I too need just a bit of help with F5m. This is very newbie question, but can the F5m board work just as well on ±25Vdc rails as it does on ±17Vdc rails with no elements in the circuit needing to be changed? I have only ±13Vrms trafo at my disposal.
Nothing will need to be changed. It will work nicely. It will, of course, have less power output.
If I keep the bias around 0.5A for starters, can I use 36V rails? My trafo has taps at both 13 and 26Vrms. The load is likely gonna be at least 8 ohm. Would the gain remain the same or quadruple?
I think that +/- 36VDC is pushing the JFETs pretty hard. Probably not advised when you could buy a different transformer worst case. What VA rating is your transformer?
It's way more than I'd ever need. It's about 5kg torroid. 600VA. I just want to experiment. And do it cheaply. So, since I have most things already, I wanted to play around with F5m now. Essentials cost nothing. So why not. Everything else I have.
EDIT: it's actually 12-24 vrms at 230, just my mains are constantly at 240, sometimes even close to 245.
EDIT: it's actually 12-24 vrms at 230, just my mains are constantly at 240, sometimes even close to 245.
I bet it's smarter to just crank bias and little higher. 18VAC secondary is the standard and that results in +/-22 to 24VDC rails.
13VAC/18VAC = 0.72
So you're getting 72% of the 25W output at 8 ohms, so about 18W. Still seems pretty good depending on the sensitivity of your speakers.
I'm not sure cranking bias higher does anything for the power, but I bet there a few tricks you could do to squeeze out a little more power. Over my head, but I bet someone can chime in on that topic.
13VAC/18VAC = 0.72
So you're getting 72% of the 25W output at 8 ohms, so about 18W. Still seems pretty good depending on the sensitivity of your speakers.
I'm not sure cranking bias higher does anything for the power, but I bet there a few tricks you could do to squeeze out a little more power. Over my head, but I bet someone can chime in on that topic.
Isn't the relationship between the rail voltage and the output power quadratic?
Load is either 6r speaker or 32r headphones
In either case I don't really need that much power. I'd prefer to keep the bias low. But higher rails sounds more fun (less effective gate capacitance?). Until it burns I guess.
Load is either 6r speaker or 32r headphones
In either case I don't really need that much power. I'd prefer to keep the bias low. But higher rails sounds more fun (less effective gate capacitance?). Until it burns I guess.
I'm thinking if you bump up the bias, you could possibly use a higher input voltage into the F5m, which would produce more power. I'm probably wrong though. I am still too much of a noob to know all the math.
Regardless, the F5m is a great amp and I suspect 6R speakers will be fantastic with around +/-17VDC rails.
What sensitivity are your speakers? That seems to be pretty important.
Headphones on F5m? That seems like crazy talk 😵
Edit: I'm sure there are other amps designs you could build that don't use the JFETs and therefore you could go with the higher rails. What about @rhthatcher classic Aleph options? I've only read good things about the Classic Aleph amp options.
Regardless, the F5m is a great amp and I suspect 6R speakers will be fantastic with around +/-17VDC rails.
What sensitivity are your speakers? That seems to be pretty important.
Headphones on F5m? That seems like crazy talk 😵
Edit: I'm sure there are other amps designs you could build that don't use the JFETs and therefore you could go with the higher rails. What about @rhthatcher classic Aleph options? I've only read good things about the Classic Aleph amp options.
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Main reason I want to do it is because it would be a learning experience, I would get to hear the F5, I don't have this kind of push pull amplifier and it would cost me around 35 Euros with shipping to get more or less everything I need to build it. So basically it's just a very cheap and definitely a rewarding project. I have a bunch of all kinds of things, so the essentials kit is all I need.
The headphones will be fine as long as there is no DC. Of course I would be careful, but planar magnetics love power.
The headphones will be fine as long as there is no DC. Of course I would be careful, but planar magnetics love power.