A power supply should provide a precise voltage completely stabilized versus perturbations from any kind, coming both from the AC source or from the load.
A preamp or an amp is like a tap put after a water tank. It has no sense to have the best tap if you have only few and spotted water to put through …
Power supplies are often considered as a secondary circuit, all the development efforts being applied to the amplifying circuit.
Well, it’s a mistake, the power supply is as much important as the circuit itself.
Just consider the supply as being part of the signal path, so therefor a lot of attention is given to this part of the amplifier. The time and work it costs me to build the power supply is more then the time to make the amplifier part itself!
Three steps are needed:
A transformer set the AC voltage to the proper value
A rectifier circuit changes the AC into DC
One or more filtering cells stabilize the DC
The power supply should not only have an extremely low impedance but this impedance should be frequency independent as much as possible.
In the time that zener diodes didn’t exist, a gas filled voltage reference tube was used to get a stable voltage. Nowadays these are seldom used and that is why I dedicated this article to explain what different types there are and how they work.
Different types of the voltage reference tube
The voltage reference tube can be filled with different gases to meet the particular voltage level. For the stabilized power supply in the flea-power, I used the 85A2 tube.
I will briefly describe the principle of a neon tube: In a small gas filled glass tube, 2 electrodes are placed opposite. Electrons and ions present in the tube get a certain speed on their way to the electrode. The speed is dependent on the applied tension and in case of the 85A2 the tension is 85V. As soon as the speed is reached, the electrons collide with other atoms and this results in more free electrons. The snowball effect will eventually result in a glowing light. The color of the light is dependent on the gas the tube is filled with. For neon, the color will be orange, for argon it will be blue.
In case of the 85A2 the tension upon the tube will remain constant. This is only applicable when the current remains between certain margins. Each tube has a certain kindling tension to start the snowball effect. When the amplifier is switched on, it will take 5 to 10 seconds (this can be type and brand dependent) before the tube flashes. Then it will shine a glowing light. This kindling tension is higher then the stabilized tension (125V for the 85A2).
For these kind of tubes, it is important that the current is held between the max. and min. working point with a resistor. These neon tubes are still easy obtainable and the lifetime is very long. A spin-off is the magnificent visual effect when the little tube is glowing on top of your amp.
Connecting a stabilization tube is simple. Even though it has 7 or more pens, internal it has only 2 connections: the anode and the cathode.
Every diy in electronics has to deal with it every now and then: soldering. When I started as a youngster, frequently a project I finished didn’t work. After investigation, the reason often was a bad soldering joint. All the more reason to pay attention to this craft.
An important aspect when soldering are the materials used. I use an older Weller magnastat. The operation and characteristic are described on the Hackaday site.
In brief: the element is heated until the curie temperature of the magnet. Then the magnet will temporary loose its magnetic characteristics. A little spring will force the contacts in an open position and consequently the heating will stop. Temperature will drop under the curie temperature again. The magnet regains it’s magnetic characteristics and the contact will be pulled in a closed position again by the magnet. The heating starts again.
From this type of iron you hear a ticking sound, you even can feel it. I got used to it, I think everyone will eventually.
In my post about the turret I explained how important it is to apply sufficient heat. Soldering is an art, you need to have a feeling for it. I add a movie to show how the tin is “sucked” between the wires when enough heat is applied
Patience is a virtue.
I use a 380 degrC tip and preferably one with a sharp point. All depends on your own preferences and the applications.
Make sure the sponge is wetted when you solder. You will see the tip gets black during your work, this pollution will eventually end up in your joints. So weep it off frequently.
I use a hand pump with Teflon tip for the big joints and litze wire for smaller work.
Turrets are mainly used in guitar amps, less in audio amplifiers
I worked with terminal-strips for a long time and actually without any problems. Every solder joint can be good if you apply the right solder technic.
I will write an article on solder technic shortly.
Turret’s have this name because they look like a castle’s turret or a chessboard turret. I think it is best to call it turret in dutch too so everyone knows it is not the place where politics takes place (het torentje)
When I saw the massive turrents for the first time on a fiberglass board, immediately I saw the potential to use it in an audio amplifier as well. From e-Bay I ordered some turrets and fiberglass board (3mm). I had to read some articles first, and on the guitarkitbuilder.com site I found most of the things I wanted to know.
To drill the holes at an even distance, I used my dremel workstation (drill-press). I had to make some tools to be able to drill as precise as possible. You can make the distance between the holes exactly even by using small tiles of wood or plastic. By adding them one by one between a stable point and the fiber board, you shift the board in even mm for every hole. I made a movie to show how I did the drilling and the pressing of the turrets. You will see I drilled a second time, this was to countersink the hole as my fiber board was too thick to get the turret flanged.
The Dremel workstation is not the most rigid when you drill in hard surface. I have the experience that the drill starts drifting when I apply more force. So sharp drills and pre-drilling with smaller sizes will help you to avoid that. I don’t know if Proxxon is better in this respect? Fortunately I have a large drill-press for the heavy work.
To drill the holes evenly spaced, I made some small tools. Proxxon has a small carpenter’s square on it’s base, for the Dremel I made one myself. And of course it has to be attached to the base so I made some clamps for that as well. In the next video I show both tools in short. Use your fantasy to make more tools that help to make life easier.
Using turret’s needs more preparation then the “normal” solder lugs. The choice which length is determined by the thickness of the board. You can decide yourself where the turrets will be on the board and also which size. In the next picture you can see some of the different sizes.
In the end of 2017, a new Dutch SE tube amplifier will be launched. The name “Flea-power” is among other things used for amplifiers with low power (0,1 to 10 Watt). The low power of this flea-power tube amplifier is no restriction to fully enjoy the music, as long as you use the right speakers.
Most important features of the Flea-power tube amplifier:
No electrolytic capacitors, only foil capacitors (MKP) are used.
No negative feedback.
PCL82 and 85A2 in the stabilized power supply, EF86 and EL95 as pre-amp and powerstage.
Stepped attenuator as volume control (24 steps)
Point to point soldering and use of turrets.
Ever wanted to try-out a tube amplifier at home?
I have made 3 amplifiers specially for trial by people that want to give it a try for 14 days. The only cost is transport cost. The amp has to be sent back to me every time so I can check it to be sure the next person will get a perfect working device again. All this is on a base of good trust. I will send the amplifier in a solid packing.
If you are interested, you can sign in via the “leave a comment” field underneath this post.
A lot of attention is paid to the set up of the components and the quality of the soldering.
If you start designing your amplifier, one thing is sure: you will need a power supply. At least you have to calculate what voltage and current your transformer will have to deliver
Determine the power of your Transformer.
As a rule of thumb, you can apply following calculations: Take the size of the total thickness of the lamination core and the width of the middle leg of the transformer core in centimeter. Multiply these values and square the outcome. Multiply the outcome with 0,64. This value will be the approximate power rating in VA that can be transformed by the core.
It is often difficult to measure the middle leg of the core as the winding will cover that part. Alternatively the width of a side leg can be multiplied by two.
Lamination thickness = 5 cm
Middle leg = 3 cm ( side legs = 1,5 cm).
The power that can be transformed by this core: (5 x 3) x (5 x 3)x 0,64 = 144 VA.
Max current of the winding’s
Next, find out if the copper wire can handle the current that we need. Therefor you measure the thickness of the individual winding’s. You can do this with a slide gauge.
Measure the diameter and calculate the Area in mm² with the formula Area = (π/4) × D2.
As a rule of thumb (again) you can calculate 3.5 A per mm²
If measuring the wire thickness of the high voltage secondary side is problematic, all lower voltage secondary wires can be measured. For each winding, the max power must be calculated in VA . Then you add all these calculated values and subtract them from the total power that is allowed for this core. The remaining power is left for the high tension.
Example for the above transformer of 144 VA:
Assume we have 2 x 400 V high voltage, and 2 winding’s of 6,3V (one for 7A and one for 3A)
The power occupied by both heating winding’s: 6,3 * 10= 63VA. Therefor 144 – 63 = 81 VA is left for the high voltage winding. At 400V we can have 81/400 = 200 mA
4 of the 78.. regulators (+5V, -5V, +12 and -12V) supply voltage to both servo and decoding boards. To my opinion this is not an ideal situation. Therefor I decided to make a dedicated power supply (+12, -12V) for the Op-amp.
Extra regulators for both NE5532 op-amp and new Tent clock
The B&O CD X doesn’t have a lot of free space so it is a matter of measuring how you can fit the new regulators in. I used this opportunity to build an extra 7 volt supply to feed the Tentlabs clock Tentlabs XO
The page doesn’t show the 4.2336 Mc frequency. If you go to the “shop” page shop, you will find it there.
And the box with the crystal. This will be installed in a next post.
This site will be set up as a blog and different subjects will be discussed. I will show as much as possible diy pictures. Most of the schematics will be hand drawn, this gives a personal touch to the site and it will spare me some time to draw it on paper (which I always do) instead of in a drawing program.
I hope this will help you all to understand the different parts of a music installation.