It seems that the purpose of this thread is to be instructive.
Posting the entire LA article does violate the copyright. Posting a snippet is clearly instructive and within “Fair Use”.
The question is; where will diyAudio and Linear Audio (Jan) draw the “Fair Use” line?
Many times I have been inclined to quote a copyright publication but I have not.
I have the impression that diyAudio has a "No Use" policy.
DT
The Linear Audio article is a quick read (only 14 pages long), but they do charge money for it. You can either purchase a hardcopy of the entire LA Volume, or a pdf download of just one single article. ... here is a link ...
The Quasimodo manual is a bit longer: 22 pages. However it's available for free, just download it from diyAudio. It is an Acrobat .pdf attachment, connected to the very bottom of post #1 in the Quasimodo thread. i.e., this very thread, the one you are reading now.
The Quasimodo manual is a bit longer: 22 pages. However it's available for free, just download it from diyAudio. It is an Acrobat .pdf attachment, connected to the very bottom of post #1 in the Quasimodo thread. i.e., this very thread, the one you are reading now.
High voltage snubbers...
I've recently checked with my Quasimodo a 460V transformer used in a DIY tube preamplifier. Required resistance is 4K7. So I installed the two caps (600VAC rated) and a 3W resistor. Its temperature is reasonable, 50/55°C (around 125°F) and I can measure 100VAC (RMS, read by a DVM) over it.
I tried to apply a Ohms law (RMS, resistive loading) and found over 2W dissipation. But I believe it'd lower because of the "low" temperature.
Would someone be so kind to give me some inputs on this matter?
I've recently checked with my Quasimodo a 460V transformer used in a DIY tube preamplifier. Required resistance is 4K7. So I installed the two caps (600VAC rated) and a 3W resistor. Its temperature is reasonable, 50/55°C (around 125°F) and I can measure 100VAC (RMS, read by a DVM) over it.
I tried to apply a Ohms law (RMS, resistive loading) and found over 2W dissipation. But I believe it'd lower because of the "low" temperature.
Would someone be so kind to give me some inputs on this matter?
Yes the full EE math with pencil and paper predicts 100V RMS across your snubber resistor and 2 watts of RMS power dissipation.
LTSPICE simulation gives the same result, schematic below.
It's wonderful that your 3W resistor is very efficient at dissipating heat into the surrounding air, without its case becoming uncomfortably hot. Some 3W resistors are not so efficient, and their exterior case does become very very hot.
LTSPICE simulation gives the same result, schematic below.
It's wonderful that your 3W resistor is very efficient at dissipating heat into the surrounding air, without its case becoming uncomfortably hot. Some 3W resistors are not so efficient, and their exterior case does become very very hot.
Attachments
This resistor (PR03) is fusible and it might blow without you even noticing …
You better find a better resistor for the job.
Metal oxide for example.
Here is the math to calculate power dissipated in the snubber resistor. It is typical of a homework problem given to 2nd year EE undergraduates taking their first Circuit Analysis class.
You may decide that the LTSPICE simulation method shown in post #1351, has much to recommend it after all. But either path will lead to your final objective.
Please remember to make the actual resistor in real life, at least 2X and preferably 3X the wattage, compared to the calculated power. This gives a margin of safety for reliability and a long, long service life.
_
- R is the snubber resistance in ohms. In the example of post #1350, R=4700
- C is the series capacitor "Cs" in farads. In the example, C = 1.5E-7 (0.15uF)
- Vin is the secondary RMS voltage in volts. In the example, Vin = 460
- f is the mains frequency in Hertz. In the example, f = 50
You may decide that the LTSPICE simulation method shown in post #1351, has much to recommend it after all. But either path will lead to your final objective.
Please remember to make the actual resistor in real life, at least 2X and preferably 3X the wattage, compared to the calculated power. This gives a margin of safety for reliability and a long, long service life.
_
Have Quasimodo V4 through hole version kits for sale in stock. The kit is $36.08 which includes free shipping to the lower states and PayPal fees. The kit is standard BOM. The boards are with ENIG finish. Parts are labeled and packaged in small plastic bags.