Click this link to stream a special two-hour Preservation Sound Radio show focusing on: Psychedelic Soul. (show starts approx 12 minutes into the file). This show was assembled in my studio and relayed for broadcast on WPKN. Audio-nerd notes: the entire program was assembled from my vinyl LP collection, freshly transferred via a vintage Denon DL207 MC cartridge through a 1:20 ADC step-up transformer unit I assembled this week. My voice via a 1950s EV 666.
Tracklist:
curtis mayfield DO DOO WAP IS STRONG IN HERE
cymande BIRD
the main ingredient SUMMER BREEZE
brother to brother I WISH IT WOULD RAIN
minnie ripperton LES FLEUR (set break)
soul searchers WE THE PEOPLE
the temptations SMILING FACES SOMETIME
junior parker TOMORROW NEVER KNOWS
manu dibango HIBISCUS
the dramatics IN THE RAIN
shuggie otis JENNIE LEE (set break)
rotary connection PAPER CASTLE
rasputin’s stash YOU BETTER THINK
edwin starr BALL OF CONFUSION
sly and the family stone TIME
james brown JUST ENOUGH ROOM FOR STORAGE (set break)
Above: prototype of a novel design for an economical all-tube headphone amplifier. I have been hunting for a way to build an all-tube cue amp into the @berlinettabrewing DJ console. I was forced to design this because no decent schematics exist anywhere online for something like this: something compact, simple, and inexpensive to make that can run either 600 ohm cans or modern low-impedance cans.
This design uses a basic voltage amp (1/2 a 12AX7, although a 12AT7 would work fine too) driving one paralleled cathode-follower 6CG7 per channel. In theory, with a big enough output cap and 300 plate volts, this SHOULD be able to drive 600 ohm headphones to a very high level. And it does. But here’s the twist: the “600 ohms” jack is a switching jack that, when blank, sends the signal to a pair of 600 ohm:8 ohm “70v” 5-watt line-to-voicecoil transformers: I used inexpensive old Stancors. These are the sort of transformers that you often find inside old schoolhouse baffle speakers.
At full rated level, the low end of these transformers is weak. But at the 1/2w that they see in this circuit, they sound absolutely fine. The amp sounds great with either variety of cans- i tried @akgaudio 600 ohm k240s and @audiotechnicausa ATHM50, which I suspect are 30 ohms-ish. Way way more then enough level, great fidelity and just great sound all around. A little experiment that paid off, coming soon to the world’s most esoteric DJ console.
I tried to imagine the sort of custom instrument preamp that a top session player might have brought to a studio in The Seventies. Similar in principle to an Alembic F2B (part of many top players’ rigs for decades) but with many crucial improvements, this compact all-tube preamp starts with a classic Fender blackface low/mid/high/bright/vol feature set but adds the following: *master volume, *hi shift, and most importantly an additional output stage that can reliably drive a 10k input at high levels with no frequency loss.
I learned a ton about the idiosyncratic Fender eq circuit by listening and fine-tuning this unit; the various compromises and ‘sweet spots’ that one can find with different cap and pot values. Basic three-stage filter power supply (output stage at 2nd leg) and c/t grounded AC heaters proved more than sufficient; the thing runs dead quiet (zero hum) other than a minuscule bit of reassuring hiss, as i used all NOS 1960s Allen Bradley carbon-comp resistors throughout (which id never do for a mic pre, but for vintage guitar/bass tone its part of the package, i think). The output stage runs at 350 volts, and the input and makeup stages are around 215, allowing for tons of headroom.
Above: the unit with the top cover removed. You can see the sub chassis with the 12AX7 and the 6C4 output driver; a huge Aerovox output cap; and the rugged fiberglass turret-board point-to-point construction.
Above: another internal view. All of the hardware bits are DakaWare, API, and Smith NOS parts from the 60s and 70s, all from my inventory. Signal wiring (orange) is stranded silver 22ga wire and the ground wire (green) is 18ga solid copper.
How does it sound? With bass guitar its absolutely magical- every classic electric bass sound is just there at your fingertips; very inspiring to play thru. Really sounds like a ‘finished’ bass track with no additional processing. The whole package is compact enough to fit in many gig bags. As for the name? “Super” as the circuit owes much to my beloved Fender Super Reverbs, and “Hugh” as an homage to one of my all-time favorite session greats Hugh McCracken.
I’ve serviced and modified many Altec 43X-series compressors over the years, but I think this may be only the 2nd one I’ve built entirely from scratch. Styled more like a Federal AM864, this unit incorporates many of the tweaks and modifications that I have come to like in these machines. Here are some images of the build.
Couple of things to point out in the photo above. Note the larger “Octal” tubes (6X5 rectifier and 6SN7 output amplifier) on the left side. I like octal tubes, as the larger sockets are easier to work with, so space-permitting I tend to use them. The original 43X used a solid-sate rectifier (with a voltage doubler) but I used a more conventional full-wave supply with a rectifier tube since it suited the look better. The 6SN7 output tube was a nice choice as there are so many variations of this tube available. It’s a direct sub for the 6CG7 in the original Altec.
Also note: behind the meter is a ‘meter null adjust’ pot. I can’t recall how this was handled on the original Altecs, but this mod is a common one shown on many internet schematics of the 436. Also note the large pot to the left of the meter. This is the Gates Sta Level output trim control (-6 to -14db cut) that I detailed on this site years ago. A worthy and necessary addition!
You can also see the enormous output transformer in the center: a massive potted unit built for Daven, likely by UTC. originally built for hi-end test gear, it is ultra hi fi and handles more level than this thing will ever see.
Above: some detail of the meter. I was motivated to build this thing solely because I found that original Altec panel meter at a hamfest for a buck. Seemed like it needed a 2nd life… Also check out that finish on the panel! That’s about 6 layers of paint and 3 layers of clearcoat, sanded between each coat. The knobs are all NOS 1960s DakaWare, acquired from Park Distributors in BPT CT (RIP).
Above: the UTC A18 input transformer, which has similar specs / ratio to the Peerless plug-in unit that an original Altec would have been outfitted with.
Above: the completed unit on the bench. The input pot is a really nice dual-gang 50K 1-watt sealed unit; I got several of these from Park before they closed. I cant imagine that any pot like this is available today for under $50. Good find. Running the length of the unit to the immediate right of the turret board is the heavy copper ground buss. Every ground in the machine connects here, and only here, and the ground buss meets the chassis at only one spot – the input jack. I swear by this construction technique. I’ve rewired a lot of old cheap tube guitar amps with this addition and the improvement in noise floor is remarkable.
I’ve been developing an all-tube rotary-knob DJ console for the soundsystem at Berlinetta Brewing. One idea I decided to experiment with was building the 4 channels of phono pre amps as little plug-in modules, similar to theatre soundsystems of the 1940s and 50s. This would, in theory, allow me to make just 5 of the modules and have “zero downtime” if/when a channel failed. Anyhow, I made one as a demo, and man what a pain in the ass! The device you see above and below uses the classic RCA circuit from their receiving tube manual RC20 plus an additional 6c4 cathode-follower output stage, all built in a tiny grey Hammond box. All i/o and power (300vdc B+, 7vDC heaters) are on an 8-pin Jones for maximum “fake historical authenticity.” It worked out fine, sounds great, very low noise floor, but it’s just too fussy working in that tiny 4x2x2 inch box I will probably end up going with a different solution. Still an interesting possibility though…
I was recently given this circa 1965 Fairchild model 663 optical compressor module. This unit was sold as part of their modular console range of the era. It requires 7V A/C power and it has a completely passive audio path! Seems incredible, but it’s true. Here’s what I did to ‘lunchbox it’ for standalone use in the studio. More details soon…
Detroit Box #001 featuring UTC Ouncer Transformer and O-17 magnetic shield
Last year I found myself with an excess of nice vintage 1:10 and 1:12 audio transformers, so I figured I would make some “Motown”-style passive DI boxes and see how they sounded. I built all of these using genuine 1960s era transformers, NOS Allen Bradley carbon-comp resistors, and NOS vintage hardware components in order to make something that ‘looked and felt’ like the sort of thing that a studio custom-shop would have built in that era. These aren’t copies of the Motown box – that piece used a particular model of transformer which I did not use, and I had my own aesthetic directions to pursue – but like the original units, they have that higher 1:12 ratio, variable defeatable pad, bi-directional operation (for use as a ‘re-amp’) and ground lift switch.
In the past I generally built my DIs with 1:5 or 1:8 ratios, so I was curious to see if the higher ratio gave a more open, detailed sound while still allowing for a sufficiently good signal-to-noise ratio. After building a half dozen of these things, I can say that yes they sound great. Here are a few examples of the units I built.
#002 and #003, a stereo pair featuring vintage UTC ouncers with magnetic shields and some NOS PREMIER-brand steel enclosures
#004 featuring a vintage UTC A-series with additional A33 shield package; in addition this unit features a stepped attenuator (rather than a pot).#005, again with a UTC O-series and shield#006; this one features a large Thordarson 1:12 transformer
I recently needed a pair of working Weston 862s. I only had one busted one, and a pair of 861s with different gfx that Weston OEM’d for some other firms. So i’ve scanned the 862 panel at 600DPI and I am going to attempt to print and re-cover the panels in the 861s. Wish me luck! Here’s the art at 600DPI if anyone else needs it:
This month’s P/S Radio show has already aired, but you can listen to the program via this archive link thru Jan 10 2020. As usual this show is broadcast 100% from vinyl. Check it out while you can, some incredible rarities here.
PS dot com reader Frank B sent in these pics of his SpectraSonics console. This 6×2 board was custom built for NBC Television in the late 60s or 70s. Here’s Frank’s description of it:
“..its one of a kind…6 preamps and two 610 limiters plus some high pass filters. It was built for nbc-tv. Im guessing this is the only one in existence….The wiring for the patchbay is unique and crazy. “
Interestingly the comp controls are located on the rear of the unit and the compressors have their own points on the bay. Frank, I am curious what that other board you have to the right of it is!
Any of yall got a custom mini-console by a big maker like this? Let us know!
