REL Studio III / Stentor III amplifier failure - solutions

RELUser

Member
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.
 

Dolus

Active Member
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
 

RELUser

Member
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.
 

IWC Dopplel

Distinguished Member
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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RELUser

Member
I have four BKElec-made, REL-branded boards, two of them over 25 years old, none ever been serviced, still going strong.
 

IWC Dopplel

Distinguished Member
Worth a watch
 

Dobbyisfree

Well-known Member
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:

 

moses

Active Member
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.
 

RELUser

Member
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.
 

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