Which amplifier for tiny PC speakers

[Rudi_Ratlos]

Hello to everybody,

I have just finished building a pair of speakers which shall eventually replace my current LOGITECH PC speaker system.

The speakers consist of an 8 Ohm TangBand W4-657B Fullrange and a Dayton ND20FA 6 Ohm Tweeter.
The speaker's case is 20cm high, 15 cm broad and 20 cm deep.
The speakers shall be placed on my desk.
The distance to my ears is less than 1 meter.

I do not know how to upload an image of my home-brew speakers - this is my first thread.

I would appreciate to also assemble an amplifier on my own.

So: the chain of components would be: PC Soundcard: Soundblaster Audigy 2 ZS -> Amplifier -> my home-brew speakers.

The amplifier does of course not need to drive hundreds of Watts - but it should sound: naturally and charming.

I do have some fundamental knowledge of electronics.
I can solder a power supply without a guideline.
But I do not have any knowledge in building an amplifier.

My question to you: do you recommend me any DIY amplifier - if possible with PCB - to whom I can connect the PC-soundcard and my new speakers?

Charming, natural, relaxing, ... to listen to the xxxx .flac on my PC?

Best regards - Rudi

P.S. Do not complain about my English - I did my best.

[Bigun]

Try this, the designer (Carlos) lives on this Forum:

http://users.tpg.com.au/users/gerski...mp/default.htm


I would pick the basic DX to start with. Not sure if you can buy pcb's though.

Another option that I know has PCBs for sale:

http://sound.westhost.com/project3a.htm

[Rudi_Ratlos]

Thank you, Bigun, for your advise.

I looked at Greg's DX - Web Site and I made up my mind to build it by myself.

Best regards - Rudi

[Bigun]

That's great, but I should warn you, you will become addicted to this

[Rudi_Ratlos]

Hi Bigun,

I have just ordered the components needed to etch (?) the PCBs.
I hope I will succeed - but since I am very patient I will finally.

One other question:

I intend to connect the DX-AMP to the output of my PC Soundblaster Audigy 2 ZS Soundcard (Cinch connection).
I can of course adjust the volume via software.

Is there any small circuit that will allow me to adjust the volume via the volume knob of the amplifier's case?

I will you the case of my old Yamaha AX-380 amplifier to house the DX-AMP.

Best regards - Rudi

[Rudi_Ratlos]

I want to post my DIY - experiences in this thread along with two questions I currently have.

Carlos' DXAMP is my first DIY-project.
I am not very familiar with electronics and do only have a rough understanding about current, transistors, relays, ...

I do not have special equipment like an oscilloscope, I own a jigsaw, an iron, a cheap multimeter, a drilling machine in a rig and my 30 years old Weller Magnastat soldering iron.
That is the equipment I started with.

The first challenge was to etch the PCBs of Carlos' DXAMP.
Friendly as Carlos is he published the DXAMP's PCB - Bottom View on Greg's Web site: Greg's Web Site

I printed the image on a special glossy paper on the printer of my PC and pressed it with my iron on a naked circuit board.
It took of course several attempts until the result was useable.
Then I etched the two circuit boards and drilled the holes with my 650 Watt Bosch drill hammer.

The result:



Soldering the boards was the most pleasant part of the project.



Soldering took of course some time, because I did it slowly and tested every part with my magnifying glass for shortcuts, cold solder points, ...

I followed Greg's advise for a suitable PSU as far as a PSU printed board that I bought from ebay allowed it and fitted everything in an old Yamaha amplifier case.



The adjustment of the BIAS current and the DC-offset was done exactly as Greg explained it on his site.

"My" DXAMP played "at first go".
It has a sound I love, "my" sound: smooth, warm and strong as well.

I want now to optimise the case, the wiring, ... and have 2 questions:

1) Should I use a bridge rectifier in the PSU (as shown on the pictures) or should I replace the bridge rectifier by 4 discrete diodes (f.e. MUR1520)?
2) When I turn on the AMP it says: "Plopp"; when I switch it off: 3 seconds of silence, 3 seconds of whispering, hissing and then a big "Plopp".
What is the reason for this "Plopp"?
I see from the PSU's schematics that the capacitors on each rail are discharged by a 2k2 resistor and a LED.
Are thes "Plopps" dangerous for my loud-speakers?
Have I to invent someting like "delayed LS turn on and immediate turn off"?

Maybe one of you can answer my questions.

Best regards - Rudi_Ratlos

[Bigun]

Wow! - you made great progress and built a very nice amplifier. The fact that it worked first time is a very good sign.

If such a thing existed I would award you the DIY First Build badge

I used discrete diodes when I built my psu rectifier based on a recommendation from Hugh (of ASKA fame). They have the benefit of being a little less noisy than regular diodes. I don't see any need to change out the rectifier you already have if you are satisfied with the sound - the differences are likely to be marginal and your time might be better spent on something new.

In terms of the 'plop', well this is the infamous turn-on thump that many amplifiers have. I don't have much of a turn on sound with mine (mainly because I don't use a CCS for the LTP - but that's likely to be a contested theory) but I do have the little squelch sound a few seconds after turn-off when the supply rails collapse after exhausting the psu capacitors.

Unless the cones in your speakers are trying to leave their boxes with a big ugly 'thump' then I don't think it will cause any harm. Commercial amplifiers usually employ relays on the speaker outputs to control this effect along with providing some protection against amplifier faults - they don't want to be liable if their amp blows up and takes out some very expensive speakers.

Whether the effort of adding output relays is worth it to you is a decision you will have make. There are various designs around on the internet but I haven't built one.

At this point - I'd punt the question to Carlos, the designer of this amplifier who knows it more intimately than I - he may have some tricks to suggest.

[Rudi_Ratlos]

Hi Bigun,

thank you for your "DIY First Build - Award".

Carlos' DXAmp is definitely my 1st DIY - project.

As Carlos said:

"Cheap": well: about 250$.
"Easy to build": if you have some practise: yes.
If you are a 1st-time DIY'er like me: it takes a lot of nights to build it; and it takes: Blood, Sweat and Tears.
eXtraordinary Sound: definitely!!

I will go on and build a nice case for the DXAmp (made of Multiplex Wood) and will equip it with an attenuator ("Lightspeed Attenuator")
and a "Smooth Power On" and a "Delayed LS Turn On" - and "Immediate LS Turn Off" circuit.

The only thing I need: some kind of curiosity ("Will it work?") and a definite amount of self-confidence ("It will work - if not: somebody in this forum will help me!).

Best regards - Rudi_Ratlos

P.S.: And of course: whenever I had a question how to proceed: Carlos told me.

[Bigun]

Originally Posted by Rudi_Ratlos

I will go on and build a nice case for the DXAmp (made of Multiplex Wood) and will equip it with an attenuator ("Lightspeed Attenuator")
and a "Smooth Power On" and a "Delayed LS Turn On" - and "Immediate LS Turn Off" circuit.

You are hooked now

[jaycee]

I would recommend the delayed turn on/off circuit for the speakers anyway. While you are at it, add DC protection. There's a few suitable circuits to do this, usually only needing a few small signal transistors, and a medium power one (or a suitable MOSFET) for relay switching.