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Old 28th September 2008, 08:29 PM   #611
clm811 is offline clm811  United States
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Bob,

I've got a pair of large (600VA, I think) transf., which each provide
a pair of +/- 72v rails for stereo use.

I can use one transf per channel (two monoblocks), and my speakers are 4ohms nominal, 3.2 min. Any suggestions or forseeable problems here?

Would the 5-transistor boards be ok, or should I go with the 6-transistor boards?




Quote:
You can go higher than 65, but then a few other things change and you need to watch the load impedance doesn't dip too low.
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Old 28th September 2008, 09:07 PM   #612
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IIRC Jens is running a 10 output device amp at 75V - adjust the front end resistors R3, R12 for the rails (watch dissipation too), and don't try to use BC546/556- use MPSA42/92. They don't have the gain, but they will withstand higher voltages.

The problems you may have at 3.2 ohms depend on phase and signal amplitude. Unless you really push hard you should be OK if your heat sinks are properly sized.

800VA should run a pair comfortably, but since you already have a pair, why not go monoblock? I have an 800 VA transfomer driving 4 channels at 60V in a biamp setup. I use it at sane levels so I haven't had a problem with rails sagging.

BTW, in case you haven't followed the best 100W output transistors thread, OnSemi has a new 150W output device pair that looks pretty good MJW0281/0302 . The best news is Mouser's price is only $1.40 or $1.33 at 25 pieces. The similar but 200W rated MJW3281/1302 are only $1.70. Almost as cheap as BrutePuppy's eBay potential fakes.
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Old 28th September 2008, 09:31 PM   #613
clm811 is offline clm811  United States
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Default Put me down for some std 10 Tr.boards

Thanks, Bob.

BTW, how many 10-transistor boards should I order for a pair of monoblocks?

How do I order- I'd like to be put down for these on the waiting list, but I find I don't know how to log in to the Wiki...


Thanks.
-chas
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Old 28th September 2008, 10:07 PM   #614
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Chas - each board is a single channel, so for two monoblocks you'll want two.

go to the wiki, scroll down to the "edit this page" link, log in again with your DIYAudio name and password. Then you're ready to go.

Tad is running this buy. I just try to help out with technical stuff.
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Old 29th September 2008, 08:27 AM   #615
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Almost as cheap as BrutePuppy's eBay potential fakes. [/B][/QUOTE]


Hey, I repent that remark!
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Old 29th September 2008, 10:17 AM   #616
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We are up too 24 pcb's at this time. If we can get interest in 25 more boards I will submit an order for the new group buy of Jens 10 transistor amplifier.
For those out there who might like too know I used the On Semi mjl4281/4302 output devices and have been extremely happy with the way they sound. Shop around and you will find a huge difference in price.
This amp is truly a keeper for those who choose to build it they will not be let down. Tad
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Old 29th September 2008, 04:03 PM   #617
clm811 is offline clm811  United States
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Got it! Let's all sign up and get these made
Thanks, guys!
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Old 29th September 2008, 06:45 PM   #618
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Tad -

What do you expect for pricing at 50? I actually heated up my soldering iron this weekend, so now I'm thinking it would be a good time to add to my project backlog.
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Old 29th September 2008, 07:47 PM   #619
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Bob, I thought I mailed you a couple of these boards from the last group buy? I have checked on the prices before but mislaid the email from Advanced Circuits. I think it will be just north of 17.00 each. Last time I got the first time buyer discount of 500.00 which made the price on 150 boards look much nicer than it should have been. Anyway I can not tell you how great this amp sounds with the bias at close to 1 amp per rail. Truly marvelous as they say. Class A all the way from now on. Well at least until the one amp runs out. Tad
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Old 29th September 2008, 10:25 PM   #620
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There's got to be one more "first-time" buyer in the wings!
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