Questions about Ohms.
- Thread starter ouimetnick
- Start date
woodj
Super Member
Cool that you are only 15 and know enough to ask questions like this. When I was 15 (back in 1958), most hifi stuff we had to deal with ran 16 ohm outputs, sometimes 8. Some radio and lofi stuff ran small loads, but the output circuits would drive most anything (some times not so loud you could hear it).
Even though I have been in the computer field on and off since 1966, I hate TLA's (three letter acronyms like THD).
Even though I have been in the computer field on and off since 1966, I hate TLA's (three letter acronyms like THD).
Jon_Logan
Addicted Member
When I was 15, I'd like to "crank it" every once in awhile. Knowing this might happen from time to time and that parties are part of growing up, I'd set the "Impedance selector" switch to "6 ohms".
The reasons of why may fall into place later. Let's just say, if the amp did get damaged while the switch was in the "6 ohm" setting, it would have failed sooner under the same conditions if the switch was in the "8 ohm" position.
The reasons of why may fall into place later. Let's just say, if the amp did get damaged while the switch was in the "6 ohm" setting, it would have failed sooner under the same conditions if the switch was in the "8 ohm" position.
Turborusty
2nd hand junkie
The switch will "step-up" the current when switched into "6-ohm" to keep the amp safe at the lower impedence. When this is done, the noise floor and distortion will typically increase. Basically like ruunning a car at sustained high RPMs, it's revved up. it's already giving all it's got.
Running the switch in 8ohm mode when you have only an 8ohm load connected will theoretically give you more headroom and better sound quality. Are these things audible? who knows. picture it like running the car at lower RPMs's, kind of cruising easily....but you still have that reserve power if you choose to step on it.
Turborusty
Running the switch in 8ohm mode when you have only an 8ohm load connected will theoretically give you more headroom and better sound quality. Are these things audible? who knows. picture it like running the car at lower RPMs's, kind of cruising easily....but you still have that reserve power if you choose to step on it.
Turborusty
Jon_Logan
Addicted Member
I'm pretty sure that in the "6 ohm" position, it will step down the rail voltage. This would affect the max output swing and have zero impact on noise floor or distortion. The distortion may change depending on the load connected, but not on the rail voltage. I agree with you about the audibility of the switch position probably being nil.
Turborusty
2nd hand junkie
You're right! instead of being labeled with ohms ratings, some amps will have a switch that's labeled as "high voltage" or "high current".
High current has less headroom but more stability, high voltage has less stability but more headroom.
Sorry, I had my terminology backwords.
If you don't need the amp to run high current(low ohm loads), then you would ideally have the switch set to high voltage, or the higher ohm rating.
I hope I was right that time. I'm going to read up on the following link.
Turborusty
Last edited:
Turborusty
2nd hand junkie
ugh, my head hurts now
Turborusty
Turborusty
Jon_Logan
Addicted Member
Hi Turborusty, I read that link you posted. Thanks for that. I can see why your head would hurt after that. I wouldn't put too much trust in that thread. There's a lot of misinformation in that.
I'm not sure how to describe the switch and it's function in the clearest way. Let's just say it's a cost cutting move used by some manufacturers with some models.
For a given volume setting and a given speaker, a voltage is applied to the load. That voltage applied to the load will allow a current to flow. If a lower impedance speaker is connected, the current is increased. The voltage remains the same. The power output is greater only because the current went up (automatically). The output voltage remains the same.
Output transistors are devices that are good at having current go through them OR voltage across them BUT not at the same time. If there is high current through them and a high voltage across them, they get closer to their limits of Safe Operating Area. There are a few techniques to get them away from their limits. One technique is to add more output transistors. This requires more heatsink area and requires more cost. Another technique, is to reduce the voltage across them by having a selectable transformer output. This is relatively cheap. This approach satisfies the Safe Operating Area problem by lowering the voltage across the output transistors. This makes them run safer while a lower impedance load is connected.
I'm not sure how to describe the switch and it's function in the clearest way. Let's just say it's a cost cutting move used by some manufacturers with some models.
For a given volume setting and a given speaker, a voltage is applied to the load. That voltage applied to the load will allow a current to flow. If a lower impedance speaker is connected, the current is increased. The voltage remains the same. The power output is greater only because the current went up (automatically). The output voltage remains the same.
Output transistors are devices that are good at having current go through them OR voltage across them BUT not at the same time. If there is high current through them and a high voltage across them, they get closer to their limits of Safe Operating Area. There are a few techniques to get them away from their limits. One technique is to add more output transistors. This requires more heatsink area and requires more cost. Another technique, is to reduce the voltage across them by having a selectable transformer output. This is relatively cheap. This approach satisfies the Safe Operating Area problem by lowering the voltage across the output transistors. This makes them run safer while a lower impedance load is connected.