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millbank power pac: 8 ohm mod?

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ceharden View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2009 at 12:29am
Just spotted the fact that they have two secondaries.  If you link them in parallel rather than series, you should in theory end up with an amp which can drive down to 12.5Ohms if I've got my maths right.  Might even handle an 8Ohm load.

I suspect if they are classD, given your description of the transformer James, the output stages are running on quite low voltage but high current rails.  Maybe you could measure them?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2009 at 12:32am
but these are 200w so..[calculator moment]...six and a quarter 8 ohm drivers would be needed or...he could drive 3 16ohm comps a side pretty nicely i suppose! James I bet you have six matching 16 ohm comps in a biscuit tin down the back of your sofa get em in a box Smile
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2009 at 12:36am
In my second post I did take into account the 200W rating.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2009 at 12:39am
Forum message timing confusion issues, your brain and fingers work quicker than mine :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 10 September 2009 at 12:47am
Only this time, I regularly take ages over a post, click submit and find that several others have already answered the question!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote james folkes Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2009 at 9:11am

hmm, i love the maths of 100 volt lines, they occasionally caused me a significant headache when installing. anyway... the two secondaries are 50 volt tappings, even if i connect in parallel then i will still be stepping up quite a bit. the primaries are on very fat wire, i suspect that they are high current, low voltage type but i haven't had a chance to have a big look at it because the millbanks have been displaced by my monitor console which i am trying to coax into life for alchemy next weekend. there's channel cards everywhere...

anyway, my latest cunning plan is to use one of the output transformers to step back down again! i can even start running turns in series if i need to mess with the voltage. reckon that should work pretty well... i ought to have a chance to look at it this weekend, but mr dda does take priority.
 
james.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jake_Fielder Quote  Post ReplyReply Direct Link To This Post Posted: 11 September 2009 at 9:33am
Originally posted by studio45 studio45 wrote:

What kind of impedance are 100v line speakers then? like <100r, >100r or 1000's of r?
I've seen 100v line attenuators marked in Watts they will allow the driver to dissipate so presumably it's a bit variable depending on how big the driver is?
 
They have a transformer in them to step the voltage back down i believe, so they will be a normal impeadence,
Its just a way of efficiently taking the power where its needed, using thin wires
 
(i think im right...)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dayglosteve Quote  Post ReplyReply Direct Link To This Post Posted: 21 December 2010 at 5:22pm
Hi

I designed this product. Nice to hear your comments !

The output stage is a full bridge Class-D. as regards the transformer it isn't part of the low-pass filter.
It has two primaries which are in parallel to minimise leakage inductance. Each however is in two halves with the protection current sense resistor in the middle.!!

If you remove the transformer you won't have any short circuit protection but it will still work. The amp rail is only 24V DC so it will only swing 13Vrms into a Lo Z load.

About 21 Watts in 8R, 42 watts into 4R. In the 100V line application the impedance looking into the transformer is about 0.8R - thus the 200W rating.

the whole thing is over-engineered cos its Voice alarm so ahs to run full power sinewave at elevated temperatures until doomsday ! .. unless Hi-Fi kit !


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Post Options Post Options   Thanks (0) Thanks(0)   Quote service dept Steve Quote  Post ReplyReply Direct Link To This Post Posted: 21 December 2010 at 5:52pm
Maybe one of the 12 volt boys might like some, couple of 12 v batteries and a couple of hundred good quality watts- who knows?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MattStolton Quote  Post ReplyReply Direct Link To This Post Posted: 22 December 2010 at 1:23pm

AFAIK, when Millbank closed down, the intellectual property (i.e. the clever staff) started up two separate companies, Application Solutions Ltd and Baldwin Boxall.

Baldwin Boxall carried on in the same vain, relays and diodes type stuff, whilst ASL went DSP. BB have now caught up to DSP.

Baldwin Boxall may be able to get circuit diagrams for some of this stuff, as there early gear was similar, whilst some of the crew at ASL may have memory of it. Worth a phone call, as both are friendly companies to chat to.


Matt Stolton - Technical Director (!!!) - Wilding Sound Ltd
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Johnamps Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2014 at 7:51pm
Originally posted by james folkes james folkes wrote:

i've just been given one of these 100 volt line amps (and it's matching power supply) to play around with, if i want them there are no less than thirty or so more of them... usual story, some contractor tells a business that their pa is screwed and they need new amps, sells a metric shed-load of them and then does a runner when it turns out there are now more faults on the system.


so anyway, these amplifiers are just beautiful. if you've ever stumbled across millbank kit you'll know that the metalwork is sublime, ludicrously over engineered, the boards are neat and tidy and loads of thought has gone into the layout. the powerpac series consists of 2u dual power supply units and a 3u amp chassis that can house two amp modules, two i/o modules and the power and system control module. at 200 watts each side, the power:weight ratio of these units is pretty horrifying, but as they are passively cooled i wondered if they might be fun in a hi-fi setting, they are so wonderfully shiny that i quite fancy a rack of them in the house! 


that and i can't say no to free tat...


http://img32.imageshack.us/i/dsc00449e.jpg/ -



http://img512.imageshack.us/i/dsc00453p.jpg/ -


and so the big question: can one bypass the output transformer on these amps without upsetting the internal protection circuitry? not only would a fair bit of weight be saved, but these things would in turn be saved from being torn apart for their copper. i have a problem with this happening, i can't bear to see any pa kit destroyed, let alone such beautiful stuff as millbank...


james.


edits: content, grammar.




Which model of the Millbank amplifiers do you have ?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2018 at 3:10pm
Anyone know much about this one?

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