Something’s going wrong.

I had an unusual valve kicking around - an ECH83. It’s a triode-heptode designed for use in car radios, with an anode voltage of only 12.6V.

I also had a couple of the ubiquitous Park G10 practice amps from my early guitar-playing days waiting to be recycled into something better, so I thought I’d see if I could concoct some sort of bastardised hybrid.

The G10 actually has quite a nice chip amp for it’s final stage; the TDA2030A. What a pity about the JRC4558 preamp stages. I really hate the sound of that particular 80’s opamp.

Inspired by this wanton ECH83 abuse by Engels, I decided to use both the triode and heptode in the ECH83 as preamp stages and salvage the silicon from the G10 for a power amp stage.

This is the result (click to enlarge):

Sorry for the lo-fi schematic; it’s scanned straight out of my notebook. I’d rather build stuff than spend ages making a pretty CAD schematic!

The TDA2030A part of the circuit is pretty much straight from the datasheet. Here’s my stripboard layout, in case has someone wants to build one (strip layouts I do use my PC for):

Note the cut at 5a, under C1, and the closeness of C3 and C4 to the chip. This is essential with the TDA2030A, otherwise it’s unhappiness manifests as parasitic oscillation. Also essential is the heatsink (also salvaged from the G10 board).

I kept the transformer, rectifier and smoothing caps from the G10 to give +20/0/-20V, and used a seperate wall adapter to give 6V for the heater. I could have used a regulator and tapped the main supply instead. It fits into the chassis of the G10 perfectly but I didn’t put it back into the G10’s cabinet as this thing really deserves a better speaker. IE, one that’s not made of cheese.

The lashed-up amp itself:

The valve socket’s led to a terminal block, with another terminal block leading to the power amp board in parallel (geographically, not electrically!). The components configuring the preamp stages are connected in between the terminal blocks.

Feeding 80’s Japanese silicon with 50’s British glass turned out a lot better than I expected. Feeding a 15″ Celestion I get an amazing warm bluesy sound with an undertone of gorgeous valve breakup, even at low volume. If you want soundclips, let me know and I’ll try and record something!

It goes much louder than the G10 did; this design runs the TDA2030A a good bit hotter than in the G10 and pushes the chip amp to give it’s full 18W. Really it could use a bigger heatsink than the one from the G10.

It makes a lovely practice amp, and if I could get rid of the small amount of 50Hz mains hum I can hear it would be a pretty decent studio amp too. Don’t know if I’d be able to replace the valve if it goes; a cursory glance at eBay shows a single ECH83 for sale at the moment. However this rig is perfect for experimenting with different strange-valve-as-preamp ideas, so I’m sure I’d come up with something.

A dream is to have a completely homemade signal chain from axe to amp; I don’t insist on making the actual guitar but I do want to try winding some pickups. Now I have an amp, and I’ve already got various homemade effects units that I’ll document here soon.

I’ve been playing guitar in various bands for a few years now, as well as producing electronica. I’ve finally got my dream band set up - Swb on drums, Bannon on bass, myself singing and playing guitar. The original power trio format!

Thought some people might like to hear a couple of demos.

Waking Drums (MP3)
“Track 2″ (MP3; no vocals on this one yet)

I’ve been getting back into electronics. High voltage stuff this time around - I’m trying to get a small Tesla Coil running at the moment (and to that end just let the magic smoke escape from my cheapo bench power supply).

Going through my camera, I found some photos of some robots I built last time I was in a soldering mood and thought I’d share and document.

Rollerbot

First up, this was an experimental BEAM rolling robot. Two different designs are shown; the idea in each case is that the weight moving inside the ball makes the ball roll along. In the large pic, the motor itself is the counterweight and is designed to be pulsed, resulting in a burst of motion each time.

I didn’t get round to fitting the control electronics and solar engine in there on that iteration of my electronics interest; I may do this time if I can find room, or a slightly bigger sphere. I think the chloroplast engine would be perfect for the task, and I do have one knocking around somewhere.

It’s a design that would be interesting if created as a single unit within a swarm of similar robots which can work together by means of simple communication to form a single, distributed articial life form. Similar ideas are being examined by NASA/MIT for planetary exploration uses, although theirs have dinky fuel cells.

CD Bot

Next up is a little PICAXE-powered bot built on a couple of CDRs stuck together.

I really love the PICAXE-08M, based around a PIC 12F683. 555 timer for the 21st century! Extremely cheap way to get into microcontroller fun.

The CD bot has differential steering, a 3.6V NICAD, onboard serial programming socket and LDR light sensors. The bottom picture shows the same bot in different clothes, and with a tiny hacked digital camera mounted, controlled by the PICAXE.

The bot was programmed to wander around, stop periodically, and take pictures if it saw something interesting, the LDRs acting as a two-pixel motion detection system.

Walkers

A couple of BEAM-inspired two-motor walkers.

My walker design uses a PICAXE-18 project board to emulate the pulse pattern of a BEAM Nv-net quadcore two-motor walker.

From Solarbotics:

Quadcore

A quadcore (with only one process circulating) will only be
operating one motor at a time. Note that the rear motor
“leads” (in terms of the pattern’s phasing), and the front
motor “follows.”

Rear motor	CW		CCW		CW
Front motor		CW		CCW		CW

A walker in action looks amazing, but I had to read that a couple of time to get just how simple the gait is. Despite the lack of the Nv-net’s beautiful feedback technique, it walked surprisingly well and looked very alive. The legs were stiff wire coathangers soldered onto brass blocks from 3A connector block, and the motors were the fabled Mac floppy drive motors; fantastic little DC gearmotors with a ratio I forget at this time of night, but perfect here. Well worth tearing out of old Macs, of which I have an atticful. I used a re-centering spring on the front legs.

The gearmotors received the full 9V from the PP9 (I’ve since seen the light and never use them) while the PICAXE got 5V through a good old LM7805.

I can provide PICAXE code and further details of the mechanical linkages if anyone’s interested.

In an effort to make a more minimal walker, the original being quite weighty, I tried the same legs and mounts on a pair of these 120:1-geared motors and a body made from angled aluminium:

The earlier, heavier walker was superior. Although prettier and capable of walking without it’s controller and battery pack, the lighter model didn’t stay on track very well, and would twist itself into a ball of tangled leg when trying to carry it’s brains.

My good friend Neil has started a tech support site aimed at your grandmother, or anyone else who needs PC things explained simply and slowly. And I’m a moderator

It’s not just for people who can’t change their wallpaper though - we’re here to help beginning coders and techies too, in an informal newbie-friendly environment.

Click here to visit!