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

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Member
Joined 2005
Paid Member
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? :)
 
Member
Joined 2005
Paid Member
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.
 
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:
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.
 
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
 
diyAudio Chief Moderator
Joined 2002
Paid Member
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.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.