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Not really wanting to argue.....
"An power amp of standard design"
There is no such thing. Look at the schematic below. With such an amp the output of a CD player or a phono stage will not be enough to reach full power. One could add an input voltage amp stage to the power amp or use a one stage pre-amp. Either way would be the same.
Now, to agree with you, if one has a power amp with enough gain, then a active pre-amp IS just more circuitry that can only mess things up. Or as you say, "any active device is a distortion generator" But there has to be enough active devices somewhere to achieve the necessary gain.
My point is; the first gain stage of a power amp can be built into the "power amp" chassis or it can be built into the "pre-amp" chassis, makes no difference.
Have Fun and Enjoy the Music
"Still working the problem"
All the time you are talking about non-standard designs.
Take the schematic you just posted. As the late Dr. Rosenberg alread said do, this is an "unsual" non-standard design by some Japanese audio nuts (there are tons of these nuts in Japan, you will be surprised - as I read a lot of those Japanese DIY audio journals).
This is a low O/P power design with pretty low Va for 300B (320V) & for parallel 6SN7 (185V). I guess the interstage driver iron primary winding would got very high impedance as reflected by its pretty high DCR which drops 5V.
This is Hi-Z primary design assmption is to concur to its design goal: "for max tonal quality". We know for interstage irons, higher the better the primary Z over the driver tube Za, which is pretty low in this parallel run 6SN7 situation.
Having said so, there is NO evidence in the schematic or in the incomplete Japanese text showing non-standard low input sensitivity of the amp that a CD player or LP phonesstage cannot deliver the designated LOW O/P power.
To correct your incorrect assumption, even if you boost up the Va of the parallel-run 6SN7 to over 300V, or add another voltage gain "pre-amp" stage on the same chasss as you suggested, you only overdrive the 300B into clipping without increasing any useful O/P power as the operation point of 300B is already pre-set this way.
Your point is NOT aimed at standard designs of a linestage or a power amp. Surely as a DIYer, you can build any "unsual" design you want, like adding extra "pre-amp" stage on the power amp chassis so that you can obtain an very very "unusual" Hi input sensivty for the power amp.
Or add an extra voltage gain stage in your active linestage to boost up its O/P voltage to say 10V instead of stanadard 1-2V. But by doing this, you are going to overdrive any power amp of standard input senstivity.
So, what is the point of your argument??????
June 13, 2005.
I have no argument.
If a person has a "non-standard" power amp and NEEDS some voltage gain then the active gain stage is a necessary evil. That's all.
The input sensitivity of power amplifiers are not standard, they are in fact all over the map. There is no standard.
The Sun Audio amp will not be over driven by 2V RMS and in fact NEEDS a line stage to reach full power.
The same amp with the addition of a input gain stage (three stage amplifier) would not need a line stage and in that situation I would agree with you that an active gain stage is redundant.
Look at it this way, Do you have a few amplifiers laying around?
Hook them up, one at a time to your passive line stage and tell me that the same volume is reached at the same volume control setting with each and every amp. Of course it won't be. Now I could turn your argument back on you. If one amplifier is more sensitive, I could argue that there is too much gain from your source and the final stage (of the source device) is "active" and is a "distortion generator".
I'm really not arguing. In fact most of what you said is true. It's just that you were, IMO, too general. And there is no such thing as "standard designs".
Now I start to get your point. "Standard designs" you meant designs of standardized or similar configuration, scheme or details. Of course, there is no such an industrial standard to govern how an amp should be designed, how many stages should be employed. But there is alway a general scheme of designing & building an audio amp where most designers & builders alike generally adopt.
What I meant is designs of standardized specs where the audio industries adopt, irrespective of whatever design in it. It can be SE, SET or PP or PPP, OTL, glassware or SS, etc.
There is always a general standard specs of most things, if not all.
For MM phono cartridges, O/P voltage rated 5mV at 47KR load. For MC (moving coil) cartridges, O/P voltage is rated for 0.5mV for 10R load. So all phonostage or pre-amps makers, comercial brandnames or DIYers alike, design & build them with such phono input sensitivity, to deliver a standard rated O/P voltage of 1-2Vrms at lowest load possible, say, 600R to match any power amp of "standard design".
Likewise, any amps of "standard designs" will have their input sensitivity of 1-2Vrsm to be driven properly without overloading or underdriven.
Of course, there are always non-standard exemptions as you already
said, but surely NOT "in fact all over the map".
Take out specs sheets of any brandname pre-amp & power amps, or intregrated amps, ALL have the similar or not identical design specs, e.g. I/P, O/P sensitivity, distortion figures, etc. This is what I meant "standard (industrial) designs".
Let me quote a couple of not so common exceptions deviated from standard designs, in term of input sensitivity alone-
Quad II monoblock power amp (original 1953 design by Peter Walker): input sensivity was 0.5V rms (15W O/P), to 'custom-match' its Quad 22 pre-amp which got O/P of 0.5V. In those good old days, these pair were considered as audio 'jewels' by many audiophiles.
Art Audio 'Carisssa' 16W+16W stereo power amp (USD4,000), using 1x845 SET class A power stage: input sensitivity of 0.6V with I/P impedance of 180KR. The maker also offers additional passive volume control built-in, for additional USD200. So that the end-user can skip any linestage !!!
What does this tell you, with non-standard high sensitivity as such,
who need any active linestage ??? Any phonostage or CD player can drive the power amp comfortably.
I'm glad to note that most what I said "is true" to YOU.
Have you ever audition a good passive linestage or try to build one?
If you are a seriously music listener, like myself, you will agree
with what I have said too.
June 13, 2005.
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