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Two Jeff Rowland 12's from one SPS ??
Two Jeff Rowland 12's from one SPS ??
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Old 17th September 2016, 02:07 PM   #1
BruceOfOhio is offline BruceOfOhio  United States
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Default Two Jeff Rowland 12's from one SPS ??

Long story short, I have semi-inherited a Jeff Rowland Model 12 amp.


This "one" Model 12 unit is actually four separate boxes: two switch mode power supplies and two amps. The power supplies are connected to the amps by weapons-grade umbilicals.

One power supply is dead dead dead, and has been dead for years. Many, many attempts to have it repaired have failed, and heck I've been trying since last November just to get someone to return my calls. Forget Jeff Rowland or any "authorized repair centeers", I think they're hiding behind the door when you try to reach them.

Rowland does not publish schematics, or offer any assistance whatsoever.

What I've eventually learned is nobody messes with these JR switch mode power supplies, even Rowland in the past has "rebuilt" them as linears, so you sent your dead smps in for repairs, he charged a fortune and you got a linear back in that same chassis.


Can I drive both amps from the surviving SMPS?

I haven't delved into JR's SMPS design too deeply (not as if you really can), but it seems plausible.

I'm in a standard size family room (12x18 maybe) type space with pretty efficient speakers (>95dB) and just don't crank Led Zep like I used to.

This would require spending a good bit of time sourcing the connectors and building a proper split umbilical. Mocking one up properly looks like it would take almost as long as shipping the connectors, so might as well just do it right the first time.


Dead JR equipment, since it can't be fixed, has an approximate market value of $zero, give or take shipping. The boxes are cool CNC machined aluminum, kind of like Lego the way they go together to make different JR equipment. But these are the stubbiest of the JR boxes, so you cant jam much in there if you're repurposing them.

I would hate to immediately fry the good SMPS, because we've been using it to troubleshoot the dead SMPS.

On the other hand, I'm functionally dead in the water unless I really get into mono.

The other down-the-road thought is, ditch the dead SMPS and build a nice linear PS into that box and use IT to drive both amps. I'd already have the umbilical!

But seriously .... thoughts on the original idea of driving both amp modules from the one SMPS?

Thank you.
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Old 19th September 2016, 02:20 AM   #2
BruceOfOhio is offline BruceOfOhio  United States
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Join Date: Apr 2007
UPDATE ... since there have been no comments, so far, I dug deeper ...

I've now been told by a couple Rowland reverse-engineering types there's no problem driving the two Model 12 amps from from one power supply ... in fact, that's the topology of both the Model 112 amp (one giant chassis containing L&R amps and one SMPS) and Model 10 (two chassis, one for the amps, one for the SMPS). Both the Model 10 and Model 112 use one of the very same power supply, it's just that you get two with the Model 12 because you paid so much more and they have to justify it somehow.

The Model 12 comes in at 200W from 150W in the Model 10 and Model 112. I'm told that has nothing to do with the power supply. It's down to thermal issues; Rowland uses the sealed aluminum chassis as a heat sink, so because there are acres and acres of chassis across four boxes with the Model 12, and thermal issues go away.

Backing up all that is the fact that the Model 12 SMPS is identical to the Model 10 SMPS, except that a dot on the back panel is in front of the "Model 12" designation instead of the "Model 10" designation. Internally, an unmolested Model 10 SMPS and a Model 12 SMPS are identical.

The proper Amphenol connectors are on order, and should arrive in a couple days. In the meantime, I'll build the "Y" power supply loom and add the connectors when they arrive. I suppose I'll stack the amp on the dead SMPS just for balanced asthetics.

I'll do some mono A/B testing to see if sharing a single power supply makes any difference to the Model 12 amps, but I doubt it will.

From my inquiries, I've found several Model 12 owners in my predicament; the amps no longer in use because one SMPS died and getting it repaired is essentially no-go.

Assuming my solution works, maybe some of these Model 12's will come out of storage. A very inexpensive solution to a potentially expensive problem.
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Old 1st October 2016, 03:55 AM   #3
BruceOfOhio is offline BruceOfOhio  United States
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Another update ...

It works fine, running both 12's from the one power supply. Ran it for several hours into various speakers, mostly Rogers LS3/5A, PS didn't show any signs of strain, no heat issues, checked the power output, it's steady and provides enough to drive both amps as it does the Model 10 and 112.

Downside is, it did take several hours to build the Y adapter, one female to two males. the male connectors are 16 gauge, the female has 14 gauge lugs. So I built it by running all 8 wires from one male to the other. Then about 1/4 of the way, stripped and tapped in with the 14 gauge to the female. Soldering 24 of those little lugs all tightly together took some patience, but I prevailed.

Total cost : $19 for four military-grade connectors (one left over, I used to test how well it soldered and took soldering heat), and about $10 for wire. Lets say $30, and I have the pair of Rowland 12's resurrected.
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Old 17th January 2018, 11:12 AM   #4
wuanqi is offline wuanqi  China
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Hi Bruce, thanks for sharing the idea, solution and result of running JRDG Model 12 from one single power supply! it is a pity that there is almost no schematic diagrams or other technical information has been shared from JRDG even for their discontinued products. I am trying to repair JRDG Model 10 (the 2 box version), can you measure the output DC voltages of the umbilical cable (Amphenol 20-7P) from pin A to pin H? Some of the IC at the amplifier section were blow up, I need to first segregate the issue, whether the DC power supply is working properly. Many thanks and regards! Andrew Wu, from Shanghai, China
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Old 6th February 2018, 02:48 AM   #5
wuanqi is offline wuanqi  China
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Default Jeff Rowland Model 10 Power Supply


Inside the power section of Jeff Rowland Model 10, there are THREE power modules (made by Vicor) mounted from the back of the PCB.

The first module (Vicor VI-ARM) mounted in the middle of the PCB converts 230V AC to 300V DC;

The other two modules (Vicor Maxi V375A24C600AL) mounted beside, converts 300V DC to 28V DC, for feeding to power amplifier.

Jeff Rowland applied standard application following the data sheet published by VICOR.
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