Helitim,
The Statement speakers are an "easy" 4 ohm load, so transformers with 40 or 45 AC volt outputs are OK.
What you need to be careful of is the SOA of the output transistors in the amp.
Andrew describes this in post 1920.
PS I am currently building the Statement speakers myself but will eventually use OS's newer amp designs which have more output transistors.
The Statement speakers are an "easy" 4 ohm load, so transformers with 40 or 45 AC volt outputs are OK.
What you need to be careful of is the SOA of the output transistors in the amp.
Andrew describes this in post 1920.
PS I am currently building the Statement speakers myself but will eventually use OS's newer amp designs which have more output transistors.
Appreciate the help. I wasn't looking for a better answer, just trying to understand the math 🙂 . I think I figured out where I was going wrong, I forgot forgot bring V back into RMS.
Referencing the bold above... what is the 50/60Vpk? Is that a simulated sine peak of th audio? Or rail Vpk?
As you've probably guessed, I asked a lot of questions growing up, lol 🙂
Thanks. I'm new to the SOA graphs. I was trying to figure out what the limiting factor was. Current ratings seem similar on a lot of the suggests. I was focused on Power dissipation.
Andrew is referring to the peak output voltage.
Safe Operating Area gets into complex math. For a pure resistive load, you can simply plot an operating points on the graph. Say that you have 65V rails and the output is +55V. At the signal positive peak the voltage across the N channel devices is 10V (rail-signal) and the current determined by Ohm's law. As long as that point is inside the SOA curve, you're good to go.
Unfortunately, the real world isn't that simple. With a pure reactive load you will have both maximum current and maximum voltage across the devices at the same time. Speakers aren't purely reactive, but can have a high phase angle between voltage and current. As Harry points out, the Statements have a fairly benign phase relationship, so they are closer to a purely resistive load than something like an electrostatic speaker. This means you can get more power out of fewer devices safely than you could with a very reactive speaker.
How to design for SOA? It seems a bit of an art to me, but I've often seen plan on a 45° phase angle as a rule of thumb. If you want to assume that the amp will go along with the Statements you can use their phase and impedance curves to determine your SOA at a given rail voltage.
Some of your design choice depends on your risk tolerance and listening habits. I generally don't listen with more than a fraction of a watt RMS input, and even with a crest factor of 30 dB I'm unlikely to significantly stress the main amp. So I tend to be a bit less worried than some about SOA calculations. My HB has TO3P outputs on 55 V rails driving a benign 8 ohm nominal load and I'm not concerned about reliability. My subwoofer is another story during movies. 😉
All in all, I think you'll be plenty safe using MJL4281/4302 and still safe if you go with MJL3281/1302.
Safe Operating Area gets into complex math. For a pure resistive load, you can simply plot an operating points on the graph. Say that you have 65V rails and the output is +55V. At the signal positive peak the voltage across the N channel devices is 10V (rail-signal) and the current determined by Ohm's law. As long as that point is inside the SOA curve, you're good to go.
Unfortunately, the real world isn't that simple. With a pure reactive load you will have both maximum current and maximum voltage across the devices at the same time. Speakers aren't purely reactive, but can have a high phase angle between voltage and current. As Harry points out, the Statements have a fairly benign phase relationship, so they are closer to a purely resistive load than something like an electrostatic speaker. This means you can get more power out of fewer devices safely than you could with a very reactive speaker.
How to design for SOA? It seems a bit of an art to me, but I've often seen plan on a 45° phase angle as a rule of thumb. If you want to assume that the amp will go along with the Statements you can use their phase and impedance curves to determine your SOA at a given rail voltage.
Some of your design choice depends on your risk tolerance and listening habits. I generally don't listen with more than a fraction of a watt RMS input, and even with a crest factor of 30 dB I'm unlikely to significantly stress the main amp. So I tend to be a bit less worried than some about SOA calculations. My HB has TO3P outputs on 55 V rails driving a benign 8 ohm nominal load and I'm not concerned about reliability. My subwoofer is another story during movies. 😉
All in all, I think you'll be plenty safe using MJL4281/4302 and still safe if you go with MJL3281/1302.
Thanks for the detailed explanation Bob. It will give me something to think about at work tonight 🙂
For the VAS: I've found some 0.063" 2024-T3 aluminum. Is this suitable? I imagine it's not to thick for thermal tracking or to thin to dissipate heat?
transistor load lines
A few years ago I wrote a small program in excel to calculate transistor load lines for output and driver transistors. File is attached.
cheers,
PS results are in magenta, blue fields/values must be edited by the user
A few years ago I wrote a small program in excel to calculate transistor load lines for output and driver transistors. File is attached.
cheers,
PS results are in magenta, blue fields/values must be edited by the user
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Sounds OK for a small heatsink.
I use pieces of this for small heatsinks usually double thickness:
Aluminum Z-Bar Hanger - MRBNYM111M - Richelieu Hardware
I use pieces of this for small heatsinks usually double thickness:
Aluminum Z-Bar Hanger - MRBNYM111M - Richelieu Hardware
Attachments
Thanks Juansz, very neat! I will play around with the parameteres and see if I can figure it out. It looks like Vcc (blue) is just for reference/ comparison to the calculated?
I have access to a piece of something similar to the Z-channel as well actually, I believe its just over 2 inches wide, but has some "cooling" holes (sloted for aircraft fasteners 🙂 ) already in it on one side...
Thanks Brian! I will read that when I get off work tonight. You guys are full of good information!
Turns out that it was quite helpfull after-all. Do I think I'll be designing my own amplifier anytime soon? Probably not. I do have a way better understanding of SOA, SOAR, and how a reactive load responds/ reacts with an amp.
I was able to use this document to understand the program Juansz made in excel, which acted as a great learning instrument when combined with the numbers AndrewT previuosly worked out . I can't thank you guys enough 🙂
Bensen posted a spreadsheet where he had turned Eather's manual calculation into an almost automated result with a pictorial output comparing the device operating area to the Safe operating area shown in the device datasheet.
I offered modified versions of the Besnsen sheet that used Tc to temperature de-rate the devices and added in BJTs instead of only FETs. A few few other add-ons.
I offered modified versions of the Besnsen sheet that used Tc to temperature de-rate the devices and added in BJTs instead of only FETs. A few few other add-ons.
Do you mean your results were Tc de-rated, or are you offering me a modified spreadsheet that takes this all into consideration?
If the later, than yes please 🙂. Call me weird, but this stuff is exciting! I wish they offered "evolutionary audiology" as a course when I was in University, LOL.
I've almost finished soldering and have some questions before I try to power it up:
1. Under what conditions should I use the D-BC option?
2. Can the LC-cap only be used when using the CMC Vas compensation mode, or does it work with TMC as well?
3. How critical is the value of L1? There seem to be now easy way to measure inductance if all you've got is a DMM
Thanks
1. Under what conditions should I use the D-BC option?
2. Can the LC-cap only be used when using the CMC Vas compensation mode, or does it work with TMC as well?
3. How critical is the value of L1? There seem to be now easy way to measure inductance if all you've got is a DMM
Thanks
So, I hate to make my first post asking for help but I'm kind of stuck. I've got my Honey Badger basically built but am stuck on C4, the 220uf, 50-100v non-polarized electrolytic capacitor. The BOM actually links to this capacitor, which is actually bi-polar (I bought it without reading the specs properly).
I've tried trawling through this thread but have found conflicting evidence. I'm guessing as a bipolar capacitor this obviously won't work. There was mention a lot earlier on in the thread of using film capacitors of varying values.
I doubt I'd be able to find a non-polar electrolytic locally easy, so until I can get hold of one, would a 220uf film be okay? Or any other values?
Thanks in advance.
-Bob
I've tried trawling through this thread but have found conflicting evidence. I'm guessing as a bipolar capacitor this obviously won't work. There was mention a lot earlier on in the thread of using film capacitors of varying values.
I doubt I'd be able to find a non-polar electrolytic locally easy, so until I can get hold of one, would a 220uf film be okay? Or any other values?
Thanks in advance.
-Bob
non polarised is not electrolytic.
Electrolytic come in two types, polar/polarised and bi-polar/polarised.
Many plastic film are non polar, but some do have a small polar effect. I think it's this small polar effect that gives rise to the small differences in distortion when they are used for filtering.
Back to electrolytic, If the capacitor must tolerate AC, then use a bi-polar type.
C3 is the feedback capacitor. It blocks DC and passes AC.
The voltages it see when the amp is working properly should be tiny. <<1Vdc and <<1Vac.
It does not need to be a high voltage type until after the amplifier breaks.
C4 is a plastic film type. any >=50V film type will do, but in this location , C4 does nothing.
The R5 side of C3 should be slightly negative compared to the other side.
Look at the diode protection provided by D1 & D2.
Thesediodes limit the maximum voltage when there is misbehaviour elsewhere.
You can ADD D1a and D2a across C3 to similarly protect a low voltage polarised capacitor. This would allow you to select a 220uF 25V component that performs adequately well when the amp is behaving and the new diodes protect the capacitor from damage if the amplifier ever misbehaves. Remember to reform your electrolytics and to thoroughly discharge them before fitting/assembly.
BTW,
I recommend you reduce the C1 value from 4.7uF to 3.3uF to reduce the AC voltage across C3.
Electrolytic come in two types, polar/polarised and bi-polar/polarised.
Many plastic film are non polar, but some do have a small polar effect. I think it's this small polar effect that gives rise to the small differences in distortion when they are used for filtering.
Back to electrolytic, If the capacitor must tolerate AC, then use a bi-polar type.
C3 is the feedback capacitor. It blocks DC and passes AC.
The voltages it see when the amp is working properly should be tiny. <<1Vdc and <<1Vac.
It does not need to be a high voltage type until after the amplifier breaks.
C4 is a plastic film type. any >=50V film type will do, but in this location , C4 does nothing.
The R5 side of C3 should be slightly negative compared to the other side.
Look at the diode protection provided by D1 & D2.
Thesediodes limit the maximum voltage when there is misbehaviour elsewhere.
You can ADD D1a and D2a across C3 to similarly protect a low voltage polarised capacitor. This would allow you to select a 220uF 25V component that performs adequately well when the amp is behaving and the new diodes protect the capacitor from damage if the amplifier ever misbehaves. Remember to reform your electrolytics and to thoroughly discharge them before fitting/assembly.
BTW,
I recommend you reduce the C1 value from 4.7uF to 3.3uF to reduce the AC voltage across C3.
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Non-polar and Bi-polar basically mean the same thing. They are meant for an ac application, so what you have is the correct part. If the capacitor had a polarity marking (usually a stripe marks negative on an electrolytic) it would be called Polar which would be the incorrect type for your application.