Score a good deal on a JBL PRX718LF active subwoofer, but the darn fan makes too much noise – these sub’s were designed for clubs/discos where the SPL is high, the people are drunk, so the fan noise is the least of their concerns. But for home use, it is just not acceptable, so I removed the tiny fan. I doubt it could cool down the Class D amplifier that much, given the small opening on the back of the chassis and the anemic fan motor. It will not be missed!
In preparation for the arrival of the DAS ST-215 and ST-218 loudspeakers, I purchased an MC2 4-channel power amplifier. It will be used to drive the 15″ drivers.
Below are some cars that I owned over the years and regret selling…
This is a follow on to my earlier post on OPT characterization. Instead of the differential amplifier, I tried using an 1:1 transformer on the output of the signal generator, so I could have floating outputs to drive the reference resistor and the transformer-under-test (“TUT”). This is the same method used by Ayumi Nakabayashi to characterize his transformers. The result was much better than the old method using the differential amplifier, since both the resistor and the TUT could be grounded on one end, making the measurement much more accurate, without noise and line interferences. Below is the resultant plot of a generic 5k SE OPT:
I recently got one for cheap, the moment I plugged it in, I noticed that it had excessive noise – a non-stop rustling sound, especially when the “Warmth” was turned all the way up. Google search turned up some threads and confirmed my suspicion that the PSU was not well filtered, and the PCB traces were not properly routed. In addition, running the 12AX7’s at 48V did not help its performance either.
Instead of doing some of the mods found at groupdiy, which involved replacing all the IC’s, and adding more local bypassing caps to the PCB. I decided it would be much easier to just scrap the stock PS PCB and replace it with a SMPS. At the same time, the tubes will run at HV with a DC-DC converter that I already have. And finally, the I/O PCB will be replaced with I/O transformers. The total budget for the above modifications should be less than $100, as I already have some of the parts on hand.
[EDIT] At the end, I decided to scrap the modifications… perhaps another time.
I got an idler turntable this weekend, it’s the ELAC Miracord 50H-II. It’s in pretty good condition except for the left channel RCA plug which was cut off, the arylic cover had some bad scratches on it, but otherwise, the mechanical condition was quite good for such old deck. The cartrige was junk, so I tried to put on a Shure M97 I had laying around, for some odd reason, I had to reverse the left hot and cold wiring, otherwise, it shorted out when the right channel was plugged in, weird! With the wires reversed, I was expecting some sort of L-R cancellation, but it played just fine, what was that about?!
The sound, even without any adjustment at all, no stylus alignment, VTA, etc., already sounded much better than the Technics SL-1200MK5G, so there’s something to the idler magic after all. I am mulling over whether to build a custom plinth for it or not. Since I like the way it sounds, I may just get some corner supports to replace the springs… we’ll see.