Repair & modification of REL Q150E

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Just finished a project that turned out pretty well and thought I'd share. The REL Q150E has known amplifier issues and can be purchased cheaply on the used market. I recently bought one for a bit less than $100 that had some "amp buzz". When it arrived I found that the rubber driver surround was also separating from the basket and the whole unit looked like it had lived in a damp basement. Rust on the allen bolt heads, mildew looking residue on the woofer cone, etc.

I first tried to fix the driver but ended up with a badly aligned voice coil. Additionally, the amp issues seemed worse. This was confirmed when I connected a different driver, the amp was making tons of noise and little else. Not wanting to invest too much I purchased a new driver and ordered replacements for all of the discreet components I could identify on the amp board, about $45 worth of caps, resistors, transistors, and other misc. parts.

The driver is an Infinity Kappa 100.9W, a very nice unit for the sale price of $99 and a good fit for the enclosure on paper. I figured I could resell it without loosing much if things didn't work out. It did require slightly enlarging the cut-out but otherwise was easy to install.

The amplifier was a bit more work and took a long evening of soldering and a morning of reassembling before I was ready to test everything. I was a little surprised and very relieved when I got some clean bass tones right out off the bat.

After bolting the amp plate back on with some new stainless bolts, I put it through its paces. I was and continue to be very impressed by the sound quality, speed, and depth of the final product. It fills my small listening room with as much bass as I want and matches very well with my main speakers (Proac Studio 118). For $250, I can't imagine a better result.


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Yeah, I had considered the Reference 1062w but read a few reports of those having the same problem with the adhesive. The cone material on the 100.9w has a lot of texture. It should allow for better adhesion and I have not seen anything about these having similar problems.

It definitely is a good match for the box/amp. I don't have any measuring equipment but running test tones and organ music it seems that the in-room output is good to 20hz or slightly lower. I'm using it for 100% music so the REL speaker level inputs and low-pass crossover are perfect for my system.
For reference, the parts I replaced to repair the amp are listed below. I don't have a 'scope or anything so I took a scattershot approach but it worked in this case.

Mouser # Mfr. # Manufacturer Desc. RoHS
Customer Part # Order Qty. Price (USD) Ext.: (USD)

660-MOSX3CT631R3R9J MOSX3CT631R3R9J KOA Speer Metal Oxide Resistors RSS3 3.9 5%TR RoHS Compliant 1 $0.21 0.21

660-MOS3CT521R123J MOS3CT521R123J KOA Speer Metal Oxide Resistors RSS3 12K 5%TR RoHS Compliant 1 $0.21 0.21

660-MOS3CT631R223J MOS3CT631R223J KOA Speer Metal Oxide Resistors RSS3 22K 5%TR RoHS Compliant 2 $0.20 0.4

660-MOSX3CR33J MOSX3CR33J KOA Speer Metal Oxide Resistors RSS3 .33 5% RoHS Compliant 4 $0.21 0.84

530-RST5 RST 5 Bel Fuses with Leads (Through Hole) RoHS Compliant 2 $0.35 0.7

512-KSP92TA KSP92TA Fairchild Semiconductor Bipolar Transistors - BJT PNP Si Transistor Epitaxial RoHS Compliant 3 $0.27 0.81

844-IRFP9240PBF IRFP9240PBF Vishay MOSFET P-Chan 200V 12 Amp RoHS Compliant By Exemption 2 $2.56 5.12

844-IRFP240PBF IRFP240PBF Vishay MOSFET N-Chan 200V 20 Amp RoHS Compliant By Exemption 2 $2.08 4.16

667-EEU-HD1A471B EEU-HD1A471B Panasonic Aluminum Electrolytic Capacitors - Leaded 470uF 10volts 8x11.5 LS 5mm RoHS Compliant 1 $1.07 1.07

598-SEK101M025ST SEK101M025ST Cornell Dubilier Aluminum Electrolytic Capacitors - Leaded 100UF 25V RoHS Compliant 3 $1.44 4.32

647-UKW1J682MRD UKW1J682MRD Nichicon Aluminum Electrolytic Capacitors - Leaded 63volts 6800uF 20%
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