Here's a screen grab from one of youtube videos by youtuber danyk666, which is about a visit to a hospital built in '70s. As he is unavailable to reply my comment, I'm seeking opinions here about construction of the transformers, say, turn numbers, core material, also the apparent output power of this system and modifications needed to turn this into an all passive audio amplifier. I'm aware of versions of magamp, but this one looks interesting because of simplicity. Thanks.
All passive zero power system
- Thread starter indr
- Start date
That appears to be a bog standard audio distribution system that are routinely used in factories, churches, retail establishments, and so forth. And it is not "passive amplification" there is no such thing, a transformer does not amplify due to the fact that there is no additional power being added to amplify with, transformers transform volts, current, and impedance to match two devices for power transmission.
Mike
Mike
70.7v is probably more common that 100v, but look up "constant voltage speakers" on google or for that matter "70.7v speakers", which is just one specific voltage for CV speakers.
Constant-voltage speaker system - Wikipedia
When you have two or four speakers, you can wire them in series, parallel, or series/parallel so the impedance suits your amp. But trying to do that for 100 speakers scattered all over the ceilings is impossible. So they came up with CV speaker systems. Now the amp cranks out a high voltage signal, and it is wired to all the speakers in parallel. But at each speaker, there is a small transformer to step that large signal down to an appropriate level. Typical in restaurants would be small 8-10 inch speakers and the transformers have taps at 10, 5, 2.5, 1.25, 0.75 watts. The taps get wired to the speaker itself. Those are the wattages the speaker will see when the amp is full bore.
And really, in a restaurant 1 watt is plenty. So instead of impedance, you simply add up the tap wattages of all the speakers, and keep it within the power of the amp. If you think of it, this is like the mains wiring in your house. No one adds up the impedances of table lamps.
This also lets them balance speakers. They may want 5 watts all over the bar, but right near the waitress station, they might set that speaker down to only 1 watt. That way they can hear orders at the bar.
Constant-voltage speaker system - Wikipedia
When you have two or four speakers, you can wire them in series, parallel, or series/parallel so the impedance suits your amp. But trying to do that for 100 speakers scattered all over the ceilings is impossible. So they came up with CV speaker systems. Now the amp cranks out a high voltage signal, and it is wired to all the speakers in parallel. But at each speaker, there is a small transformer to step that large signal down to an appropriate level. Typical in restaurants would be small 8-10 inch speakers and the transformers have taps at 10, 5, 2.5, 1.25, 0.75 watts. The taps get wired to the speaker itself. Those are the wattages the speaker will see when the amp is full bore.
And really, in a restaurant 1 watt is plenty. So instead of impedance, you simply add up the tap wattages of all the speakers, and keep it within the power of the amp. If you think of it, this is like the mains wiring in your house. No one adds up the impedances of table lamps.
This also lets them balance speakers. They may want 5 watts all over the bar, but right near the waitress station, they might set that speaker down to only 1 watt. That way they can hear orders at the bar.
Architechtural market amplifiers have internal transformers to boost output up to 70.7 (common) or 100 v (rare) distribution systems. This saves a lot of money on wiring, as the stepdown transformers are very cheap. US source is parts-express.com My Peavey MMA-875T amp has a 70 v & 24 v outputs. I would expect architectural products from QSC, Yamaha, Electrovoice, to have the same distribution system capability.
Be aware the wiring going in ceilings walls & attics has to be "plenum" rated to avoid voiding your building insurance. PVC insulation makes poison gas in a fire.
Be aware the wiring going in ceilings walls & attics has to be "plenum" rated to avoid voiding your building insurance. PVC insulation makes poison gas in a fire.
Last edited:
I was referring to what you said, "an all passive audio amplifier"...there is no such thing, for amplification to occur, you need an additional power source to amplify, there's no free lunch. As I and other's have stated, it's a simple, passive audio distribution system that works with transformers, nothing more. Also, because transformers are passive devices, not only do they not amplify, they actually dissipate some of the power as wasted heat, so you actually get a slight overall attenuation of the distributed power.
Mike
100v line is more common in UK and Europe. What wattage speakers are you using? Max power I have seen is 50w. Dont expect HiFi results from them as they are designed for Publis Address. Although this supplier can supply up to 300w. 100 VOLT LINE TRANSFORMERS - Canford but unless you are going to run the cables a long way why use one. You will also need a special amplifier with 100v output.
Last edited:
50w is more than enough. PA systems have unique acoustics that HiFi purism won't have ever. I'm new to cv system. What 100v amp you'll like to suggest?
You are assuming _power_ amplification is the only sort we talk about - it isn't. A transformer can serve as an MC preamp section, giving voltage amplification completely passively. Mechanical amplification can be done passively with levers gears etc, so long as its position or velocity of force amplification rather than power amplification.
Amplification is about making some physical quantity bigger, and not all physical quantities are conserved like energy/power. In electronics we talk about voltage amplification, current amplification and power amplification - most commonly active, but sometimes passively. Power amplification of course requires active components, but the other sorts are sometimes passively boosted with transformers or switched capacitors, etc.
[ actually switched capacitor networks are interesting in that the power is not supplied/amplified by the switching device, but rather only routed by them, hard to say if this is best thought of as active or passive ]