JLM 60Watt Power AMP Kit

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

Ok looking at just the whole Active Xover and the new 12dB/oct tweeter Xover. Changing the 82nF to 33nF and 8.2nF to 3.3nF on the woofer xover and reversing the tweeter to restore true phase makes it very flat but this if the tweeter is truely time aligned and not accounting for the tweeter/woofer roll off and phase change. So values my need to be next value smaller or larger.

Tweeter level needs to be varied over a few db up and down as if it is out it will change the summing point and stop the xover summing properly. You may need to try to get a reading at 75cm and 100cm or listening position to check the flatness at the xover point.
Joe :-)
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

um ok, i don't really understand why... won't 33n give the woofers a very much higher rolloff point, like 5k or something? is that much needed to fill the gap?

is reversing the tweeter to compensate for the cap phase shift?

not sure about time alignment of tweeter, it is mounted a little forward of where I would have though was aligned... see pic of spkr much earlier in this thread...

would i get a better result making a 24dB crossover? ( on a separate board for easier tweaking?)

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:um ok, i don't really understand why... won't 33n give the woofers a very much higher rolloff point, like 5k or something? is that much needed to fill the gap?
Moves it up from about 1.5k to 3k.
is reversing the tweeter to compensate for the cap phase shift?
12dB/oct on woofer and 12db/oct on tweeter leaves the crossover point 180 out of phase.
not sure about time alignment of tweeter, it is mounted a little forward of where I would have though was aligned... see pic of spkr much earlier in this thread...

Yes it is forward for sure. Should be deeper but see if you can get it to sum. You could leave the 33nF cap in series with the 3.3k on a shorting switch as this will move the phase 45 degree and would be a quick better worse test.
would i get a better result making a 24dB crossover? ( on a separate board for easier tweaking?)
No steeper Xovers are easier to make look good graph wise but rarely sound good in high xover points as there is no blending of the slow woofer at the crossover to the fast tweeter.
Joe :-)
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

ok, the tweeter is probably already reversed deep in the box where i can't see then , because the dip is deeper when i reverse it....

i have 33nF but not 3.3nF caps I will see what I can dig up, or order more. i guess i could test with 3n made from 3x1n paralleled

I guess i should order more different values in case they are needed for tweaking.

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:ok, the tweeter is probably already reversed deep in the box where i can't see then , because the dip is deeper when i reverse it....
Ok but make sure you try a couple of distances and double check by phase reversing if you cannot be sure of the true tweeter phase.
i have 33nF but not 3.3nF caps I will see what I can dig up, or order more. i guess i could test with 3n made from 3x1n paralleled
Yes use anything that will get both woofers close to the those values.
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

here it is with 33n and 3n on the woofers at approx 70cm

much better!

Image

greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

heres a better graph of same thing. show still some dip but much better than it was. will work on making the extra tweeter cap switchable and see what that does... its a bit tricky to get at though..

Image


edit:

here it is with the 33n in series with the 3,3k again, more of a notch.

out of phase is even worse, moving the mic around almost always makes it worse, these on axis ones are as flat as it gets.

the front of the woofer dustcaps are maybe 10mm behind the tweeter dome - not sure what amount of phase misalignment that creates, i've seen much worse...

Image

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

3dB dip at the xover is less than the other variations in the drivers and the microphone so is fine. You can try trimming the woofer xover caps down and up a small amount but I would be listening against the passive now to see how they compare and then trying stereo active so the low summation balances the speakers low response.
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

yep i listened against the passive, I think the active is now undeniably better. the bass is faster and the whole thing is punchier and clearer (these were already by far the clearest speakers I have ever listened to regularly)

I suspect that further small improvements could be made, but I'll use them for a bit and see.

i guess i should measure using some different gear and see if the 3dB dip is always there, it could be a random dip in something else not the xover at all, although it seems slightly unlikely.

is there a good way to test the phase / timing between the tweeter and woofers? impulse test? look at a 2k sine wave on the scope and see if its smudged?

anyway, i'll report when i've converted the other channel.

thanks heaps for all the instructions and help!

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:yep i listened against the passive, I think the active is now undeniably better. the bass is faster and the whole thing is punchier and clearer (these were already by far the clearest speakers I have ever listened to regularly)

I suspect that further small improvements could be made, but I'll use them for a bit and see.

i guess i should measure using some different gear and see if the 3dB dip is always there, it could be a random dip in something else not the xover at all, although it seems slightly unlikely.
Can be the width of the microphone element sometimes so is good to do the testing with a tiny 5mm element mic at 90degrees so the element has no width.
is there a good way to test the phase / timing between the tweeter and woofers? impulse test? look at a 2k sine wave on the scope and see if its smudged?
Need to do pulse or square wave testing to get the transient edges lined but there is no way of moving the tweeter it seems in the original boxes so no real point.
anyway, i'll report when i've converted the other channel.

thanks heaps for all the instructions and help!
Any luck getting the pair of speakers running active?
Joe :-)
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

oops yes sorry forgot to report.

the pair is running active and sounding good, i'm using them and liking the results, tho it may be that some more tweaking would improve further

i was using a 5mm element mic, i will try it side on sometime, will that really make a difference given that the element is 5mm anyway??

could try a square wave,what frequency?

could possibly shim the woofers out a little, or rout the tweeter deeper into the cab if it was going to make a big difference. that would make the front baffle less smooth though.

but listening position probably changes the alignment more than that so is it really worth it?

greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

whats the best way to run a BA off a AMP powersupply?

If I run it off one rail then my phantom power out will drop to 36V or so, can I run it from + and - 36v and drop the voltage by adding the regulators on the BAboard? or just a resistor and a zener each side to make +/- 24v?

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:whats the best way to run a BA off a AMP powersupply?

If I run it off one rail then my phantom power out will drop to 36V or so, can I run it from + and - 36v and drop the voltage by adding the regulators on the BAboard? or just a resistor and a zener each side to make +/- 24v?
The power supply on the amp is unregulated so cannot be used to run the BAN directly. You would need to run a TREX kit to reg a 24v to 30v rail from the +36v unreg rail (depends on the ripple on the unreg rail)

Basically it is not a good idea. Best to run the BA BAN BAD on a separate 48v regulated rail like our 48v SMPS or AC/DC kit. The BA BAN BAD only run on a +rail to 0v. So you cannot use the -rail at all.
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greenmanhumming
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Re: JLM 60Watt Power AMP Kit

Post by greenmanhumming »

Ok,i'm running the BA off a separate power supply.

this is a mini PA/acoustic amp. I want to add a line out from the BA to go to an external mixer... but run the internal AMP as a monitor too. whats the best way? i think the BA can drive 2 inputs fine, but should I buffer them from each other in some way? a transformer on the line out?

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Re: JLM 60Watt Power AMP Kit

Post by Joe Malone »

greenmanhumming wrote:Ok,i'm running the BA off a separate power supply.

this is a mini PA/acoustic amp. I want to add a line out from the BA to go to an external mixer... but run the internal AMP as a monitor too. whats the best way? i think the BA can drive 2 inputs fine, but should I buffer them from each other in some way? a transformer on the line out?
Ok if you do not need full phantom power you could use a TREX connected to the +v rail of the amp and run the BA on 24v to save on a extra power supply.

The +out and -out of the BA can go to the XLR output and amp input directly as the amp puts no real load on the BA anyway.
Joe :-)
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