Charles Hansen wrote
"Again, the question of being able to drive the EQ network is a simple one. If the circuit designer can't get past that step, perhaps he should be in a different line of work.
Regarding your comments that a passive EQ would tend to have less headroom than an active EQ, that is absolutely a wrong generalization."
I'm not talking about driving the EQ network. Most competent practitioners will understand this point and what to do to be able to handle th e increasing current drive required at highe r frequencies . You and John have already noted this.
My point is simply: If you don't carefully consider the 20Khz headroom requirements in a passive phono amp, where the front end is a straight gain stage, you are likely to have less head room than a system that uses actvice equalization with feedback brought around to the input stage.
You showed a plot of an ARC amp on an earlier post where the 20Khz distortion curve climbed quickly and at a much lower out level than the lower frequency curves. Looks like this is amp has a gain stage without feedback equalisation on the front end. So be it. I am not condemming this design, but facts are facts. An active system would not have a distortion curve like this (again, I am not claiming either sounds better - I'll leave that for someone else to decide)
Some comments were made earlier about how the different types of topologies handle clicks and pops from LP surface noise . I don't have any data on th e magnitide of these signals but this should be a consideration and how the amp recovers from these (note PMA's point wrt DC servo).
"Again, the question of being able to drive the EQ network is a simple one. If the circuit designer can't get past that step, perhaps he should be in a different line of work.
Regarding your comments that a passive EQ would tend to have less headroom than an active EQ, that is absolutely a wrong generalization."
I'm not talking about driving the EQ network. Most competent practitioners will understand this point and what to do to be able to handle th e increasing current drive required at highe r frequencies . You and John have already noted this.
My point is simply: If you don't carefully consider the 20Khz headroom requirements in a passive phono amp, where the front end is a straight gain stage, you are likely to have less head room than a system that uses actvice equalization with feedback brought around to the input stage.
You showed a plot of an ARC amp on an earlier post where the 20Khz distortion curve climbed quickly and at a much lower out level than the lower frequency curves. Looks like this is amp has a gain stage without feedback equalisation on the front end. So be it. I am not condemming this design, but facts are facts. An active system would not have a distortion curve like this (again, I am not claiming either sounds better - I'll leave that for someone else to decide)
Some comments were made earlier about how the different types of topologies handle clicks and pops from LP surface noise . I don't have any data on th e magnitide of these signals but this should be a consideration and how the amp recovers from these (note PMA's point wrt DC servo).
Bonsai said:
I guess. But there are lots of ways to skin a cat. A passive EQ phono unit does not need to have a flat gain stage in the front end. And even if it did, you would just need to make sure that it had enough drive capabilities for the situation at hand. Again, it's not rocket science, and I don't think one could fairly criticize that Audio Research phono stage because it could only put out 7 Vrms at 20 kHz.
Bonsai said:
I don't think we have enough information to determine the topology of that circuit. But at any rate it doesn't appear to be a problem in the real world. It will put out 7 Vrms at 20 kHz before distorting. The fact that it will put out even more at lower frequencies is interesting, but certainly not indicative of a bad design or bad sound.
My personal philosophy would be to have a maximum output level that is independent of frequency, but that doesn't mean all that much. I would guess that plenty of people would prefer the sound of that Audio Research phono stage to anything I've ever designed.
CBS240 said:
It does state "capacitor microphone applications" in the data sheet. I assume it is has to do with the phono pickup being inductive? Or is this another point of insight chalked up to "experience"?
These FET's are used at Idss and have to meet a max supply current spec of <400 or 500uA. They are intended for those cheap little Radio Shack capsules.
Kostya-M said:
Yeah The Fear of a little bit of noise in audio amplfiers is often not justified.
I do not mean we should ever strive to build any noisy amplifiers.
We should, especially in very high gain applications, do what we can to reduce input noise.
.... What I mean is this:
There is a point in making audio designs,
where adding more stuff / devices to take away things like noise & milliVolt DC-offset,
WHERE it no longer MAKES SENSE.
And so even many times all your extra 'addons'
will take away or reduce other important positive qualities
and frequently Add New problems to try to deal with instead.
This is something that many haven't understood .... yet
But Nelson Pass is one of them few That Certainly HAS!!!!
Thanks god, if you are there, for this fact
Most Moving Magnetic phono circuits, can be used with MC.
This is almost a standard way to make RIAA:
- Have a pre-stage head amp specially to raise the level a bit
- and then couple to MM-part input.
So, Kostya-M, your circuit would work, no problem.
With only a little more work to tweak current levels and details.
Here is your interesting and Very High Quality schematic, again: http://www.diyaudio.com/forums/attachment.php?s=&postid=1520780&stamp=1211820282
PS. Congrats to Gold in Hockey-VM and russian song Win in EuroVision SongContest.
We also once won this Contest in the 1970-ies, think 1974,
ABBA = Bjoern, Benny, Agnetha & Annifrid(Frida) = ABBA
with song: Waterloo!. DS
Regards
Lineup
Charles Hansen said:
If I will go a bit higher budget ... not that i know the actual price of the day,
there may be some good bargain second hand items at eBay
To recapture:
Now, here comes the real hookup, in my personal opinion:
Weight
12 pounds (5.5 kg)
I can get me self RIAA amplifiers, that weigh only like 200-500 grams!
What about this little fact, Mr Hansen?
Lineup, hi-fi regards
Bonsai said:
It appears that I am.
As near as I could tell, you were asserting that active EQ always had better high-frequency overload capabilities than passive EQ.
I think that is true for a limited set of specific topologies, but certainly not in general.
Please feel free to clarify my errors.
Charles Hansen said:
okay
I am non-native english speaker/writer,so I re-phrase (i think this is the expression in eng, when one put thing another way if somebody can not get your message)
Another way to put my query, to you Mr Hansen:
>>> why so heavy phono amp
>>> when obviously it is quite possible to design lower weight
hifi-regards, lineup
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