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Old 3rd February 2012, 12:26 AM   #1701
tvrgeek is offline tvrgeek  United States
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Yea, they keep coming up with stuff too. Can't let those left coast guys get too far ahead The other news item that blew me away was IBM got some time on BlueJean and came up with an electrolyte for air-lithium batteries that won't break down. Design-a-chemical program. If their report pans out, it is a world changer. We are talking about ten times the energy density. A cell phone that lasts a month, laptop a week, a car 300 miles. There are a couple more game changers coming in processors and memory that I am not at liberty to share. Lets just say the ride ain't over yet.

Simetrex, uses SPICE models. Superb. Got both theirs and LTSpice so I can go read the manuals. If I can learn enough to repeat Wahab's sim, then I'll sim the little Rotel she likes. I bet it is not only very generic, but just plain well executed.

If my friends did not already know I was crazy, this experience has proved it to them. I'm having fun.
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Old 3rd February 2012, 04:24 AM   #1702
Previously: Kuei Yang Wang
Join Date: Nov 2002

Originally Posted by tvrgeek View Post
Thanks Jan, not I did not know of that distro.
Seems you are mainly an Open Source / 'nux geek and less of a tvrgeek...

LTSpice is a spice simulator from Linear Tech that is not a "distro" but proprietary software designed by Linear Tech for internal use (it evolved from "Switchercad", and made available as freeware to any who care to use it.

Linear Technology - Design Simulation and Device Models

It runs on Micro$oft Windoze. As it is one of the few freely available and unlimited Spice Simulators it has become the de-facto standard for many DIY'ers and you often see LTSpice Files posted with threads about designs here.

It is greatly beloved by the many "Spice Jokeys" here on DIYA who routinely crow about ridiculously low THD from their Sim's that are highly suspicious to anyone who ever builds and tests real circuits with real devices.

I found the learning curve for using it rather steep when I tried to start using it a few years ago. I routinely need custom models (including tubes, a wide range of transformers etc) and excitations for my work and back then this was hard to do at the time, so I stuck what I had and which already had all the customisation done...

There are many resources for LTSpice in this community and others, here are some that came to my note (by no means exhaustive) and which I bookmarked "for a rainy day":

LTSpice and What the New User Should Know - diyAudio

LTspice Tutorial

Undocumented LTspice - LTwiki

How to simulate OPT in LTspice?

LTSpice how to measure THD+N ?


Whats the best way to show output impedance with LTSpice?

Jitter or phase noise in LTSPice

zener LTSpice model

A thread I was interested in that features extensive and at time gratuitous use of Spice Simulation with downloadable files of whole amplifiers including models etc. is here:

Goldmund Mods, Improvements, Stability

Ciao T
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Old 3rd February 2012, 04:29 AM   #1703
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Originally Posted by ThorstenL View Post
It runs on Micro$oft Windoze.
For the open source geeks it also runs passably under Wine on my Ubuntu Linux.
The heart ... first dictates the conclusion, then commands the head to provide the reasoning that will defend it. Anthony de Mello
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Old 3rd February 2012, 04:54 AM   #1704
Previously: Kuei Yang Wang
Join Date: Nov 2002

Originally Posted by tvrgeek View Post
On his later designs, he eliminated R11 completely.
Yes, this "loading VAS and shunt compensation" has fallen out of favour. However, I would suggest you first try the Amp with the original design and let your wife listen. Only then try for example the compensation Wahab has shown and see if your wife still likes the Amp. It would be an excellent experiment.

Originally Posted by tvrgeek View Post
On the multiple outputs, it would not be difficult to drill the heat sink to use two outputs.
If you have not received your replacement Fet's yet see if you can cancel the order and switch to double die TO-3 parts. They are available from a number of vendors, including Exicon:


Maybe it's just me bing lazy, but i hate doing much mechanical work on gear I'm modifying.

Originally Posted by tvrgeek View Post
I hate taking current through the mounting hardware on TO-3 packages. Learned that back in failure analysis.
Then don't...

Ciao T
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Old 3rd February 2012, 05:20 AM   #1705
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I am pretty sure his wife will like Wahab's compensation.
The Devil is not so terrible as his math model is!
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Old 3rd February 2012, 05:43 AM   #1706
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I really don't think we should throw away measurement, but there is some truth to what he says about numbers not meaning everything. I have experienced this a number of times. Honest specifications are a really good tool to understand characteristics though.
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Old 3rd February 2012, 09:02 AM   #1707
wahab is offline wahab  Algeria
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Originally Posted by tvrgeek View Post
Your version is easier for me to get my head around, that's for sure. As yo have done this sim, I will try to copy that to learn the tool and the main reason, to learn how these puppies work. As I have mentioned, reading textbooks is a great step one. Nothing beats being able to ask a question. I really appreciate your efforts and the patience of the many on this forum.

What would the sim say if you slowed down the outputs and changed R18 (23 on the mod) to 680 and R21 (R12 on themod) to 470? I am switching to the Exicon EC-10N16, P16 pair. They have half the gate cap. from the Hitachi. So the above gives about 1M for f3. Would I not risk some output stability with the 100 & 68? I am going to fly the gate resistors right off the socket.

150 on the CM emitters. OK, I was guessing 100. Actually, I happen to have some. How about a .1u across Q8?, or Q12 in the mod.

THose 2SC1775's sure do have a LOT more gain.

I gather the output network is a "typical" ?

You have moved the compensation to the output of the first and second stages into the feedback loop. No more big DC load on the VAS Do I look at them, C8/R13 and C5/R13 as if they were separate?

Simetrix. Found it. Simple is good as I don't intend to do this for a living. I am already on my third career. This is far more fun as a hobby.
The original P FET gate 470R resistor is too high and this produce
an overshoot on the positive going of the signal when checking
with a square signal.

The input differential current is 0.6mA/transistor , hence the 150R
to create a significant voltage drop of 90mV that will allow the CM
to work correctly despite components dispersion.

Shunting the VBE multiplier with a cap can be useful , i didnt check,
in case wich a 100nF cap should be enough.
Depending on the device used a 100/220pF can sometime be connected
between base and collector of the said transistor to prevent local instability.

The compensation i used is TMC , transitionnal miller compensation,
wich has been vastly popularized in this forum by Edmond Stuart.
The relevant threads can be easily found and will provide quite
an insight about this original way of compensating an amp.

As for the output network , well you re right , it s typical ,
albeit the original should be enough..

As mentionned by Thorsten you can use dual die cases
that will allow for better current capability without drilling
the heatspreader , not counting the shorter electric path
wich is instrumental with power fets.

Just be carefull to first set the iddle current to 0 after such a mod,
although the Exicon fets have higher thresholds , one never knows.......

Last edited by wahab; 3rd February 2012 at 09:11 AM.
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Old 3rd February 2012, 09:07 AM   #1708
wahab is offline wahab  Algeria
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Originally Posted by bcarso View Post
Does Simetrix allow for Fourier analysis?
Of course , here two exemples.
Attached Images
File Type: gif AWB55 LP THD1.gif (31.0 KB, 132 views)
File Type: gif AWB55 LFET IMD1920.gif (26.8 KB, 126 views)
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Old 3rd February 2012, 01:46 PM   #1709
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While on the subject of Fourier. The Power Point and all scripts from "j.j." recent seminar on FFT are now at:

Scripts for Octave
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Old 3rd February 2012, 05:12 PM   #1710
bcarso is offline bcarso  United States
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Originally Posted by ThorstenL View Post

If you have not received your replacement Fet's yet see if you can cancel the order and switch to double die TO-3 parts. They are available from a number of vendors, including Exicon:

Those look very interesting. The characteristic curves indicate that they have a negative tempco of drain current magnitude at any but very low levels, somewhat different than the Hitachi parts. And I like the availability in both packages --- I wonder which one has the lowest lead inductances?

Another question someone may know the answer for: are there built-in gate protection zeners? It would seem so from the specification on gate-source breakdown voltages.

Also, would anyone know what the capacitance of the body diode looks like, as opposed to the capacitance specifications given in the datasheet? As the body diode is rated for 16A of forward current, I would imagine that it is substantial.

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