Altec 32 Horn Nomenclature

This Altec 32 horn update was prompted by this must read article from Electravolt tracing how the Altec 32 horn evolved from the Western Electric 32A.

Altec 32A

Cast aluminum + longer throat

Altec 32B

Plastic + shorter throat

pics borrowed from sound-impression

Probably a very short run, rarely seen in the market

Note: no ribs

Altec 32C

Same as 32B but with re-enforcing ribs

Note: re-enforcing ribs

Topping D30 vs. Xiang Sheng DAC 01a

This installment is long overdue since I got distracted by a flea market find, a Yamaha T-2 FM tuner, which was aligned to factory specs by Punker X, highly recommended tuner tech! Yes, I am eating my words from this past post since I've been enjoying WRTI, WPRB, WXPN, amongst others. FM broadcasts just sounds more analog with a human DJ than streaming from the internet.

But I haven't ditched my Raspberry Pi 3B+ set up since it has its purpose.

If you are looking for a DAC to hook up to a CD transport to playback Redbook CDs STOP and GO there! However, if you need an affordable DAC for your Raspberry Pi, laptop or server, you may proceed.

Cirrus Logic CS4398

Both these units use the Cirrus Logic CS4398 chip, a well-respected Delta-Sigma type DAC that was introduced in 2003. But it is the implementation of the DAC chip which sets these two units apart.

Listening tests were done using music files mastered to CD Redbook standards. These include live concerts, CD projects and music from favorite CDs I transferred to a USB thumb drive. Streaming sources were internet radio stations via the latest version of moOde audio or Volumio loaded to a Raspberry Pi 3B+ with an Allo DigiOne HAT. I also listened using USB connections and arrived at the same conclusion.

The Topping D30 is a highly acclaimed DAC and measures great according to meter readers. It sounds pleasant, I didn't hear anything objectionable. But compared to the Xiang Sheng DAC-01A, the D30 sounds dry and lifeless. Maybe that's what others will deem as accurate? 

A hundred and twenty something dollars buys a neatly stuffed PCB with Wima capacitors in the audio stage. The PCB card slides into a nice anodized aluminum case. But Topping only provided an SMPS wall wart. Hmmm...

For about the same amount of money the Xiang Sheng DAC-01A is built on a solid metal chassis. It sports a real power supply based on an R-Core power transformer that provides an 80VDC rail for the 6N3/5670/WE396A tube buffer/cathode follower blocked by Wima coupling caps.

In spite of the decent quality workmanship, the blue LED pilot light on my unit was flickering since I got it and died a couple days later. But it was an easy fix.

Since I was planning to use it mainly as a DAC, I bypassed the volume control by setting the two jumpers to connect 2+3 and b+c. To enable the volume control, connect 1+2 and a+b. With this set up, it can also function as a stand alone line stage preamp.

The only upgrade I did to the DAC-01A was replace the stock 6N3 tube with a US made NOS 5670 (about $7 a pop), which gave a more refined sound. I regret unloading my 70s date code stash of WE396A/2C51s years ago...I can't afford to buy those back.😞 Anyway, I don't think it would have made the sound 10 times better.😉

Sonically, the DAC-01A trounces the D30. This unit sounds enticing. Maybe others will consider this colored because of the tube buffer. But to my ears it is A LOT more musical! Music IS THE BIG picture folks, leave the details for laboratory analysis.😄 

The unit has two sets of outputs; the normal out, which bypasses the tube buffer, gives up a bit of the dignified poise but still sounds more authoritative than the D30. Although I'm pretty sure the tube output stage will be a delight to pick on by scope jockeys. 😄

BTW, did I mention it also has a headphone output?

Coda

Inasmuch as I laud the Xiang Sheng DAC-01A as great value for the money, if you're in the market for a DAC to playback Redbook CDs, I'd persuade you to hit the flea markets and thrift stores to hunt for an ancient TDA1541-equipped CD player. Even an early 90s CD player with the cheaper TDA1543 chip will give more musical satisfaction than the DAC-01A. However, if you need a Hi-Res capable DAC for the Raspberry Pi music player, computer or server, this is hard to beat at this price point.

Listening Room - Minimalist no more?

Among the audio systems of my friends, this is the only set up that has no LP playback ability. Neither does the owner have interest in DVD-A, SACD or a music server/streaming device - only16 bit linear PCM sampled at 44kHz red book mastered CDs, period!

Since our last visit, a Northstar CD transport replaced a CEC TL51X, while another belt-driven CEC TL5 CD transport is being contemplated. The NOS (Non-Over-Sampling) Zanden Signature DAC equipped with a double crown Philips TDA1541A-S2 chip remains. Now you know why I hunt for unloved TDA1541 CD players from the 80s.😎

The most significant change in this system, however, is that
the Phy-HP Co-Ax speakers have been replaced by a pair of field coil powered Western Electric descendants - G.I.P. Monitor 1s.

According to the owner, the JE Labs line level preamp +
SE10 mono-blocks give life to GIP Labs! He is such a good friend. 😉

dynakit stereo 35

Before 2018 drew to a close there was a buzz on various audio forums about the auction of a vast collection of audio gear in the northeast. My attention was caught by lot number 4, a seemingly unmolested Dynakit Stereo 35. I bookmarked the site and registered for bidding.

Fast forward to mid December, my wife and I drove through the new Tappan Zee Bridge aka Gov. Mario M. Cuomo Bridge

and scenic Merritt Parkway (Route 15) to collect my loot, which included the stereo 35.

Feuillantine  - layers of dark chocolate mousse,
hazelnut buttercream, chocolate cake with
hazelnut wafer crunch

On our way home, we let the rush hour traffic subside by exiting in Pleasantville, NY. As a reward for my wife's enduring patience, we had dinner at Jean-Jacques and took home this decadent Feuillantine.

As mentioned in this JEL Arkiv entry, my passion for vacuum tube amplification was sparked by a Dynakit Stereo 35 I found in what was left of Radio Row in downtown NYC in the early 80s. Unfortunately, I had to unload it in the 90s to finance Tango and Tamura SE output transformers for my SE-DHT amp projects. It was a sentimental journey to reacquire this amp.

Removing the cage reminded me of the days when I serviced classic tube gear at Angela Instruments in the 90s. I quickly recalled the routine of checking for shorts in the multi-section capacitor and identifying continuity in the transformer windings. After those static tests were established, the amp was plugged into my trusty GenRad Variac and I slowly applied AC voltage while carefully monitoring the current draw. My hunch was right, this was a healthy amp that just needed a lot of cleaning and a little updating.

!!!WARNING!!! 
The voltages in this circuit are potentially lethal! Proceed at your own risk!

Dyna Stereo 35 Schematic

The secret to the ST35's success was its elegantly simple circuit design. It uses a 7247 twin triode which is essentially half of a hi-mu 12AX7 + half of a med-mu 12AU7. The hi-mu section functions as the input voltage amplifier, while the med-mu is configured as a cathodyne-phase inverter driving a push-pull pair of cathode biased 6BQ5/EL84 pentodes connected to wide bandwidth Dynaco Z565 ultra-linear output transformers. The judicious use of both positive and negative feedback made this a very stable amplifier.

Aside from replacing the original mylar coupling caps with polypropylene Wonder Caps in typical 80s fashion, the only mod I ever did to this amp was bypass the "green ceramic disc cap" (C1) and filter network (R1 & C2) in the input. This idea came from page 67 of Bascom H. King's review of the Mark Levinson ML10A preamp + ML9 amp in the August 1985 issue of Audio.

 Since I wanted to keep this amp as original as possible, I avoided removing parts and cutting traces like I did as a Dynaco hacker in the 80s.

This is the stock wiring of the RCA input jack. Audio signal + is connected to solder tag No. 1.

I unsoldered the wire from solder tag No. 1 and soldered it directly to the input grid, pin 7 of the 7247 input/driver tube. From above it looks stock but now the audio signal goes directly into the input grid (shunted to ground by R2) of the hi-mu voltage amp section. This mod effectively bypasses the filter network (C1, R1 & C2) which protects the amplifier from a preamp that produces DC offset at the output. If your preamp passes DC (or you aren't sure) DON'T DO this modification.

Since the 90s I've been convinced that paper in oil (PIO) caps sound more like live music. Although I'm not 100% sure whether the surplus mil-spec West-Cap/Astron cap combo I installed are PIO, the amp doesn't sizzle like it did with the original mylars.

Dynaco skimped on the power supply of the ST35 by using solid state rectifiers and a wire wound resistor in the 𝜫-filter. The least I could do was replace the original 60Ω, 5W resistor with a proper C-354 choke from Dynakit.

Minimal phase shift @ 100Hz = excellent low frequency response

Fast rise time @ 1kHz with just a hint of overshoot

Again a tiny overshoot @ 10kHz with minimal and well damped ringing

9.89 Vrms squared = 97.8121/8Ω load = 12.23 watts per channel
before clipping, both channels driven

stereo 35 sans cage

Speakers I've used in the past with the Dyna Stereo 35 include DIY mini-monitors using Radio Shack components, BBC LS3/5As and original Quad ESLs. It had a hard time driving a pair of Magnepan SMGas I briefly owned in the mid-80s, so I unloaded them. 😉

I'm listening to jazz tunes with the stereo 35 driving Altec 755Cs in 618 cabs as I type. It doesn't have the mid-range magic nor does it present micro-dynamics like my Simple 46, but this fine PP EL84 comes pretty close.

Just like Feuillantine, the dynakit stereo 35 is yummy!

Happy Holidays!

Happy Holidays and Wishing Everyone a Great New Year! 

Morikawa SE2A3 in Jose's Listening Room

Back in the 90s I used to hang out with Ding and Jose at Hamfests in the suburbs of Philly. Jose isn't your typical audio nerd who subscribes to the latest is best mentality. He goes for value for money and although not a DIYer, has an eye and ear for quality design! Even if he has a Technics SP10 + Sumiko MMT turntable combo, most of his listening nowadays is through a high quality pre-bitstream a Denon DCD 1500 and a stable platter Pioneer PD65.

Having heard that a well designed SE2A3 amp is a synergistic match for his Altec 604-8Gs, he spotted and won this Chuyu Morikawa designed Audio Professor SE2A3 amp on eBay. However, the amp had two issues. The input level controls were no longer functioning, and worse, the amp was unstable manifested by extra-musical popping and whistling sounds. Since we're practically neighbors now, I took it home for a check-up.

Under the hood 

Beautiful workmanship, typical of a handcrafted amplifier from Japan

After installing a dual ganged 100k Alps audio taper input pot, I realized that the cause of instability was the step down transformer the eBay seller sold with the amp. It was hardly stepping AC down to 100V. During the amp's residency here at JE Labs it was plugged to a General Radio Variac set to 100VAC. It was stable and quiet. Fortunately Jose also has a Variac on stand by, which he acquired during our Hamfest hunting days.

6Z-DH3A

The amp uses 4 x (2 for each channel) 6Z-DH3A, UX-6 based, high-mu triodes as input/driver tubes. This tube is electrically equivalent to an octal based 6SQ7. AFAIK, there are no plug-in compatible US or European equivalents. 

The input/driver circuitry is configured in SRPP, very similar to what I did in the JE Labs SRPP 45/2A3, albeit with textbook operating points.

5 Volts rms to an 8 ohm load at onset of clipping = 3.125W per channel

Luxman SS5B-2.5k OPT

100Hz

1kHz

10kHz

These square waves show that the Luxman SS5B 2.5K primary SE OPTs are of very high quality. Not much information is available on the internet regarding this transformer aside from completed auctions, but I've encountered this model in schematics and pictures in Asano's two volume tome on tube amplifiers.

Since Luxman SE OPTs were no longer available during the Sound Practices era in the 90s, I would date this amplifier to the 80s, at the latest. That's before Cary introduced the 6SL7 SRPP driven 300B or 2A3 AES SE-1 kit amp to the mainstream market.

I built SRPP circuits back in the day, but was never a fan of this topology. However, this amp made me reconsider my stance. Now I'm asking myself - could it be the textbook operating points and/or the 6Z-DH3A input/driver tubes which made this experience memorable? 

I truly enjoyed listening to this amp, thanks Jose!