(Re)building a Hi-Fi Room

ca. 2006

Eight years ago I vacated this space, not knowing that I would be back someday...

Late Spring 2016

Altec 861 cabinet

Among those that didn't make it into the 20 foot container in 2008 was a pair of Altec 861 cabinets loaded with generic 15" drivers. I used one temporarily to get some sounds going in the room while I figured out how to repurpose the other cabinet.

Amplification

Grommes LJ2

 This sweet "Little Jewel" PP6V6 integrated mono amp fired up with no problems after almost 8 years of silence.

Rek O Kut B12GH + Velvet Touch

My hand-carried Velvet Touch tonearm "blu-tacked" on a ROK B12GH and mounted on a state-of-the-art crate plinth. 

After a thorough cleaning and re-lubrication of the main bearing, Papst motor and replacement of motor mounts, the dreaded motor vibration is still felt on the tonearm finger lift. I have to send the idler wheel to Terry Witt for a rebuild and plan on building a heavy plinth.

Unlike the fussy Rek O Kut, this Pioneer PL6U is running quietly on its original lightweight plinth after I replaced the 3 perished rubber motor mounts with rubber grommets + light cleaning and re-lubrication. It sounds great with a $40 Stanton 500 cartridge!  

Pioneer PL6U

Line-level sources

KLH Model Twenty One

Classic Hi-Fi FM table radio found in a bicycle shop. 

Western Electric 111C
+
UTC A20

Stereo > Mono transformer mixer for the iPod Nano

Hi Eff Speaker

Since the Altec 861 (aka Madrid) share a similar internal volume with the Altec 614, I went to Lowe's to get 3/4" plywood cut to the size of the front panel. Using a Harbor Freight Router + Jasper Jig 200, I cut a hole for a rear mounted Altec 414A and a rectangular 2" x 7" port to mimic an Altec 614.

Altec 2-way

Altec 861 loaded with an Altec 414A running full range augmented on top by an Emilar EH800 horn or Altec 32A horn with an Emilar EA175-16 compression driver.

Work in progress...

Altec 605B experiments

Hot on the trail from the 1" compression driver survey, I set forth to re-evaluate my open baffle mounted Altec 605B. This Duplex system is essentially an Altec 416A woofer + Altec 806A compression driver with an integral short horn. I wanted to address a mild honk and try to squeeze out more "air" in the top end from the horn/driver combo.

605B as a 416A woofer

Since my modus operandi has always been to listen carefully to each component as a separate entity, I disconnected the compression driver from the N1600C crossover and listened to the woofer rolling off at about 1100 hz as well as bypassing the crossover, in full range mode. 

After several days of listening with and without the crossover, I realized that the "honk" actually emanated from the woofer. Perhaps this was due to the typical midrange impedance rise in a woofer exacerbated in an open baffle by the lack of a true enclosure? So I winged and auditioned a few Zobel EQ values and ended up with 10 ohms + 11uf in parallel with the woofer terminals as the "best compromise." This circuit cost a couple of dB in efficiency but did not significantly affect dynamics while minimizing the honk. 

Towel damping

Not scientific, but hanging a towel behind the driver focused the sound a bit further ;)

+ Altec 32C horn

For kicks, I did another round of listening with the 605B acting as a woofer coupled to the Altec 32C horn using the same drivers (except the Beyma) and crossover options discussed in the previous survey. But unlike the 12" Altec 414A which has a smooth roll off characteristic, the 605B woofer had to be configured as outlined above. In this configuration, the woofer blended nicely with all four drivers. In fact the 605B woofer section + 32C/802D horn combo had a similar midrange tonal balance to the Altec 2-way. Could that be a 32C horn coloration? ;)

Altec 16 ohm diaphragms

The Altec 605B was factory fitted with the aluminum voice coil 20275 diaphragm. By the time I acquired it, the diaphragm has been replaced with the newer 34852 with a copper voice coil. I've swapped the 34852 and the 20275 (from my 802D) in and out of the 605B and always preferred the midrange oriented 20275 over the more extended high frequencies from the 34852. Thus, to my ears the 34852 and 20275 cannot be used as a stereo pair. Alas, NOS 20275s are very scarce but fortunately GPA is reproducing original 34852 diaphragms. Just to make sure my 34852 is an original Altec item I posted a query at the Altec Users' Board.

34852 vs. 20275

Having confirmed that my 34852 was genuine, I compared the JEL/N1600C XO to the stock N1600C in search of more sparkle and air from the 806A. The JEL/N1600C with EQ circuit did augment the top end a bit, but not to the same degree achieved by the other drivers with more powerful magnets used in the 32B horn experiment above. With or without the Zobel network, I found too much depression in the midrange of the 605B. This was most notable in the vocal range but not as audible with instrumental music. Switching to the 20275 diaphragm improved the midrange a smidgen but I was still not fully convinced that using the JEL/N1600C XO was the proper course.

Coda

Altec N1600C + Zobel EQ

For now I'll continue using the Altec 605B with the N1600C crossover with Zobel EQ + a sparkler...

Sparkler = Altec 3000H

VPI 16.5 - New Housing

I got this machine in the early 90s from Steve at Angela Instruments when he upgraded to a more deluxe unit. It was originally a VPI 16 (note the traces of the lid mounted vacuum nozzle), surplus from Towson University Library. Eventually the turntable motor burned out and when I placed an order for a replacement motor, I also opted for the ".5 upgrade kit". 

After 8 years in the tropics, the particle board housing started to rot due to extreme humidity.  So I took it apart, labelled the wiring and took pictures for easier reassembly.

I enlisted the help of Joey's woodworking shop foreman, Badjo, to duplicate the original using higher quality phenolic plywood.

This is the new box in its final reassembly phase - vacuum motor installed, turntable motor, platter and switch plate next.

Good for another lifetime?

With over 2000 LPs to care for, I need a back up in the form of my trusty Nitty-Gritty 1 from the 80s ;)

Mar Roxas + Leni Robredo 2016

Stereo > Mono Line Level Mixer - ***Revised 4/12/21***

Mixing line level stereophonic signals into full dimensional monophonic ;)

Here's a DIY project for mono aficionados that's so basic, I should have uploaded it many years ago. But other things got in the way.

Just like an MC step-up, these are entirely passive devices. 

The simplest way to convert stereo to mono is to connect left and right channels via a Y connector. But there's a more elegant way than just shorting two channels.

Resistors can blend two signals into one better by...

...using Allen-Bradley carbon composition for warmer sound ;)

Line Output Transformers

This single UTC A-20 transformer was in a box lot of tubes and parts I picked up at a radio show. It's a high quality transformer designed for mic, mixer or line matching applications. Instead of trying to find a mate for MC step-up duty, I repurposed it for a greater calling in my mono rig.

With a claimed bandwidth of 10-50,000 hz and dual windings in the primary and secondary, it is perfect for mixing line level stereo signals into mono!

Left and right channels from a stereo source are fed into each primary winding. The summed mono output is taken from the series-connected secondary winding, which goes into the line level input of a mono preamp.

April 12, 2021 update!

The Covid 19 lockdown was a good opportunity to reassess past projects.

I realized that my original practice of connecting the left and right stereo channels to the split primaries of a single UTC A20 line transformer was sonically inferior to the 2 x Tamura line transformers with their secondaries connected in series as shown above. 

The classic UTC A20 and A21 are still very fine contenders but two are needed instead of one. Use the specs above as a guide for hunting transformers under the radar. 

If you prefer modern transformers, I highly recommend contacting dave slagle of Intact Audio. He winds fine sounding transformers to spec using high quality materials.

He generously provided the following technical explanation as to why my original recommendation was flawed.

• if the L & R outputs share the same core they are effectively in parallel even if the secondaries are connected in series
• if the L & R are on discrete cores and the secondaries are in parallel the circuit can be drawn as one channel driving the other through two transformers
• if the L & R are on discrete cores and the secondaries in series then the load is also part of the series circuit so a high impedance is reflected back

Subjectively, using a single transformer I heard truncated frequency extremes, compressed dynamics and less detail. With two transformers the sound was cleaner and more articulate with more extension at frequency extremes. Dynamic nuances at micro and macro levels improved significantly. There's also a greater sense of space and ambience!