[Mike B.]

Interesting discussion One of the masters of quiet circuits is John Curl. I have read his comments on regulators. He seems to like
power supply circuits with several levels of regulation. If one buys into the idea that the power supply is in the signal path ( Stan Warren ) then I think it is wise to at least experiment with them as a possible avenue of improvement.

[serengetiplains]

That's my pov likewise, Mike.  I go for double-regulation supplies for all critical components, where I feed a shunt reg with a series reg, and feed the latter with its own dedicated transformer to prevent ground current mixing.  Paul's shunt regs are a bit noisier than his series models, but from my and others' experience of these, his shunts are the better performers for digital supplies.  They work best if fed from a very quiet (hence series) supply.  The tx-->series-->shunt topology is very quiet, particularly with AC conditioning on the front end.

Btw, here are basic specs for his shunts:

slew rate 5,000 volts per microsecond
gain bandwidth product 1 GHz
rise time < 1 nanosecond
settling time < 10 nanoseconds
wideband noise 2 nanovolts root HZ
output impedance is less than 0.001 ohm
power supply line rejection ratio is 110 dB from DC to 200 KHz

Compare these specs to HxR specs.

[serengetiplains]

Here are HxR specs:

[jtwrace]

I don't know enough to say how it should be done but I do know this from years of sold engineering.

Implementation is key.  Swapping parts will not always and usually doesn't yield a better result.  It can simply give you a differerent result which often times is taken as better.

EDIT: and this is why objective data is SO important.

[serengetiplains]

I understand that, JT.  Implementation is key and implementation is not all---what is implemented also counts (well implemented junk = junk, or some variation thereof). 

I replaced some smd regs---you know, the 317 textbook-variety that engineers are so fond of---on my Lyngdorf.  The Hynes regs that replaced these were powered by series regs placed some 6" to 8" away, powered by dedicated transformers another 10" away or so.  The shunts added a small amount of overall length to the supply leads.

Let's add up the pros and cons:

PROs
1. vastly better *shunt* end-regulator
2. fed by a vastly better preregulator
3. which for its part is 6-14" closer to the shunt and
4. powered by a dedicated r-core transformer which is
5. less affected by amp-related line disturbances and
6. galvanically isolates the series-shunt combo to eliminate ground current voltage variations

CON
1. one cm added lead length (note: the 317s the shunts replaced are 2" to 8" distant from the chips they power, so I'm unconcerned about adding an extra cm)


There's some objective data for ya.  Listening confirmed this objective data, so I was objectively happy.

[jtwrace]

There's some objective data for ya.  Listening confirmed this objective data, so I was objectively happy.

I prefer the objective measurement data.    

Kind of like this:
http://www.audiocircle.com/index.php?topic=107040.msg1097394#msg1097394

That unit is $10k for the base.  The AP that Hypex (Bruno says they have 4) and many other audio company's use are $40k+.  That's what it takes though....

[*Scotty*]

Before mods can be undertaken someone will have to dismount the board from the "heatsink" and analyze the circuitry. The board is at least a 2 layer board and possibly more and it has been designed to be resistant to cloning which may additionally complicate matters.
It may be awhile before we see any list of recommended mods due to the aforementioned complications.
Scotty

[Rclark]

Yeah, skeptical. After reading the details of how the smps600/nc400 combo work in unison, and given the extreme performance numbers, you are going to have to better those numbers, rather than say "a veil was lifted" after I installed these parts.

[jtwrace]

Yeah, skeptical. After reading the details of how the smps600/nc400 combo work in unison, and given the extreme performance numbers, you are going to have to better those numbers, rather than say "a veil was lifted" after I installed these parts.

WOW.  I'll actually agree wtih you here. 

[serengetiplains]

I think it's a four-layer board, Scotty, so it's worse than you first said.

[serengetiplains]

Kind of like this:
http://www.audiocircle.com/index.php?topic=107040.msg1097394#msg1097394

Here's Bruno.  I'll leave you to gauge the relevance of his comment to what I'm wanting to accomplish by reducing power supply noise (= effectively increasing PSRR).

An FFT of a sine wave says nothing about frequency response, THD at other frequencies or output impedance. Also, it says little about the PSU. An amplifier with bad PSRR on a regulated supply and an amplifier with good PSRR on an unregulated supply post equally clean FFTs.

[*Scotty*]

Speaking of FFTs Mike did one on his Ncore and it looked pretty good.


Link to thread here  http://www.audiocircle.com/index.php?topic=107040.0
Scotty

[serengetiplains]

That unit is $10k for the base.  The AP that Hypex (Bruno says they have 4) and many other audio company's use are $40k+.  That's what it takes though....

I want to comment on this.  I'm just a joe who likes music.  I have no access to expensive testing gear, as very few do, and I lack both technical and training knowhow to operate such.  Do you really expect that someone like me will have proper testing gear?  If you don't, why do you keep asking me (the guy now typing who like most others interested in good music replay has no access to this gear) for objective data that only this gear can provide?  Do you want to relate to me, or are you commenting to some fictional person to make a point that cannot be answered?

[cab]

I think the point is that unless you can back up the changes as "improvements" with concrete gains in measured performance, all you can do is provide your biased self-assessments of the effects, which may in fact be merely differences you prefer, rather than objective performance gains. As a result, while you may prefer the modifications, there is nothing to suggest that anyone else will....

[jhm731]

EDIT: and this is why objective data is SO important.

I agree.

What objective data(test measurements, specs,etc,...) did you use when you
were comparing the TRL Dude to other preamps?

[*Scotty*]

Having been in the hobby for more than 35 years, it has been my experience that while we can measure many performance parameters we cannot measure how an amplifier or a circuit will be perceived to "sound" by a human being.
 It is probably possible to improve on how favorably the Ncore is perceived to sound to some people without altering its measurements in any fashion. By the same token the altered sonic performance may be off putting to those who have been impressed by its performance in stock form. 
 Bruno obviously listened to the amplifier as part of the iterative design process. What we are calling stock/cost-constrained performance, may in fact not be as sonically compromised as many see it to be.
 Unfortunately, we may not be able to elicit the critical information from Bruno about what portions of the circuit do what for obvious reasons.
Scotty

[serengetiplains]

Tube Research Labs typically does not publish traditional measurements on its equipment's performance. These measurements illustrate how machines hear, not how humans hear. We probably are years away from having measurements which we can really associate to or correlate with the listenability of a device.

Fair enough.  At the end of the day, how does the damn thing sound?

Nicely put, Scotty. 

Quite apart from how good or not these amps sound stock---I'm sure they sound fantastic---I'm certain they can sound better.  I evidently don't appreciate why thinking that is controversial. 

I think when I receive my modules (should be any day now) I will first replace resistors in the feedback circuit with Vishay Z-foils just to test (verify) my hunch that noise generated by passive components in this circuit is audible.  These resistors are outside the feedback loop, thus any noise they generate (all resistors generate noise) will appear nicely amplified on the output.  How I will find those resistors is anyone's guess.

[Ric Schultz]

Yes, I am afraid "a veil is lifted" is all you are going to get.  While I adore measurements for fun....most of the time they are very meaningless as to how something sounds.  Can you measure the difference between two resistors or capacitors or jacks?  No, you cannot.  But you can hear differences and these differences are generally agreed upon.  Look at the subjective cap tests.....independently they came to the same conclusions....that the Teflon and Dueland caps are the most transparent.  I am sorry, but at this point we don't have a way to measure these differences.  If you want your N-Core to measure better then you better pay Bruno a lot of money to take his design to another whole level.  The kinds of mods that are going to be done on the power supplies and modules will not....I repeat....will not...make the amp measure better.  In fact, when I try less capacitance on the output filter, it will measure worse.  However, some of the mods that will be done.......will make the amps "sound" better.

Check out the review my Maxcast on the tour listening thread.  He says the N-cores do not image as wide as his Stratos amp does.  This could not be related to stereo separation in any measurement way.  The Stratos is a stereo amp and the N-Cores are monos.  You would think the N-Cores would have better width.  There are many factors that allow an amp to image very wide (outside the speakers).  I am sure some of the mods that will be done on the modules and power supplies will allow a wider image.  I would bet on it.  Of course, there will be those that argue that the wider image is the result of some kind of phase error.

I find it amazing that the N-Cores have been available for 6 months and not one person has tried a better fuse (except one guy who said the AMRs blew up on turn on).  I have some Furutech fuses that I will be listening to.

[*Scotty*]

serengetiplains, if you are lucky Mouser will have the values you need. They stock some values of Vishay SMT Z Foils
See link  http://www.mouser.com/Vishay-Precision-Group-Foil-Resistors/Passive-Components/Resistors/Metal-Foil-Resistors/Metal-Foil-Resistors-SMD/_/N-8eldsZ1yzu670/?
Scotty

[serengetiplains]

I'll pop in some better fuses, Ric.  What would you recommend?

Maxcast also says the mids are recessed and highs are, for lack of a better term conveying his meaning, a bit sterile.  Bruno is a big fan of feedback, which I cannot see but veiling HF response in some manner necessarily.  Temporal realities are temporal realities, imho.

Scotty, thank you.  FYI, one can order Z-foil smds from Texas Components---any quantity, any resistance, any available tolerance (they've provided 0.005% to me in the past).

Edit: oh, I see you read my last sentence above as wondering where I might source resistors.  Then you helped me find some.  Thank you.  What I meant by that sentence was wondering how I will find the feedback resistors on the Ncore board.  Their position might be pretty obvious, but I really have no idea given the traces might be buried in some inaccessible layer.