A guide to building the Pass F4 amplifier

[Erikgunnar]

Thanks a lot guys!!

Tonight Tjärknul and Malbec! Resistors can wait!

Have a nice weekend all!

 

[Zen Mod]

that's proper High End!

 

[myleftear]

Thanks a lot guys!!

Tonight Tjärknul and Malbec! Resistors can wait!

Have a nice weekend all!

food porn
looks and sounds very nice! enjoy

 

[myleftear]

(e.g. use 1/2W for small signal rather than 1/8W)

I did that in my bugle2. Inadvertently... (their rating is kinda halved, so their size is double what I expected). I guess I was lucky I found a way to populate the board. (look here)

 

[Erikgunnar]

The gate resistors pass the sound signal to the FETs' gates, but only very little current passes (practically only charging and discharging the gate capacity, that's what makes mosfets so special as compared to bipolar transistors). In my opinion, RN60 resistors are already overkill here, so just about right.

The source resistors each pass a share of the current that is going through the speaker voice coil. Bulk foil resistors like the Fukushima MPC are probably as far as you want to go. I wouldn't use Mills MRA in that position, not much to gain really.

Concerning trimpots, Vishay has these bulk foil potentiometers:

Y40535K00000K0L Vishay Precision Group Foil Resistors | Mouser Osterreich

They would no doubt be a complete waste in that position, just use Bourns 3269 and be done with it.

Hi Rodeodave

I found the Fukushima MPC. They are metal plate resistors and available in 10% and 5% tolerance.

My question how sensitive is the % tolerance for a source/drain resistor at the FET?

I am thinking we buy matched FETs but if the resistor have a 5% tolerance the current can vary 5% as well if i get some resistors at the ends of the tolerance spectrum.

Would not a 1% resistor be better or buy 5% resistors and match them?

Or is this not important at all?

Cheers!

 

[Zen Mod]

well, I'm usually not bothering, once when I'm in 5% bracket

 

[soldersmoker]

Yeah, I'm probably impatient and not acknowledging our unique times, but I wonder what's up when my 4U chassis has been sitting at FedEx's site at Charles de Gaulle airport for eight days now. Is that within the bounds of typical shipping times?

 

[Zen Mod]

just chill

many ppl are having real problems

we waiting for goods to receive and send...... I know it's necessary food for brain, but .....

 

[soldersmoker]

What's the best way to mount a single LED on the front panel? Can I get a small bracket to screw into the pre-drilled holes on the back of the front panel without need for tapping a screw-hole? I've already drilled a ~3 mm hole for the LED to shine through.

 

[Dennis Hui]

I've used hot glue before.

 

[6L6]

As Dennis says, hot glue is a great solution.

 

[Dneu2011]

I use hot glue as well. I drill the hole on the inside large enough for the led to fit but the hole on the front much smaller so the led isn’t so bright. Glue holds it in place.

 

[Ben Mah]

I've done the two hole sizes too. I heat shrink the led wires, bend then 90 degrees and then tape the led and wires in place.

 

[Dennis Hui]

I slightly wet sand the LED to give it a more frosted, diffused look.
High value current limiting resistor also helps.

 

[myleftear]

Since I do not trust hot-glue (it "decomposes" relatively quick afaik), I'd try to replicate the shrinking-tube-fixes-LED-in-a-tight-hole trick from the ACA-build. Or try some epoxy-glue, or a mechanical solution.
BUT I have to admit that I haven't even been there yet

 

[Bigun]

Perhaps, if you drill the hole the right size, the LED will be a push-fit into it.

 

[Zen Mod]

so-so tight fit, with blob of neoprene glue

works like ..... glue

 

[soldersmoker]

Thanks, everybody. My wife wants me to put a purple pilot light on the amp. Who am I to argue, right?

Hot glue it is, and I realize it might not be a long-term solution, as myleftear says, but I will no doubt be making plenty of changes in the next few years, so that probably won't be a factor.

 

[Mark Johnson]

I've got a purple LED pilot light (example) in the front panel of my Firstwatt M2x amplifier. It's held in place by friction. The insulated (heatshrink tubing) legs are jammed against the interior walls of the drill hole by two pieces of wooden matchstick that are forcefully jammed into position. Not great in a high vibration environment, but mine isn't.

 

[soldersmoker]

More purple! Ha ha! I prefer mellow amber, and I really dislike retina-burning blue.

Maybe I'll give friction fit a try. I don't have a drill press, which would be helpful. I suppose moving up in drill sizes in conservative steps will work. Adding a dab of 3M Super 77 might also help.

Resourcefulness, creativity, ingenuity: that's all it takes, apparently.