Speach = speech (or speach…).
Demo & schematic of a 2 transistor audio filter that has a “bandwidth” in the speech range, say between 800 Hertz and 4000 Hertz, made with an old casettedeck tape record head of (say) 30 DC Ohms.
Also more info about how to make electronic audio filters, effects of capacitors, basic things about high-cut, low-cut and the typical “audio” range filters.
The tape record head acts as a high quality (High Q) filter coil. Other coils with the same properties have the same effect.
Tweak with the value that is in series with that coil, test e.g. capacitors (non polar) between 10 N and 3.3 uF. Till you find (=hear from the loudspeaer) the audio spectrum that you need.
A capacitor from base to ground of the second BC 547 transistor of 100 N (50 N) can act as a high-cut filter. A higher value series-capacitor instead of the 56 N (C2) lets more low frequencies pass.
The effects are (probably) not so clear compared to what I heard in real (when I reviewed the video afterwards) but to hear the effects properly use a headphone.
Much more info in my book “Schematics 2, audio amplifiers and loudspeaker boxes”, you can find more info about that in this textbox.
Sorry for the somewhat “shaky” video.
Video NOT made for children.
All the videos hat I have published on You Tube can be found via my Channel Trailer: Link is
In thematic order you can find these video’s under the “comments” section.
Important: to find all the links to the (+/-700) video’s on my YT Channel, select, in the comments section, “NEWEST FIRST”
My books about electronics are available via the website from “Lulu”, search for author “Ko Tilman” there.
There is an important video via which you can buy a document where I give links to many of my video’s, published between 2010 and 2018.
Link is: https://youtu.be/XXRsA24NUE0
My books are also available via Barnes and Noble and via Amazon.
Regarding all my video’s: I constantly keep them actual, so the original video’s with the most recent information are always on YouTube. That is the source, and search there. When my video’s are reproduced or re-edited on other websites/channels you can not (!) be sure about the original content (=really working electronics with real properties for a purpose) and important adaptations to the circuits.
Be aware of that, I saw on the internet my circuits reproduced in a poor or not proper way.
I also found that people probably republish my circuits under phantasy names and/or with phantasy properties. Sometimes they want to find gold with them. I take distance from all these fake claims; I cannot help that it happens, sorry. Upload 2 february 2020.