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In Reply to: RE: To split hairs... posted by E-Stat on June 02, 2016 at 13:22:10
A cathode follower buffer / driver is one in the same. It IS the output stage of the LS25 MKII.Sure, the input of the JFET will be driven by the source component and the output of the JEFT will drive the input of the next stage. In the case of the LS25 MKII that next stage is the cathode follower buffer/driver.... to drive the outboard power amp.
I suspect it will be unity gain, or less. The output of the cathode follower buffer will then drive the external power amp.
So in terms of tonal character, which was my initial point, I believe it is mostly due to the JFETs in the LS25 MKII and less to do with the 6H30 tubes.
Edits: 06/02/16 06/02/16Follow Ups:
I suspect it will be unity gain, or less.
You're welcome to your speculation. I, on the other hand, tend to rely on ARC's own description of their output stage circuitry.
So in terms of tonal character, which was my initial point, I believe it is mostly due to the JFETs in the LS25 MKII and less to do with the 6H30 tubes.
Perhaps so, perhaps not. My previous preamp was an SP9 MKIII, also a hybrid design. It was originally a MKII and I would characterize its lower midrange tonal balance as lean as well. The MKIII version, however, with its many changes sounded fuller in that range. No active devices were changed. It was merely a case of voicing.
You're welcome to your speculation. I, on the other hand, tend to rely on ARC's own description of their output stage circuitry.
"Inside, however, you will find a new motherboard architecture that incorporates a JFET input stage similar to that used in the VTM200, followed by a cathode-follower / output driver stage using two 6H30 twin triodes."
I don't think anything I said contradicts their description. A cathode-follower IS the output driver stage. I'm not sure what the disconnect is here as they say nothing about the tube providing gain. My educated 'speculation' is that it is a pretty common cathode follower with unity gain, or less.
But in any case, the LS25 MKII and LS16 MKII were nice but not quite to my taste. I like a more "tubey" sound in my tube linestage.
I don't think anything I said contradicts their description. A cathode-follower IS the output driver stage.Sure it is. Output stage , exactly! ARC's wording doesn't involve "driver" in describing the implementation with the LS25. Did you follow my embedded link to their description? That phrasing is different from your original assessment:
In this regard, it is my opinion that most of the sonic character of this linestage should be "solid-state" and slightly smoothed out (and potentially a bit rolled off) by the 6H30 buffer.
A buffer is a buffer (matching impedance with unity gain) and an output stage provides additional gain.
Do you know of any output stages that don't?
And in every gain stage I've ever encountered, there lies the ability to determine character. The tubes aren't there for show as they are with "tube buffer" products.
Edits: 06/02/16
Abe is correct. I looked at the schematic, and as you would expect the output stage is a cathode follower.
Cathode followers (a.k.a. "buffers") have a voltage gain of less than 1. In other words - no gain, in fact they attenuate the signal slightly. But they do have a much lower output impedance which is useful for a preamp.
So listen to what Abe is saying - he's got it right.
I sit corrected.How did the original version use its 6922 tubes vs the 6H30s of the MKII? Schematics on the original are easy to find, but I have not been able to find one on the MKII version. Where did you locate that?
Were two of them for gain and the other two used as cathode followers?
I seem to recall that Victor Khomenko used to say that one 6H30 could replace two 6922s hence the moniker "super tube".
edit: Abe - I got the text of your deleted post. I have found myself mistaken a number of times, especially when empirical data was unavailable. Search for "mistaken" and "corrected" and you will find numerous hits where it applied to me. You were right. I have no trouble admitting that I am wrong (now and again) :)
Edits: 06/02/16 06/02/16 06/02/16
...it's not like I've never been wrong.
The schematic is on the ARCDB site (link below). Scroll down that page and the Mk II schema is there.
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Interesting. It looks like the LS25 is "all tubes" except for a FET that appears to be a constant current source and the other two I'm not sure. For biasing?
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