6L6,
I won't be getting in on the kit because I had already ordered all of the parts. Looks like a great deal, though. Good luck with it.
For those of you that are looking for a cap that will fit next to fat C2, C3 caps such as Muse, you might take a look at the link below. I found these at home in an old bag of Gainclone parts. They will fit flat to the board with a fat C2,C3 if you tweak the leads a little. They even leave room for R29.
While they might not be my favorite, the are MKP and should be of reasonable quality.
BFC241611004 Vishay / BC Components | Mouser
gadut,
I was told by a man who has been building and selling quality amps for 30 years that silicone isolators should never be used with thermal paste. That it actually reduces performance. Also, he said that a silicone isolator pad has better performance that thermal paste alone.
I'm no expert, but I have taken his advise and had efficient heatsinks ever since. He also suggests looking at the data sheet to find the recommended max torque for the transistor to heatsink screw and trying to torque it at about 90% of maximum, in other words, very tight. Of course, you have to have a feel for the screw as the threads in soft aluminum can strip out.
I would appreciate it if those with more expertise and experience would comment and correct me.
Mouser box arrived with part of my build kit.
This is my first time using the ERX power resistors. I notice that they have a black band around one end of the body. This band is not shown in the datasheet. In a capacitor, I would have assumed it indicates polarity or preferred orientation. Any thoughts on what the band means or how to use it?
Since we are matching everything else, it there any reason to match power resistors? If so, which resistors match which?
Also, the boards have 4 GND connections that are all connected within the board. I would typically run just one audio ground line to the balanced input. I figured multiple runs would just be ground loops. Is there any reason to do something different?
This is my first time using the ERX power resistors. I notice that they have a black band around one end of the body. This band is not shown in the datasheet. In a capacitor, I would have assumed it indicates polarity or preferred orientation. Any thoughts on what the band means or how to use it?
Since we are matching everything else, it there any reason to match power resistors? If so, which resistors match which?
Also, the boards have 4 GND connections that are all connected within the board. I would typically run just one audio ground line to the balanced input. I figured multiple runs would just be ground loops. Is there any reason to do something different?
You will need to have the amp board get PSU GND somehow. And also the speaker black attaches to GND...
You don't have to connect them all at the amp PCB. But this way you have options.
Don't worry about the markings on the resistors. Just put them all in the same way so they are easy to read in photos.
If you really want to get your laser level out and adjust your bowtie,
match the source resistors together on the output fets and on the CCS fets. It can't hurt to do so.
I thought everyone matched all their resistor, all the time.
My case and PSU boards shipped today.
Question on PSU toroids. I found I could not even buy 2 plitron toroids and get to the $250 minimum, pretty tough on the DIY crowd I guess. Moving on to the AnTek toroids, they did not have the 400VA in stock, but did have the 500VA with 18/18 (for half what one Plitron 300VA costs). What are other suggestions for power transformers? I don't plan a lot of builds, and don't mind paying for quality, but I am at a loss for what would have quality = to plitron, or "better" than the AnTek. Still up in the air on 1/2 toroids and/or 1/2 PSU boards.
The ACA kit did show up today though, so I will be busy for a couple of weeks messing with those, while I firm up my BOM for the Aleph J.
My case and PSU boards shipped today.
Question on PSU toroids. I found I could not even buy 2 plitron toroids and get to the $250 minimum, pretty tough on the DIY crowd I guess. Moving on to the AnTek toroids, they did not have the 400VA in stock, but did have the 500VA with 18/18 (for half what one Plitron 300VA costs). What are other suggestions for power transformers? I don't plan a lot of builds, and don't mind paying for quality, but I am at a loss for what would have quality = to plitron, or "better" than the AnTek. Still up in the air on 1/2 toroids and/or 1/2 PSU boards.
The ACA kit did show up today though, so I will be busy for a couple of weeks messing with those, while I firm up my BOM for the Aleph J.
Bump for Antek.
You can also get the Antek 400 VA 20V at the same price as the 18V. I decided to go this way because of the voltage droop due to the Class A power draw. The AJ is expected to draw between 160 and 200 watts at idle, per earlier posts. According to the Antek specs, and interpolating between available data points, the 400VA 20V should put out 17.9 VAC at 200 watts. If my diode bridge drops 1.1V, my rails should be 24.2 VDC.
You can also get the Antek 400 VA 20V at the same price as the 18V. I decided to go this way because of the voltage droop due to the Class A power draw. The AJ is expected to draw between 160 and 200 watts at idle, per earlier posts. According to the Antek specs, and interpolating between available data points, the 400VA 20V should put out 17.9 VAC at 200 watts. If my diode bridge drops 1.1V, my rails should be 24.2 VDC.
You'll probably be a bit higher than that - It looks like cut and past struck again, the AS-4218 and AS-4220 load points in the data sheets are the same. I'd expect the same ~1V drop at 200W, but somewhere closer to 27VDC rails. Aleph-J max!
Nice! Serves me right for not doing enough research.
So lets say Bob is right and I end up with 27VDC rails. I don't need any extra power. As this is my first go at Class A, what changes with the higher rail voltage? Does this suggest I try higher bias?
This might be interesting. I am working on a liquid cooling setup that should have a bit extra cooling capacity. Measuring sink temp is straightforward. Do you directly measure the transistor temp? If so, what are you measuring for 65c?
Also, if I end up playing with bias, I understand that the bias setting procedure is pretty easy in Aleph J, just set the bias based on temperature and zero the DC offset. Do I have that right?
In other words, only try higher bias if you have plenty of heat sink, like a 5U case. Measure the sink and transistor temperatures with an IR thermometer or use the you can keep your hands on the sinks for a few seconds rule.
Heat sink gymnastics: If you have the store's 4U case your heat sinks are rated at .31C/W. If you want the sink temperature to 55C you have 30C rise available in a 25C room. PD = 30C rise/.31C/W, giving you approx 100W. Rail to rail voltage will be approximately 54V. Since I=P/V or 100W/54V gives you a TOTAL bias of 1.85A, or 24.1W per device. If you are willing to run a little hot in summer and take a 35C rise your bias limit is 2.1A, or 28.4 W per device.
This means you'll have to tweak your Source resistors a bit higher to reduce the current. Not a big deal.
Either way with ~50% current gain, you'll get peak current of ~3A giving 24W peaks into 8 ohms. You won't be voltage limited.
With the 5U case, you effectively double your heat rejection capability. The catch is you have to watch your thermal interfaces. Multiply the 50W through each output device by the junction to case and case to sink thermal resistance, best case you get a 50C rise above the sink. With your sinks at 55C, you are a bit above the 100C junction temperature target for reliability, but not too much. You'll now be voltage limited.
Heat sink gymnastics: If you have the store's 4U case your heat sinks are rated at .31C/W. If you want the sink temperature to 55C you have 30C rise available in a 25C room. PD = 30C rise/.31C/W, giving you approx 100W. Rail to rail voltage will be approximately 54V. Since I=P/V or 100W/54V gives you a TOTAL bias of 1.85A, or 24.1W per device. If you are willing to run a little hot in summer and take a 35C rise your bias limit is 2.1A, or 28.4 W per device.
This means you'll have to tweak your Source resistors a bit higher to reduce the current. Not a big deal.
Either way with ~50% current gain, you'll get peak current of ~3A giving 24W peaks into 8 ohms. You won't be voltage limited.
With the 5U case, you effectively double your heat rejection capability. The catch is you have to watch your thermal interfaces. Multiply the 50W through each output device by the junction to case and case to sink thermal resistance, best case you get a 50C rise above the sink. With your sinks at 55C, you are a bit above the 100C junction temperature target for reliability, but not too much. You'll now be voltage limited.