Nice.
3 pairs of output transistors will drive 8 ohms, but I wouldn't push it too hard. Those output transistors won't handle it. Here's an "8" ohm speaker:
Stereophile B&W683 impedance measurement
The worst point there is at about 650 Hz where the resistance is less than 4 ohms, and the phase is 45 degrees.
I can't remember all of this, but here's (I think) an easy way to see it:
Say you're driving the speakers hard, and you have a 60 V transient at 650 Hz. You're looking at a transistor current of 5.4 A and a transistor voltage of 60 V. Without derating for the case temperature you will inevitably reach, you're already very near to being outside the device limits.
Theoretically, you're looking at about 280 W for 8 ohms. You'll need a lot more than 3 pairs for this.
3 pairs of output transistors will drive 8 ohms, but I wouldn't push it too hard. Those output transistors won't handle it. Here's an "8" ohm speaker:
Stereophile B&W683 impedance measurement
The worst point there is at about 650 Hz where the resistance is less than 4 ohms, and the phase is 45 degrees.
I can't remember all of this, but here's (I think) an easy way to see it:
Say you're driving the speakers hard, and you have a 60 V transient at 650 Hz. You're looking at a transistor current of 5.4 A and a transistor voltage of 60 V. Without derating for the case temperature you will inevitably reach, you're already very near to being outside the device limits.
Theoretically, you're looking at about 280 W for 8 ohms. You'll need a lot more than 3 pairs for this.
Do B&W rate that as an 8ohms speaker?
It looks more like a 5ohms, or 6ohms, speaker in the way I read the graph.
Not just 650Hz, 85Hz and 18kHz are two more severe reactance areas.
I would rate this speaker and design the amplifier for a 4ohms severe reactance speaker where transients could hit 60degrees of phase loading.
It looks more like a 5ohms, or 6ohms, speaker in the way I read the graph.
Not just 650Hz, 85Hz and 18kHz are two more severe reactance areas.
I would rate this speaker and design the amplifier for a 4ohms severe reactance speaker where transients could hit 60degrees of phase loading.
It's bad. This curve coincides with their claimed spec in terms of minimum impedance. And I would rate it 4 ohms, not even 5 or 6. I had the 683's in my sights, but when I saw that impedance, I steered clear. I also gave them a listen, and they didn't blow me away. The Monitor Audio Bronze 6's on the other hand were great! I haven't dug more, but here's a measurement for the Silver 8's:
Stereophile Monitor Audio Silver 8 impedance measurement
And yes, when at 60 degrees, the 683's will really push the amplifier. This impedance curve is almost good enough reason to use MOSFETs (even though I'm a big fan of BJTs).
Here is the spec of the 683 S2
60v with 5.4A at the speakers ? From where ? SARA2016 power supply it is 55v. Man, you are too exaggerated with that fear. MJL4281 it is very good transistor.
Hi greierasul. If you use the 50-0-50 transformer described in post 1, it's not unlikely that the peak Vce can be 120 V. At 45 degrees phase shift of current and voltage, the current (Ic) will peak when the voltage is half peak, which is 60 V. Now, if you take a load as described (B&W 683), which at about 650 Hz has a resistance of 3.7 ohms or thereabouts, the current in the load will be about 16.2 A for a voltage peak of 60 V (which leads to the 120 V peak voltage Vce). Ic is a third of total current, so 5.4 A.
That's how I get 60 V Vce at 5.4 A Ic.
For +-55 V it should be fine for 8 ohm loads, and likely for 4 ohm loads. I haven't calculated that.
If I'm wrong, please let me know. I've done a lot of investigation into this, and I want to learn more.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.