Connect with us

Electret headphones amplifier

Discussion in 'Audio' started by spandrel, Jul 3, 2018.

Scroll to continue with content
  1. spandrel

    spandrel

    7
    0
    Jul 3, 2018
    I've just bought a pair of Stax electret 'earpeakers' on a whim. There's no adapter box with them. The box consists of a pair of step-up transformers driven from an amplifier output, with a ratio of about 1:25. It also has a thermistor on the inputs acting as a limiter. I'm going to try and buy a box but wondered if anyone knew of a circuit which could drive the headphones directly. I'm assuming this would improve the performance. They need a high voltage and are a capacitive load. Would a bridge circuit be suitable? Any ideas?

    Another issue is that the outputs need to be floating to avoid shocks. This could be a problem to arrange.
     
  2. Externet

    Externet

    732
    154
    Aug 24, 2009
    No place for 'bridges' here.
    Look in your junk box for a 230V to 3, 5, 6 V linear adapter and canibalize the transformer alone.
    Feed audio into the secondary and the earphone to the primary. If satisfactory, repeat for the other channel.

    [​IMG]
     
    spandrel likes this.
  3. spandrel

    spandrel

    7
    0
    Jul 3, 2018
    Good idea , though a 12v DC (~9AC) one would be nearer the correct ratio. It would need a thermistor as well to limit the current. I've got a 12v brick so I'll give it a go. Thanks. I'd still like to make an amp for them though. It's got to be better than a transformer.
     
  4. Externet

    Externet

    732
    154
    Aug 24, 2009
    An amplifier ? A transformer is a voltage amplifier. You do not need a power amplifier. That is already in your 'stereo' to feed the transformer. The transformer alone will nearly 'match' the impedance to your earphone needs.
     
  5. Hopup

    Hopup

    243
    32
    Jul 5, 2015
    spandrel likes this.
  6. spandrel

    spandrel

    7
    0
    Jul 3, 2018
    The up-market Stax electrostatics have amplifiers now, probably because it's better but also because it's now cheaper than transformers. This is from the blurb for the SRM-353X

    "The SRM-353X is the exclusive driver unit (amplifier) produced in order to drive STAX electrostatic type Earspeaker much more ideally. Carefully selected high-quality parts of an audio grade further improved the tone quality, and re-examination of circuit details realized much wider frequency response.
    Original low-noise dual FET at first stage as well as all-stage direct coupling class-A DC amplifier configuration with no coupling capacitor has realized natural tone quality with much amount of information.
    Further improved emitter follower at output stage has enabled wide-range reproduction resulting in both the extended dynamic range at high frequency and the improved tone quality."

    I know the transformers work but I fancied building an amp. Not sure about Class A DC-coupled though, could be tricky. I doubt the electret ones are worth the bother to be honest.
     
  7. Hopup

    Hopup

    243
    32
    Jul 5, 2015
    I would rather get good DAC if you lack one. I have some very transparent headphones and having good DAC is very important for the reproduction.
     
  8. Audioguru

    Audioguru

    2,744
    621
    Sep 24, 2016
    You do not want a mains transformer or an audio transformer in a good audio circuit. You also do not want a thermistor limiter.
    The head-fi.org thread has an acoustical frequency response curve that might have no bass due to poor coupling/sealing or a lousy mic. Some transformers cut bass and highs.
     
    spandrel likes this.
  9. spandrel

    spandrel

    7
    0
    Jul 3, 2018
  10. BobK

    BobK

    7,676
    1,685
    Jan 5, 2010
    Electrostatic drivers are capacitors.

    If the transformer was 25:1, the driving voltage is probably somewhere in the range of 100 to 400V. Do you have any specs for the headphones?

    Class A is okay because the currents involved will be very small.

    Bob
     
    spandrel likes this.
  11. spandrel

    spandrel

    7
    0
    Jul 3, 2018
    No spec for the electrets but the electrostatics are about 150pF and 150Kohm at 10KHz. I may be worrying too much about DC offsets but even more about having a few hundred volts near my ears referenced to earth. Optical input maybe?

    I'll play around with transformers for now and do some measuring.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-