Burning Amp BA-3

Apparently the information about single ended output are located in BA-1 articles.

This output stage circuit, along with a few parts to set up the bias for both halves is perfectly functional as a “power buffer” along the lines of the First Watt F4 amplifier, except that this one operates as single-ended Class A with a bias current of about 3.5 amps. The 1 ohm resistors are all 3 watt types, and the output devices are best matched for the Vgs within about 0.1 volts or so at 500 mA or so. By itself the output stage has fairly impressive performance: The noise is 30 uV, the input impedance is 49 Kohms, and the damping factor is 33.

So with the 3.5A current it will deliver 28watt into 8ohm speakers.
 
Apparently the information about single ended output are located in BA-1 articles.



So with the 3.5A current it will deliver 28watt into 8ohm speakers.
28W into 8r0 is equivalent to 21.17Vpk and 2.65Apk

mine does a hair over 21 watts into 8 ohms.
21W into 8r0 is equivalent to 18.33Vpk and 2.29Apk

In both amplifiers the maximum output can only be realised if both the peak current and the peak voltage are achievable.
 
28W into 8r0 is equivalent to 21.17Vpk and 2.65Apk

21W into 8r0 is equivalent to 18.33Vpk and 2.29Apk

In both amplifiers the maximum output can only be realised if both the peak current and the peak voltage are achievable.

hi Andrew, I am getting 37.5 volts pp across an 8 ohm load just prior to signs of clipping. I have to admit, I am having a hard time understanding the quasi output and bias circuit. Is the peak voltage achievable in the quasi comp topology?
 
37.5Vpp = 18.75Vpk
for a pure sinewave with no distortion and no clipping that is equivalent to 13.26Vac
Those numbers confirm your 21W into 8r0, at least close enough.

getting 18.75Vpk into your load also confirms that your supply rails must be greater than +-18.75Vdc

But I don't understand what you are asking.
 
Power is made up from voltage and current. Any topology can swing any voltage as long as the power supply is capable to deliver. The BA1 OPS is similar to the Aleph 30's. There is a spreadsheet that can compute the output power based on the rail voltage and the bias. Use the search to find it.

Enter different values to see how the voltage and bias affect 8ohm, 4ohm, 2ohm loads.
It is very educational.
 
Okie doke, my 5U basic came in. I machined the heat sinks for the bias and output boards. Since the plated thru-holes are the same, I can hook them up from either end, right? So that my amp is symmetrical on the inside? Does it matter where I tie the binding post "out" to? I noticed some put it on the bias board, but theoretically I could tap off the other end of the output, right?
 
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I think I answered my own question. The bias and output boards can be connected at either end, but the speaker binding posted gets connected to "out (GS)" on the bias board only. If someone can confirm, that would be great.

That's the way mine is. If you look at 6L6 build guide, it shows it nicely in his picks. However...both his and mine are complementary and the bias boards are different for the single ended. I assume the way they hook up is the same?

Russellc
 
Preview of my BA-3 SE. Front face still needs to be veneered with bird's eye maple. Waiting on Alps pot to show up. Backlit LED's need to be wired in, and then I need to bias it. Power supply tested out awesome. It's holding at 25.77 +/- volts with no load. Gain stage is mounted to the back of the front plate so that I can wire the input selector output right to the Alps, and the Alps directly to the gain stage.

3f1e1bf6-98c6-448f-b6f1-eac2adb36c52_zpshjwhso7m.jpg
 
Would it be possible at this late stage, to relocate the 6 devices so that three are mounted onto each heatsink?

I was concerned at first, but I'm not really anymore. I put some compound between the two sinks on both sides, plus this is a 5U, not a 4U, so I have some extra material. I could also put some thermal compound on the thick front faceplate before mounting, which would give me more thermal mass. If you envision 3 FETs mounted on each heatsink (perfectly centered), there would be a large portion of sink to the front and rear of the enclosure. I don't really think I'm losing much in this configuration.

BTW, thermal conduction through anodize is less than ideal. These heatsinks should really be masked on the back side before anodize to allow conduction through raw aluminum. Anodize is just aluminum oxide. Conduction through oxide layers is crap.
 
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Thermal conduction through anodise is bloody brilliant.

Alox is sold as thick thermal conductors.
anodise is a VERY thin alox

And if the alox is guaranteed scratch free, then it is also an excellent electrical insulator.
Ideal for clamping instead of through bolting.

Try again.

Thermal conductivity in W/m degree K:
Aluminum: 205 (depending on grade and temper)
Aluminum Oxide: 30

Radiation heat transfer is great when the surface is black. If the outside of the heatsink was anodized black, and the inside was masked raw and chemical coated (Iridite) to prevent oxidation, that would be the most ideal setup for cooling.
 
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Hmmm, I did mine exactly like 6L6 did his, 3 on one and three on the other. Of course we both used the predrilled deluxe 5U Chassis, which pretty much forces you to. I dont understand why you put 2 devices on one and 4 on the other...big blank spot on one end. I dont know if this is a risk, but wouldnt the 4 together run hotter than the 2 together, causing the group of 4 to hog more power and possibly "runaway"? I dont know if it would, I really dont know, just wondering.

I also mounted mine underneath the board rather than on top, in order to better facilitate full use of the sink, again, dont know if that makes much difference either. I guess I just like things symmetrical, and couldnt do with 4 on one and 2 on the other. Really, I do not know if it makes any difference at all, so dont take it as a criticism, for all I know your method is preferable.That, and I copied 6L6's excellent work to the letter knowing his way worked. I also copied his way of stacking the bias board on top of the output board, made a compact result. I see you also used the DIYAudio store delay, it seems to work fine on mine, I'm sure you will like it too.

One thing for sure, I sure am interested in the sonic results of your single ended version, can hardly wait to hear what you report!

Fire that baby up!

Russellc
 
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Those concerns are understandable. I'm honestly not worried at all about it. The two sinks are conductive to each other. Consider them one giant sink on each side. Yeah, the FETs are shifted, but if you were to center them, now you have a gap (albeit smaller) at both the front and back. I didn't mount my bias boards like 6L6 because I didn't want the boards to be cantilevered and free hanging above the output boards. I wanted the boards to be next to each other with jumper wires and rigidly mounted.
 
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Those concerns are understandable. I'm honestly not worried at all about it. The two sinks are conductive to each other. Consider them one giant sink on each side. Yeah, the FETs are shifted, but if you were to center them, now you have a gap (albeit smaller) at both the front and back. I didn't mount my bias boards like 6L6 because I didn't want the boards to be cantilevered and free hanging above the output boards. I wanted the boards to be next to each other with jumper wires and rigidly mounted.

Again, to each his own, but the 6L6 method works a very ridged result. You have to note their are short copper wires connecting the contact points between the bias board and output boards which are basically soaked in solder, besides two bolt sets.

Are you close to fire up? Really interested to hear about this versions performance. I thought about building an Aleph 2 set of mono blocks once, and a big row of single ended outputs on a pair of BA-3 single ended did cross my mind! Eventually I will build mono block Balanced BA-3, which will scratch that itch sufficiently.:cool:



Russellc