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Old May 30th, 2010, 07:21 AM   #1
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A bit confused about pre-amps

Hi,

I've recently got a PCM D-50 mainly because I like the quality of the internal mics and quiet pre-amps. Inevitably I'll want to use it with external mics too and have looked into the options. The XLR-1 provides phantom power but has no pre-amps but is expensive. The Beachtek DXA-6A is described as an audio adapter and has pre-amps whereas the Juicedlink CX231 is an 'audio mixer' and also thus has pre-amps. Both the latter are about the same price.

I have two questions: are there any real functional difference between the DXA-6A and CX231 - I can't see anything obvious? And as the pre-amps on the D-50 are so quiet wouldn't an additional pre-amp in the chain compromise this - what's the point? Is there not a simple phantom power XLR adapter out there that would do the job rather than another pricey bit of kit - or is that a fantasy?

Thanks.
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Old May 30th, 2010, 05:01 PM   #2
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There are in-line devices that provide phantom power for condenser microphones or you could use any number of perfectly acceptable dynamic or ribbon microphones.

I cannot speak to the differences between JuciedLink and Beachtek.
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Old May 31st, 2010, 04:20 PM   #3
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The DXA-6A doesn't have gain, so it's not a preamp. It's an adapter that provides phantom power. The gain knobs let you reduce the gain, but not boost it.

The CX-231 offers gain (and phantom power), so it has a preamp. The output is still mic level, rather than line level, so it's not a classic mic-to-line preamp. It doesn't have the 40 dB+ boost that you need to get to line level. It's really built for feeding a consumer-grade mic input, like on a 5D Mark II or HV-20. The idea is to boost the signal with professional grade gain, then turn the consumer preamp gain way down to reduce the hiss. It's not just hype, it really works great.

Then there are true mic-to-line preamps like the MixPre with up to 56dB of gain.

If you have a line input, you need a mic-to-line preamp.

If you have a mic input, the CX-231 provides super clean gain that benefits systems with all but the best mic preamps downstream.

The DXA-6A doesn't offer gain, so it only works well on systems with very clean mic-level preamp inputs.

I hope that helps!
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Old June 1st, 2010, 03:01 AM   #4
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Thanks Jon, that's very helpful indeed and I now understand the difference between the two units. I'm now in a dilemma - the DXA-6A would be good for the D-50 as I don't need a pre-amp but the CX-231 would be very useful for my HV-40!

When you say 'the CX-231 provides super clean gain that benefits systems with all but the best mic preamps downstream' do you mean only very high end systems which the D-50 is presumably not (it costs 450 in the UK)? If so, the CX-231 could do both jobs though does look slightly bulkier than the 6A which may present practical problems.

Oh and one silly question that i've often wondered - why are they called pre-amps and not just amps? In the D-50 there is only one set of amplifiers but they are called pre-amplifiers - pre to what?
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Old June 1st, 2010, 08:05 PM   #5
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Preamps are amplifiers, but they have some special characteristics: they work with very low level signals and are designed to have very low noise. They also have very little power. In general, a preamp gets up from transducer level (a mic, phono, tape, or guitar pickup) up to line level, and an amplifier gets you from line level up to speaker level and provides relatively high power.

Looking at the D50, I'd go with the juicedLink. The D50 has mic-level inputs on a 3.5mm stereo plug, rather than from balanced, XLR or TRS plugs. It's helpful to amplify the level somewhat into the recorder and turn down the recorder gain as it will reduce susceptibility to interference. The juicedLink gain is extremely quiet, so you won't lose quality with that setup - and it will be perfect for the HV-40.

I'm a fan of amplifying the signal cleanly as soon after the XLR jack as possible. That reduces the amount of noise and interference that you will get all the way down the chain.
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Old June 2nd, 2010, 03:38 AM   #6
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Thanks again Jon - a very clear and helpful explanation. I'll go for the JuicedLink.
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