Jump to content
Electronics-Lab.com Community


  • Posts

  • Joined

  • Last visited


Posts posted by pyrohaz

  1. Hey guys, long time since i've last been here!

    I've recently designed myself a low wattage transformer coupled transistor amplifier out of parts i've got.

    I've built it on a breadboard using literally just parts that I could find and at low voltage levels, its quite pleasing to my ear! has a quite sweet sound. I'm using Acoustic Solution Instate 90 MK 2 speakers (Picked em up from a carboot sale,


  2. Hey guys, Im currently researching into depletion mosfets I was wondering if anyone can tell me where I can get some high(er) power mosfets from, im currently using DN2540's I got off ebay. I have spice'd an amplifier (about 9w), it is only a simple one with no NFB and runs off 60v. I will include a screen shot of it. It only has about 360mA on each of the mosfets and a bias voltage of ~1.4v (Cathode voltage). For the phase splitter, I used a simple 2N7000 Cathodyne (Sourceodyne in this case? :P)

    Tips and help please :) cheers!


  3. Thats good thinking, a chip amp could make this project much easier, lots of little cheapo unbranded guitar amps use chip amps, my marshall 30w bass combo has a TDA2030 chip amp.

    Audio, wouldn't it be easier for him to understand a simple opamp preamp? I mean a simple TL071 inverting amplifier isn't too hard to understand? The jfet amp is quite nice, jfet distortion does have quite a nice sound :) Obviously not if its pushed to power supply clipping.

  4. The 74C14 is the same as the 40106 isn't it? I'm happy with the voltage it is at (the capacitors I have are only rated to 63v, hence why I only used the 4 stages). Would adding another stage not decrease the current I could supply? I was thinking of using one of these switched capacitor boosters in a guitar pedal.

    For a schottky diode, would the BAT46 be suitable? Afaik, they're rated up to 100v aren't they?

    Any other tips you can give me?


  5. Hey guys, i've recently designed myself a simple switched capacitor voltage booster, just using the simple 4069 inverter chip. I was wondering though, can you give me any simple information on increasing the efficiency of my switched capacitor booster? I will include a schematic of what mine looks like :)

    The reason is, im only using a 4 stage booster (2 of the inverters for an oscillator, the rest for voltage boosting.) And im using it to drive my tube preamp :) After I tested it, I got an output of 58v (68k load) and a frequency of 42khz. Now obviously, the calculated voltage should be 60v but im sure the combined voltage drop of 4 diodes is about 2 v (0.6*4=2.4 so actually, a little less)

    Are there any tips you can give me to improve this circuit?

    After having a quick look with my multimeter, it said it was only consuming about 7.4mA which actually seems a tad low for a voltage booster IMO. I calculated the efficiency of the current circuit at a mere 55%!

    Im using 63v Axial 1uF capacitors, they have a blue plastic coating on the outside if that helps :)
    1N4148 diodes and a PI filter on the output may be a bit of an overkill but its feeding the preamp audio stage so I want as little noise as possible.


  6. Hey guys, I have recently realised... Since the power supply for my bass amplifier is essentially just a single 48v power supply, I seem to get electric shocks when I touch the rear of my amplifier! (The case is "grounded" and metal). So what I was wondering, can I connect the metal case to earth to stop the shocks? Because since I am using two switching power supplies in this fashion, my bass is at 24v potential to earth since it is also grounded which may cause a few problems!

    The power supplies are wired up in Series to create a 48v power supply. Essentially, its just

    -  +-  +
    0 24 48

    Can I earth the supply at the 24v point?

    Thanks, Haz

  7. Hi, good luck with getting the transformer working, unfortunately if the outputs are sorted, it might be unfixable :/. If the transformer in itself is quite large, I can imagine the secondary coil is that large for the current capability of the transformer.

    Hopefully the 'Guy in the shop' will be able to give you a hand with your rectifier though it should just be a silicon rectifier with enough current capability :) here is an example of one: http://www.rapidonline.com/Electronic-Components/Discrete-Semiconductors/Bridge-Rectifier-Diodes/6A-Bridge-rectifiers/29672

    The brand or anything shouldnt matter too much aslong as it rectifies.

    For your idea with the bulbs, running them on 12v AC would be fine but for the fans, yes you will need DC. If you don't run your bulbs off the same DC supply, your filter capacitors will not need to be as large. :)

    The 7812 will only be able to provice 1A current if heatsinked. If you require more, you might want to look towards a switching regulator to save efficiency and reduce heat :).

  8. Have you tested resistance on the coils? Just to ensure that theyre not shorting or anything?

    If that all checks out, try replacing the rectifier unless the rectifier and transformer is as one package then that may be a small problem. With your other transformer, try reading each winding to get which one is the secondary and primary by using the resistance option. The primary coil with be the one with the most resistance.

    Bridge rectifiers really aren't majorly expensive and all you need is a correctly rated one (Peak of 12v = 12 x 1.414 = 16.9v but bridge rectifiers are normally quite high voltage components for voltage spikes etc. Aslong as the voltage is within the range, you would really just need to see if the current rating is suitable. a 6A 200v bridge rectifier off Rapid would cost: ~

  9. I think the output voltage will be dependant on the load. I can imagine the 220k resistor is there for safety reasons. When the night light is unplugged, the resistor will ensure that the 560nF capacitor is safely discharged. I couldn't find anything from a quick search on google but I can imagine adding parts together that this would be called a Series Capacitor Regulator?

    I'm quite sure that this will drop the load through acting like an AC potential divider. It seems as if it would be equivelant to a High pass filter.

    Example: If the capacitor has a reactance of 5.6kOhm (at 50Hz), and its driving a 100R load, due to this being the same as a potential divider I suspect the voltage across the load would be 5.95v Peak.

    (Vin*R2)/(R1+R2) Since the capacitors reactance would be R1, that value would be 5.6k. R2 would be the load so in this example, that would be 100. The voltage in would be the peak voltage of 240v afaik, (240v*1.414 = 339.36v)

    As you can imagine, as the resistance of the load varies, the output voltage will also vary.

    I made a visual represenation of this circuit on the free applet: http://www.falstad.com/circuit/

    Just click on File>Import

    Then copy in the code below and click import :)

    $ 1 5.0E-6 6.450009306485578 50 5.0 50
    c 208 144 368 144 0 5.6E-7 -62.32904764451111
    r 368 144 368 272 0 100.0
    O 368 144 480 144 0
    g 368 272 368 304 0
    R 208 144 160 144 0 1 50.0 339.39 0.0 0.0 0.5
    x 400 218 453 224 0 24 Load
    x 136 97 218 103 0 24 240vAC
    x 214 185 355 191 0 24 PP Capacitor
    o 2 16 0 34 9.353610478917778 9.765625E-55 0 -1 out
    h 3 1 0

    As you can see in the waveform, the voltage across the load is 5.97v, close to what I had calculated!

    Also, in your schematic the 100R resistor will just be to limit the current probably as a safety feature to keep the capacitor safe.

    After having a quick search of your chip, it turns out the thing I thought was a photodiode, it actually is PIR sensor, usually used within a motion sensor. I found out that the chip operates at 5v meaning you would need to use a regulator for whatever voltage you are using for this project.

    In your pictures you have shown me, I can see two Zener diodes (Possibly) so it must be an regulated supply for the chip.

    I have attached a PDF file of your chip. Unfortunately its in chinese but I hope its helpful!


  10. I think that most resistors (standard ones) are rated to 250v but im not 100% on that.

    for a cap to be "AC" I suppose it just needs to be unpolarised so really, it can be any capacitor that isnt a polarized electrolytic, e.g. Mylar or Polystyrene etc.

    To lower the AC voltage, if you put the capacitor in series with a resistor (in the sense of a potential divider with the capacitor being on the top) Due to the capacitors reactance, it will be "equivelant" to a 5684Ohm resistor at 50Hz (a capacitors reactance decreases as the frequency is increased) Therefore, if you had a resistor in series at a vaue of 5684Ohm, it would act as a potential divider of 2. The capacitor will also limit the current.

    I doubt it would be a resistor, I haven't really seen brown resistors of this shape. I have seen brown resistors in circular shapes (carbon film) but never a boxy shape. I knew it was a capacitor because if you search polypropylene 400v capacitor into google, the pictures pretty much match the capacitor in your pictures :)


    On that website, it shows multiple polypropylene capacitors that have the same brown colour and shap to yours :)

  11. One good way of possibly doing it is to filter the supply to the amplifier with an LC filter. If you know the frequency of the charger hum, you can base the filter frequency on this but otherwise, find the largest inductor that is ok with your current required for your amplifier and use that. This kind of filtering was used on most Valve amplifier to filter out the 50/60hz line noise I think :)

    Charger > Batteries > LC Filter > Amplifier

    Since you are using two TDA7240A, Am I right in assuming that they're for stereo operation?

    This equates to 40w of power I think, therefore equivelant to: 40/14.4 = 2.78A.

    Since you will probably want to filter out power supply noise down to 50Hz (just incase you are getting Line hum through the charger) Try: 4Mh Choke (available from Rapid) and a 3300uF capacitor.

    A schematic of this would as attached.

    Obvilously, just use the largest choke and capacitor pair you can get hold of to ensure your horrible charger hum is filtered :)

    Best of luck!


  12. Hey guys!

    I recently finished my first larger project (in a long time!)

    As Hero will probably remember, I was considering building a Class D Bass amplifier! Well I have done so and completed it now.

    240v Input, Dual laptop supply-age!
    170w Output (Theoretical)
    +/- 24v PSU
    Based around the TDA8920BTH in BTL mode
    4Ohm 12" speaker
    Laney Bassman 40 Preamplifier

    I had intended to convert my Laney Bassman 40 into a much better amplifier because to put it bluntly... It sounded like utter cr*p due to the lame-ass power stage!

    Luckily with this amplifier, the power amplifier and preamplifier stage were two separate PCB's meaning I could hopefully savage it and use the preamp stage with a new power stage (I diagnosed the problem of which stage sounded so bad by testing the line-out section of the preamplifier on my Marshall Bass 20 amplifier (a lovely amplifier!) and the preamp stage sounded very sweet.

    So! I ripped out the horrible power stage along with the bulky transformer (this reduced the weight a lot! And prepped the Preamplifier stage for use with my new power supply (the transformer was a 30v-30v non-torroidal one). After testing the preamplifier stage at +/- 24v, I concluded that it worked fine.

    I bought the power supply and power amplifier board off eBay for a total of:

  13. Cheers audio, I did mean what you said, sorry!

    To be honest... I would actually be prepared to use a class D IC but I find this area of electronics so interesting in how you can get such high efficiencies from such a well theoretically quite simple circuit and I am quite interested to learn through my own steps and errors. I mean, I know that you can listen to a class D IC to listen to the auditory quality but you don't really get to see the internal schematic of one of these chips (afaik) they are usually in a block diagram.

    By doing it myself using the terminology, I can create my own designs and test them for auditory quality and such, plus the price of products: (eBay being my source here)
    1x TA2024 Chip -

  14. Hey guys, Class D amplifiers but a different form this kind, this question is more on OpAmps:

    Right... I'm looking for an quad opamp that will best suit my job:

    2 Opamps being used within a triangle wave generator operating at ~140Khz
    1 Opamp as an inverting amplifier to amplify the incoming signal
    1 Opamp as a comparator to create the PWM output

    The output of the PWM op amp goes to a Source follower (?) mosfet stage etc etc.

    What would be the best opamp? I managed to get about 60Khz out of a pair of 1458's...

    I'm stuck on the Lm324 or the TL084 (power consumption when idle isn't a massive deal) Operating voltage will be ~32v +-1v

  • Create New...