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Old 29th May 2003, 07:10 AM   #21
Shaun is offline Shaun  South Africa
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You can buy (Motorola) MJL3281A and MJL1302A directly from ON. Minimum qty 25, I think at round $2.88 ea. That's where I found my magic wand.. - er, I mean, that's where I got my free samples from.

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Old 29th May 2003, 07:21 AM   #22
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Quote:
Originally posted by Duo
The transistors are about $4.00 each.
Ah. From where? The Toshibas that Digi-Key is selling are considerably less than that. Or are you talking Canadian dollars or something?

Are you looking to build a one-off amp just for yourself or will this be a commercial venture? If you're just doing this for yourself, I could sell you some Motorolas for cost plus shipping. We buy 'em by the thousand.

se
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Old 29th May 2003, 07:34 AM   #23
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Quote:
Originally posted by Duo

2000W too insane???


JH
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Old 29th May 2003, 03:05 PM   #24
Duo is offline Duo  Canada
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Steve: Yes, I'm ordering in Canadian currency. If you have motorolas for sale I'm interested is they're not too expensive. How much would is cost me for 40 pairs of transistors?
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Old 29th May 2003, 06:06 PM   #25
HighTec is offline HighTec  Croatia
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Post Need power?

Hi Duo.

Take a little peek over these schematics:

http://www.qscaudio.com/support/libr...ms/rmx4050.pdf

You can very easy get 1300W on 4 Ohms load with only....6 pairs of 2SC5200/2SA1943.
In bridge mode you can get 4000W/4 Ohms load!
This is a factory model,so don't forget about "All rights reserved"
and that kind of stuff.I think the guys wouldn't complain if you
"steel" it for your own needs and don't distribute it.
The project is a little bit complex on the first look,and I don't
recommend it for those with less experience.
I'm working on the PCB,so when I finish it I will show you if you
are interested.
Regards.
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Old 29th May 2003, 11:42 PM   #26
Duo is offline Duo  Canada
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Yeah, I guess 6 of those will work. I just ordered 10 pairs of MJ21193/MJ21194 transistors as samples from onsemi. They do 16A @ over 200V a piece. Nice transistors, and being Motorola, they would be quite nice.

Do you suppose I could use 5 pairs of these Motorola transistors?

I'm think that 5 pairs of them should do quite a bit. If they don't suffice for 2000W, then at least they should come quite close.
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Old 29th May 2003, 11:53 PM   #27
Duo is offline Duo  Canada
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Interesting design these guys use. However, I detest opamps. I might steal some ideas from the output stage and driver arrangement and use them myself after some alterations. I see how they're designing the amp and I like the output stage a lot. It's actually very similar to the design I'm using.

The output stage in my amp uses the same topology as that in the ESP 3A, and the P68. The amps use compound emitter followers and current sink bias arrangements. I like the way that topology sounds, especially with its inherent simplicity.
The construction of such an output stage is very simple and doesn't require many parts. The bias is simple as well.

Anyway, I'll keep conceptualizing for now.

BTW: How much power does the next lower model of RMX amp produce? I looked at its design with the four output pairs and that is easy to do...
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Old 30th May 2003, 12:15 AM   #28
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Quote:
Originally posted by Duo
Steve: Yes, I'm ordering in Canadian currency. If you have motorolas for sale I'm interested is they're not too expensive. How much would is cost me for 40 pairs of transistors?
We're paying about $2US a pop. I don't keep up on the day-to-day stuff and apparently we're working on a big pile of stuff for InnerSound and Doug's not willing to part with 40 pair at this time. Sorry 'bout that. I'll try and remember to see how things stand in a few weeks. Feel free to give me an EMail reminder if you'd like.

se
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Old 30th May 2003, 03:00 AM   #29
Duo is offline Duo  Canada
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How many samples does onsemi give you until you have to start paying?
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Old 30th May 2003, 05:57 PM   #30
HighTec is offline HighTec  Croatia
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Post Toshiba or Motorola?

Hi Duo.

Yes,you can replace them with Motorola transistors.Putting 5 pairs instead of 6 pairs is not a good solution.Motorola transistors can dissipate more power but we are talking about 4KW in bridge mode!The calculations allows 5 pairs if you don't bridge the amps.
My choice is Toshiba's transistors.By the way,wy the QSC guys didn't use Motorola devices?Better characteristics?Think about it.
About the OP Amps in the input stage...I agree with you.It's not the best,but it isn't the bad solution.I have a couple projects with OP Amps and they never failed me.
As you said the output stage is interesting.The good thing is that you can mount the output devices directly on the heatsink without using mica washers.The transistors can dissipate more power!Of course the heatsinks must be isolated from the chassis.
I had a opportunity to listen this beast and I couldn't belive how much sound pressure it can produce!
I've attached some RMX specs.The RMX2450 uses 4 pairs per channel,as you asked.
Regards friend.
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File Type: jpg rmx.jpg (79.8 KB, 382 views)
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