Tag Archives: equalizers

Lost to time: Check out the Fairchild 627 Equalizer circa 195nvr

fairchild_627_equalizerApologies for the poor image quiality; these came from the research department of a long-gone British broadcast-gear-manufacturer via some dampish papers that I purchased recently from a rare-books-dealer in London.  I had never heard of the Fairchild 627 ‘Variable Equalizer,’ even though I recently sold an example of its (even-more-rare) predecessor the model 540, which in retrospect seems to be the ‘boost’ sections of the 627 plus a mic preamp plus a 20-watt cutter-head power amp.  Well shit.  Now i wish I had measured the values of the triple-ganged frequency-select pots.  Why?  We will get to that in a minute.


vintage-unobtanium-fairchild-627-tube_1_99dc4f93df9c200f11996b06da8735f3image source

A quick google search suggests that there are thought to be only 5 Fairchild 627 equalizers in existence.  One seems to have sold on eBay recently in the $7000 region.  The 627 is a line-level EQ with continuously variable low and high bell boost sections as well as high and low roll offs. Unlike a Pultec, though, it is an active EQ, and it uses some pretty unusual circuitry – especially the high-cut section, which I don’t comprehend at all.


fairchild_627_equalizer_schematicOne point to note: T2 should be wired to reverse phase.  I was v excited to find this schematic, because it seems like a pretty easy piece to build – there is no mention of the proper B+ voltage, but 250 is generally a safe bet; there are no weird inductors (the UTC S-23 plate-load choke is an off-the shelf part, so we know its specs  -5000ohm DC, 300 henries); the audio transformers don’t need to handle DC and the turns ratios are spec’d:  BUT:  But.  Those triple-ganged pots.  WTF do we do about them?

Can anyone crack this case? Any insights, pls let us know in the comments section.

On the plus-side:  at very minimum, this schematic does reveal an excellent and easy way to implement a 6E5 seeing-eye tube simply paralleled to a grid in the audio path.  So at very least, now i know how to use those v excellent things in my mic preamps.  Way more evil than a VU meter.

Also: the 6SN7 output section is a neat little self-contained module; def worth trying it with a Hammond 156C choke and an Edcor 15K:600 1/2 watt.   The 156C is the closest modern part to the S23 spec; it is rated 150h and 3.7K ohm, seems close enough?  I used onna these on a hunch in my OP6-semi-clone and it worked just fine in that application, so I am guessing it may work fine here as well.  fairchild_627_boost_curvesfairchild_627_high_low_frequency_rolloffsfairchild_627_curves_2


Studio Outboard Gear Odds & Ends ’71- ’73

Urei_1176_1970Today: just a few things that caught my eye from ’71 -’73:  the ‘new’ black-cosmetic version of the Urei 1176, plus some odd bits from Soundcraftsmen and Sansui (I had no idea that they had made pro audio products), and another forgotten Quad-Eight rack device (see here for our earlier coverage of their very obscure reverb unit).  Also something called the ‘OP Reverberation’ …. anyone?  ,,,and a few unusual items from Martin.  Wrapping it up is the annoucement ad for the original API 525C, which has become one of my favorite compressors for vocals since we got one at Gold Coast Recorders.  If any of y’all are using the Martin or Quad-Eight kit, let us know!

Soundcraftsmen_RP10-12_1972Above: The Soundcraftsmen RP10-12 equalizer

Sansui_QSE_1_1971Above: The Sansui QSE-1 Quadraphonic Encoder

Quad-Eight_Filter_1972 Quad_Eight_1972Above: The Quad-Eight Variable Filter, Auto-Mix 23B compressor, EQ 312 channel EQ, and RV10 Reverb unitParasound_reverb_1971 Martin_Console_1972 MArtin_1972_2Above: the Martin SLM-1020B mixer, PEQ500 rackmount program EQ, and varispeed 3B tape machine speed controller.  API_525_1972

Forgotten 70s Pro Audio maker Gately Electronics

Gately_Stereo_Mixer_Briefcase_1970Above: Gately’s Stereo Briefcase Mixer circa 1970.

Gately Electronics was a Pennsylvania-based pro-audio manufacturing and importation/ distribution operation which seems to have operated between 1968 and 1975.  I often noticed adverts for their EM7 mixer in the old AES journals; the EM7 had a sort-of Pultec or maybe LANG vibe, and I was curious enough that when I found one AS-IS for $100 on eBay I went for it.  You can read my account of restoring my EM7 and its attendent EQ7 outboard equalizer accessory at this link.  The short version: it is a very well-built machine, and I was therefore surprised that Gately seems to be completely forgotten in the pro audio world.  Anyhow, I noticed that a pair of AS-IS Gately 1800 compressor cards went for an absurd amount of money on eBay last month, so I figured that maybe the world does need to know.  I therefore present: every piece of period documentation that I could find on Gately Electronics, its products, and operations.  Enjoy, and let us know if you are using any of this kit nowadays.

Gately_ProKitMixer_1972 Moms_Wholesome_Audio_Mixer_1973 Gately_ProKit_2_1974 Gately_PK6_EQ6_1972 Gately_C1616_Console_1975 Gately_ad_1974 Gately_1974_Micromixer

Above, from top to bottom: Gately ProKit 6-channel mixer (available as kit or assembled!), Gately’s Moms Wholesome Audio live PA board, Gately ProKit 2 mixer, and Gately EQ-6 and EK-6 equalizer and reverb accessories for the Pro-Kit (confused yet?).  Below that, John Yoder of Hope Recordings recommends the Gately C1616 studio console.  Next is an advert announcing Gately’s distribution of Ortofon lathes and Schoeps mics (yes please). Finally we see the Gately Micromixer, which appears to perhaps be the same as Moms Wholesome Audio Mixer?







Above: the Gately EM7 and EQ7, as described in my earlier article, followed by the subsequent updated versions EM7s and PEQ7.  The PEQ7 seems to have exchanged th fixed hi-shelf control of the EQ7 for a five-frequency high bell curve EQ.  Low frequency control is presumably still a shelf-type.   I can’t find any other info on the ES-7 echo unit.

In 1974 a writer from DB (I imagine Woram or Zide; no credit is indicated) traveled to Gately’s Philadelphia-area facility.

You can download the account of their trip at this link: Gately_DB_Feb74

Gately_Factory_1974_2Gately_Factory_1974If there are any Gately alums out there, drop us a line; and if anyone out there is using any of this Gately kit, please let us know your thoughts.  I have yet to use my EM7 and EQ7 on a production, but at some point I hope to be able to do a shoot-out versus some better-known contemporary units such as API and Neve.




From PS dot com reader J. Roberts:

“I have a Gately Prokit II that I bought from Bob Todrank back around 1976. Bob had one of the first audio businesses in Berry Hill.

The mixer still works, no repairs ever, factory wired, I think it may be something like serial # 101w, but I will have to look and see. I kept a search on ebay for Gately and finally something surfaced… an original manual for my mixer.

I like that mixer because it is simple, no eq or anything to mess up, just set levels and pan. Interesting that the headphone out has no volume control, but I bought an old pair of Koss with faders just to use with that mixer. It looks to have very high quality components.  I do not know about ICs, wondering if the ones in there are ok or should be upgraded.  Does not have the output transformer option either.  In a day or two I plan to feed a Coopersound micpre into the line ins and see what I get.  I guess I should lay down some tracks and make another classical guitar LP, as I did back around 1978. Mastered at NRP by Larry Boden. Very fun times.”

Cinema Sound Circa 1953

Today: some random bits+bobs of Sound-For-Film technology of the early 1950s.  Above: the All-New JBL Theatre Sound Systems, which claim to offer the higher-fidelity needed to properly reproduce the newly-available magnetic soundtracks that were being used in 35mm film at the time.  Prior to the introduction of magnetic 35mm film soundtracks in the 1950s, all film-sound was reproduced in theaters via an optical sound-track which ran alongside the edge of the film-frames.  Fidelity was limited, although I cannot say exactly to what frequency range.  Can anyone tell us what the first feature-film was to be exhibited nationwide with a magnetic soundtrack?

Above: Cinema Engineering presents… the fader!  Straight-line attenuators have certain advantages over rotary controls, such as quicker visual feedback and a range of motion that better correlates with human bio-mechanical consideration.  Nonetheless, rotary faders remained in use in pro audio well into the late 60s.  Does anyone know who first patented and/or marketed the linear fader?

Above: the Cinema Engineering 6517-E ‘Sound Effects Filter,’ aka a high-pass and a low-pass filter both built into a single instrument.   I could find this sort of thing very useful; especially for tracking multiple ‘stacked’ parts such as one singer delivering 7 vocal harmonies over a single phrase, as I found myself doing in a session earlier this week.  Just carve out all of the unnecessary super-high and super-low end… the 80 or 100 hz high-pass filter built into many mic preamps is certainly useful but it’s obvs not always the best cut off choice.

Above: an advert for Glen Glenn Motion Picture Sound Co. circa 1953.  Anyone out there work for this firm?  We’d love to hear yr stories….  drop us a line…

Above: RCA’s ‘film phonograph,’ an apparatus that records and plays-back 35 mm magnetic sound-tracks and plays-back 35mm optical sound tracks as well.  I ended up with a couple of 16mm sound track readers at Gold Coast Recorders; not sure what to do with them.  Has anyone had any luck converting an optical-track reader into a signal processing or signal generating device?  Seems like there’s some potential to make it into  interesting experimental instrument; strobe-light-controlled oscillator perhaps?



Pultec 1977 Full-Line Catalog

Download the complete twelve-page 1977 Pultec outboard audio equipment catalog:

DOWNLOAD: Pultec-1977_catalog

Units covered, with text, specs, and photos, include: Pultec EQH-2, EQP-1A3, and MEQ-5 equalizers; Pultec HLF-3c and HLF-26 filters; Pultec SP3 and MH4 mixers.

Until I saw this catalog I had not realized that the original Pultec production run had extended into 1977.  These are the solid-state Pultecs, not the more coveted vacuum tube units that trade in the $5000 range, but AFAIK the actual equalization stages are the same as in the earlier tube units.  I have never scratch-built a Pultec clone, largely because the idea of hand-building the multi-tapped inductors always seemed a little daunting to me.   I recently found myself in possession of a large batch of various MiniDuctors, though, and I am wondering if these can be put service in a Pultec-type circuit.  The mH values are very close to those in the putlec schematics, but I cannot find any reference online to anyone building a Pultec using MiniDuctors rather than a large coil-wound inductor.  Anyone have any idea about this?



Audio Anthology: Collected Hi-Fi articles from AUDIO ENGINEERING in the 1940s

PS dot com reader Paul R. was kind enough to send us a scan of “Audio Anthology,” (ed. C.G. McProud) a 124pp softcover published in 1950.  “Audio Anthology” (hf. ‘AA’) is a collection of project-construction articles aimed at hi-fi (rather than pro audio) enthusiasts.  All of the material had been previously published in Audio Engineering magazine during its first four years of publication (1947 -1950).  See here, here, here, here, here, and here for previous 1940’s AUDIO ENGINEERING MAGAZINE coverage on PreservationSound. 

Above, an interesting boost-EQ stage that could be helpful in an instrument or mic amplifier.  Can any of our helpful readers advise which caps or resistors in this circuit could be modified (and within what range) to alter the turnover frequency of the two filters at work here?  I am guessing that the answer is: all four caps that follow the input DC blocking cap… which would basically get us back to this piece, which i swore i would never build again…

Above, the most complicated tube amp I have ever seen.  Kinda feel like Shadow Hills Engineering must have come across this image at some point.  Dynamic noise suppressor, phono pre, two eq controls, visual feedback of high and low frequency drive, variable metering, tons of input switching… talk about the kitchen sink.  This project is organized around the very interesting 6AS7G dual-triode power amplifier tube: basically two 2A3s in one glass envelope with a 6V heater supply.  This is potentially some useful information, especially when you consider that a 6As7G is only about $13 from AES (priced out 2A3s lately?). I think that there could be a unique new guitar amplifier in the works soon…

My lord.  At least they didn’t try to thrown in an AM/FM tuner.  Follow the link at the end of the this post for schematics and parts lists for some 6AS7G amplifiers.

‘Audio Anthology Vol 1’ is available at Amazon dot com.

FOLLOW THE LINK BELOW for 6AS7G project schematics…

Continue reading Audio Anthology: Collected Hi-Fi articles from AUDIO ENGINEERING in the 1940s

UPDATE: Vacuum Tube Program EQ project – Part 2

The vacuum-tube powered program EQ that I described in this previous post is nearly complete.  This thing has sat on the shelf for a while, as it was a little daunting dealing with all those parts inside a 17x4x3 chassis.  So far so good, though…  very excited to fire this thing up in a session.

Here you can see the frequency-selection switches all wired up.   The switches are 5-way, single-deck switches with the exception of the hi cut, which requires a 2-gang switch.  The EQ has separate boost and cut sections, like a pultec, with 5 selectable frequencies for each.  The amount of boost shelving is variable via a pot, while the attenuation controls are fixed cut.  It would be easy to make the cut controls variable as well, but as you can see I am a little short on space!  I suppose I should use a 3U enclosure the next time.  Alright stay tuned…

UPDATE: This piece was finished, and it sold to a prominent producer/engineer before I had the chance to record a thorough demo of it.  It worked out very well. The circuit performed as-advertised, and the only problem was that it had a little too much gain – enough to use a mic preamp in the majority of situations.  Since it has sold it’s been used on several major records; when these albums are released I will provide links to some of the sounds tracked through it.