music, guitars & other obsessions

Audio

JBL PRX718LF

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!

JBL PRX718LF

Useless fan:

Back Panel & Class D Amp

Back Panel – notice the tiny opening for the fan on the lower left

Advertisements

NAD: MC2 T4-250

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.


ELAC Miracord 50-HII

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.


Output Transformer Comparison

There were some recent discussion on the quality of the output transformer – vintage vs. modern, etc. It’s often been said that vintage Partidge OPT was hard to beat, but is it true? Pulling data from a couple of sources, I came up with the following comparison chart, it is pretty clear that there is indeed some truth to the Partridge’s legend… -3 dB at 80kHz!

OPT Comparison

OPT Comparison

Sources:

1) Transformer Shootout- Hammond vs Magnequest vs Dynaco vs HW

2) Partridge technical datasheets


NAD: Brunetti Mille

I just got a vintage Brunetti Mille from Italy, I believe this one is the original version which was modelled after the CAE 3+ SE. It is very well built and came with Ruby 12AX7’s. My initial impression of the unit is very positive, surely better than most of the amps that I have built myself… So the preamp stage do make a big difference, duh!

Before I bought the unit, I was think about building one myself, there are some kits on the market, but after factoring the cost and time, especially the front panel and chassis drilling involved – the price on the used Brunetti was simply too good to pass up. As much as I like DIY, there is no way to make it as professionally looking and robust (unless you have all the necessary machining tools and how to use them) as the factory built unit.

Below are some pictures that I got from net, I actually quite like the unusal blue color of the front panel, it reminds me of the old Orban equalizers that I used to work on – and perhaps will acquire one of these days if the price is right.

Mille with Silverbullet Amp

Mille with the Silver Bullet Amplifier

Very nicely made PCB

Very nicely made PCB, this one with a MIDI interface, which I do not have…


What To Do With the JBL-4730A?

As mentioned in the previous post, I have a few options to improve the performance of the 4730A, I chose to start with the easy one – getting rid of the bullet tweeter and the mid-woofer and replace them with the Markaudio Alpair 12 Gold, since the 2226H is a lot more efficient than the Alpair, I had to add a pad on the 2226H to bring its level down. While the Alpair is brand new and not broken it at all, a quick listen showed some promise, although when A/B between this setup and the Tannoy DMT12, it revealed that the JBL/Markaudio was far inferior, which was not really surprising since the Tannoy is a great studio monitor, unlike the kludgy solution that I came up with for the JBL/Markaudio.

2226H with Alpair 12 Gold

2226H with Alpair 12 Gold

Moving on… I went looking for other alternatives, and guess what, one of the more popular designs for Econowave uses the JBL 2226H driver – the 4Pi design by Pi Speakers seemed to be a winner, and I even have the D220Ti driver with the horn, how perfect is that?! I just need to order some parts to update the crossover and get some cabinet to house the horn, since I want to keep the 4730A original – but I will remove the existing crossover board from the speaker cabinet to make it easier for tweaking.  Another bonus, most of the components on the exisiting crossover can be re-used in the new 4Pi design, so that will save me some money on parts.

4730A Crossover Board

4730A Crossover Board

[Added on 9/24/2014]

I ordered some crossover components for the 4730A, here is the modified crossover: