Will phono pre > passive pre > amp work well enough?

[soldersmoker]

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?

 

[stratus46]

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.

G²

 

[DF96]

This is one of those rare situations where a low gain line stage will actually do something useful.

 

[soldersmoker]

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?

 

[jan.didden]

There's no compression, as the relative levels will all remain the same. It will just sound very quiet.

jan

 

[soldersmoker]

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.

 

[soldersmoker]

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.

 

[Chris Hornbeck]

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

 

[charlieblue]

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.. : |

 

[cbdb]

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.

 

[cbdb]

If you want dynamics you need head room. Unfortunately modern recordings don't have dynamics so you usually don't need HR. old vinyl has some dynamics so there pres need some. The only way to test them is with a test record that has a nominal test signal on it.

 

[Chris Hornbeck]

0VU into 600 ohms is +4dbm (almost 2 volts) Always. A 2 mv output from a cartridge is more like -30 VU.

And most commercial gear adheres to the -10 dbm nominal output voltage.

This isn't really strictly true, and is the source of lots of confusion. "VU" has no single relationship to voltage level. Over the years, and in different settings, various voltage levels for "0VU" have been adopted for particular uses, but these are only conventions, not definitions.

For example, telephone company lines, open air at several inches spacing, have about a 600 Ohm characteristic impedance. This number was adopted for radio station use, and a nominal level of +8dBmilliWatt at that impedance gradually became the nominal "0VU" for a while. This evolved into a lower +4dBmilliWatt at 600 Ohms balanced and -10dBVolts unbalanced, both still in use today as "0VU" between connected chassis.

But it's important to keep in mind that "VU" has no fixed-in-stone voltage (or power, or acoustic volume, or anything else) level attached. It's purely a convenience for a particular application. "0VU" for a mastering room is 85dB SPL measured with pink noise. "0VU" for digital recording might be an internal signal voltage chosen to be 15 to 30dB below peak signal level. On a vinyl record "0VU" is typically an excursion of 5cm/sec at midband - just for a few examples.

Thanks,
Chris

 

[Salas]

I use 63dB gain for an LMC Denon 103R cart that gives 350-400mV at 0dB vinyl cut level depending on input load. Then a buffer (gain=1) pre and 26dB gain power amp on 94dBSPL sens speakers. In that system the records play about as loud as the DAC at same volume pot positions. If the speakers were something like 88dB sens I feel that I would need 6-10dB gain in the line preamp for that particular system for any audio source the way the recordings are.