I’ve always wanted to build a one-knob guitar amp, so I did. It’s another Champ/Princeton clone without the tone control. 1 x 12AX7, 1 x 6L6 (not 6V6!), ‘canonical’ 5Y3 tube rectifier. The main lesson I learned was that a one-knob guitar amp is cooler in theory than it is in practice, and that adding minimal tone-shaping (in other words, a ‘High’ or ‘Bright’ rolloff) is worth the (minimal) effort.
On the other hand, it was interesting to try to balance the output for a range of instruments (guitars). I used a Telecaster, an SG, a Strat, and a Les Paul with custom pickups when I was deciding what values to ‘hard-code’ for bypass capacitors and whatnot (see C2 and C5 in the schematic below). The video was done with just a Tele because I was too lazy to include anything else.
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Here is an action-packed video of the ‘Uno Knobbo’:
And here is the schematic:
Note: the schematic shows the feedback resistors connected between the output jacks and the cathode of the second preamp stage. I thought the result was muddy so I disconnected them for the video above.
Also, the schematic specifies a 6V6 as the power tube but I used a 6L6 instead, because I thought it was a little more articulate at high gain levels. As I recall, I used the 5k tap of the output transformer for the 6L6 (brown wire), instead of the 8k tap (red wire).
Please refer to the 5f2 clone I did a few years ago for more.
What I came out with this time was fiddly and awkward because I didn’t think the layout through as well as I could have. A better layout for this sort of 5-Watt clone would be the the previous project referenced above. If I do anything like this again and I use one of those Hammond Enclosures again, I’ll probably use that layout, with separate, smaller turret boards. Here is the layout for good measure:
Here is a 5f2 schematic
I tried the Uno Knobbo with several speakers and I like the Eminence Lil’ Texas the best, maybe because they rolled off the piercing high end and the two Jensen speaker I tried didn’t. All the speakers I tried were 12″ because I don’t have any 10’s.
By the way, if the enclosure looks weird, it’s because I tried doing my own powder coating on it, with limited success. That was fun though.
Also, I stuck a TH Audio badge to it because I had a few lying around – I’m not planning to sell these (yet) under my side business.
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Here are two videos of the Spirit of 86. The first one is done with a Fender Telecaster and the other is with a Gibson SG. Scroll down for photos and an erudite philosophical discussion.
This is the Spirit of 86… or as I like to call it, the Buttrock Express. It’s like a little shrine built around an EF86 tube (http://en.wikipedia.org/wiki/EF86). A couple of years ago, I started wondering why I knew of a number of amps that use an EF86 as a first preamp stage, but I’d never heard of any amps that use a preceding tube to drive an EF86 (of course, that doesn’t mean there aren’t any). I thought it might have been because it would just sound horrible or because resonance and microphonics would get the best of the EF86, but I really wanted to find out. So after dawdling around for several months, I put one together last year, with parts and components I happened to have handy, and I tweaked it every few weeks until a few days ago when I decided to immortalize it in a blog post and stop fiddling around with it.
To the right are a schematic (above) and a diagram for a possible layout which is close to the one I used for the amp. Of course it’s not the only possible layout, and the positioning of the elevated heater supply (upper right) is arbitrary – I wound up kludging it onto the end of the turret board.
In the layout, the ground connections (thick blue lines) are an approximation, but most of the points that connect to a specific location such as the from the Gain control to the turret board are drawn that way for a reason – to reduce noise – because this project was probably the most noise-prone one project I’ve done to date. The biggest problem was AC hum. Randall Aiken has a good article about grounding in tube amps and why it’s not always good to perceive the ground as a sort of uniform field:
… and I try to do whatever the voices in Randall Aiken’s head tell me to because it almost always pays off. Side note: I tried grounding the EF86 tube to a couple of different points on the turret board instead of running the ground back to the star. I really thought it would make a difference in noise level but didn’t, to my ears anyway.
This project has been interesting and educational for me, but I still can’t decide if I like the way it sounds or not. The overdrive is aggressive and “gnarly” for lack of a better term (which makes sense because the EF86 is a pentode), but it doesn’t have a lot of sustain or the “squishiness” of cascaded triode stages. I suppose that might be a good thing for articulation and clarity if this amp were being played by someone with better guitar skills than I possess.
The Buttrock Express might serve as a template for an overdrive channel at a future date. Getting a nice loud clear clean tone out of it is an exercise in futility.
The Thomas the Tank Engine sticker on the front face is there to cover a drill hole that I would up not using. The TH Audio badge is there because I had some extras – this is just an experiment, not something I’ll be offering through TH Audio (my side business for effect pedals and, eventually, amplifiers).
Controls are, from left: Bass, Mid, Treble, Gain, Bright, and Master Volume. The Bass/Mid/Treble controls are a fairly standard Marshall-style 3-band EQ positioned after a cathode follower. The EQ stage uses a couple of unusual values: 68k for R7 (see schematic) and 250k log for the Bass pot (instead of 500k or 1M, to counteract the mounds of low frequencies that pile up). The Bright and Master controls are connected near the input to the power tubes, like one might see in a Vox AC15.
The amp dishes about 20 Watts, with a 6.6 kOhm output transformer and a 6L6 push-pull pair. At 20 Watts, the 6L6’s aren’t doing much, but I keep them there because a) the OT I’m using is a nice match for them (better than the 4k OT I was using previously, b) a 6V6 pair sounded glassy and midrange-y, and c) I wanted to hear the EF86 overdrive without an extra layer of power-tube breakup.
I used a tube rectifier instead of some diodes because… well, because I could, I guess… although the tube rectifier might be introducing a little ‘sag’ that mellows the general gnarliness of the pentode overdrive. To be honest, I don’t know if it does or not.
For this project, I used Tung-Sol tubes because… well, because I already had some. I’ve swapped out the Tung-Sol set with an Electro-Harmonix set, and I don’t hear much difference at all. In either case, it wasn’t difficult to get something close to 90V at the plate of the EF86, once I figured out the voltage drops. Normally, I like JJ tubes and have used them in a number of projects, but to my ears, the JJ EF86 sounds weak in this particular project (I tried two different ones).
One last thing: this amp is *not* a clone of the Dr. Z Route 66. The Route 66 uses a single EF86 into a passive EQ section, to a phase inverter and a fixed-biased KT66 push-pull pair. The Spirit of 86 uses 12AX7 -> passive EQ section -> EF86, into a phase inverter and a cathode-biased 6L6 pair (which is hardly doing any work).
-T. Hallenbeck, Oct. 2014
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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.
Below is an exciting video documenting the tail end of this build. Please keep in mind that I’m not exactly Tony Levin.
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.
2. 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.
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.
6. 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.
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Originally uploaded April 2013
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.
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.
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.
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.
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.
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.
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.
Here 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.
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.
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.
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:
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.
I 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.
The 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.
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.
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.
The back of the body. At this point, the whole thing is sanded up to 220 grit, after 80 and 150 grit.
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.
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.
I should have clamped every two inches or so but that’s all the clamps I have.
“Bass” side after filing and sanding the neck flush with the fingerboard.
“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.
“Treble” side after filing and sanding.
Headstock 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.
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.
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.
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.
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.
This 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.
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:
- Hold the the instrument at a position and angle that will imitate the dimensions of a real cello.
- Provide the three contact points where a real cello touches the player’s body: upper chest, and insides of both knees.
- Have an end pin of adjustable length that touches the floor.
- Be detachable and modular so that it will fit into a carrying case along with the instrument.
- Be relatively strong and rigid.
- Be relatively light.
I used to have a link here to the late, great Mstislav Rostropovich playing cello at Checkpoint Charlie when the Berlin Wall came down, but I don’t know what happened to it. It shows the endpin I modeled this one on.
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.
From 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.
The 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.
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.
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
This 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.
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.
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
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.
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.
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
I made this back in 2000. The photos here are the only ones I still have.
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.
The 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).
The tuners are bass guitar tuners, like on cello #2.
The fingerboard is premade, from ebony.
I made this back in 1998. The photos here are the only ones I still have.
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.
Another 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.
The 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).
If 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.