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From: olivier.scalbert on 13 Oct 2008 09:44
Hello,

First, I must say that I have not done analog electronics since a long
time. So please be indulgent !

I want to do a small class-A music amplifier + preamp. I want to find
the best trade-off between simplicity and sound quality.

My approach is very incremental. I have started with one old 2N3055,
polarized with voltage divider composed of 2 resistors.

As the gain of the transistor is to low I finally put a (too?) small
BC546 in front of the 2N3055 (Darlington).
See schema:
http://scalbert.dyndns.org/electronics/amplifier/ampli1.png

As I need a preamp for the volume control, I have add another BC546 to
amplify the input signal.
See schema:
http://scalbert.dyndns.org/electronics/amplifier/preamp1.png

The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V
to 12V as the 2N3055 heatsink is to small.

When I first test it, I was expected to have a crappy and plastic
sound, and even smoke, but I was very surprised. The sound is clean
and contains a lot of details (speaker: B&W DM110).

What I want to do now is to improve:
- the schematic (there are certainly mistakes ...)
- the component choice (better capacitor ? , better transistor ?)

Any remarks and suggestions are welcomed !

Thanks very much,

Olivier

From: john jardine on 13 Oct 2008 13:29

<olivier.scalbert(a)algosyn.com> wrote in message
news:cb07c7ff-4a90-4d6e-b7aa-fa2f172aecf2(a)t65g2000hsf.googlegroups.com...
> Hello,
>
> First, I must say that I have not done analog electronics since a long
> time. So please be indulgent !
>
> I want to do a small class-A music amplifier + preamp. I want to find
> the best trade-off between simplicity and sound quality.
>
> My approach is very incremental. I have started with one old 2N3055,
> polarized with voltage divider composed of 2 resistors.
>
> As the gain of the transistor is to low I finally put a (too?) small
> BC546 in front of the 2N3055 (Darlington).
> See schema:
> http://scalbert.dyndns.org/electronics/amplifier/ampli1.png
>
> As I need a preamp for the volume control, I have add another BC546 to
> amplify the input signal.
> See schema:
> http://scalbert.dyndns.org/electronics/amplifier/preamp1.png
>
> The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V
> to 12V as the 2N3055 heatsink is to small.
>
> When I first test it, I was expected to have a crappy and plastic
> sound, and even smoke, but I was very surprised. The sound is clean
> and contains a lot of details (speaker: B&W DM110).
>
> What I want to do now is to improve:
> - the schematic (there are certainly mistakes ...)
> - the component choice (better capacitor ? , better transistor ?)
>
> Any remarks and suggestions are welcomed !
>
> Thanks very much,
>
> Olivier
>
For a starter, increase C1 to 1000uF. 'T'll get the response down to about
20Hz.


From: Eeyore on 13 Oct 2008 20:59


"olivier.scalbert(a)algosyn.com" wrote:

> Hello,
>
> First, I must say that I have not done analog electronics since a long
> time. So please be indulgent !
>
> I want to do a small class-A music amplifier + preamp. I want to find
> the best trade-off between simplicity and sound quality.
>
> My approach is very incremental. I have started with one old 2N3055,
> polarized with voltage divider composed of 2 resistors.
>
> As the gain of the transistor is to low I finally put a (too?) small
> BC546 in front of the 2N3055 (Darlington).
> See schema:
> http://scalbert.dyndns.org/electronics/amplifier/ampli1.png
>
> As I need a preamp for the volume control, I have add another BC546 to
> amplify the input signal.
> See schema:
> http://scalbert.dyndns.org/electronics/amplifier/preamp1.png
>
> The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V
> to 12V as the 2N3055 heatsink is to small.
>
> When I first test it, I was expected to have a crappy and plastic
> sound, and even smoke, but I was very surprised. The sound is clean
> and contains a lot of details (speaker: B&W DM110).
>
> What I want to do now is to improve:
> - the schematic (there are certainly mistakes ...)
> - the component choice (better capacitor ? , better transistor ?)
>
> Any remarks and suggestions are welcomed !

Stop mucking about with stuff you don't understand and simply buy a modern
hi-fi amp. Power amps are a real speciality (especially if you want them
to be stable). It's no place for a beginner.

Do you understand stabilty criteria for example. What's a Bode plot ? etc


Graham (designer of stable pro-audio power amps since 1980)

From: mrdarrett on 14 Oct 2008 00:11
On Oct 13, 5:59 pm, Eeyore <rabbitsfriendsandrelati...(a)hotmail.com>
wrote:
> "olivier.scalb...(a)algosyn.com" wrote:
> > Hello,
>
> > First, I must say that I have not done analog electronics since a long
> > time. So please be indulgent !
>
> > I want to do a small class-A music amplifier + preamp. I want to find
> > the best trade-off between simplicity and sound quality.
>
> > My approach is very incremental. I have started with one old 2N3055,
> > polarized with voltage divider composed of 2 resistors.
>
> > As the gain of the transistor is to low I finally put a (too?) small
> > BC546 in front of the 2N3055 (Darlington).
> > See schema:
> >http://scalbert.dyndns.org/electronics/amplifier/ampli1.png
>
> > As I need a preamp for the volume control, I have add another BC546 to
> > amplify the input signal.
> > See schema:
> >http://scalbert.dyndns.org/electronics/amplifier/preamp1.png
>
> > The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V
> > to 12V as the 2N3055 heatsink is to small.
>
> > When I first test it, I was expected to have a crappy and plastic
> > sound, and even smoke, but I was very surprised. The sound is clean
> > and contains a lot of details (speaker: B&W DM110).
>
> > What I want to do now is to improve:
> > - the schematic (there are certainly mistakes ...)
> > - the component choice (better capacitor ? , better transistor ?)
>
> > Any remarks and suggestions are welcomed !
>
> Stop mucking about with stuff you don't understand and simply buy a modern
> hi-fi amp. Power amps are a real speciality (especially if you want them
> to be stable). It's no place for a beginner.
>
> Do you understand stabilty criteria for example. What's a Bode plot ? etc
>
> Graham (designer of stable pro-audio power amps since 1980)


Come now Graham, he didn't mention he wants to become an EE... why be
so mean?

Olivier, why not try this one?
http://diyaudioprojects.com/Solid/ZCA/ZCA.htm

2SK1058 lateral mosfets can be hard to find however.

Michael
From: John Larkin on 14 Oct 2008 00:15
On Mon, 13 Oct 2008 06:44:49 -0700 (PDT),
"olivier.scalbert(a)algosyn.com" <olivier.scalbert(a)algosyn.com> wrote:

>Hello,
>
>First, I must say that I have not done analog electronics since a long
>time. So please be indulgent !
>
>I want to do a small class-A music amplifier + preamp. I want to find
>the best trade-off between simplicity and sound quality.
>
>My approach is very incremental. I have started with one old 2N3055,
>polarized with voltage divider composed of 2 resistors.
>
>As the gain of the transistor is to low I finally put a (too?) small
>BC546 in front of the 2N3055 (Darlington).
>See schema:
>http://scalbert.dyndns.org/electronics/amplifier/ampli1.png
>
>As I need a preamp for the volume control, I have add another BC546 to
>amplify the input signal.
>See schema:
>http://scalbert.dyndns.org/electronics/amplifier/preamp1.png
>
>The DC is provided by a lab power supply (0-30V, 0-3A). I use from 5V
>to 12V as the 2N3055 heatsink is to small.
>
>When I first test it, I was expected to have a crappy and plastic
>sound, and even smoke, but I was very surprised. The sound is clean
>and contains a lot of details (speaker: B&W DM110).
>
>What I want to do now is to improve:
>- the schematic (there are certainly mistakes ...)
>- the component choice (better capacitor ? , better transistor ?)
>
>Any remarks and suggestions are welcomed !
>
>Thanks very much,
>
>Olivier

The passive pull-down resistor really limits the negative swing into
the speaker. A constant-current sink would be better.

John

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