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Old 2nd May 2013, 07:48 AM   #21
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Quote:
Originally Posted by kgrlee View Post
I'm a newbie with LTspice and am often frustrated by the auto scaling
Me too. I asked how to auto set 0 phase = 0 dB a while back and no correct answer. The auto scale is rubbish. Not too hard to do manually however.
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Main grouse at present is I must show phase from 0 to -360 so can't have it cycle and show +/-180. I tried to turn the Tian probe round but I failed to get that to work...
Yes, the Tian probe is symmetrical. Usually seen as a convenience that you can't stuff it up.
Would it work for you to add or subtract 180 to the result and call it "Phase Margin"?
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My obvious contention is that TMC has no advantage over 'pure Cherry' and is usually worse.
The extra free parameters allow a better result for TMC in theory.
Whether that makes a difference in practice I want to learn.
Quote:
[deleted: 21 pages of pedantic rant about why it should be called 'pure Cherry']
OIC is shorter than "pure Cherry"! and when someone finds an earlier reference then we don't all have to rename it.
Edmond, in his modesty, didn't call TMC after himself, so did not have to climb down when the earlier patent turned up.
And descriptive names are easier to learn too.

Best wishes
David
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Old 2nd May 2013, 08:06 AM   #22
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Default modesty

Quote:
Originally Posted by Dave Zan View Post
[...]
Edmond, in his modesty, didn't call TMC after himself, so did not have to climb down when the earlier patent turned up.
And descriptive names are easier to learn too.

Best wishes
David
As a matter of fact, It was Bob Cordell who inspired me to baptize my baby 'TMC'. He was the first one who used the word 'transition', describing the compensation changeover between OPS and TIS.

Cheers,
E.
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Old 2nd May 2013, 08:29 AM   #23
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Quote:
My obvious contention is that TMC has no advantage over 'pure Cherry' and is usually worse.
Quote:
Originally Posted by Dave Zan View Post
The extra free parameters allow a better result for TMC in theory.

Whether that makes a difference in practice I want to learn.
Well this is why I started this thread. Anyone care to use the extra free parameters to approach the 'pure Cherry' performance? Only 20dB THD to catch up on.

There's been a lot of pontificating about poles & zeros etc but its the final result that matters. How simple? How stable? What distortion? Will this hold in 'real life' with different loads & devices?

The one I want gives the best results for these and I dun care whether its got apple, oranges, poles or zeros inside.[*]

Quote:
OIC is shorter than "pure Cherry"! and when someone finds an earlier reference then we don't all have to rename it.
Edmond, in his modesty, didn't call TMC after himself, so did not have to climb down when the earlier patent turned up.
And descriptive names are easier to learn too.
Dem be not descriptive names but TLAs which are even more obfuscating to the uninitiated unwashed masses en piple luk mi hu kunt reed en rite

eg waz iz TIS? I gather its a VAS but wat it mean?

[deleted: 12 pg rant why TMC should be called Baxandall's compensation cos he was the first to explain the need and analyse it in detail ... even if he wasn't the first to use it bla bla ... and it isn't better than 'pure Cherry' .. but he's a guru ... etc .. and I've scored more pages of rant than you even though they've been deleted ... ]

[*]OK, I confess. I do want to know about poles, zeros, apples etc but only if they help me meet those targets. They mean nothing in themselves.

Last edited by kgrlee; 2nd May 2013 at 08:34 AM.
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Old 2nd May 2013, 08:31 AM   #24
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Originally Posted by Edmond Stuart View Post
As a matter of fact, It was Bob Cordell who inspired me to baptize my baby 'TMC'.
You were both wise, an excellent name!

Best wishes
David
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Old 2nd May 2013, 08:37 AM   #25
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Originally Posted by kgrlee View Post
Well this is why I started this thread. Anyone care to use the extra free parameters to approach the 'pure Cherry' performance? Only 20dB THD to catch up on.
When I said "I want to learn" I didn't mean "I want someone to work it out for me"
I have started to work on this. You have only showed the phase for one of the loops in each case. As was learned earlier, this can be deceptive.
In OIC case it is the Output loop that is critical.
Even for the outermost loop the OIC phase is worse.
More soon.

Best wishes
David

TIS = Trans Impedance Stage = Current in, Volts out. It is a descriptive TLA
I have started to prefer just IS = Intermediate Section. Makes no presumption about how the amp will eventually work.
Minor layout recommendation. It would be nice if you turned of the grid for the ASC pictures. Less clutter on the screen.

Last edited by Dave Zan; 2nd May 2013 at 08:55 AM.
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Old 2nd May 2013, 09:04 AM   #26
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Originally Posted by kgrlee View Post
One of the culprits was a large famous Class A Golden Pinnae Amp (actually 2 of their models) in Stereophile/TAS good books.
This isn't the first time I've come across this gentlemen's agreement not to name poor amplifiers. What's the background? No doubt it won't look quite so **** weak once explained.

On the topic, Cherry had a few recommendations for successful/stable use of Pure Cherry/OIC which are listed in his 1997 Electronics World article 'Ironing Out Distortion'. I don't have that article with me now, but I remember that capacitors from the bases of the output drivers to the rails was one of the recommendations. I don't see these in the schematic of post 4. They were included in the calculation that showed the VAS emitter resistor aiding stability (1982 JAES article).

Ricardo, Pure Cherry won't catch on as a name, I'm afraid. Doesn't have enough letters in the initialism.

Edit: The irony... **** weak censored. But at least I've learned that I had the swearing hierarchy wrong: kunt allowed; **** weak not allowed.

Last edited by steveh49; 2nd May 2013 at 09:07 AM.
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Old 2nd May 2013, 09:27 AM   #27
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> Pure Cherry won't catch on as a name, I'm afraid. Doesn't have enough letters in the initialism.

What about Pure Cherry Compensation, PCC?
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Old 2nd May 2013, 10:20 AM   #28
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Dave Zan View Post
Hi Andrew
Why do you prefer Zobel on the amp side?,.........
A different Andrew's view,
the Zobel before the output inductor is there to provide an HF load for the amplifier. That HF load MUST have low inductance, else it can't effectively load the output stage @ HF.
That low inductance requires the Zobel to be closely coupled around the output stage devices and the HF decoupling attached to the output devices.

One CANNOT achieve HF loading capability, if the Zobel is remote from the output stage.
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Last edited by AndrewT; 2nd May 2013 at 10:29 AM.
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Old 2nd May 2013, 11:03 AM   #29
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Originally Posted by AndrewT View Post
One CANNOT achieve HF loading capability, if the Zobel is remote from the output stage.
Yes, a Zobel after the inductor requires the inductor to be on the board and a non-inductive damper resistor.
But Cherry discussed both possibilities as do-able, with some benefits each way. .
I am inclined to a distributed Zobel before the inductor and a pi circuit, with some capacitance after as well.
Never had an answer from Mr Cordell about whether to connect the distributed Zobel directly to each output emitter (and thus before the emitter resistors rather than after as is usually done). Makes sense to me, you want to jump in on that question too?

Best wishes
David

Last edited by Dave Zan; 2nd May 2013 at 11:06 AM.
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Old 2nd May 2013, 11:13 AM   #30
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Makes sense to me too!
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