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Everybody needs a 603

By John, 7 October, 2012

So I decided to try my hand at soldering surface mount components. I mean, lots of people are doing it these days, how hard can it be?

I read a bunch of how to solder SMT tutorials, and they all said the same thing. They said, start out with the larger passives, like 805s, and once you get the hang of those, 603s are relatively straightforward.

Being a bit of an idiot, I thought to myself, I'll just start with the 603s, how hard can it be? So I ordered some, and they came in the mail. You want to know how small a 603 1k resistor is?

A 603 resistor sitting on the top of a nickel.

About the size of a single digit of the date on a nickel. Thereabouts.

NES guitar + the Stella Amp

By John, 27 September, 2012

A guitar made out of an old Nintendo Entertainment System

I was at The Hack Factory last night helping a gentleman put together a Stella Amp that he had bought from the vending machine. (We have a kit vending machine at the Hack Factory, it's great. And although my kit is in the machine, I have to be honest and say I've put more money into the machine buying other kits than I have made from kit sales. It's a little addictive.)

He had this amazing NES guitar made by my friend Alex at getlofi.com. The guitar looks great, as you can see, and it sounded great too.

Labor day weekend sale

By John, 31 August, 2012

We're having a Labor Day Weekend sale: 10 percent off on Stella Amps!

The Stella Amp on a table with a guitar, as the sun sets

As summer winds down, it's not too late to pick up a Stella Amp for fall camping season. Sale price is for a limited time, or while supplies last. Get yours today!

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From the mailbag

By John, 10 August, 2012

William wrote in with a great photo of his new Stella Amp:

Thank you very much for sending the replacement resistor. The Stella
amp is fantastic. Not only is it the best clean sounding battery
powered amp, but the overdrive sounds are stellar. It's so good that I
made it into an amp head so I can use it with any number of speaker
combinations. I've included a picture of the Stella connected to my
Emery Sound mahogany cabinet with a 10 inch Weber Alnico Blue Pup.

A stella amp build in a clear case, with all of the components visible

I love that clear case! You can see the jack when you are plugging and unplugging the guitar cable, and everything.

Adding diode pairs to the Stella amp

By John, 9 August, 2012

Phil Graham (@Roadstead) wrote in on twitter with a question and a comment. My reply was just a bit long for twitter, so I thought I'd answer it here.

Going to build my brother in law a Stella. Have you played with diode pairs or bridge between trim -> level or trim -> ground?

No I haven't! One of the things I did when I designed the front end was to put a little op amp distortion in there. Playing with diode distortion is on my list of things to do. I know a lot of theory behind it but I haven't played around with actual circuits before.

If you get something working that you like the sound of, let me know! Make a video of it if you can, and I'll post it here.

Also, you could add a cap in series with R1 to bleed off some of the higher harmonics like the miller capacitance does

I also have not played around with adding a tone circuit but if I did want a tone circuit, that's pretty much where I would put it. Except I would put it after the trim and level pots and before R1, or before the two trim and level pots entirely. I did experiment with a funky tone circuit that was integrated in to the entire backend, and it should have worked but it did absolutely nothing. So I got discouraged, but I should really dig that out and see if I can get it working. The idea was that it would cut the higher harmonics even if the back end amplifier was distorting, which sounded awesome on paper but in real life did not work at all.

Phil G (not verified)

12 years 1 month ago

John,

I'm leaning towards an asymmetrical LED pair bypassed with a small cap, and with a small feed forward resistor to bleed a bit of the clean input. The goal, for me, is mild asymmetric clipping, not the high gain "jar of bees" sound. I'm not sure what color LEDs I'll use.

I'm thinking that putting the 2 diodes and a small cap in path to ground from trim should give the most control over the diode clipping onset, but i"ll probably try it in the gain path, too, to see how the character is different. I've also contemplated beefing up the DC isolation cap between the op amp and power amp, to lower the chances of undesirable IMD products.

Personally, I'll probably end up with single pole lowpass before the power amp, and possibly a larger Cp cap after the amp. This depending on how much of a lowpass I'll get from the 10" speaker.

Dr. Geddes and Lee's various work on harmonic and IMD distortion perception are a pretty interesting read. It certainly makes me mindful of how sensitivity grows for increasing distortion order: http://www.gedlee.com/distortion_perception.htm

Any chance of posting the fancy tone control circuit?

Cheers,

-Phil G

Member for

13 years 3 months

John

12 years 1 month ago

Sounds like a plan! The only thing I'll mention to keep in mind is that the distortion characteristics of the Stella Amp change depending on how much voltage you use to power it. Nine volts is a different amp than four volts.

Also the type of guitar you use has a surprising impact. It's hard to quantify, but there is an interaction between amp and guitar that I was not expecting. I suppose if I threw in an extra high impedance input buffer that wouldn't happen, but I didn't bother, because I don't find it objectionable.

So build it up stock (leaving yourself some extra wire at various points so you can add mods later) and see how it goes, and then start adding your extra stuff. Give the op amp a shot, I tried several of them out, and this one was the least harsh and most musical.

The general rule is, if you crank the gain pot, roll back on the trim, and vice versa. The trim pot is there to keep the whole amp from crazy oscillating when you crank the gain too much. But if you want a clean tone you roll the gain back and crank the trim up.

Phil (not verified)

12 years 1 month ago

The guitar, cable, pickups, pot, and input generally form an rlc conjugate filter, so not only can the guitar matter, so can the position of the volume pot. There's some guy on the internet, whose link escapes me, that does a very nice job of describing and calculating this effect.

One of the appeals, for me, was the "softness" of the psu, as it relates to potential tone. I'd even considered some sort of zener diode on the supply side to play around with the stiffness of the power to the opamp.

Basement flooding

By John, 28 July, 2012

A leaky dishwasher while we were on vacation lead to some flooding in our basement. The flooding led to moisture and the moisture led to mold!

The worst of the mold damage was confined to my electronics workbench and my collection of antique cameras, of course.

Cleaning up the mess has taken up every bit of free time available over the past week. Of course I had just recently moved my shipping operations to the basement, so that's where all of my stock of kits was, and everything. It will be a while before I have more kits in stock. More information can be found on the status page.

If you want to be notified when Stella amp kits are back in stock, sign up for my email list!

Vacation

By John, 21 July, 2012

The solar powered stella amp sitting on a railing with a harmonica and microphone

I went on vacation recently, and took the Solar Stella with me. Most of the time it sits on the shelf in the living room, and I haven't really taken it anywhere. I figured this would be a good chance to test out the ruggedness and build quality to see how well it holds up. Plus I didn't want to worry about batteries, which is why I built the thing to begin with.

I did find a couple of issues with it, using it on a daily basis, shlepping it in and out of hotels, taking it to the beach, trying to keep it out of the reach of my toddlers. I'm still investigating one of the problems I had with it (I know what's wrong, just have to figure out how to fix it), but in the meantime, I'll post a few photos I took as I move them off my flash cards and get them edited.

The downside of making all of your products out of aluminum

By John, 15 July, 2012

About thirty minutes ago, I was sitting at my desk. It's a hot summer day, I'm upstairs, and sweaty. My iPod nano was sitting on the desk, connected to my Apple Cinema Display, happily syncing and charging.

I shifted my arm to get a better angle with my mouse, and suddenly OW!

That's odd. The sharp edge of the iPod nano must have hit some nerve in my arm. I picked up the nano and a sharp jolt went right through my hand. Yeeeowch!

That's an electrical jolt. Why is my iPod electrified!? Is my charging cable frayed or defective somehow?

More importantly, what am I connected to? I'm sitting in a plastic chair on a hardwood floor. Current should not be flowing through ME. Then suddenly I realized: I've got my Macbook Pro sitting on my lap, charging.

Now, I am wearing pants. I'm not even in shorts! But it's hot and sticky enough, (and my arm was definitely sweaty enough) that I conducted a current from my iPod to my Macbook.

The Macbook is plugged into the socket on the near wall, and the Apple Cinema Display (which was not connected to my Macbook in any way) is plugged into another socket across the room. Those two sockets must be on different household circuits for there to be such a potential difference! (Either that or my Cinema Display is electrified!)

Yikes!

Being a good electronics geek, I tried to measure the potential difference and I couldn't do it. I don't know why, but the probes on my meter just wouldn't make a good connection with the metal on the Macbook. Even when I tried to measure resistance from point to point on the metal case, it measured Inf. ohms. But if I angled an LED just right, I could get the LED to light up, with one leg connected to the Macbook and one connected to the metal case of the Cinema Display. Pretty cool!

A few minutes later, I had another, more serious realization: I just took an electrical current across my heart. Several times, actually.

Now, as far as I know I have a strong heart, and don't feel any ill effects. But if you do have heart trouble, be careful with your metal cased Apple products!