EWorkshop1708 said:
How's the bass? Also, is the woofer doing well with this new big amp? You got a lot of power there
I have to say that there isn't much difference between this one and the original. This was expected as the original was providing the same amount of power into the 4 ohm load.
The LT is better made in this one, with exact value component's and a better opamp and clean regulated power supply (In the original, I dropped the amp supply to +/-15VDC with zeners for the LT). It looks better, that's for sure and it is most likely more dependable (although I didn't have any problems with the original)
Bass is amazing. With movie sound effects, the response goes down to <10Hz and with these 2 big 18" woofers pumping in and out, you start to feel queasy. It literally shakes the house.
I designed the sub cabinet to fit in a corner (it's triangular), but there is too much room gain with it in that position. I have moved it out away from the corner and it's perfect solid bass, with no boom.
Getting a few things done tonight. Took the amp down to my lab and did some stuff.
First, I replaced the input cap on the LT with a 100nF, down from 2.2uF. This will help cut below 20Hz and help prevent clipping, and reduce some of the ultra low frequency from the LFE track.
Second, I routed the wires properly to the IEC connector and installed the permanent leads for the +/-15v supply. With these out of the way I'll be able to try the amp with it's cover on - to see how hot it gets in there.
Third, I turned it on to see if it would blow up, and luckily it didn't. I then let it warm up driving my 8 ohm dummy load. About 80 watts into that for about 15 minutes. This got my heatsink up to ~54*c (about the maximum it got to yesterday during a movie viewing at window rattling volume). I then checked the idle current and saw that it was still at ~12mA/ device. I checked the temperature at several places, but found it hottest near the second stage (the MJL4302A/4281A drivers) of the Darlington triple - about 5*c warmer there
I measured the temp on the VAS heatsink, and saw it was ~50*c. About the same yesterday. I'm thinking this heatsink needs to be a bit bigger, to cool this low power transistor better. It will have the benefit of the bottom fan blowing cool air at it, once I get that hooked up, but a bigger sink wouldn't hurt.
Forth, I added the input RCA jack on the back panel. The banana jacks for output were already there, as well as the IEC connector. Very plain on the back.
A good possibility to get this finished this weekend
First, I replaced the input cap on the LT with a 100nF, down from 2.2uF. This will help cut below 20Hz and help prevent clipping, and reduce some of the ultra low frequency from the LFE track.
Second, I routed the wires properly to the IEC connector and installed the permanent leads for the +/-15v supply. With these out of the way I'll be able to try the amp with it's cover on - to see how hot it gets in there.
Third, I turned it on to see if it would blow up, and luckily it didn't. I then let it warm up driving my 8 ohm dummy load. About 80 watts into that for about 15 minutes. This got my heatsink up to ~54*c (about the maximum it got to yesterday during a movie viewing at window rattling volume). I then checked the idle current and saw that it was still at ~12mA/ device. I checked the temperature at several places, but found it hottest near the second stage (the MJL4302A/4281A drivers) of the Darlington triple - about 5*c warmer there
I measured the temp on the VAS heatsink, and saw it was ~50*c. About the same yesterday. I'm thinking this heatsink needs to be a bit bigger, to cool this low power transistor better. It will have the benefit of the bottom fan blowing cool air at it, once I get that hooked up, but a bigger sink wouldn't hurt.
Forth, I added the input RCA jack on the back panel. The banana jacks for output were already there, as well as the IEC connector. Very plain on the back.
A good possibility to get this finished this weekend
luka said:
Hi luka,
Yes, the idea is to have this run as silent as possible. You need to remember that I am counting on getting a lot of cooling from the chimney pipes that are in the case. These will "suck" hot air from the heatsink and pump it up through the pipes. This can be as effective as fan cooling. In the meantime, I have the two front fans installed for backup. These will kick in when the temp goes up.
The single fan at the bottom of the case, near the front end amp board will be running constantly, mainly to keep air circulation around this circuit board. I have connected that using a dropping resistor to have it run at 6VDC. At this speed, it is nearly impossible to hear, even with the case cover off.
While I had it on my bench, I checked the power supply sag under load. No load voltage on the rails was 71.5VDC. This dropped to 67VDC driving the 8 ohm load to clipping. This is about what I expected from this power supply.
I have slipped the cover on to see how hot it gets. I have only had a chance to see it at idle (will do some demanding test today). I see the chimneys appear to be working. Heatsink temp in open air before putting the cover on was ~40*c. After the cover went on this climbed to 43*c. I could feel the heat coming out of the pipes. I held a small slip of paper above and there is some good air movement. I'll run it hard later to give it a real test.
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Wait, wait, what you're saying ... is that after you putted the cover on the temp rised by 3 degrees, and you say that the chimneys work ?? Isn't the temperature supposed to be lower maybe... ?
Anyways, I have a question. What's the point of making a kilowatt amp ... dead silent ? I mean ... isn't it supposed to be very...very...very...LOUD !! 
Oh, and another one - where did you get your output devices from ?
Anyways, I have a question. What's the point of making a kilowatt amp ... dead silent ?
I mean ... isn't it supposed to be very...very...very...LOUD !! Oh, and another one - where did you get your output devices from ?
kalmara said:Wait, wait, what you're saying ... is that after you putted the cover on the temp rised by 3 degrees, and you say that the chimneys work ?? Isn't the temperature supposed to be lower maybe... ?
Anyways, I have a question. What's the point of making a kilowatt amp ... dead silent ?
Oh, and another one - where did you get your output devices from ?
Outputs are genuine On-Semi from different sources. MJL21193/21194 plus the drivers.
The chimneys work better as the temp goes up. More temp = more convection = more cooling. Imagine the temp inside a wooden case with this much heat production.
If I can keep the temp below 60*c on the centre of the heatsink during intense use, I'll be satisfied. I'll make that the threshold for fan operation.
Anyway, I'm monitoring it now. I have played a few bass heavy tunes and see the temp at 47*c. Now playing "The Island". Lotsa explosions, rumbling and such to give it a thorough workout.
Loud yes, noisy with fans running NO! I hate fans, but they are a necessary evil. Last thing I need to hear during the quite scenes are a couple of jet engines roaring.
MJL21193 said:
It didn't get that hot. Even after an hour and a half of nearly non stop high volume bass, 57*c was the hottest it got. This was measured near the middle of the heatsink with the probe touching the thick part. I also measured the air temperature at the exit of the chimney pipes - 41*c, so it's pretty clear they are doing what they are supposed to.
So, in the end, a bit of a waste to install fans for the amp to drive the 4 ohm load. In the future if I decide to run a lower impedance, then I'm sure they will be needed. Also, the ambient temperature here today was only ~20*c inside. During the summer it will be hotter.
Still have a few things left to do but I'll put those off until the fall maybe. Concentrate on other projects for a while.
I got a decent picture today. I took it out to my shop to grind the back plate a bit so the cover would go on fully.
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nigelwright7557 said:
Yes fans work well as long as they and the heatsink they are cooling is clean. Anyone who has cleaned a blown heatsink (CPU cooler for example) will know what I mean.
Fans are hard to make quiet. Even if you get rid of the mechanical vibration noise, you still have the air flow noise to deal with. I solved these with the constant running fan in the amp by slowing it down and mounting it on small coil springs (see pic below).
I have christened this project "Terremoto" - Spanish for earthquake. Cheesy enough?
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MJL21193 said:
Yes fans work well as long as they and the heatsink they are cooling is clean. Anyone who has cleaned a blown heatsink (CPU cooler for example) will know what I mean.
Fans are hard to make quiet. Even if you get rid of the mechanical vibration noise, you still have the air flow noise to deal with. I solved these with the constant running fan in the amp by slowing it down and mounting it on small coil springs (see pic below).
I have christened this project "Terremoto" - Spanish for earthquake. Cheesy enough?
One of the ebay amps I bought has a air filter on it to clean the air.
When I bought my big heatsink it came with a mains fan and that moves a serious amount of air but as you say it is very noisy.
My other amp uses a couple of low current 12 volt DC fans and they are much quieter.
MJL21193 said:
Yes fans work well as long as they and the heatsink they are cooling is clean. Anyone who has cleaned a blown heatsink (CPU cooler for example) will know what I mean.
Fans are hard to make quiet. Even if you get rid of the mechanical vibration noise, you still have the air flow noise to deal with. I solved these with the constant running fan in the amp by slowing it down and mounting it on small coil springs (see pic below).
I have christened this project "Terremoto" - Spanish for earthquake. Cheesy enough?
For the record, there are some ultra quiet fans offered from AKASA.
The one type it is the orange series AK-184 90mm with double ball bearings.
The second type offered up to 120mm (the larger the more quiet) with double ball bearings and a pre-installed thermistor in the output of fan thus the rotation speed it is automatically controled, depending on the temp of the outgoing air.
I've installed in my workstation PC five AK-184 fans on the side covers and two 120mm (thermistor type) on the back plate with special ruber bolts of SHARKOON and the resulted noise it is indeed very low.
Fotios
Fans
http://www.scythe-usa.com/product/acc/002/sflex_detail.html
These are about as silent as you can get for fans...and 150000 MTBF ! I put two in the last amp I built...sitting within 18 inches of the amp with the fans running constantly you cannot hear the fans. They are not cheap but can increase the cooling capacity many times over convection.
http://www.scythe-usa.com/product/acc/002/sflex_detail.html
These are about as silent as you can get for fans...and 150000 MTBF ! I put two in the last amp I built...sitting within 18 inches of the amp with the fans running constantly you cannot hear the fans. They are not cheap but can increase the cooling capacity many times over convection.
Great looking project, really glad you managed to finish it . Would love to hear how that sounds with the sub, bet its really clean and low. I'm planning sealed LT compensated woofers for my 3 way but they arn't nearly on this scale!
On the subject of fans, I have these in my PC:
http://www.noctua.at/main.php?show=productview&products_id=4&lng=en
They are practically silent when slowed down but don't move all that much air. With a very close spaced fin heatsink it should be pretty effective.
. Would love to hear how that sounds with the sub, bet its really clean and low. I'm planning sealed LT compensated woofers for my 3 way but they arn't nearly on this scale!On the subject of fans, I have these in my PC:
http://www.noctua.at/main.php?show=productview&products_id=4&lng=en
They are practically silent when slowed down but don't move all that much air. With a very close spaced fin heatsink it should be pretty effective.
Re: Fans
I put a filter on the first PC i did and it was every other day taking it off to clean it. I'm not into maintenance - too busy and lazy for that. Now, if it could be self cleaning, like with a wiper blade that scrapes the dust off into a tiny vacuum... Next time.
Thanks fotios. I'll look into getting a couple of these. Nice to have on hand instead of the cheap noisy ones I have.
I'm taking notes and saving these links! Nice to get recommendations. Thanks.
Thanks DrEM. The sub sounds LARGE! It's the fact that it is not straining to produce huge amounts of bass that sets it apart. A tone generator sweep down to 10Hz is a good form of torture for anyone sitting in the room with it at high volume.
Good luck with your project. It's the best way to build a serious sub IMO. Relatively small box, cheap drivers and a powerful amp.
Thanks also for the fan suggestion. I"m thinking about some other projects that fans would be very necessary for, and I may replace the 2 temp controlled ones in this amp, IF i use it for a lower impedance.
nigelwright7557 said:
I put a filter on the first PC i did and it was every other day taking it off to clean it. I'm not into maintenance - too busy and lazy for that. Now, if it could be self cleaning, like with a wiper blade that scrapes the dust off into a tiny vacuum...
Next time.fotios said:
Thanks fotios. I'll look into getting a couple of these. Nice to have on hand instead of the cheap noisy ones I have.
zlast said:
I'm taking notes and saving these links! Nice to get recommendations. Thanks.
Dr.EM said:Great looking project, really glad you managed to finish it
On the subject of fans, I have these in my PC:
http://www.noctua.at/main.php?show=productview&products_id=4&lng=en
They are practically silent when slowed down but don't move all that much air. With a very close spaced fin heatsink it should be pretty effective.
Thanks DrEM. The sub sounds LARGE! It's the fact that it is not straining to produce huge amounts of bass that sets it apart. A tone generator sweep down to 10Hz is a good form of torture for anyone sitting in the room with it at high volume.
Good luck with your project. It's the best way to build a serious sub IMO. Relatively small box, cheap drivers and a powerful amp.
Thanks also for the fan suggestion. I"m thinking about some other projects that fans would be very necessary for, and I may replace the 2 temp controlled ones in this amp, IF i use it for a lower impedance.
whoandcar said:Hi, MJL. Have you any idea what is your PMPO???
PMPO? Well there's a whole list of ways to calculate it, each depending on how dishonest you are
One way is to take the actual sinewave peak output into the load. In this case, it was 36.6Vrms into 1.5 ohm load. That's 51.8V peak, so the peak power would be 1788 watts.
Another way, based more in fantasy world of car audio and home theater in a box, is the calculation that uses the max rails voltage. So in this case, that's +/-73VDC. Into that same 1.5 ohm load, that would be 3552 watts! Not bad, huh?? We like big numbers.
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