Simple Class A amplifier

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M0UKD

M0UKD

Member
Joined 2012
m0ukd.com
Hi guys.

I have been playing with some simple single ended class A amplifiers today. I had some 2SC3281 transistors laying about and I came up with the circuit below. I have made similar circuits before but with MOSFET's.

I have a question. Being a transistor, the input impedance is relatively low. Originally I had a 10uF on the input, but the audio lacked bass. I replaced it with a 100uF and all is OK. I am driving it from a laptop and have tried my iPhone, both which drive the amp nicely. The MOSFET circuits I have built in the past, which are very similar in design, I have only needed a 0.1uF on the input due to the higher impedance.

I don't have any line output source here at the moment, but I was wondering if line out, say from a CD player, would work OK with this type of circuit, or would I have to build some kind of pre-amp to drive the low impedance?

Thanks for any help :)

John.

An externally hosted image should be here but it was not working when we last tested it.
 
L

lvcas vilches

Member
Joined 2012
;)querido john: claro que tienes que construir un pre amplificador... por supuesto en pura clase A ya que el amplificador es en clase A . tal vez con un trasformador de acople en la salida lo puedas llevar a mas watts & con un capacitor de 1500 micro faradios x 35 volts los bajos serán mas profundos e intensos que con uno de 100.
 
G

godfrey

Member
Joined 2009
Courtesy of Google translate:
your scheme very interesting ..... Now I wonder .. few watts of output has this amp & if possible to make himself a coupling transformer???
Click to expand...
dear john: of course you have to build a pre amp ... course in pure class A amplifier since the class is. perhaps with a coupling transformer at the output it can lead to more watts & a 1500 micro farad capacitor x 35 volts low will be more profound and intense with a 100.
Click to expand...
Wow! I'm impressed the translator copes so well with lousy grammar.
 
R

redsky

Member
Joined 2011
M0UKD said:
Hi guys.

I have been playing with some simple single ended class A amplifiers today. I had some 2SC3281 transistors laying about and I came up with the circuit below. I have made similar circuits before but with MOSFET's.

I have a question. Being a transistor, the input impedance is relatively low. Originally I had a 10uF on the input, but the audio lacked bass. I replaced it with a 100uF and all is OK. I am driving it from a laptop and have tried my iPhone, both which drive the amp nicely. The MOSFET circuits I have built in the past, which are very similar in design, I have only needed a 0.1uF on the input due to the higher impedance.

I don't have any line output source here at the moment, but I was wondering if line out, say from a CD player, would work OK with this type of circuit, or would I have to build some kind of pre-amp to drive the low impedance?

Thanks for any help :)

John.
Click to expand...

Hi John,

Many Thanks for your schematics. I was build mini ZCA base on multiple BD139 (cause i just have it on hand, and it same like 2SC3281 transistor). But I follow Marks Houston schematic for biasing voltage. See my projects in DIY Audio Projects Forum • Mini ZCA dual mono 2.6 watt.
 
MarianB

MarianB

Member
Joined 2011
electronistul29.wix.com/electronicacudjmarik
@godfrey your translation is not acurate at all, you rely too much on google translate!

lvcas vilches said:
muy interesante tu esquema..... ahora me pregunto.. cuantos watts de salida posee este amplificador & si es posible confeccionar para el mismo un trasformador de acople?????
Click to expand...

In english:
Youre schematic is very interesting... now i wonder...how many watts does it delivers? ( how much power output ) ,and is it possible to built a coupling transfomer for it?

lvcas vilches said:
;)querido john: claro que tienes que construir un pre amplificador... por supuesto en pura clase A ya que el amplificador es en clase A . tal vez con un trasformador de acople en la salida lo puedas llevar a mas watts & con un capacitor de 1500 micro faradios x 35 volts los bajos serán mas profundos e intensos que con uno de 100.
Click to expand...

In english:
Dear John, ofcourse you need to built an preamplifier, and of course it has to be in pure class A since the amplifier is in class A, and with a coupling transformer on the output you could get more watts from it, also with a 1500uF/35V capacitor the base would be much more profound ant intense than that with a 100uF capacitor.

PS: @lvcas vilches, 1500uF capacitor en la entrada? no es mucho? ( @lvcas vilches, 1500uF capacitor on the input? isn't it too much? )
 
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