Hi Plott,
since you are in 230V country, probably something like 1.6A to 2.5A T (slow-blow) should work. As to sizing: the lowest value that only blows at switch-on once every three months or so. That's how I size my fuses. I suggest buying a 10-pack of 1.25A, 1.6A, 2A, 2.5A each. For example, at TME or Reichelt.
As to rail fuses: I don't feel they are necessary with an M2. In fact, none of my Pass amps have rail fuses. Only my tube amps do have them for B+ (high voltage).
Best regards, Claas
since you are in 230V country, probably something like 1.6A to 2.5A T (slow-blow) should work. As to sizing: the lowest value that only blows at switch-on once every three months or so. That's how I size my fuses. I suggest buying a 10-pack of 1.25A, 1.6A, 2A, 2.5A each. For example, at TME or Reichelt.
As to rail fuses: I don't feel they are necessary with an M2. In fact, none of my Pass amps have rail fuses. Only my tube amps do have them for B+ (high voltage).
Best regards, Claas
Maybe this other thread might be of some utility
Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
since it discusses M2x mains-fuses blowing due to inrush current at power on.
In addition to the first post of the thread, also have a look at post#17 , post #25 , and post #41
Not thrilled with CL-60 inrush limiter in USA/160W Class A First Watt designs
since it discusses M2x mains-fuses blowing due to inrush current at power on.
In addition to the first post of the thread, also have a look at post#17 , post #25 , and post #41
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Ya I guess it's just a quick easy way to get a ballpark number for folks that have chosen a transformer thats sized appropriately for the circuit being powered, i.e. not using an 800W rated transformer on a puny 160W load. A bigger transformer will have a larger magnetic structure to fill with energy (inrush current, even with no load), saturated impedances are smaller. That inrush shoots up once we hang a bunch of big reservoir caps off of it. Decades worth of cussing and discussing on dealing with that problem of course... I use a pair of NTC's in series with the primary to deal with the inrush, and then bypass those with a second switch after a few seconds so as not to throw away any secondary voltage, and avoid scorching hot parts running in the chassis all the time. Crude, dumb, and lazy.... I know, I accept the dumb-ness, just sticking with what works for me ("normal" sized fuse that never blows)...
I know, I knowthose MDF bards are great for bridges cooling, so feel free to proceed with full amp, like that
the chassis will arrive in two days, I just wanted to know whether the PSU works.
Yes, I'm planning to do that. For the snubber-parts there is a dedicated place on the bridge-pcb.
The whole PSU will be doubled, with two 300va Anteks, 4 bridges and two cap banks. This thingie was just a test run for the cap banks.
Here is the bridge-pcb, I'm sure you know it:
When you 'test' the power supply, you really need to have a load equivalent to the amplifier current to see that the power supply is behaving itself under working conditions - I suggest you connect a 16R load to emulate a current rate of approx 1.5A thru the load to check the power supply is functioning properly.
Regrettably, this isn't a standard procedure for many diy folks and, IMHO, it should be ....
Regrettably, this isn't a standard procedure for many diy folks and, IMHO, it should be ....
The switch should work if its current rating is higher than the fuse current rating.
I usually test a power supply unloaded with a Dim Bulb Tester and then under load with resistors. However it may be difficult to test under load since the power rating of the load resistor may need to be quite high. For instance, 1.5A at 16R is 36W. Fortunately I have a bag of 5W and 10W resistors that I can use to series and parallel connect to achieve high Wattage. However, I usually test to less than design current as the resistors get quite hot, even when a safety factor of two or more is applied to the resistor Wattage.
I usually test a power supply unloaded with a Dim Bulb Tester and then under load with resistors. However it may be difficult to test under load since the power rating of the load resistor may need to be quite high. For instance, 1.5A at 16R is 36W. Fortunately I have a bag of 5W and 10W resistors that I can use to series and parallel connect to achieve high Wattage. However, I usually test to less than design current as the resistors get quite hot, even when a safety factor of two or more is applied to the resistor Wattage.
Hi Plott -
I'm not sure if they're readily available near you, but a few 250W / 300W non-inductive load resistors from a reputable source are nice. I also got a few 4 and 8 ohm 100W resistors (inductive) for much cheaper on a reseller site. I like the larger ones for work with (with heatsinks) for power amps. The little ones (even with a heatsink) get pretty warm / hot even during a standard 1W distortion measurement. I got a couple of the ones linked below except in 250W format. For the price difference, I'd go with 300W. The 250W remains nice and usable up to 75W (with a heatsink), which is the highest I've ever tried (so far). Just a couple ideas.
Example -
https://www.mouser.com/ProductDetail/ARCOL-Ohmite/NHS300-8R0-1?qs=sGAEpiMZZMtlubZbdhIBIKR5oQtBrv7qbN6MvD0i4F0=
Pic of a good 250W vs. a reseller 100W.
Loving your amp projects and the Pumpkin!!
Edited to add - this type comes highly recommended from another trusted user, but I haven't tried them myself. To my knowledge, they're not available in 4 or 8 ohm, but 10 ohm is certainly usable.
https://www.ebay.com/itm/2541988218...nGb4Ec+LVcNGffLTieJ8bLtPI=|tkp:Bk9SR_jk4r_nYA
I'm not sure if they're readily available near you, but a few 250W / 300W non-inductive load resistors from a reputable source are nice. I also got a few 4 and 8 ohm 100W resistors (inductive) for much cheaper on a reseller site. I like the larger ones for work with (with heatsinks) for power amps. The little ones (even with a heatsink) get pretty warm / hot even during a standard 1W distortion measurement. I got a couple of the ones linked below except in 250W format. For the price difference, I'd go with 300W. The 250W remains nice and usable up to 75W (with a heatsink), which is the highest I've ever tried (so far). Just a couple ideas.
Example -
https://www.mouser.com/ProductDetail/ARCOL-Ohmite/NHS300-8R0-1?qs=sGAEpiMZZMtlubZbdhIBIKR5oQtBrv7qbN6MvD0i4F0=
Pic of a good 250W vs. a reseller 100W.
Loving your amp projects and the Pumpkin!!
Edited to add - this type comes highly recommended from another trusted user, but I haven't tried them myself. To my knowledge, they're not available in 4 or 8 ohm, but 10 ohm is certainly usable.
https://www.ebay.com/itm/2541988218...nGb4Ec+LVcNGffLTieJ8bLtPI=|tkp:Bk9SR_jk4r_nYA
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Good grief! You don't need anything exotic for this "dummy load"
Any 16R/100w wire wound resistor will do the trick (for each rail/channel) and you can parallel 2 of them for an 8R load for a single power supply for both channels - then you can use the same units as passive load for the amplifier output (ie full power soak testing, etc)' - they're readily available for a few $s ea.
Or, in the true spirit of diy (!), make up 25W versions (ie 6 x 100R/3w units in //) for each rail and dump them into 2 jugs of clean water
The Dim Bulb test is a good one - I prefer the old idea of a simple Variac (aka mains Auto Transformer) to catch mistakes at low voltages - an essential and inexpensive "bit o' kit" IMO!
Any 16R/100w wire wound resistor will do the trick (for each rail/channel) and you can parallel 2 of them for an 8R load for a single power supply for both channels - then you can use the same units as passive load for the amplifier output (ie full power soak testing, etc)' - they're readily available for a few $s ea.
Or, in the true spirit of diy (!), make up 25W versions (ie 6 x 100R/3w units in //) for each rail and dump them into 2 jugs of clean water
The Dim Bulb test is a good one - I prefer the old idea of a simple Variac (aka mains Auto Transformer) to catch mistakes at low voltages - an essential and inexpensive "bit o' kit" IMO!
Many thanks, yes, I could buy a 4.7 ohms 100w thingie tomorrow, would it be okay? I mean, it's neither 4 nor 8 ohms...
I used cheap, inductive, wirewound resistors . . . . plus a bit of science , to construct a higher power noninductive resistor.
Building my own noninductive 8R 150W load using wire wound resistors
Building my own noninductive 8R 150W load using wire wound resistors
