I’m genuinely curious about this topic. Like you already said part availability is a key factor to take into account, but aside from that…
Is transformer regulation/stabilization an issue for a constant current draw class A amp? I can understand the benefit for other amp classes where the current draw varies, and I understand designing In some margin, but a 20:3 factor seems excessive. Maybe this is my poor understanding, let me explain my thoughts:
If a transformer’s long term power rating is thermally dependent (maybe an incorrect assumption?), with a constant power draw it’s easier to determine the long term mean/ RMS compared to when it’s dependent on the input signal. Assuming most reputable transformer manufacturers design in some margin for their power rating, I would think that doubling the power rating would be plenty, meaning you could get away with less than double and still be fine. As was explained to me: time and temp are the two key factors for reliability testing.
Is there much of an efficiency difference between running a smaller transformer at half (or more) of its rated power compared to running a larger one at 1/6th or 1/8th? If there is a significant difference that would mean less power dissipated inside the chassis/case which would definitely be a factor in the reliability of the amp. My thought is that the larger, cooler transformer would be slightly more efficient with less resistive losses, but my guess is it would be only a negligible difference. For example if the smaller transformer was say 90% efficient and the larger is 92% with a 3W load the difference would be only 60mW, 3300mW vs 3240mW.
Thanks in advance!
olen
Is transformer regulation/stabilization an issue for a constant current draw class A amp? I can understand the benefit for other amp classes where the current draw varies, and I understand designing In some margin, but a 20:3 factor seems excessive. Maybe this is my poor understanding, let me explain my thoughts:
If a transformer’s long term power rating is thermally dependent (maybe an incorrect assumption?), with a constant power draw it’s easier to determine the long term mean/ RMS compared to when it’s dependent on the input signal. Assuming most reputable transformer manufacturers design in some margin for their power rating, I would think that doubling the power rating would be plenty, meaning you could get away with less than double and still be fine. As was explained to me: time and temp are the two key factors for reliability testing.
Is there much of an efficiency difference between running a smaller transformer at half (or more) of its rated power compared to running a larger one at 1/6th or 1/8th? If there is a significant difference that would mean less power dissipated inside the chassis/case which would definitely be a factor in the reliability of the amp. My thought is that the larger, cooler transformer would be slightly more efficient with less resistive losses, but my guess is it would be only a negligible difference. For example if the smaller transformer was say 90% efficient and the larger is 92% with a 3W load the difference would be only 60mW, 3300mW vs 3240mW.
Thanks in advance!
olen
^ I'm always curious re: this topic also... but... one of the questions you ask above may be making an assumption that is not always true...
Is transformer regulation/stabilization an issue for a constant current draw class A amp?
If the amplifier had a constant current draw, I believe the answer is ... no, that factor alone would not contribute to stabilization. Regulation is a function of the constant load, but it ... should be stable.
However, as I've read more about this recently, I've seen it mentioned many times (but I don't yet quite understand) that the current draw can vary with the signal, and that is design dependent. Truthfully, I don't know how much of that factors into the overall 'comfort multiple' rule of thumb for VA vs. actual power draw, but... it's fascinating nonetheless.
Here's one of many threads I found fascinating.
https://www.diyaudio.com/community/threads/power-supply-impedance-and-class-a-amplifiers.307829/
Is transformer regulation/stabilization an issue for a constant current draw class A amp?
If the amplifier had a constant current draw, I believe the answer is ... no, that factor alone would not contribute to stabilization. Regulation is a function of the constant load, but it ... should be stable.
However, as I've read more about this recently, I've seen it mentioned many times (but I don't yet quite understand) that the current draw can vary with the signal, and that is design dependent. Truthfully, I don't know how much of that factors into the overall 'comfort multiple' rule of thumb for VA vs. actual power draw, but... it's fascinating nonetheless.
Here's one of many threads I found fascinating.
https://www.diyaudio.com/community/threads/power-supply-impedance-and-class-a-amplifiers.307829/
it's simple as this - when I'm ordering xformer, declared Vac is under full load condition
with 20VA, little Donut is less hysterical than 10VA, so I'm less thinking about actual Vac in circuit, under actual load
xformer - no need to think of efficiency - it's simple - you're thinking of load conditions and that xformer is properly (over)dimensioned for same
xformer is, by itself, having no-load-current, and that one is diminutive vs. current sag under load
so, in short - if you have amp sucking 100W per channel ( presume A Class) , it's pretty much irrelevant for your bill did you put 300VA Donut or 800VA DOnut
with 20VA, little Donut is less hysterical than 10VA, so I'm less thinking about actual Vac in circuit, under actual load
xformer - no need to think of efficiency - it's simple - you're thinking of load conditions and that xformer is properly (over)dimensioned for same
xformer is, by itself, having no-load-current, and that one is diminutive vs. current sag under load
so, in short - if you have amp sucking 100W per channel ( presume A Class) , it's pretty much irrelevant for your bill did you put 300VA Donut or 800VA DOnut
This is Texas!…bigger is better!
Oh wait, ZM is from Serbia…🤡
Unrelated to technical considerations,and more possibly financial and logistical in nature, often the size transformer you want is not the transformer companies want to sell you.
I suppose its related to what ZM said about it being more difficult to manufacture very small transformers.
They want things to be cost/time effective.
I just looked into finding a backup transformer for my current project which has 300VA 36+36 toroids.
Couldn’t find 36+36 off the shelf from any reputable local supplier.
OK, 35+35 then? Well, if I want extra windings along with them I don’t need then I could get an Antek.
In the end I found Avel had some 35+35 in there catalog. No one had them in stock.
I contacted them to try an order directly. Bingo!
When I got pricing I looked into units that were offered in higher wattage.
Options were 330VA-$86, 500VA-$106, 625VA-$99
No idea why the bigger model was cheaper.
Since I was buying it as a backup and my justification was that if I didn’t need it now I would use it later in an Aleph build I got the biggest one.
Go figure…🤷♂️
Oh wait, ZM is from Serbia…🤡
Unrelated to technical considerations,and more possibly financial and logistical in nature, often the size transformer you want is not the transformer companies want to sell you.
I suppose its related to what ZM said about it being more difficult to manufacture very small transformers.
They want things to be cost/time effective.
I just looked into finding a backup transformer for my current project which has 300VA 36+36 toroids.
Couldn’t find 36+36 off the shelf from any reputable local supplier.
OK, 35+35 then? Well, if I want extra windings along with them I don’t need then I could get an Antek.
In the end I found Avel had some 35+35 in there catalog. No one had them in stock.
I contacted them to try an order directly. Bingo!
When I got pricing I looked into units that were offered in higher wattage.
Options were 330VA-$86, 500VA-$106, 625VA-$99
No idea why the bigger model was cheaper.
Since I was buying it as a backup and my justification was that if I didn’t need it now I would use it later in an Aleph build I got the biggest one.
Go figure…🤷♂️
Thanks for the replies. ZM, that explanation make sense, thank you. But the pricing chromenuts found doesn’t 🙂 I’ll be sure to read through the linked thread about the power supplies 👍
FWIW - I am just wandering in a maze running the "right hand rule"... eventually I'll find my way out.
Until (cough... if...) I actually firmly grasp the topics, I just go with experts' advice. Nothing I say is meant to disagree with using the rules of thumb. I've curated a stack of the rules and put them in a document for easy reference. However, somehow, someday, some waaaaaaaaaay (cue Barbra) I might actually understand a little chunk of it. Also, after years of wandering the maze, I've cut and pasted enough to point toward some good threads vs. trying to retype what I don't understand...
Edited to add - Clearly I don't use even use my own rules... or the rules of thumb. My personal balanced Iron Pre has dual 50VA donuts.
I had them... and the space... and the covers... why not?
Until (cough... if...) I actually firmly grasp the topics, I just go with experts' advice. Nothing I say is meant to disagree with using the rules of thumb. I've curated a stack of the rules and put them in a document for easy reference. However, somehow, someday, some waaaaaaaaaay (cue Barbra) I might actually understand a little chunk of it. Also, after years of wandering the maze, I've cut and pasted enough to point toward some good threads vs. trying to retype what I don't understand...
Edited to add - Clearly I don't use even use my own rules... or the rules of thumb. My personal balanced Iron Pre has dual 50VA donuts.
I had them... and the space... and the covers... why not?
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Run... quickly over to the BA-3 thread...
https://www.diyaudio.com/community/...eamp-build-guide.258022/page-143#post-7379262
Well, it looks like I'm getting my nasty hands on a balanced kit with some ancillary parts. 🙂
That means I have to waddle through some 1000+ posts....
Got to start ordering the chassis, etc...
That means I have to waddle through some 1000+ posts....
Got to start ordering the chassis, etc...
There is an Easter Egg that will unlock 20dB of gain and 80Vpp. Best to read every post along with the .html code.
Mwah, ha, ha, ha, ha, ha...
Seriously though, glad you got your hands on a kit. 🙂
Mwah, ha, ha, ha, ha, ha...
Seriously though, glad you got your hands on a kit. 🙂
Aaah.... balanced 80Vpp.... I feel like Don Quijote, riding at the windmills.
Hmm.. I have to ask... do they make balanced transformers? I can't think I've ever entertained the idea...
You know, take a balanced input, output a balanced output for a nice 1:6 gain? How would such a thing be possible?
I suppose putting one on each side of the balanced lines would be nuts as the transformers can not be so matched? I have some of them 1:6 gizmos laying around...
( Note: just asking... please don't flame me over the Parasound Z in parallel...).
Hmm.. I have to ask... do they make balanced transformers? I can't think I've ever entertained the idea...
You know, take a balanced input, output a balanced output for a nice 1:6 gain? How would such a thing be possible?
I suppose putting one on each side of the balanced lines would be nuts as the transformers can not be so matched? I have some of them 1:6 gizmos laying around...
( Note: just asking... please don't flame me over the Parasound Z in parallel...).
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Didn't know you got kicked out of the Caboose and took to the trails...
One of them rich folks in first class fell off the carriage and we picked him up.... I was at the front of the caboose. Had to fight them folks behind me. 😉
Hmm... Note To Self: check to see if the old fire extinguisher still works.
Hmm... Note To Self: check to see if the old fire extinguisher still works.
I recently had similar experiences regarding donut VA.
What I needed was 2x 18v @ 50VA. What I ended up with was 100VA as this was cheaper than anything smaller at Farnell where I normally go for donuts.
What I needed was 2x 18v @ 50VA. What I ended up with was 100VA as this was cheaper than anything smaller at Farnell where I normally go for donuts.
Yep.
I guess I made more noise that you and he thought of me first. Wooohooo! Money sent.
Now just waiting for the Mighty American Mainstream Delivery Machine.... Let's see how that works. Let's hope they don't pull a job like last week with DHL. The package went through my county.... north... until they realized.... oops!... and it came back. What should have been three days took 10 days. The dreaded "exception" on the status web page..
The caboose will sound pretty good soon. 🙂
I got some Edcors in a box... five feet to my left as I type.