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Old 24th November 2012, 05:14 AM   #141
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Hi Gabor,
I'll try your circuit with TIP142/147 as I have some already and don't mind if they blow ! Need to find out what you have been hearing. Sounds interesting.
You've been running the bias very high . Was that intentional or you couldn't control it or did not bother ?
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Old 24th November 2012, 08:02 AM   #142
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Don't like to be a kill joy but common guys this geriatric semis ....I refuse to work on something like Tip 142-147 which is actually a transistor to drive solenoids and you may check on any data sheet there is no audio specifications ....

my position about darlingtons is stated here many times before don't have to repeat it once more .

I simply challenge you to place the datasheet of various Tip 142 from trusted manufacturer up in the air so everybody can see and you will understand that each and every one of them has a different configuration between the driver and the output transistor ....

That exists in the datasheet in real life will be also batch and order depending ....

You cant guarantee specs like that .....

kind regards
sakis
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Old 24th November 2012, 08:12 AM   #143
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Hello
Yes the the high bias was intentional. Sound a bit better. With lower bias the amp stable and sound great to, probably with higher bias if get the right size heat sink stable to.
Please use on the input BC550C/ 560C or 2SK170BL 2SJ74BL. The J Fet has to be rotated 180 degree.
I advise use the MJE 243/353 for VAS and TIP will do the power section.
To get read of the offset you can play with the input transistors or better to replace one of the 68K with a 100K (set up around 68K) multi turn trimmer and adjust it until the bias 0V.
I warn you when you do any adjustment please do not use your speakers under any circumstances!
The transistor blow up that $2 or so but a speaker can be $$$...
The amplifier is very sensitive even to the last piece of wire.. The input capacitor 4.7uF , I use BG non-polar. That is the best to me. If you build one PS for the two channel please use at least 4X10 000uF caps like CRC set up.
Once you hear the amp after you can't give it up!
You can use the layout I uploaded earlier, I will help with the stuffing.

Greetings Gabor
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Old 24th November 2012, 08:23 AM   #144
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Hello Sakis
Would you please!!!!!! you already posted here these message a couple times.
If the TIP 142/147 or MJ11015/16 transistor works (and good as a replacement) to Nelson Pass A40 Class A amplifier why not good here???
Did you tested the amp?
If yes please post your opinion otherwise let those people who want test it and post their opinion.
Nothing personal I just don't like you always come with these because you hate all Darlington devices. I read your opinion about all Darlington many times!
All my respect to you! I know you are a guy with a lot of knowledge & experience but sometimes we need to taste that food to (feel the taste) decide if is good or bad...
Again nothing personal OK, all my respect to you!
Greetings Gabor

Last edited by gaborbela; 24th November 2012 at 08:28 AM.
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Old 24th November 2012, 08:39 AM   #145
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Hello
In these case we can look up the very popular IRF240 Hexfet data and what we can see is not for audio???
That not always work that way.
I just gave an example.
By the way where you got the BD829/830. I want to test the P3A using the transistors you advised.

Greetings Gabor
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Old 24th November 2012, 10:41 AM   #146
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Yes Sakis doesn't like Darlingtons and he is allergic to even see them being mentioned / recommended here !

No harm done. I'll build a discrete Darlington also and see how they compare !
Easy to do that with hand made boards.
Cheers.
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Old 24th November 2012, 11:36 AM   #147
djk is offline djk
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"if the TIP 142/147 or MJ11015/16 transistor works (and good as a replacement) to Nelson Pass A40 Class A amplifier why not good here"

The original transistors in the Pass A40 were selected for their very low value of the base-to-emitter resistor that is not seen in other parts.

Discrete connected components are to be preferred.
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Old 24th November 2012, 11:46 AM   #148
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Hello

If you have TIP just give them a try. There are many device not made for audio and many designer use those successfull.
Also many valve was not made for audio and they are great for audio project, some of them are the best.
You can find a lot of circuit where the darlington was built up from two transistor like the Hiraga Class A so on.
I did tried to build up the darlington from two audio transistor but the result was not very promissing at all. You have to calculate the speed , capacitance etc
I know Sakis hate all the darlingtons, AND I respect that.
He should respect also those who use those devices or at least give a try .
Several famous amp was built with darlington power transistors. Not very popular but still can be found or used.
Sanken produce darlingtons for audio to. There are several darlington pack (IC) for audio to.
I do respect Sakis I did learned a lot from him I hope I will do in the future to! I do not want to write about these topic any more.....
Again if N Pass can use these device at the A40 we can to. That is a great sounding amp. Many people still use the A40 even do that is a very old design.

Greetings Gabor

Last edited by gaborbela; 24th November 2012 at 11:48 AM.
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Old 24th November 2012, 12:32 PM   #149
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"Again if N Pass can use these device at the A40 we can to."

Q7-10 are special complementary Darlington transistors, chosen
especially for their rugged safe operating area and the 25 Ohm value of
their internal driver's emitter resistor. These cannot be adjusted by the
user and most manufacturers use about 100 Ohms in this spot, which
results in far less bias on the driver transistor.
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Old 24th November 2012, 01:02 PM   #150
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Darlingtons and CFP amps are usually precise units. The transistors are prone to instability (and consist of 2 fixed parts) so the design is rarely flexible to part change.

With BJT amps we can usually roll transistors, but usually not with darlington amps. TIP142/147 is probably one of the most problematic. I can't even find a spice model that works. MJ110xx are also very prone to instability.

If the amp was designed for BDW, then even if they are slow or not good according to Wahab, they are usually better than better transistors not suitable for the circuit.

Try 2N6284/6287 darlingtons here. They tend to be a lot more stable and have good harmonic structure. It is not difficult to work with this topology once you are familiar with it (Read SSA thread to know more).
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