What am I missing? Pre/power gain and input sensitivity.


I’ve read a few posts about power amps with lower gain needing a pre with additional gain, but no one seems to mention input sensitivity in those conversations. If my source outputs 2V and my power amp input sensitivity is only 1.2V then whether the power amp gain is 16dB or 26dB my pre amp is attenuating the signal and the amount of gain on the pre doesn’t matter at all. With a given set of speakers, to get the same SPL with 2 different amps they should just need to output the same voltage, regardless of how they get there.

Am I missing something?

cat_doorman
See, here's the thing about the internet: zero editorial standards.  Anyone can post anything. On this site your odds of being read are actually higher the greater the BS. Our #1 has 21k posts and when you ask if someone can find even one of value the question is removed and the 21k grows to 22k. 

So yes you are missing something: the necessity of DYODD. And no, you are not missing something. They are.

@millercarbon - You probably need to add more fish to your diet, buddy. You’re starting to blather again.
@cat_doorman, in the case of the example you cited you are not missing anything. The main effect of different preamp gains would simply be that the volume control would be set to different positions for a given SPL.

Preamp gain can often be a significant consideration, though, in the case of phono sources (or tuners, tape decks, and other sources which typically have much lower output voltages than CD players and DACs).

For example, using some typical numbers, if a phono stage provides 40 db of gain for MM cartridges and 60 db of gain for LOMC cartridges, and the cartridges are rated to produce 5 mv (MM) or 0.5 mv (LOMC) under the standard test conditions, in each of those cases the phono stage will output only 0.5 volts when a recording is causing the cartridge to provide its rated output (which corresponds to a volume that is quite high). If substantial additional gain is not provided by a preamp in that situation much of the power capability of many power amps will not be able to be utilized on many recordings, even with the volume control at max.

Regards,
-- Al

The funny thing is, most digital sources due to Redbook standards put out too much voltage for most amps- IOW connecting them to a power amp will cause the amp to run at or near overload!


So the signal has to be knocked down, which is dumb IMO/IME. This requires a volume control and is why passive volume controls have become common. The problem is that most passive controls have an artifact which is to decrease impact at all frequencies if less than full volume. This problem is eliminated by buffering the control. So you'll need active circuitry in any event; it would have made more sense if the Redbook standard was set to 1 volt like tuners and consumer tape machines had been prior to digital.


I've noticed some confusion around this topic over the years so here are two things that are related to it:

the volume control **does not** say how loud you are playing the system. The signal level does.
Amplifier gain is different from amplifier power. Two amps can put out the same amount of power but one can have 25dB of gain and the other 35dB; obviously the one with the higher gain will play louder with the same signal level, but in the end both amps will only get as loud as their power allows.
See, here’s the thing about the internet: zero editorial standards

Some people need to prove this every day.

Think of gain as a voltage multiplier. 26 dB of amp gain ~ 20x the input voltage.

16 dB ~ 6x the input voltage.

Of course, every device has a fixed output voltage, set by the voltage rails of the power supply. This is one of the amp watt limits.

To drive an amplifier with 16 dB gain to the same level, you must provide 20/6 more volts, or 3.33 x the voltage.

This will require your pre to put out more voltage than normal, and also more noise.

Another way to think about this is that 1 Watt into 8 Ohms is 2.83 Volts.

At 26 dB, the input required is 0.141 Volts to create a 1 watt signal.

At 16 dB the input required is 0.47 Volts to create a 1 watt signal.

Best,
E



Thanks for the confirmation, guys. No matter how much I read and think things are obvious, I start to doubt myself.

With standard digital outputs being so high it almost makes sense to use a lower gain amp so you don't need to attenuate the signal so much (all other things being equal).

I guess what I was missing is how different things are with analog. I didn't fully appreciate just how much gain MC phono stages need just to get some of those low output cartridges amplified to 300mV. So with an analog system of course you would need some gain in the preamp. While at typical listening levels you may not need it, it would be a shame if your system was limited to only what you absolutely needed.

I do know I have a big blind spot when it comes to vinyl. As a kid, once I got a Walkman, I switched to cassettes over 45s on a Fisher Price record player. I started collecting CDs in college and am now streaming more than I ever thought I would. Couldn't bear to listen to a cassette the last time I even bothered connecting my tape deck. My main objection to vinyl is the ticks, pops, and noise. I'm easily distracted. The nicer systems with well cared for records may sound incredible (haven't had the pleasure), but the price of entry to get to that level is quite a barrier (as well as not owning any records).

Right now I'm using a Schiit Saga+ (unity gain) as an inexpensive interim preamp while I explore some different power amp and speaker types. I think as long as I don't try any really inefficient speakers or go for face melting SPL I should be okay. For now. 
Remember that preamps tend to have fixed gain stages internally.
So how did we get into this situation, too much voltage from digital players and too much gain in preamps and amps, and how do we get out of it?
@cat_doorman It sounds like we are roughly the same age based on your walkman story.  I am also running all my music digitally, through my Marantz DAC and into a bottlehead tube preamp and then into Bob Latino VS-120, Zu Audio Omen DW speakers.  I have been experimenting with different preamps, a lot, even though my amp has an attenuator / preamp section.  I just don't find that I get the same "richness" out of my music without the additional preamp.  I have also been swapping in different tubes, and that make an enormous difference (12ax7, 12au7, 12at7).  I know you were more interested in gain, but I suggest strongly that you experiment with good tube preamps, if you like that sort of sound as much as I do.  I was using, and just sold a Rogue Audio 66 preamp, and that thing sounded magical with my setup.
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I've been reading some of these discussions, and had to chime in here, as I've been trying to get to the bottom of what constitutes a good match preamp to amp as well.
I am finding it comes down to gain, output impedence of preamp to input impedence of amp, voltage output of preamp, and input sensitivity of amplifier. Transconductance apparently comes into play with tube preamps as well.

Here is a link from Steve Deckert at Decware that describes these factors: https://www.decware.com/paper55.htm

I currently have a Decware Torii Junior, 20 watt tube amp, and Canary Audio C630 tube preamp. Looking to replace with a Rogue Audio RP-7.

 Cannot get above 86dB spl at 10’ without pushing both units above 70% full throttle on some recordings. But at these sound levels, the music is liquid velvet, gorgeous. Just want a little more headroom, and volume.

Canary output impedence: 1600 ohms; Torii Jr Input impedence 100k ohms

Also, Decware amps are set to 2 volt input sensitivity, compared to industry standard of 1 volt or less.

These two specs reveal this is probably not a good match. Lower output impedence (50-100 ohms) matched with a high input impedence (100k+) is a happier balance. Higher max output voltage on preamp and higher gain helps as well.

Of course for those of you who have 100 watt+ amplifiers, this is all a moot point.

Enjoy hearing good sound! Like a gourmet meal!


@switlikbob I recently got Omen DW (97dB, 12 ohm), too! Pretty impressed so far. It’ll be interesting to see what I think after a few months acclimating when I finally get around to switching back to my Dynaudio Audience 82 (87dB, 4 ohm) again to compare. I’m using a Primaluna DP HP (26dB, 1.2V max in) so my pre needs no gain from my ~2V sources - Oppo BDP-105, Bluesound Node 2i. I’ve been lusting after a First Watt F7 (14.5dB, 2.7V max in) but was running the numbers first. At my listening position I rarely hit 90dB and most of the time am <80dB. So both of these amps would probably be at ok with any of the speakers I’m interested in.

I’ve been making too many changes all at once lately - cables, speakers, amp, streamer. So I’ll probably leave upgrading my pre until later. I still haven’t even played with tube rolling the Saga+ yet. I’ve been making a list of preamps to look at eventually. There’s a recent thread that has a bunch of 6SN7 based options.
My main objection to vinyl is the ticks, pops, and noise.
@cat_doorman A lot of ticks and pops that people react to when playing vinyl are caused by the phono preamp itself (due to high frequency overload) and aren't actually on the LP itself. Its a bit technically complex to describe quickly, but has a lot to do with the fact that the phono cartridge has an inductance and the tonearm cable has a capacitance- together they can create Radio Frequency energy that can overload the phono section's input stage for very brief periods- the ticks and pops. So if the designer didn't take this into account, you get more ticks and pops. And yes, most of the phono sections out there have this problem!
I’m a prime example of what Ralph has stated above. For about 6 years I owned a well thought of phono pre and just thought the tics and pops were part of the vinyl. Couldn’t believe the difference and improvement when changing phono preamp. If playing a clean copy can’t hear anything but the music.
As to the gain/voltage equation, the purchase of an amp with only 18db of gain negated the use of my preamp, which had only 12db of gain. To add to the imbalance, the amp requires 2.5 volt input to reach full power. Purchased a preamp with 20 db gain that definitely pushed the amp to full power. The preamp manufacturer actually mentioned that the amp’s lower gain would be a plus in combo with his preamp. All in all things are matched up very well. And I’m done for the foreseeable future.
Posters like Ralph (AtmaSphere) and Almarg are very valuable to this forum. The technical info they provide can guide you to make sound purchases.