Behringer v-tone GMX212 Hybrid tube amplifier mod

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Davide Gironi wrote a post on his blog showing how he modified the Behringer v-tone GMX212 Hybrid tube amplifier:

For this project I’ve used 12AX7 vacuum tube. This tube is one of the most used for the guitar preamplification. So there are many resources available on web.
The first problem i faced it’s the power stage. Tubes needs high voltage in order to work properly. The solution I’ve found was to connect a 230V/9V power transformer with secondary and primary reversed. That way, connecting it to the 10.5V AC output of the main Behringer transformer i can get almost 160V DC.
Any tube also needs a low voltage current to power up the heater. I choose to use a 7805 voltage regulator, shifted by 1.3 volts using two switching diodes. This gives me the 6.3V DC I need.

More details at Davide Gironi’s blog.

Check out the video after the break.

UCload: revisited

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Sjaak has posted an update on his uC controlled dummy load project we covered previously:

I finally found some time to check out the UCload project. A couple of weeks ago I quickly soldered the PCB and wrote a quick’n’dirty firmware for it. The basic functionality was working, but it wouldn’t do good for the shiny display.
Today I locked myself in my mancave and shut myself off from the world. Turned the light down, pulled loud music from the speakers and started coding like hell!! Not exactly but I found some time to write some more decent firmware for this load. In a previous revision of the PCB I forget the pull up resistors and swapped the SDA and SCL signals. I corrected that and made some small other changes (still ****ed up the silkscreen) in revision 2. The hardware is quite OK and rock solid (prolly more due to the robust FET then my analogue skills :)). However I managed to use a 1n4148 diode to measure the temperature. Connect it to the heat sink and if that one gets to hot turn on a fan. It accuracy is terrible but capable of detecting over temperature :)

More details at smdprutser.nl project page.

App note: WM8731 Suggested power-On/Off sequence

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Interesting app note from Cirrus Logic on how to minimize popping sound on the output when turning on/off the DAC on their WM8731 digital to analog converter. Link here (PDF)

As with any consumer audio product, it is important that any on/off power noise be kept to a minimum. Generally, this is done with some sort of external mute circuit at the output socket of the application. Although effective, this does increase the BOM (bill of materials) cost, which in many cases is a critical factor.

With this in mind, the WM8731 DAC signal path may be powered-on in such a way that power on/off noise is kept to a minimum with no need for an external muting circuit, reducing the BOM cost.

App note: CS3001/2/11/12 & CS3003/4/13/14 Chopper-stabilized Operational Amplifiers

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Cirrus Logic’s app note, discussing their own designed chopper amps. Link here (PDF)

The chopper-stabilized amplifiers designed at Cirrus Logic are unique. These amplifiers offer performance benefits that combine the best features of bipolar amplifiers with the best features of chopper amplifiers. The intent of this application note is to understand Cirrus Logic’s unique technology and to see how it can be applied in various measurement applications.

App note: Output buffer options for Si53X/55X/57X/59X XO/VCXO devices

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SiLabs’ application note: Output buffer options for Si53X/55X/57X/59X XO/VCXO devices (PDF!)

The Si53x/55x/57x/59x XO/VCXO devices can be ordered with one of four different output buffer types: CMOS, LVPECL, LVDS, or CML. Each output type has its own particular benefits and disadvantages. This document describes each buffer type, proper biasing and termination schemes, and related technical trade-offs.

A 1-meter-diameter small transmitting loop for 7 MHz, part 1

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qrp-gaijin has been working on a 1-meter-diameter small transmitting loop for 7 MHz:

I’ve decided to try constructing a smaller, more traditional loop of 1-meter diameter. A smaller loop means smaller radiation resistance, and that means that small values of loss resistance become more significant. Great care must be taken in all aspects of construction to minimize the loss resistances.
This series of articles will detail the progress of the project.

Project info at qrp-gaijin blog.

Therm RTD

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Matthew Reed writes:

Therm RTD is an addition to the Therm PID Controller family, with support for RTD temperature sensors. RTDs (or Resistance Temperature Detectors) use a coil of fine wire made from a material (usually platinum, copper or nickel) that has a very predictable temperature coefficient of resistance (or change in resistance as temperature changes). RTDs are generally more accurate and stable than thermocouples, and have a much greater range than thermistors – although they can tend to be more expensive than both.

More details at Protofusion.org.

Elektor 500ppm LCR meter case tips

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NopHead wrote a blog post review of Elektor 500ppm LCR meter:

I recently bought a 500ppm LCR meter from Elektor because I didn’t have anything for measuring inductors or the ESR (equivalent series resistance) of capacitors, both of which are important for modern electronics, particularly switch mode regulators that have become ubiquitous.
It is also more accurate than any of my multimeters and has wider measurement ranges. For example it can measure resistance from 0.1mΩ to 1GΩ and capacitance between 0.1pF and 0.1F. This means I can now measure parasitics like contact resistance, stray capacitance and lead inductance. The principal reasons it can do this while my multimeters can’t is because it uses a four wire Kelvin connection to the device under test, and as well as measuring voltage and current, it also measures the phase between them.

More details at HydraRaptor blog.

1″ 100W hot-plate for SMT reflow

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kevinhub88 over at the Black Mesa Labs writes:

Black Mesa Labs has been using a $20 hot plate for a year now for soldering QFN ICs to PCBs. Only issue so far has been the size ( 10″x10″x3″ ) and thermal mass of the thing as it consumes precious microscope work area and unfortunately stays quite hot for 30+ minutes after a quick 4 minute reflow job. BML boards are mostly 1″x1″, so a 800W hot plate with a 6″ diameter heating surface is overkill for most jobs.
Wanting something much smaller for a typical BML PCB – stumbled across this 24V DC heating element on Amazon for only $14. It is rated for 24V at 5-7 ohms ( or 4.8Amps ). A surplus 19.5V DC 5A laptop power brick laying around BML seemed like a perfect match for this element. BML has safety rules avoiding designs above 48V – so the 100Watt 20V DC supply coupled with the 24V element seemed like a great way to make a lot of heat in a small surface area in a short amount of time.

Details at Black Mesa Labs project page.