On Pre-Amps

Peter W. wrote:

You will need to specify the Peak-to-Average of the signal in question.
You will need to specify Vout as compared to Vin.
You will need to specify Watts/RMS at the amplifier.
You will need to specify speaker efficiency.
I will stipulate a Transient Capacity of RMS x 10. Typically, it will be better for very well designed solid-state devices. About that for well-designed tube devices. Could be as low as 3.

None of these numbers have any impact on the point we are debating (that is, whether two amp in series are better than one larger amp), but we can define them all if you like. It makes no difference to me what these numbers are so I'll pick some that are easy to work with.

How about:
peak to avg ratio = 4
pwr amp 12.5 Watts RMS into 8 Ohms for 1 volt RMS input. (This makes the pwr amp gain an even 10)
Speaker efficiency = 100 dB/watt 8 Ohms
Preamp gain 5
Variable attenuator (Volume control inside the preamp like you mentioned) set to -10dB (i.e., a factor of 0.32 linear)


Is this ok by you?

In the interest of keeping the board relevant to most of us, could you guys get a room and pm this thread back and forth ad nauseum?

.

Bob Latino wrote:

audiobill wrote:You are getting lost in the engineering, again.

Just listen!!!

I am going to go along with audiobill here ... Sometimes people can get caught up in technical stuff that (many times) does not bear out when you use your ears to determine > "what sounds better". Example > Most solid state amps will give you better distortion and bandwidth figures than a tube amp YET > when you compare a solid state amp with a tube amp, many times the tube amp will "sound better" or sound "more like real music" or "have better soundstaging". You would think that a lower distortion rating would get you closer to the music but this does not bear out in many instances ..

Bob

I'm with these guys. I once heard a ridiculously expensive though seemingly well engineered stereo. I think it cost around $100K! Yet no matter what music I played through it, it was missing something and left me bored out of my mind. I also remember the first time I heard a stock ST70 driving a pair of old AR something speakers in a musty smelling hifi shop back in the early 90's. I was not impressed as it sounded like there was a heavy blanket over the speakers.

Synergy of components is a key factor. Not just the numbers but the character and voicing of a given component.

I really hadn't thought much about tubes in my early days as an audiophile until I worked at an electronics repair shop. One day I was tasked with troubleshooting an ancient suitcase turntable that was brought in. It was a fascinating looking piece to behold from the start. But it was the single channel amp and speaker built-in that turned me around. While inspecting it I noticed between the turntable output and the amp input was a single RCA connector. Out of curiosity I plugged my Sony CD Discman into that input and played my kind of music. Despite the amp being woefully out of spec it did something to the music I had not heard before. It sounded kind of like a live event. I understood that it was filled with distortion but something about it absolutely blew my mind! That set me on a path to learning more about tubes and their effect on music.

We eschew technology on most weekends. (Phones & internet). More Monday.

audiobill wrote:You are getting lost in the engineering, again.

Just listen!!!

We get into the engineering when we're not listening.  

Besides, without engineering, you wouldn't have anything to listen to!

I feel this is a good discussion on a topic that has been around for many years -- why do we need a line preamp when the source can drive a power amp directly?

rjpjnk has found that adding a PAS3x preamp to his system there was no discernible positive improvement (in this related thread: https://dynacotubeaudio.forumotion.com/t3782-on-the-use-of-a-preamp-to-improve-sound-quality-with-vta70)

In my case of a phono-only system, I have a phono preamp.  It sounds wonderful.  But do I need a line preamp?  I tried adding my old Adcom line preamp and the sound became dry, flattened.  So to carry the experiment forward I'd need to get a very good one, such as the VTA SP-14.

Anyway, I hope this topic continues on and we learn the ultimate answer about power, transients, amplification, distortion and the meaning of life.

dave

Well, finding the meaning of life may be stretching it a bit Dave, but I appreciate your support of technical discussion. To me, the suggestion that I would ever stop thinking and just listen is downright depressing frankly. Where's the fun in that? But that's me being the engineer I guess. My primary interest IS the technology. If I just want to hear a great sounding stereo I can go sit in may car.

However, I do want to be sensitive to the nature of the forum. Maybe it's not a good idea to hold debates like this if only two people are involved and not a topic of general interest because it makes the thread look inordinately active.

As for the "Is a preamp necessary" issue. We will not solve this here. It will go on forever. Best we can hope for is interesting discussion. As Bob and others have said, sometimes it just sounds better even if there's no good reason it should.

I think it may be like art. Can we say one painting is better than another? Or more accurate? No, but we can PREFER one more, and rightfully pay lots of money for it if we want to own it. I think there is art in audio electronics as well, and I respect that.

What I have a hard time with, however, is missinformation. Let's not say a preamp is so good, so transparent, so perfectly excellent at not coloring the sound, and then at the same time say it is so much "better than a wire". What is the truth here? What does it do specifically that makes it worth it's price? Could the honest truth be that it MUST color the sound, and that this, in fact, is what makes it so valuable? I don't know, but at this point it is the only answer that seems plausible to me.

.

http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm  

None of these numbers have any impact on the point we are debating (that is, whether two amp in series are better than one larger amp), but we can define them all if you like. It makes no difference to me what these numbers are so I'll pick some that are easy to work with.

No, that is not the debate.  Or, it confines the options to the exceptional.

At no time did I ever dispute that an all-powerful amp could not do complete justice to a (nominal) 2V signal.

a) All signal/range is present in a well-engineered recording. We can agree on that.
b) I will not accept your peak-to-average of 4. That would be a 40 dB spread - there is very little in source recording that even could encompass such a spread other than, perhaps an active Foundry. But, lets apply it to the full dynamic range of the recording. And, let's set the P/A at 30 dB. Still pretty rare, but not off the scale.
c) A speaker with a 100dB @ 1 watt at 1 meter will be a remarkable beast - but let's accept that. It kinda-sorta matches the flea-powered amp.

So, let's assume you listen at an average of 70dB. This is active conversation. And your peak would be, then, 100 dB. Your most quiet passage would be 60 dB.

Your flea-powered amp into those speakers would be 100% up to the job without the necessity of an active pre-amp. An exceptional condition, but within all the parameters given and accepted. BUT, if you were listening to that foundry, you would hear the loudest transients at 10 dB down. Under most conditions, that may be a blessing.

Now, let's take my example:

Speakers at 84 dB @ 1 watt @ 1 meter (Magnepan MG IIIa)  
Average listening level of 80 dB
Same P/A as above
VTA 70 as the amp

So, 1 watt gives me 84 dB
10 watts gives me 94 dB

-line-level source cuts off at about 97 dB (35 watts).  

100 watts gives me 104 dB
1,000 watts gives me 114 dB (rimshot) (down 17 dB from a line-level source - down 6 dB via an active pre-amp).
10,000 watts gives me 124 dB (foundry) (not gonna happen).

Go the other way - set line level at peak (104 dB)
Down 10 dB (3.5 watts) goes to 94 dB
Down 10 dB (0.35 watts) goes to 84 dB
Down 10 dB (0.035 watts) goes to 74 dB.
Down 10 dB (0.0035 watts) goes to 64 dB (Most quiet passages). Dubious - although the numbers work, few amps are capable of a cogent signal at that level, and fewer speakers will accept it as above the noise floor.

AND positing a  X 10 transient capacity (350 watts), the rimshot will be ~ 5dB down. The foundry will be 15 dB down.

AND, still not very good. And that even with an active pre-amp.

Same example, with my brute-force 200 wpc/rms amp:

1 watt gives me 84 dB
10 watts gives me 94 dB
100 watts gives me 104 dB

-line-level source cuts out at about 107 dB

1,000 watts (rimshot) gives 114 dB, down 0 dB using an active pre.
At X 10, the foundry strike would be down only 7 dB - were not that I would do that to good speakers.  

And that would be the point. In order to get a realistic differential, the full capacity of the amp must be realized. Or, the loudest passages are muted. Or, the softest passages go below the noise floor. A simple line-level input will not drive an amp to reproduce transients under typical real-world conditions.

Peter W. wrote:http://www.sengpielaudio.com/TableOfSoundPressureLevels.htm  

None of these numbers have any impact on the point we are debating (that is, whether two amp in series are better than one larger amp), but we can define them all if you like. It makes no difference to me what these numbers are so I'll pick some that are easy to work with.

No, that is not the debate.  Or, it confines the options to the exceptional.

At no time did I ever dispute that an all-powerful amp could not do complete justice to a (nominal) 2V signal.

Peter W, if you now agree that the series combination of a preamp and power amp offers no dynamic benefit that a single power amp alone of sufficient gain could not provide even better, then I think we can close this discussion. That was the primary point of contention in both of these threads, at least from my point of view.

a) Not everyone has an amp capable of the necessary dynamic range within its RMS rating.
b) Not everyone will be happy with the limits thereby imposed.

i went by the way of my laptops ext sound box (all settings flat) to the line in on a receiver with decent sound quality, mine is a(HK730).and the headphone jack out of the HK with a adapter cable (1//4 stereo plug to dual RCA's) direct to the input of the ST-70. and use the volume on the HK 730 for attenuating. thats a lot in the path,BUT! i get flex in nuance because
1---i can bring up the volume on the sound box and turn down the vol on the HK. OR--
2---bring down the volume on the sound box and turn UP the vol on the receiver, resulting a little differences of tonality between them.
in my case it seems 1 results in more dominant tone from the sound box
and 2 results in more dominant tone from the HK
ive have found myself setting to the middle parameters of both and working with that to get all the shape because i get incredible drive from the HK's mid bass,and really sweet mid highs from the soundbox, together with the soft sub and smooth highs of the ST-70. i get a really really nice sound range to bring out those subtle nuances.
but of coarse my speakers/..... yea my speakers..... custom designed sealed/insulated 205 watt, 8(6) ohm semi shallow box,i read a book-advanced speaker design, and designed around the speakers going into it (factored in the Q,the VAS.and all) with 4 way with high attenuation. a 12 sub,, a 6 sub/mid, a 3 mid tweet, a 3 cone tweet, and i made a custom dual coil crossover for them all also. i only wish i had a bigger room to listen in and be able to space out my speakers more from the wall and themselves a bit. THEN id have a pretty nice soundstage. as it is, where i sit,and where the speakers are is about as good as it can get.... i think (thinking/scratches chin)
sorry... i couldn't help myself from putting that out there.