Tag: equalizers

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Publications Technical

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”
Categories
Custom Fabrication Technical

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. 

Categories
Technical

A Few Interesting DIY Audio Projects c. 1955

Circuit for a simple bass/treble parametric equalizer that uses no inductors.  Could be  a useful piece.  Not sure if 250k/500k dual pots are still available?  Since I have still not finished building the last tube EQ project that I described, so I’m not likely to craft this thing anytime soon.  If anyone out there picks this up and builds one, LMK…

Going back to AUDIO magazine in the early 50s: a few circuits that caught my eye. As always, if any of y’all out there build any of these, drop us a line and let us know how it went.

A ‘cascode’ preamp which features very high gain and defeatable compensation for phono cartridge.  I am not aware of any available mic preamp that uses this circuit.  a lot of gain available here…

A low-gain preamp that mixes two high-impedance signals to a medium-impedance output.  Add a few transformers (500: 50K inputs, 15k:600 output) and this could be a useful tool for selecting/blending two mic signals to one track of (tape).  IE put a couple of mics on a gtr amp, blend to taste… I generally do this using submasters (busses) on the console but here’s a potential way to do it that uses a much simpler signal path, IE right from the mics into the convertor (or tape machine).

A 50-watt ultralinear power amp using 6550 power tubes

A 12-watt 6V6 power amp with some negative feedback and a pentode input stage.

A simple 8-watt power amp that uses a 6SH7 input tube and a single 6L6 output.  This circuit uses a great deal of negative feedback in order to supposedly get more linear response with cheap output transformers.  I’ve never used the 6SH7 tube before…  curious though.

A simple design for a variable sawtooth wave generator.




Categories
Altec Pro Audio Archive

Pro Audio hardware of the early 1950s

The General Electric (GE) BA-5-A Limiter

Continuing our review of the first two years of AUDIO magazine, today we will look at some of the more interesting bits of pro audio kit in evidence during 1954/1955.  AUDIO magazine had just made the transition to its new moniker in the wake of the introduction of the AES Journal (Audio Engineering Society), and for the moment, AUDIO sill covered a bit of the pro audio equipment that would soon largely leave its pages.

The GE BA-5 pictured above is, AFAIK, the largest and most complicated analog audio compressor ever made.  Although it has much less tubes, it’s kinda even more sophisticated than the Fairchild 660/670.    Here’s the schematic if you are interested.  From what i recall,  the BA-5 works by creating an ultra high frequency sidechain to obtain the control voltage value for the compression; I can’t recall the details at the moment but the basic concept was to allow the unit to have huge amounts of compression with very fast timings, but without any pumping or dipping artifacts.  Which was also the intent of the 660/670 design.  If anyone out there has a better explanation of this monster, please chime in.

The General Electric BA-6-B remote amplifer/mixer

The General Electric BA-9-A compressor, a much more basic pro audio compressor.  Circuit is essentially the same as the Gates Sta-Level.  The BA-9 is also known as the the uni-level; schematics are readily available online.

The General Electric BA-1-F plug-in preamp and BA-12-C plug-in power amp

The Hycor 4201 equalizer.  Similar to a Pultec program EQ but without the makeup gain amp; the Hycor is a fully passive device.

Langevin 5116 modular preamp

The full Langevin modular line of 1954: 5116 preamp, 5117 power amp, and 5206, 5208 power supplies

Another remote amp from 1954 – the Magnasync G-924.  Looks very cool.  Magnasync would soon be merged with the Moviola corporation and become a brand name for sound-for-film equipment.  See this previous post for an experiment with the Magnsync URS device.

An early ad (1955) for the Altec 604 duplex loudspeaker.  The 604 would remain a studio-standard recording/mixing monitor speaker well into the 1970s.

Okay this is getting pretty tech-y but here’s an advert announcing some new-ish tubes you might want to consider: the Tung-sol 12AX7 and the 5881 (AKA ruggedized 6L6).   Transistors were on the market at this point (1955) but were a ways off from reaching the performance and reliability that these great tubes offered.

Categories
Pro Audio Archive

Orban Audio Processors of the 1980s

Download the four-page circa 1984 Orban ‘condensed catalog’:

DOWNLOAD: OrbanCondCatalog

Photos and descriptions (no specs) of the following models: Orban 111B reverberation; 245F stereo synthesizer; 418A stereo compressor/limiter; 424A Gated compressor/limiter/De-Esser (i.e.,  ‘make-it-as-loud-as-the-FCC-will-allow’ box); 516EC 3-channel De-Esser; 526A De-esser; 622B 2-channel parametric equalizer; 672A equalizer; 674A stereo equalizer.

I have been using a 111B reverb for many years in the studio to augment the usual reverb plug-ins.  It is the best spring reverb unit I have come across.  I have found that it absolutely needs a little pre-delay applied, or else weird phase cancellation occurs when I sum the reverb output back into the board along with the direct signal.  There are may easy ways to do this, but it is worth noting.

Orban was founded three decades ago by Bob Orban.  They have always made audio equipment aimed at the radio broadcast market.  Prices for their classic 80’s gear were reasonable until recently.  Plenty of these out there, tho, so if yr patient and you will get a deal.

Since Orban is in the business of supplying broadcasters, their website have excellent technical support.  You can download the original manuals for all their products at this link on their site.

Categories
Uncategorized

Fostex ‘Personal’ Outboard Equipment of the 1980s

Download fourteen-pages of original product information regarding FOSTEX’ “Personal Multitrack” outboard-equipment line of the 1980s:

DOWNLOAD: Fostex_Outboard_Gear_1986

Included in this download:  “Echo Buss Vol II, Take 1,” a FOSTEX newsletter to pro-sumer users of the 80s.  Plus 2-side product sheets for the 2050 line mixer, 3030 Graphic Equalizer, 3070 Compressor/Limiter, 3180 Reverb, and 6301 powered monitor speakers.

The 3180 offers a unique feature among line-level stereo spring reverb units:  a non-adjustable 24ms pre-delay hardwired before the spring drive amp.

Interesting to note that FOSTEX makes no attempt to disguise these pieces as pro-studio equipment; they were designed and marketed specifically for use in the new ‘personal studio’ of the early 1980s, alongside such other FOSTEX offerings as the personal reel-to-reel multitrack and the FOSTEX 250 cassette four-track.  See previous posts here, here and here for information on these recording devices.

The Fostex 6301 powered monitors did enjoy wider use, though; true to the photo at top, these compact 10w powered speakers did in fact experience wide use in video-facility machine rooms as basic program monitors.  Many are still in use in this role.

Categories
Technical

Simple Tube Program EQ project

From the September 1947 issue of RADIOCRAFT magazine: an interesting ‘response equalizer’ project that looks to have great potential for use in the recording studio.  Download the complete article with schematics:

DOWNLOAD: ResponseEQ1947

You will need to download and read the article for complete details, but essentially this circuit provides the following functionality, with 7 controls:  4-position high-pass.; variable low-end boost with 4 selectable frequencies; 4-position low pass; variable high-end boost with 4 selectable frequencies; 10db overall gain with variable output trim.  And it does all of this with no inductors or transformers, and just one very cheap 6SJ7 tube.

To use this circuit in a complete studio-ready device, we will need to add several things:  First, an output stage capable of easily driving a 15k:600 output transformer.  I am going to try the very simple output circuit show above, taken from tubecad.com.

A 250-300v DC power supply (plus 6.3v filament power) will also be necessary; plus input and output transformers.  Once I get this all together, I will also need to figure out a good, silent bypass-switching arrangement.   Should be a good inexpensive tube eq project.   The overall application is very similar to the Pultec EQP-1A; this unit will not have as precise control due to the lack of inductors; but it will cost a heck of a lot less (likely $250 of parts verses $800 to build a Pultec).  Plus it allows one to boost and cut at different frequencies, which the Pultec does not offer.  Expect some build-notes, images, and audio examples here soon.