AX84 noise immunity.

Adding some noise immunity!  Here's some brand new twisted filament wires.  I re routed them so they are as far away from the signal wires as possible (green/white twisted wires)

It seemed to help a bit, but at high gain levels, there's still plenty of 60hz hum.  I was advised by another AX84 building to use a filtered AC input module, so I'm going to get a hold of one of those.

I also realized that the schematic had indicated that I need to ground the speaker outputs.

I didn't ground it exactly to point B... I just ran a wire directly from the AC input earth ground to the speaker output.  It's the lone green wire in the picture below.

I was able to solve some of the odd oscillations in the tone stack by adding three components.  This does result in some losses on the high end... hopefully it's not too noticeable.

I also found neat tone stack calculator from Duncan Amps, available for free!  It should prove useful for future designs.

Once I add a filtered AC input module, and probably a bottom plate for the chassis, this baby is going to be ready for an enclosure.

AX84 Noise issues...

Now you can see and hear noise issues from the AX84 hi octane.

After the video, I did some more probing on the tone stack, and found that in certain parts of the circuit, when I put the probe on, the oscillations would stop.  Those voltage probes have a small capacitance to them, so I added caps into the circuit and it seemed to stabilize.  I still don't know *exactly* what I'm doing... but it seems to be helping.  I'll have to post some new clips as the debugging continues.


After some online reading of other folks troubleshooting these amps, I might have an explanation for the 60hz hum.  Each tube needs a low voltage to heat the filaments.  This amp has a 6.3V AC signal to do that job (green wires on the tube sockets).  I made a mistake in my wiring... I should have twisted the filament wires together and kept them as far away from the signal wires (red wires on tube sockets) as can be...  Neither of which I did.  There's only a few wires to re route, so it should take more than 10 minutes.  Did you notice in the video how I switched out a gain stage and the 60hz stopped?  That could be because that particular gain stage has one of those AC filament wires running directly underneath the signal wire.

At least I have some possible solutions, eh?


Questions?  comments?   Ideas for reducing nose?

Email me or leave a comment!

AX84 Hi Octane build part 4: Wiring, testing

So I left off with installing all the parts in the chassis and ruining the finish in the process.  Now it's time to wire everything up.  Following the schematics and wiring diagram is easy enough, just takes a while.  First thing I noticed is that when I drilled the hole for one of the tube sockets, the chassis wasn't clamped well enough and it vibrated around, making the hole a bit too large.  The socket isn't secured and needs to be fixed to the chassis.

A little epoxy should do the trick

Then, on to finish the wiring... through the magic of internet it's all done, yay!

So, working with tubes is dangerous, the voltage rail is around 300 volts, and it can be deadly... so I'll be careful.  I ran through a "first power up" check list that I found online.  You basically take out the tubes, and turn the unit on.  If nothing blows up, you measure voltage rails and make sure they're at appropriate levels.  Everything checked out so I plugged in the the tubes and fired it up.

Plugged in a guitar, and no sound... hmmm.... After some digging around the circuit for a while I found a shielded wire where the conductor had shorted to the ground shield.  I replaced it, and then found another shielded signal wire that I had just forgot to connect... ooops.

With a now complete signal chain, I turned the amp on again, and I finally got actual noise!  Not very much though... I can only heard anything with the gains and volume knob turned all the way up.  Turns out I also forgot to connect a filament wire for one of the tubes.  Grrr...

So, I connected the last filament wire and finally I have sound!  LOUD sound!  It's only 5 watts, but you'd be surprised how loud 5 watts gets.  I messed around with the knobs for about 15 minutes, and discovered that there's some settings that hum a bit too much for comfort.  So I have some work to do fixing the hum, but it already sounds quite nice, especially on the high gain settings... mmmmm... harmonics!  I'll post some audio clips eventually...

Questions?  Comments?   E-mail me or leave a comment.

AX84 Hi Octane build Part 3: Ruining the finish

A word about finishing metal...

This is the third metal enclosure I finished.  The first two were metal stompbox effects units.  I'll start with the worst; a compressor from Build Your Own Clone.  It's a nice pedal, and he sound is great, but I tried to hand paint, and it was a miserable failure.  It's terribly ugly.  It would have looked better had I just left the aluminum bare and written the knob labels on the thing with a sharpie.  Once I saw how terrible it was, I said screw it, globbed a bunch of paint on it, and embraced the ugly.  It is a nice compressor though, so maybe I'll refinish it at a later date.

The first one (the Tube Screamer), I spent a long time on the finish.  I sprayed very thin layer of paint every 15 minutes or so, and then I let it sit over night between the primer, the color, and the clear coat.  Between the color and clear coat, I also baked the case in a toaster oven I bought at thrift store.  The baking isn't necessary, but if you bake the unit for an hour at 300-350F, the paint will almost completely cure, and when you handle it, you won't get finger prints embedded into the soft pain, or mar the surface.

I rushed through finishing the AX84 chassis.  I put the clear coat on too thick and got runs in the paint, and then I didn't let it cure enough before I installed the pots, switches, transformers, etc.  The toaster oven won't fit this chassis, and I don't want to bake it in my cooking oven, so I just left it outside over night.  I thought 9 hours of drying time would be sufficient for curing, but I was wrong.  I really dinged up the finish.  It looks pretty bad in places... and goes to show the importance of patience if you want your piece to look nice.  I'm going to build this amp into an enclosure of some sort, either a combo amp or a stand alone guitar head, so I'm not too concerned with how it looks.  A few coats of clear coat would have been fine to prevent corrosion, but I gave it color on a lark.  If nothing else, I learned how important the patience I used on the tube screamer pedal really pays off.

So here it is!

Doesn't look too bad, eh?

Parts installed

Inside

Oh no! The finish!   I killed it!

That texture there is from the a seam in my pants.  Seriously

Tightening nuts ruins your finish

That's a finger print and a few nicks.

That's probably from my heavy paint layers

Took a nice ding out of the side there... oops.

Oh well, I'm going to wallow in shame for a while, and then finish up the wiring.

AX84 Hi Octane Build Part 2: Circuit board

Part 2:  Building the circuit board.

I guess instead of getting a "real" circuit board made, these people chose to include this eyelet board, which has little metal eyes installed to solder the parts to.  I've never actually used a board like this before, and if I were going to make another amp, I'd be inclined to make a custom board so I don't have to muck around soldering all the jumper wires which you'll see later.  I built the circuit board in the time between applying coats of paint to the chassis.  Just set a timer for 30 minutes for applying new coats.

Lonely eyelet board, parts, schematic, wiring diagram.

Through the magic of the internet, I present to you, an eyelet board with all the parts installed.

The Eyelet board has friends now!

This part was the biggest pain... connecting all of the voltage rails and the ground.

Red and blue wires are the supply voltage

Black wire is ground

With the wiring complete, I just need to let the chassis cure overnight, then it's time for the final wiring.

AX84 Hi Octane Build Part 1: Chassis

Part 1: Preparing the chassis.  Since I have access to a drill press and didn't feel like spending an extra $65 to get a pre drilled chassis, I have a lot of drilling to do.  Luckily, the folks at http://www.ax84.com/ we nice enough to offer a drill plan for download.

Words of wisdom for you... It's good to have some double sided tape on the paper so you don't rip up the guide, however, be sure to use some double sided tape that will release... I used some 3M VHB, but it's not meant to be released... ever.  I spent a good hour spraying the thing with adhesive remover and scraping.  It took longer to remove the tape than it did to drill the holes.  On top of that, the holes I needed for the input/output jacks were not labeled correctly, and I drilled the holes too small.  The hole size I need is 7/16'' and none of my bit sets include one.  I guess it's off to the hardware store again..

Okay, zip to the future, and I've gotten the new drill bit, along with some spray paint: grey automotive primer, some goldish colored enamel, and clear enamel.

After drilling the new larger holes for the input jack, I went over the whole piece with an orbital sander and a deburring tool to smooth everything out.  It was raining outside, so I set up shop in the garage.  First, a wipe down with rubbing alcohol to clean the metal, followed by a few coats of primer. 

And of course, a few more coats of the gold enamel spray.  I let the gold enamel cure for a few hours and applied some decals.  I printed a whole sheet of random words and tube decals for my Ibanez Tube screamer replica, and I was able use decals from that sheet... I included a few of the tube decals as well, just for fun.  These are water release decals, so you just print the sheet, cut the decals out ,soak them for a minute in water and slide them off onto the chassis.

Just in case the actual tubes don't give it away that this is a tube amp.

And that's that!  I let the decals dry and then it's back to the garage for clear coat!   Let it cure overnight, and tomorrow, it's time to assemble everything!

AX84 Hi Octane Tube Amplifier

Ermigerd!  Tuuuuuubes... it's like Christmas in April. 


I got this kit from http://www.ax84.com/ and I was so excited to start putting it together that I could barely sleep last night.

First step, drill the holes in the enclosure, but I'm home today tending to my lovely lady friend who had her wisdom teeth removed, so I don't have access to a drill press...  I did however stop at the Home Depot amid picking up smoothie ingredients and prescription painkillers and purchased some paint for the enclosure.

Come tomorrow... it's on!

Repairing Yamaha Delay Part 2

So... after a few weeks off I finally have some more time to finish continue working on this Yamaha delay unit...

Why U no work?

So... we left off with me going to buy fuses...

Alright, get this... I go to home depot to buy fuses, and I tell the guy I need some 3/4 amp fuses.  He doesn't  have any in stock, so he hands me a box of 1 amp fuses and says they'll work just fine...  seriously...  he doesn't even know what I'm doing with it.  That 3/4 amp fuse might be protecting the whole unit from exploding in a giant fireball of epic proportions, raining death and radiation to the entire United States and for some reason, parts of Brazil.

Thanks a lot, Home Depot guy

Or maybe I'm just being over dramatic... whatever.  I bought 1/2 amp and 1 amp fuses.  Go figure, the 1/2 amp fuses blew right away.

Turns out the 1 amp fuses didn't cause an explosion (you win this round, Home Depot guy), but a heatsink was getting hot enough to fry an egg, and that tends to indicate a problem.  Sure enough, I found some nifty voltage test points on the board... there are 8, +15, and -15 volt rails, and the 15V rail was dead.

Awww yeah!

I'm no expert on power supplies, so I tried to find a schematic to see what I'm dealing with.  I guess those dudes at Yamaha don't want a "non Yamaha certified" person to repair their stuff... go figure...

I guess I'm on my own...

Well, after an hour mapping out the power supply and testing voltages, I still had nothing.  Of course I measure the one that was working, and the one that wasn't (which is a mirror circuit with PNP transistors).  No dice... the voltage was sagging all the way up the power supply.

Yup... BJT fo life

So... lets cut the rest of the circuit out... find out what's failing.

What's a jumper or 2 between friends?

I guess that did the trick... the power supply is actually at -15 volts, and the other end of the circuit which it should be hooked up to is shorted to ground...which means my problem is the rest of the circuit.  Luckily for me, every other part of the circuit had it's own jumper connecting it so I just kept cutting until I found the offender.  A tantalum capacitor!  My mortal enemy.

You see, unlike electrolytic or ceramic capacitors, which fail open, tantalum caps fail shorted.  I just pulled it out and reconnected that section to the -15 rail and voila!  

And then... fail...

A different tantalum cap blew.  And another...

Oh well, I wasn't sure what they did, so I just pulled them out.  I tried to replace all 3 with ones that had a higher voltage rating, but for whatever reason, that circuit really doesn't like those caps...  Every time I cut one off, the circuit worked, and as soon as I tried to replace them, it would fail... so screw it, I took them all off.

Oddly enough, when hooked up a guitar, it worked again... hehehe. It turns out they're just some bypass caps to smooth out ripples on the power line, so hopefully there isn't any noticeable hum, or maybe I just accidentally created the greatest rack mounted analog delay of all time... we'll just have to find out.  

I'll have to get this back to Chout at the Fortress of Desire and see how he likes it!

Questions? Comments?  Want to tell me how great I am?  

get a hold of me at soundular-electronics@gmail.com

P.S.

For all you aspiring electronics people out there... even pros make mistakes.

Don't see it yet?  Let's look closer

You have brought shame to Yamaha

You see those three grooves cut into the board?  Someone screwed up, and after this PC board was made, someone (or a machine, it is Japan, after all) had to go through and make 3 cuts in EVERY SINGLE one of these.

I only recognize this because that's exactly what I had to do to fix my drum light boards... derp...

Dissecting a human head. I'm totally serious.

Well kids, you wanted it, you got.  Here at soundular electronics, we are dissecting a human head and replacing a defective left ear.  I'll let that sink in.

Dissecting... a... human... head...

Seriously.


 Let us meet our subject.  Say hello to HATS (Head And Torso Simulator)!

Hello!

HATS' left ear is out of calibration, and had to be sent back to the factory.  He's been using a dummy plug in his left ear for many months now rendering him deaf (oh noes!), and we finally got donor ear (packed in dry ice, of course)

HATS' new ear!

I prepped for surgery, acquired my tools, and knocked out HATS with a quick left jab.  POW!  In order to properly replace this ear, I then had to remove HATS' head...

CRACK!

With the neck cracked, we can pull out what I can only assume is a spinal cord and esophagus.

That is one soft spinal cord.

Next we'll bring the head to the operating table to remove HAT's ears and the screws that keep his head together.

Pre Mike Tysonized

Mike Tysonized

Remove the screws, and crack the skull!

It's amazing, that's what we all look like on the inside

Hmm... notice the brain (pillow) in the skull cavity.  It's soft and classy, just like me.

Check this out, this is the speech center of HATS' brain.  In addition to being able to listen, he can talk! It makes him quite useful for testing out headsets

Alright, enough fun... it's time to replace the ear.

Remove the microphone preamp capsule and cable

Remove the ear simulator/microphone capsule

Oh snap... I was so excited putting HATS back together (also late for a meeting) that I forgot to take picture putting the ear pieces back together.  Imagine the previous two pictures, only in reverse.

There you have it!  A whole brain assembly.

Back in the head with you

HATS' new left ear!  Hooray!

So... 30 minutes later, and one human ear replaced.  HATS has been revived and can hear in his left ear for the first time in over 6 months.  It's another medical miracle, thanks to Dr Roedy.