That's more along the line of advice i'm after. The speakers are nominally 8, supposedly, with good swaths of 4 ohm. I'm not familiar with the math, I just know getting that source resistance down has some benefits. Matching pairs to parallel isn't something I want to dig into at this point for a number of reasons. I may employ copper heat spreaders to make the sinks more effective.
It will work and probably sound better. Do you have enough heatsink for the dissipation?
Rush
Technically, the amplifier rails will be above the 25V spec of the P channel jfet. It will survive though.
Amplifier will run hotter. And you will be able to achieve less bias at same temp as lower voltage transformer.
I use transformers with 24V secondaries just fine. You may see voltage a little over the 25V on power supply output, but that's nothing to worry about. I've been putting 32V through LSJ74's for a few years now with no problems. I put little heatsinks on mine for good measure, but I doubt you'd need to do that.
Just built an F5 with SMPS. I used the SMPS300R (+/- 24VDC) from a French supplier (who obtains them from China) audiophonics.fr.
At the moment I'm running a stereo F5 off a single PSU, which limits me to approx. 1A biasing. Above 2A continuous load the PSU starts to protes and run too hot. So ultimately a single PSU per channel is better (dual mono).
I must say that the result is very good. The amp gets a bit more "get up and go" compared with the regular trafo-based PSU. I actually prefer the SMPS version. At 79 Euros and much less weight you can't go wrong.
At the moment I'm running a stereo F5 off a single PSU, which limits me to approx. 1A biasing. Above 2A continuous load the PSU starts to protes and run too hot. So ultimately a single PSU per channel is better (dual mono).
I must say that the result is very good. The amp gets a bit more "get up and go" compared with the regular trafo-based PSU. I actually prefer the SMPS version. At 79 Euros and much less weight you can't go wrong.
Maybe this was mentioned elsewhere, but I believe there is a typo in the First watt F5 manual (http://www.firstwatt.com/pdf/prod_f5_man.pdf).
On page 13, under Parts Selection:
Isn't Q3 the P-ch and Q4 the N-ch ?
On page 13, under Parts Selection:
Isn't Q3 the P-ch and Q4 the N-ch ?
Could be, but on the previous page in that document, Figure 6 the schematic has Q3 and Q4 reversed.
The v3 circuit is basically references the same schematic.
When I originally ordered parts, I did it based on the schematic and thats how I built it. Right before I soldered the output MOSFET's, I decided to read the manual one final time and thats when I got confused as then I thought I had the parts reversed.
My dac have 2V output, in F5 as input have a voltage divider 1/10, because K170 J74 can only handle 200mV input, you can change the the divider for higher input but this will not change the acceptable gain of K170/J74. I think with a preamp you will get more distortion for higher signals of 2V.
My point is to get more headroom from the input stage by changing K170/J74
Please correct me if I am wrong..
My point is to get more headroom from the input stage by changing K170/J74
Please correct me if I am wrong..
You could very well be correct.... I am a novice.
Best for others with more experience to chime in....
What happens when you feed more than 2V to the F5?
If the input can only handle 200mV, I assume that the output stage provides sufficient gain in order to provide 25W full output, i.e 14.14Vrms.
Best for others with more experience to chime in....
What happens when you feed more than 2V to the F5?
If the input can only handle 200mV, I assume that the output stage provides sufficient gain in order to provide 25W full output, i.e 14.14Vrms.