Tape recorder electronics: how to make it pt 5: final overview

Series of video’s about how to make a tape recorder yourself, with electronic schematics. More info in my book: “Schematics 2, audio amplifiers and loudspeaker boxes” available on the Lulu website. ISBN 978-1-4475-733-4. Upload 22 nov 2017.

Part 1: introduction and basics about how to record information (e.g. audio) on a magnetic tape. It shows that you need a pre-amplifier connected to the low impedant pickup (record-playback) tape head (DC 500 Ohms). PLAYBACK MODE = the pre-amplifier (detailed dscription in part 4) amplifies that (tiny) audio signal to a certain level (here 0,2 V), this signal is sent into a normal audio amplifier (20 Hz-20 KHz) from 3 Watt to a loudspeaker. RECORD MODE = to the output from that same 3 Watt (or so) audio amplifier the record/playback head (DC resistance say 500 Ohms) is connected. While recording the erase head is active too. This has 2 functions: this erase head erases the magnetic tape before it reaches the record/playback head and it delivers (at the same time) a sine wave from say 23 or 30 KHz that is sent into the record/playback head. This “bias” frequency from 23 or 30 KHz is mixed into the record head with the help of a potmeter, here 10 K. That potmeter aligns the balance between the levels from the bias oscillator and the end-amplifier that sends its audio signal into the record head. More info in the video.

Part 2: detailed description from the bias oscillator, consisting of a sine wave oscillator on a frequency between 23 KHz and 30 KHz. That sine wave signal is amplified with the help of a 3 Watt audio amplifier and sent (via a series capacitor) into the erase head from (say) 5 DC Ohms. The erase head must be tuned to its resonance (!!) on the bias frequency with the help of 2 capacitors: the series capacitor to the head + the parallel capacitor connected over the electrodes from the head. Fine tuning to a good “peak” (connect your scope over the head electrodes) goes via the potmeter inside the bias oscillator and experimenting with the values from the mentioned capacitors. More info in the video.

Part 3: how to eliminate all kinds of disturbances on the power supply line, caused by the electromotors on (in my case) 6 Volt DC. They can give enormous noise into the power supply line that disturbs the (very sensitive) electro magnetic audio amplifiers. Reason: the noise from these small DC motors is also electromagnetic. But with the showed schematics you can get your small electromotors completely “silent” and you will not hear them run when you are recording a piece of music. They are electromagnetically “isolated” from the power lead. More info in the video.

Part 4: schematic from a properly working pre-amplifier for a tape head (playback) from (say) 500 Ohms DC resistance. The picked up signals from the electromagnetic tapes are tiny and also in an environment that is electromagnetic noisy. So you need shielded wiring to the playback/record head. Also shielded wiring tot the erase head. Important: the capacitance from the wiring tot he erase head plays a role during tuning the erase head to its “peak” frequency. (nb: it is a tank circuit).

Part 5: final overview from all the circuits.
All links:

VIDEO 1: basics rec/play amps & bias

VIDEO 2: bias oscillator

VIDEO 3: noise cancelling from DC motors

VIDEO 4: pre-amp for a rec/playback tape head

VIDEO 5: final overview

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. My books about electronics are available via the website from “Lulu”, search for author “Ko Tilman” there.
Link is https://www.lulu.com/shop/search.ep?keyWords=ko+tilman&type=
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) and important adaptations to the circuits.
Be aware of that, I saw on the internet many of my circuits reproduced in a poor or even not proper way. I can not help that, sorry.