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A guide to building the Pass F4 amplifier.
A guide to building the Pass F4 amplifier.
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Old 7th October 2019, 07:23 PM   #1521
JeffYoung is offline JeffYoung  Ireland
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A guide to building the Pass F4 amplifier.
What a cool fault. I get to learn something too.
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Old 7th October 2019, 07:29 PM   #1522
Zen Mod is offline Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
Quote:
Originally Posted by Dennis Hui View Post
..... (I hate desoldering 3 pin
devices. )
.....
that's why you're having two soldering stations on your bench - one with smallish tip , for soldering all those little buggers and another one - with 6-7mm wide knife-like tip , for soldering fat wires (increased temperature inertia is important there) and desoldering 3 pins at once

melt all-pull out-clean pads one by one later
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Old 7th October 2019, 08:41 PM   #1523
ItsAllInMyHead is offline ItsAllInMyHead  United States
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You guys are awesome! One down and one to go. I feel like a one man Pass "F4" pit crew with as many times as I've taken this amp apart and put it back together.

So, I took the PSU out, toroid out, "Channel 2" board out. Took out the 10k of the 22k1 + 10k pair at R8 and replaced 10k with 47k5.

Lookie Lookie Lookie... Woo Hoo.
IMG_1561.jpg

Left is the voltage across the source resistor. Right is the voltage between the gates.

I wanted to get it up to 0V2 just to make sure that I did't run out of room later.

On to add 47k5 to Channel 1 R8.

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Old 7th October 2019, 10:41 PM   #1524
Dennis Hui is online now Dennis Hui  Canada
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A guide to building the Pass F4 amplifier.
Default Desoldering 3-pin critters

Thanks for the tip, Mighty Zen Mod.
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Old 8th October 2019, 12:36 AM   #1525
ItsAllInMyHead is offline ItsAllInMyHead  United States
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Another F4 is born with help from the family here! I let it cook for an hour at 0V250 and nulled the offset. Once the correct components are used it is exceptionally simple and very responsive / sensitive to changes to dial it right in. I think b/c the Vgs of my N and P were relatively close, even when I altered the bias substantially, DC offset didn't budge very much from the initial nulling.

I listened for 10 mins or so on the test bench and felt comfortable enough to move it to the main rig. I don't have proper gear to test the distortion levels etc, but Jim mentioned his "sweet spot" was 0V300. I'll monitor temps, but I'm only at 44C on the heatsinks at 0V250. I'll judge by ear and whether I want it to warm me up. MN in the winters is chilly.

As always... My most sincere thanks to @Nelson Pass. I've embarked on a journey of learning and musical enjoyment that would not have been possible without your generosity. I hope to shake your hand in November.

I could never have done it without Jim's build guide. That's how I get started on all my builds.

I certainly never could have done it without the MIGHTY and very generous Zen Mod, Dennis, and Jeff. With a hats off to Dennis. I read and reread around post #694 to learn from the gentleman that had a very similar issue, but I still could not solve it on my own even with post #705 re: the specs for the different TI voltage regulators. Your collective knowledge and patience with noobs is both remarkable and heartwarming. Live and learn, learn, learn.

Time to jam!
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Old 8th October 2019, 12:54 AM   #1526
Zen Mod is offline Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
Dodosssessss

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Old 9th October 2019, 08:01 PM   #1527
cal3713 is offline cal3713
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Quote:
Originally Posted by ItsAllInMyHead View Post
Another F4 is born with help from the family here! I let it cook for an hour at 0V250 and nulled the offset. Once the correct components are used it is exceptionally simple and very responsive / sensitive to changes to dial it right in. I think b/c the Vgs of my N and P were relatively close, even when I altered the bias substantially, DC offset didn't budge very much from the initial nulling.

I listened for 10 mins or so on the test bench and felt comfortable enough to move it to the main rig. I don't have proper gear to test the distortion levels etc, but Jim mentioned his "sweet spot" was 0V300. I'll monitor temps, but I'm only at 44C on the heatsinks at 0V250. I'll judge by ear and whether I want it to warm me up. MN in the winters is chilly.

As always... My most sincere thanks to @Nelson Pass. I've embarked on a journey of learning and musical enjoyment that would not have been possible without your generosity. I hope to shake your hand in November.

I could never have done it without Jim's build guide. That's how I get started on all my builds.

I certainly never could have done it without the MIGHTY and very generous Zen Mod, Dennis, and Jeff. With a hats off to Dennis. I read and reread around post #694 to learn from the gentleman that had a very similar issue, but I still could not solve it on my own even with post #705 re: the specs for the different TI voltage regulators. Your collective knowledge and patience with noobs is both remarkable and heartwarming. Live and learn, learn, learn.

Time to jam!
Congrats! It's a great amp. Hope you love it!
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Old 9th October 2019, 08:08 PM   #1528
ItsAllInMyHead is offline ItsAllInMyHead  United States
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Quote:
Originally Posted by cal3713 View Post
Congrats! It's a great amp. Hope you love it!
Thank you very much!

My speakers are pretty efficient (98dB @ 2.83V/1m) 4Ohm nominal. My primary preamp has 20dB of gain and will provide 10V with the current set up. I can easily see me investing in another set of F4 boards and doing mono blocks. Being able to get the full 20V swing from my pre-amp with a balanced configuration would be ideal. I've also never tried monoblocks. It could be a great learning experience.

It sounds exceptionally good to my ears (as does every First Watt design I've tried).

Edited to add - I hit submit too soon. I also have really been looking forward to pairing it with a few tube amps. That will come later. There's still a lot I need to learn before doing that. I read the posts earlier in the thread, but some of it went over my head re: selecting the proper resistance to use.

Last edited by ItsAllInMyHead; 9th October 2019 at 08:10 PM.
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Old 9th October 2019, 09:36 PM   #1529
cal3713 is offline cal3713
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I also built the full mono-blocks, but didn't find it necessary for my speakers (Coincident Pure Reference Extremes; Impedance: 8 ohms - never dipping below 6 or going above 10 ohms, Sensitivity: 94 db @ 1M - 1 watt).

I first tried vertical biamping my speaker's passive subwoofer units & the head-units (both require their own speaker connections). That hurt coherency pretty significantly. Eventually moved to paralleled inputs and outputs to double current, but that didn't provide any real benefit, and I think introduced a bit of smearing to the sound. Tough to say how much difference there really was, but I clearly didn't need the power and ended up just running them in a standard dual mono block build... a single channel in each chassis with its own power supply. I think if you don't need the power, then that's the way to go. An added plus is that you can put a different board in the other half and just switch amps when you feel like playing with a different flavor.

If you haven't already, I'd check and see how much power your speakers pull at max volume... A Test. How much Voltage (power) do your speakers need?
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Old 9th October 2019, 09:56 PM   #1530
Zen Mod is offline Zen Mod  Serbia
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A guide to building the Pass F4 amplifier.
F4 is for Sissies

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