Here's the finished Inverse RIAA. I haven't done extensive testing yet, but it works as promised AND it measures exactly the same on both channels. I'm really happy with the result.

Get the gerbers for this project here: invRIAA.zip

If it's going to be called accurate, you'd better get two identical channels. Here's how the invRIAA fares:

In order to construct this board, I built the vacuum pickup tool:

The lead free paste was applied using a stencil, which is extremely convenient. To do the actual soldering, I used this reflow heater bought cheap on eBay (Nope, I don't have space for a reflow oven...). The only negative with this heater is that the LCD back light is more on the front, so you need to tilt it to see what it says.

You really don't want to go with a normal heat gun for this. They push about 600 liters of air per minute, which will blow away all the components. This one does about 30 liters/minute, and it's adjustable both on the tool itself and by replacing the nozzles.

I even bought an Atmega based transistor tester as a kit, and it contained three SMD components. Here's how that turned out:

The instructions give you three alternatives for powering the Muffsy Phono Kits. Here's another one:

This step-down power module is available on Tindie, and can provide up to two amperes of power. Use two of them and connect a 15V DC power supply at VIN/GND as shown in the picture above, and you will get a +/-12V output. This will provide sufficient headroom for the Muffsy Phono Kits.

The ripple is some 18-20 mV. This is waaaay higher than the Muffsy Power Supply, but should work reasonably well. Especially if you're strapped for space.

A small word of caution: The output voltage is set using very small surface mount resistors (included). You will have to do SMD soldering. It keeps the common ground though, so it should be able to work alongside other power supplies with all grounds connected.

No complaints on the price either, I paid $20 for five of these modules and international shipping is $3.

This is my first venture into SMD components, so I'm going to have some fun with tools, solder paste, stencils and hot air. :)

Get the gerbers for this side project here: invRIAA.zip

An inverse RIAA circuit has been on my wish list for a while, as it makes testing frequency response so much easier. But how, you might ask?

Well, the first problem you'll encounter when trying to test a phono stage is the fact that few signal generators produce a signal level low enough. If they do, they're often not very accurate at those levels.

The second, and most pressing problem, is that the phono stage applies equalization to your signal. Input a 50 Hz signal at 5 mV, and the output will be almost 5 mV. Input a 20 kHz signal at 5 mV, and the output will barely be measurable. You won't be able to see the frequency response from the readings, without doing a whole lot of conversions (and taking DMM/scope tolerances/misreadings into consideration).

What's needed is something that takes your signal and turns it into what you'd find on a record. That's your inverse RIAA equalizer.

Feeding your signal through an inverse RIAA equalizer, and then through a phono stage, will create a flat output at all frequencies. If this inverse RIAA equalizer is sufficiently accurate, it can be used to measure the accuracy of your phono stage. It's got the added benefit of bringing a higher input signal down to cartridge level.

I got Hagerman's inverse RIAA filter, and while it's a nice little device, I wanted to get one with better accuracy. That's achieved with a lot more components to even out their tolerances.

Not one of my designs, this is the Accurate Inverse RIAA from HIFISonix. I decided to make a stereo version. As I already have lots of screw terminals and DIP switches, I decided to use them too.

There's a lot of components in there, which is why it's SMD (the board size is approx. 8 x 5 cm). All SMD components are 1206 size, so it should be manageable to solder them in. I thought I'd use a hot air gun for the soldering.

I still have to get the boards manufactured, and I need components for it. Not sure how long it'll take, but I'll definitely let you know when it's done.

UPDATE (2017-03-09):

All components have arrived, and a few boards have been ordered. I also sprung for a cheap hot air soldering "pen" on eBay, and a stencil for the SMD-components on the board.

I managed to get the board size down to 84 mm (83.98 mm to be exact) x 51 mm. 84 mm width is what's needed for the board to fit into one of those B0905 enclosures. :)

UPDATE (2017-03-10):

Here's the final layout. The caps have all been changed from 1206 to 0805, since I only found them in that size at a decent tolerance of 2%.

The attenuation for MM is -44 dB, and for MC it's -68 dB.

I got a vacuum "tweezer" that was completely useless for these small components, so I ordered a fish tank air pump to make a real vacuum pickup tool based on this video:

UPDATE (2017-03-16):

The boards and stencil are here:

I've been looking for a stamp to add resistor values, instead of writing them by hand. I did find some, but they weren't customizable and the shipping price was upwards to $100.

After some more searching, I found Itou-Kinzoku in Japan. They offer fully customizable rubber band stamps, so I thought I'd give it a go. I got four bands with the letters, numbers "1 2 3 4 5 6 7 8 9 0 M K". Itou-Kinzoku's representative made sure that I got the right height and width, and the right kind of rubber for my use.

It all worked out as I had imagined. Not only does it look a whole lot better, but it took less than half the time it used to, to assemble the kit.

This project is freely available, and you can have the boards produced yourself. That's not for everyone though, so I've decided to sell the PCBs for the BSTRD on Tindie.

The Bill of Materials on hackaday.io has been greatly improved, and even contains a Mouser shopping cart for all parts except the tubes, tube sockets, LED resistors and transformers.