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In the Forum: Melquiades Amplifier
In the Thread: Valve Preamplifier for Macondo/DSET
Post Subject: The last paragrapher worth to read a few times...Posted by Romy the Cat on: 8/16/2020
 anthony wrote:
Have put all my DHT's on the curve tracer to see if pairs can be matched for preamp duties.  

 
It was very interesting to read about all of it. If you have a socket for YO186 then you can accommodate all 4V tubes and I site like them If you do have a chance, try the a pre-WW2 RE604. This is a day of all 4V stube, and I do like it for full range applications. It is expensive nowadays however. In Milq you do not use then in full range however.
 
 anthony wrote:
Now that all three are on the same absolute polarity and have been listened to quite a bit I thought it time to write down my impressions.  From least preferable to most: 
….
Dinner is on the table.  I will add some more comments later. 


 
Again, it was very interesting, but… Let agree that methodologically you did not try Placette as it performance was masked out by you need to use your Neurochrome buffer to get gain. Your chain will sound as the worst element is and in case of 10Y you have the worst element removed. I do have high high probability that if you were able to run Placette and 10Y directly then they will sound identical as the same volumes. I think it is simple to test. I do not know what output in your Phasure DAC. Get any DAC with a op-amp in output stage, most of them are. Find where a feedback provided to the output op-amp and reduces it to gain10-12dB more gain from the DAC. If Phasure DAC has no op-amp in output stage, then get any other DAC. The quality of the DAC is not import you need it purely foe prove the methodological concept. Then repeat the experiment. I think that you will find then Placette will hold his own.
 
 
 anthony wrote:
The Phasure dac is completely filterless...nothing, nada, zip.  The digital filter is applied in the computer software and sent to the dac in 32/768 which just plays the file NOS without additional filtering at all.  As such the Phasure dac is wide open frequency wise.  Plus the BNC cables I use are video spec and have something like 1dB attenuation over 100m at 6GHz and they are not filtering any UHF either.
"Ferocious dynamics" is not something that I am associating with the sound that I am getting here from this dac, and sometimes I might correlate that sort of sound to washed out or white mids with an emphasis on highs, but the sound here seems very well balanced.

 
Anthony, this exactly answer all questions then. You need to reinterpret at the result of your experiments in context of what I will be writing now. You see, there is school of thinking that if a DAC operate at very high sampling rate then the post DAC filter is not necessary, or a file might be very shallow as all post DAC nastiness  will be at very high frequency that is very far from auditable range, It is very legitime way of think and indeed some of the systems do sound spectacular wit DACs like this. I did a LOT of looking into it. The excessive HF that is sent by DAC works out ONLY if later one in the chain you have some kind of lowpass filter the strips that HF component. I your case use you 10Y buffer you have via the auto-former that is bandwidth limited. Placette is the worst in your case as Placette has a huge bandwidth, as I told it runs video signal. So, in case of Phasure + Placette you have the whole HF nastiness HF from DAC sent directly to Milq. A reasonable question would be why Power Amps filters do not act as the power is frequency limited as well. The legitimate question to ask but unfortunately it does not work in this way. I have written about it years back. My theory was that audio components get “poisoned” by excessive HF and they have a memory of that poisoning.  Do not ask me to explain it, I do not know how, I am just a practitioner and the depth of electronics design is not a feld that I am interested in. Anyhow. What I say is very easy to test it. Wake your phono stage and disengage your RAAI filter. Play music for an hour. It will be a horrible HF only sound, but you do need to play it laud. Then put the phono filter back and play it normally. It will be sound horribly because you power amp is “poisoned” by HF. It will take a good day of a normal operation to recover good sound from your amp until the HF “poison” will de dissolved.
 
So, I do think that in your case, considering the DAC you are using in case you use too HF transparent preamps you “poison” you power amp with HF. You can put a simple first order low pass subtraction filter before Placette and you will have better sound.
 
So, where it lives you. Obviously if you have frond-end with more output then I am very convinced that Placette will fulfill all your expectations, I am not kidding it is very hard to beat it. However, if you had this arrangement then you most likely would not like you DAC as much as via Placette it would sound not too gentle enough. If you willing to use your DAC then keep your 10Y preamp as it acts a great low pass filter for your system. If you would like to use Placette then you need a DAC with a post conversion filtration (preferably analog) and more output voltage.  
 
What is very important to understand that in case you have both of the scenarios implemented then you should have identical result the end. Another very important message you might consider is that in case of your 10Y the main beneficiary to sound is not the quality of tube or your auto-former but a presence of preamp that acts and post-DAC low pass filter.
 

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