[Gliding Dutchman]

Hi there

It has been a long time since visiting here and I thought I'd share my latest DIY project as it is of high relevance of this forum!

I first set out to understand, for myself, better how amplifier circuits work - you know, what makes them tick! So I asked help on various forums from people with a good technical understanding of these stuff and they kindly guided me to construct a basic amplifier. I had some solid-state devices in my parts bin which turned out to be a rather common amplifier device - the famous 2N3055 NPN transistor (I have lots of NOS Siemens units) - also have some BC550's at my disposal.

Whilst testing I used my headphones to check the circuit and so I decided that I can develop this tutorial project into a working unit. I needed a headphone amp as my stereo amp is very minimalist and doesnt feature a headphone amp. The circuit developed nicely with help from friends - I am very happy with the sonic results. To put is plainly the sound is the best I heard from my cans EVER!

Here it is - the (DEWAUDIO) MINIMA SE, CLASS-A, H-AMPLIFIER.

Here is my project exicuted on Veroboard. (I hate veroboard but it works for this job)

The circuit is fully class A and the output transistors gets extremely hot!
Power is currently supplied by a 12v battery but I am working on a propper regulated PSU for highest fidelity.

Later I would like to do a popper PCB as well in a neat cabinet.

(NOTE: Current transistors used in the Veroboard unit is SJE5300's from Motorola mounted in old CPU heatsinks for a LAN switch)

Cheerio
Dewald

 

[Nick 214]

Nice Job!

That looks great.

 

[synaesthetic]

This is both channels, or one channel?

 

[Tridacnid]

I see two RCA inputs, so I assume it is both channels.

 

[synaesthetic]

I mean the schematic, but I only see 3 transistors on the board.

oh wait, I'm blind. a few are TO-92.

 

[Gliding Dutchman]

Quote:

Originally Posted by synaesthetic /img/forum/go_quote.gif This is both channels, or one channel?

This is a stereo unit. FLTR: Regulator (where LED stems from), Right channel (signal in by green wire), Left channel (signal in by white and green speckled wire).

Pure class A - single ended. High heat, low output. Sweet but brilliant sound!

The schematic is for a single channel - obviously...

D

 

[Gliding Dutchman]

Yes... the BC550 are TO-92 packages.
Power transistors are TO-220 or TO-3.

BTW - My hps are AKG K240's (600 ohm)

D

 

[Gliding Dutchman]

The "prototype is built up from allsorts of parts I had lying around. I am busy ordering "matched" parts and want to make some DIY PCB's.

D

 

[synaesthetic]

Low output... would this be good for low impedance, high-sensitivity phones?

It seems like an interesting and inexpensive amp, I'm curious about building one. =D

 

[Gliding Dutchman]

Quote:

Originally Posted by synaesthetic /img/forum/go_quote.gif Low output... would this be good for low impedance, high-sensitivity phones? It seems like an interesting and inexpensive amp, I'm curious about building one. =D

Hi there

Well, it drives my AKG K240 (600 ohm) phones very nicely. Detail is amazing!
You will however need a well regulated PSU as to prevent buzz from mains ripple - or just use a battery.

Note: R6 needs to be a high power resistor - it gets very hot!

Go ahead and tell me what you think... I am very impressed with this brew!

D

 

[synaesthetic]

K240 sextetts are pretty hard-to-drive 'phones. This may not work so well for my Audio-Technica fetish...

 

[Gliding Dutchman]

I am not too sure about that - are mine the Sextettes? Well, this amp drives them very nicely also my AKG K141's

D

 

[synaesthetic]

I'm anal about having a lot of usable range on my volume knobs, though. It may work well but if the knob at 9 o'clock is deafeningly loud, then I'll get annoyed with it.

What sets the gain on this amp?

 

[Gliding Dutchman]

Oh yes.. there is lots of volume range with this amp. Infact, my current prototype has no volume control and is connected directly to my PC soundcard (Creative Live). There is a comfotable range to adjust the volume.
I am also finiky about propper volume control and this unit gets my approval.


You can exchange the listed LOG POT on the schematic for say a 100K unit or just use a propper external pre-amp. The choice is yours. Also you can up the gain by upping the supply voltage I think - a few resistors must then simply be adapted as well.

Firstly, try the amp as it is then do the adjustments.

D