music, guitars & other obsessions


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


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:

New Speakers – JBL 4730A

[Update 7/31/2014]

After listening to the speakers for a few days, I could not stand them! So I had to take them down – the frequency response was just too far off for the EQ to work out the kinks. They were very hard to listen to, sigh… So there are few things that I can try to address the problem:

  1. re-work the passive crossover to smooth out the response – however I don’t think this is a trivial problem and would require a lot of measurements and component fine-adjustments;
  2. re-wire the speakers for bi-amping with electronic crossover (via foobar2000’s DSP) – this probably is a bit easier to do than the passive crossover, since I think a lot of the problem were due to the poor interaction between the drivers – which could be potentially dialed out with DSP;
  3. replace either the woofers or the mid-woofers – but this kind of defeat the purpose of having “JBL” speakers;
  4. get rid of the bullet tweeter – I think they are too directional in my small space;
  5. a combination of 3 & 4 above.

In any case, the poor frequency response was not easily dealt with equalization as I originally thought, oh well, worst case, I can always part out the drivers, which are actually worth quite a few dollars… seems a shame though.


Scored a pair of vintage JBL PA speakers yesterday, the JBL 4730A is a 3-way design with 2226H 15″ woofer, 2118H 8″ mid-woofer and the 2402 bullet tweeter replacing the original 2403 super tweeter with bi-radial horn in the original design.

4730A With & Without Grill

4730A With & Without Grill

The first impression upon listening to them was that these speakers were too bright, a quick check of the data sheets of the tweeters revealed the reason why – the 2402 was 5dB more sensitive than the 2403, so the HF response was drastically exaggerated from about 2.5kHz and up.

2402 Bullet Super Tweeter

2402 Bullet Super Tweeter

So right off the bat, the crossover needs to be modified a bit to tame the 2402.  In the meantime, I am just using the built-in EQ of the audio player; which reveal another thing, that these speakers were very analytical, i.e., they reveal the recording – warts and all – many recordings were just poorly done and very hard to listen to without some equalization so forget about “natural reproduction”…


I had to re-route the turntable signal to the PC because for some reason, the Nuforce AVP did not work properly with analog inputs! Really?! I thought it would be simple matter  to use any audio program to playback the input of the soundcard – not so! After trying a bunch of programs – foobar, Audacity, CoolEdit, etc.  I discovered that I need to bypass the kmixer in Windows and use ASIO (for better fidelity and monitoring). Unfortunately, none of the program on hand did that by default, but after some Googling, the solution was simple, I just needed to get a version of Audacity complied to run with ASIO which standard version does not support due to licensing issue.

Here is a shot of the Audacity re-complied to use the ASIO I/O:


Success! Technics SL1200 Repair…

After our recent move, the left channel went out on the Technics SL1200 turntable, after some quick troubleshooting, I determined that it was the RCA cable – hardly ever seen that happen before since the cables were well insulated and tied down to the PC board, what could cause it to break?! Anyway, it did, so I had to take the darn table apart to get to the wires below the deck, after replacing it with a pair of vintage Nakamichi RCA cables, the deck was all good to go, whew… This saved me the trouble of replacing the tonearm wire which I initially thought was broken, that would have been expensive and a PITA to do.