JLM 60Watt Power AMP Kit

Support for JLM Audio Kits

Moderator: Joe Malone

martthie_08
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Post by martthie_08 »

my Auratones told me that they are really excited about this new product of yours, Joe :D

cheers, Marten

LapTop006
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Post by LapTop006 »

As will mine. The only thing I see that's missing is a clipping LED for those "oh s*#t" moments.

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squib
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Post by squib »

Broadcast is making available completed versions of these amps for anyone who'd rather leave the soldering iron in the toolbox and spend their time making music.
Details here : http://www.broadcastproaudio.com/new.htm

These are a great performing unit, either our completed versions or the kit.

Rob

chrisp
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Post by chrisp »

Here's a good DIY project for those with too much spare time.

I bought a couple of Joe's prototype amp boards (one of the few remaining after Squib bulk buyed most of the batch for his amp box - smooth work, Rob!) to build a pair of active monitors. I'm not through construction or finishing of the boxes yet, but here's a little Work in Progress report.

Driver selection was critical: I wanted a driver that was well matched to the amp (in terms of quality and power handling) and that stood out for its frequency and phase accuracy - that's what separates monitors from loudspeakers. I settled on the full range Jordan JX92S - 4 ohms, slightly less power than the amp (50W cont cf 60W for the amp) which is how it should be, and audiophile in quality.

This full range driver lets me use a 8L crossoverless ported enclosure with a frequency response from in excesss of 20KHz down to about 56Hz (remember, this is a single 4" driver). Here's a couple of photos of the two sides of the back panel of the enclosure, showing the JLM amp circuitry and the heatsink/connectors.

Image

Image

Just a couple of add on comments: the white wires connected to the mains earth pin ground the XLR input body and the heatsink itself. This means these can never pose a safety threat even if something goes astray voltage wise inside the box (or at least for so long as the power cord is properly wired). The white putty on the power connector covers some bare metal which in real life will be at 240V: GREAT DESIGN you idiots, you trying to kill someone?

The 1.5mH inductor and 3.9 ohm resistor on the driver + lead form a passive bass compensation circuit, as recommended for this enclosure by Ed Jordan, the driver's designer. It smooths off the lower bass response.

I've placed the PCB's power indicator led under the driver.

Image

I'll finish off the enclosure construction, slap on a bit of paint, and she'll be good to go! I'll post a pic of the final box.
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

Ausrock
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Joined: Mon Aug 13, 2007 1:49 am

Post by Ausrock »

'Ello, 'ello all :lol: . Thought I'd better come over here and see what you guys are up to.

Chris, when can we expect to see finished pics?



Joe,

What is the current status or availability of the amp pcb's/kits?

ChrisO 8)
Digital information lasts forever......................or maybe five years.

Whichever comes first.

chrisp
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Location: Sydney, Australia

Post by chrisp »

Hey Ausrock

Here's Serial No:0001, with 2 undercoats, 3 main coats and 3 polyurethane top coats.

Image

Serial No:0002 is finished construction, and should be painted this weekend.
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

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Joe Malone
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Post by Joe Malone »

What is the current status or availability of the amp pcb's/kits?
We have only about 8 kits left until the final batch of 500 PCB's arrive in a few weeks.

Chrisp from the photo you have a Zobel LCR or Step filter LR to flatten the drivers response? What info do you have on the driver and those parts? As I could easily rework the altered response curve into the AMP by attaching a couple of small parts across the vol pins on the amp PCB. This would keep the damping on the driver even and would be cheaper as no parts between the amp and driver would be needed. Also bass extension could also be done easily this way as well.
Joe :-)
JLM Audio
Capturing Audio without Injury

chrisp
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Post by chrisp »

Joe

the driver is the EJ Jordan JX92
http://www.ejjordan.co.uk/drivers/jx92.html

The circuit is bass compensation to smooth the response at the lower end. Resistor is 4 ohms, inductor is 150 mH. Got it from the bottom of Ed Jordan's site page for the 8L cabinet design:
http://www.ejjordan.co.uk/systems/jx92_system.html

Regards

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Joe Malone
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Post by Joe Malone »

Hi Chrisp
I think you mean 1.5mH in parallel with 4ohm like the website says. When you get the speakers finished try removing the 1.5mH inductor and 4ohm resistor and wiring direct to the driver from the AMP and adding a 180nF cap in series with 2.2k resistor across the +vol- point as this will give the same step in the frequency response.

Let me know what you find as both ways will sound different due to the uneven load of the speaker to the inductor and the added resistance in series with the driver will also affect the damping.
Joe :-)
JLM Audio
Capturing Audio without Injury

chrisp
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Post by chrisp »

Hi Joe - interesting - especially as I've got the +vol- tags free in this application.

and yes, 1.5mH is correct. For 150mH I'd be running a coil around my house ;-)

I assume from the circuit that the resistor can be relatively low power - a normal 1/2W 1% should be fine. And a MKT or poly for the cao.

Its certainly a cheaper and lighter option.

I'll let the current build get settled in so my ears can adjust, and try this out in a couple of months. Thanks for the input.
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

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Joe Malone
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Post by Joe Malone »

Yep normal 2.2k 0.5watt metal film and 180nF MKT is all that is needed.
Joe :-)
JLM Audio
Capturing Audio without Injury

greenmanhumming
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Post by greenmanhumming »

how much do those drivers cost?

I contacted Jordan, but they are away until october 10....

looks like a worthwhile project!

(BTW whats the latest on availability for the AMP kits?)

chrisp
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Post by chrisp »

Try Brian Maddern at Decibel Hi Fi in Brisbane. They are the Oz stockist.

They also stock enclosure kits. I'm really tempted to build up a 8L TL on that nice woodgrain.

Prices at http://www.decibelhifi.com.au
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

greenmanhumming
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Post by greenmanhumming »

I'm in the UK. but the price gives me an indication thanks!

pricey drivers. I eagerly await further reports on how they sound!

I'm wondering about doing a triangular cab as described on the jordan site.

BTW has a price been set for the AMP kits?

greenmanhumming
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Post by greenmanhumming »

any news on these? I want 3. I have a project waiting on at least one....

sorry to be impatient!

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