I used my ACA on OBL-11, MEPER.
It sounds great and can play more than loud enough, but at very high levels more powerful amplifiers seemed to have more control.
I think the OBL-15 will be much the same.
My ACA does however not have the strongest power supply, using two rather small toroids instead of the SMPS, I think they are about 100Watt each though.
Good to know!
Think I will build the ACA.
Did you build the 5W version or have you "upgraded" to 6W?
You could recognize the OBL-15 from the picture I guess.....
If I may voice my opinion... (I have tested the 5W and 6W versions)
Whether you should do the R15 mod or not, will depend on your heatsinks. If you have decently sized heatsinks, you may as well do the R15 mod for 6W. But beware, Q1 and Q2 will then run about 10°C hotter (measured on the body of the Mosfet).
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One thing I learned from the ACA is that the max temp of your room and how enclosed the shelf it sits on make a huge difference. The difference between a 60cm wide 25cm deep shelf with back and sides, and sitting on an open shelf with no back and sides was a LOT.
The current PCB’s all have a place for R15 added.
Efficient speakers like 94 dB are one of the important things IMHO although computer speakers near field not as critical of course.
All the above ishould be obvious I admit, but doesn’t hurt to be reminded!
The current PCB’s all have a place for R15 added.
Efficient speakers like 94 dB are one of the important things IMHO although computer speakers near field not as critical of course.
All the above ishould be obvious I admit, but doesn’t hurt to be reminded!
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My PCB's(from diyaudio store)have a place for the R15 'mod' so I am using that, but have not changed the value of R12.
It is running on about 21Volts, don't know how many watts it can put out but enough to make the OBL-11 play more than loud enough for me.
Not using my OBL-11 any longer though, simply too wide for my room.
The 15 inch is in a slob now and the JA-8008 is in a midbasshorn, sounds even better in my biased opinon.
And you guessed correctly, or I did, from the picture
When you get the PCB's from the DIY store are there any documentation in he package with component values, the modifications that are possible etc?My PCB's(from diyaudio store)have a place for the R15 'mod' so I am using that, but have not changed the value of R12.
It is running on about 21Volts, don't know how many watts it can put out but enough to make the OBL-11 play more than loud enough for me.
Not using my OBL-11 any longer though, simply too wide for my room.
The 15 inch is in a slob now and the JA-8008 is in a midbasshorn, sounds even better in my biased opinon.
And you guessed correctly, or I did, from the picture
Or do you have to search this forum?
The official documentation is back from 2012 and I assume there has been new revisions of the PCB and the modifications was not describes at that time I assume.
Is there one place to get the latest full documentation incl all mods.?
what wattage 2.21k register for R15 (6w mod) do we need to use.
will 1/4watt register be enough or do we need to use higher wattage register here?
I cannot remember there being a single page that had all the info on it.
I used the build list below.
If you going to 24V, R12 is changed to 39.2k. I used .5 watt.
Bias is set to 12.5V instead of 10.
As said before R 15 (not on list) is 2.2k. Again I used .5 watt.
The use of .5 watts is because I am to lazy to keep .25 and .5 in my stock box so I use .5 for everything.
Tony
I used the build list below.
If you going to 24V, R12 is changed to 39.2k. I used .5 watt.
Bias is set to 12.5V instead of 10.
As said before R 15 (not on list) is 2.2k. Again I used .5 watt.
The use of .5 watts is because I am to lazy to keep .25 and .5 in my stock box so I use .5 for everything.
Tony
Attachments
I bought bare PCBs and I don't think there was any documentation, it should be easy to get what you need in the first posts of Nelsons thread though.
Amp Camp Amp #1
The only change on the ACA1.1 is the addition of the 2k21 R15, the rest is as the original.
If I have got it right, the ACA will come in a new version ACA1.2 with a change of value for the R12 and a change of topology, that's it.
Hello Max.
That will be a big benefit for you. No more need to fine tune the dc voltage output by using a voltage dropping resistor in the power supply. Instead just use LCLC and get the output within 1 volt of 23 volt.
I remember the ACA i heard and inspected in Vietnam a few weeks ago did run rather hot within half an hour. It was biased with 1,4 A at 19 volts. The chassis was rather small so all the parts inside were at kind of tropical temperature all the time.
The transformer and chokes can take loads of heat but usually caps dont like it.
Good idea to make the heathsinks bigger or put them in a well ventilated area if you turn up to 24 volts and/or bigger current.
Greetings, Eduard
That will be a big benefit for you. No more need to fine tune the dc voltage output by using a voltage dropping resistor in the power supply. Instead just use LCLC and get the output within 1 volt of 23 volt.
I remember the ACA i heard and inspected in Vietnam a few weeks ago did run rather hot within half an hour. It was biased with 1,4 A at 19 volts. The chassis was rather small so all the parts inside were at kind of tropical temperature all the time.
The transformer and chokes can take loads of heat but usually caps dont like it.
Good idea to make the heathsinks bigger or put them in a well ventilated area if you turn up to 24 volts and/or bigger current.
Greetings, Eduard
Hello Ed
So the R15 modification is the same with 19 V or 24 V if I want 6W out using 24V supply?
I can ask the transformer company helping me making the calculations. If they make both chokes and transformers it should be possible to hit the voltage if they know the current. Assume 1A bias is still the goal.......
So the R15 modification is the same with 19 V or 24 V if I want 6W out using 24V supply?
I can ask the transformer company helping me making the calculations. If they make both chokes and transformers it should be possible to hit the voltage if they know the current. Assume 1A bias is still the goal.......
Hi
Below is a list of some ACA I have read about.
1. 19v supply without R15 (2k2) mod is original 5W ACA.
2. 19v supply with R15 (2k2) mod is 6W ACA. Bias roughly 1.15A
3. 24V supply without R15 (2k2) mod is improved 6W ACA. Best sound IMHO.
4. 19v supply with R15 and R12 mod. 6W ACA1.
You can also use a regular power supply, etc..
BR
Eric
Below is a list of some ACA I have read about.
1. 19v supply without R15 (2k2) mod is original 5W ACA.
2. 19v supply with R15 (2k2) mod is 6W ACA. Bias roughly 1.15A
3. 24V supply without R15 (2k2) mod is improved 6W ACA. Best sound IMHO.
4. 19v supply with R15 and R12 mod. 6W ACA1.
You can also use a regular power supply, etc..
BR
Eric
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Thank you!
So no. 3 is the one to go for. This has still 1A bias I assume.
It is the original ACA just with 24V supply.
I don't know if the holes line up, but it isn't difficult to make more. Just know whether you're tapping the hole (to bolt directly into), or if you're drilling all the way through and putting a nut on the back side (which I did, after buying the drills and taps for 3mm bolts).
I presume you mean this one: Deluxe 4U Aluminum – diyAudio Store
If you look in the Heatsink section, there's a link to their "universal mounting system" - clicking on it takes you to a page explaining some of the details. On it is a link to the PDF file with the actual measurements on it. Here's a direct link if that's too much work. 8) https://cdn.shopify.com/s/files/1/1006/5046/files/universal-mounting-specification-v2.1.pdf
As for a 4U case, that's probably overkill. I have a 24v power, R12 mod & R15 in a 2U case (300mm deep) and it runs cool enough to put my forearms on the fins for as long as I want, and only be mildly uncomfortable.
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I know it could be overkill but I plan to build dual mono PSU with LCLC filtering so I need some space. I will wait and see when I get the PSU components how high they are. A 3U may do it. The 4U Deluxe has cuts out for main plug etc. in the back plane. This is nice.....esecially the square hole.....and you can get a kit for it.
Agreed. Putting the square hole for the power inlet was a royal pain. I used a nibbler as my back panel was made of thin steel.
I edited my earlier comment, so you might want to look back one, as there's a link to the actual measurements for the holes.
...edit...
wow. If I did the measuring and math right, you can put one ACA in the center up kind of high, or two, one on each outer third. So you could build a 4 channel ACA (for biamping a set of speakers). 8) Sounds like you're golden.
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