I guess you would slowly ramp up the voltage to 90vac while monitoring bias and offset and looking for other signs of trouble. If after a while everything looks good, then slowly up the voltage to full mains and dial in the amp to spec.
Could it? Absolutely yes. Using a variac assumes you know what to look for, and how to react properly if things go south.
A dim-bulb is passive and basically foolproof.
As Jim mentioned, the bulb tester is pretty foolproof. For me, its main use is to check for unexpected and significant current draw (for example, at the initial power up after you have checked that there should be no shorts and the bias currents are low/off) Once that's verified you need to remove the bulb tester before starting your bias procedure.
Variacs are nice, but you need to be mindful of how an amp might behave with lower than expected AC. Some vfet amps, for example, can be damaged if the AC is too low for the bias controls to work properly and you end up with very high current through the vfets.
Variacs are nice, but you need to be mindful of how an amp might behave with lower than expected AC. Some vfet amps, for example, can be damaged if the AC is too low for the bias controls to work properly and you end up with very high current through the vfets.
Thanks for all the info. I'll build a DBT. Should I get a 100W bulb or 25W? I don't yet see the benefit of having three 25W bulbs in 'parallel' since any issue would be found when only 1 bulb is turned on? I'm also envisioning the three bulbs in series and not in parallel....
Also, to confirm, do I turn TRIMs fully clockwise or counter-clockwise to turn down the bias offset? ( not sure if resistance move bias up or down )
Also, to confirm, do I turn TRIMs fully clockwise or counter-clockwise to turn down the bias offset? ( not sure if resistance move bias up or down )
The trimmers should be turned counterclockwise prior to your initial power up. You can verify by measuring the resistance across the two circled pins for R8 and R9. (Ideally they wil be close to zero and you'll likely have to measure from the underside of the PCB.)
@roboDNA check out this thread regarding DBT. There's a solution suggested that is very inexpensive and was not the route I had taken for my DBT.
I believe (probably wrong) a 100W is probably a good incandescent bulb to get if you only get one. I have 25W, 40W, 60W, 100W, & 150W on hand all purchased this year from various sources including Home Depot, Lowes, Menards, Amazon, eBay. A 25W will likely work if you're just testing the PSU [it glows briefly as the caps charge, then goes out if there are no shorts], but the moment you hook up the boards, if there is any bias current flowing through the transistors, a bulb with that low of wattage will glow and you won't know if you're "protecting" the amp boards, or if they are just trying to draw their normal current. I suspect a 100W will cover both checkout of just the PSU on it's own, as well as the amp boards. I used a 150W bulb and I felt it at least protected me from any shorts for both checkout scenarios 1) PSU on it's own and 2) PSU with amp boards connected.
I believe (probably wrong) a 100W is probably a good incandescent bulb to get if you only get one. I have 25W, 40W, 60W, 100W, & 150W on hand all purchased this year from various sources including Home Depot, Lowes, Menards, Amazon, eBay. A 25W will likely work if you're just testing the PSU [it glows briefly as the caps charge, then goes out if there are no shorts], but the moment you hook up the boards, if there is any bias current flowing through the transistors, a bulb with that low of wattage will glow and you won't know if you're "protecting" the amp boards, or if they are just trying to draw their normal current. I suspect a 100W will cover both checkout of just the PSU on it's own, as well as the amp boards. I used a 150W bulb and I felt it at least protected me from any shorts for both checkout scenarios 1) PSU on it's own and 2) PSU with amp boards connected.
The reason I’m using three bulbs is not just to make it overly complex. Hehe. I can’t buy a high wattage incandescent bulb where I live so I opted for three 25W bulbs which when connected in parallel would be about the same as one 75W bulb. The bulbs are connected in series with the tested device as the normal DBT just in parallel to each other. I opted to add switches so I could vary the amount of power the DUT would be allowed to draw, because if I wanted to test a pre amp or some other low power device, a 75W or 100W bulb would probably allow more than enough current to flow to ruin my day if I had done some stupid mistake. I also have a switch to bypass the bulbs altogether so I don’t have to shut down and disconnect it to continue with biasing or whatever.
I tested the power supply on my F5m build today, and opted for just one 25W bulb in series and the bulb stayed bright for a surprisingly long time. I was just about to shut it down when it started to dim and went dark. I guess I went a little overboard with the caps. 232000uF total for both rails stores quite a bit of energy.
The left dmm is connected across the thermistor to ground and the right one shows the rails.
I tested the power supply on my F5m build today, and opted for just one 25W bulb in series and the bulb stayed bright for a surprisingly long time. I was just about to shut it down when it started to dim and went dark. I guess I went a little overboard with the caps. 232000uF total for both rails stores quite a bit of energy.
The left dmm is connected across the thermistor to ground and the right one shows the rails.
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Good info. on DBTs, thanks. @Lars1210, that makes sense now. I'll keep it mind if I ever have trouble finding 100W bulbs.
I also found this build guide which is what I was going to use. ( was heading out to home depot as I'm reading these posts )
DBT Example
I uses just 1 switch ( to avoid leaving it closed by accident which I would for sure do ), and has a 'plug' to bypass the bulb instead.
NOTE: I had posted the wrong link, and just updated it now
I also found this build guide which is what I was going to use. ( was heading out to home depot as I'm reading these posts )
DBT Example
I uses just 1 switch ( to avoid leaving it closed by accident which I would for sure do ), and has a 'plug' to bypass the bulb instead.
NOTE: I had posted the wrong link, and just updated it now
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Rough duty bulbs are on the shelf at my small town hardware store and are absolutely worth the money imo. I first learned of their existence when I had to replace the bulb in my drill press (100W) and later used the second one in the pack for my DBT. I've since picked up a pair of 60W and years later, despite randomly being moved about in the shop, have never broken one
Those bathroom power outlets have a 'GFCI' protection with reset button... does it makes sense to use one of those for added safety?
@roboDNA , that's an interesting option that I think can't hurt. Worth giving it a try. I'd be curious if anyone has given that a try. I was too cheap when I made my DBT and went with the $1.50 outlet, but a Ground Fault Circuit Interrupter almost feels like it's purpose could replace the DBT entirely.....wait...did I just say that...No No, I like my DBT. It makes me feel all warm and fuzzy inside when I power up an amp/PSU for the first time. The use of a incandescent light bulb to protect by limiting current just seems like the best use of the KISS principle. Give the combo the try and report back. Inquiring minds want to know.
Higher currents dont indicate a ground fault but as ground faults are a possibility, it couldn't hurt as an addition
Don’t use a GFCI. Don’t overthink the DBT. You need nothing more than a power cord with a bulb fixture wired into it. No outlets, no breakers, no switch, just a cord with the bulb because you can’t screw it up, and the entire point for the DBT is that it’s passive and will work if there’s a problem.
I agree wholeheartedly, though my own DBT seems to tell a different story. 😆
Mine spiraled out of control when I couldn’t buy a large bulb and one thing led to another. Of course I take no responsibility and blame the government for not allowing me to buy what I need. 🤣
Mine spiraled out of control when I couldn’t buy a large bulb and one thing led to another. Of course I take no responsibility and blame the government for not allowing me to buy what I need. 🤣
I asked AI if it could help me find speakers that matched the F5m and it said the following but not sure it is accurate:
"What are the most highly recommended speakers mentioned in the diyaudio.com forums that would be a good match for the F5m amp?
On the diyAudio.com forums, the Klipsch Heresy IV and the MartinLogan Descent iX are highly recommended as good matches for the Nelson Pass F5m amplifier. Both speakers have a relatively high efficiency and a low impedance, which makes them compatible with the F5m's output capabilities. They also offer a wide and deep soundstage, making them suitable for larger rooms like yours. However, keep in mind that the recommendations might vary based on individual preferences and listening habits."
and this:
"Sure, here are five more floor-standing speaker recommendations under $2,000 per pair that would pair well with your Nelson Pass F5m amplifier:
Those recommendations don't seem that good to me... maybe AI still needs to do some learnin'
Note that I asked AI to summarize content specific to Nelson Pass, and the F5m found on dyiaudio.com in the hopes I could get an overview of user recommended speakers which is not possible otherwise. I did not ask AI for it's opinion on speakers, but what diyaudio members mentioned and liked.
"What are the most highly recommended speakers mentioned in the diyaudio.com forums that would be a good match for the F5m amp?
On the diyAudio.com forums, the Klipsch Heresy IV and the MartinLogan Descent iX are highly recommended as good matches for the Nelson Pass F5m amplifier. Both speakers have a relatively high efficiency and a low impedance, which makes them compatible with the F5m's output capabilities. They also offer a wide and deep soundstage, making them suitable for larger rooms like yours. However, keep in mind that the recommendations might vary based on individual preferences and listening habits."
and this:
"Sure, here are five more floor-standing speaker recommendations under $2,000 per pair that would pair well with your Nelson Pass F5m amplifier:
- Sonus Faber Sonetto III: These Italian-designed speakers offer a natural and engaging sound, making them a great choice for music lovers. They have a relatively high efficiency and low impedance, making them suitable for your amplifier.
- Paradigm Premier 600: With their advanced technologies and sleek design, these speakers deliver a refined and detailed sound. They have a high sensitivity and low impedance, making them compatible with your amplifier.
- KEF Q550: These British-designed speakers feature a unique Uni-Q driver array and deliver a precise and immersive sound. They have a high sensitivity and low impedance, making them suitable for your amplifier.
- Monitor Audio Gold 100: These speakers offer a balanced and dynamic sound, with a focus on clarity and detail. They have a high sensitivity and low impedance, making them compatible with your amplifier.
- Bowers & Wilkins 705 Signature: With their advanced technology and sleek design, these speakers deliver a detailed and engaging sound. They have a high sensitivity and low impedance, making them suitable for your amplifier."
Those recommendations don't seem that good to me... maybe AI still needs to do some learnin'
Note that I asked AI to summarize content specific to Nelson Pass, and the F5m found on dyiaudio.com in the hopes I could get an overview of user recommended speakers which is not possible otherwise. I did not ask AI for it's opinion on speakers, but what diyaudio members mentioned and liked.
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I don’t think this kind of stuff is going to be the sort of things ai would be any good at. It cannot possibly know what sounds good to you. It just lists speakers with high sensitivity and low impedance.
If I were to look for new speakers, neither high sensitivity nor low impedance would be a criteria for me. I guess it would make for getting a lot of sound, but no guarantee I would like the sound.
I have B&W cm9’s and with 89db sensitivity I guess they are in the low middle range regarding sensitivity. The ACAmini with its 5-7Watts has no issues reaching sound levels more than I need 95% of the time. And sounding absolutely amazing doing so. I know we all have different tastes and opinions so my great, might be another’s meh.
What speakers do you have now?
I would listen to the speakers you have now with the F5m and compare it to your other amp/s and find out what you like about it and what you might like to be a little different and maybe see if there is a speaker that might give you more of what you want or maybe less of what you are not as pleased with, if anything.
If I were to look for new speakers, neither high sensitivity nor low impedance would be a criteria for me. I guess it would make for getting a lot of sound, but no guarantee I would like the sound.
I have B&W cm9’s and with 89db sensitivity I guess they are in the low middle range regarding sensitivity. The ACAmini with its 5-7Watts has no issues reaching sound levels more than I need 95% of the time. And sounding absolutely amazing doing so. I know we all have different tastes and opinions so my great, might be another’s meh.
What speakers do you have now?
I would listen to the speakers you have now with the F5m and compare it to your other amp/s and find out what you like about it and what you might like to be a little different and maybe see if there is a speaker that might give you more of what you want or maybe less of what you are not as pleased with, if anything.
I don't have speakers yet. ( only active powered studio monitors ) I"m mentioning speakers as part of the build since many new builders such as myself will not have much in-depth knowledge of speaker specs and wonder which need to be considered when matched with a current driven Class A amp like the F5m. Many of you have been at this for decades so it may not be obvious to you 😉 As a new builder, I think perhaps a simple list of speakers everyone is using with their F5m build would be more than enough info. to buy a first pair without going to far down the rabbit hole. I asked AI for is a summary of what speakers members are using, and posted it here to see if it made sense. I realize a list of speakers is low priority and won't be needed once I learn more about speaker specs, or look at various DIY builds. ( I'm getting a sense that building my own speakers to match the amp exactly may be the way to go )
read, ask, think, ask again
but lay of AI, at least in areas where subjective criteria is of equal importance as objective