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In Reply to: RE: Disagree on the passive pre-amp..................... posted by PakProtector on January 28, 2010 at 10:00:11:
Hey, Douglas!
I think that you are laughing, so go ahead.... have a good time, the drink is on me.
You know that neither myself, or anyone else is going to be able to change all the resistors in a 48 position Ladder Attenuator at a whim.
You also know that high-impedance vacuum tube sources will do better with lighter loading than will a solid-state source that is much lower in impedance, or a vacuum tube cathode-follower source that might not be as non-critical as advertised.
You know that the attenuator must be set up somewhere in the middle of these requirements, and then left alone, and used as is.
You also know that both source output and amplifier input impedances can be designed to be fairly non-critical, as far as impedances are concerned, but that even if they are, if you can get closer to them, the audio system will sound better..
You also know that most solid-state (current mode) source outputs do better if they are looked upon as current-drives, and that they like lower impedances than most vacuum tube output sources. Of course, you can have a cathode-follower output or a transformer output and get very close to the solid-state device's output impedances with tubes.
If you're going to mix vacuum tube and solid state components on the same attenuator, cathode followers and transformers can have a place on tube outputs, but neither is the best that you can do.
Of course, one could choose a low impedance output tube and plate-load it. And I would like that.
You know that the load impedance of a ladder attenuator is not going to change to the source, so all I am saying is that you can and should choose the attenuator's load-to-source impedance to get as close as is practical to the requirements of what you're driving the attenuator with.
Pretty simple, and that is all you can do unless you are working in your own system and are able to design an attenuator for only one source.
I can't do that because, like anyone else who designs equipment for others to use, I have to look at a range of input sources.
All you have to do is call the manufacturer of those source components and find out at what load their equipment performs best. You can also measure the source component and evaluate it yourself. This isn't going to be practical on someone else's equipment!
Most solid state sources will fall into a fairly predictable range, and so will many vacuum tube sources.
Is this just silly, then, because one can't design the source component-- the user already has several, and they're all a bit different?
No, it's still worth considering. You can set your attenuator's load impedance to fall into a useful range that will sound better than it otherwise would for the kinds of sources that will be used on it.
For your question, I would want to know all of the source's impedances, and then I'd have to choose a value likely to work well for all of them.
If one source was very different from the others to be used in load impedance requirement, I would want to try it both on its ideal load, and then on the load chosen for the attenuator's use on the other sources.
Let's see what it actually does-- how does it behave?
I know you're laughing! That's OK-- have fun on me. If you want an attenuator for just one source, then we could both calculate that.
That isn't the question here. It can't be.
---Dennis---
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Follow Ups
- RE: Disagree on the passive pre-amp..................... - tube wrangler 11:58:59 01/28/10 (1)
- RE: Disagree on the passive pre-amp..................... - PakProtector 13:16:39 01/28/10 (0)
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