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Author Topic: Can DC preamps match the AC ones?  (Read 3609 times)

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Offline lagoausente

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Can DC preamps match the AC ones?
« on: April 06, 2007, 09:48:51 PM »

  Preamps need internally high voltages. For use from a battery, DC-DC conersion is needed.
 DC is practical, but exist any Dc powered preamp at the level of the big AC guys?
 If you want a critical recording gear, would you go for an AC preamp+ a pure sine wave inverter, or is any DC powered one who have nothing to envy to the AC ones?

Offline guysonic

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Re: Can DC preamps match the AC ones?
« Reply #1 on: April 07, 2007, 08:09:45 AM »

  Preamps need internally high voltages. For use from a battery, DC-DC conersion is needed.
 DC is practical, but exist any Dc powered preamp at the level of the big AC guys?
 If you want a critical recording gear, would you go for an AC preamp+ a pure sine wave inverter, or is any DC powered one who have nothing to envy to the AC ones?

Here is some perspective from recent personal experiences.

The need for 'high' voltages (higher than batteries can easily supply without resorting to DC boost circuitry) or not in a pre really depends on the LINE input signal voltage (dBu) requirements of a particular deck model. 

Most decks require more or less ~ 1.5 volt rms (~ +3 dBu) maximum line input level for unbalanced input, or +9 dBu for balanced line in. 

For these decks, I make several models of preamp running WITHOUT DC-to-DC boost. This insures having lowest levels of circuit noise as batteries are inherently VERY low noise suppliers of power, and are way quieter than most any AC power supply source.  These miniature preamplifiers produced have amplifier circuitry with full rail-to-rail output ability, so using only two AA 1.5 cells gives a true bipolar +plus/-minus 1.5 volts DC supply, and this is the maximum output swing voltage of the preamplifier.  These have great advantage to run a VERY long time with two AA L91 type batteries running one model for 200+ hours, and simpler preamp running 500+ hours. 

An example of a deck needing very high voltage line inputs is the SD 744 model that requires up to +24 dBu line signal. 

A preamplifier suitable for this deck requires having +plus/-minus 15-18 volt supply rails (30-36 volts total).  So little practical chance for running directly off batteries. Instead, usually a 6-12 volt battery is used to power DC switching boost supply, and then this supply also requires very careful noise filtering engineering so not to contaminate the audio signals. 

I also make a twice size 4 channel preamp model for 744 type of deck that's unique in quietly running the DC boost supplies 15+ hours off 4 D alkaline cell power sled.
« Last Edit: April 07, 2007, 08:13:46 AM by guysonic »
"mics? I no got no mics!  Besides, I no have to show you no stink'n mics!" stxxlth taper's disclaimer

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Offline lagoausente

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Re: Can DC preamps match the AC ones?
« Reply #2 on: April 07, 2007, 10:14:25 AM »
 
  Guysonic, do you make the preamps DIY, or for sale?

  I couln´t find m148 and no rmod on the web for sale, are them comercial preamps or not?

Offline WiFiJeff

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Re: Can DC preamps match the AC ones?
« Reply #3 on: April 07, 2007, 02:02:13 PM »
If DC and not compactness is what you want, you might check out the DC-option version of the DaviSound TB12, which I think I got the first model of in January, and I love the sound, though I have not done comparison tests.  I power it with a bank of 9V cells (four or five, the five cell unit to get the phantom output high enough for my Josephsons, four works fine for AKGs), made for me by Sound Professionals, they run it 10-12 hours.  Definitely a retro look (wood), it looks like something you built in 1952 from designs in Popular Mechanics. 

Jeff

stirinthesauce

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Re: Can DC preamps match the AC ones?
« Reply #4 on: April 07, 2007, 02:06:18 PM »

  Guysonic, do you make the preamps DIY, or for sale?

  I couln´t find m148 and no rmod on the web for sale, are them comercial preamps or not?

m148 was a boutique pre-amp, made for a number of years by Doug Oade but no longer made by him for sale (though he will still service them).  Do a search on hear and their will be plenty of info.

rbox is short for the reutelhuber box.  A variation of the bill box (correct me if I'm wrong folks  :)  ) and no longer made.  Also a boutique box manufactured to act as the microphone body (pre-amp) for the schoeps capsules.  The current manifestation of the rbox is the nbox, which is still made.  Do a search on here for schoepsnbox for info.

Offline guysonic

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Re: Can DC preamps match the AC ones?
« Reply #5 on: April 07, 2007, 02:55:45 PM »

  Guysonic, do you make the preamps DIY, or for sale?

 

The first 14 years of recording, and running Sonic Studios (my company), I designed external mic preamplifiers only for my own.  Then when DAT decks became obsolete, and newer flash/hard disk recorders became available with mostly too noisy internal preamp circuits, production mic pre models became available to provide practical lower noise/wider bandwidth solution.  

See these at www.sonicstudios.com/access.htm#micamp

Designed mostly to power DSM type mics, the simpler lower costing PA-3SX model (unbalanced input/output design) may also be used with other types of 'self powered' mics with internal battery power, or with external phantom powering and balanced to unbalanced connector adapter.  

The more complex/featured PA-24 series might also be used with conventional mics (unbalanced configuration) if each channel input is preloaded with 1000 ohm load resistor to ground (with adapter) so DC servo circuitry operates in fullest linear region.
« Last Edit: April 07, 2007, 03:17:43 PM by guysonic »
"mics? I no got no mics!  Besides, I no have to show you no stink'n mics!" stxxlth taper's disclaimer

DSM HRTF STEREO-SURROUND RECORDING SYSTEMS WEBSITE: http://www.sonicstudios.com

 

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