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R/E/P => R/E/P Archives => Oliver Archut => Topic started by: RMoore on January 02, 2005, 07:04:54 PM

Title: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: RMoore on January 02, 2005, 07:04:54 PM

  Hi Oliver - I just saw the thread: 'Fletcher, have you tried the new Tab-Funkenwerk V-78?'

< for each V module you need a separate +48V ramped circuit (that can be feed from a main supply), sure most V units make it about a year or so without, but as soon as you hear slight crackling, loss of low and/or high end, you have a compromised input x-former. The circuit posted works quite well, is fairly cheap (about $5 in parts) and also takes care of the nasty pop you get if applying +48V. To be precise you need a at least 55V supply so the regulator works properly.

I had several heated arguments with hard core EE that +48V is absolutely save, etc. , but that again everybody send me the broken stuff as soon as it breaks for rewinding and complains about the cost. Take some time for preventive maintenance.... >

Thanks for the info & your ramped phantom circuit diagram,

Question: should it be possible to fit this circuit into an existing V series rack, assuming there's enough physical space?

Thanks again!

Ryan Moore

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: RMoore on January 02, 2005, 07:27:11 PM

BTW - thats great you are being a guest host here,
thnx in advance!
RM

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: Oliver Archut on January 03, 2005, 01:29:58 AM

Hello Ryan,

you can and should retrofit any U/V module or better historic gear with this circuit in case you use +48V.

This year alone I rewound several V72/76 an 77 input x-former that had an electric short, all customers described the problem the same, first a crackling noise than, loss of low end, all in conjunction with 48V use.

Rewinding is a pain in the butt job and quite expensive, the parts are only a few bucks and can save a lot...

Attached is a pic of a bad input , taken while switching 48V on, please see the small arc in the high lighted area....

Pleasure to be here!

Best regards,

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: RMoore on January 03, 2005, 05:20:25 AM

Hi Oliver - Ok, thanks..so theres hope,
Seems like blowing up the xformers is a situation to be avoided!
All the best,
Ryan

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: permeke on January 07, 2005, 07:45:33 PM

Is that correct ?
Is this a 24V regulator ? (LM2824) to put after the regular 48V P ?

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: Oliver Archut on January 07, 2005, 08:05:14 PM

Hello Permeke,

an 24V voltage regulator modified with a 24 zehner diode reference will put out 48V. Please be sure to understand that the ma.x current and wattage rating will be reduced, but a 500mA regulator will work on 15mA phantom (dead short) without a problem.
There are several different variations, lots of room to play and modify...

Best regards,

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: Radd 47 on January 07, 2005, 09:27:02 PM

Hey Ollie, do we need a ramp down circuit also or just ramp up?
Also, do your current V series transformers need the 48 volts to be ramped?

Also, what is meant by your "soft ground " switch?
Is this just a resistor to ground type of deal? 100 ohms or something?


Thanks!

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: Oliver Archut on January 07, 2005, 11:24:14 PM

Hello Radd47,

thanks for pointing out the typo...

Thanks to Teflon, and Mylar the insulation resistance of the in production V-series x-former is several times higher than the historic ones. However a ramped circuit is employed to protect the tube after the x-former...

The historic as well as the new V modules have a 0V layout that is isolated from the chassis/PE ground, this can be switched either 0V to ground or via a 100 Ohm resistor to avoid 99% of all hum, RF noise etc. Even with the worst possible grounding you get the best noise floor possible...  

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: markus on January 10, 2005, 05:38:28 AM

so did i get this right - an external phantom power unit will also not work?
i've got a sennheiser external 48v supply i want to put between my mic (at 4047) and my v72. does it put 48v on the outputs as well?

Title: Re: FAO - Oliver re: ramped 48v circuit for V series modules
Post by: Oliver Archut on January 12, 2005, 12:54:20 AM

Hello Markus,

it has been quite a while since I use an external P48 supply, the last ones I checked had a blocking cap to decouple, but if you switch it on, there is still the charging time of the caps that draw a current primary to core, so you still have (maybe reduced) problem. Talk to your local tech, he should be able to help you out with a ramped mod...

Best regards,

Oliver