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1000 Watt Sub Amp: Design / Build
1000 Watt Sub Amp: Design / Build
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Old 23rd May 2008, 12:14 AM   #281
EWorkshop1708 is offline EWorkshop1708  United States
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Quote:
Originally posted by MJL21193


The current state of affairs: Works like a charm.
That's great news! Glad to see you got it done.

How's the bass? Also, is the woofer doing well with this new big amp? You got a lot of power there
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Old 23rd May 2008, 03:35 AM   #282
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by EWorkshop1708

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.


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Old 23rd May 2008, 07:52 AM   #283
MitchZ is offline MitchZ  Canada
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Caraudio.com actually has really good box making, etc.
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Old 24th May 2008, 01:35 AM   #284
MJL21193 is offline MJL21193  Canada
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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
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Old 24th May 2008, 07:42 AM   #285
luka is offline luka  Slovenia
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1000 Watt Sub Amp: Design / Build
Hi

This was all without fans? forced air cooling will make huge diffrence in heatsink's temp
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Old 24th May 2008, 01:16 PM   #286
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by luka
Hi

This was all without fans? forced air cooling will make huge diffrence in heatsink's temp

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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Old 24th May 2008, 02:39 PM   #287
kalmara is offline kalmara  Bulgaria
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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 ?
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Old 24th May 2008, 04:25 PM   #288
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by kalmara
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 ?


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.
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Old 25th May 2008, 02:16 AM   #289
MJL21193 is offline MJL21193  Canada
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Quote:
Originally posted by MJL21193



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.

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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Old 25th May 2008, 02:19 AM   #290
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally posted by MJL21193



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.


I have bought a couple of cheap amps off ebay and the general way with those is to skimp on the heatsink and add a cheap fan to force cool the amp. It must be a few pounds for a fan but many pounds for a good heatsink.
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