Hi!
I have just finished up my preamp boards and am moving on to the power supply for my Xono. I have found a number of designs out there, two of which have caught my attention. My question has to do with the proper fuse and thermistor configuration. My toroids are dual 50VA Plitron toroids rated at 30 VAC x 2 at 0.83A with 13% regulation. I am using a Delta 06AK2D inlet, which contains an EMI filter, and a 6A fuse (by default). I'm not sure if I should use two inlets or just one, so I'd like to pose that question as well. The design I plan on following (closest) is located here:
http://www.r-stens.de/diy/AlephOno/Rev2/PowerSupply.pdf
http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf
However, I'd like to add the inrush protection. I have found another Xono schematic, which I'm attaching, that includes inrush protection that might be a good model.
Also, I have looked at the power supply for the F4 located here, which has a similar use of thermistors as the attached schematic:
http://www.passlabs.com/np/F4 Power Amplifier.pdf
I guess my question is that there are a number of possible configurations, including not using any inrush protection at all. I was wondering if you guys could help me sort out what's best in this case for my Xono.
So in summary, I'm asking about fuse rating, thermistor configuration and number of IEC inlets. 😀
Thanks!
I have just finished up my preamp boards and am moving on to the power supply for my Xono. I have found a number of designs out there, two of which have caught my attention. My question has to do with the proper fuse and thermistor configuration. My toroids are dual 50VA Plitron toroids rated at 30 VAC x 2 at 0.83A with 13% regulation. I am using a Delta 06AK2D inlet, which contains an EMI filter, and a 6A fuse (by default). I'm not sure if I should use two inlets or just one, so I'd like to pose that question as well. The design I plan on following (closest) is located here:
http://www.r-stens.de/diy/AlephOno/Rev2/PowerSupply.pdf
http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf
However, I'd like to add the inrush protection. I have found another Xono schematic, which I'm attaching, that includes inrush protection that might be a good model.
Also, I have looked at the power supply for the F4 located here, which has a similar use of thermistors as the attached schematic:
http://www.passlabs.com/np/F4 Power Amplifier.pdf
I guess my question is that there are a number of possible configurations, including not using any inrush protection at all. I was wondering if you guys could help me sort out what's best in this case for my Xono.
So in summary, I'm asking about fuse rating, thermistor configuration and number of IEC inlets. 😀
Thanks!
I'm not familiar with this particular project, but why do you think you might need two mains inlets?
I don't think you need inrush limiting for 30VA. Ten times that VA then I would start thinking about it.
I don't think you need inrush limiting for 30VA. Ten times that VA then I would start thinking about it.
luvdunhill said:
1A slow blow, any thermistor similar to a Keystone CL60 or so,
and 1 IEC outlet.
😎
hi! okay, that's short and sweet! What about the configuration of said thermistors? Should I do something like in the F4, where there are three, two between the IEC inlet and the toroid primaries and one between the output ground and the chassis ground (which is shared with the IEC inlet earth) *or* is there no need for something this fancy...
as to richie00boy's question, well I see a lot of products with two IEC inlets, and besides the fact that it looks cool, I could never figure out why they did it, except for a bit more isolation when using power conditioning? who knows, probably all marketing hype...
How many things have you seen with more than one power connection? With the arguable exception of a dual mono amplifier in a single chassis, I fail to see any use for such a thing.
I'm also not sure why you see the need for inrush limiting on a low level piece of equipment. The usual application is to keep from blowing fuses when charging a very large capacitor bank in an amplifier (note that the F4 is a power amplifier). In a phono stage, you're going to have to go into some really heavy capacitance to need such a thing. Any other variation would be as well served by a straight resistance, e.g. reducing the rail voltage.
Grey
I'm also not sure why you see the need for inrush limiting on a low level piece of equipment. The usual application is to keep from blowing fuses when charging a very large capacitor bank in an amplifier (note that the F4 is a power amplifier). In a phono stage, you're going to have to go into some really heavy capacitance to need such a thing. Any other variation would be as well served by a straight resistance, e.g. reducing the rail voltage.
Grey
Grey:
Points taken. I believe the piece of equipment I was referring to with two power cords is one of the Aesthetix phono stages, but I cannot find pictures at this point to confirm.
In any case, the Xono is indeed dual mono in both the preamplification and power supply portions of the design.
As to your point about the amount of capacitance and straight resistance, I am following this schematic here:
http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf
which is part of this larger design:
http://www.r-stens.de/diy/AlephOno/Rev2/PowerSupply.pdf
Finally, the last attachment is another Xono design that incorporates thermistors, hence my interest in the subject.
It may be useful to note that this is definitely a tour-de-force phono preamplifier design
Points taken. I believe the piece of equipment I was referring to with two power cords is one of the Aesthetix phono stages, but I cannot find pictures at this point to confirm.
In any case, the Xono is indeed dual mono in both the preamplification and power supply portions of the design.
As to your point about the amount of capacitance and straight resistance, I am following this schematic here:
http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf
which is part of this larger design:
http://www.r-stens.de/diy/AlephOno/Rev2/PowerSupply.pdf
Finally, the last attachment is another Xono design that incorporates thermistors, hence my interest in the subject.
It may be useful to note that this is definitely a tour-de-force phono preamplifier design
luvdunhill said:
So I had assumed, but I see no thermistors in the schematics you linked to, only fixed resistors, and you haven't suggested anything that would necessitate their use.
Grey
well, the attachment in my first post named ono_unreg. pcb_schematic.pdf shows two thermistors labeled TH1 and TH2.
Also, the second link in my first post (http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf) shows 80,000uF in the power supply chassis. In addition, there will be another 37,600uF in the preamplifier chassis before regulation. Hence my concerns.
Also, the second link in my first post (http://www.r-stens.de/diy/AlephOno/Rev2/PSAnalogDC.pdf) shows 80,000uF in the power supply chassis. In addition, there will be another 37,600uF in the preamplifier chassis before regulation. Hence my concerns.
I took the pdf you're mentioning to be yours, not someone else's; so of course it shows them because you put them there. Perhaps I misunderstood.
There are numerous ways to look at power supplies. My point of view--and I do not claim that it's shared by everyone--is to reduce the impedance looking upstream into the AC line to a bare minimum. Resistors and thermistors are contraindicated. Yes, there are times when they're necessary, but I avoid them if I can. 80,000uF doesn't scare me, but if you feel that it's a problem, then use the thermistors, but bear in mind that by using a lot of capacitance fed by resistance you are engaging in a tug-of-war with yourself. One of the reasons for using a lot of capacitance is to lower the impedance seen by the circuit when it demands current. By definition, putting resistance in the line will work against that.
Your response to that will probably take one of two forms: The resistance is on the other side of the power transformer--or--I'm not storing energy, I'm making the rail quiet.
If the first, my reply is that any impedance will retard the flow of charge to the power supply caps.
If the second, my response is that caps are good, but there are more elegant ways to make a rail quiet than brute force capacitance.
Again, if you want to use a lot of capacitance, I'm all for it. If you feel that thermistors are part of your vision of how to get where you want to go, then have at it. For something small like a phono stage, even assuming an inrush current problem (which I'm still not convinced is the case), you could use something like inductors wound with heavy gauge wire--minimal impedance, except at turn-on. Or use a circuit topology that sums to DC for current draw. Or use a capacitance multiplier. Or active regulation. Or...any number of things.
Incidentally, I don't see that schematic showing 80,000uF. Are you sure we're talking about the right schematic?
Grey
P.S.: Bear in mind that since you're referencing schematics showing CRC filters, everything after the R will, by definition, not develop much inrush current because the R will show an increased voltage drop due to the current. One the surge is over, things will assume a more modest value.
There are numerous ways to look at power supplies. My point of view--and I do not claim that it's shared by everyone--is to reduce the impedance looking upstream into the AC line to a bare minimum. Resistors and thermistors are contraindicated. Yes, there are times when they're necessary, but I avoid them if I can. 80,000uF doesn't scare me, but if you feel that it's a problem, then use the thermistors, but bear in mind that by using a lot of capacitance fed by resistance you are engaging in a tug-of-war with yourself. One of the reasons for using a lot of capacitance is to lower the impedance seen by the circuit when it demands current. By definition, putting resistance in the line will work against that.
Your response to that will probably take one of two forms: The resistance is on the other side of the power transformer--or--I'm not storing energy, I'm making the rail quiet.
If the first, my reply is that any impedance will retard the flow of charge to the power supply caps.
If the second, my response is that caps are good, but there are more elegant ways to make a rail quiet than brute force capacitance.
Again, if you want to use a lot of capacitance, I'm all for it. If you feel that thermistors are part of your vision of how to get where you want to go, then have at it. For something small like a phono stage, even assuming an inrush current problem (which I'm still not convinced is the case), you could use something like inductors wound with heavy gauge wire--minimal impedance, except at turn-on. Or use a circuit topology that sums to DC for current draw. Or use a capacitance multiplier. Or active regulation. Or...any number of things.
Incidentally, I don't see that schematic showing 80,000uF. Are you sure we're talking about the right schematic?
Grey
P.S.: Bear in mind that since you're referencing schematics showing CRC filters, everything after the R will, by definition, not develop much inrush current because the R will show an increased voltage drop due to the current. One the surge is over, things will assume a more modest value.
Grey:
First of all, thanks for the well thought out response! I realized I never thanked you.
Grey and Co.:
Well, I'm now out of 1A fuses 
I was really jonesing for some Mahler last night, so I stuck in a 3A fuse after my last 1A blew and listened to Solti and Mahler 1 on Decca 
To clarify, I have two power supplies, each of which has a total of 24,700uF per rail before the regulator. 20,000uF of this is in a separate power supply chassis, and the other 4,700uF is in the preamp chassis right before the regulator. So, there are a total of 8 x 10,000uF in the power supply chassis. Maybe pictures would help if this is clear only to myself?
So, it seems that I am meeting your requirement of "blowing fuses when charging a very large capacitor bank". So, should I just use a larger fuse, or consider adding a thermistor, or something else?
Thanks in advance!
First of all, thanks for the well thought out response! I realized I never thanked you.
Grey and Co.:
Well, I'm now out of 1A fuses
I was really jonesing for some Mahler last night, so I stuck in a 3A fuse after my last 1A blew and listened to Solti and Mahler 1 on Decca To clarify, I have two power supplies, each of which has a total of 24,700uF per rail before the regulator. 20,000uF of this is in a separate power supply chassis, and the other 4,700uF is in the preamp chassis right before the regulator. So, there are a total of 8 x 10,000uF in the power supply chassis. Maybe pictures would help if this is clear only to myself?
So, it seems that I am meeting your requirement of "blowing fuses when charging a very large capacitor bank". So, should I just use a larger fuse, or consider adding a thermistor, or something else?
Thanks in advance!
Hi,
I see three alternatives.
1.) T1.6A fuse the 30VA transformer.
2.) Thermistor or resistor in primary feed to 30VA transformer.
3.) Thermistor or resistor in secondary feed to smoothing bank.
If you adopt either 2. or 3. then consider adding a timed bypass relay to short out the added resistance feeding your pre-amp (addresses Grollins' concern).
The usual resistor added to a power amp transformer is of the order of 10r to 20r for 110/120Vac supplies to allow T5A or T6A fuses to be used in the primary.
Your tiny transformer would be relatively unprotected by such a large fuse. Consider what value of resistor (could be 100r or so) would suit 30VA and allow a T1A fuse to survive repeated start-ups.
Is your IEC filter rated for 1A or for 6A (fused at 6A by default).
You should be using a 1A filter to obtain the higher inductance in the common mode inductor, the caps are usually of similar values.
I see three alternatives.
1.) T1.6A fuse the 30VA transformer.
2.) Thermistor or resistor in primary feed to 30VA transformer.
3.) Thermistor or resistor in secondary feed to smoothing bank.
If you adopt either 2. or 3. then consider adding a timed bypass relay to short out the added resistance feeding your pre-amp (addresses Grollins' concern).
The usual resistor added to a power amp transformer is of the order of 10r to 20r for 110/120Vac supplies to allow T5A or T6A fuses to be used in the primary.
Your tiny transformer would be relatively unprotected by such a large fuse. Consider what value of resistor (could be 100r or so) would suit 30VA and allow a T1A fuse to survive repeated start-ups.
Is your IEC filter rated for 1A or for 6A (fused at 6A by default).
You should be using a 1A filter to obtain the higher inductance in the common mode inductor, the caps are usually of similar values.
AndrewT said:
I'm not exactly sure, I'd assume 6A. It's a Delta 06AK2D.
GRollins said:
I am (well, was) using the following Digikey part number: F2419-ND, which is a 1A Slow Blow.
Hi,
T rated fuses when sized to about three times the nominal maximum current draw for feeding motors and transformers usually survive.
30VA * 3 =90VA. Divide by 110Vac and you arrive at a normal T1A fuse. I guess the fairly high capacitance is asking the elevated current to last just a bit too long for that fuse rating.
Try T1.6A.
Apply the same formula to the bigger power amps and you begin to see why some form of current limiting is often considered necessary.
T rated fuses when sized to about three times the nominal maximum current draw for feeding motors and transformers usually survive.
30VA * 3 =90VA. Divide by 110Vac and you arrive at a normal T1A fuse. I guess the fairly high capacitance is asking the elevated current to last just a bit too long for that fuse rating.
Try T1.6A.
Apply the same formula to the bigger power amps and you begin to see why some form of current limiting is often considered necessary.
ok, now that I think about it, these are two 50 VA toroids. Sorry for the misinformation. I think the exact part number is Plitron #027017201 30 VAC x 2 @ 0.83 A.
So, by your math I should look at 1.36 A nominally, so either a 1.25 A or 1.60 A are available in the fuse I was using before.
Another interesting thing is that on the Plitron website, they state the following:
"Inrush Current
The high remanence of grain oriented silicon steel, lack of air gaps, and the excellent magnetic properties of toroidal transformers can cause a high magnetizing current on turn on, limited only by the low impedance of the primary winding. However, the duration of the inrush current is rarely longer than a half a cycle. The effect of this inrush becomes greater with an increase in toroidal power. 8 VA to 300 VA transformers should not require any protection. For transformers 300 VA and up a slow-blow fuse, delayed action circuit breaker, or some form of soft start circuitry should be considered."
I guess I've proved them wrong ...
So, in general, when does one stop increasing the rating of the fuse and try and solve the problem a different way? Seems kinda strange to say "just use a bigger fuse, no worries" when NP himself recommended a 1A fuse 😎 Obviously I don't want to go any higher than possible to keep myself safe and the fabulous new preamp safe as well 😎
So, by your math I should look at 1.36 A nominally, so either a 1.25 A or 1.60 A are available in the fuse I was using before.
Another interesting thing is that on the Plitron website, they state the following:
"Inrush Current
The high remanence of grain oriented silicon steel, lack of air gaps, and the excellent magnetic properties of toroidal transformers can cause a high magnetizing current on turn on, limited only by the low impedance of the primary winding. However, the duration of the inrush current is rarely longer than a half a cycle. The effect of this inrush becomes greater with an increase in toroidal power. 8 VA to 300 VA transformers should not require any protection. For transformers 300 VA and up a slow-blow fuse, delayed action circuit breaker, or some form of soft start circuitry should be considered."
I guess I've proved them wrong ...
So, in general, when does one stop increasing the rating of the fuse and try and solve the problem a different way? Seems kinda strange to say "just use a bigger fuse, no worries" when NP himself recommended a 1A fuse 😎 Obviously I don't want to go any higher than possible to keep myself safe and the fabulous new preamp safe as well 😎
AndrewT said:
No,luvdunhill said:
the twin 50VA =100VA, now apply the standard rule for transformers and motors. The maximum current, after the very short term peak has passed, is about 2.7A, so you are left with T3A as the next larger value. You could try T2.5A but this may suffer nuisance blowing occasionally.
Note that these transformers will never continuously draw 100VA during normal operation, so you can consider fitting a soft start to allow a smaller fuse to be used. I would try to close rate the mains fuse. In my opinion T1A would be a good target for close rating and I would adjust the soft start resistor values until T1A does not suffer nuisance blowing.
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