Biasing/thermal compensation of Thermal Trak transistors - Page 12 - diyAudio
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Old 22nd August 2007, 01:28 AM   #111
anatech is offline anatech  Canada
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Hi Bob, Jim,
Given that the diode is a separate part of the assembly, I'll bet it's the same part. Why on earth would they change it?

-Chris
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Old 22nd August 2007, 03:59 AM   #112
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Quote:
Originally posted by anatech
Hi Bob, Jim,
Given that the diode is a separate part of the assembly, I'll bet it's the same part. Why on earth would they change it?

-Chris

Hi Chris,

I agree; that is what I'm assuming.

Cheers,
Bob
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Old 9th January 2008, 07:18 AM   #113
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Default !

I am following this thread from the beginning and at some stage, I
transferred Mr. Cordell's idea of biasing of TTrak devices to Dr. Jagodic.
Here is one possible solution done by him recently as a prototype. I asked
him for permit to publish schematic of this design and he didn't objected
but he wasn't particulary interested neither. His general policy is not to
discus and elaborate his designs in public and for real experts here that is
probably not necessary.
All I can say is that prototype sound amazing and is rock stabile in all
aspects. Some changes were necessary because it was impossible to reduce
total bias under 550mA with original values. Now bias is 150mA per pair and
is rock stabile and drop just 5mA from cold to 70*C. Output ofset is +1,2mV.
My contribution was to design and produce PCB based on Dr. Bora remarks and
requirements.

Click the image to open in full size.
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Old 9th January 2008, 07:43 AM   #114
roender is offline roender  Romania
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Congratulation to Dr. Jagodic and to you Viktor.
I have done it in a much simpler way, knowing TC of outputs BE junction, NJL diodes and CFP driver at bias current
The bias current is 260mA in the first seconds after startup and it drop to 170mA and stay there regardless of output stage temperature.
http://www.diyaudio.com/forums/attac...amp=1194852081
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Old 12th January 2008, 10:38 AM   #115
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Default !

Some general explanation of operation (to the best I understood from few
chats with Dr. Jagodic ):
-Input stage is modified and improved Quinn cascomp according to research
of some Mr. James Woo. Even Mr. Woo version is little more modified and
simplified by Bora
It was very essential to do perfect possible matching of most input PNP
devices to have good results and also of two VAS NPN-s.
-VAS stage is Dr. Jagodic favorite standard differential type but as he
frequently do, it is buffered to keep best performance of good specs of
small transistors in VAS without need to set them in high current and
disipation and to isolate VAS from capacitances of following stages
-predriver/driver & output is according to Mr. Cordell idea, but in
practice it was necessary to be little modified because quiescent current
was more than 500mA and no way to reduce it. That stage also use Baker
clamp.

PCB was real pain in the ***! To keep PCB single sided and tracks
reasonably short, Dr.Bora suggested small accessory board mounted
verticaly on main board and containing majority of output stage
components.

If there is interest, I can post PCB design file and layout file if
someone want to try.
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Old 17th January 2008, 09:02 AM   #116
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Default !

What's with this topic?!Bob,would you write something about schematic?
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Old 10th March 2008, 03:44 AM   #117
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From what I've gathered so far in this thread.....

For Designing an amp with just a single pair (or two pairs) of output transistors, just using the diodes to bias, with a pot or resistor in series with the diodes should be all that's necessary to use the thermaltraks, right?

You don't have to use a VBE mult if you don't have to right?

What about using a resistor in parallel to the diodes instead of series? I'm thinking of making a quick test output stage to compare.

I have the NJL4281/4302 variants. I want to use them in a simple 4 channel setup with a single pair per channel. It would be nice and simple to build if all it needed was 2 output transistors each channel, and the thermal diodes, and a fixed resistor (calculated) to set the desired bias. I wouldn't care if the bias was perfect, but as long as it didn't run away when hot.
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Old 10th March 2008, 04:14 AM   #118
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a little off topic but........

I like the 5 lead TO-264 package.

It would be cool if they put MOSFETS in the same 5 lead package, but used 1 lead for gate, and used 2 leads each for source and drain to carry more current than a regular 3 lead package.
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Old 10th March 2008, 08:10 AM   #119
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by EWorkshop1708
For Designing an amp with just a single pair (or two pairs) of output transistors, just using the diodes to bias, ..................I have the NJL4281/4302 variants. I want to use them in a simple 4 channel setup with a single pair per channel. It would be nice and simple to build if all it needed was 2 output transistors each channel, and the thermal diodes, and a fixed resistor (calculated) to set the desired bias. I wouldn't care if the bias was perfect, but as long as it didn't run away when hot.
I don't think two series diodes will give sufficient temperature compensation.
There might be enough but so far I 've only seen 4diodes being used.

The Leach which uses separate diodes in a modified Vbe with 4 in series is overcompensated.
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Old 10th March 2008, 08:21 PM   #120
KSTR is offline KSTR  Germany
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One could possibly hook it up in a diamond buffer style. That is, as a basic scheme, from input via the diode and series resistor to a current source, and from the node below the current source to the base (via stopper), plus the usual emitter R, and probably some caps as AC shunts. And the complementary likewise, mirror imaged. According to various preliminary sims (haven't tested the TT in real life as of yet) there is a combination of current source, series R and emitter R which gives a good operating point, and adjustable amount of compensation tempco, spanning both negative and positive tempcos.

Cons: single wire input (you'd need a good buffer stage ahead of it) and current limit / SOAR protection is a bit tricky to implement. I might suspect problems for a typical class-A/B stage (I simmed only class-A, with occasional class-B transients -- a complementary push-pull cyclotron as the design concept).

- Klaus

BTW: Is there any known info on the response delay (time constant) from the transistor to the diode?
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