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- DrewsBrews 3:21AM
- jholtz 3:21AM
- rjj45 3:21AM
- Tom_S 3:21AM
Another amp project
Time to tackle another amp project - a Pass F6 kit. This is the DIYAudio.com board & parts kit. It's a very well documented project with a long build thread and the Burning Amp F6 presentation by Nelson Pass transcribed and posted on his Firstwatt site.
I have been slowly buying parts over the past year or so and I finally have everything in-house. The power supply is total over-kill for a 25W/Ch amp, but Antek only had the 500W transformer in stock at the time. 176,000uF ought to be enough, right? 
I found the Italian made chassis kit is a bit underwhelming, considering the price. It'll need a few modifications to brace the back panel.
My power supply board isn't very pretty, but it should do the job. So far the hardest part was getting the caps in the right holes before the hot melt glue cooled off. Connections on the bottom was a head-scratcher, since I didn't buy the $25 PS board at the time. Next time I will! With the pref board, I tried solid 12 gauge wire twisted around the cap terminals, but there just wasn't enough surface to hold it in place. I opted to use some little terminal tabs and run stranded wire through them to connect the caps and resistors.
Comments
I think the PS board looks cool! It echos the look of the perforated chassis.
Holy power supplies Batman! You could do some light gauge TIG welding with that setup Man!
FWIW I have had a few Nelson Pass designed amps... Soundstream D series II (60, 100, 200) car audio amps. In my opinion they were the best sounding amps I ever heard when I was building systems, then later judging car audio.
Edit: I see two bridge rectifiers. Are you going to add snubbers on them?
...and when your neighbors lights start flickering...
Do they have different types of hot glue, ie. some stronger, slower setting, etc.?
Small space heater?
... and yes, you know I am watching this too.
There is a F5 ps board on Ebay that is actually very nice, I used it for an F5 build that also used an Antek 500va transformer and 256,000uf capacitor bank. Nice job with the perf board, looks nice, but I know it was a headache.
This one? https://ebay.com/itm/CRC-Power-Supply-PCB-PASS-DIY-F5-TURBO-First-Watt-class-A-Power-amp-amplifiers/154306937554?hash=item23ed6902d2:g:tD8AAOSw1QpaTFHd
I always forget about looking on Ebay. Lots of Pass clone stuff! Crap, that PS board would saved me lots of time too.
I'm not sure if Nelson is a big fan of snubbers. But this will have bleeder resistors & thermistors. I'm still waffling about whether to bypass the electrolytics or not.
Nick - how do you like your F5? Did you do stick pretty close to the original design?
@Kornbread said:
That's the board. I see that the price has increased, but on the plus side it's a thick board with heavy traces.
Tom, I stuck to the design, with the exception of a heavier power supply. It's a nice amp, I could definitely live with it long term, but it's not my primary amplifier. Some of the guy's here have heard it and may chime in. The F5 has a refined sound, maybe a touch sharp on the top end in comparison to the Aragon 8008.
After thinking about it I would say that sharp is the wrong term, it is a touch more forward than the Aragon.
A little more progress and I'm just a few connections away from the preliminary smoke test. I had used some 3 pin molex connectors from Radio Shack for the power connections back when I built my last Gainclone. That was years ago - before The Shack closed all their retail stores. I wanted this one to look a little more streamlined, so I trimmed and soldered some female bullet connectors right onto the boards. It seems pretty sturdy - we'll see how it holds up.
Houston, we have bias. I was thinking I forgot to connect something when the I first brought it up on the variac and no bias voltage at all. I don't know how many turns these trimmers are, but it took a heck of a lot of turning to get this thing up to 500mv. Everything seems pretty stable on this channel. I'll power up the other side tomorrow night.
A belated update - I finished this one a few weeks ago. It sounds great! My ears are not what they used to be, but it beats my trusty old Audio Research D52b. It actually generates a little less heat than the AR too! I'll try to get some finished photos in the next few days.
Are you getting close to the point that maybe a soft-start on the power supply would be in order? That looks like the transformer and caps are getting up there in size, so I wonder how large the in-rush current is when you flick the switch.
Yeah, I've been thinking about that. I have a pair of CL60 in-rush limiters on the primaries, but that's a lot of capacitance to charge all at once. I may change those to CL70s for a little more initial resistance. I'm also wondering if I need some sort of speaker protection in case there's any appreciable DC offset while everything is warming up. I should probably measure that and see.