralleling of large number of output devices as well as driver stage adjustment to deliver base/gate drive to output devices...
Large Filter Storage, Power Transformer...etc..

You can also see this thread for N-channel Mosfet amp.....
NVMOS amplifier
You can scale my design upto 2KW very easily

regards,
K a n w a r
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Old 12th April 2006, 11:08 PM   #4
swagboy is offline swagboy  United States
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Hey guys,

Thank you for pointing me in the right direction.

I am building this amp for driving pro or semi-pro subwoofers. Thus, I am shooting
for 600 watts into 8ohms and close to double that for 4ohms. I know I can probably
go out and buy a crown Macrotech 2400 for less (maybe), but I would rather have the
fun of building my own. PLus if it blows up, I am much more likely to be able to fix it.

Thank you for the advice on the topology and the output devices. Sounds like I need
to use something other than the Mj15003/4 pairs.
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Old 13th April 2006, 09:29 AM   #5
djk is offline djk
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Download the Crown schematics for the VZ5000.

The VZ5000 uses 8 pair of MJ21193/94 per channel to get 2.5KW, that ought to be enough power for you.

http://www.crownaudio.com/pdf/amps/m...schematics.zip

You can simplify things a bit if you lower the voltage to that used in the VZ3600, only 1.8KW per channel, and use 12 pair of outputs and skip the rail switch.
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Old 13th April 2006, 09:44 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
we're into big money here!
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regards Andrew T.
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Old 14th April 2006, 01:39 AM   #7
djk is offline djk
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Big money?

You want cheap? Buy four Behringer EP2500s and run them all at 8 ohms bridged, 6KW for $1200. The Crown is much more.

The outputs for a VZ5000 will cost you $80 for two channels. The main cost, as always, is the chassis, power supply , and heatsinks.
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Old 14th April 2006, 10:19 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
Quote:
8pair outputs as VZ5000 will cost you $80 for two channels
I wish I had access to US pricing.

Probably more than double that in the UK/Europe.

eg. I just ordered soldering stations from the US and by the time they arrive the dollar price has become UK pound price, yes a 74% mark up. But still much cheaper than anything available here.
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Old 14th April 2006, 03:15 PM   #9
Eva is offline Eva  Spain
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Given the power level and the target application (PA and low frequency) you may also wish to look for class-D designs. This is a somewhat complex approach, though (it may appear simpler due to the much lower power supply, heatsinking and power transistor requirements, but conceptually it's far more complex than a linear amplifier).
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Old 15th April 2006, 12:21 AM   #10
djk is offline djk
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The 2KW class D subwoofer amps can be had for USD $300, I don't think I would try and build one for that.

These days DIY is not cost effective for most people, unless you want something quite different.
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