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Il D'oro Bass Guitar Amplifier

A blend of vintage and modern, analog and digital, form and function.

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The Il D'oro bass guitar amp will be 200W, tube amplified and solid state rectified, digitally controlled, either full or half stack, and optimized for extended ranged instruments.

I've wanted to build my own amp for quite a while. For bass guitar, the selection of amplifiers you can buy is pretty lack-luster, and mid-volume studio amps are hard to find. It seems like most of what's available is either a practice amp or a stadium rig, neither of which I need.

Enter Il D'oro - a true studio-minded bass amp. Since much of my experience is on the digital side, I'm going to include some digital bells and whistles for the project, too. Here's an overview:

- 200W - just enough to faithfully reproduce all the frequencies of an extended range bass guitar

- All tube amplification section (pre-amp, output/power amp), but with a solid state rectifier and power supply stage to make it lighter and more reliable.

- An ARM based digital control system - savable EQ settings, digital effects, and system monitoring

- LED Rotary encoders (instead of pots) with light spectrum readout, and an LCD screen to display metering and other system information

- Custom cabinet with 6", 10", and 18" speakers and 1 tweeter

There are still tons of details to iron out, but here's my plan for the process: Start with a basic tube-amp build using spare parts I've got around the house (EL84, 8 inch Peavey speaker, left-over plywood, etc.) just to get some practice under my belt, and use a dev-board (probably a Launchpad) as a prototype for the controls. Then, I'll design and build the amplifier in standard form. Once that's operational, I'll work on the digital additions. I'm shooting to finish this project by the end of 2015, and to log it all here on Hack-a-Day Projects! (and on my website, which I'll post when I'm satisfied with it... you might be waiting a while).

  • Not Forgotten

    Istantinople10/30/2015 at 17:37 0 comments

    Every now and then a skull still roles in for this poor project, despite the serious lack of actual work getting done. Thanks for all the skulls y'all! I appreciate it.

    As for why the lack of work, well two reasons. One: My wife recently gave birth to my first born child. I don't think I need to explain how that will put side projects on hold.

    Two: I work in the Oil and Gas Industry. Honestly, that's not an industry I was ever excited about joining, but living in New Orleans your options are pretty limited as an engineer when oil makes up the vast majority of the tech jobs in the area. And as you may have heard, layoffs and cutbacks are rolling through O&G right now, with my own company included. I'm spending a lot more time than before worrying about my job, especially when I think of the new little one back home.

    But I still think about this project. Most of what I have worked on in the last several months has been aesthetics. I'm working on a way to rat-nest the Spuntone electronics onto the surface of the amp, rather than burying them inside. I'm thinking about CNC routing channels into the surface of the wood for the electronics and putting something clear over the top of them. How will this affect the acoustics of the cabinet, though? No idea. But I can think of some ways to make it look really cool.

    In all likelihood, this project will drag on for years before I get a finished bass amp. There are just too many variables right now. But I hope you'll all enjoy the (slow) ride with me anyway.

  • I know I know I know I know I KNOW...

    Istantinople02/06/2015 at 13:44 0 comments

    Ok, so, this project is still entirely ones and zeros. I KNOW. Serious lack of follow through on my part. In my deference, this is where I am right now:

    That little blue dot in the Atlantic has been home for the last week. Also, my wife is pregnant with our first. It's been tough to justify working on a bass amp recently. But I'm still trying to find a little time here and there, and I had an idea a while back that I'll share today!

    I may have found a solution to my digital pot problems. There just don't seem to be off-the-shelf digital pots designed for this type of analog circuitry, as far as I can tell, but what is a digital pot anyway?

    Its just a network of fixed resistors and transistors (if you're over-simplifying it, which I am). There are plenty of those out there for the voltages I need. So I'll just make them myself! All I should need are 1) high watt resistors (duh), and 2) transistors that a) can handle CE voltages of ±550V, and b) can be activated by logic level voltages. I've already located some transistors that fit the bill, although their audio properties remain to be determined.

    Here's what I'm thinking: "pot cards". Design the digital pot onto a separate PCB that gets inserted into a socket on the main board, using a decoder to reduce the number of contacts. This way I'll be able to replace them if I screw it up somehow, or upgrade them if I decide I need something different, say a transistor with better audio qualities, more resistors for finer control, or an entirely different idea if this proves to be a terrible one. I'm planning to start with 16 steps of resolution for my test-set with Spuntone, which is very coarse but should be an adequate proof-of-concept. If the whole putting-it-on-a-card concept isn't a complete failure, I might include it on the 0.1.0 build of the D'oro and see how it goes.

    I've started thinking about some design aspects that I'd like to include for the Spuntone's cabinet design. I'm not sure why I care, since I don't plan on using this amp much long term, but I feel the need to make it special somehow. I'm planning on including an interesting kick-back feature, and I've made some drawings of the full form to get an idea of what the finished product should look like (yes, more crappy hand drawings like the main picture on this project, which I don't plan on posting since they're crappy).

    I'm not going to bother with timelines anymore, since they inevitably fall flat, but lets hope I can get some progress going soon. Be on the lookout for a parts-purchase update, followed by a my-first-tube-amp post.

  • Update 2

    Istantinople11/12/2014 at 22:13 0 comments

    I've dusted off LTSpice, and I'm getting started with some circuit simulations!

    While I've learned a lot, what's probably the most important thing is this: when they say tube amps are dangerous, they are not kidding. The power stage of this ity-bity 5 watt Spuntone operates at 275V loaded, and theoretically can produce 550V unloaded (although from what I've read, people are measuring more like 400V in reality). I'm not sure yet how much the voltages scale upwards with the wattage of the amp, but I imagine a 200W all-tube quad KT88 configuration will contain voltages well beyond lethal potentials.

    I haven't had a chance to look further into high voltage digital pots or voltage controlled resistors yet. In the interest of getting this project out of the computer and onto the workbench, I'll be making the first iteration of the Spuntone with regular old manual pots first. Then I'll look into retrofitting with the fancy stuff, as we'll still need to test everything that goes into the final build on the smaller scale.

    Expect a functioning build of one kind or another by the end of the year, and a finished Spuntone sometime in 2015 (hopefully in the spring).

    P.S. - thanks for the skulls! I'm still getting skulls every now and then despite the slow progress and lack of test data, which is super cool. Let me know what you're interested in and what you'd like to know about the project. And please point out any mistakes or errors in assumption that I'm making; after seeing those voltage numbers, I'd rather be shamed on the internet than burned in the workroom.

    Also, a buddy of mine from college, currently living in Seattle, is getting to work on his own custom tube amp. I've been talking to him about these projects, and we might be borrowing each others ideas, so this may turn into a bass and guitar amp project! You know, besides the dinky guitar one I'm already making.

  • Rule of Pi

    Istantinople10/07/2014 at 15:22 0 comments

    Back in college, one of my professors explained to us the Rule of Pi. While that probably meant something different in the math building, in the engineering building it meant the following:

    All engineering projects, big or small, will take approximately as much time as the original estimate multiplied by pi.

    -Dr. Paul Hummel, PhD

    One of my other professors later explained a related rule:

    Engineering projects can be good, they can be fast, and they can be cheap, but they can only be two of those at once.

    -Dr. Davis Harbour, PhD

    I have chosen good and cheap for this project, because I want a quality product and I don't have a lot of time/cash to put into it all at once. And so, I allotted about a year to finish the project. Then, as I found less and less time to work on my amp, the Rule of Pi started popping into my head.

    I really don't want this project to drag on for three years.

    I hope to have a new post in early November, with a plan of action around that tone-stack problem and some experimental data to post. At this point, I'm hoping that at least the practice build will be finished by the end of 2014.

  • ‚ÄčThe Hard Part

    Istantinople08/08/2014 at 16:07 0 comments

    As with all projects, there comes a point when you find you've exited your comfort zone, and this mysterious world of endless yet seemingly unachievable possibilities lies before you, leaving you with the choice of trudging forward magnificently or collapsing into a weeping puddle of ineptitude (panel 8/9). I'm currently doing a little of both.

    Here's a picture of the schematic for the BH5 which I found here, with thanks to Craig Barnett for creating it.

    I've started building this design stock (hope to have it functional within a month or two), but in looking at the project, I've found my first major design hurdle (one which should have occurred to me long ago, but oh well). Notice that tone stack? Notice how it's after the first valve? From my limited understanding, the first valve increases the input signal, then the tone stack absorbs much of the power which the second valve replaces before feeding the signal to the output tube. Amplifying the signal before the EQ helps with the signal-to-noise ratio. Now think about replacing those tone stack pots with digital ones. Yeah, that's the problem. 

    The high voltages in the tone stack might be too high for the vast majority of digital pots, not to mention some other nasty situations might occur during start-up or shutdown of the amp when various caps charge/discharge. I've found some digital pots, like the Analog Devices AD5290, which can handle 30 volts, but I'm not sure if that's enough depending on the situation. Digital pots sound very bad when they clip, so even a little extra voltage above the limits, while it might not damage the chip, isn't acceptable. And even though I might be able to get away with digital pots on the 5W Spuntone design, the 200W design might require higher voltages in the preamp stage (although it might not... after all, it's the preamp stage).

    There are alternatives to digital pots, however. JFET (second link) or MOSFET transistors can be used to create voltage controlled resistors rather simply. While more complicated, op-amp VCR's (page 12) are also an option to consider. Is it possible to move the tone stack to before the first tube? Maybe, although it would need to be redesigned for the drastically lower voltages and far less optimized signal-to-noise ratio (this would effectively be the same as placing an EQ in your effects chain and replacing the tone stack with fixed resistors or removing it altogether). 

    Either way, it's time to hit the workbench and the simulator, not to mention the phone to call my buddies who got good grades in college for some pointers. Now that my home and work lives have finally calmed down, I've actually got some time to devote to my hobbies again; but still, the end-of-2014 deadline is starting to look reeeeeeal shaky.

  • Update

    Istantinople04/24/2014 at 15:08 0 comments

    Hey everyone!

    First off, thanks to those following the project. You're awesome!

    Just wanted to supply an explanation for the inactivity. I recently relocated to NOLA (that's my home town, so it was more of an un-locating), and I've got a new job in a new industry. That's keeping me busy - long training hours at the office, frequent trips for certifications, finding a place to live, etc. It's going to be hard finding time for hobbies for at least a month or two.

    As I stated in a past post, the goal is to finish the project by the end of 2014, and I still think that's a valid timeline. I'm determined to complete this project and to document it all right here! So thanks for bearing with me during the transition.

  • Amp Names

    Istantinople02/27/2014 at 19:34 0 comments

    I feel like I should explain the names I'm giving to these amplifiers. Both names, Spuntone and Il D'oro, are in Italian because I happen to like the way that language sounds. Spuntone translates to "spike", and is a reference to the aesthetics I plan to give the amp. Il D'oro loosely translates to "the golden one" in English and "el dorado" in Spanish.

    El Dorado, of course, is the fabled "Lost City of Gold", but it's also the city in Arkansas where I currently reside. Although I'm doing my best to move back to my home-sweet-home of New Orleans, I wanted the name to be a tribute to my time here in The Natural State. I also thought that the lost city of gold was a good metaphor to a tone-hunter like me, who is constantly tweaking in the search of an unattainably perfect tone.

    I'm hoping to post an initial Spuntone schematic by the end of next week, so stay tuned!

  • Block Diagram and Version 0.1.0

    Istantinople02/27/2014 at 19:18 0 comments

    Today, I created a block diagram for the practice build, which I'm going to refer to as "Spuntone". We'll consider this Il D'oro Version 0, since the main point of the build is proof-of-concept for the final version.

    I'm going to use the BH5 "Little Giant" guitar amplifier from Blackheart Engineering (which itself is based off a Valve Jr.) as the base for this amp. When I design the bass amp,  I'll be starting from closer to scratch, but I saw no need to do that for Spuntone. This amp will include the RGB rotary encoder EQ, savable settings, and possibly a digital effect or two (not sure yet). The BH5 was designed with a solid-state rectifier, so that will match Il D'oro as well. Instead of designing out a PCB for a microcontroller system, like we'll do for the bass amp, I'm going to use one of my dev-boards to control Spuntone (I'm leaning towards a Launchpad right now).

    Spuntone will be far fewer watts than Il D'oro, and won't have as many features, but one thing it does have that wasn't in the Il D'oro design is a switch to reduce the output from 5W to 3W. On the BH5, that's done adding a switch and a resistor to the output tube. However, I have been thinking about adding a switch to change between dual and quad output stages on the bass amp, which would have the same effect of reducing the total output wattage. That's probably harder than it sounds, but I'm keeping it in mind as the project progresses.

  • T-Minus (some amount)

    Istantinople02/25/2014 at 01:08 0 comments

    ‚ÄčAs can be gleamed from the current details section, this project is still in its infancy. However, I'm getting the process started and hoping to pick up steam and get to work on this soon! I'll be submitting a rough schematic for the practice amp inside of two weeks (after everything is smoothed out with a new job), and I'll try and make at least one update per week until I've got my dream bass amp sitting in the music room. 

    If you're interested in the project, or you have something you'd like to contribute, I'm always glad to have someone to discuss it with. I'd also be grateful for helpful hints, or additional resources anyone is aware of for building valve amps. I'm also willing to collaborate on it, after all this is a community website, right! Shoot me a message (istantinople@gmail.com) if you've got something to share, and thanks.

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William wrote 03/22/2019 at 14:10 point

Glad I read further along... EL84 (6BQ5) valves/tubes at most, and pushed, deliver 20W a pair... but in reality are closer to 15-18W a pair in P-P AB1.  KT88 or 6550 tubes/valves will get you the most power per tube/valve in audio power. 100W a pair.

If you look at the old Ampeg SVT series amps (still made as the classic model) you'll notice they push 500-550VDC at the plates of the power tubes... definitely fatal and pushes the parts to their limits. I forget how much the old Sunn amps used. (Max rating on the 6550/6550A is 600vdc// the 6550C max is 800vdc)

If there is a need to source transformers, check to see if Hammond has what you need. There's also Edcore in New Mexico USA who for a fee, can custom wind you transformers if they don't have what you need.

For the benefit of those who don't know yet: You can use a voltage doubler (i.e. take the 275v mentioned and bring it up to 550v... You should know that the amount of usable current is halved. (Basic electronics.) Using the 6550 tube should require about 750mA (rough estimate for two pairs + the compliment of tubes for the phase inverter and pre-amp on the HT side. Mains side will be more.)

  Are you sure? yes | no

vibrolax wrote 05/14/2014 at 00:36 point
My background is software, and self taught in hardware. It's a good idea to understand the classic designs before heading out into the weeds on your own. And use LTspice, there are vacuum tube models ready to use with it.

  Are you sure? yes | no

vibrolax wrote 05/12/2014 at 00:08 point
How were you planning to get to 200W RMS for a tube power amp? That's 4+ x KT-88's, 8 x EL34's. The output transformer must, by necessity, be huge to be good at bass frequencies. For a linear power supply, it's a huge power transformer, too, with a B+ >500V. I think you've chosen a great approach to building your Spuntone as a first tube amp. My most recent build is an Ampeg SVT preamp, which I'll publish in a couple months.

  Are you sure? yes | no

Istantinople wrote 05/13/2014 at 16:15 point
That's a great point. I was planning on using quad KT-88's, but I know that transformers might be an issue. There's a reason you don't see many high-wattage bass amps that don't use a solid state class D power stage. I'm sure 200W is possible, but I'm not certain it's practical yet. I might have to settle for lower power in the name of practicality, and build something more like the EBS Classic T90. Even if I can get 200W, the size of the transformers might screw up the "Dual/Quad" switch I mentioned in one of my posts (but I'd only half-way thought that through anyway).

That being said, I play a 6-string bass, and I would really like 200W to get the most out of low B on an 18" driver. I'm itching to get that far in the design.

I'm glad you think that about the Spuntone. My background is in digital hardware and control systems, so I'm a little out of my comfort zone with all this analog business, but it's sure been fun learning about it. The BH5/Valve Junior design seemed unintimidating without being absolutely basic.

  Are you sure? yes | no

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