About make an audio power amplifier.

[Nikolai Petrenko]

Most transformers have secondary wound over primary.

 

[Tony Stewart]

You would have at least 30% more efficiency and lower peak currents to use the 42Vac and make a simple bipolar Buck Regulator at 40kHz or so to convert down to +\-4V above your peak output signal desired using 4A rated plastic caps. Then no monster cap and less heat wasted using continuous triangle currents and low ESR caps with even less ripple and higher dampening factor. Intermod noise will be still ultrasonic and low.

 

[Tony Stewart]

I don't know, my multimeter dead recently.

Dont let that stop you from fixing it or replacing it. Only $5 here

 

[spec]

Most transformers have secondary wound over primary.

Yes- that's what I meant to say.

spec

 

[Tony Stewart]

I would not advise rewinding with the same wire to avoid insulation failure if there are sharp ferrite edges. I would consider the Buck mode solution but is may be too much work for you just to gain 30% more power and efficiency ( not really big but depends on your needs)

 

[Nikolai Petrenko]

You would have at least 30% more efficiency and lower peak currents to use the 42Vac and make a simple bipolar Buck Regulator at 40kHz or so to convert down to +\-4V above your peak output signal desired using 4A rated plastic caps. Then no monster cap and less heat wasted using continuous triangle currents and low ESR caps with even less ripple and higher dampening factor. Intermod noise will be still ultrasonic and low.

In can buy copper enamel wires very easy and pretty cheap (the store only 700m away from my house). I also know how to wind a toroid transformer.

I would not advise rewinding with the same wire to avoid insulation failure if there are sharp ferrite edges. I would consider the Buck mode solution but is may be too much work for you just to gain 30% more power and efficiency ( not really big but depends on your needs)

Edge? The core has been wrapped with prespan paper, no edge can scratch the insulator. Ferrite??? This transformer use in 50Hz, isn't it silicon-iron?
Buck regulator is a good idea but:
The transformer have voltage high enoguh to blow my amp but current only enough for 2 board, while my amp have 3 board, so curent hungry will occur when reach the peak output power.

 

[Nikolai Petrenko]

Yes- that's what I meant to say.

 

[Nikolai Petrenko]

Dont let that stop you from fixing it or replacing it. Only $5 here

The multimeter has been broken, the moving coil is damaged, no change to fix it
Yes, the price you have shown very close to what sell in my local.
But I want to look for sth can measure capacitance. The one can measure inductance or frequence seem be much more expensive.
I also don't have oscilloscope, but I think I can make one:
Download oscilloscope software and install it, then build a attenuator.
The "soft" oscilloscope also can measure inductance by: use capacitance meter to measure some capacitor, then make a LC oscillator with C already know capacitance and L that need to measure. Use "soft" oscilloscope to measure output frequency. Finally, with f and C => L.
Do you think it will possible?

 

[Tony Stewart]

The multimeter has been broken, the moving coil is damaged, no change to fix it
Yes, the price you have shown very close to what sell in my local.
But I want to look for sth can measure capacitance. The one can measure inductance or frequence seem be much more expensive.
I also don't have oscilloscope, but I think I can make one:
Download oscilloscope software and install it, then build a attenuator.
The "soft" oscilloscope also can measure inductance by: use capacitance meter to measure some capacitor, then make a LC oscillator with C already know capacitance and L that need to measure. Use "soft" oscilloscope to measure output frequency. Finally, with f and C => L.
Do you think it will possible?

If you make it resonate in audio band,,Audacity free windows software, which many sweep generators or wave generators and scope for any audio input to measure shunt current or voltage with time sweep trace to find parallel resonance . You can use speaker out and aux input. YOu can calibrate with 1.5V or 3V lithium battery Pulse it or sweep it and find resonance. if less than 25 ~20kHz. Many things.. even log spectrum analyzer.

If torroid, then it is big iron powder core for low frequency, don't push it too high in PWM rate. Test it on Audacity for SRF using RLC-Z nomograph from web use parallel pot to load with low audio out voltage to sweep and determine resonance and operate below this for PWM. 40 kHz may be too high on secondary,,depends....usually SMPS DC-DC use small torroids for more current at higher f because magnetic constant is V/f is important ratio to understand.

 

[Nikolai Petrenko]

If you make it resonate in audio band,,Audacity free windows software, which many sweep generators or wave generators and scope for any audio input to measure shunt current or voltage with time sweep trace to find parallel resonance . You can use speaker out and aux input. YOu can calibrate with 1.5V or 3V lithium battery Pulse it or sweep it and find resonance. if less than 25 ~20kHz. Many things.. even log spectrum analyzer.

OK, I will try.

If torroid, then it is big iron powder core for low frequency, don't push it too high in PWM rate. Test it on Audacity for SRF using RLC-Z nomograph from web use parallel pot to load with low audio out voltage to sweep and determine resonance and operate below this for PWM. 40 kHz may be too high on secondary,,depends....usually SMPS DC-DC use small torroids for more current at higher f because magnetic constant is V/f is important ratio to understand.

I will use normal unregulated power supply so no PWM to cause pulse overload. The toroid core is made from spirial silicon-iron laminate, not iron powder (the biggest iron powder core I have seen is the inductor of a old Soviet touch activated lamp 0.8x1.25cm core area, I haven't seen any bigger ones).

 

[Nikolai Petrenko]

Can anyones tell me how to design good passive crossover and loudspeaker box?
I also want to know advantage and disadvantage of wo-way or three-way system when use with my amp.
Thanks.

 

[spec]

Can anyones tell me how to design good passive crossover and loudspeaker box?
I also want to know advantage and disadvantage of two-way or three-way system when use with my amp.

As you are going for a bass sub definitely go for a two way system rather than three way. Two way is simpler, cheaper and has less cross over problems. Crossing over from one speaker to another is always undesirable.

Ported cabinets are currently favored rather than closed box (infinite baffle). Besides, a ported cabinet can easily be turned into an infinite baffle, but not the other way around, at least not easily.

There are heaps of suitable designs for speaker systems on the net.

The most critical aspect is what speaker chassis you can access and afford. HiFi speaker chassis are very expensive

In terms of tweeter there is a broad choice to be made: bright or smooth; at one end there is the metal dome types and at the other end there are the soft (silk) dome tweeters. I favor the former, but it is a matter of taste.

And there is also a choice to be made in bass/mid driver: fast and articulate or powerful sounding. I prefer the former, but again it is a matter of choice.

Your best bet would be to buy secondhand speakers, rather than make your own.

As I have said before, don't worry too much about matching the speaker power rating to the amplifier. For example a 100W amplifier driving 20W speaker will be OK. The other way around will not. Bass subs need more power capability though, perhaps 40W. But you do need to match the sound of the amplifier and speakers. For example, a fast articulate amplifier driving fast articulate bass/mids coupled to bright tweeters, would be very revealing and may emphasis any shortcomings in the source material or other components in the audio chain. On the other hand, a smoother system may be more forgiving and easier on the ear.

At the end of the day, it is all down to taste.

spec

PS: don't worry too much about speaker impedance either: the impedance varies greatly through the audio spectrum. In terms of your amplifier there are roughly four Ohm and roughly eight Ohm speakers.

You will also see a load of stuff about low amplifier output impedance and damping. The fact of the matter is that the equivalent circuit of an eight Ohm speaker chassis, for example, is approximately a six Ohm resistor in series with a motor. In this case the effective output impedance of any amplifier can never be lower than six Ohms, never mind how astonishingly low the actual output impedance of the amplifier is. Some speakers do have very low loading impedances at certain frequencies though, even as low as two Ohms.

 

[KeepItSimpleStupid]

The type of music you listen too makes a difference on your selection. A friend and I did a comparison of my homebuilt Leach Amp and his Macintosh tube Amp using Voice of the Theater Speakers http://www.audioworld.com/audio-production/pro-audio/2003/altec-lansing-legacy-a7-loudspeaker/ in a very large room.

It was an interesting comparison because he didn't think a solid state amp could sound as good as tubes/valves.

The speakers had horns AND classical sounded better with the horns. Also with only a little power, they sounded loud unlike the Leach Amp.
Bass was better with the Leach Amp by far.

I like folk music and "prefer the sound of the dome tweeter.

So, a hammer dulcimer would seem to do better with a dome tweeter and a violin would seem to do better with a horn. We didn't compare them.

 

[spec]

That is quite true. I have listened to quite a few HiFi shoot outs and when you compare systems side by side, especially speakers the difference is surprising.

In one case we compared the BBC bookshelf speaker (two way) against some transmission lines (four way) against a pair of ported semi book shelfs. The BBC was miles ahead for choral work and speech. The transmission lines were way ahead for orchestral and the semi book shelfs were best generally for popular music.

spec

 

[Nikolai Petrenko]

As you are going for a bass sub definitely go for a two way system rather than three way. Two way is simpler, cheaper and has less cross over problems. Crossing over from one speaker to another is always undesirable.

Yes, I am thing so. Most three-way system has no subwoofer. With a complex load like speaker, more driver need more crossover and give more loss/increase in sum response. Like you said: Cheaper and simpler are so important to increase reliabiliy.

Ported cabinets are currently favored rather than closed box (infinite baffle). Besides, a ported cabinet can easily be turned into an infinite baffle, but not the other way around, at least not easily.

I also like ported cabinet, because they give more efficiency and more nature sound, especially with sub and woofer.

In terms of tweeter there is a broad choice to be made: bright or smooth; at one end there is the metal dome types and at the other end there are the soft (silk) dome tweeters. I favor the former, but it is a matter of taste.

And there is also a choice to be made in bass/mid driver: fast and articulate or powerful sounding. I prefer the former, but again it is a matter of choice.

I like rock and dance music so certain go for bright tweeter and fast and articulate woofer. "Powerful" will make by subwoofer
Oh, what about horn tweeter?

Your best bet would be to buy secondhand speakers, rather than make your own.

Good secondhand speaker systems like BMB or Bose still expensive and have make higher power rating than my amp so not good. I want to buy secondhand discrete speakers than make cabinet for they since thick MDF are very popular and not expensive. I will search for 60-100W woofers and 30-50W tweeters (lower power rating seem be rare).

 

[spec]

Oh, what about horn tweeter?

Definitely not. Go for a dome tweeter with around 1 inch diameter dome.

... 30-50W tweeters (lower power rating seem be rare).

Hi Fi tweeters are normally around 6W to 12W or even less. The tweeter gets very little power from an audio system.

You make no mention of the bass/mid range speakers or is that what you mean by woofer which I took to be bass sub.

spec

 

[audioguru]

Altec Voice Of The Theater speakers are VERY old and sound awful. The woofers are boomy and the horn tweeters are full of ringing resonances with nulls between them. They were made when vacuum tube amplifiers did not produce much output power. The peaks on their uneven frequency response were loud when driven with only a few Watts. Half-decent dome tweeters have a flat frequency response and good dispersion.

 

[spec]

Altec Voice Of The Theater speakers are VERY old and sound awful. The woofers are boomy and the horn tweeters are full of ringing resonances with nulls between them. They were made when vacuum tube amplifiers did not produce much output power. The peaks on their uneven frequency response were loud when driven with only a few Watts. Half-decent dome tweeters have a flat frequency response and good dispersion.

We are lucky in the UK; most of the cinema (movie house) sound systems are large horns, I think, but anyway they sound superb even going back to the 1950s.

The very worst audio systems are the cabinets with a 10 inch to 12 inch bass/mid and large horn tweeter. The cabinets are normally mounted on a pole at stock car meets and outdoor concerts for example. At our local track I often listen to them in amazement and wonder how they manage to incorporate so much distortion and nastiness in one box- a truly amazing audio engineering achievement.

Then there is the amplifier (no polyprop caps here) that drives the speakers and the whole thing is topped off by the source, either 'music' or live microphone.

The stock car track is in a hilly area and, under the right conditions, you can get reflections and echos from the hills and valleys which further enhances the effect.

spec

 

[Nikolai Petrenko]

Definitely not. Go for a dome tweeter with around 1 inch diameter dome.

Got it.

Hi Fi tweeters are normally around 6W to 12W or even less. The tweeter gets very little power from an audio system.

Well, I haven't bought any yet

You make no mention of the bass/mid range speakers or is that what you mean by woofer which I took to be bass sub.

Oh, I have misunderstood your word, you mean sub but I talk about the woofer?

 

[Tony Stewart]

I was reasonably impressed by Wharfdale speakers in 1970 but opted for Philips 12" tuned reflex DIY speakers for my budget of $50/pair. Being broadspectrum speakers without crossover, My Bogan tube amp could pack a powerful punch w3ith very high efficiency. Even 1 W from a tiny 6V radio could sound plenty loud as a Gheto Blaster. WHen using MDF the front panel was two layers thick for extra rigidity and no breathing sounds. Direct cut albums were so clear , you could hear a musician quietly turning a page of sheetmusic during a solo. Phase Linearity was good with 2D acuity of each instrument on stage. I even mounted one 12" Philips speaker in the centre console of my '63 MGB which wasa significant improvement.