Thanks . . .
alas . . . on my F5 I was able to match Toshiba 2sk175 + 2SJ55 pairs ( that I use in parallel without source resistors ). No, I won't revisit and change them around. [It sounds marvelous like it is on the Maggies]
But maybe add a very small resistor on the P-side on the source, that will destroy the 'very good Complementary Characteristics, say 0,05 to 0,1 ohm? Would only require a very small DC adjustment, no current change (I have 1.4A) required I think.
Are SMPS power supplies a good alternative to linear supplies?
In audio equipment, I see them used in class D amps and a few El Cheapo units.
Did they need additional filtering?
Do they create RF around them?
Would it make more sense to move them to a separate chassis?
Why did you choose dual mono, did you find that a shared SMPS was not enough or was that, simply, your choice?
Getting all of that in a 3U chassis is impressive. It does look packed with stuff, but nice wiring.
What's with the pink plastic? PS filtering? 3D printed?
In audio equipment, I see them used in class D amps and a few El Cheapo units.
Did they need additional filtering?
Do they create RF around them?
Would it make more sense to move them to a separate chassis?
Why did you choose dual mono, did you find that a shared SMPS was not enough or was that, simply, your choice?
Getting all of that in a 3U chassis is impressive. It does look packed with stuff, but nice wiring.
What's with the pink plastic? PS filtering? 3D printed?
Birdbox has his own reasons, but I can share a few of my own... along with a few answers.
Yes, sometimes. I've found them to work exceptionally well with every amp I've tried.
Sometimes. What do you mean by "additional"? Some amps have great PSRR... that "ripple" will likely be very different. So, the filters will look very different.
Dunno.
Does it make sense to put a toroid or other component that emits radiation in another chassis? My experience is that SMPS in the same chassis has been just fine.
That is not dual mono. It is two power supplies wired in a bipolar configuration.
That's a 2U, which makes it all the more impressive.
AmyAlice
Yes
I have finally started building my F5M amp after it sat for months. I have built other kits where understanding what I was assembling was not necessary. But with the F5M I have decided to try and understand what I was doing and why. I just watched 6L6's video from Burning Amp 2024 on power supplies and feel like Neo in the Matrix after he had his first download. The presentation was crisp, easy to digest and actually made sense to me. That is no simple feat as I am late to amp building and nothing is intuitive or easy for me. But maybe this is the beginning of the "light bulb" finally starting to glow dimly in my understanding all of this. Makes me also think I should try and get myself to CA for 2025. Regardless, for any newbies you really should watch this video.
Thank you @6L6.
Thank you @6L6.
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@birdbox
Fantastic rendition! You are now a fine artisan/craftsman of diyaudio! Love the ingenuity.
Best,
Anand.
Fantastic rendition! You are now a fine artisan/craftsman of diyaudio! Love the ingenuity.
Best,
Anand.
Ratz... just as I get my toes back into building, now I get stuck with SMD.
I'm just getting out from point to point wiring vacuum tubes and wire wrapping boards into soldering them new fangled solid state thingies -transistors you call them- into holes... and now it's surface mount.
I mean, I've seen SMD since the 80s, but at work, with very expensive machines or highly trained techs...
Thanks for the feedback. Yes, a stereo F5(m) into a U2 is something else.
birdbox
Very nice build! It's really tight and I was studying to see how the two SMPS were connected to the boards but can't figure it out. Could you detail how you made the connections?
Thanks!
^
Post #193
Here's what I came up with for a drawing of a dual rail SMPS power supply with quad AmyAlice filtering. I've flipped the caps and diode on the two AmyAlice boards for the negative rail. I think this is correct and I'm hoping folks can either confirm or deny the accuracy of the wiring scheme including the star ground.
Post #193
Those were cheap knockoffs I just happen to have lying around so I wouldn't recommend using them. If I had legit Bourns on hand in 1kohm, I would have used the brand name ones for peace of mind. Additionally, the knockoffs had linear leads, so I had to bend them manually into the offset configuration to fit on the board (not ideal at all).
Bourns has a similar version with a finger grip knob for the single turn 3362 and 3386 series. The datasheet for both series says add a "T" to the end of the part number. It does make bias and offset a little easier to set when you can turn both pots simultaneously.
Personally, I prefer multiturn pots over single turn and have the Bourns brand trimpot screwdrivers that work quite well.
Here's the Bourns brand single turn with the knob ("T" suffix part number) on F5m boards.
Bourns has a similar version with a finger grip knob for the single turn 3362 and 3386 series. The datasheet for both series says add a "T" to the end of the part number. It does make bias and offset a little easier to set when you can turn both pots simultaneously.
Personally, I prefer multiturn pots over single turn and have the Bourns brand trimpot screwdrivers that work quite well.
Here's the Bourns brand single turn with the knob ("T" suffix part number) on F5m boards.
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Yep, this is the one right?
https://www.mouser.com/ProductDetail/Bourns/H-90?qs=nS9uH9%2BmxhzS2pH7coy5Fw==
https://www.mouser.com/ProductDetail/Bourns/H-90?qs=nS9uH9%2BmxhzS2pH7coy5Fw==
This weekend I should be at a point where I can turn on and test my amp. I have two multimeters but have seen posts where folks are using 5 at startup. His many do I truly need? Also, I just purchased variac and would greatly appreciate guidance on using it to start up this amp. I believe this was already provided earlier, but I can’t locate it now.
You could get away with just one digital multimeter (DMM), but two make it a whole lot easier....and safer. You can bias one channel at a time and read DC offset accross speaker terminals on one DMM while reading bias through one of the two 0.47R resistors on the second DMM.
If you don't have "mini-grabbers", then that's what I would suggest spending a little money on.
I'll let others chime in on variac question. I find the DBT (dim bulb tester) a more useful first start up tool. Do you already have a DBT?
@TomR. If it's any help: I used a DBT on my build with no variac and it worked well. I used 2 meters even though I have 3. Make sure one of your meters can read mV to 3 decimals and use your other meter for DC offset. I connected 1 meter across a resistor on the amp to get the gain, and the second meter on the output to measure DC offset. I first ensured the DC offset was around 10mV by adjusting one trim up or down. I then turned 1 TRIM up until the DC offset was 50mV and then adjusted the second trim to get the DC offset back to under 10mV. This allowed me to creep my way up to 450mV bias for my first speaker test. So I overshoot the DC offset using 1 trim, and then adjust the DC offset back down to under 10mV with the second trim as I get close to my target gain voltage. Hope this makes sense. ( I also wear rubber work gloves and keep 1 hand in my pocket when adjusting trims so I don't get bit )
After I adjust 1 channel, I put the cover back on and let it heat up for a hour or so. I can see what the final target voltage is. I then take the cover off and let it sit for a few minutes so it cools and take a note of the voltage reading for gain on the channel I just adjusted. I remove the meter and connect it to the second amp to adjust its gain. Move the DC offset meter to the other outputs and I try to aim for the same target voltage as the first channel with the cover off, assuming it will get to the same target after it heats up with cover back on like the first channel.
After I adjust 1 channel, I put the cover back on and let it heat up for a hour or so. I can see what the final target voltage is. I then take the cover off and let it sit for a few minutes so it cools and take a note of the voltage reading for gain on the channel I just adjusted. I remove the meter and connect it to the second amp to adjust its gain. Move the DC offset meter to the other outputs and I try to aim for the same target voltage as the first channel with the cover off, assuming it will get to the same target after it heats up with cover back on like the first channel.
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This is something I have to get around to doing, too. Part of the fun will be sourcing 100w incandescent bulbs.
I've been looking at building something like this one and just bolting it to my workbench.
https://retrorepairsandrefurbs.com/2022/06/13/building-a-dim-bulb-tester-for-vintage-radios-tvs/