STC 4021 (Apple & Biscuit) 1935-1960s One of my all time favourite mics!

Through my Focusrite Twintrack the STC4021 sounds absolutely gorgeous on acoustic guitar, cello,and flute. Due to its spherical shape and the properties of its ‘Romanow’ screen, the frequency response is extremely uniform from any angle (.Tech Spec STC4021 )  As a drum ambient mic (up in the air over the drummer’s right shoulder) it gives a big punchy sound with loads of bottom end weight and smooth silky cymbals.. Not what you would expect from a mic designed in 1935!
Certainly begs the question ‘Has microphone design improved much in the last 75years?’ !!!!!


A number of people have asked me about the wiring of this mic. Pin 1 is hot (ie pin 2 on an XLR)  G is  earth (pin 1 on an XLR) and pin 2 is cold (pin 3 on an an XLR)

Also, How does the ‘Biscuit’ work?

In order to understand how the ‘Romanow’ screen on this microphone helps to create the truly omnidirectional response of the 4021 here below is the 1935 patent describing its function.

Romanow Screen Patent 1935


And now……. My very first YouTube video which just happens to be about this mic!



14 responses to “STC 4021 (Apple & Biscuit) 1935-1960s One of my all time favourite mics!

  1. Pingback: Vitavox Admiralty Pattern No1359 (1944 D-Day) | Martin Mitchell's Microphones

  2. The apple and biscuit was also known within the BBC as a “thistle” in fact the numerous cables terminating in the 3 pin STC connector were known as “thistle cables” even though they were more commonly used for 4037s 4033s and 4038s. I have not seen any reference to this on the ‘net.


    • Thanks for this comment John. Since posting my piece on the 4021 three years ago several retired BBC staff have mentioned this. It seems that the ‘thistle’ nickname was widely used, as was ‘thistle cable’ for the leads. I wondered if the different names were used in different BBC regions?
      Sometime soon I will produce another post including the 4021 and will make a point of mentioning this.


  3. Pingback: How to get that Vintage Mono Sound. A 1930’s Microphone Shoot-out! | Martin Mitchell's Microphones

  4. I have one of these gems in my studio, and have used it to great effect “taming” cranky Marshal and Peavey amps when the metal-heads come to record. Thanks for your insights, I will do a semi-permanent mount by the drums for room recording during rehearsal. Been thinking a while about how to best grab the room without always having my Neumanns installed.

    Liked by 1 person

  5. Congratulations on your video Martin and the update to the 4021 information. There seems to be more to this baffling business than I first thought. I have 2 4021s that have considerable differences to the standard 4001B disc, here are some pictures:


    Leevers-Rich were known in the BBC as tape recorder manufacturers, but I didn’t know they dealt with microphones. Their baffle is bigger than standard and sits on a gasket in contact with the 4021. The other 4021 has a thick baffle with a piece of cloth sandwiched between 2 gauzes and has spacers to lift it away from the front of the mic. The final picture is not strictly a baffle, it is the mounting arrangement for the 4021s in Alan Blumlein’s WW2 ‘acoustic radar’. One day I’ll try and measure the characteristics of these mics to see what the baffles actually do.

    Liked by 1 person

  6. Thanks for this John. Fascinating stuff. It would be really interesting to know exactly what these other baffles do. Please let us know 🙂


  7. Hi Martin,
    Do you have any information about the STC 4034, a vintage Apple and Biscuit microphone for acoustics laboratories? I have three of these microphones, and I would very much like more details on them than I’ve managed to find so far. I’ve put together a blog entry with what I presently know, complete with photographs. You can find it at –

    Any information would be of great help, they are part of my late father’s microphone collection. He was an electro-acoustics engineer.

    Kind regards,
    Roger Curry


    • Hi Roger,
      Interesting stuff! Up until now I had never heard of the STC4034. It would appear that this is a very specialised model for use with telephone test equipment. The information on your blog is all I can find. The production of microphones was a very small element of STCs business. Most of their work was concerned with the production and development of telephones, telephone exchanges and long distance cables. (including right across Russia)
      Their modern successors Coles (who bought out the microphone business) do have some archive information about vintage STC microphones. It may be worth contacting them. Meanwhile good luck with your sale.
      All the Best


  8. Cheers Martin,
    I’ll try Coles. Thanks so much for your time and interest.


  9. Pingback: The STC4001B Acoustic Baffle for the STC4021 (Apple & Biscuit) circa 1935. | Martin Mitchell's Microphones

  10. Pingback: 1962 BBC Training Manual | Martin Mitchell's Microphones

  11. Pingback: STC4032-D Outside Broadcast Microphone Ex BBC Circa 1955 | Martin Mitchell's Microphones

  12. Pingback: STC 4035 Omnidirectional Dynamic (Circa 1953) | Martin Mitchell's Microphones

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