[Tymkrs] Tombstone Guitar Amplifier

tymkrsTombstone

[Atdiy and Whisker], the team behind [The Tymkrs] YouTube channel, are at it again with a tombstone guitar amp project.(YouTube playlist link) Their amp began life as a Philco Tombstone radio which had seen better days. By the time [Tymkrs] got their hands on it, it was just a shell of its former self, as someone had already stripped all the electronics.

The amplifier itself is a disused Leslie tube amp [Tymkrs] had on hand. An LM386 serves as the pre-amp, making this a hybrid solid and vacuum state machine.

The tombstone speaker is especially interesting. [Tymkrs] went with an electrodynamic field coil speaker. Field coil speakers have no magnets, instead using a high voltage (approx 90V DC) coil to create a magnetic field for the voice coil to push against. This sort of speaker was commonplace in the 1930′s, as large magnets couldn’t be made lightweight enough to be used in a speaker. As magnet technology improved, permanent magnets became a staple in speakers.

[Tymkrs] paid special attention to the finish of the amplifier. They brought the tired old radio back to a high shine, then added a Metropolis inspired overlay from aged copper-clad board. The result is an amp that looks great and sounds great!

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Automatic Audio Leveling Circuit Makes Scanning More Fun

alan-scope1

[Alan's] friend came to him with a problem. He loved listening to his scanner, but hated the volume differences between stations. Some transmitters would be very low volume, others would nearly blow his speakers. To solve the problem, [Alan] built up a quick automatic leveling circuit (YouTube link) from parts he had around the lab.

[Alan's] calan-scope2ircuit isn’t new, he states right in the video that various audio limiting, compressing, and automatic gain control circuits have been passed around the internet for years. What he’s brought to the table is his usual flair for explaining the circuits’ operation, with plenty of examples using the oscilloscope. (For those that don’t know, when [Alan] isn’t building circuits for fun, he’s an RF applications engineer at Tektronix).

Alan’s circuit is essentially an attenuator. It takes speaker level audio in (exactly what you’d have in a desktop scanner) and outputs a limited signal at about 50mv peak to peak, which is enough to drive an auxiliary amplifier. The attenuator is made up of a resistor and a pair of 1N34A Germanium diodes. The more bias current applied to the diodes, the more they will attenuate the main audio signal. The diode bias current is created by a transistor-based peak detector circuit driven off the main audio signal.
But don’t just take our word for it, watch the video after the break.

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Beams of Light: An Oscilloscope Demo

beamsoflight

The demoscene is alive and well, with new demos coming out on a multitude of platforms, including oscilloscopes. Beams of Light is a new demo released at @party in Boston by [TRSi]. Beams isn’t the usual .EXE file format for PC based demos. It’s distributed as a 4 channel wave file. The rear left and right channels are stereo audio. The front channels, however, are vector video to be displayed on an oscilloscope in XY mode.

Beams of Light isn’t the first demo to use an oscilloscope. Youscope and Oscillofun preceded it. Still, you can see [TRSi] pushed the envelope a bit with his creation. He used Processing and Audacity to create the vector video, and his own line tracing algorithm to reduce flyback lines.

[TRSi] included an updated copy of a python based oscilloscope emulator so you can play the demo even if you don’t have the necessary hardware. We wanted to run this the right way, so we powered up our trusty Tektronix 465 and hooked it up to a 1/8″ stereo plug.

Sure enough, the demo played, and it was glorious. We did see a few more retrace lines than the video shows. This could be due to our scope having a higher bandwidth than the 10MHz scope used in the YouTube video. XY demos are one of those rare cases where an analog scope works much better than a low-cost digital scope. Trying the demo on our Rigol ds1052e didn’t yield very good results to say the least. Sometimes good old phosphor just beats an analog to digital converter.

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Homebrew Programming With Diodes

diode

Diode matrices were one of the first methods of implementing some sort of read only memory for the very first electronic computers, and even today they can be found buried deep in the IPs of ASICs and other devices that need some form of write-once memory. For the longest time, [Rick] has wanted to build a ROM out of a few hundred diodes, and he’s finally accomplished his goal. Even better, his diode matrix circuit is actually functional: it’s a 64-byte ROM for an Atari 2600 containing an extremely simple demo program.

[Rick] connected a ton of 1N60 diodes along a grid, corresponding to the data and address lines to the 2600′s CPU. At each intersection, the data lines were either unconnected, or tied together with a diode. Pulling an address line high or low ([Rick] hasn’t posted a schematic) pulls the data line to the same voltage if a diode is connected. Repeat this eight times for each byte, and you have possibly the most primitive form of read only memory.

As for the demo [Rick] coded up with diodes? It displays a rainbow of colors with a black rectangle that can be moved across the screen with the joystick. Video below.

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The Basics of Frequency Modulation

fm-modulation

[brmarcum] takes us back to analog building block basics with his Frequency Modulation and Demodulation tutorial. Frequency Modulation (FM) sounds simple at first, but understanding the electronics behind modulation and  demodulation of an FM signal can be confusing. We’ve covered the basics before, but FM is so tightly associated with broadcast radio that searches often become muddled with references to RF, stereo, antennas, and transmitters.

[brmarcum] hopes to fill that gap with a simple circuit that modulates an audio signal to FM, then demodulates and amplifies it to be played on a small speaker. He used a Digilent Analog Discovery kit in his experiments, but an oscilloscope (an older analog scope would be perfect here) would work for output. Signal generation duties could easily be handled by a 555 circuit at the low end, and a computer sound card at the higher end.

[brmarcum] obviously put some time into his tutorial, but it’s not a tome of FM modulation. He’s broken down the modulation and demodulation circuits into their basic op-amp stages with examples of what the signal should look like on a scope after each stage. That’s the beauty here. By building and testing each section, anyone new to analog can learn how things work. In places where the theory behind what’s going on gets too in-depth for an Instructable, [brmarcum] gives links to Wikipedia.

Programmable Logic I – PLA/PAL

C64-B

Yeah I am still a little pissed that the competition is still around and we aren’t, and by “we” I mean Commodore Business Machines (CBM). It was Commodore that had the most popular home computer ever in the C64 (27 Million) and it was a team of MOS engineers after all, that had the idea to make a “micro” processor out of a 12 square inch PCB.

MOS Technologies logo and address

MOS Technology in King of Prussia/Norristown

Of course they did work at Motorola at the time and “Mot” did not want anything to do with a reduction of the profit margin on the pie-plate size processor. Of course MOS got sued by Motorola but that was an average Tuesday at MOS/CBM. I absolutely credit CBM with buying the MOS Technologies chip foundry, as together we could make our own processors, graphics chips, sound chips, memory controllers, and programmable logic.

With this arsenal at our call we didn’t have to make compromises the way other companies did such as conforming to the bus spec of an industrial standard 6845 or having to add extra logic when a custom extra pin would work. We could also make sprites.

6502 Design Team

6502 Design Team (EE Times 1975, archive.archaeology.org)

The compromise we did have to make when designing was cost, and I mean the kind of cost reduction where finding a way to save a dollar ($1USD) saved millions in the production run. I knocked $.90USD out of a transformer one day and I couldn’t focus the rest of the day due to elation.

Cost reduction is a harsh mistress however as you can’t just do it a little some of the time or only when you want to. The mental exercise of multiplying anything times a million was always there, it made it hard to buy lunch — I’d be blocking the lunch line while figuring the cost of a million tuna sandwiches FOB Tokyo [Read more...]

(Better) Full Motion Video On The First PC

Ladies

Ten years ago, [Trixter] created 8088 Corruption, a demo for the original PC, the IBM 5150, that displayed full motion video using a CGA card and a SoundBlaster. It was hailed as a marvel of the demoscene at the time, garnered tons of hits when it was eventually uploaded to Google Video, and was even picked up by the nascent Hackaday.Now, ten years later, and seven years after [Trixter] said full motion video using the graphics mode of a CGA adapter was impossible, he’s improved on his earlier work. Now, it’s possible to display video at 640×200 resolution at 30 frames per second on a 30-year-old computer.

[Trixter]‘s earlier work used the text mode of the CGA adapter, only because the 40×25 character, 16 color mode was the only graphics mode that could be entirely updated every single frame. It’s still one of the high points of the PC demoscene, but from the original video, it’s easy to see the limitations.

A while back, [Trixter] said displaying video using his computer’s graphics mode was impossible. He’s had years to think about this statement, and eventually realized he was wrong. Like the developers of modern video codecs, [Trixter] realized you don’t need to change every pixel for every frame: you only need to change the pixels that are different from frame to frame. Obvious, if you think about it, and all [Trixter] needed to do was encode the video in a format that would only change dissimilar pixels from frame to frame, and manage the disk and memory bandwidth.

After reencoding the 10-year-old demo for graphics mode, [Trixter] turned toward his most ambitious demo to date: playing the ‘Bad Apple’ animation on an 8088. As you can see in the video below, it was a complete success.

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