As usual I arrive, tail between my legs, because I have not kept up my end of the bargain. That said, Part-1 of my Fender Hot Rod Deluxe mods is now in the February issue. Part-1 implies Part-2 and, like Sourdough starter, I am already working on Part-3 even though Part-2 has not yet been put to bed.

Zooming in on a guitar amp with a microphone has a tendency to reveal certain flaws that might not get noticed at rehearsal or at a live gig. As a recording engineer with geek abilities, I wanna know how to make ‘one of THOSE amps’ sound good in the studio, especially when my ‘clients’ are students on a limited budget. It’s not hard and it’s ‘mostly time,’ lol!

Meanwhile, in the first three weeks of Electronics Class, we covered voltage dividers, series and parallel circuits, Ohm’s Law and the Power Formula. Power Supplies and basic soldering skills are currently in the cue. We learned, about half wave, full wave, voltage doublers, filter capacitors and regulators.

When I showed up to class this week, students had drawn their power supply schematics 15 times in prep for a from-memory mid-term exam. Now we can ‘relax’ and stuff some components into the circuit board and solder away. Next week we start JFETs.

Here are some review links from my own site and afrotechmods.com

Basic Electricity

Voltage Dividers

Series Parallel and Resistor Color Code Test

Rectification Video

Rectifiers…

Regulation Video

Regulation Homework

JFET TUTORIALS

JFET Video

JFET PDF

JFET LINK

Some of these videos are not as well done as the stuff Afrotech does, some of the audio is absolutely horrendous! That said, our minds are all wired a little differently and it’s good to check multiple sources.

FET VID-1

This one has terrible audio, but it seems relevant…

Recently a ‘cartoon’ pointed out that the penalty for sharing a Michael Jackson file was 5 years, while killing him was only good for 4 years. It points to the media industry’s heavy handedness – and laziness – like ‘scared straight’ for the down-loader instead of ‘the owners’ finding a more viable solution.

I propose a way to make every file sharer an asset instead of a liability. It was once tested on a small scale at the early part of this century…

A better file distribution system would thwart piracy. To make file sharing a viable business requires a DRM format that embeds paying customers’ ID into the files they share.

Imagine this:

1.) Audition a file (music, video etc) to confirm it’s what you want – just like iTunes, Amazon, etc.

2.) Pay for it (this embeds your ID into the DRM for that file).

3.) Share the file with a friend. That person also gets to audition to confirm that the file is what it purports to be. Your friend pays, and you get a taste of said payment.

4.) EACH PERSON IN THE DISTRIBUTION CHAIN is compensated when someone pays for file. That gives everyone a vested interest in the system working.

5.) This system was attempted on a small scale in the early part of this century by Steve Turnidge. It was called WEEDSHARE. I had the exact same idea, Steve just had the ability to bring it to market, although my guess was that his project was under-capitalized. I was disappointed to see that it didn’t fly. Maybe it deserves a second chance?

Students often get ask about sub kicks and while I have not experimented other than to prove a speaker can be a microphone – I get plenty of low end from the kick without trying – I wanted to point out the where the sub kick resonance comes from to assist DIY’ers in their selection choices.

All ‘woofers,’ large and small, have a Free Air Resonance, or Fs. It is pretty much what you might imagine, the natural resonance of a woofer in free air.

There are a range of resonant frequencies that are useful in augmenting an overly dampened kick drum – really, whatever your preferred frequency might be, 65 Hz plus or minus 15 Hz is the ballpark.

To find an off-the-shelf woofer, all ya gotta do is go to web site that caters to loudspeaker components, like MCM, Parts Express and Madisound. When used for their intended purpose, better woofers manufacturers are more likely to provide more detailed specs. A sub kick doesn’t need much more than an Fs

Below is an 8-inch woofer available from MCM Electronics. Notice the Fs is 65Hz…
http://www.mcmelectronics.com/product/55-2805

This 5 1/2-inch driver from Parts express has an Fs of 82 Hz…
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=299-956

And from Madisound, this Fostex product sheet goes into remarkable detail about all of the essential loudspeaker component parts. Fs is is determined by the cone’s mass – both material, thickness and larger diameter generally translate into high mass, lowering the Fs. More compliant surround material lowers Fs while stiffer surround raises Fs. Behind the cone is the ‘spider,’ which is used to center the voice coil in the magnetic gap. Not that the frequency response charts also show include an Impedance curve that reveals both the Fs and the effect the voice coil has on inductance (a gradual impedance rise at high frequencies).

http://www.madisound.com/store/manuals/FF-WK_manual_all_eng.pdf

Wow! Winter break simultaneously went by all too fast and yet, it seems like forever ago that I was teaching analog recording, doing a Zed Lep cover for our penultimate class. On the final class, everyone was so burnt out by final exams that we played vinyl for THREE HOURS! (Gentle Giant’s KNOTS, Frank Zappa’s MOVIN’ TO MONTANA, The Robins’ SMOKEY JOE’s CAFE, Sinatra, Gene Vincent, Johnny Guitar Watson, Les Paul – it was quite the journey.)

That said, my brain is flying with zillions of ideas that must be well focused in time for my students’ first electronic experience – I don’t want to scare anyone off. To soften the landing, hands-on is heavily emphasized – starting with the familiar 9-volt battery to the tongue and then…

MULTIMETER 101
Learn how to use a Multi-meter, a piece of Test Equipment that, as the name implies, does multiple things – measure volts, current (in amps) and resistance (in ohms)…

http://www.tangible-technology.com/ipr/AE230/html/wk_1/volts-amps-meters.pdf

After proving the 9-volt battery is worthy, it’s time to get hip to the solder-less breadboard. With a little experience, it can used to demo a simple stomp box circuit and just about any idea you can throw at and fit on it!

http://www.tangible-technology.com/ipr/AE230/html/wk_1/ae-237-lab-1b.pdf

GET PHYSICAL
I said ‘hands-on,’ right? Seeing the images, touching all the parts, getting familiar enough to make the breadboard do your bidding is key. Students connect a battery, a Light Emitting Diode (LED) and a Resistor. When the LED lights up, it’s time to take a union cig break and pat yourself on the back..

With just this little bit of familiarity under our belts it’s time to delve into the schematic symbol codex – the visual language of electronic circuits…

http://www.tangible-technology.com/ipr/AE230/html/wk_1/led_circuit-Aug-10.pdf

We see the circuit as a physical entity, learn the schematic symbol for each component and then whip out the multimeter and take some measurements.

I’m off to do it for real, so L8R!

With the help of Chris Juried, whose father took this and many other pictures of New York City studios…

To visit this work in progress, click on the link below.

I have identified some of the equipment, but feel free to comment, especially if you can identify the mystery gear – console, white boxes over Pultecs (which Pultecs??), name of that style patch bay, pix of dual-pronged patch plugs, etc.

MiraSound NYC circa early sixities

I teach, therefore I am constantly experimenting, so when students ask “How long have you been doing this or that,’ sometimes my reply is “I just tried it for the first time.”

Of course, we ALL rotate through the ‘known’ tricks until satisfied. Last week, a student walked in with TWO B&O ribbon mics and we immediately put them to good use. (The mics were borrowed from another instructor, Tom Garneau, the B&O design inspired Speiden and then Royer.)

For our control room rehearsal session we set up three mics about 5 feet from the drum kit. About 1 1/2 feet off the floor were the B&O ribbons on a Cascade T bar. Four feet directly above was an EV-664A hyper-cardioid to catch the top side of the kit.

You can hear the tracks in isolation at the link immediately below. Spoiler alert – the tracks were essentially solo’d from the mix so they have EQ and Compression.

0:00 – 0:42 = B&O
0:43 – 1:06 = EV 664a
1:07 – 1:29 = Live chamber + all three mics
1:30 – 2:08 = Bass DI (left) + Bass amp (right)
2:09 – end = other instruments added.

REHEARSAL AUDIO

DYNAMIC PREFs
I have been favoring dynamic and ribbon mics as they tend to have less top end, better rejection and work well in ensemble sessions where rejection is useful.

OMNI
If you want more space and no proximity effect the EV635A is great – on acoustic guitars, drums and even those guttural metal vocals. It’s still manufactured and @$119 street, is affordable.

NO FEAR OF REJECTION!
A pair of ribbon mics on a singing acoustic acoustic guitarist can deliver remarkable isolation, presence and warmth. I’ve had access to several ribbon mics, including the Royer, Reslo, RCA 44A and 74 Junior, Coles 4038 and Cascade. All are unique but only the Cascade models are within a student’s budget. I have a pair of Fatheads and a Vin Jet (RCA 44 ribbon style) in my classroom mic cabinet.

FATHEAD

VINJET

The cascade Fat Head (short ribbon) is $175 and is great on guitar amps – about 2 feet from the cab works pretty well. The VinJet (long ribbon) is a bit like the RCA 44. like all ribbons, they do not exaggerate the amplifier grit that brighter mics do.

This past week, my class used a stereo pair of Fatheads on the drums – as described above – along with the EV-664A (plus a Sennheiser shotgun to catch the room bounce). Here’s a mix of the session, mostly live, with fatheads on the lead and tremelo guitar ODs.

Student ‘Zed Lep’ Session Recording

Students should keep in mind that ribbons should not be ‘eaten’ by humans or drums (avoid extreme close-ups) because the ribbon is delicate. They also have low output, but you can get an external preamp / booster. One version is called the Cloud Lifter – available in mono and stereo versions.

CLOUD Ribbon Mic Helper

Another vintage fave is the EV-664 another ‘isolationist’ mic that’s good on vocals, kick and toms.

The bass amp on both of these recordings is an SWR LA-8 practice amp with either an EV RE-11 or a Shure SM-58 directly on the cab. The DI is via a JFET preamp with an optical limiter of my own design.

When capturing bass amp tone, I rely on proximity effect to do the heavy low-end lifting, tweaking the amp EQ a little bass shy so that the mic gets what I want. That plus getting the amp off the floor a helps alot with ‘de-stimulating’ the room and reducing leakage.

If you’re new to recording, please let me know if you find these tips helpful and feel free to share your own.

eddie

PS: My thanks to James Andrew Meadows (Drums), Dillon Marchus (Bass), Zach Johnson and Shaun Ortman (Guitars and Eng), Peter Vel and Jake Goodroad (Eng and Tape Op), Michael Freeman rogers (Vocals – although not featured in these mixes), John Kargol (Tech Support) and Stan Coutant for his awesome microphone site!

I teach an Analog Recording Class four times a year – five weeks of editing, flanging and 4-track plus five weeks of 24-track. While not trying to ‘sell’ the various analog tape formats – I embraced in-the-box mixing last century – I do ask my students to take a step back from the one-instrument-at-a time, pitch correction, beat detection, plug-in mania and consider recording a live rhythm track – no click, no headphones, just musicians listening to each other and ‘mixing themselves’ on the fly.

The goal is to transfer what was learned in the process back to the Digital Lo Mein. If they decide to buy a used tape machine, well, that’s icing on the cake! There is nothing like an emotion-modulated soaring flange rather than the oscillator driven version – hardware or plug-in – or rolling your own live chamber. And let’s face it, in this economy, for students trying to find their way, the minimalist approach works economically and emotionally – perhaps the ‘discerning listener’ will feel more connected and not quite understand why…

People Will Come, Ray!

We start with four track half-inch tape and a handful of preamps. I give them a little breathing room in that the target is one instrument / one microphone per track, UNLESS we take advantage of a two-input, one-output mixer-limiter (the Altec 1612) to combine Bass And Drums (one mic each) to one track of tape.

But first I show them this video – one cheap omni condenser mic on a drum kit – no EQ or dynamics processing. Just a good drummer, a decent sounding kit and an untreated space. My students call this the “Crotch Mic Technique!” Oh, and this microphone is working extra hard by driving six pre-amps at once.

BASS AMP ONLY
I once was a Bass DI + amp guy until one day when recording a rehearsal, I stumbled upon a trick that has worked ever since. David Trampe is the student bassist on this track. (For this session, we simultaneously recorded to analog and digital formats. This is the digital version.) David played my UNIVOX P-Bass copy through his SWR LA-10 amplifier. I chose what was available – an Shure SM-58. You can pretty much use anything, but I recommend the following.

- Bass cab off the floor to minimize boom-in-the-room
- 8-inch to 10-inch small-speaker cabs for a tight, controlled tone
- Start by EQ-ing the bass amp for a clear, tone (minimize the mud), less bassy than bassists would normally choose (this also applies to live)
- Use any directional mic as close to the speaker as possible to take advantage of proximity effect – this restores the warmth lost by the previous step, it also reduced mud and leakage in the performance area
- Almost any mic preamp and limiter (the latter gently kissing the peaks as needed)
- Once you get this far, tweak the amp EQ as necessary to get as close to the desired tone as possible.

FOUR TRACK FUN
Here are two songs we did in class. Four Rhythm tracks bounced to one leaving three tracks for overdubs.

PICTURES OF MATCHSTICK MEN
Vocals Overdubbed

ME AND BOBBY McGEE
Live vocal, acoustic and lead guitar overdubbed.

EIGHT OF of 24-TRACKS
FIVE AGAIN (live)

24 TRACKS LIVE (no waiting)
IF YOU WANT ME TO STAY (live)

Many entry level converters only have two microphone inputs, which is fine when you’re working at home or doing live stereo recordings. But with ‘the right bit of clever’ you can convert line inputs to mic inputs with a simple adapter. Several years ago I did this with DigiDesign’s 002 (it has four mic and four line inputs). I currently own an M-Audio 1814 (2 mic inputs).

Inside the adapter shown is a Low Impedance (balanced) to High Impedance (unbalanced) matching transformer- nothing fancy – and likely to saturate with high-level sources – sometimes that’s the ‘color’ you want. Parts Express also has in-line adapters for polarity reverse and attenuators (pads) which are handy beyond this application. Every ‘audio emergency kit’ should have a few.

If you wanna pimp your converter, check out the ‘shiny transformer’ links. (PS: Requires, fine motor skills like metal shop, wire stripping and soldering.)

PARTS EXPRESS

Shiny High-Performance Transformers

ALTRAN

CINEMAG

JENSEN

SOWTER

EDCOR

LUNDAHL

PLUS…

A BOX TO PUT IT IN

http://www.tubesandmore.com/scripts/foxweb.dll/moreinfo@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?item=P-H1590A

Hi Eddie,

I’ve always enjoyed your writing! I’m not really that much of a tech, but I have a lot of old stuff (I mean vintage), and your MIX column gives me faith that I will be able to find someone who can repair my prized gear.

Today I wanted to repair a Pro Jr. input jack, and I am certain that once upon a time you had an article in Mix detailing your repair of one of these. I can’t find it on the web. I hope this isn’t too annoying, but, do you have that article stored anywhere?

Sorry to bug you, and thanks!

David
~~~~~~~~~~~~~~~~~~~~~~~~
D!

I have a Pro Junior that I’ve done some mods to, but I don’t recall anything about the jack. That said, this link below should help! Antique Electronic Supply is very tube amp friendly.

http://www.tubesandmore.com/scripts/foxweb.dll/EXTPAGE@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?PAGE=SUBCAT&SEARCH_TREE01=JACKS/PLUGS

I was off on vacation for a week so there’s some catching up to do. For starters, I am going to post some links and, over time, come back and explain in more depth how these links can help you…

OBSOLETE PARTS?
As mentioned, upgrading opamps in the audio path can a bit of a mine field. But not ALL opamps are in the signal path – the side-chain of vintage dbx compressor-limiters, for example, have opamps that do all sorts of fun stuff. So, when an opamp’s functionality is circuit-critical, check the manufacturer’s website first, because sometimes you can get lucky and find a compatible replacement.

As the link shows, the LM308 has been DISCONTINUED, but to the right is a link to the LM308 DATASHEET as well as it’s replacement – in the ALSO RECOMMENDED box – the LM8261. You’ll want to download the datasheet for both parts…
POWER SURPRISE
Power Supplies are often the weak link in many products, not necessarily by circuit design so much as the lack of consideration of how heat shortens life over long periods of time. In general, electronics components should not be so hot as to burn, but ‘too hot to fail’ happens all too often, especially when you consider how often rack gear is mounted with no space in between. Over time, parts just burn themselves out.
RECTIFIERS Convert AC to DC and there are many types, from Half Wave to Full Wave, Single Voltage to Bipolar as well as Voltage Doubler.

Can You NAME THAT RECTIFIER?

Once AC is converted to DC it needs to be regulated – it must tolerate variations at the power outlet – it can’t sag when the Air Conditioner or Heater comes on and must be there if the device being powered demands more juice.
SIMPLE REGULATION
Theses days, pretty much every solution comes as a single Integrated Circuit or IC, with a minimal amount of support parts. But if you work on vintage Gear, you’ll see many Variations on the Regulation Theme.

If you ever wanted to know more about regulated power supplies, National Semiconductor published this useful FUNDAMENTALS pdf.

CAPACITOR CONFUSION
Back in the vacuum tube daze, capacitors were big enough to tell you alot about themselves. Then, large and small value caps relied on color code. Now reading and translating much small conventional (axial or radial) capacitors can be confusing, because limited space forces manufacturers to abbreviate. It’s even crazier with surface mount (SMT) parts. I’ll be posting a chart soon, but in the meantime, here’s a cool link that explains alot about what some of the abbreviations mean. Note that some of these abbreviations might be on the schematic as well.

more to come…