#1 Gain - Have I Got this Right?
Posted: Wed Aug 19, 2020 9:49 am
I've got plans to build a MoFo Power Buffer and I've got many of the required parts collected already. I've been thinking about how much voltage gain I will need in front of the MoFo in the context of my speakers, which are BLHs using 15ohm Lowther drivers.
My speakers are nicely efficient and I've been using them hooked up to flea-power OTL amps outputting a Watt or two, which is plenty enough to create high volumes in my listening room. The amplifiers I'm using, being valve based, are limited by their current capability (compared with solid state devices) and using 15ohm drivers gives the amps a slightly easier time; as Mr. Ohm tells us;
To deliver 1W to an 8ohm speaker requires 2.82V at 0.35A
To deliver 1W to a 15ohm speaker requires 3.87V at 0.25A
So, if we assume 1W is sufficient in my 15ohm speaker system context and also assume that my source component has an output of 2V, then I need 3.87V at the input to the MoFo so my source components output needs a voltage gain of 3.87/2 = approx x1.95. OK so far?
At this point it occured to me that with a MoFo using 15ohm drive units may actually be a disadvantage because it is a current gain device and to deliver 1W with 8ohm drive units would require less voltage gain - 2.82/2 = appprox x1.41 - that's pretty close to being able to drive the MoFo straight from the source component (something I think Steve S actually did).
What am I missing?
My speakers are nicely efficient and I've been using them hooked up to flea-power OTL amps outputting a Watt or two, which is plenty enough to create high volumes in my listening room. The amplifiers I'm using, being valve based, are limited by their current capability (compared with solid state devices) and using 15ohm drivers gives the amps a slightly easier time; as Mr. Ohm tells us;
To deliver 1W to an 8ohm speaker requires 2.82V at 0.35A
To deliver 1W to a 15ohm speaker requires 3.87V at 0.25A
So, if we assume 1W is sufficient in my 15ohm speaker system context and also assume that my source component has an output of 2V, then I need 3.87V at the input to the MoFo so my source components output needs a voltage gain of 3.87/2 = approx x1.95. OK so far?
At this point it occured to me that with a MoFo using 15ohm drive units may actually be a disadvantage because it is a current gain device and to deliver 1W with 8ohm drive units would require less voltage gain - 2.82/2 = appprox x1.41 - that's pretty close to being able to drive the MoFo straight from the source component (something I think Steve S actually did).
What am I missing?