Category Archives: Technical

The Limits of Control

How much control over their audio do music-listeners want and need? At the very least, we can agree that they need to be able to turn the sound on and off.  Control over volume (level) is probably the next most important thing.  But beyond that… what is really necessary, what is really desired, and what is just marketing?

I came across this RCA  vacuum-tube reverberation system this past weekend at the flea market.  It was new, in the box, never removed from its packaging.  Likely an ill-advised Christmas gift from the Eisenhower era.   It cost me one dollar.

This device was sold as an add-on to certain RCA stereo hi-fi consoles of the late 1950s.  Owners of these certain consoles could purchase the unit, open up their console, install a few metal boxes, plug in some cable harnesses… and voila.

The listener would then be able to selectively add reverb (ie., artificial echo) to whatever audio they were listening to.  Overall, the whole operation is about as difficult as installing your own car stereo.

This concept seems patently absurd to me, and i love reverb.  I love reverb on my guitar amp, i love the reverb chambers and plug-ins that I use in the studio…  but the idea of adding reverb to a recording which has already been mixed a certain way…  it simply would never cross my mind.

Getting back to my earlier line:  beyond on/off and level, what do we really want/need as audio listeners?  Someone decided a very long time ago that Bass and Treble control was pretty much a necessity, and there knobs (or sub-menus, as the case may be) have graced pretty much every audio amplifier since.

These controls were originally marketed as a solution for ‘poor room acoustics.’  Really?  It seems a little fishy to me.  If I go into a room that is bright-sounding, do I attempt to speak in a bassier-voice?   Used properly, there is no harm i suppose.  OK so Bass and Treble (note the convenient binary; also the reference to the musical staffs) seem alright.

So once we’ve given listeners control over the relative amounts of low-and-high frequencies, the next thing that manufacturers introduced were these reverberation units.  And they made them for everything.  Hell, they even made them for CARS.

(web source)

So weird.  Here’s a few 1970’s Japanese-made units.  This was clearly not a short-lived craze.

(web sources)

So we’ve given listeners the ability to control frequency response.  We’ve given them the ability to manipulate the apparent size of the space in which the recording took place.  What’s next?  In the 1970s, the DBX corporation sold hundreds of thousands of units just like this.

(web source)

A dynamic-range controller for home audio listening.  Now consumers could elect to give their recordings more dynamic range (IE more volume difference between loud peaks and quiet passages).  The stated intent of this was to make up for all the dynamic range that is ‘lost’ in the recording process.  Really?  I am pretty sure that whoever recorded that album was conscious of the dynamics that were present.  Why mess with it?  Anyhow, certain of these DBX units could also compress the source material.  IE., give the audio LESS dynamic range.

Equalization control and artificial reverb augmentation still exist in most home audio amps today.

They have renamed the reverb control as ‘sound space’ or something like that, but it’s the same idea.  ‘Take an audio signal and put it in a different space.’  The do-it-yourself dynamics processors seem to have been largely phased out though.  I don’t consider myself an audio purist, but there is something about all of these devices that really seems nonsensical to me.  Overall i get the feeling that  designers  ran out of knobs to put on the boxes, so they had to make new boxes and populate them with more knobs.

There’s one more angle that i’d like to consider:  So over the years, consumers have been given the 3 main types of audio processing that recording engineers have used in the studio for 60 or more years:  those 3 categories are *frequency balance, *ambience, and *dynamics.  In the past 20 years, though, recording engineers have been given tremendous new control capability due to Digital Audio Workstations, e.g., Protools.  What could this mean for consumer hardware?  Will audio waveform editing, time compression/expansion, and automation control soon be available in consumer audio hardware?  Is it already?

Does anyone actively engage with the ‘sound-space’ controls on their Hi-Fi receiver?  Are they useful?


The BE-100 is a plug-in equalizer module that was made for use with the RCA BC-100 mixing console.  I have never seen a BC-100 in the flesh, nor am i aware of any albums that were recorded with a BC-100.  Since it was a product aimed at the broadcast market, and fairly rare, it’s possible that no albums ever were made on one.  From what i can gather from the forums, the BC-100 was apparently a custom-built product, and the pre-amps in these consoles were apparently built by API for RCA (no word on RCA’s involvement with the BE100).  A few years ago i was at a local flea market and some guys had a box truck with the contents of a storage-unit forfeiture sale.  I bought about 25 lbs of electronic parts, mic parts, etc., for a few bucks.  I also got some very interesting AES journals (interesting insofar as who had owned them) which i’ll post soon.  Anyhow, one of the parts i got was this BE-100.  just the raw module.   I bought a copy of the BC-100 manual from a dude who had been selling other parts from these RCA consoles on eBay.  He was not in the business of selling manuals, but agreed to sell me one for $25.  a very fair price.  he even spiral-bound it!  Here’s the schematic for the BE-100:

I added an old NOS BUD case, +/- 15v powersupply, a NOS UTC line-to-transistor input transformer from the local electronics warehouse, and an output transformer i pulled from an RCA broadcast phono pre of the same period.

I was too lazy to look up the specs on the transistors used in the BE100 to confirm that i was using transformers with the correct impedances, but my ‘good guess’ must have been close enough:  it works just fine.

The unit sounds…  grungy.  Aggressive.  not subtle, and not hi-fi.  It is quiet (IE no hum, white noise, etc).  I have not measured the freq response, but it sounds like it’s pretty much full-range…  i think the transformers i used are pretty decent.  The most interesting feature is the 40hz low boost.  it sounds awesome.  this will definitely find some use in the studio.

Has anyone else used one of these?  any tips or suggestions?

Does anyone know any records/studios that used these?

Recycled Champs

one of the most famous electric instrument amplifiers of all time is the tweed-covered Champ amplifier made by Fender in the 1950’s thru early 1960s.  Here’s a image of one from 1959 that i pulled off the web:

Fender made true vacuum-tube champs until the late 1970s, but the tweed-covered Champ (and it’s close cousin the tweed-covered Princeton) differ from their later namesakes in a lot of ways.  In the case of the final Tweed Champs, the lack of bass and treble controls  means that there is roughly 20db more gain available vs the later Black Tolex-covered Champ.  This does not necessarily make for a louder amp.  This does, however, make for an amp that can get super distorted and generally Sound Like Awesome.

Tweed Champs cost a fortune to buy.  Eric Clapton apparently used one for the Derek And The Dominos record.  This fact became widely known, and they have been very expensive ever since.  Fender now even makes a ‘re-issue’ (never a good idea) that sells for close to $1000.


The schematic is posted above for anyone interested in checking it out. They are very very simple.   Anyhow, since these things do sound so great and they are so simple to build, it’s a lot of fun to build them into Any Old Thing that catches your eye.  Here’s a quick survey of some Champs and Princetons that i’ve built into found enclosures.  You’ll see recycled Intercom units, school PA system speakers, and 16mm film projector speakers.  The circuits in these are all new, built with new or lightly used parts; but the cabinets (that part you actually SEE and touch) are straight up ancient.  I generally take plenty of liberties with the circuit, changing parts, adding features (reverb, add’l gain control, EQ, etc), even building them using different (but similar) tubes, and i’ve yet to be disappointed.

Hey it’s one of those old horn speakers

Along the lines of the ‘Carbon Mic’ (see earlier post) are these early horn speakers.   They are visual icons that have become separated from their actual sonic function due to the fact that they do not interface with any other audio equipment that any normal living person would own.  But don’t those things look great?  yes they do.  They look very similar to the acoustic horns that are mechanically coupled to the needles of ancient record players, but in fact these are electrical.

here’s an example of a very old record player which has a horn mechanically coupled to the needle:

On the other hand, the early electro-mechanical horns were made for use with early Tube radios. They have drivers with permanent magnets attached to the base of the horn.  Driver:

These type of speakers date from the 1920s, and they are the earliest common electro-mechanical transducers.  I picked up this example, made by Music Master of Philadelphia, at a yard sale.

Here’s the base of the unit, which contains the driver.

i plugged the very frayed cloth-covered wire into an old receiver and…  sound!  it worked.  the volume level was very very low, tho, even with the 50 watt receiver turned up all the way.

Turns out that these early speakers require a slightly different sort of amplifier than we use nowadays.  Not surprising.  So i built something to do the trick.  I describe the process below for those who want all the bloody details.  Once i had this thing running properly, tho…  the big question… how does it sound?  well, when listening to music recorded in the 1920s (like my Blind Willie Johnson), it sounds fine.

Later music sounds pretty bad.  and not even in an interesting way.  just bad.  But old classical and gospel are cool.   Hearing those old recordings played back on the same sort of system that folks would have used 90 years ago…  wow.  it’s fun.  I have the horn (and it’s attendant special amplifier) hooked up to an Apple Airport Express which hides in the base of a corner cabinet in our house.

Other rooms in the house have their own full-range systems with their own Airports, so it’s really easy to switch up the playback systems depending on mood etc.  Love iTunes on the laptop.

Here’s the tech-y stuff for those of you who care.  So why did the speaker not play back at a decent level when used with my old SONY receiver? A quick bit of online research revealed that these old horn speakers have an effective impedance of 1000-2000 ohms.  WAY off from the 8 ohm speaker output of a contemporary receiver.   Anyhow, to confirm this, i inserted my handy University Sound universal impedance matching transformer (wired to couple 8 ohms to 600 ohms) and what do you know.  the speaker worked fine.   Decent volume level with the volume knob set at 10’o-clock.

Anyway, rather than run this thing all the time with a giant shitty receiver, i decided to simply build a tiny 5watt tube amplifier with the highest impedance that i could easily generate – 600 ohms.   I had some Edcor 5K/600 single-ended transformers lying around from a mic preamp project that i aborted because…  well…  the Edcors don’t have enough low end response to make a good mic preamp.  In this decidedly lo-fi application, though, they work just fine.  I used a 6J7 (for the old-timey look) into a 6V6 tube with a 5V rectifier.  I initially built the unit with a 6L6, but the edcor was getting REALLY hot (i guess they mean it about the 5watt rating) so i switched the tube to a 6V6 (and changed the cathode resistor appropriately).  It runs cool now.

Anyhow, this little amp also has the added feature of two RCA input jacks that passively mix to the input grid of the 6J7.  which is a necessary feature since i use this to listen to (stereo) music from iTunes via the Airport Express.  Also: super-nerdy but maybe worth mentioning – dig the old ‘screw-lug’ speaker connection.  i have been using these a lot lately and i think they add a little charm, even tho they do generally require some dremel-ing to the chassis in order to mount. (i hate the dremel and will do almost anything to avoid it.  Greenlee punches 4eva)

If you find one of these speakers for a good price (mine was $25, down from the sellers asking price of $80), and you can confirm that it works, you might want to pick it up.  One caveat: i apparently got lucky with the speaker that i bought.  Apparently, it’s common in these older units for the magnets to actually have lost their charge, and if that’s the case, they will need to be re-magnetized using wire and very high voltages.  Dangerous and irritating.  There are a few pages on the web that describe this procedure.  It’s pretty incredible to me that this technology is so old that the magnets have lost their charge.  crazy.  will this happen to all of our permenant magnet speakers some day?  will all of those coveted old Alnico drivers be useless at some point?  when?  2050?  Can’t wait for “The Day The Tone Died”  haha i can’t believe i said that….   awful.    Hate ‘Tone’ as a synonym for ‘pleasing sound quality in an electric-guitar sound reinforcement scenario.’

Does anyone out there use one of these speaker systems for music listening?

Anyone have a dedicated ‘antique’ system for listening to certain genres/ periods of recordings?

ICON: “gimme one of those real old mics…” :::UPDATED:::

When you are creating a set for a musical performance, nothing says ‘old school’ and ‘authentic’ like one of those mics…  those real big old mics with the springs…  what the F are they called?  Turns out that they are called Carbon Microphones, or more specifically, Double Button Carbon Microphones.

And while many a rapper, RnB singer, or songwriter type may favor them for their music video, i can promise you two things:  *)no one would be able to actually hook the mic up and use it, and *)if they did, they probably would not dig the sound.

Carbon mics are the oldest microphone technology still in (albeit limited) use today.  They actually pre-date vacuum tubes.  Wikipedia has a great article on their history and use, so no need for me to retread those waters.  Carbon mics are used in landline telephones, so we all have a basic idea of what they sound like.  midrangey, a little crunchy (distorted), compressed…  hey wait a minute!  that sounds pretty good to me!  Aren’t there like a million expensive DAW plug-ins in order to give you ‘that sound?’ Anyhow, we all know in general what they sound like… but how do those big old music-video props sound?

In order to find out, it turns out that it’s necessary to actually build a power supply.  Carbon mics need a few volts of a DC current moving through them in order to operate.  I found this handy schematic online and put it together.

I added a DC voltmeter so that i could monitor the effect of varying the voltage on the sound (the mic i have seems to like 6 volts).

I used a double-button mic input transformer salvaged from an ancient tube PA head that i had.  To the output of this transformer i added a second transformer to bring the impedance back down to Low-Z mic impedance so that i could use this whole rig with whatever mic preamp i wanted to.  The particular mic i have is a Lifetime Model Six.

I bought it years ago on eBay along with a little tube amp and some shitty speakers (and about a mile of useless rotten old speaker wire) for $150.  Anyhow, i won’t bless you with any vocal performances, but here is an acoustic guitar recording from my living room.  The left channel is the Carbon mic.  The right channel was recorded simultaneously with good equipment (414/omni into an API 512) so you can get a pretty good idea of what i was hearing in the room.  I put a little EQ on the Carbon mic to make it more audible (low pass at 3k, 5 db peak at 1.7K). No other processing was used.  Check it out.


Does anyone out there use double-button Carbon mics for audio production work these days?  Music recording? Sound design work?

I heard recently (maybe Tape Op mag?) that someone was making new-production ‘professional’ carbon mics.  Has anyone used these?  thoughts?

UPDATE: I recently had the chance to use this Lifetime Model Six Carbon Mic in a modern-recording context.  We tracked the following cut at Gold Coast Recorders, using the Lifetime for the vocals.  It sounds pretty outstanding…  I feel like you could get 90% of the way to this vocal sound with an SM57 and a fuzz pedal, but that extra 10%…  it’s a game of inches, ain’t it.   This is ATLANTIC CITY, my studio project with T.W.   Take a listen:  Ten Past Midnight