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Old 24th November 2011, 02:26 PM   #31
sidiy is offline sidiy  Canada
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Some good reading on lead-lag compensation:AN1604 from National. It is also treating the single resistor case and gives a design methodology for the RC network.

I plan to test this very soon in practice (waiting for the parts)...The goal is to stabilse a LM4780 to a gain of ~two, see if it works OK...
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Old 24th November 2011, 02:48 PM   #32
jcx is offline jcx  United States
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that app note's "lead-lag compensation" is "noise gain compensation" - I find the lead, lag terminology can be confusing

since the "lead"+"lag" mostly cancel their respective phase adjustment functions the net result is to change the gain at the intercept frequency - so I think the "noise gain" name is more descriptive of what is achieving the compensation

but it is useful to have terminology that differentiates between full bandwidth noise gain increase with the R vs the series R,C that lets you keep more low frequency loop gain
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Old 9th December 2011, 02:51 AM   #33
bernhix is offline bernhix  Philippines
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I am new on this discussion and it worth to read.... thanks guys.
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Old 24th September 2012, 12:31 PM   #34
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I'm with AndrewT on multiple, smaller, compensations being, possibly, less audible than 1 fell swoop.

However, my take on this is going to be very strange, involve (mis)use of diodes and is mostly voltage activated instead of current activated.
On a Circlophone (ltp) that does have a feedback cap, RF filter cap, output RC, I added my new accessory: http://www.diyaudio.com/forums/attac...e-softclip.gif
It is from in+ to in- but its not exactly a resistor. I wish to take a moment to note that the diodes are capacitive and that RC multi-pass is present.
For reference point, the Circlophone amp is using a 20+20vac transformer and is set for very high gain with a 22k feedback resistor with the dynamics up in similar proportion. . . but otherwise, the amp is a match for the standard edition.
Prior to installing my accessory, the low volume pitches had level response but loud playback got darker as if treble roll off.
After installing my accessory, the low volume pitches and loud playback have similar treble with no observable difference.
However, the soft clip function is not significantly effective (as intended, else you hear it switch).
The most noticeable benefit is that loud playback is at considerably higher resolution than it was previously.
That last effect looks like a near miss match to Mooly's description of resistor from in+ to in-.

The accessory was necessary for my application when after discovering the consequences of setting Circlophone to far higher gain, it became so dynamic that the volume control dial was nearly useless AND both low volume and loud playback will occur on a single track. The tone shift between quiet and loud was disturbing when repeatedly occurring in the middle of songs. The accessory fixed it and the tone is level no matter if quiet or loud--same tone.

The Circlophone and its in+ to in- accessory remain together and in active service. I consider it less expensive than concert tickets and the audio is comparable. I don't always want something to show off big, but when I'm in the mood for that, I use this amp for it.
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Last edited by danielwritesbac; 24th September 2012 at 12:36 PM.
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Old 24th September 2012, 01:06 PM   #35
Mooly is offline Mooly  United Kingdom
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An interesting read Daniel
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Old 25th September 2012, 08:34 AM   #36
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I'm not sure, but we might be on the same track.
Wish I knew what that was.

Both the resistor and my crazy circuit causes bigger soundstage and greater clarity at the expense of more forwards tone. With the power op-amp, this can be unscrewed by using bigger amp board decoupling caps; however, we need an amp that naturally wants small caps, as a starting place I got one! non-inverting TDA7294 wants a pair of 220u in addition to a rail to rail RCR of 2u. Well, we could replace those 220u with 470u (low esr compact type) to straighten out the harmonic frequency response caveat.
No idea if this will work.
But also integrated amp boards (power supply is aboard with the amp) could be used since amp board decoupling is as huge as the reservoir and therefore these extra dull things might could be perked with your resistor idea. Although these are more ideally fixed on the power-side, one could use that type amp for any sort of "perk-up" experiments for which it has excessive tolerances.

So, if you happen to have either sort of power amp available, or even a discrete amp that wants 100u amp board decouping caps (that you can replace with 220u or 330u low esr type), then you might try the resistor trick with a power amp to see if it will put on a show.
In some cases, we might have to decrease the gain, adjust the feedback current and/or adjust the other compensations.

Good luck with your nobel endeavors for sound stage, since THAT artwork is the tallest order for an audio amp.
I was a bit upset to discover that the scope was utterly blind to an audio amplifier's most difficult task. Is it impossible to measure electronically?


I believe that soundstage promotion of an audio amplifier is best observed in monophonic so that stereo separation doesn't pollute the observations.

P.S.
If you want to demonstrate epic soundstage at the expense of other factors, the answer is quick, easy, daft, inexpensive, and right here: Bridged TDA2003 (mine is run from regulator)
When I asked KeanToken what means that amplifier could possibly have for hi-fi class soundstage he replied: "Singleton on regs. Of course." as if it was totally expected.
Mooly, I propose that you and I have hindered some part of the LTP for much the same effect, and I propose exploring NTP and SSA inputs as an alternative.
Sorry, but I cannot guess much further, except:
All of the experiments need to use regs/k-multi/capmulti so that the LTP doesn't throw the baby out with the bath water from power noise in the feedback loop and so the singleton doesn't amp power noise. Somehow that is all related and highlights a need to subtract power noise prior to making comparisons.
And, finally, I've run out of guesswork.
Would be nice if the scope showed something on the topic though, since guess, try, repeat, is a bit slow.
I want to know who's going to be the first to measure meaningful soundstage, and say congrats on the groundbreaking head start.
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Last edited by danielwritesbac; 25th September 2012 at 08:41 AM.
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Old 26th September 2012, 08:30 PM   #37
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As far as I know what is called, "sound stage", is related to cross talk between stereo signals, exactly what anything in this topic has to do with that I am not sure.
rcw
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Old 27th September 2012, 12:19 PM   #38
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Quote:
Originally Posted by rcw666 View Post
As far as I know what is called, "sound stage", is related to cross talk between stereo signals, exactly what anything in this topic has to do with that I am not sure.
rcw
Then do it with only one speaker and you'll be sure.
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Old 2nd October 2012, 05:43 AM   #39
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Quote:
Originally Posted by rcw666 View Post
.... "sound stage", is related to cross talk between stereo signals......
Principally, yes but the presence or not of small amounts of low order, upper mid-treble distortion products has much to do with enhancing the apparent image sharpness - nothing to do with add-on stereo width circuits though. The results can be intentional or serendipitous as any user or sensible modder of old but still popular models will attest.

This is just one strategy for subjectively improved stereo imaging. It can be very impressive and result in big ticket sales if you get it right for your product and target audience.
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Old 3rd October 2012, 12:26 PM   #40
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Quote:
Originally Posted by Ian Finch View Post
Principally, yes but the presence or not of small amounts of low order, upper mid-treble distortion products has much to do with enhancing the apparent image sharpness - nothing to do with add-on stereo width circuits though. The results can be intentional or serendipitous as any user or sensible modder of old but still popular models will attest.
Does this remain true regardless of the number of channels? For example, mono, stereo, trio, surround, etc. . .? I've found that if I make the soundstage judgements in monophonic first, then, later, when I connect more channels, the imaging is extraordinary. Simply put, that's because it was extraordinary in monophonic.

I wonder what type "small amounts of low order, upper mid-treble distortion products" are generated by resistor (or resistor series to diodes) across the LTP from IN+ to IN-? Is there some specifics on the type?

I didn't know about that. Previously I had assumed that all you needed was phase linear to beyond 1mhz, a "just right" amount of compensation, and a very sharp square wave test with just barely a hint of acutance pattern but never rounded.

P.S.
The only case I've seen where noise was beneficial was for post processing MP4, Itunes, HDradio and similar/same types of codecs. Some people get headaches from those, and triode harmonic distortion removes the headache problem without really disturbing the ear. But, that is oddly a case of noise cancellation. Are we looking at something similar here?
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