REL Studio III / Stentor III amplifier failure - solutions

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By the looks of things on this forum, what happened to me (with the Studio III) has happened to others, and likely will continue to happen.

Because these subs have tremendous cabinets, highly capable drivers, and amplifiers made of cheese.

Don't throw these fine subs away! There is a quick and simple solution, and a slower and more complicated one.

As you'll find out if you try, modern REL are not able to repair these amp boards, nor will they release any technical information to help anyone else in doing so. They want you to buy their new subs, of course. You may well have luck getting the board repaired by a third party, but there are at least 2 other effective solutions.

1. Buy a Quake for peanuts and use its plate amp. Yes, I know this sounds insane, but it works surprisingly well. The strength of these subwoofers is in their ARM loading (in the cabinet) and the drivers. It's a direct swap; the connections are the same, the nominal impedance (3.8Ohm) is the same even on the Studio III with its paralleled drivers. You've only 100w of power rather than 300w (Studio III was claimed to be 500W/1000W peak, then please explain why it has a mere 300VA trafo?) but you'll be amazed at what just 100w can do with that cabinet. I used a Quake amp, but perhaps the Q200 or Q400 amp would be even more interesting, at greater expense.

You now have a functional sub whilst you explore a more longer term solution, either a lengthy wait for a repair of the original amp, or something even better:

2. The Hypex FA501 plate amp has 500w of unflappable NCore power, both high-level and low level connections, and on-board DSP. This is not plug and play, and you'll need lots of faffing with a laptop to set it up, but the flexibility to create a customised filter and power is far greater than that offered by the original analogue amp. The built-in adjustable soft-clip is ideal for protecting the drivers (replicating REL's "set-safe" feature) and it runs cool and quiet. I feel the new power and clarity offered by this board is a substantial upgrade over the original amp and lifts the Studio III to a new level of performance whilst preserving its remarkable low-frequency extension and musical timing.

I hope someone finds this information useful in extending the life of their big REL. Modern subs may well be far ahead in terms of pure home cinema power, but there is something quite magnificent about how these heavy boxes play music, and for a "music first" setup such as mine they're perfectly adequate for LFE duties too.
 
Good post. :)

Have you considered if the BK Monolith amp 300W or Monolith Plus amp 500W would be a viable alternative?

From the Monolith sales page:-

The Amplifier:- At the heart of the Monolith is our B.LAT Amplifier, starting it's life in the original REL Studio and Stentor subwoofers this amplifier has been continously refined and now includes an array of features and controls not found on any other subwoofer in this price range. Controls include volume adjustment for both high and low level inputs, low pass frequency contour 40 to 120Hz and a continous phase adjustment. With all these functions avalible to hand the Monolith Plus amplifier will allow the end user varied connection options and ease of fine tuning. This amplifier is built here at our UK factory and is rated at 300W RMS and 600W RMS peak dynamic.

Monolith-FF
Monolith Plus -FF
 
Indeed, the longevity issues of the ST series III amps do appear to be coincidental with REL's change of supplier away from BKElec at that point!

That board looks good apart from one thing - the minimum of 40Hz for LPF upper rolloff. The original Studio/Stentor amp can go down to 22, and even the Quake plate amp can do 26, which is one of the reasons why it works so well as a substitute despite it being from such a small box. 40Hz is much too high for bass-capable floorstanders, which pair very well with the large RELs in 2.1 channel music-first setups.

I can see this being a decent solution for an LFE-only setup, though, especially for those who want a more turnkey solution.

The PWM amp I mentioned is a bit more expensive but allows even more flexibility on rolloff frequency and slope, and even includes PEQ, but is not a turnkey solution.
 
I run four of the BK 500's, a notable improvement on the inboard Sonus Faber amps and drives my 18" very well, very quiet, clearly powerful and they seem very well built

1217CDE2-B531-4E5C-93E7-12A4355A6DA3.jpeg
 
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I have four BKElec-made, REL-branded boards, two of them over 25 years old, none ever been serviced, still going strong.
 
Worth a watch
 
Indeed, the longevity issues of the ST series III amps do appear to be coincidental with REL's change of supplier away from BKElec at that point!

Yes, that will be why BK will not service (or as they call it "bring back to factory specification") the Series III. See here:

 
I suspect, looking at that video, it will be a challenge to find anyone who wants to service these boards.
 
Indeed, the longevity issues of the ST series III amps do appear to be coincidental with REL's change of supplier away from BKElec at that point!

That board looks good apart from one thing - the minimum of 40Hz for LPF upper rolloff. The original Studio/Stentor amp can go down to 22, and even the Quake plate amp can do 26, which is one of the reasons why it works so well as a substitute despite it being from such a small box. 40Hz is much too high for bass-capable floorstanders, which pair very well with the large RELs in 2.1 channel music-first setups.

I can see this being a decent solution for an LFE-only setup, though, especially for those who want a more turnkey solution.

The PWM amp I mentioned is a bit more expensive but allows even more flexibility on rolloff frequency and slope, and even includes PEQ, but is not a turnkey solution.
i agree that the 40hz rolloff is too high, when i last ordered the 500 watt amp from BK for my Rel Studio III they done a modification to the filter section which was fully adjustable from 25hz, you just need to ask for this filter modification when ordering.
 
Great news! So that makes a third solution to keep these boxes going. Does the BK board fit well into the amplifier recess?

The Quake amp is too square to fit, but the Hypex amp is small enough to fit over part of the hole. I chose instead to put mine completely inside, allowing more room for the cable egress and so the sub to sit closer to the wall.
 
the BK Amp will not fit into the same opening, so i am using mine in an external box.
 
Hi,
My Stentor has suffered a drive failure, rattles like hell with low frequencies, especially the white noise test tones for setting up. Dirac set-up results in "too much background noise" until the level setting is very low, which then causes inaccuracies. Looking at the drive unit, removed from cabinet but still connected, there doesn't seem to be any detached elements of the cone, spider or dust cap. My conclusion is that the voice coil has detached from the spider and/or cone.

Anyone else had this problem, ideally with a solution 😉

Video showing the problem:
 
A new driver? I think (but worth confirming) it's the Volt B2500.1. They're available and aren't cheap., but cheaper than a new subwoofer!
 
A new driver? I think (but worth confirming) it's the Volt B2500.1. They're available and aren't cheap., but cheaper than a new subwoofer!
I had already spoken to Volt and they said the Rel driver was "heavily modified" and they had none available. When asked about various others, including the B2500.1 (applies to all 10"), none are available until June and most of those were on back order. Volt retailers say you must pay up-front when ordering and they can't say when they can supply! I asked Volt about reconing my existing driver and they can, but can't say when, the cost is nearly £300 and they want payment up-front. I then asked if they could supply the "reconing kit" with the intension of doing it myself, again, they can, but can't say when they can supply and haven't even given a cost... I'm now asking for the various specifications with a view to obtaining the necessary parts myself, not heard back after a few days.

However, Rel have found a few spare compatible drivers and have now agreed a reasonable price, I'm just waiting for them to give a payment method... So, hopefully sorted with a new driver replacement winging it's way soon. Nice one Rel.
 
Hi. I read with interest the original post which is very helpful, thanks,. I have a Studio iii and althought the amp is working (following a repair some years back) I'm seduced by the idea that the Hypex offers an upgrade. I'm not phased by the need to figure out how to use it once installed but, wonder if it is a drop in to the cabinet itself or whether this needs modifying in some way?
 
Size-wise it's not a drop-in as it's much smaller, in all dimensions, than the REL plate amp it replaces.

No cabinet mods are needed barring a few extra holes to drill (or just self-tapping woodscrews) in the inset ledge for the amp if you want to mount the plate of the Hypex facing outward as per the original. In this arrangement it will only be possible to attach to two of the four lips of the inset ledge. and leave much of the opening unfilled, although I imagine it would be quite easy to arrange a third "beam" screwed across the width of the opening. Probably advisable to fill in the remainder of the opening to stop stray fingers/pets reaching in and possibly touching mains voltages on the rear of the PCB.

There is also more than enough room in the recess to swallow the entire Hypex board, fully connected, and lying with the exterior connections facing up. In this case due care is necessary for cable routing, heat dissipation, and as above inaccessibility for stray pets/fingers.
 
BK Electronics have just repaired my Storm 1
amplifier board. Their service has been second to none. Sadly they are unable to repair the amplifier board on my REL Stadium iii. I’m considering one of the BL BSB PV 300 amp boards to fit externally to the Stadium. Has anyone used one of these amplifiers on a Stadium iii please ?
 

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