Breadboard mock-up

Okay, parts are now pouring in for my amp project. I would like to finish this by the end of Spring Break. That includes a whole week off for a business trip (Chicago!) with the kids. Knowing me, I will be anxious about getting that trip over with so that I can come back and mess around with the amp.

Of course, my guitar is still being worked on.

Earlier, I told you that I wanted to build a 2x10 mini speaker cabinet that has switchable speaker combinations (A, A+B, A|B, B) and drew a diagram of the switch configuration. When I told an electronics friend that I wanted to do this, he asked incredulously "why wouldn't you want your amp and speakers to be operating at peak efficiency?" He deals with home and car audio, so I guess I understand his ignorance about how the guitar amp is part of the instrument.

My first speaker cabinet will have two different 10" speakers in it. (Okay, this is embarrassing, the model names are Ragin' Cajun and Delta Demon. I wish I could tell you that they were models E1121 and E1031 or something, but I suppose Eminence is appealing to a mentality slightly different than me.)

If you are freaking out about the 10 inchers, remember that this is for a 5 watt amp. I want to be able to crank this amp up a bit, but I really don't need the cone size of 2 12" speakers working for me.

So, it makes sense that I will want to have them able to play independently. In my switch, this is position 1 or 4. Then I want to hear what they sound like in series (8ohms + 8 ohms = 16 ohms). And, I might as well throw in parallel (8 ohm speakers in parallel is 4 ohms impedance).

I mocked up a breadboard configuration, because I found the switch at Mouser.com. The breadboard uses two lamps, and 24 gauge wire, but the real version will have speakers and speaker wire (duh).

Here is position 1, which will be one speaker:


In position 2, you can see that two lamps working in series doubles the resistance. The speaker corollary to this situation is that the impedance will be doubled. But, I think this gets the point across:


Here is position 2, parallel circuits. Notice that each lamp can pull the same full current through them. (If you are wondering what kind of light bulb works on 9v batteries without frying, they are 12v auto bulbs I had lying around. This would kill a typical flashlight bulb.)


And, to complete this presentation, we have speaker B, position 4:


My experiments with a boxjoint jig was not successful. I think the jig works fine, but it was set up to move in 1/32" and 1/16" increments, and my table saw has a little play in it. Okay, I will admit that the jig I made is a little "racked." I really wanted to make nice and strong box joints for my speaker and amp cabinet. I own a router, but not a router table. So, I bought a template. However, the template is for through-dovetail joints. Those used to be fancy, but anyone with a router and template can make them which is why I wanted regular finger joints - they seemed less pretentious (this is about speakers and amps, not wood working). In case you are figuring that dovetail joints are stronger than box joints, you are correct. However, I really didn't want to have to use them. (I could have bought a box joint template for 50% more! I would have to PAY MORE MONEY to APPEAR LESS UPPITY!)

So, I wimped out and bought a template. If I am brave enough, I will take a picture of my aborted effort at table-saw box joints. (I hope you like my crappy camera phone pictures! It's my only camera.)

--gh

My winter habit

I have two new things that have been working for me.

First, every morning if the bathroom floor feels cold - I should put on moisturizing lotion. I know that doesn't sound very manly, but I am getting old. (Two more years until the 1/2-way point!)

Second, (...and I should have told you about this in November or something), every time I hear someone at work mention anything with the word "sick" in it, I clean my hands. I either use soap and water in the sink, or use Germ-X. They might be saying they were sick, or a friend was sick, or whatever, but it prompts me to clean my hands more than bathroom breaks and before eating.

That and my Flintstone's Chewables have kept me from even having a sniffle all winter long (and it seems like some horrid stuff has gone around).

--gh

Switchable Speakers

I am building a speaker cabinet to accompany the amplifier that I am trying to put together. They will be matching designs, and make a tiny, tiny 1/2 stack. I guess here is my design and approximate size.



The 2x10 speaker cabinet is going to be cute! I already have the speakers downstairs and they are heavier than I thought they would be. They are Eminence brand, but should do fine.

I wanted to be able to switch the output around because I will use two different speakers. So, I wanted the most elegant way to switch Speaker A only, Speaker B only, and both speakers in series and parallel. I drew this in Illustrator to see if a 4-position switch will work. I ordered a CW Industry 1138s 2pole-4position switch, (from Mouser.com), so I hope this does work. (Uh, let me know if you see a problem.)



Our department secured copies of Photoshop to accompany Illustrator, but I haven't done anything "cool" with it yet to share with you here. The amplifier design has multiple outputs with 4-8-16 ohm impedences, so I wanted to mess around with that a little.

--gh

Just a dream...

When you end someone's life, you have to wake up. I guess that is just one of those rules of dreaming.

I don't want to say any more about that.

--gh

New Project

I have a new project... a single ended class A tube amplifier.



I have started amassing what I need to start my first home-made electronics device since junior high. I have turned to the The AX84 Project for the design and parts list. It is described as an open project - but it sure looks like everyone turns to one guy eventually.

This is not a kit affair, though. They do not sell parts and believe it or not - there are no instructions! We're not talking Heath Kit here, so I hope I am up to it. Then again, if it was Heath Kit, I would feel a little cheesy. That's probably not fair to all those champs out there that cut their teeth on building radios and signal generators from Heath Kit. But for me, having a company in between made it seem like you weren't really building on your own.

I never had a tube amplifier for my guitar. I am starting with this project, a "smaller" sized 5 watt amp. I am pretty sure that it will be plenty loud for home use!

So, if you don't know a little about tube amps, single-ended means that the signal runs through each component in the amp. (A push-pull amp splits the signal and handles each half separately.) Class A amps do this by running the tube wide open (figurately speaking, of course) which makes them inefficient and explains why hi-fidelity abandoned this technology over 50 years ago.

So, my hands are covered in dried glue. Why? Because I am trying to make a box-joint jig for my table saw. Why? Because I want to make my own box to hold the amplifier in. Also, I will make a speaker cabinet. I don't want to cover it with carpet or tolex, so I will just finish them like furniture.

Okay, I'll keep you posted.

--gh