Hifi Preamps for your Record Player

By: skrodahl | June 15, 2018

It's become evident that I need a better solution for photographing my projects. So I went out and bought some surprisingly cheap LED panels:

LED Panel
LED panel, (c) MIA Worldlight

But then I had no idea on how to build this into a suitable light box. So I spent the time buying suitably sized vinyl backdrops and some clamps from the UK based eBay seller photogeeks11. I can't thank the seller enough, small sized vinyl backdrops are very hard to find. They are also of excellent quality.

 
Black backdrop
Black backdrop, (c) photogeeks11
 
Mini clamps
Mini clamps, (c) photogeeks11
 
White backdrop
White backdrop, (c) photogeeks11

My first lightbox...

The first lightbox was three pieces of scrapped wooden planks. Just to hang the backdrops from. The two side LED panels leaned against the planks, and I managed to somehow balance the top LED panel long enough to take one picture. Then it all crumbled and fell to the floor. (Nothing broke, luckily.)

My first lightbox
My first lightbox

It did produce one good picture before the whole construction fell apart though. Keep in mind that this is taken using my Galaxy S7 Edge with default settings.

My first lightbox picture
My first lightbox picture

Rethinking the lightbox (the one that didn't fall apart)

Since I wasn't in the mood for having my (albeit cheap) LED panels crushed, I set out looking for alternatives to scrap wood.


I finally found some nice square aluminum tubing and plastic joints. So I brought out my old trusty (and very dull) hacksaw. Here's the result:

 
Second lightbox, partly assembled
Second lightbox, partly assembled
 
Second lightbox, fully assembled
Second lightbox, fully assembled

Pictures, or it didn't happen!

Well, I have only one picture. It's of my B&O IcePower module, on white vinyl backdrop.


This picture is also taken with my Galaxy S7 (the system camera is now on a tripod in front of the light box). I had to change exposure, and do some post-editing though. 

IcePower 125asx2
IcePower 125asx2

I think that's quite a beautiful result. Now that I have the system camera mounted, I've finally found my lightbox solution.


It wasn't exactly cheap though, it came in at just above US$ 300. It's tailor made to my needs, which is why we all do the DIY-thingie in the first place. Right?

By: skrodahl | March 26, 2018

While I've been sharing a lot of my work on muffsy.com, I've never really clarified how my view is on people using my work (or derivates of it). This is now changing.

I've decided to release all of my content (barring a few exceptions) under the Creative Commons Attribution 4.0 International license.

What does it mean?

It means that everything on muffsy.com, except where specifically stated, is open source. You have the right to:

 

  • Share — copy and redistribute the material in any medium or format
  • Adapt — remix, transform, and build upon the material for any purpose, even commercially.
  • This license is acceptable for Free Cultural Works. I, as the licensor, cannot revoke these freedoms as long as you follow the license terms.

 

If you're going to use any of the content on muffsy.com, you will have to adhere to these conditions:

  • Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.
  • No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.
  • You do not have to comply with the license for elements of the material in the public domain or where your use is permitted by an applicable exception or limitation.
  • No warranties are given. The license may not give you all of the permissions necessary for your intended use. For example, other rights such as publicity, privacy, or moral rights may limit how you use the material.

There are also some conditions for muffsy.com to follow. Most notably is that the shared information must be in an open format. The only possible violation to this are my Autodesk Eagle design files. They can be used, but not always processed, by the free version of Autodesk Eagle. They can also be opened and edited (although not always perfectly) in the open source tool KiCad.

What are the exceptions?

The only exceptions to the Creative Commons on muffsy.com is for a few of my PCB designs, mainly variants of those that I'm currently selling. They are free for personal or non-commercial use, but you cannot use them commercially without my approval.

The fact that the schematics are open source will of course allow you to design your own PCBs for any desired use, as long as you comply with the terms of the license.

At the time of writing these are the only exceptions:

If not stated otherwise, everything is free to use as described above. That's right, text, pictures, schematics, design files. The lot!

Category: News 

Tags: muffsy, open source, website 

By: skrodahl | March 13, 2018

I'd really like a stereo input selector with relays, but those things are hard to find! (Apart from some of dubious quality on the *Bay)


Better make my own then. This one's got a custom footprint for an ESP32 devkit module, but it can also be controlled with a rotary switch.

Muffsy Stereo Relay Input Switch

I decided to use five Panasonic TQ-2 relays. The ESP32 module and relays are powered separately, power ground and signal ground are separated to avoid injecting any clicks, pops or noise into the audio channels.


The whole project is open source, free to use as you wish. Eagle project files, gerbers, the Eagle library for the ESP32 module and BoM are all available on the hackaday.io project page.

Muffsy Relay Switch on Hackaday.com

By: skrodahl | November 26, 2017

Check out this post for test setup and limitations.

ITU-R IMD is one way to measure intermodulation distortion. I am feeding the circuit with two test tones at -6 dBV, which will sum to 0 dBV. The test tones at 19 kHz and 20 kHz will produce a modulated signal at 1 kHz. The difference between the test tone and the modulated signal is the ITU-R IMD.

The ITU-R IMD for Burson V6 Classic is -118.1 dB / 0.000124%.

Burson V6 Classic - ITU-R IMD at 1.36 dB gain
Burson V6 Classic - ITU-R IMD at 1.36 dB gain

How does it fare in comparison to the audio analyzer itself and, equally interesting, our OPA2134 reference IC op amp?

Well, the audio analyzer can measure down to -122.2 dB / 0.000078%, so the Burson measurements are well within the analyzer's capabilities.

QA401 - ITU-R IMD
QA401 - ITU-R IMD

The Burson V6 Classic loses out to the OPA2134 once again. The OPA2134 measures -121.0 dB / 0.000089%.

OPA2134 - ITU-R IMD, 1.36 dB gain
OPA2134 - ITU-R IMD, 1.36 dB gain

Category: Measurements 

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By: skrodahl | November 25, 2017

Following up on the THD measurement of the Burson V6 Classic (which also shows the test setup and limitations), here's its frequency response.

These measurements are showing up now because the QA401 is not linear. The measurements had to be compensated for that.

The frequency response is measured with an output of 0 dBV / 1V rms and a gain of 1.36 dB / 1.17X.

The Burson V6 Classic's gain is 0.1 dB lower than expected. It performs great otherwise, showing -0.2/-0.1 dB all the way from 10 Hz to 80 kHz. This is as high as I can go with 192 kHz sampling frequency. The graph uses a relative scale since it would otherwise disappear under the 0 dB horizontal line.

Burson V6 Classic - Frequency response at 1.36 dB gain
Burson V6 Classic - Frequency response at 1.36 dB gain

But how high does it go? Time to whip out the Rigol DG1022 function generator and the Rigol DS1054Z oscilloscope. ~1.5 MHz is the answer (with the noise starting at about -20 dB below the signal). Go beyond that and the amplification still holds for a while, but the signal is no longer a sinus.

The signal is down -3 dB at approx. 3.7 MHz. By then it's a pure saw tooth signal.

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