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Old 8th December 2011, 04:44 AM   #18841
Previously: Kuei Yang Wang
 
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Hi,

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Originally Posted by Bonsai View Post
Power Amp with Hawksford VAS and EF triple here Audio Amplifier Design and Circuits | hifisonix.com.
I know. Have you fixed it's tendency to self destruct yet?

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Originally Posted by Bonsai View Post
BTW, re Cdom I was referring to local feedback around the VAS stage, not global feedback.
I am well aware of that too. However as this only happens in the context of a circuit that also has an outer feedback loop this is not a case of feedback increasing with frequency. Of course Cdom compensation also has other problems.

What really happens is that for the whole system feedback decreases with frequency while at the same time distortion increases with frequency, so less feedback is available precisely where it is needed to linearise the amplifier, making a strong case for broadbanding and linearising an amplifier maximally prior to closing any feedback loop and to keeping the feedback constant over the operating range of the feedback amplifier, as defined by it's input filter.

Of course, if we have done this to a sufficient degree we may conclude that the global feedback loop has become optional and possibly even counter productive...

Ciao T
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Old 8th December 2011, 06:49 AM   #18842
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It is fixed and running again. As to the root cause, I do not know, but extensive testing during design and more recently during the repair and then a bit later to TMC comp it tells me it was not instability. Getting carted from EU to Japan and then to Taiwan is probably not the best way to treat something like this.

I think linearizing before closing the loop is a given. As to wide OLBW vs high loop gain and LOLBW, I doubt there will ever be agreement on that. For that reason my new amp is jumper selectable for std MC, TMC and VAS loading although not MIC. This will allow for some experimentation. Of course, it's EF triple again and >100V/us, so no TIM issues.
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Old 8th December 2011, 07:20 AM   #18843
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Hi,

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Originally Posted by Bonsai View Post
I think linearizing before closing the loop is a given. As to wide OLBW vs high loop gain and LOLBW, I doubt there will ever be agreement on that.
Let me put it this way, if the LOLBW Designs where pure, absolute theoretically ideal integrators there would be no debate. And of course, in theory there is no difference between theory and practice.

You may, in your amp, when it blows up the next time (trust me, it will) reduce the VAS loading and increase VAS degeneration significantly and swap your triple for a Lateral Fet Driver and standard output... The 2SK214/2SJ77 remain available for the job...

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Of course, it's EF triple again and >100V/us, so no TIM issues.
Somehow triples seem more likely to blow than EF2... N-Joy. Better sort out reliable speaker protection... :-)

My next Amp will be open loop, except the output stage, which will use all lateral fet Sziklai circuits... Not sure about the rest, maybe I'll just stick an open loop tube there, maybe I'll do open loop Fets...

Ciao T
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Old 8th December 2011, 07:44 AM   #18844
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The main selling items are <snip> Bedroom DJ Gear.
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All I can ask anyone to do is to use IC's, beat me at my own game of audio design, and get rich and famous for it. Then, I will know that IC's have 'come of age' and I can concentrate on systems design in future. No excuses however, will impress me, if you fail.
Well, yesterday I purchased AMR CD-777, a CD player designed by Thorsten Loesch, having a tube analogue stage. The most analogue sounding CDP I ever heard. (I didn't hear the better model, AMR CD-77, since I can't afford it).

Each is welcomed to ones' own conclusions.
As for myself, it reminds me the English saying: "The proof of the pudding is by eating".
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Old 8th December 2011, 07:59 AM   #18845
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Tube analogue stage, Joshua? That sounds OK to me. I don't know why, but tubes do help quell digital problems. I find most IC based, CD analogue stages very weak, including the Sony SACD player that I use. Garbage, actually.
Now let me be clear. I am NOT against IC's. I have played with IC's since 1966, when they cost $100 each. I have measured them, hooked them up in simple circuits, and even designed them into instrumentation, 4 years before 1970. They are great for many applications, but I have always had some trouble with them for audio. Not necessarily unacceptable, sonically, but compromised compared to the best tube and discrete solid state circuits. That is where I stand, today. Now, if someone makes something that meets or beats Charles Hansen's or my best with IC's, well my hat is off to them.
However, the world must acclaim your design, before I will believe you.
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Old 8th December 2011, 08:03 AM   #18846
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Hi Joshua,

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Originally Posted by Joshua_G View Post
Well, yesterday I purchased AMR CD-777, a CD player designed by Thorsten Loesch, having a tube analogue stage. The most analogue sounding CDP I ever heard.
Merci beucoup.

Do try in DAC Mode with a Computer Transport as well, it is quite good...

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As for myself, it reminds me the English saying: "The proof of the pudding is by eating".
Bon appetit. I would suggest a topping of nice NOS Tubes. The Soviet 6N1 sounds pretty good for something readily available, but better sounding tubes exist.

Incidentally, this CDP not only uses tubes but also omits looped feedback, though I have not gone to any extraordinary length to avoid local degeneration (I just did not design a lot of it in). It also allows the bypassing of any analogue and digital filters.

Ciao T
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Old 8th December 2011, 09:15 AM   #18847
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I would also buy one . But before doing so, I would like to hear it
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Old 8th December 2011, 01:43 PM   #18848
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Scott,



Why don't we instead compare apples with apples, shall we?

Let us say we have a discrete OPA with 120dB DC Gain and 20Hz bandwidth with an SE class A output.

Due to the vagaries of epectronic design the 20Hz bandwidth corner is modulated by around +/-2Hz over the whole swing of the OPA VAS. What is the effect in band for a 20Hz-20KHz bandwidth? Non-Linearity (whatever you want to call it) from bandwidth modulation.

Now let us take the OPA and degenerate input by 20dB and VAS by 40dB (Yes, this will loose us output swing and increase noise, we may need more supply current, all no-no's in IC design, but "fair game" for audio). We will find we need to change our compensation to a much smaller one as well.

We now have appx. 70dB DC gain (because the VAS operates in current input mode, and degenerating raises it's input impedance and thus the gain if the IPS) 70dB gain at 1KHz and even close to 70dB at 20KHz. There is no or very little bandwidth modulation, as the parameters that cause it are all stabilised much better due to degenerating the devices Gm.

Ciao T
I would say you made an orange out of the apple. IIRC "The Love of Three Oranges" was one of the old RCA "super disks".
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Last edited by scott wurcer; 8th December 2011 at 02:05 PM.
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Old 8th December 2011, 02:23 PM   #18849
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Hi Thorsten,

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Originally Posted by ThorstenL View Post
Merci beucoup.
Do try in DAC Mode with a Computer Transport as well, it is quite good...
Thank you for my enhanced joy in listening to music.
My music computer is kaput right now… however I will definitely try it.

BTW, the previous upgrade to my sound setup was a power amp by Nelson Pass, which made marvels to the sound of me setup.

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Originally Posted by ThorstenL View Post
Bon appetit. I would suggest a topping of nice NOS Tubes. The Soviet 6N1 sounds pretty good for something readily available, but better sounding tubes exist.
Yes, I plan to roll the Soviet 6N1 with some NOS E88CC tubes I have.

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Originally Posted by ThorstenL View Post
Incidentally, this CDP not only uses tubes but also omits looped feedback, though I have not gone to any extraordinary length to avoid local degeneration (I just did not design a lot of it in). It also allows the bypassing of any analogue and digital filters.
I tried all the options and I prefer the default one, NOS (no oversampling) with analogue filter.

I have a feeling that part of analogue sound of that CDP is due to the DAC chip used, which AFAIK isn't being used in any other commercial product. Also, I noted very big output caps. So, it seems that everything matters.

Anyhow, after eating the pudding I've found that your design principles are working.
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Old 8th December 2011, 09:36 PM   #18850
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In thinking of product ratings and design one category that has done well with IC's is DACs and CD players. My favorites have been discrete along the lines John has pointed out, but many over the years have had IC opamps not revealed in reviews. Of course the D1 was discrete as a matter of principle.
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