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Are the addition of a tube buffer after the CD player, and the installment of a tube output stage in a CD player, basically the same thing?
The tube buffer can't get too wet without warping, while the tube output stage can get much wetter without a problem.
Thank-you for all of the useful information. I have access to some very well-designed tube buffers (Space-Tech Labs), or I can have what is purported to be an excellent tube output stage installed (Underwood/Pcx). It sounds like the one inside makes more sense. Unfortunately, the one that makes the most sense is about $900 more expensive. Oh, the woes of the audiophile!
morricab: I was wondering elsewhere on AA about the differences between that Monarchy M24 and the Lite Audio 60 (or the Pacific Valve upgrade, the 62), other than the M24's preamp section. Would you know if the Pacific Valve 62 has the same tube output linestage, or does it use opamps? TIA.
They are not the same. A buffer, tube or solid state, presents a high impedance load (easy to drive) at the input and a low impedance output. The op-amps in cheap CDP's or mp3 players benefit from a buffer by not having to generate significant current. This gives more dynamic range and probably improves the sound. Buffers are usually unity-gain and low-distortion devices. They are not very useful for adding tube coloration. And you are still listening to the output stage of your CDP. Replacing the output stage with an excellent tube output stage will almost certainly give better sound. Depending on how the output stage is voiced, it could add a bit of tube coloration.
Some CDPs and DACs have a gain stage while others don't. The gain stage is done in the analog domain and can be accomplished using solid state components or tubes. The gain stage can be buffered or not. As morricab said, a CDP's gain can be achieved with opamps (among other circuits) and then buffered by tubes. An Ah Tjoeb would be an example of this. One purpose of using a buffer is to lower the output impedance of the digital source so as to make it an easier load for the preamp. Not all digital sources have gain stages, but most of these don't have sufficient voltage output (relative to an amp's input sensitivity) to be used with say a passive pre.
not usually. A tube output stage at least implies the tube stage is providing the necessary gain to be sent to the preamp or amp. A buffer has a gain of 1 (or a bit less). Typical practice seems to be to put a tube buffer after the opamps in a normal cd player to give "tube" sound. Generally, it just degrades the sound.
A real tube output stage is providing the gain so opamps are often not used at all. A case in point is the Monarchy M24 DAC. It uses a tube output stage in an SRPP configuration. No opamps or transistors are used.
I have an older Delta Sigma with a tube output. Another nice feature is built in analog gain controls. I use it to drive a Threshold amp directly.
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