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Old 7th December 2012, 12:38 PM   #221
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Hello
Catalin I hope you do not get upset because.....
You know so many guy wrote "I'll build or "I'll test that amp", please send these or that etc and until now nothing..
To me over the 22 years or so the best sounding amp I built.
I stated many time it was my fault the thermal runaway. We can not set up a new amplifier bias high and fall sleep.. Also many darlington device from ISC BDW83/84 (high power garbage)!!! I powered up the amp and after 20-30 min. the darlington gone at 50mA low bias.
The lower power BDW93/94 from SC micro worked perfect even on 100mA bias for weeks!!!
If you don't find BDW83C/84C from SC micro (sometimes marked Morocco) please buy TIP142/147
I didn't meet a guy ever who heard the amp didn't like the sound.
One think keep in mind these is not a PURE Class A amplifier. Those darlingtons can't take the heat specially not at 40V rail.
padamiecki can you lead me to the thread where you took the circuit.
It would be great if I do not need to go over a few hundred page.
Wahab if you have at your hand the Japanese version of these amp (original) I would love to see it.
I'm interested to what type of transistor was used for VAS etc.

Greetings Gabor
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Old 7th December 2012, 12:43 PM   #222
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Quote:
Originally Posted by gaborbela View Post
padamiecki can you lead me to the thread where you took the circuit.
It would be great if I do not need to go over a few hundred page.
was it here? http://www.diyaudio.com/forums/solid...ml#post3264029 that you asked?
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Old 7th December 2012, 12:52 PM   #223
wahab is offline wahab  Algeria
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Quote:
Originally Posted by gaborbela;3274600
[B
Wahab [/B]if you have at your hand the Japanese version of these amp (original) I would love to see it.
I'm interested to what type of transistor was used for VAS etc.
It can be find on post 14...

http://www.diyaudio.com/forums/solid...ml#post1659097
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Old 7th December 2012, 01:46 PM   #224
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Quote:
Originally Posted by wahab View Post
How will it be unstable ??.by wich mechanism that a simulator couldnt spot.??..

Also , keep in mind that we re talking of the circuit in this thread ,
not eventual versions that you perhaps has trouble with.
Do you think that your transistor models accurately simulate BJT tempco ???

I havent ever had trouble with this circuit, build it first time about 22 years back and with some input from JLH himself, the original designer.

In this case one can get away to some extent with the vas bias stability as the darlingtons are biased high and no regard is taken to THD, its even better with the circuit in class A operation but what happens when you want accuracy.
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Old 7th December 2012, 08:27 PM   #225
wahab is offline wahab  Algeria
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Originally Posted by homemodder View Post
Do you think that your transistor models accurately simulate BJT tempco ???
Why souldnt it be the case ?....
I dont understand why you think that such a basic parameter
is not accounted.

In sims i checked the variation from 20C to 80C , and the numbers
correlate of course accurately with the theorical behaviour.
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Old 7th December 2012, 09:35 PM   #226
Bigun is online now Bigun  Canada
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Quote:
Originally Posted by wahab View Post
How will it be unstable ??.by wich mechanism that a simulator couldnt spot.??..
the solution is here: TGM5 - all-BJT Simple Symmetric Amplifier

post 22.
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Old 8th December 2012, 12:08 AM   #227
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Hello Guys

Let s stick with the given circuit to comment that!
I do not say not to write about similar amplifiers only just we do not lose the focus.
Here I had these circuit which I think wahab made it "more" stable..
How I understood all the similar amplifier design suffer from the same problem.
By the amp warms up the bias rise up to, (that is true about the Mosnster Hiraga to, I built it. Mostly the bias after total warm up almost was double like at the start up)
Now if these not compensated with a large enough heatsink it will lead to thermal runaway. That is 100% sure. Doesn't matter if the amp use power Darlington, normal BJT, or mosfet.
I read someone had similar issue with power mosfet!!!
Again that mean these amplifiers req. the adequate heatsink size.
What I ask here if we can slow done these bias movement a bit.
wahab came up with a solution which will be tested soon, thank God and thank to wahab for the help.
Also if I understood well if we take the feedback only from the input pair these drifting will be reduced by a lot. Now I'm not sure until I don't test how that effect the sound is anyway at all. We will see soon.
Here is nothing to do with anything else. We (I) do not want to upgrade the sound of the amp!
The amp sound better than someone can expect from!
I'm happy to see we have conversation about similar amplifiers. That is great , I want to learn.
But from a outsider (just came here now) it will look like we have a terrible unstable problem here.
I want to emphasise that is not true in these case!
If my M Hiraga did not had large enough heatsink the thermal runaway it would happened with that to. That is 100%
So I'm not sure all these SSA tend to act these way, but one think I'm sure these amplifier need large enough heatsink to stop that thermal and bias rise.
Also I mentioned these amplifier with 3 pair darlington from 18VAC transformer it was biased 3A. The amp was stable because I used large enough heatsink!
Another experience probably the darlington tend to produce more heat because that (small)cheap contain 2 BJT, diode, 2 resister com pare to the large TO 247 case simple BJT.
Only I wrote all these if someone read the topic not to have that feeling he must run from here because these amp (or what ever we talk) acting so weird better not to touch it.
Other wise please keep going on these topic, that is how we learn!

Today I cut done the clad-board for etching these PC boards...
Greetings Gabor

Last edited by gaborbela; 8th December 2012 at 12:10 AM.
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Old 8th December 2012, 12:18 AM   #228
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Quote:
Originally Posted by padamiecki View Post
Hello
Did these amp was tested in real life?
I know sim a amp it help a lot, sometimes I wish I could has access to simulate to.
But the real test in real life how it act or more important sound.
Sim not always give 100% accuracy specially about the amplifier sound.
Sometimes our ear hear something different like the sim result...
I had a friend in Budapest, he build speakers, amps, TT etc for sale.
Taylor Acoustic- not the same Taylor from N America...
He always told me the best toll to really test a new product the ear!
Greetings Gabor
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Old 16th December 2012, 03:50 PM   #229
wahab is offline wahab  Algeria
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Quote:
Originally Posted by Bigun View Post
the solution is here: TGM5 - all-BJT Simple Symmetric Amplifier

post 22.
May i ask , the solution to what ?..

Seems that this topology s drawbacks are still not very well understood
by many people , not talking of you but of absolute beginners , think that
i ll soon make a little tutorial in this very thread to explain basicaly the
voltages and currents dependencies between the nodes , this will allow
non experimented people to yield an acceptably stable design.
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Old 16th December 2012, 04:49 PM   #230
Bigun is online now Bigun  Canada
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It is the solution to an unstable Vas current influencing the output device bias point. The common Vbe multiplier does not hold a very constant voltage differential under fluctuating current conditions, but the Hagerman topology offers a significant improvement - good enough perhaps. This is what I used and it measured good.
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