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Budget Active nearfeild monitor: Edifier R1200
Budget Active nearfeild monitor: Edifier R1200
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Old 18th February 2009, 05:38 PM   #1
DcibeL is offline DcibeL  Canada
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Join Date: May 2003
Location: Saskatchewan
Default Budget Active nearfeild monitor: Edifier R1200

I have purchased a cheap cheap active speaker system for only CAD$56, the Edifier R1200. It's intended use is as a nearfeild monitor for my computer. Let me tell you about the R1200:

-5/8" real MDF enclosure (not fibre board like most cheap speakers)
-very good build quality
-4" coated paper/fabric (not exactly sure) woofer with foam surround
-3/4" fabric dome tweeter with large surround roll
-crossover consists of an electrolytic cap across the tweeter
-two inputs, input A has some high freq EQ applied
-input stage is a single op-amp NE5532
-only controls are volume and bass
-amp is a TDA7269 and is powered by a +/- 12V transformer rated at 1.15A

Surprisingly, this cheap speaker system doesn't sound terrible, but doesn't exactly sound fantastic either. So what DIY modifications can be done to make this better? I would like this system to still act and behave as stock when modifications are complete, so...

First things first:
-add stuffing to the enclosure, and maybe cut a couple of dowels for braces
-modify the input circuit to remove the EQ on input A

I was thinking to replace the amp with a Tripath TA2024 amp. The transformer is really not suitable for this, so I was thinking of an external SMPS. This would also remove the mass displaced by the internal transformer. However, I still need a negative supply to power the op-amp for the input circuit. So I thought to use something simple like this.

These modifications should be fairly simple for me as I already have the TA2024 amp, and a 12V LCD monitor SMPS that has worked well with the Tripath amp for the past few years. I'll just build the -12V supply on perfboard and glue it to the inside of the cabinet.

The tricky part becomes what to do with the speakers? I could just replace them with something else, and design a proper crossover. I would like to go the cheapest route initially and improve the crossover, but unfortunately don't have the ability to measure frequency response. I can measure impedance however, so should be able to get a starting point by measuring impedance of the tweeter with no cap, and with cap to see just what is being done electrically...

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