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In Reply to: RE: ARC LS-25 Mk I v. Mk II opinion? posted by George S. Roland on June 02, 2016 at 09:49:17
I cannot comment on the ARC LS25 MkI but I owned the LS25 MKII (and the ARC LS16 MKII).
To my ear the LS25 MKII was smooth with an expansive soundstage but I felt it was lacking in robustness or that full-bodied sound I prefer in some tube linestages (like the Cary SLP-05). The LS25 MKII was lacking "weight" in the mids and lower. It sounded more solid-state to me, but with weaker bass slam and dynamics.
I much preferred the Aesthetix Calypso and Calypso signature over the ARC LS25 MKII, but my all time favorite tube linestage was the Cary SLP-05.
You are correct. The LS25 MKII will require and external phono preamp if you wish to use it with a turntable
P.S.
The LS25 MKII uses a solid-state JFET input and the 6H30 tube as a cathode follower. 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.
I believe the original LS25 (non MKII) is all tubes using the 6922 so it may have a more 'tubey sound' to it but I have not heard one.
Follow Ups:
The LS25 MKII uses a solid-state JFET input and the 6H30 tube as a cathode follower.
ARC's claim is slightly different:
" 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. "
You don't need a pair of 6H30s for mere buffering. They are the final output stage for the coupling caps.
A cathode follower IS a buffer in that it provides a low impedance output and acts as a buffer between the signal and the load -- the output load in this case would be the power amp.
The 6H30 is a dual triode. I suspect they use one 6H30 per channel and two triode sections of the tube to accommodate for the +/- voltage swing for the balanced output. Repeat for the second channel. Hence, the need for two dual triode 6H30 buffer tubes.
I don't have a schematic but here's what I envision, per channel:
A pair of JFETS for gain each driving 1/2 of the 6H30 cathode follower then out to the power amp.
Repeat for the second channel.
A pair of JFETS for gain each driving 1/2 of the 6H30 cathode follower then out to the power amp.
Note that ARC refers to the JFETs functioning the same as the input stage of the VTM200s. Naturally, both also have output stages as well (if not using different output tubes).
That's the path with the 6H30s providing output stage functionality as well. More than merely a unity gain buffer.
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 06/02/16
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.
.
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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