Warming up the Denon DL102

Ever since I acquired a Denon DL102 for my first dedicated mono hifi set up, I found it sounding rather distant and a bit frosty compared to the GE RPX and VRII. 

Since Denon recommends a 1000 ohm load for flattest response, I tried soldering a 1k ohm resistor in parallel with the 47k input (47,000 x 1000/47000 + 1000  = 980 ohms) of my variable EQ phono preamp. Unfortunately, the sound became even more glacial.

I could have been basking in warmth by now (without losing stereo LP compatibility) if I saved up for an Ortofon SPU mono but the DL102 body fits a Gray Research or clone tonearm slide perfectly. Besides, I would rather add more stereo SPUs to my cache.😉

Since I've been using 1:1 line transformers as digital sound processing devices at the output of my CD players for ages, I decided to try the same trick by wiring the Altec 15356 and UTC A20 with a mild step up - 150:600 and 125:500, respectively. Even if both primaries reflected significantly less than Denon's recommended 1000 ohms, what I heard encouraged me to continue to experiment. 

Although I'm not anal retentive about impedance matching, I was curious too see if the sound would improve by using transformers that reflect at least twice the 240 ohm internal impedance of the Denon DL102. I managed to procure the three transformers above: to the left is allegedly a Tamura 600:3k, then I tapped the McMartin MT-4's 10k:60k winding, and at the center is a permalloy 10k:40k, which sells for about $50/shipped from Chinese sellers on AliExpress and eBay. 

 

In the context of my mono hifi set up, the McMartin MT-4 was a bit too warm for my taste. However, even if I upload videos merely for the visual spectacle, the permalloy (above) and Tamura (below) transformers are lush enough for me.😉

But as usual in this hobby, YMMV. 

Happy Listening!😊

Altec 405A

This ain't no April fool's joke!😆

Since the mid-60s (scroll down to pdf page 31), stateside audio experimenters have been trying to squeeze the last ounce of performance from the Coral/Sony "Holey" and Foster/Fostex FE103/Realistic 40-1197 family of 4" drivers. Meanwhile, Japanese aficionados like Old Joe (above), whom I follow on YouTube, kept snapping up Anaheim-manufactured Altec 405As in multiple quantities to stuff into their mini A7 VOTT projects. 

Because of the dearth of units left in the States and my indifference towards engaging in a bidding war versus fellow Asian hobbyists, I patiently hunted them for 20+ years via other channels.

Altec 405A specs

The 405A is a 4"  60-15,000 Hz wide range driver with a sensitivity rating of 92dB/4ft/1W. It's equipped with a massive Indox magnet that's almost the same diameter as its cone.

IMHO and experience, Altec cabinet plans always deliver sonically. Aside from a full understanding of the physics of sound, their engineers used their ears as the final arbiter in a design brief. To me, that trumps any design completely derived from a mathematical formula or computer simulation. So I asked my buddy @ Hommage Audio to fashion a Bonsai pair of Altec 614-style boxes based on the above dimensions.

Interior stuffed with Dacron

For sentimental reasons, I have a pair Realistic Minimus 8s on my test bench. I always thought they were above average, although not extraordinarily special. Same deal with the "Holey Frame" drivers I pulled out of a Sony TC500A RTR machine. To my ears, both FE103 derivatives have an upper midrange resonance, which require an EQ/contour network to make them more listenable.

614 style 405A cabinet

I found the 5.25" Realistic 40-1354A more impressive in spite of its narrow band whizzer honk. Back in the 90s, I played with it in a ported box similar in size to the above Altec 405A cabinet, as well as in a TQWT. Both speaker projects came from the book Designing, Building, and Testing Your Own Speaker System by David B. Weems.

Silbatone box + 755C and 405A in a 0.4 cubic foot ducted port box

Spoiled by years of exposure to Altec 755As and 755Cs in open baffles or 2 cf boxes, and more recently, in Silbatone cabinets, I considered this Altec 405A + Bonsai 614 style enclosure project as a mere novelty experiment.

 

As soon as I hooked them up to my near-field hifi system, I was pleasantly surprised that they play like their bigger brothers, albeit at a reduced scale. 

It's physically impossible for the 4" cone of the 405A to extend much below 90 Hz, but the roll off is gentle and there's enough harmonics to suggest bass lines. I hear a slight trace of peakiness in the presence region. For my taste though, an EQ filter isn't necessary. 

Although the Altec 405A can't replace the Altec 755C (much less the 755A) in my near-field set up, its midrange depth, micro dynamics, detail resolution and overall tonal balance makes it worthy of the Altec badge!👍😊