Tips & Tricks

At this page I want to give you some common informations and useful hints about the development for DIY audio electronic.

 

Table of Contents

Replacement for Dual-JFET

2016/01/25

The Toshiba Dual-JFETs 2SK389 (n-channel) and 2SJ109 (p-channel) are no longer in production. Also the below listed single JFET’s from Toshiba are no longer manufactured in the meantime. However there are direct replacements from Linear Systems on the market. But today the single transistors are easy to buy – even matched. Please be careful with the double JFET’s, most of the parts on the market are fakes nowadays.

 OriginalErsatz / ReplacementBemerkung / Comment
n-Kanal2SK389BL2× 2SK170BLToshiba
2× 2SK370BLToshiba
LSK389BLinear Systems
2× LSK170BLinear Systems
2SK2145BLToshiba, Dual-JFET, SMD, Common Source
p-Kanal2SJ109BL2× 2SJ74BLToshiba
2× 2SJ108BLToshiba
2× LSJ74BLinear Systems

On the photo below you can see an example from the XOno how to replace a 2SK389BL with 2× 2SK170BL.

2× 2SK170BL replacement for a 2SK389BL

AC Phase

2016/01/27

We all know that the AC power plug can be connected in two positions in a lot of areas around the world. Normally there is no difference between both possibilities, but not all audio equipment are designed symmetrically in their power supply. This is the reason why it is worth to make the measurement which I describe below and to connect the AC power plug in the “right” position.

  1. You have to unplug all connectors – with the exception of the AC power connector – from the audio device you want to measure.
  2. Now you can measure with a normal digital meter the AC voltage between the earth (at the power outlet) and the audio signal ground. The easiest point to measure this ground is the outer contact of a cinch jack.
  3. After this first measurement you must switch off the audio device and plug the AC power connector in the second position (turn it at 180°). Now switch the device on again.
  4. Make the same measurement as above (see 2.).
  5. The measurement with the lowest AC voltage is the “correct” audio position of the AC power connector.

What you see here is that you don’t need an expensive phase measurement system from an audio store. All you need is a cheap digital meter from an electronic store. The nice secondary effect is that you have a measurement device for more than one special measurement – and of course every DIY audio guy has a meter available.

In a DIY audio device you can connect a 230V/AC LED between phase and earth to show the correct position of the AC power connector. With that small circuit you only need to measure the above described measurement once (before you wire the LED). How such a circuit looks like you can see at the 230V/AC wiring in my Aleph P (LED DS3).

230V/AC DC-Filter

2016/01/27

The description I found for the first time at www.saque.de (sorry – this page is written in German).

Which partly “dramatically” effects with a 230V/AC power connection DC filter in an audio device you get I have heard with my Zen amplifier. Since than I always use the below descibed filter in the 230V/AC line of my DIY audio components.

The physical effect of such a filter is easily illustrated :
If you analyse more precisely the voltage coming out of the power outlet, you get depending of your geographical position and the time of day, partly terrifying results. The voltage is not necessarily sinusoidal and has often also a small amount of DC offset. Exactly that DC offset is the topic of the filter I descibe here. With this DC offset you get a premagnetization of the power transformer in your audio device which can have a big influence of the sound (see above). The DC filter “blocks” the offset and impeded securely the negative effects of the premagnetization – you see, there is no voodoo here !!!

The circuit you can find e.g. at the 230V/AC wiring of my Aleph P (BR1, C1…C3). The capacitors are blocking the DC offset and the diodes taking care that the voltage over the capacitors can only achieve a maximum of ≈1.2V (two diodes in series). I use two capacitors in parallel with the benefit that the overall capacitance is a sum of both. However I take into account that always one capacior is working with the wrong polarity during one half cicle. I made the experience that this is working without any problems as long as the voltage is not bigger than 1.2V and the capacitors have a maximum voltage not lower than 25V. But of course the more safty way is to use two capacitors in series (either both minus or plus poles connected together) to get an overall bipolar capacitor with half of the capacitance.

For the dimensioning of the filter you have to take into account that the voltage at the capacitors with the maximum current flow is lower than the diode voltage (here 1.2V). I took my Zen power amplifier to calculate the filter as an example.

The values of the transformer at the secundary side are 2×15V / 5.7A. This gives us a power of

    \[ P = U \cdot{} I = 2 \cdot{} 15\mbox{V} \cdot{} 5.7\mbox{A} \approx 171\mbox{VA} \]

and out of that we get the maximum current at the primary side (we assume that the transfomer is lossless)

    \[ I = \frac{P}{U} = \frac{171\mbox{VA}}{230\mbox{V}} \approx 0.74\mbox{A} \]

With two diodes in series the resulting voltage at the impedance of the capacitors must be lower than 1.2V. We get

    \[ X_C \le \frac{1.2\mbox{V}}{0.74\mbox{A}} \approx 1.62\Omega \]

With

    \[ X_C = \frac{1}{2 \pi{} \cdot{} f \cdot{} C} \]

we calculate a minimum capacitance of

    \[ C = \frac{1}{2\pi{}\cdot{} f \cdot{} X_C} = \frac{1}{2\pi{} \cdot{} 50\mbox{Hz} \cdot{} 1.62\Omega} \approx 1900\mu\mbox{F} \]

If we use now a capacitor with 1900μF we have no spare voltage left for the DC offset. The voltage at the impedance of the capacitor is in the region of the maximum voltage we get from the bridge rectifier. We have to take a bigger capacitor to get a filter for the DC offset. In my Zen power amplifier I use 2× 10000μF. A good reference value is :

per 100VA ≈ 10000μF

With this reference value we get the following voltage at the impedance XC of the capacitor

    \begin{eqnarray*} U_C & = & I \cdot{} X_C \\        & = & \frac{P}{U_{AC}}\cdot{}\frac{1}{2\pi{}\cdot{} f \cdot{} C} \\        & = & \frac{100\mbox{VA}}{230\mbox{V}}\cdot{}\frac{1}{2\pi{}\cdot{} 50\mbox{Hz} \cdot{} 10000\mu\mbox{F}} \\        & \approx & 0.14\mbox{V} \end{eqnarray*}

Now we have more than 1V left for the DC offset (if we use 2 diodes in series). The results for the dimensioning of my Zen amp is

    \[ U_C = \frac{171\mbox{VA}}{230\mbox{V}}\cdot{}\frac{1}{2\pi{}\cdot{} 50\mbox{Hz} \cdot{} 20000\mu\mbox{F}} \approx 0.12\mbox{V} \]

Here are two examples from the “real” life (found at saque.de) :
A class A power amplifier with a 1000VA transformer from Mark Levinson has 3 diodes and 40000μF (4000μF per 100VA) and Teac takes one diode and 6600μF for a maximum power consumption of 400VA (1650μF per 100VA).

The capacitor dimensioning of Mark Levinson is lower than mine, but they use 3 diodes in series (≈ 1.8V) and therefore the result is more or less equal. The circuit from Teac you only can understand when you take into account that it is not a class A amplifier and that they don’t need permanentely the maximum power consumption – so I think even this dimension will work under normal conditions.

Snubber Network

2016/02/24

A circuit with a transformer and a rectifier – you find it in nearly every power supply – has very often a high frequency oscillation on the DC voltage at the output. You find some very good articles describing this effect on the internet. They included the theoretical and mathematical models to calculate a damping network for this oscillation. The problem with this models are that you need data’s from the transformer and diodes which are hard to find.

On diyaudio.com you can find a very interesting discussion about a possible investigation of the snubber network parameters with the help of a test circuit. You can download the article of this circuit at the end of the first contribution of the thread

Simple, no-math transformer snubber using Quasimodo test-jig

I build the test circuit and set up the power supply in the XA30.5 with snubber networks. On the following pictures you see the measurement of the transformer without (left) and with an adapted (right) snubber network.

The B channel (blue line) shows the output of the secondary winding of the transformer. Please notice the horizontal (500ns) and vertical (10V) resolutions,

SB1pro & Vinyl Cleaning Liquid

2016/01/27

I’m a proud owner of a SB1pro cleaning machine from Sven Berkner. The machine uses a small point vacuum where the cleaning liquid is transported at the push of a button and the small movement of the distance filament is done automatically. I became aware of this machine the first time in 2010 during a lecture of S. Berkner at the Analog Forum in Krefeld and I bougth this machine a couple of month later. This step I never regret, the machine is working very practical oriented and extremly reliable. Moreover Mr. Berkner has an extraordinary support. My machine gots in the meantime two improvements out of the running series, both without charge – this I call support !!!

Directly after I bought it I used the liquid provided with the machine, but I started also immediately to look for an adequate recipe to mix the liquid by myself. A colleague from the AAA had the right hint and I want to provide these information also with you.

Menge / QuantityChemikalie / Chemical
500mlDr. Wack 1:300
250mlIsopropanol
250mlEthanol
2,5ml25% Ammoniaklösung / 25% Liquid Ammonia

The Dr. Wack liquid is the glass cleaner concentrate Dr. Wack 1:100 super which you have to mix with distilled water at a ratio of 1:300. The destilled water has to be as “clean” as possible, we have ultrapure Ampuwa in use. The glass cleaner concentrate you get from car accessory shops here in Germany.

The add on of ammonia solution with a mixing ratio of 1:400 is a tip from Sven Berkner.

This cleaning mixture achieves astonishing good results. I had a new record with residues from the pressing which the original liquid is unable to remove. After soaking the record for 5 minutes with the recipe from above everything was gone and the sound was as good as I expect from a new audiophile record. I also can play my up to 35 years old records which I play wet in the past now dry without noteworthy background noise.