So what is "beyond...?"
Thanks for the reply, and what you stated is what I understand. I see that builders are often increasing the capacitors up to 20,000uFx4 and a 400VA and 500VA (Antek) transformers can be used as long as they have 2 x 18V secondaries. My questions are (1) the 18V is a constant, there is no range, correct? (2) 300VA load is the minimum for the designs. Anything above this is more than sufficient and add cost to the build (Question 2A - so what does this get you in the end?). (3) Is there a minimum or maximum current acceptable to the designs given that the Load and secondary voltage will influence this?
I was trying to follow the thread on using the Toroidy products from Poland, as they appear to be an upgrade to the system. I got lost trying to determine is they had 115 V products and which of these might be appropriate for the First Watt build. Same thing with researching Lundberg and Hammond transformers. As far as I can tell they do not have an equivalent 300VA 18V+18V toroidal transformer. How does one select a component that provides the appropriate voltage and current and is not overly powerful to damage the circuitry?
Thanks again
Thanks for the reply, and what you stated is what I understand. I see that builders are often increasing the capacitors up to 20,000uFx4 and a 400VA and 500VA (Antek) transformers can be used as long as they have 2 x 18V secondaries. My questions are (1) the 18V is a constant, there is no range, correct? (2) 300VA load is the minimum for the designs. Anything above this is more than sufficient and add cost to the build (Question 2A - so what does this get you in the end?). (3) Is there a minimum or maximum current acceptable to the designs given that the Load and secondary voltage will influence this?
I was trying to follow the thread on using the Toroidy products from Poland, as they appear to be an upgrade to the system. I got lost trying to determine is they had 115 V products and which of these might be appropriate for the First Watt build. Same thing with researching Lundberg and Hammond transformers. As far as I can tell they do not have an equivalent 300VA 18V+18V toroidal transformer. How does one select a component that provides the appropriate voltage and current and is not overly powerful to damage the circuitry?
Thanks again
Everything you need is here and a nice light read:
Solid State Power Amplifier Supply Part 1
1) 18v isn't constant and will range depending on the load from the amplifier and the incoming mains. Formula's are in the link for you to work it out. Toroidy, will build you a transformer of any VA size to achieve a specific voltage for a specific current on the secondaries if you provide them the expected current requirements. This isn't a major problem unless you are really oversizing..
Just to add, your focusing on AC and you should be focusing on DC after Rectifiers and Smoothing Caps.
2) Best thing is to read that article, so you can see how to size your own transformer for a specific power rating/impedance.
2-A) Over sized power supply can allow you to hit 2 ohm power goals and transient peaks.
3) I don't understand?
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You could use 10,000uF as well.
The difference between the 2 and 4 amp version is only the installed fuse.
Use a bolt through the case and those lugs (in your dimension) to connect the wires to it.
No, it's not constant. Two (or more) things can affect the secondary voltage:
mains voltage and load. See Antek spec sheets under "load test". It usually doesn't vary much, but it's not constant. See your question 3 below.
It's generally the minimum suggested. Note - VA is not the load. 300VA is the rating. It's the manufacturer's way of saying that 300VA is their highest recommended load. 400VA can be used with an amp that uses more power. 50VA would be used with an amp that uses less power.
Some people go with more for their own reasons. Perhaps in the future they want to use them with amps that use more power, and they're planning ahead. Too low, and the voltage sag and potentially physical hum will get worse. Too high, more money than potentially needed, and potentially more EMI.
2.5 to 3 times the total dissipation seems to be the ballpark recommendation. Maximum only has detriments listed above. Also, if you take Antek as an example, they don't manufacture shielded transformers above 400VA.
One more time to help it sink in. The transformer does not "provide" current. The circuit will draw current through the transformer. Bigger transformers are needed for circuits that draw more current. A higher current rated transformer is not "overly powerful", it can just work better under higher current loads. It's the amplifier that draws the current, the transformer does not "push" current. You won't harm anything by using a 1kVA transformer, but there may be some drawbacks, see above.
Choose the secondary voltage based on the PSU you intend to use and back calculate it from the DC rails required for the amp and any expected voltage loss in the PSU circuit and some sag. The transformer should not have way more secondary voltage than needed (in general). You would not want 36V secondaries as an example, but many people use transformers with 20V secondaries.
Example - VA Rating
For an amp that dissipates ~120W, a 300VA to 400VA transformer fits nicely into that 2.5x to 3x rule. If that person knew that they wanted a beast of an amp that dissipated 300W (like a fully built Burning Amp for example) they would want a higher-rated transformer or they may go with dual mono to share the total load across two transformers.
Example - DC Voltage requirement to Secondary voltage
An amplifier that requires 24VDC rails using a PSU that drops about 2V for losses and sag. (24V + 2V) / 1.4 => ~18.6. 18 and 20VAC are available from Antek. 18 is closer. 20 is fine.
Have fun!
Responses to Tranformer sizing questions
Thanks to both sebbyp and ItsAllInMyHead (yes, truly). Your replies are very complementary and I appreciate the thoughtful responses. I'm developing a much clearer picture now. At this point in the hobby, I'm only trying to follow basic plans and getting a fine sounding product. I'll get creative later.
This amplifier design stuff is complicated! ;-) It makes one very appreciative of the art and science involved in both the design and manufacturing of high quality music recording and reproduction.
Cheers!
Thanks to both sebbyp and ItsAllInMyHead (yes, truly). Your replies are very complementary and I appreciate the thoughtful responses. I'm developing a much clearer picture now. At this point in the hobby, I'm only trying to follow basic plans and getting a fine sounding product. I'll get creative later.
This amplifier design stuff is complicated! ;-) It makes one very appreciative of the art and science involved in both the design and manufacturing of high quality music recording and reproduction.
Cheers!
Bowlrider, i am trying to read a bit “deeper” into your questions. I think I have a different understanding of what you meant when you asked about the 18V being “constant”.
Where you asking if you NEEDED an 18V secondaries or if you could, for example, buy a 20V one or a 16V and then work with that? Or where you asking if an 18V transformer would be a source of “constant voltage”?
Re-reading your posts, people have answered assuming scenario 2. If it was scenario 1, then the answer is: 18V secondaries are 18V RMS, which when fully rectified to DC, gives you around 25DC, which, after some loss, gives you the +-24VDC needed to run most PW amps.
So that is why you want an 18V secondaries transformer.
If your question was really about 18v being “constant”, you have the answers above by much more knowledgeable people than me.
Hope this helps,
Rafa.
Where you asking if you NEEDED an 18V secondaries or if you could, for example, buy a 20V one or a 16V and then work with that? Or where you asking if an 18V transformer would be a source of “constant voltage”?
Re-reading your posts, people have answered assuming scenario 2. If it was scenario 1, then the answer is: 18V secondaries are 18V RMS, which when fully rectified to DC, gives you around 25DC, which, after some loss, gives you the +-24VDC needed to run most PW amps.
So that is why you want an 18V secondaries transformer.
If your question was really about 18v being “constant”, you have the answers above by much more knowledgeable people than me.
Hope this helps,
Rafa.
Rafa, Yes, I think you closer to my intent (I just did not want this inquiry to drag on and create greater confusion). Thanks.
To your point, what I meant by "constant" was not constant voltage, but that the 18V secondaries were needed to provide the 24VDC -/+ required by the design. If a transformer with 18V secondaries is out of stock (as with Antek currently), can a transformer with 20 V secondaries be substituted, e.g., the AS3220 in place of the AS3218 or AS4220 in place of the AS4218? I hope this helps clarify my question.
I am a humble, novice builder and trying to understand the "why" behind the different parts of the amplifiers.
To your point, what I meant by "constant" was not constant voltage, but that the 18V secondaries were needed to provide the 24VDC -/+ required by the design. If a transformer with 18V secondaries is out of stock (as with Antek currently), can a transformer with 20 V secondaries be substituted, e.g., the AS3220 in place of the AS3218 or AS4220 in place of the AS4218? I hope this helps clarify my question.
I am a humble, novice builder and trying to understand the "why" behind the different parts of the amplifiers.
Sure, you should isolate the unused secondaries as they will be live each time you turn on the transformer.
Since you are most likely using diodes / rectifiers for the DC conversion, what I understand is that the diode will simply “take” the ACs 25Vpp (18Vrms) from the signal, and “pass them along”. If you go with a 20V secondaries, that would give you around 28VDC, which is above of what you want.
I guess you could use regulators to go back to 24V, but that opens a few Pandora’s boxes, and given the high currents of these amps, I would have no idea where to even start doing that.
Maybe others have more insight, but I am also fairly newb myself.
Although working, by isolating the second secondary, you would put half the tranny‘s capacity in idle mode, while the connected one has to do the whole job. Better to connect them in serie, then you‘ll have the full power at your disposal.
(Be sure to make verything correct, research „transformer secondary serial“ here and elsewhere!)
I recently had this situation (secs in series)… The dots are indicators. They might be wrong as seems to be the case with some edcor 600:600. measure the output to be sure. They will be correct 99.9%…
https://www.diyaudio.com/forums/pass-labs/369990-ludef-51.html#post6756719
https://www.diyaudio.com/forums/analogue-source/129126-simplistic-njfet-riaa-1888.html#post6611687
