I'm building up a home theater so I thought about the audio.
And saw the many projects using chips.
I decided to give it a try and build a 5 channel chip amp (the sub already has its amp).
I now have 2 channels operating, the other are waiting for speaker terminals I don't yet have. I have used LM3886 because it was readily available.
Configuration is inverting, 330k/15k sets the gain, a 1k from + to ground gave an offset of 22mV at the output. A 2.2uF MKP from the 15k to a 100k linear pot is the input. These pots are intended for balancing the surround speakers, not master volume. Output has zobel 2.7ohms/0.1uF and 12 turns wound on 10ohm in series with the output. A 0.068uF is connected between V+ and V- pins and two 1500uF for filter. Mute is disabled with a 18k to V-. I have not used a series resistor at the output, why would that be needed?
For the moment they are fed with a 24+24V 200VA transformer, 2 bridges with 100uF caps as prefilter on them. The amps are rock stable it seems, perhaps because they are inverting.
I'm a tube nut and did not expect any sound of these, just good enough for movie sound. But, I'm simply amazed, I have never heard sand state sound this good. I have never heard such good control in the lower range, my bass reflex speakers sound almost like horns.
The bass on Simply Red: Pictures have always been a problem but this amp was able to 'control' it. Another problematic disc is Camille Saint-Saens symphony 3 C minor in a recording from Davies Hall, San Fransisco (Philips 412 619-2). That organ is really deep. This disc is still a problem it seems, I'm not sure yet but it sounds like the deepest bass is too weak.
Pictures can be seen here
And saw the many projects using chips.
I decided to give it a try and build a 5 channel chip amp (the sub already has its amp).
I now have 2 channels operating, the other are waiting for speaker terminals I don't yet have. I have used LM3886 because it was readily available.
Configuration is inverting, 330k/15k sets the gain, a 1k from + to ground gave an offset of 22mV at the output. A 2.2uF MKP from the 15k to a 100k linear pot is the input. These pots are intended for balancing the surround speakers, not master volume. Output has zobel 2.7ohms/0.1uF and 12 turns wound on 10ohm in series with the output. A 0.068uF is connected between V+ and V- pins and two 1500uF for filter. Mute is disabled with a 18k to V-. I have not used a series resistor at the output, why would that be needed?
For the moment they are fed with a 24+24V 200VA transformer, 2 bridges with 100uF caps as prefilter on them. The amps are rock stable it seems, perhaps because they are inverting.
I'm a tube nut and did not expect any sound of these, just good enough for movie sound. But, I'm simply amazed, I have never heard sand state sound this good. I have never heard such good control in the lower range, my bass reflex speakers sound almost like horns.
The bass on Simply Red: Pictures have always been a problem but this amp was able to 'control' it. Another problematic disc is Camille Saint-Saens symphony 3 C minor in a recording from Davies Hall, San Fransisco (Philips 412 619-2). That organ is really deep. This disc is still a problem it seems, I'm not sure yet but it sounds like the deepest bass is too weak.
Pictures can be seen here
200VA is not enough for full sustained power out. You have to look at the application though, a surround system. There, most power is needed in the front pair, then the center and last the rear pair.
Front + center has 90dB (vented boxes) and rears 86 (infinite baffle). The sub has a 100W amp in it.
Movie sound is very intermittent and bursty, the difference between peak and average power being much higher than music.
I'll see later when it's finished and used for some time. If the 200VA iron becomes too hot I'll beef it up. I could save some power by adding highpass filters to the center and rear (70Hz).
For a 2 channel stereo version? 300VA I would say 🙂
Cost? So far about the same as the cheapest surround receivers. I may buy a cheap used receiver and rip the power amps out of it and use it as a preamplifier. I have not decided yet, my DVD drive has builtin DD and DTS.
I once had a horn. A beast with a 12" driver. A 2W amplifier was enough to cause the window glass to rattle 🙂 It was larger than all my current 7 speakers together.
Status for the moment: still waiting for the remaining 3 pairs of speaker terminals.
Front + center has 90dB (vented boxes) and rears 86 (infinite baffle). The sub has a 100W amp in it.
Movie sound is very intermittent and bursty, the difference between peak and average power being much higher than music.
I'll see later when it's finished and used for some time. If the 200VA iron becomes too hot I'll beef it up. I could save some power by adding highpass filters to the center and rear (70Hz).
For a 2 channel stereo version? 300VA I would say 🙂
Cost? So far about the same as the cheapest surround receivers. I may buy a cheap used receiver and rip the power amps out of it and use it as a preamplifier. I have not decided yet, my DVD drive has builtin DD and DTS.
I once had a horn. A beast with a 12" driver. A 2W amplifier was enough to cause the window glass to rattle 🙂 It was larger than all my current 7 speakers together.
Status for the moment: still waiting for the remaining 3 pairs of speaker terminals.
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