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:

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:

Ivo, who created the SMD version of the Muffsy Phono Preamp, has sent me a lot of nice pictures and a description of his project.

Here's what Ivo says about his project:

I wanted to build a compact turntable preamp with some adjusting capabilities such as gain, impedance and input  capacitance . So I found the Muffsy PP-3 as a very good and valid starting point for my build project. 

At the same time i wanted to do something rare in a audiophile world and SMD seems to be rare. Using SMD components allow to reduce the size of the board. The smaller the size of the components and PCB, the lower the possible external interferences. So I decided to try to build this project with SMD components.

It was very hard selecting the components, and the cost increase for a single board is high. For my PP I chose all resistors in 1206 package and 1% tolerance, and all the capacitors in 1206 package and 5% for the capacitors (excluding the RIAA and the output capacitors).

The RIAA eq network capacitors are high quality KEMET PPS capacitors (case 1210 and 1812 5%) and the output capacitors are PET capacitors from WIMA (10% tolerance, case 2824). I also put some attention to keep the signal path as short as possible and equal length between left and right channels.

I decided to build the PP and the PSU on the same PCB, but leaving them disconnected and connect the two circuits by wire. The boards can then be separated, if needed.The final dimensions for the PCB (PP + PSU) is about 12cm x 9cm and it fits exactly in a B1304 enclosure.

• Power ripple/noise: 12mVpp, 0.166mV RMS
  
• Output noise with shorted input: 7.12mVpp, 0.173mV RMS
  

That's the project in Ivo's own words. He has been very focused, with a clear design goal from the start. The end result has become very nice because of this.

I particularly like how he mounted the LED in the front panel. This nice effect came from drilling about 80% through with a 5mm drill, and finishing with a 2mm drill. The remaining hole was filled with hot glue and polished.

It was great to be able to support Ivo in this project, and I am very happy for him that everything worked out as he wanted it to.