JLM 60Watt Power AMP Kit
Moderator: Joe Malone
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- Posts: 12
- Joined: Wed Jun 06, 2007 7:31 pm
- Location: Stuttgart, Germany
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
Details here : http://www.broadcastproaudio.com/new.htm
These are a great performing unit, either our completed versions or the kit.
Rob
Active Monitors
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.
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.
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.
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.
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.
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
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I do lots of things. I believe eclectic skills are best.
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I do lots of things. I believe eclectic skills are best.
'Ello, 'ello all . 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
Chris, when can we expect to see finished pics?
Joe,
What is the current status or availability of the amp pcb's/kits?
ChrisO
Digital information lasts forever......................or maybe five years.
Whichever comes first.
Whichever comes first.
- Joe Malone
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- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
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We have only about 8 kits left until the final batch of 500 PCB's arrive in a few weeks.What is the current status or availability of the amp pcb's/kits?
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
JLM Audio
Capturing Audio without Injury
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
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
- Joe Malone
- Site Admin
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- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
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.
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
JLM Audio
Capturing Audio without Injury
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.
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.
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.
- Joe Malone
- Site Admin
- Posts: 2081
- Joined: Wed Jan 24, 2007 11:35 pm
- Location: Brisbane, Australia
- Contact:
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- Posts: 117
- Joined: Tue Apr 10, 2007 1:19 am
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
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.
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.
-
- Posts: 117
- Joined: Tue Apr 10, 2007 1:19 am
-
- Posts: 117
- Joined: Tue Apr 10, 2007 1:19 am