Wednesday, April 17, 2019

Hashimoto H-203S from Kasuga Wireless

In September 2018, I lamented the demise of Noguchi Transformers. Fast forward to November, my brother-in-law visited Tokyo, and was kind enough to pick up a couple of transformers at Kasuga Wireless.


How to get to Kasuga Wireless

Kasuga Wireless

Address: 1F, New Akihabara Center, 1-16-10, Kotobuki, Chiyoda-ku, Tokyo 101-0021

Hashimoto H-203S



The H203S was installed as a 3.5k primary Z output transformer in the je2a3 mono integrated amp


Testing

Top trace = audio generator
Bottom trace = amplifier output

100Hz

1kHz

10kHz

5.324Vrms to an 8 ohm load = 3.5W 

In the past, I've used Hashimoto transformers for a pair of SE2A3 and a pair of SE10 mono-blocks I built for friends. I know these transformers are well designed, are of high quality construction and sound excellent. Thus, before Hashimoto ceases production, I had to add it to my collection. 


My mono SE2A3 integrated is ready for prime time!


Now I have to find a nice circuit for a pair of Kasuga KA6625ST OPTs. 😉









Monday, April 1, 2019

Altec 753C

After many years of raving about the Altec 32 horn, the only stone left unturned was using it as it was originally designed, that is, with the compression driver oriented to radiate upwards.

Last year, I received a message from John Piro, whose beautifully crafted preamp project was previously featured in this blog. He sent me pictures of his interpretation of the legendary WE753C using an Altec 414-16B woofer + Altec 32A + Faital Pro driver

Altec 414A + 32C + 802D + 20275 

I was very impressed and requested if he could build a pair for me. We finally met at the Kutztown Radio Show last September. He and his wife had dinner here at home when he delivered my beautiful cabinets!

A Western Electric 753C used as a monitor at WABF in the early 50s

As an homage to the legendary Western Electric 753C, which was a major inspiration for this project, I henceforth christen this speaker system as the Altec 753C.

Altec 2-way XO redux

I've settled on running the 414A woofers in full range mode (ala J-Rob) and replaced all the crossover resistors with non-inductive 12W Mills. This took away the last vestiges of grain in the upper frequencies.


RTA Graphs

Altec 2-way

Altec 614 + 414A + 32C + 802 with GPA34258

The above RTA was taken from this blog entry

VS

Altec 753

Altec 753 + 414A + 32C + 802D with 20275

I could've lived happily with my Altec 614 or repurposed 861 (aka Madrid) cabs + the inverted 32 horn situated on top. However, with proper horn orientation, the sound was taken to another level of refinement. Now the blend between the 414A and horn is practically seamless and I bask in the airiness of the top end, which I attribute to significantly improved high frequency dispersion, precisely as envisioned by Western Electric engineers.

In spite of the stellar midrange performance of the Open Baffle mounted Altec 755As, I started the Altec 2-way project in the late 90s to address the following issues:

1. More efficiency
2. Extend the frequency extremes
3. Less congestion in dynamic peaks with complex musical passages

After 20-some odd years, those goals have been realized. The Altec 753C is pretty much end game!


Thanks to my buddy Joe Roberts, who explained the intricacies of proper 32 horn orientation. The idea was carefully stored in my mind. I just had to wait for the right opportunity to implement it. And of course, a big thanks to my friend John Piro (aka RCA NUT), craftsman extraordinaire!

Let's hear some music. 😊









Tuesday, March 19, 2019

Ikea Knarrevik


Ikea Knarrevik 

I use it as:

component stand

turntable stand

speaker stand

Best $10 I ever spent on Hi-Fi! 😉








Tuesday, March 5, 2019

John Linsley-Hood 1969 Class A Amplifier aka Nobsound NS-02g

Original JLH1969 Class A amp schematic

The John Linsley-Hood 1969 Class A amplifier circuit is a classic solid state design that is carefully studied by audio designers. Even the great Nelson Pass revisited this circuit when he embarked on low wattage amplifier designs.

It has been described as one of the most tube sounding solid state amplifier designs, which is not surprising since John Linsley-Hood's references were tube amplifiers. Here's a link to the 1969 article published by Wireless World.


Since I am a DIYer at heart, I originally considered buying a pair of these circuit boards on eBay. But when I spotted a built unit for $170/shipped, I calculated that by the time I factored in the cost of a power transformer and a massive heat sinked chassis, it didn't seem wise or cost effective to go the DIY route.


The JLH 1969 Class A clone I got is branded Nobsound NS-02g but I've seen the same chassis and guts in silver or gold sporting a Krell logo!


It is very compact- a hair over 13" wide x 8.25" deep and 3" high- but it weighs 12 lbs. due to the heavy gauge chassis, massive heatsinks and power transformer. Parts quality is surprising for a $200 amplifier requiring discrete components. Input impedance is set by an Alps Blue Velvet 10k Ohm logarithmic potentiometer. There are no IC chips in this amp, just a couple pairs of transistors, a handful of resistors and capacitors + a lot of copper wire wound in the toroidal transformer. This is a true Class A design from the late 60s built at the end of the second decade of the 21st century.


When I first fired up the amplifier, I heard a buzz when the input level control was at maximum. I traced this to the IEC socket which was not grounded. Strapping the center pin (green cloth insulated wire) to ground took care of the buzz.


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


Set Up and Adjustments

NOTE: Red probe to test point, black probe to chassis ground

Idle Current


Out of the box, the amp sounded pleasant but I was not hearing anything magical. I was suspicious of the meager 0.5 amp AC current draw at 120V I monitored on my GenRad Variac. So removed the top cover to study the circuit and determine the purpose of the two potentiometers on each channel's PC board. 

The pot towards the middle of the PC board is for idle current adjustment. Since I didn't have a manual and couldn't find one on-line, I took the cue from this video by a JLH 1969 Class A kit amp builder.👍 His circuit board looked similar enough, thus, the proper voltage must be closer to about 20V(?). I measured 26.5V and 26.2V on my unit. So I turned the pot clockwise until I got about 24 volts DC on both channels. The AC current draw was now over 1 amp and I started feeling heat emanating from the chassis. 

AC Balance



The next step was to adjust AC balance. I loaded each channel's output with an 8 ohm, 20W wire wound resistor and then injected a 1 kHz sine wave at the input jacks. I adjusted the AC balance pots on both channels while observing the clipping behavior closely for best symmetry - both phases of the trace should "square off" simultaneously.


Tweaking the idle current

137℉ @ the heatsink

I checked the idle current once more and listened. 26V yielded almost 10 watts per channel on the bench but I felt the sound can be sweeter. At 21.5V the amp sounded excellent. But the chassis was running physically too hot. Just to be conservative, I backed off a bit and actually found the sweet spot between 22V - 24V. I also made sure there's always ample ventilation around the amp.  

On the Test Bench

Top trace = signal generator
Bottom trace = amp output

100Hz

1kHz

10kHz

Not perfect, but nice and clean square waves from a half a century old solid-state design


Input sensitivity = .25 Vrms > ~ 6.8 watts per channel rms into an 8 ohm load with both channels driven

Tweaks



A slight glare in the upper midrange was ameliorated when I by-passed the 2.2uf input capacitors with 0.47uf Vitamin Q "Hyrel" PIOs and the 2500uf output capacitors with 10uf KBGs. Before reassembly, I also replaced the red LED pilot lights with blue LEDs. Much easier on the eyes especially in a dimly lit room.


 The Nobsound clone amp spent most of its time in the system above, driving a pair of Altec 755Cs in 618 cabinets and also a pair of moderately efficient Radio Shack LX4s. I also listened to it in the main system driving the Altec 2-way. In both cases it never failed to sound sweet, fatigue-free, with a tube-like quality and depth in the midrange, maybe not the tightest bass but definition was good + airy highs.


The only time it betrayed its solid-state identity was when I spun an LP of Shostakovich Symphony No. 11 in the main system. It went into nasty clipping during orchestral peaks like a typical solid-state amp. Maybe it was asking too much from a Class A amp with a measly 7 watts rms per side to cope with the 16 ohm load presented by the Altec 2-way? However, with the same piece and on the same speaker system, my 4 watt per channel Stereo SE2A3dx with Tango NY15s went into overload with grace and composure at a similar SPL.


It is a testament to John Linsley-Hood's engineering and hearing abilities that his 50-year-old circuit is still a very capable music maker. Even if it can't replace any of the tube amplifiers in my collection, this is a much more listenable amplifier than the handful of contemporary Class D switching amps I've heard thus far.







Friday, February 15, 2019

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






Wednesday, February 6, 2019

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, WPRBWXPN, 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.