Desta vez quero apresentar um dos amplificadores de potência que construí de raíz há uma série de anos e ainda hoje uso no dia-a-dia, pois ficou com uma qualidade muito boa e tem um tamanho e aspeto que o faz integrar-se na perfeição no ambiente da nossa sala. Uso-o como amplificador final na minha aparelhagem Hi-Fi principal, tendo um pré-amplificador, igualmente caseiro, ligado entre ele e as fontes (nessa aparelhagem tenho o meu Marantz CD40 fortemente modificado, o meu Philips CD104 (stock), o Nakamichi CR3E e um Tuner da Technics que agora não me recordo do modelo preciso).
Na altura em que o comecei, tinha já construído um "Gainclone" à base do LM3886 mas devido a precisar de um amplificador no meu carro, com um chipamp um pouco mais "estável" (os LM3875/3886 tendem muito a ter problemas de oscilações se não tivermos bastantes cuidados; o ambiente num carro nunca é livre de interferências), fui à descoberta de alternativas e descobri o TDA7294, um chipamp muito bom em termos de qualidade de som e também bastante potente, mas sobretudo muito estável e simples de implementar. O amplificador do carro foi um sucesso e então fui em frente com este projeto para casa (tinha encontrado dois belos transformadores bem potentes e dois dissipadores, provenientes de velhas colunas amplificadas).
Na altura costumava frequentar muito um site com forum que era uma espécie de "alternativa" ao conhecido DIYAudio, o DIYHiFi. Fui então debater lá as minhas ideias e absorver os conhecimentos e a experiência incrível de alguns dos membros para aperfeiçoar o projeto. Infelizmente o site hoje já não existe, mas tive o cuidado de guardar os meus tópicos. Segue o primeiro post no tópico que abri no forum e os esquemas e fotos. Mas antes, uma rápida intro em inglês, desta vez não há o artigo completo, porque também já tem as citações originais em inglês:
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English: This article is about one of my home built power amps which I still use almost daily in my main system. It's based on TDA7294 and sounds really good. Optimization of circuit and power supply was done with generous support from the very knowledgeable and experiences Hi-Fi-Wizards in a small, but very nice forum that existed years ago as an alternative to well known DIYAudio. Unfortunately gone long ago. But I saved the topics and posts. Here is the initial post and then follow the schematics and some pics. Enjoy!
Hi ppl
As I figured in future I am going to need an additional amp (good excuse, right?
), just started another new project, a gainclone-amp based on TDA7294.
Will be dual mono style, but in one case.
I got lucky and recycled two nice 45Vct 140VA trannies and two ca. 1.5ºC/W heatsinks from two old mono blocks.
So, amp will have around 2x 50W RMS into 8ohm, or 2x 60W RMS into 4 ohm (max spec of TDA with reasonable THD and not yet risking to overload the transformer).
It might get a DC speaker protection circuit and a LED level meter, aswell as a volume Pot. But nothing more this time lol...Just finished the preliminary schematics, here they go.
PSU is unregulated, and independent for each channel (remember, dual mono), total of 26400uF per channel. Yes, I have all those 2200uF caps lying around here, that's why.
Design is heavily oriented at Carlos' Snubber GC PSU.Amp schematic is almost directly like datasheet standard app circuit. Only changed a little bit some component values, hopefully for the better (especially I prefer to set freq cut off way lower).
Gain is 30dB, as I don't have any active buffer this time. I figured it wouldn't be needed, as they claim that the TDA runs happily with this high gain.And that's all for now.
Any suggestions or critics (as long as helpful) are very welcome.
And I do have some questions, obvious!
), just started another new project, a gainclone-amp based on TDA7294.
), total of 26400uF per channel. Yes, I have all those 2200uF caps lying around here, that's why.
Seguiram-se trocas de ideias, melhorias, e acabei por chegar a estes esquemas finais e também PCB layout:
Fonte de alimentação:
PCB:
Then, the result:
E aqui o post final no tópico no forum:
Hi ppl.
Great news: Amp is finished!!
And the result not only meets my expectations, it actually exceeds themSound is great, I like it really a lot: very transparent highs and mids, warm and perfect bass.
I never thought the TDA's would sound that good. Because some people out there tend to say they are inferior to LM3886/Lm4780, but now that I can hear them for real, I don't think so at all.
They do sound a little different, that's true. Which is quite logical, as they have completely different output technology. But certainly not for the worse, I would even risk to say: possibly I like their sound even more...And also implementation was uncredibly easy and straight-forward:
my PCB layout worked perfectly, from the first test on. No oscillations (I've always had this problem with LM3886 and LM4780, if you don't put caps "everywhere", they really like to oscillate. The TDA's don't. I've only one small RF filter cap in input, nothing else.)
Also no on-off clicks or pops at all, and no humming also, at least not in form of ground-loops (Carefully avoided them). Induced hum, there's a very little of it, probably due to me having used those old EI trannies. I moved the cable positions a little, and optimized it. Can't hear any hum or noise from speakers, unless I put my ear directly at it.Regarding output power, I designed this amp having home use in mind. But it will easily exceed 40 W RMS, without the chips getting hot (tried it into resistive load). Actually they run much cooler than LM3886.
And the amp even looks quite nice hehe... especially with the red very bright VU level meters (with LM3915. If anyone wants the PCB layout and schematic of them, just ask, I'll post them).
Some additional detail: the POT is an ALPS Blue 10k. And the buffer is simple non-inverting LM4562 with only one pair of Panasonic FC decoupling caps, just like in the schematic.
I finally got myself to try that new "miracle" opamp from national lol... very hard to get in europa... not even Farnell stocks them
Sound is good, very neutral and natural. Possibly a little better than OPA2134, but that's hard to tell for me (would need better speakers).Anyway, that's one more amp to the collection lol.
