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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

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Old 13th February 2013, 10:10 PM   #1
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Default Will phono pre > passive pre > amp work well enough?

I will find out soon enough, but I was wondering if I can expect a Rega Fono Mini's 200 mV output (rated at 2 mV input; my cartridges should generate at least double that) to be enough to drive my Classe CA-100 adequately? By "adequately," I mean typical small room volume levels.

The Rega is an earlier generation, not the new Mini's with USB.

The Classe requires 950mV input for rated output (the factor that jumps out the most to me); input impedance is 75k. The Rega's minimum output load impedance is 10K.

The passive pre is a 47 Labs Treasure 0447, with 50k pots.

Speakers are Advents, about 90dB sensitivity.

I'm thinking it should work okay. Am I deluded?
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Old 14th February 2013, 06:52 AM   #2
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That amp sensitivity is specd at 1.3 V RMS. Your phono preamp is coming up short by 6:1. You'll hear things but I bet you'll want a 10:1 gain boost over the phono stage.

G
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Old 14th February 2013, 11:28 AM   #3
DF96 is offline DF96  England
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This is one of those rare situations where a low gain line stage will actually do something useful.
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Old 14th February 2013, 01:44 PM   #4
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That's what I was afraid of. I suppose I can take this as an opportunity to build a "simple" 10-15 dB single input stereo preamp. I guess when I listen to records as this system will be, I should expect compressed dynamics as the most obvious failing?
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Old 14th February 2013, 02:40 PM   #5
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There's no compression, as the relative levels will all remain the same. It will just sound very quiet.

jan
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Old 14th February 2013, 03:06 PM   #6
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Quote:
Originally Posted by jan.didden View Post
There's no compression, as the relative levels will all remain the same. It will just sound very quiet.

jan
Thanks for correcting my misperception, Jan.
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Old 22nd February 2013, 08:17 PM   #7
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Just an update: the playback level was not as attenuated as I had expected with a Grado 8MZ/Red1, but not ideal either. "Reasonable" playback with pot at 3:00 o'clock, versus about 11:00 o'clock with an active preamp. It would work in a pinch, but I'll be using an active preamp.
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Old 22nd February 2013, 09:36 PM   #8
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Phono cartridge output levels are specified at a 0VU of 5cm/sec lateral. Peak outputs of +10dB VU are common, sometimes a little more. This doesn't translate directly to the 0VU of modern digital sources, which are spec'ed at peak output.

All good fortune,
Chris
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Old 28th August 2013, 01:03 PM   #9
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Yesterday I read Pano's article "What is Gain Structure"
If I understood anything about what is in this paper, then turning the pot at 15:00 to listen to a descent level is a good thing !
If not, then I had better re-read the paper.. : |
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Old 29th August 2013, 07:30 PM   #10
cbdb is offline cbdb  Canada
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0VU into 600 ohms is +4dbm (almost 2 volts) Always. A 2 mv output from a cartridge is more like -30 VU. Most digital sources don't have VU meters, they are dbfs. (Full scale) so 0 fs is the max level before clipping, (when setting up digital recorders you set the nominal level 0VU to -20 dbfs ( give or take 6db ) so you have 20 db of headroom (give or take 6db). so the readings are always negative and relate to output voltage only relatively. DBVU and dbm tell you a voltage, but I don't trust most meters that are not in professional gear. And most commercial gear adheres to the -10 dbm nominal output voltage. This is not the max output, that should depend on headroom. Max out=nominal out +headroom. So gear with 15 db of HR will have a max out voltage before clipping of 5dbm or 1Vu. The digital gear and loudness wars has confused a lot of people who think the nominal level and max level are the same thing. This gives you no headroom. Not a huge problem unless your recording or building gear but something to keep in mind.

Last edited by cbdb; 29th August 2013 at 07:34 PM.
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