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Old 25th November 2012, 11:55 AM   #3091
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Getting the D1 circuit that qusp and opc are involved in. Will get mix xformer so all options will be availsble.
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Old 25th November 2012, 12:10 PM   #3092
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ess9023 can driver direct headphone (Audeze LCD-2 60ohm 91db)

PS if can set bal. with two chip
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Last edited by nicoch58; 25th November 2012 at 12:22 PM.
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Old 25th November 2012, 12:26 PM   #3093
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yeah well I consider that folklore, high output impedance and current limiting make driving LCD2 and other headphones directly with es9023 an unfriendly concept.

it is possible to take minimalism too far.

power to you if you are getting good sound, really. I just think this gets posted around a bit too much and any cases it works properly will be rare, also lacking volume control

going balanced will make them work harder

Last edited by qusp; 25th November 2012 at 12:48 PM.
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Old 25th November 2012, 12:29 PM   #3094
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@ ZM : optimized? hmm maybe not, just used passive IV into TX, but i'm pretty addicted to the NTD1, nothing ive tried since has really done it for me, I had planned on using something else for the tweeters, but i've just ended up buying parts for another D1, despite the fact I will end up with a 4 channel dac that dissipates about 100W in the IV stage and is as big as a poweramp....

i'm just not sure its possible to match, nevermind better the opc/pass NTD1 with transformers. Matching as it does, the THD and detail a high quality opamp IV, but with no global feedback and less than a handful of parts in the signal. it gave me that ease of sound but without paying the penalty in detail.

Besides i'm pretty keen on drawing a line under the dac section of my rig, being 4 x balanced mono with another 2 channels on the way, to replace it would not be a cheap or efficient exercise, so I shouldnt really even consider it; but it wont stop me trying it since i'll have the parts on hand. there are other things that need attention, i've spend too much focus and budget on the dacs as it is.

feed it direct and you have issues of loading the dac and added parasitics, non-linearity, feed it through passive IV first and you lose in performance. a jfet or mosfet follower/buffer/current conveyer could be placed in front of the TX to drive it and do IV in between, but then thats basically the D1 + F6

i'm also not prepared for urushi painted permalloy cores built by ninja artisans $$$$

I do like what you and AR2 did with his Ackodac and jfet buffered TX, bet it sounds great, but best I continue with my best foot forward in the direction I have started

but enough on this topic probably. I wish we had those spoiler 'click to show' objects some other forums have. It sounds like i'm sorted for TX, I have 18vac/300VA antek tx, I have the jfets, I jave most resistors; are there any other really critical parts you guys are discovering have a profound effect? everyone is using LEDs or zeners for references?

Last edited by qusp; 25th November 2012 at 12:55 PM.
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Old 25th November 2012, 12:39 PM   #3095
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Quote:
Originally Posted by qusp View Post
...

it is possible to take minimalism too far
pretty straightforward - cartridge's needle right into the vein

or , if you want it permanent - you can always (black humor mode on) - just take Syd Barret's approach - " one day almost genius , another day without any needs"


regarding DACs - for my modest and limited experience - nothing beats differential I output DAC(s) directly feeding xformer primary , with appropriate load strictly on secondary , followed by either SUSY or Supersymmetric ( or mix of two) gain stage

using xformer in I/V just as amplification device , not I/V conversion itself , is .......... say it mildly ........ stubborn and not elegant

and I saw that more than once , unfortunately not just hyped out of proportion , tnx to power of web
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Last edited by Zen Mod; 25th November 2012 at 12:45 PM.
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Old 25th November 2012, 01:30 PM   #3096
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Originally Posted by Zen Mod View Post
coffee is brewing , now ... so take this with grain of salt
why is "buffered" still on attached sketch ?



best arrangement is when lunch is right between two coffee sessions

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Old 25th November 2012, 02:45 PM   #3097
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Originally Posted by Zen Mod View Post
not so simple

mainly because of this
Zen Mod: The curve at 39 dB is a bit surprising. It implies that the transformer is performing poorly despite its excellent specifications by Jensen. Its only purpose in the current source amp configuration is to faithfully transmit the input signal, and be unperturbed by its surroundings. You know transformers very well. What's going on?
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Old 25th November 2012, 02:54 PM   #3098
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The capacitance of the windings is high, and this has been amplified by the
output gain of the circuit.

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Old 25th November 2012, 03:08 PM   #3099
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Originally Posted by Antoinel View Post
Zen Mod: .....What's going on?
I can't give you exact recipe , not having experience with exact Jensen type ;

whatever - speaking strictly of xformer - loading each secondary with nominal impedance (150R) will result in better bandwidth

be aware that Jensen guys made it exactly that way

don't think even for a sec that Pa doesn't know that - he just took different approach - to correct entire amplifier , killin' seven flies with one blow

1938 - Mickey Mouse, Minnie Mouse - The Brave Little Tailor - YouTube
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Old 25th November 2012, 03:40 PM   #3100
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Originally Posted by OllBoll View Post
Hello there,

I just read the article some more and stumbled across one thing:

If I understand correctly the circuit should be converted to a current source amp by removing the loop feedback. So my question is, would this be easy to do by simply skipping some parts or would it be more complicated and require redesigning the circuit?

OllBoll: Your questions and Zen Mod's reply post are relevant, and valuable. Please follow this discussion:
  • Withou loop feedback, F6 is a current source instead of a voltage source amp.
  • The open loop gain of F6 is 39 dB [shown in the reply post by Zen Mod]
  • The closed loop gain of F6 is 14 dB.
  • You and DIYers have up to 24dB of available gain to burn [a term used by Mr. Pass].
  • One can methodically apply overall negative feedback [burn gain] like in F6 and end up with a closed loop gain of 35 dB, 30 dB, 23 db etc..
  • As available gain is consumed, OLG F6 moves methodically from a current source to a voltage source amp. Thus, the parent output impedance decreases, its audio bandwidth increases, its harmonic distortion [Zo] decreases etc.
  • One can burn the right amount gain to stop at a Zo =8 Ohms which is the output impedance of the SIT amp by Mr. Rothacher. Or stop at a Zo = 6.5 Ohms to drive the highly acclaimed Arpeggio loudspeaker. Or stop at Zo = 4 Ohms which is like that of the SIT amps by Mr. Pass.
In order to fully appreciate the following paragraph, please go to the thread in the Pass Labs Forum which is entitled "O. H. Schade (1938) meets MOSFETS". Go to post # 29 and watch the video link provided by DIYer avincenty. There is a high probability that the intrinsic pentode characteristics of the output stage in OLG F6 get reorganized to triode-like characteristics as the closed loop gain decreases; just like in the video. This burnt gain in F6 [IMO] is a special Pass Feedback used in his FET circuits like that of Schade Feedback in vacuum tube circuits. Overall loop feedback to a summing juction emanating from the ouput of a current source amp must be electrically different from that emanating from the output of a voltagte source amp and terminating at the same summing junction.
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