New Speakers!

When your amp isn't making a joyful noise and waking up the neighbors or shattering windows, it's not a time to sulk. There are other things that you could be doing, like sprucing up your sound with a new set of speakers.

The cab with Eminence designed Fender Speakers. Recording session, March 2012.

I use a home-built open back birch plywood cabinet for the business end of my amplifier setup. The cab was bought second hand loaded with two 12 inch Eminence designed Fender speakers, with 50 watts power handling each. They were satisfactory speakers, and sounded acceptable at lower volumes, though at higher performance volumes sounded spiky and uneven. Needless to say, I was never too happy with their sound. 

Upon removing them from the cab, I noticed what looked like two significant tears in both speakers, that were haphazardly repaired with a putty of some sort. I guess now seeing the ramshackle way they were patched, no wonder things sounded as odd as they did. 


So I took the plunge into the shallow end of the pool and bought some relatively inexpensive speakers made by Weber VST, the Ceramic Signature 12B. As stated on the website the Ceramic 12B would be an economic replacement for the Jensen C12N, which greatly interested me since the Jensen C12N is what was commonly used in the blackface Fender Twin amplifier. You may be thinking, "dude, you play a Marshall clone; why not use Celestion Greenbacks like the old Marshall cabs?" Yes, that would be the clear way to go, but I'm kinda a weirdo. There is something about the Marshall-meets-Fender thing that really interests me. So I ran with it. 


These speakers when shipped weighed impressively more than the lightweight Fender speakers and installed effortlessly into the speaker cabinet. Weber VST have a reputation for great sounding, quality speakers, and have been long used as a replacement or even upgrade for vintage Fender guitar amplifiers. 

Cab loaded with Weber Ceramic 12Bs.

Speakers are sometimes the unsung hero of the amplifier setup. Everyone talks about the head, what tubes your packing, but speakers, the different Celestion, Jensen, Eminence, Oxford, etc. models offered, wattage rating, speaker efficiency, alnico versus ceramic magnets; these discussions don't come up as much. And I will admit, the idea of different construction methods of speakers are quite complex and I don't understand them all too well, but upon listening to different models, even made by the same manufacturer, sure exerts a great deal of influence on ultimately how your amplifier will sound. Distortion character, frequency content, dynamic range, touch, and even perceived loudness of your amplifier is ultimately governed by the speakers, how many, and in what cabinet.


Needless to say, I can't wait to get the amplifier finished, so I can start rocking on these bad-boys.

It's Alive! The Amp Rebuild Part 3.

Open chassis ready for a line check.
Outlet for the lightbulb series limiter in top left corner. 

After soldering the last few connections to the output tube plates, and connecting the various B+ voltages to their selected points, it was time to power up. Not a full power up, but a graduated one that would start with a 75 watt lightbulb in series with the amplifier to prevent destroying any of the precious components: transformers, tubes, capacitors, or staring a fire.
For the first power up, I would do so without any tubes installed, just to make sure. 


If you are curious about putting a 75 watt bulb in series for debugging, read my previous blog post "Amp Rebuild, Part One." 


With the 75 watt bulb in place, AC cord in the power outlet, and safety goggles on, I flipped up the mains switch into the ON position. To my relief, no sparks, no fire, no snap, crackle or pop. With the necessary precaution, I measured the voltages across the primary and secondary winding with the voltmeter, as well as the B+ voltages, with everything checking out just fine, if not slightly under voltage due to the loading created by the 75 watt bulb. It is important to be wearing rubber shoes in order to prevent your body from being the path to ground, and electrocution . 


I then turned the amp off. Since there are no tubes installing in the circuit, the smoothing filter capacitors do no discharge, which means they can be storing up to 450 volts in some cases. With one hand in my back pocket, I connected a short clip lead to the chassis and proceeded very cautiously to touch the positive (+) terminals of each of the polarized capacitors in the circuit. Remember, it is very important to be wearing rubber shoes in order to prevent your body from being the path to ground, resulting in electrocution. Be advised, when discharging polarized capacitors, large sparks are likely to leap from the positive terminals to your clip lead as the capacitors ground out their charge. 


Still with the 75 watt bulb installed, I repeated the power up, except this time with tubes. Again with the precaution of wearing rubber shoes and keeping one hand in my back pocket and other holding the voltmeter test probe (making sure not to touch any B+ voltages and ground points simultaneously, which would cause a short), took all the measurements again. This time the voltages were even slightly lower, to be expected with the tubes installed (drawing more current, lowering the voltages). Again no sparks or pops and voltages to be expected with a 75 watt bulb in series.


I then repeated the same test with a 150 watt bulb in series, then full line current/voltage, and everything looked great on paper. The true test came when I plugged my Stratocaster in and turned up the volume controls just to see if I got any hum from the single coil pickups. Nothing. Not a peep; the amp was dead silent. Problems. Hopefully not serious ones, but problems nonetheless. 


It's alive, but it's still not talking. The saga continues. 

Rogue waves in the Roadwaves.

Thus far, "Roadwaves" has been a interesting project. Both as a band and personally as a recording engineer, I had never experienced anything so rigorous, challenging, strenuous, and as rewarding as the recording of this album. Despite the numerous setbacks, both scheduling, performance and equipment-wise, it has been a great experience and I haven't learned so much in such a short amount of time about musicianship, recording engineering, producing, and I guess, just being a human being. 


Since my fairly documented amplifier failure a couple of weeks ago, the band and me have decided to go forward with the project recording Alec's bass parts as my amplifier awaits completion. We have attempted to record some bass over top the completed drum tracks, but weren't all too satisfied with the resultant sounds. So this second time around we came up with some pretty cool, simple solutions to some age-old questions we had recording bass.


DI versus AMP. Why not both?


Bass guitar (and other low-frequency dominated instruments) do not have as much directionality in a stereo field as instruments that include higher frequency components, such as guitar, snare drum, cymbals, etc. Since about the mid to late 1960's, it has been a common practice to record the electric bass guitar directly through means of a impedance balancing transformer, more commonly known as a "direct inject" box, or DI. This gives a clean, electronic representation of the bass guitar sound as what come straight from the bass guitar's pickups (well, routed through the volume and tone controls on the instrument too). The DI does away with the anomalies associated with bass amplification, speakers, microphones, the environment of the recording space, and the distance the microphone is placed from a speakers, giving a drier, up front, and direct sound, which can sound sterile on it's own. 


Another practice is to mike the bass amplifier with a quality microphone; a Sennheiser MD421, AKG D112, Electrovoice RE20 or something of the like. This normally yields a "live, in the room" type sound, which is typically more natural and fuller, though can be hyped in certain frequencies or suffer from distortion as a result of the amplifier or speakers, or phase issues because of distance of the microphone from the speakers. Some engineers however swear by the amp and microphone technique, since it is most true to form when seeing a band perform live.


With modern digital (especially DAW based) recording platforms, higher track counts, almost unlimited track counts are possible, which allows the engineer to record multiple signals dedicated to a single instrument. This can be very useful for bass, allowing the engineer to record both direct and miked bass sounds, and blend them to taste in final mix down. With recording both, it is very, VERY important to observe phase relationship between the direct and miked signals. You should avoid as much as possible phase cancellation and/or phase reinforcement which may cause uneven frequency response of the bass, to avoid a week or otherwise boomy sounding bass sound. 


THE ROGUE WAVE.


So Alec and I settled on a scheme where the direct signal would provide a clean bass sound that would represent the full frequency response of his Fender Jazz Bass, while the amplifier would provide a more focused, mid range sound. The amp would be driven a little harder through means of a Boss Super Overdrive or EH Big Muff in order to add some harmonics to give the bass a more pronounced sound in the mix. The challenge was to record a clean DI signal that would be unaffected by the distortion pedals that were on the front end of the bass amp.


Since I didn't have an instrument-level signal splitter box (or any type of splitter for that matter) we used a somewhat unorthodox, if not "incorrect" method. The signal would leave the Jazz Bass, into a DI box, through an XLR cable to my Yamaha MG12 mixer, of which would be then (through one side of the stereo buss) routed through an ART tube compressor then to the A/D conversion. Part of that bass signal would be tapped from the mixer channel via an AUX send, through another instrument cable to a distortion pedal, then to the bass amp. Thankfully this particular amp, a cheap 30W Carlo Robelli bass amp with a single 10" speaker, had an active pickup input. Though line level is not quite the same as a bass with active pickups, the signal level would be closer active level than passive instrument levels. From there, the bass amp was close miked with a Sennheiser MD421 in close proximity with careful attention to phase relationship with the DI signal. The whole setup was then covered in a heavy packing blanket in order to minimize room reflections on the miked bass amp sound.


Note: using a mixer AUX to send an instrument signal is not the recommended way to go when multing a signal to used as both a direct signal and one to be the input signal for an amplifier. A re-amp unit would be much better at doing this, because of impedance and signal level differences.  In our situation, it was all we had, and honestly, sounded pretty darn good for how primitive the method is. 


Oh yeah, here are some pics of the session. I will post the pictures of the DI/mic signal chain in the near future. 

Alec and the Jazz Bass.

Alec and the invisible engineer... I guess I can't take photos and be in the shot at the same time.

My modest, yet effective recording setup. Yamaha MG12, ART VLA compressor, M-Audio Fast Track 8R, and Mac Book Pro armed with Pro Tools 8

The Amp Rebuild, Part Two.

After almost two weeks wait, the new transformer finally came from the good folks over at Weber VST all the way in Indiana. I promptly got the thing mounted in the chassis and started laying down the filament wires to the tubes and the connected the wires leading to the primary winding (the 120V side of things). 

Just to make sure my power transformer doesn't short out again, I connected the power plug to the the 125V winding, since my wall outlet read 121V. 

Brand spankin new power transformer.

6.3V filament taps to the power tube socket. These wires
are wound to and ran close to the chassis to
minimize noise from entering the signal path.

Filament wires to the preamp tubes. Pins 4 and 5 are
connected in series to create the 12.6V necessary
to run the 12AX7 preamp tube.

Up next: mounting and connecting the main circuit board and rectifier circuit.

The Amp Rebuild, Part One.

In my last entry, I talked about how my Marshall hodge-podge clone, that I lovingly named "Katie" died mid recording session, and how I am now fully vested in nursing her back to health again. I'm not too sure how many guitar players get to see (or really are interested in seeing) the innards of the box that makes all their noise possible, but I decided it would be a cool thing to document the deconstruction and reconstruction of my personal noise making box. 

The Lightbulb Limiter

Fig. 1: The Lightbulb Limiter.

Before pulling the amp completely apart, I had to run some tests with live electricity running through the amp just to see what had gone wrong. I had suspected some part(s) of the circuit had shorted, causing the mains fuse to blow, cutting off electricity to the entire amp. In order to run diagnostics on the amp, I installed a new fuse and then built a "lightbulb limiter." This crude device limits current by putting a lightbulb in series with the amplifier, so all electricity flows through the lightbulb before hitting the amplifier. 

If you are interested, the lightbulb limiter works on the wattage principle:

Watts = Voltage x Current

where if you take an X watt lightbulb divided 120 volt line voltage coming off the wall will equal the total amperes of current available to whatever device you have plugged in downstream of the lightbulb (in series).

For example... 150 watt bulb / 120 volts = 1.25 amps 

For the actual diagnostic I used a 75W bulb, limiting the current to 0.625A, well below the value of the mains fuse, so the fuse would no blow if there were any shorts.

I constructed the lightbulb limiter from:

-plastic wall lamp holder

-2 gang utility box

-dual wall outlet

-single three-way light switch 

-plastic outlet/switch wall cover panel

-tool replacement power cable

-75 watt lightbulb

-14 AWG stranded wire

If any of you would like a schematic and/or layout of the limiter, just email me. 

Trouble, trouble, trouble. 

With the 75 watt bulb in place I plugged the amp into the limiter outlet and flipped the on switch on the limiter, then on the amp (with the amp still on standby) and found a problem right away. If nothing is wrong with the amp, the light should no glow at full brightness, indicating that the amp is not drawing excessive current, but the light lit up to full brightness, even with the amp on standby. This indicates a short on the primary winding. The primary of any power transformer should read around 115 to 120 volts in the States, but only read 2.5 volts on the multimeter. The short in the primary probably caused a huge current spike to occur through the rest of the amp, causing some of the damage to smoothing capacitors before the fuse blew.

Fig. 2 Burnt KT66 tube. 

Another issue was the burned tubes. I'm not sure if the power transformer failure caused the tubes to burn, or vice-versa, but somehow I think they are related events. I had heard that power tube failure can sometimes cause a power transformer failure as well. In my amp, this makes perfect sense if the problem originated at the power tubes first, being that I had these in my amp for nearly six years (stupid me!) and I never checked up on them to see if they needed replacing or drifted out of bias. Stupid of me; I will definitely never let that happen again. 

The Cleanup.

Fig. 3: Main circuit board with old cloth wires.

So began the cleanup. I first removed the two circuit boards and their connective wires, then tested each part with a multimeter, marking on the schematic with a highlighter which components were suspect for either damage or otherwise not reading their intended value, reserving the suspect components in a small jewelry organizer. 

Fig. 4: Staying organized.

I eventually had to remove almost everything from the chassis to take out the failed transformer.

Fig. 5: Cleaned up chassis.

Fig. 6: The dead transformer, which had a good run for a time. You did good, kid. You did good. 

Stay tuned for more updates.

Amps Gone Wild.

I had always dreamed of owning a vintage Marshall, or something that could get me that tone. I loved the sounds of Eric Clapton from "Bluesbreakers" and "Fresh Cream," and Paul Kossoff from Free's eponymous album. I could not afford one, so I ended up teaching myself enough electronics chops to build one.

Paul Kossoff (Free) and his dual Marshall 1959 model 100 watt stacks.
Much too loud for my gigs, but his tone is incredible. 

I started off with a Weber 6m45p amp head kit and modified the circuit as I went along. So what I ended up with was roughly a cross between the Marshall 50 watt Lead model 1987 and the later 2204, possibly an amp that never really existed: dual KT66 output tubes (instead of the usual EL34), 12AT7 phase inverter (30% less gain than the usual 12AX7),  with some capacitor changes that were more similar to the mid '70s Marshal Master Volume model 2204, yielding a somewhat brighter sound just without the increased gain, and the all important post phase inverter master volume (PPIMV) that would allow me to dial in any gain level at any volume. I loved the sound of the amp; it was very dynamic and open sounding, with a creamy, smooth breakup that was more akin to the mid 1960's Marshall 1987 than the 2204. When playing a Les Paul, the sound was very similar to Paul Kossoff's tone on "Alright Now," especially when played through a 4x12 cab with Celestion Greenbacks (which I no longer own), but when paired with the Jazzmaster, it was a unique tone all my own. It was great!

Me and the amp at the Golden West College Battle of the Bands, April 2012.
The cab is a home made open back 2x12 with two Fender OEM Eminence speakers
pulled from a Fender Twin.

The amp was fail proof for five years, logging hundreds of hours of shows, recording sessions, and rehearsals. It was all good until three weeks ago when the amp went POOF! in the middle of recording a guitar solo for the Short Term Melody's upcoming album. 


It literally sounded like someone was frying bacon in the middle of the guitar solo, then a quickly diminishing output. Then the smell of burned capacitors (like burning plastic)... OH SHIT was all I thought. After I let the amp cool down I pulled the chassis from the cabinet. Everything looked fairly normal except some of the caps were leaking an oily fluid from them. Upon further examination, the power tubes and the mains fuse had indeed burned out.


So began the journey to get my sick amp back to health again.