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04-28-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	21
Post ID:	25392
Reply to:	25388

You may well be right...

...especially about the difficulty of making a transparent preamp. It seems to be a general concensus.

But I need gain for most of my sources apart from perhaps the FM Tuner. The dac, pc streaming, future cd/bluray/dvd player all will have 2VRMS output or less and there is no way to change this. Perhaps the phonostage will have enough gain, I am not 100% sure, but even in the best case 3 out of 5 sources will require more gain. I just had a look at the thread about your new Placette gain stage and it looks like x4 is possible. This is certainly enough for all sources but the Phasure dac as I run it now. Perhaps I should do some experiments with less attenuation that -6dB as I am running now: -3dB will give me 0.94V output, -1.5dB will give me 1.1V output. Multiply those by 4 and we have enough gain. Actually, I should run a sine wave through the dac and measure the output myself rather than relying on specifications.

I do really like the idea of just getting more output from the dac, but Peter seems reluctant.

Romy the Cat wrote:
Ok, thanks for explaining. I few things I would like to note.

I need to say that I am not exactly understand the Phasure ecosystems. It is DAC that works only from software player and if it so then why no one talk about the sources of the material that is being played. There is a huge difference between ripped CD and raw digital files, how the files were ripped and many other subjects. I do not understand the notion of volume control at software and DAC level and many other things. Not that I need to but I would certainly would like any attention at digital level to be wide open. It sounds to me that Phasure has SS chip in the output and this is where you can experiment. There are new op amps out there that reportedly good you can play with them; I so feel that the absolute transparency you will find at SS level not at tube level.

Rgs,
Romy the Cat

The software that Peter has written, XXHighEnd, is very successful with minimising the effects of computer hardware on sound quality. He has been doing it a long time and in my opinion is THE pioneer in the field...two steps ahead of the next guy and five steps ahead of most. Much of this is because he not only writes the software but he designs the hardware (dac) as well, and he has set up an ecosystem that either sidesteps the cause of the problem in the first place or the software attempt to minimise the damage.

So the Phasure NOS1a G3 is a non oversampling dac using I think eight PCM1704K chips. It is DC coupled, PCM only, has zero digital filtering onboard, and zero sound processing, upsampling, oversampling or anything like that, and no volume control. It is also a single input dac...USB only from a computer. The onboard FIFO buffering and galvanic isolation on the USB input is current state of the art...but the computer hardware and software still affects sound. It is a one trick pony because it takes whatever the computer sends and does not mess with it...it just plays it, whatever it is.

The software on the computer, XXHE, does the upsampling and digital volume control. Redbook is generally upsampled x16 (this is configurable) to 705k and digital attenuation applied to a 32bit upsampled file. Also, the digital filters are applied during upsampling and there are a number of filters available including one called ArcPrediction which has zero pre or post ringing. As far as I am aware this is the only zero ringing digital filter in existence and Keith Johnson of PM2 fame did not believe that such a filter was possible, but it is possible if the filter is applied in software before it is sent to the dac.

So the general workflow in XXHE is as follows:

Create your playlist or select your albums in the XXHE library.
Press play. XXHE then upsamples your music, applies the digital filter, loads it all into RAM (sounds better), then shuts down the operating system so that only a handful of process remain running, slows down the cpu so that it is almost stalled, sends the music files to the dac, shuts down the computer screen and displays a wallpaper of what is playing.
Then the music starts (and sounds great)
You can change volume with keyboard commands, or if you are running the whole thing from a tablet (which I do) you just press a button on the tablet and the volume is changed.
At the end of play, or when you cancel play, the screen comes back on, the operating system comes back to life, the cpu is sped up so things go faster and you are returned to the library in XXHE.

It is a different workflow to all other software, but it works and the sound quality is definitely improved. It is a bit slow though. Romy, you should hear the difference between various operating systems, even different versions of the same operating system.

So yes, as Rowuk mentioned above, Peter is definitely "experimental". He is the bleeding edge of digital (just need 3V output from the dac).

04-28-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	22
Post ID:	25393
Reply to:	25391

We have different definitions of streaming

Romy, I like many, would define streaming as the "live" playback of files (that you do not own) as they are streamed from the internet. Youtube is streaming, the Tidal app is streaming.

I would call playback from files stored on a computer as simply "computer playback".

As yes, mastering is THE big thing thing for quality of sound. It is the very reason that I am going back to the technically inferior LP's.

04-29-2019

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rowuk

Germany
Posts 454
Joined on 07-05-2012

Post #:	23
Post ID:	25394
Reply to:	25392

Experimental is not bleeding edge.

Alrhough the phasure stuff does sound very good, I do not consider it to be “the bleeding edge”. I consider a preamp allergy to be very typical of those “making a point” for instance! Declaring that only 0.6V sounds good on the DAC demonstrates yet more DIY mentality. Please do not forget that Peters 2 way speakers are open back, use DSP correction and “modified” BMS coaxial compression drivers. With those “references”, he is describing a “different” Sound than is possible with the Melquiades/Macondo.
Phasure is more of an exclusive club to me than a playground for bleeding edge technology.

You made some system decisions and this requires some thoughts and actions about gain management. Peters stand - no preamp means that you are stuck with “other” amplifiers and speakers. It sounds to me like you need a different DAC (of which there are enough to select from). On the other hand, if you have the balanced output, more gain could be as easy as a transformer.

Whenever I feel blue, I start breathing again.

04-29-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	24
Post ID:	25395
Reply to:	25394

It's 1.25VRMS output

Rowuk, a couple of corrections, but I am certainly not arguing. First, the dac outputs 1.25VRMS, or thereabouts...I am going to measure it. The 0.6VRMS is because I run it at -6dB into the Placette because for some strange reason it sounds better. Other than full blast, -6dB is the only attenuation I have tried. With my SS amp and 86dB speakers this is well loud enough in my room.

Secondly, the speakers Peter has are three-way, and as far as I know Peter only designed the crossovers and the DSP in the bass. I don't know how they sound. I would think that they can sound very good, but I have never really been fan of open baffle bass/anything.

Yes, Phasure are sort of an exclusive club. Peter seems to make a lot of personal connections to people on the forum and I think he prefers to operate that way. It is not a trivial digital ecosystem to get into, it can be quite complex, and the personal connection certainly helps Peter get things running for his clients. But I also look back at the things that Peter has done first in digital and wonder how he could not be at the bleeding edge.

No balanced output on my NOS1a. I had it removed and replaced with BNC, so my dac is singled ended output only.

04-29-2019

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	25
Post ID:	25396
Reply to:	25392

Sometime a cigar is not a just a cigar..

Anthony , having a room slightly bigger than your and the rest the same I feel that 3V I get from my frond end is just barely enough. I have some CD recordings that are have very low compression and recorded with wide dynamic range (Pop Music’s Gogol Suite for instance) that I run at full volume and wish I had a few DBs more. Granted that I have a tendency to hear much louder if I want it. Try the Gogol Suite’s Ferdinand coda and tell me if it is possible to hear it at low volume. Get only Mark Gorenstein’s version. I think if you get your 3V you should be fine. Ironically you tuner outs somewhere the same, you should have a point of reference. BTW, in you tuner is very easy to adjust the output gain by changing one resistor.

I am not familiar with the whole XXHighEnd ecosystem and I am not so savvy in digital topologies to be able to associate or another DAC design decision with predictable results. I might repeat what others say but I never had my own experimentation with digital other than listening ready to go commercial units. The minimization of sound processing in Phasure DACs certainly very appealing part but many people do it or claim to do it with very different outcomes. I am a bit concerned that you guys stay purist refusing DSP in DAC but at the same time tolerate digital volume controls (typically horribly implemented) on you playback software.

There is another concern of mine that I would like to voice, primary that I pick up from you explanation of streaming. I call streaming a process of playing files stored on a computer or what you call “simply computer playback". The process of streaming from Youtube or from any other public providers I would not call streaming in contest of high-end audio objectives. I stream concerts from zillion sources, I love your Australian Broadcast Corporation Classic FM BTW, but I would never consider to make any audio session base upon that streaming. In fact I very rarely use main system to play THAT time pf the streaming, this is what pilot playback is for. Here is where I would like to propose a suggestion and I am not convinced that I am right. It is possible that in some cases playing those bad streaming sources some digital processing can “improve” a perceived sound but the same digital processing will not be beneficial with better digital sources. So, what I would sagest you to do is download some kind of very good digital files of know quality (there are plenty of them around) and use THAT for sound check, not some kind of Youtube streaming.

Sure, there is another concern. :-) I am not sure how to explain it. Try do not feel that I am trying to make an effort to compromise you judgment. I am trying to identify the differences between your and my methodological approaches. From what I hear from you it seems to me that have more tendency to practice “delta listening”, where one component is evaluated against another. This is certainly a legitimate way to go and it is widely practicing by audio people. I do it sometimes but also I frequently practice different assessment paradigm. What I do I discard the given performance of a component A and component B in comparative terms and I evaluate the sound of component A and component B against an abstract model of sound that I have in my head. I just listed the music, a specific interpretation, I know what I need to get out of this or that interpretation, and I impersonate myself as I am a conductor who want to stress this or that aspects of a given reading. Then I can see how the component A and component B help or prevent me to do it. The irony is that using this evaluation techniques many surrogate criteria of common audio evaluation juts stay outside of prentices and not in play anymore. For uninformed person it sounds like capitalized subjectivism but the really is that this is the only objective method of audio expletives know to me. If you hear a sequence of notes properly done and you know with very high level precision the amplitude of let say patriotism in that phrase then the component A witch does it properly will automatically have all pure audio tricks done. The complexity come when component B delivers higher amplitude of that patriotism then you expect. Does it make the component B “better”? Not necessary and it take some time to understand it within yourself. You need to work with yourself, your undersetting of the work, learning about the performer and circumstances of the play, the recording techniques, listen many other interpretations, listen your own objectives and interests…. then the answer of “interpretation properness” will come to you. A component that “helps” you and that create less ambiguity of your own confusions should be recognized as better. A component that will push you for more polar or radical interpretations should be recognized as better but it has to be viewed in context of other this as well. A component that pushes you listening preferences away from bad music or weak interpretations should be recognized as better.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

04-29-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	26
Post ID:	25397
Reply to:	25396

So playful

I cannot find the Gorenstein version of Gogol Suite in Australia but it is available on Discogs and Amazon overseas for extortion prices. Streamed it from Youtube, not Gorenstien, but someone else, and it really made me smile. Listened to another version on Tidal, but not as playful a performance. I do like it.

ABC Classic FM is pretty good. I have it on the radio in my ute all the time and have picked up some gems over the years. Mind you it is the only classical music station on our airwaves, at least where I live, so I have nothing to compare.

As a general rule my digital sound quality list is as follows, from worst SQ to best: Internet streaming via Youtube >> Internet streaming via Tidal >> playback from local computer files via XXHE, whether they are downloaded from Tidal or ripped from CD.

To my way of thinking apart from Youtube MP3's, the difference in sound between internet streaming from Tidal and playback of those very same downloaded files is computer hardware, and how it is managed. XXHE does this management brilliantly.

Mastering to me is a whole other thing. I am getting back into vinyl because it gives me access to different mastering. So much of the music that I listen to is compressed rubbish but I still manage to adore it no matter how much I wish the compressor stayed out of the production.

Yes, I certainly do practice delta listening, at least from time to time. It is useful in particular circumstances where I am trying to figure out if I should sell my dac for another one (haha) but unless one has an eye for the "whole picture" delta listening can be detrimental. A good example of this is the Killerdac that I mentioned earlier in this thread. It is so, so good at what the owners listened to that I was envious, but when it tried to play my kind of music it fell in a pile...it was not even good. The dac had been infinitely tuned and tweaked selecting this tiny length of "god" wire here, this particular $$$ capacitor there, this particular resistor there et cetera and perhaps the tweaker only listened to the same narrow music selection (I don't know if this is true, it is just a guess) the dac was a fail with complex music. Anything that does not sound good on the Killerdac is said by the group to be poorly mastered or compressed. Well, I don't know. Maybe they are right. The implication of that thinking is that when playback attains a "certain level" you can only stand to play be best recordings? I don't buy it. And I don't want that. Well I do want to get to that "certain level" but in doing so I do not want the poorer quality recordings to sound more like festering turds than they do on a lesser playback, because I like a lot of poorly produced music. If they sound ordinary that is fine, but not worse, surely.

So, apart from the delta listening, I also practice long-term listening where I let things sit and not think about them. I get to play whatever music my mood determines for a week or a month. Sometimes there are certain things about a change that I enjoy at first but it has some detrimental side-effect that I did not notice at first. Digital is like that, at least to me. Mood is such an influence on my musical enjoyment: I hear things differently if stressed or happy or introspective or busy or if I expect something to help or am ambivalent about a change. Long-term listening evens out those mood peaks and troughs and lets me figure out what it is that satisfies me.

Romy the Cat wrote:
Does it make the component B “better”? Not necessary and it take some time to understand it within yourself. You need to work with yourself, your undersetting of the work, learning about the performer and circumstances of the play, the recording techniques, listen many other interpretations, listen your own objectives and interests…. then the answer of “interpretation properness” will come to you. A component that “helps” you and that create less ambiguity of your own confusions should be recognized as better. A component that will push you for more polar or radical interpretations should be recognized as better but it has to be viewed in context of other this as well. A component that pushes you listening preferences away from bad music or weak interpretations should be recognized as better.

I am on-board with this style of thinking, but am not "there" yet. Here is an example of "learning the performer and circumstances of play" and "interpretation properness" and "more polar or radical interpretations". I have had a musical crush on Beth Gibbons since I was young and she was the lead for trip-hop duo Portishead. Her solo album is still played regularly. For this work she learned to sing the Polish lyrics to Gorecki 3 and absolutely nailed it I think. Certainly not a traditional interpretation or performance but she is the queen of mourning and loss and does it as only she can. I love it...you may disagree.

Here is the Tidal link...for a better quality version.

...or the second act on Youtube

https://youtu.be/zrYxBNziy24

04-30-2019

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	27
Post ID:	25398
Reply to:	25397

An adagio...

Yep, the Gorecki 3 is a famous work. There was some controversy around. Jewish interests highjacked the work it as the Sorrowful theme of Holocaust but Gorecki admitted that it was not his intention although closer to the end of his life he was more included to agree with jewdification of his work. I do not like the cheap publicity. If the society feel so companionate about Holocaust then Pease Nobel Peace in 2007 should not be withdrawn from polish lady Irena Sendler and be given to a multimedia clown. Anyhow, if you like Gorecki 3 then you might try the Andante from Mahler 6 symphony.

https://www.youtube.com/watch?v=LyrBhI7LrcU

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

04-30-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	28
Post ID:	25399
Reply to:	25398

I finally measured the dac output

...and it is a neat 1.5VRMS with zero attenuation. So with my -6dB it puts out 0.75VRMS, so not quite as bad as I thought. I will have to do some listening to try and determine whether -6dB is needed or if I can get away with less attenuation (zero would be ideal).

Last night I did the maths on the LCR phono that I intend to build and it should have 0.9V output with a balanced SUT or 1.8V output with a singled ended SUT, which equates to 73db-79dB total gain. Again, I wish there was more output but it is what it is. The balanced input is roughly the same as my attenuated dac.

Also, I've contacted Guy Hammel about a Placette line amplifier so I will see were that goes. I do not want another box so it is going to have to fit into the current linestage box if I decide to go that way. This afternoon I will order a bit more stuff to finish my diy SS pre with gain and try to get it finished as quickly as I can so that I can measure just how much voltage input I need for the DSETs in my room.

05-04-2019

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Paul S
San Diego, California, USA
Posts 2,672
Joined on 10-12-2006

Post #:	29
Post ID:	25401
Reply to:	25390

Burson and SMD

Anthony, looking again at a possible least approach for upstream gain for your developmental stage, I thought the Burson "discreet" OpAmps were often used as "substitutes" for more typical SMD type op amps, and therefore SMD compatible. Since I don't have gain problems, I still haven't invested much time on this but only followed up out of curiosity.

https://www.diyaudio.com/forums/parts/290827-burson-supreme-sound-opamp-v5-experience-4.html

Setting aside the evaluations, it seems like there is the potential for relatively inexpensive, reasonably painless gain, along with local parental support, given the clean PS and DC blocking also mentioned.

Best regards,
Paul S

05-10-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	30
Post ID:	25404
Reply to:	25399

The Placette has died

Well, probably not up in smoke, but it is just not functional any more. I was away for a few days and came back to my room to find the Placette refusing to change volume or select a source input, so something is amiss. Perhaps something has been amiss for some time which may explain why I have not found it as transparent as Romy and others.

There is no time at the moment to look under the hood for the fault. I've been listening to my dac directly connected to the DSET and it is so nice...but not loud. The amps are getting the full 1.5V output but it is not loud enough, of course.

On another point, I have been reading a little about pre-amplification and current output and output impedance. Up to this point I had not realised that the ability of a preamp to drive capacitive loads has almost nothing to do with low output impedance, but is all to do about current output. A beast such as the DSET with 6 x triodes and a few inductors and capacitors at the input is likely to be a mighty capacitive load. This needs to be measured. If one stage cannot sink enough current into the next (i.e. the current clips) higher frequencies will roll off. The limiting factors are input capacitance of the DSET, desired frequency response, preamp voltage output and desired headroom.

DSET Input Capacitance: to be measured
Desired Frequency response: The RAAL ribbons are good to 50kHz or so I think, so I choose that
Preamp voltage output: 4VRMS to drive DSET to clipping
Desired Headroom: x10 (20dB)

So, I have to measure the input capacitance of my DSET and then do some math to figure out how much current my preamp needs to produce in order to satisfy the load.

05-11-2019

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	31
Post ID:	25405
Reply to:	25404

Not necessarily...

anthony wrote:
Well, probably not up in smoke, but it is just not functional any more. I was away for a few days and came back to my room to find the Placette refusing to change volume or select a source input, so something is amiss. Perhaps something has been amiss for some time which may explain why I have not found it as transparent as Romy and others.

Ok, your Placette did not die. This is “normal” for Placette, I wish it did not have it but it does. The way how Placette is made it need to be plug in all time. If you unplug the Placette for prolog period of time then it need a few days to be powered to have the remote control functionality start operating again, the manual controls still should be working, if you have them. So, let it run for a day or two and your Placette’s control will be back. Another very important thing. The Placette is powered by main 120V power that drive output stage and by flimsy computer-grade low voltage adapter, connected separately. Why Placette was made this way is beyond me but it is what it is. The voltage adapter should be not in operation after the volume was changed so, it should not be a factor in quality. However, over the years I have seen that the low voltage adapter get weaker and impact the remote control functionality. Also, the type of the low voltage adapter I used did have very profound impact to sound, which absolutely makes no sense. I had 4 or 5 of them over the year and the difference was very noticeable. Again there is no explanation for it but it is what it is. Ask Guy to send you a new power adapter, it costs like $20-$30, and you might find that it worth it.

anthony wrote:
On another point, I have been reading a little about pre-amplification and current output and output impedance. Up to this point I had not realised that the ability of a preamp to drive capacitive loads has almost nothing to do with low output impedance, but is all to do about current output. A beast such as the DSET with 6 x triodes and a few inductors and capacitors at the input is likely to be a mighty capacitive load. This needs to be measured. If one stage cannot sink enough current into the next (i.e. the current clips) higher frequencies will roll off. The limiting factors are input capacitance of the DSET, desired frequency response, preamp voltage output and desired headroom.

Yes, it is factor but it is also not. There are very few topologies that can give out a very low, let say sub 10R output. Mostly we are taking about SS DC coupled topologies… It happened that in the realm of a few oHms output any devise will drive a capacitive load.

PS: I need to say that the subject of you post “The Placette has died” make me to cringe. I imagine if my Placette dies then why the hell I would be doing!? In my experience it is VERY hard to find sub 10R pream with proper sound and if my Placette died it would be a disaster for my system

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

05-13-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	32
Post ID:	25412
Reply to:	25405

The damn wall wart

Romy the Cat wrote:
However, over the years I have seen that the low voltage adapter get weaker and impact the remote control functionality. Also, the type of the low voltage adapter I used did have very profound impact to sound, which absolutely makes no sense. I had 4 or 5 of them over the year and the difference was very noticeable. Again there is no explanation for it but it is what it is. Ask Guy to send you a new power adapter, it costs like $20-$30, and you might find that it worth it.

Interesting. Yes, the remote has been suffering from reduced functionality but the batteries still measured 1.5V each so I put them back in. The wall wart getting weaker might be the problem. Since it has arrived, I've run the Placette from a step down transformer feeding it about 120V instead of the normal 240V in Aus. To achieve this both the power cord and the wall wart for the Placette are plugged into the variac, which I had forgotten about until I turned it off the other day. The wall wart power is used only to change the relays and should be plugged into a different, general household, power circuit to the power cord for the linestage circuits, and of course I have never done this because I have only one variac to step down to 120V. The long-term intention was always to change-out the transformers and wall wart to suit 240V mains so I can plug things directly into the wall, but it has never happened.

I must say that with the Placette turned off the Phasure dac direct driving the DSET has never sounded so good. Perhaps my Placette transperancy issue is caused by the wall wart injecting noise into my audio mains circuit when it should be injecting it into a different circuit. Perhaps it is the variac causing the issue, or even the Placette itself as I originally thought.

First thing to do is make good on converting that wall wart to 240V so it can be plugged into a different circuit. Output according to the label is 5V 1A, and I have some linear power supplies already made for a different (abandoned) project that will handle that easily. So when I get some time I will re-purpose one of them and experiment further with the Placette.

Romy, thanks for your input here, I had put looking at it in the "let's do that later" basket which probably means quite some time down the track. I would be interested to hear roughly how the different power supplies have changed the sound, and if you plug the wall wart into a separate non-audio circuit or if it goes into your PP3000.

05-13-2019

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	33
Post ID:	25415
Reply to:	25412

My experience might be limited but....

Come on, Anthony, you need to “clean your room” as Peterson say before you move forward. Variac is notoriously bad for sound, at least 3 types that I tried were horrible. I do not see why Placette cannot run from 220V, confirm it with Guy. Both line stage circuits AND the adopter that powers the switches circuit MUST be plug into good quality of power source. The adopter that powers the switches in my view much be replaced each 3-4 years and they get weaker for some reasons. Each time I updated my adopter I got better sound, do not ask me why as they should be affecting sound at all. Be advised that I still at suspicion of what you do as I personally do not feel that your DAC can stress Placette into being not transparent. I owned some nice gear and I NEVER was able to recognize Placette as being less transparent element in chain. I do not insist that I am right and I understand that I should not never say never but from what I have done personally I feel that Placette is quite unique in term of bypassing performance.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

05-13-2019

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anthony
Posts 338
Joined on 08-18-2014

Post #:	34
Post ID:	25420
Reply to:	25415

It's not just the dac...

...there is a degree of "sameness" with all sources into the Placette. It may just be the variac or the wall wart or both.

I talked with Guy back before I made the purchase and his recommendation was to use an external step down transformer rather than replacing the internal transformers. Well I do not have a step-down but I do have the small variac so that is what I used. I just pulled the lid off my Placette and the power transformers actually have dual 115V primaries, so I will be able to convert the unit to 230V operation. Everything is glued down in there and directly soldered in place so I will talk to Guy first before I make the change...it might be a little bit tricky.

08-03-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	35
Post ID:	25901
Reply to:	25420

DHT Preamp update

So, it has been a while. I have DSET/Macondo in stereo now although there is still some work to do to finish it and tune it to the room. As discussed earlier in this thread I need a preamp with gain and the Placette is just not cutting it for me (no gain). There are three sources for which gain is needed: 2 x phono stages; and dac.

Over the weekend I prototyped a 10Y/801a/VT25/VT62 preamplifier just on a lump of MDF. It uses one of Ale Bartolas Hybrid Mu-Follower boards, a regulated B+ power supply and a locally designed CCS for the DHT filaments and Slagle Autoformers at the output for volume control. The build was relatively simple and trouble free, and when finished it had something like 0.003mVDC on the outputs but a little (3mVAC) AC pickup up through the autoformers (they will require better separation or shielding). Plugged into the DSETs the preamp is silent...no noise.

Output impedance is about 30R before the autoformer, gain is x8, but the autoformer reduces the output impedance logarithmically with attenuation so in normal or even loud use case is going to be 1R or below. 20mA plate current.

Listening to it tonight for the first time I am really hopeful that this is a good solution. Still the honeymoon period but it seems to have hit quite close to the design brief in terms of loudness and sound quality when driving the DSETs. No signs of lag or loss of detail or softening of the sound or overt warmth. I have three SS gainstages here that also get the volume, and this DHT preamp seems to be everything my favourite is and more, at least on the phonostage I listened to tonight.
All dressed up.jpg

08-05-2020

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	36
Post ID:	25902
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Very interesting, how does it Sound?

Hm you are true in the “terra incognita” territory as far as I concern. The preamps are mystery to me. All my attempts to make any decently sounding preamp or even buffer failed. To me Placette was truly God sent and if I got burned that I am looking with fear what will I do.

The idea to make a tube-based preamp is noble one and 10Y is a very good tube. The 30R before the autoformer is good and if you are able to drive it lover with autoformer them it is wonderful, even I am not so comfortable with the ideas of autoformers. The changing preamp output impedance is very bad for the Milquades as each preamp output impedance will change the setting of the input filters. However, if your impedance slides under a few Ohms then it might have no auditable impact at all. You can calculate how your moving output impedance impacts your amp filters. I do not care about the fact that it moves a few Hz up or down. I am care about phase. If you time aligned two channels and move volume of your preamp, then will the changing the preamp output impedance result the channels juts out of alignment? They certainly will BUT the it is possible since the impedance number are so low the timing error will be very much within the margin of errors of your time alignment.

I do not have the answer if the changing of the Rout would be prohibitive in this situation. What I would like you to consider is that in 10 years you will find your DPoLS and then you might realize that your playback can maintain the DPoLS only with let sat 30% of your volume and then the phase micro-shifts kick the system out of DPoLS. I do not mean to “scare” you, juts present you an architectural concept.

Romy the Cat

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

08-05-2020

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Paul S
San Diego, California, USA
Posts 2,672
Joined on 10-12-2006

Post #:	37
Post ID:	25903
Reply to:	25902

Active vs. Passive Placette?

Anthony, congrats on your amazing progress! I know how hard it is to carve out time for this stuff! I see you are looking for gain from your pre-amp, which makes me wonder if you have been using the passive Placette, as opposed to the active unit, which I understood has +6 dB, not to mention a VERY low, locked output impedance. What I am getting from Romy is that a constant, very low output impedance from the pre-amp is as critical for driving your Milqs properly as the input voltage. Not to steer you toward greater expense, but it would be a shame to put out all the time and effort building a pre-amp only to wind up with a reactive situation, where your channels' crossovers are in constant flux. With all the complexity of the greater circuit here, it would be nice to start with pre-amp output locked down. But perhaps you've already considered this fully with the design you're working on?

Best regards,
Paul S

08-05-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	38
Post ID:	25905
Reply to:	25902

Nice

Romy the Cat wrote:
Hm you are true in the “terra incognita” territory as far as I concern. The preamps are mystery to me. All my attempts to make any decently sounding preamp or even buffer failed. To me Placette was truly God sent and if I got burned that I am looking with fear what will I do.

Early days of course, but at the moment the 10y preamp sounds nice. I do like it. There may be ways to wring more performance from it and I am mulling over several alternative options for loading the tube. No doubt those DHT's do enable something nice with the sound, that hint of extra dynamics not really heard elsewhere.

Romy the Cat wrote:
The idea to make a tube-based preamp is noble one and 10Y is a very good tube. The 30R before the autoformer is good and if you are able to drive it lover with autoformer them it is wonderful, even I am not so comfortable with the ideas of autoformers. The changing preamp output impedance is very bad for the Milquades as each preamp output impedance will change the setting of the input filters. However, if your impedance slides under a few Ohms then it might have no auditable impact at all. You can calculate how your moving output impedance impacts your amp filters. I do not care about the fact that it moves a few Hz up or down. I am care about phase. If you time aligned two channels and move volume of your preamp, then will the changing the preamp output impedance result the channels juts out of alignment? They certainly will BUT the it is possible since the impedance number are so low the timing error will be very much within the margin of errors of your time alignment.

I do not have the answer if the changing of the Rout would be prohibitive in this situation. What I would like you to consider is that in 10 years you will find your DPoLS and then you might realize that your playback can maintain the DPoLS only with let sat 30% of your volume and then the phase micro-shifts kick the system out of DPoLS. I do not mean to “scare” you, juts present you an architectural concept.

Romy the Cat

I am not sure how phase changes depending on the activated winding of the autoformer, unless you are saying that the preamp Zout will possibly change the DSET filter phase somehow?

Below is an old DSET input impedance measurement. I bumped the 10kHz Channel F filter aircaps upon reassembly and did not bother to reset them (better to get the amp into the room) so above 10kHz may not be indicative. The green phase and yellow impedance lines deviate near each of the crossover frequencies but phase is pretty much well controlled until the highest octave or two, near the bad filter. This measurement needs re-doing.

DSET Input Impedance 2V Pink Noise FFTsmaller.jpg

DSET Input Impedance 2V Pink Noise FFTsmaller.jpg

With the autoformer at the output of the preamp, impedance will vary from 30R to 1R in my normal listening volume range. Of course I can swap it to the preamplifier input and have 30R full-time regardless of attenuation.

08-05-2020

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anthony
Posts 338
Joined on 08-18-2014

Post #:	39
Post ID:	25906
Reply to:	25903

Active for sure

Paul S wrote:
Anthony, congrats on your amazing progress! I know how hard it is to carve out time for this stuff! I see you are looking for gain from your pre-amp, which makes me wonder if you have been using the passive Placette, as opposed to the active unit, which I understood has +6 dB, not to mention a VERY low, locked output impedance. What I am getting from Romy is that a constant, very low output impedance from the pre-amp is as critical for driving your Milqs properly as the input voltage. Not to steer you toward greater expense, but it would be a shame to put out all the time and effort building a pre-amp only to wind up with a reactive situation, where your channels' crossovers are in constant flux. With all the complexity of the greater circuit here, it would be nice to start with pre-amp output locked down. But perhaps you've already considered this fully with the design you're working on?

Best regards,
Paul S

Hi Paul,

Yes, I definitely have the Active Placette linestage, but it is unity gain only. I have talked to Guy about sending it over to him to add a bit of gain but have not progressed on that front. Freight over the Pacific and back will be significant, especially these days, and I am not 100% convinced it is the best option for me. It may be the best option in the end but I would like to try to sort out my own preamp incarnation to see what I can achieve. There are several features that I would like to build into my diy pre that are not available on the Placette: HT bypass, switch between SS and DHT gain/line stages, networking options etc. It will be the hub of my system.

Anthony

08-07-2020

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Romy the Cat

Boston, MA
Posts 10,184
Joined on 05-28-2004

Post #:	40
Post ID:	25907
Reply to:	25905

Of cause but I do not know if it maters.

*** … unless you are saying that the preamp Zout will possibly change the DSET filter phase somehow?

Yep, this is exactly what I am saying. Look the impedance of your preamp is factored in the source impedance of your channel’s filter. The argument you can make is that your channel is approximately 5kR each and your Zout is let say 20R. it very much might be negligible, but it might be not. You might see if the frequency crossover point change if you short the amp inputs vs load it with let say 50R. It might not have any practical meaning but on theoretical level the crossover point will certainly move, so will be the phase shift. What I would do is to listen a recording with very complex multi-layers imaging and see if the imaging will “curve” with the change of the preamp volume.

"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche

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