Dear Friends,
please excuse my queries somewhat provoking and almost always a little silly.
I wonder if it is possible to build a line preamp just with one small power darlington.
If I am not wrong it could provide voltage gain and low output impedance to drive adequately a normal power amp.
Opinions are very welcome and appreciated.
Kind regards,
beppe
please excuse my queries somewhat provoking and almost always a little silly.
I wonder if it is possible to build a line preamp just with one small power darlington.
If I am not wrong it could provide voltage gain and low output impedance to drive adequately a normal power amp.
Opinions are very welcome and appreciated.
Kind regards,
beppe
Bazukaz said:
Thank you very much for your kind and valuable reply.
1) I have to say that my interest for very basic topologies has pitched after reading the thread about the Threshold NS10 line preamp and its exceptional sound quality.
So I am wondering how could sound a single darlington stage.
More minimal than that coud be hard to achieve after all.
Regarding the problem of distortion, I feel that this topic is not completely clear.
For instance not everyone agree about the importance of getting a clean distortion spectrum.
My questions are:
a) do smal power darlington exist?
b) where can I find a suitable schematic to be used as a line pre?
The cost of the experiment should not be that great.
2) op-amps still provoke mixed feelings within the audio community.
Someone mention the high number of maybe unnecessary gain stages, so the high feedback required and so on.
If measurements should lead the choice then that would be in most cases the perfect solution.
But one day someone told me that usual measurements do not tell everything, so ...
Anyway I would like to know if "on principle" a darlington could provide the voltage gain and the buffering action to be used as a line preamp.
Being very much impressed by a line preamp based on a Sziklai pair it seems to me that a darlington is very similar in some ways to a one piece Sziklai pair.
Thank you very much again.
Kind regards,
beppe
Hi Beppe,
why a power darlington?
At the low voltages and currents used in a pre, a power device is a waste and the compromises it will have to incorporate reduce it's performance almost everywhere else.
Just use a To92 cased single as a follower. Highish impedance input and lowish impedance output.
why a power darlington?
At the low voltages and currents used in a pre, a power device is a waste and the compromises it will have to incorporate reduce it's performance almost everywhere else.
Just use a To92 cased single as a follower. Highish impedance input and lowish impedance output.
peranders said:
Dear Mr. Peranders,
thank you so much for your always kind and valuable reply.
I am trying to fix some points to get some "tools" to assess the sound quality of audio equipment.
One was for instance the distortion spectrum.
Now I understand that it tells nothing.
I am expecting that some expert now tells me that frequency response and residual noise mean nothing.
In this scenario I strongly think that everything could be possible.
So it could be possible to build a single darlington line stage that performs superbly from a sonic point of view.
No certainties, only a lot of different opinions often conflicting.
Maybe one day I will discover that V=RxI is only a legend.
Thank you very much indeed.
Kind regards,
beppe
AndrewT said:
Dear Mr. Andrew,
thank you for you kind and valuable reply.
1) I meant a small power darlington, if this kind of device exists of course.
Not a TIP 141 of course.
2) because I thought to get some voltage gain but maybe I am wrong.
As I said all started from the consideration that I did build a prototype of a line preamp with a Sziklai pair (with very good results. It was better than a commercial preamp) and noticing that the darlington topology has some similarities to that.
But am I completely wrong ?
Maybe is a darlingtonusable only as buffer (i.e. current gain)?
Thank you again.
Regards,
beppe
I feel like paraphrasing any number of american movies: "Just answer the goddamn question!"
Yes, you can use a small power darlington for this purpose. However, I suspect you mean a small signal darlington, such as BC516(PNP) or BC517(NPN).
Connection would be pretty much identical to you Sziklai pair preamp, with just the polaritiy of the second transistor reversed.
How it would sound? Well, you'll be the judge of that. It's easy enough to test with two regular transistors in a darlington connection.
Rune
Yes, you can use a small power darlington for this purpose. However, I suspect you mean a small signal darlington, such as BC516(PNP) or BC517(NPN).
Connection would be pretty much identical to you Sziklai pair preamp, with just the polaritiy of the second transistor reversed.
How it would sound? Well, you'll be the judge of that. It's easy enough to test with two regular transistors in a darlington connection.
Rune
runebivrin said:
BC517, NPN, looks like a normal little TO-92 transistor. (Also called SOT54 package)
But as it is two (darlington) transistors in one package, it has very high hfe-gain. (high beta)
It is minimum 30.000, tells Philips data.
So, 1 uA into Base, will make 30 mA flow Collector->Emitter.
An externally hosted image should be here but it was not working when we last tested it.
Here is philips product page for BC517:
http://www.semiconductors.philips.com/pip/BC517.html
Download datasheet PDF:
http://www.semiconductors.philips.com/acrobat/datasheets/BC517_6.pdf
===============================
In this page you can find all types of Philips Transistors with info:
http://www.semiconductors.philips.com/catalog/219/282/50805/index.html
runebivrin said:
Dear Mr. Rune,
thank you so much for your kind and helpful reply.
1) So is feasible. Good.
The problem is that I have no idea of the topology to use.
I need to find one working with just one darlington that could give lte's say a voltage gain of about 3 and some current gain.
Just to make a simple experiment.
2) You have perfectly understood.
I am not talking about a darlington with a 10A of Ic, max of course.
The question is: is it possible to build a line preamp with just one BC517 or I need of at least two because from one I cannot get at the same time voltage and current gain?
As you can well understand I am just a curious idiot, and of the worst kind.
3) I am very eager to test it.
Nevertheless I would try with just one darlington if this is possible.
If you have any suggestion about a topology working with just one BC 517 I would be very pleased to test it right away.
Thank you very much indeed.
Kind regards,
beppe
beppe61 said:
Beppe, you seem to be a bit misunderstanding about amp stages and devices, you do not need a Darlington to get voltage gain. Voltage gain will depend on the circuit configuration and feedback, not the current gain of the device used (well it will to a tiny extent but that's not the issue here).
You can use a Darlington or a single BJT as a voltage gain stage and either will be fine. For a line stage I would myself use a single BJT as the less active devices the better in a way, and you have no control over the Darlington insides.
As somebody has said look for common emitter amplifier, it's really very simple. The best implementation uses four resistors and one BJT, maybe with a couple of capacitors.
richie00boy said:
Dear Sir,
the topology I was looking for is one of the kind Mr. Rozak has posted.
With that circuit I can get at the same time voltage and current gain out of just one small signal darlington.
That is what I intended in my query.
Now I will have something of feasible to test.
I strongly think a line stage cannot come simpler than that.
It is just a curiosity and as I am not a cat ... I have nothing to be afraid of.
Thank you very much indeed.
Kind regards,
beppe
richie00boy said:Yes the schematic posted by Rozak is exactly what I was suggesting.
Have fun
Thank you.
I will test the circuit but first I have to build a nice power supply to go with it, as from the schematic all the noise from the PS will be present at the output with the signal.
Anyway I think that a regulated PS based on a LM317 should suffice.
If you have any suggestion for a really great 0-50V single voltage power supply I am all ears (or link to relevant DIYAUDIO's threads of course).
Regards,
beppe
If you look at my website you can easily adapt the op-amp supply or the high voltage supply to your needs A 50V supply is not needed at all, 18V would be sufficient, but some component values would have to be scaled down.
The high voltage supply would fit in with your philosophy of minimal parts and has no loop feedback.
A 50V supply is not needed at all, 18V would be sufficient, but some component values would have to be scaled down.The high voltage supply would fit in with your philosophy of minimal parts and has no loop feedback.
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