Message started by Zilch0 on 05/29/13 at 00:04:11

Title: ZSTrAnGE observations
Post by Zilch0 on 05/29/13 at 00:04:11

Hi everyone,

I'm the third owner of the ZSTAGE that was originally delivered to  meraklya (Sean) in August 2012, went back for warranty service and came back to him two weeks later, and was later sold to Orangecrush (Will) in March 2013, who sold it to me three weeks ago.  Amazingly, it's still in "Mint" condition - truly, it looks brand new - but I'm not selling it - not yet, anyway!


This poor thing has had a hard time finding a home, it seems, but I'm already feeling attached to it.  Still, I've made some unexpected observations that are somewhat disconcerting.

First, let me proclaim that I am completely satisfied with the transaction I had with Orangecrush (Will) - no complaints, whatsoever.  He sweetened the deal with a couple of PSVANE 12AU7s in addition to the stock JJ, I paid a lot less than what the bundle would have cost new, and I didn't have to wait three months.  


Prior to this purchase, I've been a solid state guy.  My goal in buying the ZSTAGE was (is) to make the following chain, which is fairly neutral and slightly laid back (fourth row seating), and lacking in both dynamics and bass energy, a lot warmer in the mids, more forward (front row), punchier, and hopefully, a little stronger in the bass:

WAV > Foobar 2000 w/WASAPI event > USB > CEntrance DACmini CX (line out) >  Burson Soloist > Beyerdynamics T1

The ZSTAGE has been inserted ahead of the Burson Soloist, but on first receiving it, I was unimpressed.  I had no reason to believe it wasn't working as designed and I'm still not convinced that it actually has a problem.  It seems to be functioning perfectly, except for one annoying observation:

With the JJ 12AU7, for example, The ZSTAGE is supposed to permit a decrease or increase in dynamics, with a simultaneous decrease or increase in weight.  Steve Deckert writes (in the ZSTAGE manual) that a decrease in dynamics and weight can be had by adjusting the ZSTAGE gain control to something less than unity gain (less than the DAC's output - as with the ZBOX), while volume-matching with the amp's volume control to maintain a desired SPL at the headphones or speakers.  An increase in dynamics and weight can be had by adjusting the ZSTAGE gain control to something greater than unity gain (greater than the DAC's output), while volume-matching.

Quoting the ZSTAGE Owner's Manual:

Approximately 1/2 way up is “unity” meaning it is neither adding or subtracting gain.

Now, it's easy to understand that the point at which unity gain would occur could vary with the tube I'm using, especially if I were to use a 60 mu 12AT7 instead of a 20 mu 12AU7 - at least I think that's the case, as I've not yet tested any 12AT7 tubes.

Using an SPL meter (an iPhone app by JL Audio) and a white noise WAV file, I've determined that, with the stock JJ 12AU7, unity gain occurs just below 3:00 o'clock on the gain control of my ZSTAGE.  Thus, nearly 75% of the range of adjustment available to me will only reduce gain to the amp (theoretically reducing dynamics and weight).  Only the top 25% of the ZSTAGE's available range of gain control actually increases the gain to the amp,  (potentially increasing dynamics and weight), AND when ZSTAGE gain is turned all the way up (even a few degrees shy of maximum), I can hear distortion - unacceptable distortion.

Without explaining why I was asking, Burson support has responded to a query telling me that they've tested the Burson Soloist with inputs as high as 12Vrms, without any evidence of problems.  CEntrance support has assured me that the line level output of the DACmini CX is 2.0Vrms, so I'm thinking that I'm somehow overdriving the JJ tube when ZSTAGE gain is set to maximum - rather than overdriving the Burson Soloist, but I really don't know for sure where the distortion is happening.

Keep in mind, however, that the ZSTAGE manual specifies it having an adjustable output of only 0 to 5 Vrms - far short of the Burson's claimed tolerance for 12Vrms.

One thing's for sure:  I'm only able to use about 20% of the total adjustment range of the ZSTAGE gain knob for increasing the gain above unity gain, and thus, I have a very narrow range within which I have any hope of increasing dynamics and weight.  

The result was that I really wasn't hearing much, if any, improvement in dynamics and weight, before I start getting distortion.  

Rolling in either of the PSVANE 12AU7s yields the same results.  

It then occurred to me that perhaps the ZSTAGE was just not happy with the DACmini CX' DAC section putting out 2.0Vrms (why not?), so I whipped out my trusty Sanza Clip+, which I once read has been measured with an output voltage (at full volume) of only 0.55Vrms.  

Replacing the 2.0Vrms DACmini CX with the Sanza Clip+ did the trick!  When I feed the ZSTAGE with the low, 0.55 Vrms output of the Sanza Clip+, "riding the gain" of the ZSTAGE actually makes a dramatic difference in dynamics and weight - a big difference from what I have been experiencing with the DACmini CX feeding the ZSTAGE with 2Vrms!  Previously, my SPL meter evidenced unity gain occurring at just shy of 3 o'clock - using the DACMini CX and any of my three 12AU7 tubes.

But when using the 0.55Vrms Sanza Clip+, unity gain occurs with the ZSTAGE knob at only about 8 o'clock, which gives me more than 3/4 of the ZSTAGE gain adjustment range with which to increase dynamics.   I have to set the amp's volume much higher than when using the 2Vrms DACmini CX, but the weaker 0.55Vrms output of the Clip+ permits a much larger adjustment range on the up side of unity gain, vs. on the down side of unity gain - and I haven't detected any noise problems that could be associated with driving the amp with less gain.

Best of all, when I spin the ZSTAGE knob fully clockwise (and turn down the Soloist's volume control to maintain a desired SPL), I'm no longer getting any of the distortion I was hearing with the knob near or right at maximum gain, where it was especially noticeable in the bass.  

Given that ZSTAGE specs show a maximum output of 5Vrms, I'm (somewhat) convinced that the distortion I was hearing with the DACmini CX when ZSTAGE gain was at or near its maximum was coming from the ZSTAGE itself - as if the ZSTAGE does not like having an input as high as 2Vrms.  It is MUCH happier with an input of 0.55Vrms, where I hear no distortion at any gain setting.

The lower output voltage of the Sanza Clip+ has converted the ZSTAGE from being nothing more than a tube buffer (offering no gain)  into the gain stage it was designed to be - offering a great deal of sonic tailoring, just by "riding the gain." (Not to mention tube rolling.)

So...  With this observation, I ordered some (inline) 6dB Harrison Attenuators to bring down the DACmini CX output, when using it to drive the ZSTAGE.   They're working great with the DACmini CX line level output reduced by 6dB.  Unity gain with the DACmini CX is now at about 7:30 on the ZSTAGE gain adjustment, instead of at 3:00, with no distortion heard at maximum gain - making the DACmini CX output more like that of the Clip+.  


Since installing the Harrison Attenuators, I've ordered two more 12AU7s - a Siemens and Radiotechnique, and they, too, just as with the stock JJ and the two PSVANE's, are a lot happier when the DACMini CX line level is attenuated.  Keep in mind that I'm getting almost exactly the same gain from the 6dB attenuated DACmini CX as I get with the Sanza Clip+, so it's not as if the DACmini CX was somehow putting out a lot more than 2.0Vrms.  No... my ZSTAGE just can't handle 2.0Vrms of input voltage.  It's much happier with 0.50Vrms.

So, now I'm waiting on my first 12AT7 - a Mullard.  At 60 mu vs. the 12AU7s' 20 mu, I'm wondering if I will hear distortion and where exactly unity gain will be with the 12AT7 rolled in.




Title: Re: ZSTrAnGE observations
Post by Rivieraranch on 05/29/13 at 02:50:20

Since you asked for comments I will say that you might find the 12AT7 to upend all your calculations and tweaking. It will give a lot more gain quicker - most likely quicker than you need.

You may want to stick with the 12AU7 family. I have used 5814 in the ZSTAGE as well as a 5963. I am currently using a Phillips Holland 7062 E180CC and it performs extremely well.

I think you might have a synergy issue rather than the specs of these pieces of equipment fighting each other.

Title: Re: ZSTrAnGE observations
Post by Zilch0 on 05/29/13 at 04:40:23

Thanks for the quick reply!

I hear you regarding the possibility of a synergy issue.  I could try using some other DACs and amps, to rule this out, but everything I have is solid state.  Is it possible that tube amps are somehow more sensitive/responsive to varying input voltages than solid state amps?

I know that 12AT7s have three times the gain of a 12AU7, but I don't know that this will put me back into getting distortion when the ZSTAGE gain is set to maximum - with or without the 6dB of input attenuation.  I'm only guessing, but I suspect that as long as my ZSTAGE is only seeing a 0.5Vrms input when using the 12AT7, I won't hear any distortion at the far end - assuming, of course, that the ZSTAGE output doesn't exceed whatever the Burson Soloist can handle (which, according to Burson support, is something greater than or equal to 12Vrms).

For sure, I'll get a more rapid change per degree of arc as I adjust the ZSTAGE gain knob, than when using a 12AU7.

I will follow-up later, but thanks very much for your recommendations.  I'm stumbling along here, just trying to figure out how it is that other ZSTAGE owners are getting no distortion in the absence of 6dB attenuators.



Title: Re: ZSTrAnGE observations
Post by will on 05/29/13 at 18:02:17

Interesting observations guys. From my experience with the Zstage, I am thinking this is technical stuff and synergy.

I don't really remember at what point on the knob my Zstage got overdriven with the ZDAC which is I believe 1.8v out. I ran mostly 12AT7s with it and imagine it could get to a point of distortion, but I don't recall getting upset that I could not go past say 3pm. I seem to remember the most useful range sound-wise being between about 10AM and 2PM with it, and depending on the recording, the area that was neutral sounding roughly between 11-1. This neutral area depended on tubes too, some making it darker/warmer and some leaner/brighter, but generally this area would cover most recordings and I could then weigh toward pushing the Zstage harder or running it leaner depending on taste for that recording and that day.

I suspect the unity gain is dependent on source, and there is no doubt the Zstage circuit gets overwhelmed in my system with more gain from the source and/or more gain in the Zstage itself.

My Tranquility DAC is I believe around 2.25v and it made my useful range on the Zstage volume knob notably lower than with the ZDAC. With this issue, and my tube selection being mostly the hotter 12AT7 (though I could attenuate the signal into the Zstage by software volume reduction in my PureMusic player) I just stopped using the Zstage with the Tranquility finding the sound improvement versus degradation with the Tranquility sort of borderline... some aspects a little better and some a little worse....I do have tubes in my amp though so my use of the Zstage was not necessarily about tube sound.

This was of course within my system synergy, and with the 12AT7 choices I had. Preferring 12AT7s with the ZDAC initially, I followed that direction and only had a few 12AU7s and a good selection of AT7s. I did not like the 12AU7s I had as well with the ZDAC. With the Tranquility, I seemed to like the RCA cleartop 12AU7 best, but did not love the combo enough to use it.

Now with Jupiter caps in the Zstage (really good...very open and revealing with a natural organic quality that keeps the edges friendly) and with more 12AU7s, I have been running the Zstage with the Tranquility happily, glad to have my gain riding adjustability back.

But even with the 12AU7s and the Tranquility, to get my favorite sound range from the Zstage, on hot recordings, I need to cut back the software pre in PureMusic by 2-3 Db to allow me to get  the gain on the Zstage up to 2:30 - 3 PM without distortion...and interestingly, 2:30 is still about as high as I like to take it in terms of its shift to the darker/heavier side of neutrality in my current system.

How this software pre being before the source equates with an attenuater after the source I can't say. With 12AT7s I have to run the software pre down by 6 Db to keep my favorite useful range on the Zstage (maybe 10-2:00). I have not explored 12AT7s as much as 12Au7s since I got the "new" Zstage (modded with Jupiter beeswax caps) and subsequently finding definate benefits of the Zstage after the Tranquility. I do like 12AT7s still, and the additional gain over the 12AU7 as reflected in volume and distortion is not as much as I might have expected, so I find them easy enough to use in the Zstage. This is with the ability to attenuate the signal though. Without attenuation, 12AT7s and the Tranquility are not great together...too little gain before distortion.... Sound-wise, 12AT7s do push harder though, and will therefore reflect sound quality issues more than the gentler 12AU7 family. Where I definitely preferred the AT with the ZDAC, I like them with the Tranquility also, but with the open transparency of the Tranquility, the synergy thing is perhaps more important.

With your 6db attenuator you might or might not get distortion with 12AT7s, and the knob way up, but the question is, does it matter in your system. Do you get enough of the range off neutral to utilize the benefits of Zstage well. It is all so dependent on so many things...but from my system/room, I guess I can imagine that one may want to drive the Zstage to max, but here, that is not a great sound.

Within the useful range, the effects of gain riding with the amp and Zstage it is pretty clear....riding up the Zstage does bring weight and a denser/darker tonal range, and riding it down will reduce weight and open/brighten the sound. But what happens when you introduce other attenuators? Like the Harrison, or in my case, the Pure Music pre? Sound-wise, the Pure pre seems designed to be transparent, and may be close to that...functioning more as a volume control. In this case it would appear that they have compensated somehow to eliminate electronic adjustments/influences like the Zstage uses to do its magic.

Zilch0, can you hear the Harrison attenuator you got at all. I find this an interesting approach.

Title: Re: ZSTrAnGE observations
Post by Zilch0 on 05/29/13 at 22:51:39

Thanks very much for that detailed reply, Will!

I can say that your experience brings me some satisfaction in that it leads me to believe there's nothing wrong with my ZSTAGE - that it's reasonable to experience some distortion when the gain knob is at or near maximum with an input voltage near 2Vrms.

I'm especially assuaged by your use of software attenuation to accomplish pretty much the same thing as I've done with the Harrison Attenuators.  

You've also satisfied my curiosity about what to expect when my Mullard 12AT7 arrives.  It seems I might have to apply even more attenuation going in to the ZSTAGE, if I'm to enjoy a large adjustment range on the gain control.  Otherwise, I could find myself back to having a very narrow arc within which gain exceeds unity gain while not causing distortion.  I will post my findings later, once the 12AT7 has arrived and I've burned it in.

Answering your question, I'm convinced that the Harrison Attenuators are wonderfully transparent.  I've used them before and have never found fault with them.  They come in different "strengths," so they might not perform as well at higher attenuation levels, but the 6 dB versions sound very clean to me - with no coloration or noise of any kind. but I've never really dug deeply into A/B testing them at different frequencies, so YMMV.    Just to avoid any noise vulnerability along my interconnect cables between DAC and ZSTAGE, I've got them mounted at the input jacks of the ZSTAGE - not at the output jacks of my DAC.  

Quote:  How this software pre being before the source equates with an attenuater after the source I can't say.

I can't say with certainty, but I'm concerned that you might be reducing your bit depth by using software to reduce the output voltage of your DAC. I know that most DAC manufacturers prefer that you maximize the "volume" in your OS and/or player software (Foobar, etc.) because dynamics can be reduced with a reduction of bit depth.

Thanks again for you input!



Title: Re: ZSTrAnGE observations
Post by will on 05/30/13 at 07:21:42

If I recall correctly the Zstage is rated to 2v input max. I don't know what in it overloads, and yours may not get into distortion with the 6 db attenuator even with the 12AT7. I look forward to your thoughts on that tube when it gets burned in. I have a Mullard /Blackburn 12AT7 that I like...warm with good detail. Also found a Zaerix labeled pair from a Ukrainian seller that is exactly the same tube and was dirt cheap.

Thanks for the thoughts on the transparency of the Harrison attenuator. I think I will order a pair to explore.

Also thanks for the caution on software attenuation. I am not very up on the software tech stuff, but PureMusic is a pretty sophisticated software which I have found I like the sound of quite a bit once I learned how to adjust all the various parameters to fit the best case tech objectives, and my tastes.

I can't say if I am lowering bit depth by software volume reduction. As far as I can tell from the instructions and sound though, I think I may be OK. At first I avoided any messing with dithering wanting the purest setup with my DAC. But as I got to know the software, I found that I generally agreed with the software makers sonic decisions and learned their tools. The program runs at 64 bits and does all dithering at 64 bit, so when the gain is set to be dithered, I think it is processed at 64 bits for whatever sampling you have it set for in relationship to the DAC. I do get nervous about reducing the gain with Pure though as I have never figured out clearly if there is not some minor sonic sacrifice. That said, the way I have it set up, I prefer it over what seems to be the favorite Mac software player these days...Audirvana Plus.

Any more thoughts are welcome.

Looking forward to your explorations.


Title: Re: ZSTrAnGE observations
Post by Zilch0 on 05/30/13 at 23:49:35

Hi Will,

From the sounds of it, it's possible that your software is smart enough to avoid reducing bit depth when adjusting the "volume" sent to the DAC.  I really can't contribute much more to reassure you, but I do know that you'll want to keep your OS volume control turned all the way up, in any case, as that will definitely reduce bit depth, and therefore dynamics.

I suspect the Mullard 12AT7 that I've ordered from Brent Jesse is the same one you are using.  Here is his description of the tube:

12AT7 Mullard 1965 dated, selected and audio quality screened for Wollensak-3M

New Old Stock whitebox. "Wing shaped" riveted greyplates, fine old British tubes. These rare tubes all have the same 1965 Blackburn UK Mullard factory date codes, and were screened for use in Wollensak 3M audio and recording equipment, and have the Wollensak-3M label. They also have the B date codes and "Made in Great Britain" on the glass. Job-boxed for repair service use, but never used. They were carefully stored, and now, 50 years later, they still test and sound as fresh as the day they were made. Don't miss out on these absolutely NOS tubes that are fantastic in guitar amps as well as the most revealing audio and professional recording equipment!

It should be here soon, so I'll be sure to follow-up with my findings.  I'm as much interested in the warmth it will bring to my somewhat cold Beyerdynamic T1 as I am interested in finding out how it behaves in the ZSTAGE, being that it is a 60 mu tube, with three times the gain of a 20 mu 12AU7.   I'm really encouraged by your use of this tube (or 12AT7's in general).

More later!



Title: Re: ZSTrAnGE observations
Post by will on 05/31/13 at 16:08:20

Yes the OS volume is up, and most OS system and audio bypassed for optimal music playing. Not sure from the Mullard description if this is the same tube or not. They made a lot of tubes! But of the few Mullards I have tried, the 12AT7, some 6DJ8s and 6922s, they did make really good sounding tubes by my tastes. The higher output of the AT7 will show up for you, but maybe not quite as expected... I look forward to your thoughts and hope the tube sounds good in your system...

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