Hifi Preamps for your Record Player

By: skrodahl | August 31, 2017

YouTube user Blake G has posted a couple of vinyl-rips using the Muffsy Phono Preamp onto the video site. Although YouTube probably alters the bitrate, you can still get an idea on how the Muffsy Phono Preamp performs in his setup. His setup, btw, is:


    • Turntable: Sony PS-X500
    • Cartridge: Empire 999ve/x
    • Phono Stage: Muffsy PP-3
    • Line In: Behringer UCA202

Muffsy Vinyl-rip on YouTube

Here are the links to Blake G's two rips:

 
 

Category: News 

Tags: muffsy, phonostage, vinyl, youtube, rip 

By: skrodahl | April 19, 2017

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

Accurate Inverse RIAA completed

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

invRIAA Frequency Response - Both Channels

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

Vacuum pickup tool pump
Fish tank pump and tubing
Syrringe for vacuum pickup tool
A 3 mm hole in the syringe works really well
Sealing the vacuum pickup tool
Some silicone sealant to make the pickup tool airtight

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.

SMD reflow heat gun bought on eBay
SMD reflow heat gun bought on eBay

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:

 
Close-up of SMD components on the transistor tester kit
 
Full view of the transistor tester

By: skrodahl | March 15, 2017

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

 
Step-down power converter - Dual power supply
 
Step-down converter - Size comparison

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.

By: skrodahl | March 04, 2017

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.

RIAA curves, normal and inverse

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.

Accurate Inverse RIAA Equalizer - Stereo and SMD

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%.

Muffsy Accurate Inverse RIAA Equalizer - Final Version

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:

Inverse RIAA PCBs and stencil

By: skrodahl | January 27, 2017

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.

Resistor values using a rubber band stamp

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.

Category: Uncategorized 

Tags: stamp, packaging 

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