Monthly Archives: December 2013

D.I.Y. Ampeg B15n Fliptop Clone (2013)

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Originally uploaded September 2013

This is more or less a clone of the head section of the Ampeg B15n, known as the Portaflex or “fliptop.” I’ve been wanting to try building a tube bass amp for a while and I’ve been curious to find out why fliptops sound the way they do.

B15n Clone - back view, complete   B15n Clone - schematic

B15n Clone - partial layout

 

 

 

 

 

 

Below is an exciting video documenting the tail end of this build. Please keep in mind that I’m not exactly Tony Levin.

B15n Clone - interior #1   B15n Clone - action shot

My fliptop interpretation preserves most of the “canonical” aspects of the original(s), like the extremely high input impedance (5.6M Ohms), the Baxandall tonestack, -50V fixed-bias (*not* cathode-bias!) and the unusual phase-inverter configuration. But this one sports a few departures from the original:

1. The instrument input uses a decoupling capacitor (22nF) before the biasing resistor of the first preamp grid input.

B15n Clone - interior #22. The resistor and capacitor values for the DC filtering stages aren’t anywhere close to the original(s) – I used 50uF can caps because I had some available. The difference in the filtering stages probably changes the whole sound but I don’t have a way to find out because I don’t have access to a real fliptop. I’ve seen some B15n schematics specifying diodes for rectification and others specifying tube rectification. Mine uses diodes. I wound up with about 465V at the plates of the power tubes, which might be a little too high, but I haven’t done a round of tweaking lately.

B15n Clone - top, no cabinet #13. My version has one channel instead of two like most others do, because I wanted to keep the interior as uncluttered as possible for the inevitable 5 million little adjustments I made.

4. I used a great big filter choke rated for 500 Volts, because I could. I found that a choke helped reduce noise and hum.

5. I always try to use elevated heater supplies (see schematic), even for push-pull amps. In this case, the filament divider resistors are tied to the -50V bias (see schematic). That’s one way to deal with 60Hz/120Hz hum from 6SL7/6SN7 tubes. I guess this doesn’t qualify as a “departure from the original” but it’s how I got rid of most of the AC hum, along with isolating the ground lines for the filter capacitors from the other grounds and busses, like I should have in the first place.

B15n Clone - top, no cabinet #26. I found that I could coax more clean headroom out of the unit by using 6SN7 tubes for the preamp stages instead of 6SL7 (think: 12AU7 vs. 12AX7, sort of). For bass, I like clean headroom. I looked at the signal from input to output with an oscilloscope and found that clipping was most likely to happen first in the preamp stage. That can sound nice, but for this unit, it sounded awkward and nasty, to me anyway. Swapping 6SL7′s (higher gain) for 6SN7′s (lower gain) reduced the strength of the preamp signal but gave more headroom before the nastiness kicked in. The drawback for 6SN7′s is that they demand twice as much filament current as 6SL’s (~=600mA instead of ~=300mA) but the power transformer is quite capable of handling that increase (see schematic).

My version puts out somewhere around 30 Watts at the most, from what I can tell. I used a Classictone 40-Watt output transformer, so I don’t want to try to push the output higher than it already is. To be honest, I’m guessing at the Wattage, assuming about 20% or 25% power loss for the push-pull output transformer.

The tubes are all Tung-Sol. I tried a pair of Tung-Sol 7581′s for the power tubes, and a pair of JJ 6L6GC’s, but I liked the Tung-Sol 6L6GC-STR’s for their relatively wide frequency response.

B15n Clone - interior, no board #1

B15n Clone - interior, no board #2

B15n Clone - front, completed

B15n Clone - top, no cabinet #2

B15n Clone - back with cabinet

D.I.Y. 5f2 Champ/Princeton Clone (2013)

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Originally uploaded April 2013

5f2 Clone

5f2 Clone - action shot

This is my first single-ended amp build. It puts out about 5 Watts, which is plenty loud, but not bonecrushing. It’s based on the Fender 5f2 “Princeton” circuit, which is quite similar to the 5f1 “Champ,” the main difference being that the 5f2 has a tone control. This is not a kit – the chassis, cage, and filter choke are from Hammond and I kind of winged it with the drilling. The transformers are from Classictone and the tubes are JJ.

Princeton/Champ DIY builds have been done many times, but now that I’ve built my own, I can see, and hear why so many people like having at least one of these around.

If you see anything I’ve said here that might be inaccurate or wrong, please let me know so I can correct it.

5f2 schematic

Below are the schematic diagram for this build (left) and a possible build layout (right), and a video to prove that my latest squid launcher actually works. The layout diagram is close to what I actually built but not exact, and it’s not to scale – it just shows where things can go for minimal wire-crossing and halfway-decent ground distribution.

5f2 Clone schematic   5f2 Clone - layout

Take the layout diagram with a grain of salt – the resistors that connect directly to the grid inputs of the tubes (R2, R5, and R10) really should be soldered directly to the socket pins, with as little exposed lead as possible. Also, the cathode resistor for the power tube (R11) probably should be rated > 3W.


Since I’ve never gotten my grubby hands on an original 5f2 or 5e2, everything I’ve learned has come from schematics, sound samples, video clips, other people’s blog posts, and discussion boards. But from what I do know, the main differences between this build and a ‘canonical’ 5f2/5e2 are:

1. Different location for the ‘tone’ control. I put ‘tone’ in quotes because it’s just a low-pass filter. For this build, ‘tone’ is situated after the second triode just before the power stage, as a 10n capacitor to ground and a 250k pot.

2. Larger values for the B+ filter capacitors. The 5f2 used ~= 8uF whereas this build uses a 10uF after the rectifier, and 47uF for B+2 and B+3.

3. 6L6 power tube instead of a 6V6. I like 6L6 in general.

4. The 5f2 had a feedback resistor between the secondary side of the output transformer and the cathode of the second triode stage. This build doesn’t. Originally I had one but I thought it made single-coil pickups sound too harsh so I got rid of it.

5. This build has a (relatively) large bypass capacitor in parallel with the plate resistor of the first triode stage. It rolls off high frequencies and helps to alleviate the ‘icepick’ effect at high volumes.

6. This build has a 220k grid-stop resistor at the input to the second triode stage of the preamp. Like the cap mentioned in #5, it helps to roll off high frequencies.

7. This build uses an elevated heater supply (see schematic) with a DC offset of about 45 Volts for the filaments, to reduce AC hum.

8. This build has separate outputs for 16, 8, and 4 Ohms. The 5f2 usually had a single output.

5F2 Clone - complete   5f2 Clone - back view

I’m sure there are other differences I’ve forgotten to list. There is a little AC hum but it’s quickly overpowered as the volume knob goes up. Overall, the build is a little messy – I didn’t really know how it would go together when I started it, and I made a zillion little tweaks to it. I left the transformer leads a little bit long in case I reuse the transformers for other projects. Next time, I’ll use a chassis that’s higher than 2 inches, and a little wider for better component spacing – the choke just barely fits. Near as I can tell, I’m getting about 5 Watts at the output (assuming 50% loss for a single-eneded output transformer). That’s plenty of cowbell for just sitting around playing.

Like the original Champ, this build does not use a master volume control. That means the power stage is always running near full boil. As the Gain knob goes clockwise, the volume increases, but so does the clipping.

The Classictone output transformer I used (40-18031) has two different leads for 5k and 8k primary impedances. I’m using 5k here for a 6L6. 5k would also work for an EL84. 8k would be good for a 6V6.

5f2 Clone - top view

Above, from left: 12AX7 preamp tube, 6L6 power tube, 5Y3 rectifier. All the tubes are JJ. I’ve been  getting good results with JJ tubes lately, especially the JJ 6L6. The ‘sag’ from the 5Y3 rectifier is really obvious in the sound of the amp: to me, it’s like the signal is hitting a rubber wall when I lay into the strings. The knobs, from left, are volume and tone. There is no ‘master’ level control. The volume pot controls the strength of the signal from the plate of the first tridoe stage in the preamp to the grid of the second triode stage.

5f2 Clone - another top view

Below are photos of the interior. It’s pretty obvious that I had some issues with the layout.

For this build, I tried ‘floating’ the filament wiring (green twisted wires) instead of having them hug the chassis.

5f2 clone - interior #1

5f2 Clone - interior #2

5f2 Clone - interior #3

5f2 Clone - interior #4

Tube Guitar Amp #1 (2012)

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Videos are at the bottom of this page.

As of April 18 2012, my first D.I.Y. tube guitar amp appears to be functioning normally. I made a huge mess and a lot of mistakes with it but it came out fairly well for a first try, and was definitely worth the time and expense because I learned quite a bit.

hta1_roughHere is a schematic that’s more or less like what I made, which is based on the AX84 designs (see ax84.com, a website for tube-amp enthusiasts). This schematic is incomplete and has some mistakes in it – the tonestack is not represented and the filament supply of the Hammond 270FX power transformer should marked 5 Amps, not 3 Amps. The transformer, a Hammond 1650F in this case, is matched better to a pair of 6L6’s than to EL34’s, and the poweramp section isn’t right for a pair of 6V6’s, which start red-plating right away.

See below for why the tonestack is left out. If you want to see tonestack schematics you can probably bring up 500 of them in Google in about 20 seconds.

ta1_interior3   ta1_interior2

The vertically-mounted perfboard is for the the power tubes’ negative bias voltage, which I wound up not using because I opted to cathode-bias them instead.

One of the dumbest things I did was to cram most of the DC filter capacitors onto the turret board. I should have used dual can caps for all the filter-cap stages instead of just the first two, so all the ground lines could be run straight back to the star ground.

ta1_underside   ta1_interior1

Since the poweramp is cathode-biased, I don’t have to adjust a negative supply voltage every time I change tubes. I’ve been able to load EL34’s, 6L6’s, and 6V6’s, all with very distinctive results, although I can’t keep using 6V6’s because they overheat in this circuit.

The EQ is not a standard 3-band stack. The bass control is just a high-pass filter, the mid is a twin-T notch, the treble is a low-pass filter. And they’re wired in series, respectively. I’m not thrilled with the EQ but a standard 3-band Fender-style EQ sounded awful with the overdrive stage, probably because of impedance mismatches and certain sections I didn’t wire up all that well.

The tubes in the photos are 6V6’s but I stopped using them because they red-plate (overheat). I used EL34’s for the videos but I’ve been using a 6L6 pair lately because they give me a better low-end response than the EL34’s. That isn’t surprising since the impedance of the output transormer (about 7.7kOhms) is way out of whack with an EL34 pair would expect (3-4kOhms would be better). I’ve got the amp wired for a single 16-Ohm output because at this point all I’ve got is a single 16-Ohm speaker.

ta1_top1   ta1_top2

ta1_back1   ta1_back2

Crunchity-crunch, with a Gibson SG:

Medium/high gain, with a Gibson SG:

Sort of clean, with a Fender Strat:

Medium/high gain, with a Fender Strat:

Electric Viola #1 (1999)

m_viola_boardComments are disabled because I got tired of the endless spam. For questions, comments, and/or dilemmas, email th@thallenbeck.com.

Before it was a viola, it was a plain maple board. Maple is a preferred wood for solidbody instruments because it’s dense, close-grained, and carves well, it holds up to changes in air pressure and humidity, it’s strong and doesn’t warp, scratch, or split easily, and it transfers sound well, which is good for instruments that require electronic pickups or transducers.

m_viola_frontI carved the body from the maple board pictured above and attached it to a separate curved piece at the bottom to support a chinrest and the transducer jack. The fingerboard is made of ebony and was purchased at Ifshin Violins in Berkeley, CA. I bought the fingerboard in a semi-finished state – it was already shaped, but I smoothed it out with two steps of fine sandpaper and polished it with #0000 steel wool.

The bridge is a standard viola bridge (the kind with adjustable feet, good for a flat surface), also obtained at Ifshin.

To reduce the weight on the top end, I mounted the tuners – in this case Schaller Rotomatics – on the bottom end rather than where the peghead should be. The strings are threaded through small holes at the top of the neck and anchored to the underside with rubber washers.

I got the dimensions for this instrument from a 16-inch viola.

m_viola_closeThe black wire from the transducer jack to the bridge ends in a folded copper tab that slides into the bridge slot; the tab transfers vibration in the bridge to a piece of piezoelectric material that converts this vibration into electricity, which is in turn converted into sound by an amplifier. The transducer is a Fishman violin pickup.

The chinrest came from Ifshin. I splurged for a nice wooden one instead of a plastic one.

The tuners are mounted on the underside of the body because that’s how you’d mount them on a guitar – notice the absence of a standard tailpiece. Fine-tuning pegs are not an issue here, because guitar tuners provide more precision that standard tuning pegs do.

The tonguelike thing underneath the instrument is a shoulder rest shaped from maple and attached to the underside of the body.

 

Electric Cello #4 (2008)

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This is a copy of records I kept during 2008. Last update was 4/19/08. Note: a couple of the photos show drawings with measurements. I do not have those anymore. I don’t know what happened to them.

This is the fourth electric cello I’ve made. I did the others several years ago and it’s been a while since I’ve broken out the hand tools. I’m making this one to 1) try to address issues that I never quite resolved with the others, and 2) save myself some money.

After scrawling out a few semi-coherent sketeches, I got a board of rock maple at MacBeath Hardwoods in Berkeley CA and made some rough measurements.

ecello4_001_board_01   ecello4_002_board_02

ecello4_003_board_03

After rough carving. I cut the basic shape with a circular saw and a handheld jigsaw, trimmed up the sides with a ryoba saw and a hand shaver, and shaped the neck, headstock, and body with bench chisels, some rasps, and more hand shaver action. The body as measured was way too heavy, so I narrowed it considerably.

ecello4_004_roughcarve_01

ecello4_005_roughcarve_02

 

The back of the body. At this point, the whole thing is sanded up to 220 grit, after 80 and 150 grit.

 

 

ecello4_006_roughcarve_03

 

The neck heel and thumb heel. They’re not entirely symmetrical and neither is the headstock but I’m not going to worry about it too much because it should be playable as is.

 

Below: fingerboard clamped to body after gluing. The fingerboard is made of graphite. I got it from Moses Grapite in Eugene OR. I haven’t decided if I like graphite or not. At least I think it’s graphite – maybe it’s carbon fiber. Maybe they’re the same thing. Whatever it is, it carves well and behaves much like ebony, but when sanded, it leaves gray gunk all over everything that’s tough to remove, especially from wood. I don’t know if graphite is toxic or not, so when I carve or sand it, I wear a respirator, goggles, and gloves.

ecello4_007_fboardclamped_01

I prefer Titebond for wood glue, and fortuitously, Moses recommends it for gluing their graphite (carbon fiber?) products. I like Titebond II for fingerboards, because it has a shorter set time than the original flavor.

I drilled the tuner holes in the headstock with a 1/2-inch bit and reamed them out a little to acommodate Gotoh bass tuning machines. The holes are on a diagonal so that the strings can reach the tuning posts from the nut (which will sit at the top end of the fingerboard) without bumping in to anything inbetween.

ecello4_008_fboardclamped_02

 

I should have clamped every two inches or so but that’s all the clamps I have.

 

 

ecello4_009_neck_01

 

“Bass” side after filing and sanding the neck flush with the fingerboard.

 

 

ecello4_010_neck_02

 

“Treble” side before filing and sanding. I deliberately cut the neck a little too wide so that it would trim up flush with the fingerboard.

 

ecello4_011_neck_03

 

“Treble” side after filing and sanding.

 

 

 

 

ecello4_012_pegheadveneerclamped_01Headstock veneer, glued and clamped. The veneer is Macassar ebony, which is easier to get than Madagascar ebony, which has a more uniform dark-brown color. I got the veneer wood from Luthiers Mercantile International in Windsor CA.

 

 

 

 

I trimmed the veneer with a dozuki saw and then filed and sanded it flush. Since I don’t own a router, I cut the hole in the middle by drilling at the top and the bottom, cutting between the holes with a jewelers saw, and then cutting and filing until the sides were reasonably straight and the top and bottom curves matched. Ebony is good for that sort of thing.

ecello4_014_pvtrebleside_01   ecello4_013_pvbassside_01

A lot skipped here: installation of Gotoh bass tuners, finishing of the body (see below). I sanded the body from 200 grit to 400 and then 600 grit. Then: three thin coats of shellac with an amber stain, sand at 600 grit between and after the final coat. Then: two thin coats of tung oil, rub the first coat down with a cloth. Final coat of tung oil -> dry -> sand with 1200 and then 1880-grit micromesh. The camera doesn’t really pick this up, but the body now has a very light amber/honey color.

ecello4_016_afterfinish_02

ecello4_017_afterfinish_03

ecello4_019_afterfinish_05

March 14, 2008: rough fit. Last night, I strung up the cello with the tailpiece, a bridge borrowed from one of my previous instruments, a makeshift piezo transducer pickup, and the rough-carved nut. Shown below are the tailpiece, bridge, and pickup.

ecello4_021_rough_tailpiecebridge_01  ecello4_022_rough_tailpiece_01

The tailpiece is TIG-welded plain steel. Originally, I had the strings mounted through the holes in the bottom piece, but I didn’t like the angle of the strings from the bridge, so I welded the brackets on and bent them with pliers so that the angle of the mounting holes wouldn’t strain the strings too much. I might replace the 7mm hex bolt with something more elegant, and I’ll probably either paint the taipiece or use some sort of blackener on it. The 1/4″ jack is attached to the extension at the bottom to provide some grounding for the transducer pickup.

ecello4_022_rough_bridge_01

The copper-wrapped tab under the bridge is a thin film of piezoelectric material wrapped in copper tape, which can be found in most gardening sections of hardware stores, because snails and slugs don’t like copper.

The piezoelectric material responds to the vibration of the bridge with small changes in the electrical field it’s part of. An amplifier can convert these small fluctuations into sound.

One big problem with piezo pickups is noise. Some people say that shielding the circuit doesn’t help much, but I’ve found that it does somewhat, although piezo noise tends to be more from lack of a proper ground than from lighting fixtures and such. The noise is akin to a low-frequency hum that sounds to me like it’s DC current that has no way to leave the circuit. Isolating the piezo side of the circuit with a transformer unit usually helps. A DI (direct box) can be used for that purpose. So can a preamp unit. Some preamps seem to act as buffers that eliminate piezo hum noise even if you run a 1/4-inch unbalanced output instead of an XLR (balanced a.k.a. properly-grounded) output. But not all do, so you have try different things. A DI, however, is probably a better bet for ground loop suppression.

Grounding the piezo to piece of metal, like I did here, helps a tiny bit, but that’s still a floating ground, not an “earth” ground, and is effective really only when the player is touching the strings, which in turn touch the tailpiece, which in turn touches the piezo circuit. In other words, the player is the ground. Update 4-19-2008: Contrary to previous: shielding does seem to make a big difference, at least with the MSI piezo tab I used for this project. Grounding through the instrument to the player doesn’t make much difference. DI ground loop isolation is more effective. Doesn’t mean it’s applicable to all piezos, though – Fishman pickups are different.

Another big problem with piezo pickups is that they can sound tinny and weak. That’s often because of impedance mismatches. Piezo pickups have extremely high impedance (AC resistance, denoted by Z) in Megohms, and when they’re plugged into an ordinary guitar or bass amplifier, they can sound screechy, because most guitar/bass amps aren’t designed to handle inputs with impedances that high. Z matching can be done with a direct box in many cases. I’ve been using a passive DI in tandem with a preamp unit – more about that below.

A piezo transducer pretty much begs for a preamp of some sort, especially if you’re going to be using a cable more than a meter long. A number of preamp units offer very high input Z (4 to 10 MOhms), and output Z matched more to an amp or a board. In addition, many preamp units have both an instrument-level 1/4″ output (Z ~= 100k to 220k Ohms, sometimes balanced, sometimes not), and an XLR output (Z ~= 600 Ohms) for direct connection to a mixing board.

This is the signal chain I’ve been using lately:

1. Cello into SansAmp Para DI preamp (Z ~= 4.7 MOhms, seems to be perfect for this pickup).

2. XLR out from Para DI into the XLR output of a Radial passive DI box (600 Ohms to 600 Ohms).

3. 1/4″ input from DI into a Roland DB-700 bass combo amplifier (100kOhms to amp).

***Note that the DI box is wired “backwards.” This is known as reamping the input signal.

Although I could just run the Sansamp’s 1/4″ output straight to the amplifier, I’ve found that I get a cleaner and much stronger signal through the backwards DI box. The DI also deals with the ground-loop problem mentioned above.

There are quite a few DIY folks out there who have done a lot of interesting things with instrument amplification. Just type something like “piezo impedance circuit” into Google and you’ll be swamped with information. Although I tend to use amps with high-impedance inputs designed for acoustic instruments, I may build an impedance-matching buffer preamp in the near future anyway – perhaps something like the Mint Box Buffer.

ecello4_023_rough_headstock_01This photo shows the nut with rough-carved grooves that hold the strings in place. I need to do some more filing and shaping here, but it does do what it’s supposed to. By the way, a cello is tuned C-G-D-A. The C string (thick one, leftmost), is sitting a little high and needs a less extreme angle on its way to the tuner post, so I’ll have to break out a wider file.

ecello4_024_rough_headstock_02Another view of the nut. The tuners, by the way, are positioned so that each string can make its way from the nut to the tuning post without running into anything else.

 

 

 

Pending: finishing on tailpiece, the real piezo pickup, end pin brace.

March 30, 2008: brace pieces

The instrument is shaped like a cricket bat with strings. It’s playable, but without some sort of bracing system to hold it at the proper position and angle, the player would be a hunchback in a week.

The bracing system has to:

  1. Hold the the instrument at a position and angle that will imitate the dimensions of a real cello.
  2. Provide the three contact points where a real cello touches the player’s body: upper chest, and insides of both knees.
  3. Have an end pin of adjustable length that touches the floor.
  4. Be detachable and modular so that it will fit into a carrying case along with the instrument.
  5. Be relatively strong and rigid.
  6. Be relatively light.

At right is a photo of the late, great Mstislav Rostropovich, at Checkpoint Charlie when the Berlin Wall came down. I’ll use this photo as an example of a real cellist playing a real cello. Not how the fingerboard and bridge are several inches away from his body. Also, note how the endpin floats the instrument.

Most cello endpins extend parallel to the plane of the instrument. Note the angle of the endpin in the photo. It’s decidedly not parallel to the plane of the instrument. Rostropovich was notorious for this construction tweak, which was considered unusual. Here at Hallenbeck Labs, we consider it good and will emulate it, for reasons discussed below.

ecello4_025_brace_all_01From the front, the brace is cross-shaped. The vertical section (middle in photo) aligns with the body of the instrument. The crosspiece (bottom in photo) bolts to the vertical section at a 90-degree angle. The end pin (top in the photo) slots into the bottom of the vertical section.

ecello4_027_brace_endpin_01The vertical section is angled back at the top and the bottom to provide contact points in the proper positions. The piece that looks like a cane handle at top of the vertical section is shaped roughly to the dimensions of the back of a real cello at the neck heel, where the instrument rests against the player’s upper chest. The bottom of the vertical section is angled back to simulate the way a real cello balances on its end pin.

When I built a wooden model of this, I had the end pin extending straight out, and it didn’t feel right that way – the end pin of a real cello touches the floor closer to the player’s feet. To me anyway, the overall arc shape of the vertical section seems to mimic the dimensions of a real cello. Thus the emulation of the ‘Rostropovich angle.’

Below left: the part that sits against the player’s chest, behind the instrument. Below right: one of the pieces that sits near the inside of the player’s knee.

ecello4_026_brace_upper_01   ecello4_028_brace_side_01

The brace section bolts to the back of the instrument and is of course removable. The sleeve on the bottom side of the instrument is for the tailpiece.

ecello4_029_brace_mounts_01   ecello4_030_brace_on_01

Above right: this award-winning shot shows the instrument mounted on the brace. The vertical section is bolted to the back – note the curved piece peeking out behind the top section of the body and upper left. The crosspiece section is bolted to the vertical section. The endpin slides inside the lower end of the vertical section and is held in place by the set pin. Better photos of the brace later… after I clean up the huge mess I’ve made in the basement.

The final tweak to the brace will be rubber or foam of some sort over the parts that make contact with the player’s body.

Next: Final assembly and tweaks

ecello4_031_bridge_01This is the tailpiece after I applied a blackener solution. I use a room-temperature gel called Tool-Black made by somebody named Precision Brand. The stuff is kind of expensive so I have to be judicious about how I use it. I figured this was worth it. After applying the blackener, I wiped the tailpiece down with a rust sealant.

 

ecello4_032_bridge_pickup_01   ecello4_033_assembled_01

Above: tailpiece, brand-spankin’-new transducer, and brand-spankin’-new bridge. This transducer uses a Neutrik 1/4-inch phono jack and also has a ground wire because the Neutrik jack has a plastic (not metal) casing. I shielded the jack with copper foil tape just like the piezo end. Since the jack’s shielding makes contact with both the jack’s ground terminal and the tailpiece, the ground wire isn’t really necessary, but I thought it would be good to have in case the shielding gets munched. Eventually, I’ll replace the alligator clip on the end of the ground wire with something less unsightly.

I had to move the piezo tab of the transducer around for about an hour to find the best position for it. Placement is very important for a piezo pickup – moving it a couple of millimeters can radically alter the signal it sends to an amplifier. Between the ebony piece and the body, under the D and A strings, the response is strong and even all across all four strings. Beats me why that’s the sweet spot, but anything piezo-related is funny that way.

ecello4_034_newbridge_01

Above: another view of the bridge. It’s probably too thick and I may swap it out with something better in the future… but it seems to work and I’ll keep it for now to see how it goes.

I made the bridge a two-piece assembly (maple upper, ebony lower) to maxmize the number of possible positions for the piezo film tab, which can be positioned between the ebony piece and the body, or somewhere between the upper and lower pieces, which are not glued together. The ebony piece has feet to reduce interaction with the body, and is notched on the top of both short sides to allow the piezo tab to be inserted parallel to the bridge, if necessary, without damage to the contact plugs at the end of the tab.

The bridge assembly is not glued or fastened to the body in any way – it’s held in place only by the tension of the strings. For bowed strings and mandolin-style instruments, that’s how you want it. Fixing the bridge in place would be bad because it would prevent any adjustments for intonation (unless the bridge were to have moveable string mounts, like a Gibson Les Paul bridge).

Since I wound up placing the piezo tab under the foot of the lower piece, I didn’t really need to make the bridge a two-piece mousetrap. But I’m glad I did, because I learned a lot about how (not) to do it next time.

April 18, 2008: Done for now

ecello4_035_f_full_01   ecello4_036_f_full_02   ecello4_037_f_back_01   ecello4_040_f_fingerboard

Actually, it’s been done for now for a couple of weeks. The only real change is that I put shrink tubing around the pickup jack.

ecello4_039_f_tailpiece

Above: tailpiece and transducer jack. As it turns out, the ground wire isn’t really necessary, because 1) the copper foil is making contact with the tailpiece, and 2) the shielding seems to have been a lot more effective than I thought it would be.

ecello4_038_f_back_02   ecello4_041_f_brace_01

ecello4_042_f_brace_02   ecello4_043_f_bridge

Quick-‘n-dirty sound samples

Recorded April 19, 2008, Oakland CA, in ProTools 7.3.1 on a G5 iMac. I ran the cello pickup through a Fishman Pro-EQ II preamp directly into an MBox, to see how clear a signal I could conjure. It fared pretty well in my humble opinion.

C-major scales/arpeggios. Demonstrates the full pitch range of the instrument (except for extreme highs on the A string).
Bass line that fits “King of the Road.” Demonstrates the pizzicato (plucked) tone.
“Blue Moon of Kentucky,” more or less, with two tracks panned left and right.

Piezo transducers aren’t really meant for direct console input – they’re more for playing live, for bowed instruments, anyway. Consequently, these sound clips have a weird, cheesy, old-synthesizer tone one might hear at, say, the public hanging of Bubbles the Clown.

Lately, I’ve had the cello chompin’ happily through a standard bass amplifier and it sounds a whole lot better than the clips above, with much less of the “Clown Must Die” tone.

That’s it for now. Thanks for reading. I hope this build report has informed and/or inspired you. -TH

 

Electric Cello #3 (2000)

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I made this back in 2000. The photos here are the only ones I still have.

Electric Cello #3 (2000)With my third solidbody electric cello, I decided to try a more compact design and concentrate more on function than on form. So I went back to the ‘baseball bat’ concept of cello #1, and came out with something like the Village Idiot version of the electric cellos made by Jensen or Ned Steinberger. Instead of mounting the tuning pegs on the headstock like my previous two cellos, I put them at the bottom like on viola #1. I don’t know if that was a good idea or not, but it certainly looks futuristic, doesn’t it?

The scooping of the body, to allow for a more-or-less normal-height bridge, was an interesting but irrelevant experiment. Since the cello is suspended and the player doesn’t have to rest it against his/her body, there is no need to shape the instrument to match the physical layout of a standard cello. I probably should have done the whole thing flat, used a lower bridge, and mounted the tuning pegs at the top. Live and learn.

Electric cello #3 (2000): bridge and tunersThe cello is mounted on an assortment of drum hardware I got at Univibe Music in Berkeley, CA (long live Univibe). I had to mix and match pieces to put together something that would serve up the proper angles, but the assembly is reasonably stable and seems to adsorb most extraneous vibration.

Instead of dropping big bucks on another transducer, I made my own this time. Actually, I pulled the plastic casing off a Radio Shack piezo transducer (available for about three dollars), and soldered the leads to an audio jack (inside the black box on the back of the instrument). After putting the strings on, I moved the tranducer around to test the tones, and concluded that placing it under the treble-side foot of the bridge (near the A and D strings) gave the most even sound. See viola #1 for more on transducers).

Electric cello #3 (2000): sideThe bridge is a standard cello bridge that I filed down to fit the dimensions of this instrument. It’s a 3/4 bridge, because I couldn’t find a cheap full-size one.

The tuners are bass guitar tuners, like on cello #2.

The fingerboard is premade, from ebony.

 

Electric Cello #2 (1999)

Comments are disabled because I got tired of the endless spam. For questions, comments, and/or dilemmas, email th@thallenbeck.com.

I made this back in 1998. The photos here are the only ones I still have.

Electric cello #2 (1999)This was my first real mostly-from-scratch woodworking project. I made lots of mistakes and bad design decisions, but I’m still proud of it. The body is about 42 inches long from the top of the headstock to the lower end, more or less like a full-size acoustic cello. The two maple crosspieces behind the body do a mediocre job of simulating a real cello when you sit in a chair and play it – the bottom piece is a too heavy, but it gets the job done. The endpin is real cello endpin threaded through the bottom crosspiece and held in place by a keyed screw. The fingerboard is ebony (I bought it premade), and the black goblet-shaped thing at the bottom is a metal cello tailpiece. All the parts came from the same places the viola parts came from (see viola #1), for about the same prices, except for the tuners, which cost more because they’re bass guitar tuners.

The body, neck, and headstock are carved from a single piece of alder. I’d seen alder body blanks for electric guitars, and they were hard as rocks, so I went out and got an alder board figuring that alder just came that way. Near as I can figure, alder body blanks must be treated with something. I discovered that although alder is close-grained and sturdy, it’s a little too soft and scratches easily. I arrived at this conclusion when I was almost done carving the body, so I just went ahead with it because I was in too deep to chuck it.

Electric cello #2 (1999): side of neckAnother problem with untreated alder is its acoustic properties: it seems to either dampen higher frequencies or amplify lower ones – I can’t tell which. Of course, I didn’t discover this until I had the whole thing together and popped on the transducer. The tone isn’t bad, but the high end needs assistance from a preamp to sound right.

The neck heel (where the neck flares out to meet the body) is carved to mimic the neck heel of a standard cello. For violin-family instruments, you know the neck heel is shaped properly if you can place your thumb in it, your index finger directly over it on the fingerboard, and play a perfect fifth above the open string. Of course, bridge placement is also a factor, but it’s easier to place the bridge properly if you’ve done the neck heel correctly). This instrument, I’m happy to say, satisfies the perfect-fifth requirement.

It’s hard to tell from the photos, but the headstock is angled back to provide tension for the strings where they sit in the nut grooves. I carved the nut from a block of ebony.

Electric cello #2 (1999): backThe tuners are mounted on the headstock so that they will point away from the player’s (in other words, my) head (I’m a southpaw but I still play right-handed). Having machine tuners for a cello is great, because you don’t have to mess around with pegs.

The bottom photo shows the body up close. The ornamented rectangular thing below the fingerboard is actually there to cover up a big gouge I made in the body with a chisel. The bridge is cut from a thin maple board – I couldn’t use a standard cello bridge because the fingerboard sits so low. The transducer is fastened to the metal tailpiece to reduce ground hum (a persistent problem for Fishman cello transucers), and the black wire from the transducer is connected to folded piece of copper inserted in a small tab in the bridge (see viola #1 for more on transducers).

Electric cello #2 (1999): lower halfIf I had it to do again, I’d mount the back crosspiece lower (and make it less bulky), so that there is less endpin sticking out. At some point, I’m going to saw off most of that top stablilizer backpiece, because most of it is unnecessary. Once again, live and learn.

Electric Cello #1 (1998)

Comments are disabled because I got tired of the endless spam. For questions, comments, and/or dilemmas, email th@thallenbeck.com.

I made this back in 1998. The photos here are the only ones I still have.

m_cello1_1This funny-lookin’ dealie is proof of Bertolt Brecht’s assertion that ‘art is not pretty.’

Since this was my first foray, I wasn’t overly concerned with materials; the body is made from an oak floorboard. The fingerboard, which I got at an Oakland, CA repair shop for about fifteen dollars, is some kind of hardwood, perhaps maple. The bridge is poplar or something like that, and the body is finished with black spray paint and a spray laquer.

Despite the shortcomings is design and construction, the darn thing actually plays. The sound is a little tinny and synthesizer-y, but still workable. It’s difficult to play, though – I had to construct a Rube-Goldberg-like contraption out of metal bars and clamps to hold it in place.

 

 

 

Electric cello #1 (1998): headstockLike cello #2, this cello uses bass guitar tuners on the headstock instead of pegs. In this case, I used the cheapest ones I could find. Since I went ahead and just did everything instead of thinking about it first, I discovered that once I’d drilled the holes for the tuners, the tuner for the C (leftmost) string would stick right out at the player’s temple. So I carved a hole in the headstock so that the C tuner could be angled to sit inside it and thus no longer be a threat to the player’s health.

Electric cello #1 (1998): backElectric cello #1 (1998): bridge and tailpieceThe string guides are hex bolts that I found in the trunk of my car, and that oh-so-lovely sheen is from the Testors model paint which I mistakenly thought would look cool.

On this cello, I started experimenting with ideas that I continued with on instruments. After messing around for a few days I got familiar with carving curves, cutting and shaping my own bridges, fiddling around with tailpieces transducers, and general body constructions.