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Old 27th February 2006, 09:37 AM   #1
beppe61 is offline beppe61  Italy
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Default Single darlington line preamp.

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
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Old 27th February 2006, 09:42 AM   #2
Bazukaz is offline Bazukaz  Lithuania
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And it would give much distortion , too.Why not to go with an op-amp ?
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Old 27th February 2006, 10:00 AM   #3
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by Bazukaz

1) And it would give much distortion , too.
2) Why not to go with an op-amp ?
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
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Old 27th February 2006, 10:01 AM   #4
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Beppe, why would you do it? Sure you can use one transistor but how good do you want it to be? It will hardly be any high-end.
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Old 27th February 2006, 10:11 AM   #5
AndrewT is offline AndrewT  Scotland
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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.
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Old 27th February 2006, 10:15 AM   #6
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Agree with Andrew. It's perfectly possible and if you Google for university lab sheets you should be able to find 3 different examples each of varying result. It's probably the first thing with transistors I did at uni.
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Old 27th February 2006, 10:16 AM   #7
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by peranders
Beppe, why would you do it?
Sure you can use one transistor but how good do you want it to be?
It will hardly be any high-end.
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
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Old 27th February 2006, 10:23 AM   #8
Bazukaz is offline Bazukaz  Lithuania
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What you need is a common emitter amplifier.Google for it.There are lots of very simple schematics.Don't expect good sound quality.
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Old 27th February 2006, 10:23 AM   #9
beppe61 is offline beppe61  Italy
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Quote:
Originally posted by AndrewT

Hi Beppe,
1) 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.
2) Just use a To92 cased single as a follower. Highish impedance input and lowish impedance output.
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
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Old 27th February 2006, 10:37 AM   #10
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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
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