Tag Archives: RCA

The Future Of Audio (1962 edition)

IMG_0001In May of 1962 “AUDIO” magazine celebrated its 15th anniversary.  IIRC, AUDIO was the more consumer-facing half of what had initially been AUDIO ENGINEERING magazine; the AES Journal being created sometime in the 50s to carry the more professional articles.  Anyhow, for their 15th, AUDIO asked some of the experts of the time to weigh in on THE FUTURE OF AUDIO.  Harry Olson, certainly one of the greatest inventors of sound equipment who ever lived, had some comments that struck me as being incredibly prescient.  I’ve never seen this reproduced anywhere, so check it out, enjoy it, share it, and take a minute to speculate on where this is all going.



The 1959 Ikegami-Tushin Limiter Inspired by the RCA BA6A

NHK_D_1Reader S. Komiya recently contacted us with some information regarding the Ikegami-Tushin limiting amplifier, an RCA BA-6A inspired piece that was built for Japanese broadcaster NHK in 1959.

SK has been so kind as to provide the schematic for this obscure device, as well as some background information.  I am posting the schematic full-size, so you can control-click it and download it for detailed viewing.

00_schematics_ikegami-limiter1959NHK_E1The photos in this post come from this Japanese auction website; the device pictured here recently sold for just Y30,000 ($300 USD).  And in working condition. 

600x450-2015011900002Here’s what SK has to say about the Ikegami-Tushin Limiter:

‘(It is) very much inspired by the RCA BA6A for sure.  It even looks a bit like it.  The tube format is very similar:  just change 6sk7 to 6ba6, 6j7 to 6au6 those goes into 6v6 PP and transformers between 6au6.  6ba6 were popular and cheap in japan because we made those a lot in japan in the 1950s and 60s.

6sk7 and 6j7 were never made in japan.  This unit also has an extra gain stage before first stage, which is pretty neat.  The components seem very high-end and some are custom made for this.  When i was gathering info about the ba6a in old tube shop, an older ham radio guy told me that he DIY’d one of these a long time ago…’NHKH_1NHKF_1*************



20141230_123551SK also recently built his own BA6A from scratch.  It is depicted above, and you can hear audio samples of it at his soundcloud page.  SK has also scratch-built the Federal AM864 tube limiter, and he has this to say about the projects:

“The sound you will hear in soundcloud is a good comparison with the fed864.   The fed has good high open but compressed sound,  the ba6a has low mid, ton of low mid. I love them both.  The first time I used them was at a studio in Chicago back in 90s when I was living in US.  At that time I was using LA-2A mainly, but that studio had a Fed864 and BA6A.  They blew my mind, and since then I wanted them so bad!’

SK also provided some build-notes on his BA6A project; if you are planning on building you own BA6A, you might find these useful:  S_Komiya_RCA_Ba6a_DIY_notes

RCA 100 Series Broadcast Components of the 70s – complete tech info

RCA_BE100_faceYears ago I ‘lunchboxed’ one of those above-depicted RCA BE100 equalizer modules.  The RCA 100 series of the early 70s was the end-of-the-line for RCA’s pro audio gear.  The series consisted of the MI-141651 op amp, the BMM-100 Mixer (channel strip, aka MI-141550), BE-100 EQ (aka MI0141560), BA-101 and BA-103 preamps (also designated as MI-141501, MI-141503), BMM-110 Submaster module (aka MI-141570), and BIM-100 Isomix amplifier (aka MI-141520).

RCA_opampsSince I seem to be one of the few fools who has publicly admitted to spending time messing around with these things, I’ve gotten several requests over the years for the accompanying data and schematics. Well guess what. TIME HAS COME TODAY.  Download all of the tech date for all of these modules.



RCA Solid State Audio Projects c. 1968

RCA_1968I’d never been particularly interested in learning solid state electronics.  There just didn’t seem much point; considering that you can buy a 4-channel Sytek mic preamp for $900, there just ain’t much to motivate anyone to DIY ss kit.  Tube stuff is another matter – it’s a different sound, and well-made ‘real’ high-plate-voltage, transformer i/0 tube gear is super-expensive.  So I learned to make the tube gear both for my own studio and as a way to make some add’l income by custom-building for other engineers.

All that being said, there is an undeniable appeal to be able to build something useful that doesn’t require a heater circuit and the attendant 60-cycle-hum battles that come from those hi-current windings.  Solid state is just easier, which is prolly why it has won-out in the world of consumer electronics, if not necessarily in the pro-audio world.  In my endless diggin for ancient tubes and transformers and bakelite meters I invariably come across stashes of ole germanium and silicon transistors, and I recently decided to take the plunge and try and cross this bridge once and for all.  Cos I can talk tubes and tube audio circuits up+down, but frankly I don’t know shit abt solid-state and maybe it’s time I learned.


The old RCA Tube Manuals have always been my primary source of information for my tube-audio builds and experiments.  The circuits that they recommend are the most solid, reliable, and practical that you will ever find.  I trust them implicitly.  And why not?  After all, this was the company that made the tubes themselves!  So when I decided to try and get into SS, I started with the RCA Solid-State Hobby Circuits Manual.  In the scan above you will find a mic preamp, a line-level compressor, and a fuzz pedal.  I’ll be building all three eventually and I will LYK how it goes.  In the meantime, if any of y’all beat me to it, drop us a line and report back,,,

RCA_SS_MicPre_Schem RCA_FuzzBox_1968_schematic RCA_SS_Comp_1968



RCA’s ‘Starmaker’-brand prosumer mics of the 70’s

Starmaker_RCADownload an eight-panel catalog for the RCA “Starmaker” lineup of 1970s prosumer microphones:

DOWNLOAD: RCA_Starmaker_Mics

Not to be confused with the RCA BK-4 “Starmaker” hand-held ribbon mic of the 1950s, these later Starmakers were cheap prosumer and consumer units.  Models on offer included the Starmaker 96, 97, 98, 101, 99, and 100.  The top-of-the-range 96 has decent specs and useful features; gonna keep an eye out for that one.


UPDATED: Compressor Roundup c. 1963

Compressors_1963_1Today on PS dot come: a short but v v informative piece from BROADCAST ENGINEERING , July 1963, which gives specs for nearly all of the broadcast compressors that were available that year.  Models covered include: Collins 26J Auto-level, Collins 356E, Fairchild 666A, 666, and 663; Gates M-5167 Sta-Level, GE BA-9 Uni-levele, ITA AGC-1A, Langevin AM-5301 Leveline, Quindar QCA-2, and the RCA BA-25A

DOWNLOAD: Compressors1963

UPDATE: T. Fine was so kind as to provide the entire 3-part article as a compact PDF.  click here to download it: BrdctEngnrgAudioLeveling_1963


RCA microphones circa 1963 – 1965

RCA_mics_1963Above: RCA 77, BK1, BK5, and a slew of others, all referred to by their ‘alternate’ MA-designations: the MA-2311, 2313, 2314, 2315, 2316, 2317, 2318, and 2319.   Can someone tell us why RCA used standard model names, MA designations, and MI designations?  Was it so they could charge certain customers more money for the same products?

RCA_Mics_1964Oh and let’s not forget the SK–designations.  Anyway, here’s the SAME products in the SAME publication one year later.  Confusing.

RCA_BK5B_1965So true.  What more DO you need in a mic?  The RCA BK-5 is one of my all-time favs.  No other ribbon mic sounds remotely like it.  If you dig ribbon mics, save up for one of these.  You will not be disappointed.  Especially if you need to tame a sibilant vocal while retaining an overall ‘bright’ and forward sound.   Also killer on piano, guitar amps, and probably everything else, actually…

RCA BC-2B Recording Studio Console c. 1952

Reader T.F. sent me this scan from AUDIO ENGINEERING c. 1952: the introduction of the RCA BC-2B Console.

LEFT: The BC-2B incorporated the RCA MA-11241 dual mic pre-amp unit; a two-stage circuit, each channel used a single 12AY7 for, I would suppose, about 25 – 30 db of gain.  The schem for the 11241 is posted below here.  Notice that, similar to the earlier octal-pentode based RCA mic pres, the full B+ current flows through the output transformer; this severely limits your choice of output transformer: the only vintage full-fidelity units that I am aware of are the UTC A-25 and LS-27.  Lundahl makes a modern unit that satisfies this spec, as does Hashimoto (HL-20K-6); very expensive pieces tho!  Any of you fellas know of  other 15k:600 1/2 watt transformers that handle 8ma unbalanced DC and still pass 40 – 20K?

(image source)

Here’s a dude that’s cloning the BC2B preamp; price is $650 for the preamp plus another $450 for the power supply.  Assuming that the build-quality is good, $1100 is a pretty fair price for this thing; I know how much those Lundahls cost ( I use the same O/T in my BRDCSTR as well) plus phantom power is a pain in the ass to build in.

RCA OP-6/BA-2 Hybrid Mic Pre Amp: Listening Test/Shootout

Alright!  So earlier this week I described the successful completion of the RCA OP-6/BA-2 microphone preamp.  Check out this previous post for all the construction and technical details.   The short story is: the RCA OP-6 is one of the most fetishized vintage mic preamps out there; I have always wanted to try one out; the easiest/cheapest way for me to do this was to build one (or at least as close as I could get).  The problem is that the input stage requires a special attenuator device, exact values unknown; therefore I had to substitute an input stage from another device.  I chose the input stage from the RCA BA-2, as I have built many of these and they always work great.  The result: a hybrid of the OP-6 and the BA-2.

OK so there it is.  Anyway, the very helpful+generous TW came by to help me out on this one.  I wanted to try the OP-6/BA-2 Hybrid (hf. OBH) on a couple of different sources with a couple different types of mics. We a/b’d the OBH with an API 512.  I use the API 512 as a benchmark for mic-pre shootouts because it’s a high-quality unit that many people own and use regularly.  What you are about to hear are identical mics tracked through the two different preamps, direct to Pro Tools via a Lynx Aurora.  Levels were matched. No other processing, level adjustment, or manipulation was done.  You are hearing exactly what came out of the preamps.  To appreciate the differences between the units, you will need to listen to these files on good headphones or a full-range speaker system.   If you listen on a system with a subwoofer (we used the Blue Sky system at Gold Cost Recorders), you will hear some dramatic differences.

OK.  So first up: let’s listen to the drum kit above.  These are vintage ludwig drums, 30″ kick, 12″ and 14″ toms, 14×5 wood snare.  Cymbals are fairly dark old Zildjans.    You are hearing two identical Shure SM-81s placed right next to each other, approx 8 feet in front of the kit, pointed directly at the kit.  The 10db pads on the SM81s are engaged.  The SM81 is not the prettiest sounding mic, but they have a very flat frequency response.

First: here’s the API 512:


…and here’s the OBH:

LISTEN: Drums_RCA_hybrid

Our impressions were as follows: the OBH has more low end extension.  On the Blue Sky system, the kick drum in the OBH signal moved the room in a way that the API simply could not.  The API seemed to move the kit a little closer to the plane of the speakers, but at the same time the top end was not as in-focus.  There is a definite low-midrange boost going on with the API.  I can say this with relative confidence because I measured the frequency response of the OBH and it is totally flat from 15Hz – 10K, with only a very slight raise above 10K.  In terms of operation: the API gain control was at 3 o’clock; the OBH was at 9 o’clock.  WOW that is a lot of gain.

Next, let’s listen to some acoustic guitar.  TW played an old Martin D-19 (same as a D-18) that i mic’d with a well-matched old pair of Beyer M260s ribbon mics. The M260 has a built-in gentle roll off that starts at around 200hz

Alright so take a listen.  First, the API 512:


…and now the OBH:

LISTEN: AcGtr_RCA_Hybrid

Our impressions were that the OBH had more low bass but less low mids; it had a more ‘mellow’ feeling.  The OBH also had better high-end extension.   This also resulted in slightly more HVAC (air conditioning) room noise in the OBH.  Although I like the sound of the OBH again here, it is less of a clear-cut choice.  The mid-boost that API seems to deliver is very welcome in this particular setup.

In summary: TW put it this way: ‘(the OBH) is like a pair of gentle shelves (shelving EQs) on the very highs a lows.’  I think this is very accurate.  The OBH seems to give what I think of as an English sound: that sort of larger-than-life, hyper-real sound that UK records have always aspired to.  I highly encourage your DIY’ers out there to give this project a shot; you will find it to be a very useful tool.

Thanks again to TW for his help with this listening test; T’s band THE STEPKIDS is just back from LA where they did a direct-to-vinyl (!) live set in front of a studio audience (!!!) at Capsule Mastering Labs.  Check out the details of this very cool endeavor here and here.