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Old 16th August 2010, 02:38 PM   #1891
Salas is offline Salas  Greece
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Quote:
Originally Posted by Marra View Post
Finally managed to read through all the posts.I'm really looking forward to receiving my Blue Hypno boards and starting my build.
Regarding the Selectronique R core transformers would I be better off going for the 12+12 secondaries as they seem to output more volts than spec or do I just strap the mosfets to the case and run hotrodded?
Run with 10R 5W and Mosfets cooled on the box's floor. Cheapest & easiest sinking. Fixes the thing down best for vibrations too since it grabs it from more points along its length.
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Old 16th August 2010, 02:41 PM   #1892
AndrewT is offline AndrewT  Scotland
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if you intend running at the standard +-10Vdc then the 12Vac secondaries may be below recommended limit when mains is low.

I doubt the Rcores you have in mind are out of specification.

I used 15+15 for my DCB1. CCS set to 60mA and the CCS FETs run a bit hotter than I would like, but they could run permanently at that dissipation.
I choose to add a heatsink. The Shunt FETs do not need a sink. They only dissipate 10V * 40mA = 400mW
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Old 16th August 2010, 02:44 PM   #1893
Salas is offline Salas  Greece
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A 2X15 Rcore 50VA Selectronique I have here gives me 2X16VAC under 100mA load @ 230VAC primary.
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Old 17th August 2010, 02:19 PM   #1894
Marra is offline Marra  United Kingdom
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Salas and AndrewT thanks for your quick responses. I only ask as the mains voltage here generally runs at 240v and regularly hits 245v so I would be running approx 9% high most of the time. I guess its not a problem>
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Old 18th August 2010, 08:54 AM   #1895
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In Spain we use to have lower mains, around 230. With 245 you should have no problems, just a slightly increase in temp in the mosfets. But your country is a few degrees colder average, so guess what, we will end with the same mosfet's temperature
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Old 18th August 2010, 12:34 PM   #1896
Marra is offline Marra  United Kingdom
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You could be right its a comfortable 19/20 degrees here today.
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Old 18th August 2010, 12:45 PM   #1897
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We are having today around 30 "comfortable" degrees. They are nice compared to the whole rest of the summer. In the hottest days, some gear is warm at touch even having it disconnected!
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Old 18th August 2010, 12:52 PM   #1898
Marra is offline Marra  United Kingdom
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A comfortable 30 degrees! I'm sure I'd Melt
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Old 18th August 2010, 04:00 PM   #1899
Malka07 is offline Malka07  England
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Just wanted to give an update on my Dcb1/Optivol.

First of all i cut out a hole and installed a fan in the roof of my chassis. This helps keep the mosfets cool. At first i was running the fan at 12vdc...but i found that the fan was too noisey and was interfering with the music, so now im running it at 5vdc and the fan is now so quite, it is almost silent

Click the image to open in full size.Click the image to open in full size.

I add some Granite to weight the top of the chassis down, so that there are no vibrations, as i hav'nt screwed the top of the chassis down yet...makes it easier to get inside as im still modding this wonderful pre amp

Also as can be seen, i run the optivol, with a Salas Shunt Reg 5v, i also have up'd the currents on the Dcb1, i now run...

+PS 2.09v/6ohm = 348ma
-PS 1.73v/5ohm = 346ma

I check the heat of the mosfets after 2 hours of playing music...the heat is just warm, definitely hotter then before as before it was cold...but this is understandable as the fan is running slower...The sound of this preamp now is just AMAZING...adding the Salas Shunt reg to run the Optivol, improves it alot...and uping the current's from circa 250ma to 350ma also improves the SQ..i will now up the current's further, little by little making sure each time that the mosfets dont get too hot...but in my listening tests, every time i have up'ed the current's a noticible improvement can be heard. Well worth doing.

Click the image to open in full size.Click the image to open in full size.

As im running circa 350ma now, would i gain improvements by changing the two 4700uf caps to two 10,000uf caps?

Thanks

Alon
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Old 18th August 2010, 04:05 PM   #1900
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To effectively reduce the vibration issue you described, you need to mechanically decouple the fan from the cabinet cover - a rubber gasket is a good start.
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