Showing posts with label DIY Audio. Show all posts
Showing posts with label DIY Audio. Show all posts

Thursday, February 22, 2024

SE171A Amp Remastered

My dad would've turned 97 today. To celebrate his birthday, the video clip above features a recording of his favorite violinist, Nathan Milstein, playing Presto from Bach's Sonata No. 1 in G minor for unaccompanied violin. While he was doing post-graduate studies at The Juilliard School in the mid 50s, he was fortunate to have attended concerts of the great violin virtuosos of that era - Jascha Heifetz, David Oistrakh, Nathan Milstein, etc.

He would later recount that Nathan Milstein's performance of the Glazunov violin concerto was the most unforgettable! Even if he never got a chance to add this violin concerto to his repertoire, he conducted the Manila Chamber Orchestra with me playing the Glazunov violin concerto in 1987. The music of the slide clip above is the middle movement from our performance.

Before I bore everyone reminiscing about my dad and our life as musicians, let's get on with the subject at hand. The amp featured in this upload uses a directly heated triode power tube that was introduced around the time my dad was born.

Friday, October 6, 2023

JE Labs Choke-Capacitance Coupled SE2A3 amp

Canon P + Canon 50mm f1.8 LTM 
Foma 100 in Rodinal

Inspired by my plate choke-loaded 76 line stage preamp adventures, I was curious how a similar driver circuit configuration would sound in an SE2A3 amp. So I pulled out my Radiotron Designer's Handbook, 3rd Edition to gain a better understanding of choke-capacitance coupling (aka plate choke loading) vis-à-vis resistance coupling.

Below are highlights of relevant information I gathered.


Friday, August 18, 2023

Ortofon STM-72 + Weller WTCPS repair + Hakko FX-888D



One morning, I discovered the right channel of my Ortofon STM-72 was dead. While waiting for the Weller WTCPS soldering station to heat up, I carefully peeled the foilcal to pull apart the 2-piece tubular housing so I can resolder the broken cable connection(s). 

Friday, July 7, 2023

Japanese Idler-Driven Turntable Part 4: Realistic Mark-7


Here's a tale of two idler-driven turntables of Japanese origin sold by Radio Shack in the late 50s. They share the same model badge and engineering features but they aren't exactly twins.🤔

This turntable/tonearm combination has been in my collection for over twenty years. I wired the tonearm for stereo because I particularly enjoy using it with the Shure M3D and M7D

I couldn't find this in any of the Radio Shack Catalogs issued from the late 50s to the early 60s unless it escaped my tired, old eyes.  

from page 2 of the 1957 Radio Shack Sale Flyer

However, the A-3 tonearm, which is essentially a Calrad SV12/Musicmaster Model 12/Velvet Touch sibling, was featured in the 1957 sale flyer above.

from page 4 of the 1958 Radio Shack Sale Flyer

This is the Mark 7 turntable recorded in the Radio Shack Catalog Vault

Based on the shape of the chassis, this Mark 7 is perhaps the younger of the two since it looks very similar to the succeeding Mark 8, which I will discuss in a future installment.

DIFFERENCES

Although not quite as heavy and massive as a QRK or Russco, the cast aluminum chassis is very rigid on both units. The earlier MK7 chassis above is configured to accommodate a 9"-10" tonearm, while the later MK7 below was designed as a "motor unit" like the Garrard 301 and 401.  

The speed selector linkage to the idler wheel in both are similar, but due to a slight difference in the motor mounting layout, the idler arm and idler wheels are not interchangeable.

SIMILARITIES

Except for the paint color, this hysteresis motor is exactly the same unit fitted to my NEAT P58H, which I covered in Part 2 of this series. Click here for motor servicing information.

The main bearing is an oil lubricated design, which supports a 3-lb. cast aluminum platter.

MODs & TIPs


Before moving on, the younger MK7 depicted above had a serious issue - the motor has a bent rotor spindle!😔 Will I be able to save it by adapting the motor from another Lafayette PK245 (don't ask my wife how many turntables I own 😆) with a warped platter?🤔 

While planning the motor transplant, I examined the MK7 idler wheel condition and decided it might be worth rejuvenating.

So I mounted it on a handheld drill, deglazed the rolling surface with 400 grit sandpaper, and soaked it in brake fluid for over a week. This was suggested to me decades ago by a kind soul who visited the Rek-O-Kut Tips page in my old website. It has worked with two other Japanese idler wheels but I've never tried it on a Lenco or Rek O Kut. Back in those days, it was more convenient to just send Lenco and ROK wheels to Ed Crockett, RIP 😞 or Terry Witt 👍, who's still catering to the needs of audio DIYers.  

The above idler wheel was resurfaced by Gary of VoM. 👍

 Even if the rubber motor mounts were still supple, I replaced them with springs. A nice lesson I learned from servicing my NEAT P58H.

 To my ears, the spring mounted motor + 8 mm ball bearing/nylon countersunk washer thrust pad help lower the noise floor.

Realistic Mark 7 stepped pulley specs


MUSIC VIDEOS 😉

I have a close affinity for the Mark-7 + A3 since this was the very first Japanese idler-driven turntable I acquired.



Turntable: Realistic Mark 7 + A3 viscous damped tonearm
Phono Cartridge: Shure M7D
Phono Preamp: DIY 6J7 + passive RIAA EQ + 6SL7 + 6SN7 cathode follower
Line Stage: JE Labs Loctal
Speakers: Altec 406Zs in Coronado cabinets + Azzolina Audio KS12024 horns + Altec 806A
drivers


Turntable: Realistic Mark 7
Phono Cartridge: Ortofon SPU #1s
MC Step Up: Tamura TKS83
Phono Preamp: DIY 6SL7 split/passive RIAA EQ + 6SN7 cathode follower
Speakers: Altec 406Zs in Coronado cabinets + Azzolina Audio KS12024 horns + Altec 806A drivers

Turntable: Realistic Mark 7 + A3 viscous damped tonearm
Phono Cartridge: Shure M7D
Phono Preamp: DIY 6SL7 split/passive RIAA EQ + 6SN7 cathode follower
Line Stage: JE Labs Loctal
Amp: JE Labs SE171A with Tango H5S OPTs
Speakers: Altec 406Zs in Coronado cabinets + Azzolina Audio KS12024 horns + Altec 806A drivers

Enjoy! 🎶




Friday, June 23, 2023

JE Labs Plate Choke Loaded 76 Line Stage Preamp



I acquired this pair of James JS 4120N, 200H @ 15 mA nickel plate chokes from Keith Tan of Euphonia Audio in late '04. Due to my busy performing and teaching schedule back then, they remained boxed up close to two decades.

After going home with me to Manila and back stateside, I finally found time to try the JS 4120Ns in my preamp. After adjustment of voltages and operating points, I was impressed by the increased detail and resolution brought forth by replacing the Allen-Bradley plate load resistors while retaining the sonic aura I've come to treasure from my Bruce Berman-derived 76 > 1/2 6SN7 line stage circuit from Sound Practices Issue 13.

Unfortunately the JS 4120Ns have been out of production for quite a number of years. 😞

!!!WARNING!!! 

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

NOTE: According to the 7N7 data sheet, it has a maximum cathode to heater (filament) voltage rating of 90V. To get around the 142V at the cathode, I lifted the filament potential 65V above ground via a voltage divider network in the B+ supply. Hence, 142 - 65 = 77, which brings it back to spec

100 Hz, 1 kHz and 10 kHz square wave output 
from 2 x Hammond 156C plate choke loaded 1/2 7AF7
+ 1/2 7N7 cathode follower

I tried the budget-friendly Hammond 156C plate load chokes in the circuit above on my loctal preamp as well as on my main preamp with the 76 line stage below.

Detail improved but I missed the micro dynamics and organic quality in the midrange of the JS 4120Ns. That said, I'm now using this topology in the nosTDA1541tube DAC in my main hifi set up. Meanwhile the loctal preamp line stage has been reverted back to its original state with Allen-Bradleys.

NOTE: This choke saturates instantly past 8 mA!

Since the Hammond 156Cs are easy on the wallet (just like the 125ESEs I wrote about decades ago😉), why not try and judge for yourself? If you hear potential, then proceed to the nickel plate choke-equipped circuit below.😊

Custom wound Intact Audio 250H nickel plate chokes

When my cousin commissioned his hifi system, I had to search for an alternative to the JS 4120N. Fortunately, Dave Slagle of Intact Audio willingly obliged to custom wind Ni-rich plate chokes for that project!👍

I was so impressed with Dave's nickel plate chokes👏 such that I ordered a pair for myself so I could use the JS 4120Ns for other tubes and circuits. I also confirmed that in order to get the most out of the plate load choke topology, one needs a competent winder, and nickel should be part of the equation!

Even if I always used more rugged 6SN7 GTA and GTB types in the cathode follower section, when I built this preamp over two decades ago, the power supply was configured so that the filament potential was about 75V above ground.

I've always admired the sound (or more appropriately, the lack thereof) of nickel permalloy, having owned the Tamura F7002 and Tango NY15S since the 90s. Even if these output transformers are hefty beasts, which helps the low frequencies, it's not their bass response that captivates the listener. Instead, they present a very natural midrange replete with rich and harmonious overtones, which are virtues I also hear with Finemet.

100 Hz, 1 kHz and 10 kHz square wave output 
from an Intact Audio nickel plate choke loaded 76
+ 1/2 6SN7 cathode follower

After praising the merits of exotic core material, I wouldn’t want readers to get the impression that nickel or Finemet are the quintessential elements to great sound. Tube choice, circuit topology and operating points, parts selection, etc. not to mention the synergy of components in the hifi chain, all contribute to the sonic stew. That's why I encourage audio hobbyists to listen and experiment so that they can carve their path towards their own musical satisfaction. 

Although this video is merely a proof of concept, I got inspired and used my Sony A7II + Voigtlander Ultron 28mm f1.9 LTM lens mounted on a tripod rather than my usual iPhone. So plug in your Koss Porta-Pros or Sennheiser HD6XXs and (hopefully) enjoy!🎶🎹🎻

CD transport: Marantz CD52
DAC: JE Labs nosTDA1541tube + PCLoctal output
Preamp: JE Labs PCL76 line stage 
Amp: JE Labs SE300B mono blocks with Tango NY15S
Speakers: Altec 753C

Maybe 🤔 I'll talk about my plate choke adventures with SE amps next time!😉






 

Saturday, May 6, 2023

Japanese Idler-Driven Turntable Part 3: Lafayette PK245

 

Page 12 of the 1958 Lafayette Radio Catalog


This is a Lafayette branded turntable manufactured by Teac of Japan in the late 50s. The drive system is an innovative implementation of the basic Rek O Kut L34/37 Rondine Jr. design.



I got this unit with pulverized motor mounts.


Since the original motor mounts are no longer available, I had to improvise by using rubber grommets... 

...and 1/2" x 0.72" 302 stainless steel springs 😊 from Grainger. IIRC, it was part number 1NDJ1.🤔

!!!UPDATE!!!

After further listening tests, I determined that the rubber shock mounts used in the Gray Research turntable were better suited to this design. They can be sourced from Surplus Sales of Nebraska, part number RPS 426-0001.



 The main bearing isn't as substantial compared to the Rek O Kut.


However, the captive bearing is highly polished and the threaded bottom cap houses a hardened gun metal blue thrust pad.


I used SAE 30 non-detergent oil for the main bearing and "Blue" 3-In-One for motor lubrication.


The aluminum platter is a little over 3 Lbs.


This hysteresis motor is similar to the unit fitted to the NEAT P58H. Please click here for full details on servicing that motor and etc. 

The pictures below highlight features unique to the PK245.


Top shell motor bearing reassembly sequence


The bottom shell motor bearing reassembly is exactly like the top shell except for the motor shaft terminating with a 3mm ball bearing on a thrust pad as shown above.


Motor wiring schematic



Gary at The Voice of Music refurbished the idler wheels above.


Idler wheel components


Reassembly sequence


Top = 78 rpm idler wheel + arm
Bottom = 16/33/45 rpm idler wheel + arm


Idler wheel reassembly sequence


60 Hz pulley dimensions + click here for more details regarding motor pulley alignment.



Happy tinkering and listening!