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!

2018 Index

January: Altec 2-way XO redux + Temporary Hi-Fi

February: Altec 32A, 32C, Emilar EH1210, EH800, EH500 and Faital Pro STH100 + RFI/2C22

March: Audio Silente TD124 idler wheel/main bearing end cap + XtremPro X1 USB DAC

April: Garrard 301 minor resto + M42 Camera bodies and lenses

May: Man Cave 2018 + Kutztown Spring Radio Show

June: Velvet Touch/Calrad SV12/SV16 viscous damped tonearms + Ortofon SPU#1s/Denon DL103 variants/spherical stylus

July: Lafayette SK98 reunion + Raspberry Pi 3B+

August: Parts Express 1" Horn/Waveguide Specials + Magnavox CDB473/Philips TDA1541
September: Azzolina Audio KS12024 + Noguchi Transformer Co. Closing

October: Kutztown Fall Radio Show + Hi-Fi Show in Manila

November: '70s Direct Drive Turntables + Manila Hi-Fi Show Pics- showcasing G.I.P. Laboratory

December: Denon Aluminum Cap + Susumu Sakuma + Morikawa SE2A3 Amp + Holiday Greetings/2018 Index

Happy Holidays and Wishing Everyone a Great New Year! 

Morikawa SE2A3 in Jose's Listening Room

Susumu Sakuma

Susumu Sakuma, RIP

(1943-2018)

Photo courtesy of my Flickr friend silver_night 300b 

more Sakuma photos

Sakuma-san and Brian "monofantastico" Clark were my mono hi-fi system heroes!

Denon Aluminum Body Cap

I've been a Denon DL103 user for more than two decades but never considered risking my $250 investment to modifications which involved removing the old and installing another body. 

To circumvent the risk of damaging the stylus/cantilever assembly, Steve Bedard came up with the Denon Aluminum Body Cap.   

The finely machined aluminum cap slips over the Denon DL103 body. I noticed a slightly tighter fit on the DL103R and DL103C1, due to the different housing material used for these higher end models.

Two longer metric bolts are supplied to fit the original Denon nuts to compensate for the added thickness when mounting the cartridge/cap combo to a head shell. 

It has been my experience in this hobby that every time the frequency extremes are improved, something gives and usually, it is the midrange that suffers. 

The classic DL103 is a case in point. It has a wonderful midrange but it has a tendency to congest in the high frequencies during complex musical passages. Brighter recordings can also sound sibilant while the lower frequencies can gain more definition. 

Through the years, Denon has addressed these issues with "upgraded" DL103 versions by revising the coil with finer quality wire and by using more inert materials for the housing. I have two of them - the current DL103R and its predecessor, the DL103C1. Both models refine the frequency extremes but at the expense of a drier and "less colorful" midrange.

Thankfully the "capped DL103" retains and focuses that midrange warmth, almost mimicking an SPU, while the frequency extremes are tidied up. There's just a hint of sibilance and congestion left with the "capped DL103."

Even if there was improvement across the audio band with the aluminum cap installed on either DL103R or DL103C, what was most apparent was better definition in the lower frequencies. 

Could it be that the upgraded DL103 models benefit less from the cap? Perhaps the distinction might be system dependent and/or merely a matter of taste? Just remember, I'm not a mainstream audiophile. 😉 

What I like most about the Denon Aluminum Body Cap is, it doesn't dampen the virtues of the DL103/103R/103C1. It highlights and improves upon what's already there. 

In the big scheme of things, it's hard to find this level of sonic upgrade for under $100. My DL103 is "capped" for good, highly recommended! 👍

November 2018 Hi-Fi Show Pics +

G.I.P. Laboratory

Room 646

GIP Monitor 1 (black)

GIP 225

GIP Monitor 1
+
GIP 225

Ben, Lin and Ayie

Francis, Ben and Mickey

Ben, Joey (Harana Audio), Allan (DEQX) and Suzuki-san (G.I.P Labs)

G.I.P. Laboratory + Harana Audio

Room 647

Tim de Paravicini of EAR
+
Tony aka November Hi-Fi Show head honcho

 A Visit to G.I.P. Labs

'70s Direct Drive Turntables (and Tonearms)

This is a follow up on the road less travelled article. In 2017, I went on a quest for direct drive turntables that I could acquire for under $250. For the past year I've been tinkering and listening to these four 70s era direct drive turntables to find out whether a direct drive turntable has a place in my ever-growing collection of audio equipment.

Each unit has its own unique approach to direct drive turntable design and was available either as an integrated unit (with tonearm) or as a plain motor unit. The Denon DP1250,  Kenwood KD500 and JVC QL5 are mid-priced models from the late 70s, while the Sony TTS2500 was a first generation early 70s top of the line direct drive unit designed to compete with the original Technics SP10, which, unfortunately, was not within my budget. 😞

Turntables

JVC QL5

JVC introduced the world's first quartz locked turntable in 1974. The QL5 employs quartz locked circuitry to control its 12 pole 24 slot DC type motor. Its jet black plinth is made out of heavy particle board. The motor unit was also sold sans tonearm as the QL50.

Kenwood KD500

Instead of the complex electronics found in the Denon, JVC and Sony, the KD500 uses a relatively simple servo circuit referenced to a frequency generator modulating an 8 pole 24 slot brushless DC motor. This turntable developed a following in the late 70s due to the use of a highly inert and heavy synthetic marble plinth.

 This particular unit was loaned to me by my buddy Ding. He's had it stored for many years. It ran way too fast at first turn on so I replaced these four bulging capacitors immediately.

Denon DP1250

Unlike the two preceding turntables, the DP1250 uses an AC motor which minimizes cogging, according to period Denon sales literature. The motor is governed by a unique tape head inspired speed regulating system. The plinth is a substantial plywood/particle board laminate similar in mass to the JVC.

Sony TTS2500

The Sony TTS2500 is the motor unit of the worldwide bound Sony PS-2250/2251. Just like the Denon, it also uses an AC motor regulated by a servo circuit that is claimed to be practically cog-less in operation. This JDM (Japanese Domestic Market) model requires a 100V step down transformer. The half-finished laminated plywood plinth was DIY'ed by yours truly.😎

Tonearms

In a typical audiophile shootout these turntables would have been fitted with the same tonearm/cartridge combination and plinth. But this was not practical since I wanted to test under real world conditions. So to satisfy JE Labs' retro-centric streak,😉 for the Denon and Sony, I chose period correct gimbal bearing type tonearms that are known to perform on a similar musical level as those supplied with the QL5 and KD550.

JVC QL5 Tonearm

The QL5 is equipped with a tonearm that looks like an economy version of their well regarded UA-5045. With an effective length of 245mm, it is a bit longer than the three 237mm tonearms below.

Kenwood KD550 Tonearm

Ding had a Grace 707 installed before moth-balling this KD500. For some reason that tonearm went AWOL. Fortunately I had the original tonearm supplied with the KD550 in my stash. There are claims that this may have been OEM'd either by Acos or Micro-Seiki?

Rega R200

It would've been nice if I had something along the lines of a Denon DA305 to fit on the DP1250. However, the Acos OEM'd Rega R200 I installed is also a well respected 70s classic. 

Grace 540L

I've always had a soft spot for Grace/Shinagawa tonearms ever since the Grace 707 opened my ears that fine quality tonearm design produces nice sounds. This Grace G540L has similar mass to the other three above. The lack of a cuing device and anti-skate betrays its pro-application heritage. It is the oldest of the bunch making it the perfect partner for the TTS2500.

Cartridge

Denon DL103R

 For critical listening I relied on a Denon DL103R mounted on a Sumiko HS-12 head-shell. But this didn't prevent me from mounting a variety of cartridges in my stash ranging from the cheap 'n cheerful AT 3600L to an Ortofon SPU.

Time travel to the 70s

 Without hesitation, I would choose any of these turntables over the 3-point suspension belt drive turntable I used and tweaked to the max in the 80s. The direct drive system has the sure-footed speed stability which eventually lured me to the TD124 in the late 80s. I should've jumped at bargain priced top of the line direct drives to play with in the 90s...alas, hindsight is 20/20.

Since direct drive solved the ills of wow and flutter, and noise which plagued the belt and idler drive system respectively, there should be minimal difference in the way any direct drive motor unit should sound, right? Not quite...

Denon AC motor (top)
Kenwood DC motor (bottom)

My most surprising discovery after living with all these turntables this past year was the difference in sound between the motors that power them. The DC-motor-powered JVC and Kenwood consistently sounded analytical, cold and forward, akin to a digital source, while the AC-propelled Denon and Sony were characteristically more laid back and warm, just like what I associate with analog sound.

 However, to put things in perspective, the Sony still outperformed the other three direct drives in key musical aspects. In particular, there is a "hardness" and loss of composure in complex musical passages that prevailed on the three units with the Sony exhibiting only the very least amount.

Sony TTS2500 + Stax UA-3NL

Still, the TTS2500 could not eclipse the performance of the 301 or the TD124s. But it is the only direct drive in this group to come close in mimicking the stately authority of the esteemed idler driven classics. 

For this achievement, I crowned the Sony with a 12" Stax UA-3NL tonearm.🍻