A few years ago I built one based on a specialized circuit, LA-xxxxx (I forget the code) but it was dependent on the power supply from the socket as it consumed quite a lot and needed a symmetrical power supply.
And the case was a bit big and ugly....
A little while ago I saw an ad for sale for a 10W amplifier based on the Class D circuit, the PAM8610.
This is a modern amplifier intended for use with 10-15W speakers with 8 Ohm impedance.
I remembered that I also have such a module that has been lying around for a while in my junk boxes and I thought I could use it for a headphone amplifier, which can also be used on speakers if needed.
The major problem is that the speakers are driven on each channel by a symmetrical "H" bridge, without a common ground circuit.
For this reason, connecting stereo headphones, which have three wires, becomes problematic.
My first impulse was to search the boxes for two small signal transformers to make the adaptation but laziness won out and I was left staring at the ceiling, comfortably seated on the sofa thinking of a less bulky solution...
I won't go into the details of how amplifiers work in Class D but there is the possibility of making a contrivance to connect common grounded headphones.
The figure below shows the schematic I used successfully and the finished product, encased and powered by a 9V battery type 6F22.
The resistance values are:
R1 - 150 Ohm (two in parallel!)
R2 - 560 Ohm.
All resistors are 0.25W.
To reduce crosstalk it is best to use as equal resistors as possible on the two branches.
The 17-20 mA power consumption in operation, with LED makes it suitable for powering from this type of battery, the amplifier running down to 6.5V, on test.
It sounds great!
De mult timp simt nevoia unui amplificator de casti care sa poata fi conectat la diverse surse de semnal, stereo sau mono.
Acum cativa ani am construit unul bazat pe un circuit specializat, LA-xxxxx (am uitat codul) dar acesta era dependent de alimentarea de la priza intrucat consuma destul de mult si avea nevoie de sursa simetrica pentru alimentare.
Si carcasa era cam mare si urata....
Cu putin timp in urma am vazut un anunt de vanzare pentru un amplificator de 10W bazat pe circuitul in Clasa D, PAM8610.
Acesta este un amplificator modern, destinat a fi utilizat cu boxe de 10-15W cu impedanta de 8 Ohm.
Mi-am adus aminte ca am si eu un astfel de modul care sta de ceva vreme prin cutiile cu troace si m-am gandit ca il pot destina unui amplificator pentru casti si care, la nevoie, poate fi utilizat si pe difuzoare.
Problema majora este ca difuzoarele sunt actionate pe fiecare canal de cate o punte tip "H", simetric, fara un circuit comun de masa.
Din acest motiv, conectarea castilor stereofonice, care au trei fire, devine problematica.
Primul impuls a fost sa caut in cutii dupa doua transformatoare de semnal mic pentru a face adaptarea dar lenea a invins si am ramas cu ochii in tavan, comod asezat pe canapea gandindu-ma la o solutie mai putin voluminoasa...
Nu intru in detaliile modului de functionare a amplificatoarelor in Clasa D dar exista posibilitatea de a realiza un artificiu pentru a conecta casti cu masa comuna.
In figura de mai jos este prezentata schema pe care am uitilizat-o cu succes precum si produsul finit, incasetat si alimentat dintr-o baterie de 9V tip 6F22.
Valorile rezistentelor, obtinute prin tatonare sunt:
R1 - 150 Ohm (cate doua in paralel!)
R2 - 560 Ohm.
Toate rezistentele sunt de 0.25W.
Pentru reducerea diafoniei este bine sa folosim rezistente cat mai egale pe cele doua ramuri.
Consumul de numai 17-20 mA in functionare, cu tot cu LED il face potrivit pentru alimentarea din acest tip de baterie, amplificatorul functionand pana la 6.5V, pe testare.
Se aude minunat!
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