Vintage Japanese Drivers

One of the main reasons audio lovers have been apprehensive about getting into single ended micro power amps is the relative scarcity of efficient speakers. There are a few decent commercially available units but they are hard to find and audition. DIYers have discovered Fostex drivers which are not cheap but some of their mid-priced models are affordable and represent good value for the money. Prices asked for vintage WE, Altecs, EVs, Jensens and etc. have soared because of the demand from collectors. Another complicating factor is the size of vintage horn systems. Aficonados have also discovered old German radios and consoles from Telefunken, Saba and Siemens.

Vintage Japanese speaker units are just beginning to be appreciated. Prices at eBay for desireable Pioneer and Coral, full range, coaxial and triaxial units are starting to rise due to collectors and SE amp users realizing their merits. Look for old stereo consoles or table top radios and even early solid state models. The logic behind this is, power was at a premium in those days and for mass market consumption, manufacturers used efficient drivers to fill the living room with sound from amps with less than 10wpc. Likewise some of the speakers [plywood cabinets usually indicate good drivers inside] that were sold along with compact stereo systems are good candidates for SE amp use.

In my opinion, some units like the SK98, is on par or better than some of their Altec or Jensen counterparts. The others are good alternatives to mid-priced Fostex drivers which can be acquired cheaply at thrift stores.

The following drivers are no longer easy to find especially the alnico models, but the ceramic versions sound good too. These still come up at thrift stores or maybe sitting in the basement or attic of an older relative. This list is notcomprehensive, it is just a guide for those of you who like rummaging through yard sales, flea markets and thrift stores. Enjoy!

6" Full Range

Pioneer PIM16 OEM for Lafayette as found in SK124 bass reflex cabinets. This is the predecessor of the PE16M re-issue.Mechanical "2-way", perhaps a Japanese interpretation of the Altec "Bi-Flex"? MJ issue no. 2/2001 listed the following specs for this unit: 3W nominal, 70-16Khz frequency response, 11,000 gauss 850 gram Alnico magnet, 90db/1W/1M sensitivity and Fs = 70-85hz. Introduced in 1959.

Found inside a pair of Sony speakers originally sold with a compact system at department stores.

Same story as the Sony above, but these came from Panasonic branded boxes.

Another Panasonic but bigger magnet, 16 ohm voice coil and a whizzer cone.

Sonic Impressions - The PIM16 is probably the best of this bunch, it has slightly less bass response than a DiatonePM610B but the midrange is more 3 dimensional and has a smoother top end. The Panasonic RAS16PO2 above is also pretty good, although one can hear a slightly grainier midrange and top end, perhaps due to the ceramic magnet. The Sony and other Panasonic are decent too but not in the same league as the latter two.

I use these drivers in a recycled Coral cabinet - 14.5"H x 10.5"W x 8.75"D approximate outer dimensions and built with 3/4" plywood. 

I modified this into a bass reflex by replacing the front baffle and back cover with a 1.5" x 4" rectangular port with light poly-fill damping. 

I use them as rear surrounds but they are also ideal SE friendly mini-monitors for those who live in small apartments or dormitories. I have tried them also in open baffles, but given the foot print of the baffles and the frequency range of a 6" driver, I don't deem it practical since a decent 8" can give better bass extension.

8" Full Range

Lafayette SK98, the 1961 catalog list the following specs: freq. response = 40-16,000 cycles, Fs = 55-70 cycles, 99.5dB/watt sensitivity, 10,500 gauss/56,000 maxwells alnico magnet and 8 ohm voice coil. Notice the similarity of cone construction to the above Pioneer PIM16 and PIM8L below. I'm almost sure these were Pioneer OEM units.

This Pioneer PIM8L is very similar to the SK98 with economy cosmetics - bare metal frame and no magnet cover. Voice coil impedance is 16 ohms. These 8" drivers are pretty damn good sounding, Perhaps these are Japan's answer to the Altec 755. I rate them as the equal of a 755C or 755E with a slightly lightweight presentation. If I'll draw a car analogy, it is rather like a Honda Civic Si, smooth and high revving but light on torque as opposed to a torquey VW Golf GTi [755C or E].

12" co-axial

Lafayette SK58 12" driver with a co-ax mounted 3" cone tweeter. I modified the crossover slightly to get rid of the slight upper midrange harshness by adding another 4uf cap in series with the stock 4uf paper in oil can type. This shifts the crossover an octave higher and sounds smoother, very efficient not quite the snap in the midsas the SK98/PIM8L and the 3" tweeter not quite extended but still very satisfying.

Tweeters

Pioneer PT-3K horn tweeters came with the PIM8L above. This tweeter is in between the size of an Altec 3000 and Jensen RP103 with a 1 5/8"H x 4"W horn mouth. 16 ohm voice coil and 2.8khz recommended crossover. I use it as a super tweeter [x'over above 7khz] and this unit sounds sweet, silky and extended highs. Better than the Fostex FT17H in my opinion. Not quite as good as an Altec 3000 but quite close.

Trio/Kenwood horn tweeter Jensen RP103 clone[?], same horn dimensions. Can't remove the magnet cover but my gut feel is that this uses a ceramic magnet, the diaphragm is probably mylar. Not quite as articulate as an RP103 but slightly more extended in the top end.

Sonics AS-304A, 70s Japanese 4-way speaker with a 12" woofer, 5" midrange, 2" cone tweeter and horn loaded super tweeter. I guesstimate efficiency to be in the lower 90s but plays loud with an SE2A3 amp. It can be used "as-is", but for best sound I probably will pull out the drivers and mount the purest sounding combination of woofer + high frequency driver in an open baffle. 

Have fun and happy listening!

Hammond 125ESE Part 1

Hammond 125ESE

For years I have been searching for a truly affordable SE OPT that is flexible enough for experimentation with various triode output tubes. Last year I found a DIY SE2A3 amp project featured in MJ 2/00 using a Noguchi universal OPT [pri.Z = 2.5K, 3.5K and 7K], the PMF10WS for JPY 6,800. They even have a lower priced model, the smaller, PMF 6W for JPY 3,500 for people who want to build an amp around a 71A or 112A. Unfortunately they do not export and their fax no. specifically states "not used overseas". This is a clear indication of a well developed market in Japan that caters to the audio hobbyist that makes it unnecessary for manufacturers and dealers to look beyond their shores to thrive. 

Even if the SE/DIY revolution in the USA started in the early 90s, the availability of a true high-fidelity airgapped SE OPT for under $100/pr. is practically nonexistent. This could be one of the main reasons why in such a huge and progressive country, proportionately, the number of audio/DIY enthusiasts remain small. 

The Audio Note UK "experimenter series" at $75/each was a pretty good performer but has been unavailable for quite a while and it still would have cost over a hundred bucks for a pair. The early Hammond transformers I tested [125E and 1627SE] back in '97 had some issues that fell short of my expectations. Although the 1627SE had pretty good bass extension [due to the massive laminations], the upper midrange to high frequency was very rough, whereas the 125E without an air-gap just didn't have anything below 150Hz with more than 20ma. of DC unbalanced current flowing and forget about the upper range. But that was 4 years ago and I am well aware that the 1627SE is a popular choice for satisfied builders of my SE 300B project while the 125E is a favorite for my Simple 45/2A3 and Bob Danielak's Darling SE 1626 [Sound Practices 15]. I can just assume Hammond has improved the performance of these products based on the market success of these models. 

By chance, I stumbled by the new air-gapped 125ESE at $35/each while surfing Angela Instruments' website. After some deliberation I whipped out my credit card and ordered a pair. I also took the chance to say hello to Steve since I have not seen him or the shop for almost two years. Within a day or two they arrived at my doorstep. The 125ESE is an open frame unit weighing a little over 3 lbs and uses M6 silicon steel laminations according to the data. It is indeed twice the size of the original 125E but instead of solder tags, it came with long color coded leads.

Here is a picture of the 125ESE beside a Tango U808 for size perspective. It actually reminded me more of the Tango U708 in terms of size and weight. 

detailed specs

The primary is adjustable between 2.5K, 5K and 10K and claimed to handle 80ma. of DC unbalanced current. There was no data on inductance [relevant for bass performance] but it looked promising enough despite my reservations about cosmetics. 

I installed them [2.5K mode] on my current test mule, a stereo SE2A3 [schematic below] amp to play background music in my second system and had the surprise of my life because I was actually hearing music and found myself spinning various LPs and CDs. After a while I noticed one channel had a very slight tendency to spit out sibilance in the upper frequencies and confirmed it by switching cables between channels and it remained on the same side.

The amp was taken to my test bench for basic power output, frequency response measurements and I injected square waves to see how the OPTs were behaving. Sure enough OPT 2 had a slower rise time, an overshoot and some ringing at 10kHz, even at 1kHz the overshoot is quite evident [not a good sign]. 

OPT 2 @ 10kHz

OPT 2 @ 1kHz

However OPT 1 at 1kHz and 10kHz compared favorably with the Tango U808. 

OPT 1 @ 1kHz

OPT 1 @ 10kHz

Tango U808 @ 1kHz

Tango U808 @ 10kHz

[Note: top trace is the input signal from the audio generator and bottom trace is the amplifier output]. 

In spite of my reservations about OPT 2, the 10khz performance was still better compared to the early '97 1627SE and significantly better than the 'ungapped' 125E across the entire audio bandwidth. 

Obviously, what I heard [and confirmed on the scope] was a serious mismatch between the two 125ESEs, that is why it can be detected through critical audition. If I had two identical units like OPT 2, I would not have detected the anomaly, although I surmise that the sound would not be as clean as having a pair that measured like OPT 1. 

I brought the amp to NYC so that my friend Ding can offer another perspective and I could also hear them through 604-8Gs. He was very impressed and thought they were great value for the money although he did mention hearing something slightly funky about the high frequencies on one channel. On some material he found it more extended but on other tracks it sounded a bit rough. But he qualified that it was not really very apparent and only noticeable when he listened for it. He also made me promise to bring the amp on my next NYC trip because he really liked it. Meanwhile I had already emailed Steve requesting for another pair of 125ESEs because of my earlier findings and wanted to get a handle on quality control. By the time I returned home, the package was already in my apartment. 

The first pair was replaced by the second pair. I turned on the amp to play background music for about an hour and then started serious listening evaluation in my main system with the Altec 2-way speakers. I used another SE2A3 amp with Tango U808 OPTs as a reference point. The circuit is virtually the same in both amps with bi-plate 2A3s running at 18W plate dissipation and the U808 set to 2.5K mode [usually set to 3.5K, but I wanted to limit variables]. I listened to a variety of music ranging from LPs by Sinatra, Ella, Billie, jazz/big band, 80s pop/new wave, to Mahler sym. # 5, Bartok concerto for orchestra, Mozart string quartets, Ravel piano trio and DAT masters of live performances I recorded. 

Do not be discouraged by the specified +/- 1dB, 100Hz-15kHz bandwidth because it was easily exceeded in my listening evaluation and test bench measurement results. I could hear down to 50Hz, perhaps the fundamental was already rolling off but the bass note overtones [harmonics] were right, which is very important to hear good bass definition. The U808 offered more air and space indicating a higher bandwidth ability and gentler treble roll off, it also sounded more controlled and composed in the bass. If I was to nitpick, I would say that the U808 has the edge in the ability to resolve detail and more transparent overall with a slight tendency to sound dry and clinical. In spite of a bit more grain across the audio spectrum, the 125ESE always delivered the emotional impact of any pre-recorded material. This is what I deem as high-fidelity in the true sense of the word, honoring the music. The relative lack of transparency will not be apparent unless the units are pitted against superior and more expensive units. 

Assuming OPT 2 was a fluke, I give the 125ESE my highest recommendation. It should not take that much time nor effort for Hammond to keep quality control within the standards set by OPTs 1, 3 and 4 while keeping the same cost. Based on the impressive performance noted, the 125ESE deserves metal shrouds to cover the core even if the 2 - bolt mounting tab arrangement is kept. This way it can be painted giving DIYers some flexibility with aesthetics. I also no longer endorse hacking PP OPTs from vintage tube integrated amps for use with my Simple 45/2A3 project; the 125ESE will perform much better in this application. 

If I had the time I will not hesitate running 300Bs with these transformers. But watch the current, even if it is specified to take 80 ma. the core may still saturate [just a hunch, based on the 100Hz square waves I saw], you may be better off backing down to around 60-70ma. For those who really prefer their 300Bs hot, the 1627SE is a safer bet and will assure greater bass extension. 

Given the performance and flexibility the 125ESE offers at such modest cost, it should bring the joy of SE DHT amplification to a wider audience and the unavailability of affordable OPTs is no longer an excuse not to build your own SE amp. Place your order for 125ESEs at your favorite dealer so that Hammond will continue improving their products and come out with quality transformers like the 125ESE for DIY enthusiasts. While you are at it, snap up the remaining American made 2A3s, 50s, 45s, 10s/VT25s, 71As before they dry up and watch out for vintage paper cone alnico drivers, because you will need them.

Go to Part 2

Hammond 125ESE Part 2

Test bench results for the Hammond 125ESE

[Tango U808 used as a reference point]

Foreword

"Reflections of a scope jockey"

These tests are by no means definitive and I still rely on my ears more than anything else. However the techniques I employ have served me pretty well as short cuts in troubleshooting.

Although some tonal aberrations can be recognized on the scope, it should not be taken as the last word. I have tested amplifiers that looked good on the scope but failed to satisfy me musically or two amplifiers with dissimilar circuit topologies that looked and measured the same but sounded totally different from each other. But these were mostly amps with a lot of negative feedback. Negative feedback can extend the bandwidth of an "ill conceived" circuit or output transformer while overshoot and ringing at high frequencies can be "cured" by judicious use of picofarad value caps. So keep these "band-aids" in mind.

I passed up on several opportunities to purchase a good harmonic distortion meter cheap at hamfests, mainly because I do not think it has anything to do with music. On page 32 of the Radiotron 3rd edition, I quote, "The total harmonic distortion is not a measure of the degree of distastefulness to the listener and it is recommended that its use should be discontinued", this was written by someone in 1938 and knew better then.

To a certain degree measurements can be helpful just like what you will see in the case of unit # 2. I also take measurements and observe the behavior of recently completed amp/preamp projects to make sure the circuit is functioning properly. As long as the waves look clean and the math [operating point and etc.] works out right then the unit is ready for an audition.

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In the following, all transformers were installed and tested in SE2A3 amps with the same 76-DC-6SN7 input/driver circuit cap coupled to a 2A3 running at 17-18W plate dissipation [60ma. DC unbalanced current through the primary] with no NFB [negative feedback] employed.

Frequency response in 2.5K mode @ 1W output into an 8 ohm load [0 dB = 1W]

Hammond 125ESE [all dated 02/27/01]

• Unit # 1: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -3.5 dB], rolloff is smooth.
• Unit # 2: 20hz - 20khz = started rolling off at 10khz [ -.3 dB] @ 50khz [-6 dB], rolloff is rough
• Unit # 3: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -4 dB], rolloff is smooth.
• Unit # 4: 20hz - 20khz = flat +/- 1 dB, @ 50khz [ -3.5 dB], rolloff is smooth

Tango U808 [2.5K mode]:

• Both units: 20hz - 20khz = flat +/- .5dB, @ 50khz [-3 dB], rolloff is very smooth.

NOTE: Typically the bandwidth of any "universal" type output transformer will diminish when used to step down at the secondary taps. So expect less bandwidth at 5K and even more at 10K primary Zs. However, I do not think this would have any serious sonic consequence in the case of the 125ESE units 1, 3 and 4.

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Hammond 125ESE square wave response at 100hz, 1khz and 10 khz

Top trace is the signal from the audio generator at less than .1V rms and the bottom trace is the amp output at around 2.2V rms into an 8 ohm load.

OPT 1 @ 100hz

OPT 1 @ 1khz

OPT 1 @ 10khz

OPT 1 - looks good overall!

OPT 2 @ 100hz

OPT 2 @ 1khz

OPT 2 @ 10khz

OPT 2 - the spike at the leading edge of the 1khz square wave is a manifestation of the harshness heard in the treble. At 10khz the rise time is comparatively slow compared to the other 3 units. The overshoot is an artifact of that seen @ 1khz. a slow rise time tend to curtail transient signals resulting in poor treble resolution.

OPT 3 @ 100hz

OPT 3 @ 1khz

OPT 3 @ 10khz

OPT 3 - slightly slower rise time at 10khz compared to OPT 1 and OPT 4 but still fine. There is a tendency to ring but it is well damped. These slight aberrations were not detected by my ears and sound identical to OPT 1 and OPT 4.

OPT 4 @ 100hz

OPT 4 @ 1khz

OPT 4 @ 10khz

OPT 4 - almost as good as OPT 1 except for the slightly rounder leading edge at 10khz. All four 125ESE units showed greater tilt at 100hz compared to the U808.

  

Tango U808 @ 100hz

  

Tango U808 @ 1khz

Tango U808 @ 10khz

Tango U808 [both units looked identical] - less "tilt" at 100hz [greater inductance?] compared to all the 125ESEs and may well be the reason why the bass sounds more articulate and extended. Tango had tight quality control procedures based on several models and samples I've tried.

Back to Part 1