3.5mm 4-pole Extension cables

o.w.varley

Well-known member
Hello all,

I've got an odd issue with some 4-pole 3.5mm audio extension cables that I'm using with the Teensy 4.1 and audio shield. I've got three different branded cables and a sketch that links an I2C input (mic) to a set of headphones. With one of the cables it works fine and you can hear yourself perfectly, however, with the other two cables the audio is distorted and there's a lot of background squeeling. Other than the obvious potential quality issues, could the distortion and squeeling be reduced or removed by manipulating settings on the sglt5000?

I'm going to spend the afternoon playing with some settings but was wondering whether anyone had experienced this before and might be able to put me out of my misery.

Kind regards,

Owen
 
You probably have some CTIA<->OMTP adapter cables then, which are have different pinouts at the two ends.

I'd stick to TRS (3-pole) 3.5 lead for standard audio (as opposed to computer/phone headset use). There are several
unofficial standards for TRRS (4-pole) 3.5mm and they are not all compatible. CTIA may work with the audio adapter
socket from what I can see of the contact positioning on my rev D audio adapter, but for standard audio connections
a TRS cable is used.

https://www.reddit.com/r/audio/comments/bhhr3d/question_about_trrs_connector/
 
Thanks MarkT,

I did some further investigation and actually the squeal is determined by the volume level. I've got a potentiometer that will adjust the SGLT volume between 0.0 and 0.85. With the dodgy 3.5mm cables, a single cable will squeal above 0.8, two daisy chained cables is about 0.7 (roughly) and three is about 0.65. There's a background buzz in addition to the hum that goes away when you touch the connector.

I'm going to do some more accurate measurement of the volume versus distance and see if I can figure out the exact correlation better than "more length = more squeal at high volumes.

The extension cable that works with no squeal at 0.85 is a high quality one that's double insulated and has large gold connectors which no doubt has something to do with the reason why the audio quality is better...
 
Hey Mark,

I've done some reading up on TRS cables and the short answer is, I'm not sure whether that's what I'm using.

The cables I've got are:
1) https://www.amazon.co.uk/KabelDirek...3fcb1c4d9d4&pd_rd_wg=JkLSJ&pd_rd_i=B00SWYTLTM

2) https://www.amazon.co.uk/gp/aw/d/B07S6MJ1WC?psc=1&ref=ppx_pop_mob_b_asin_title

3) https://www.kenable.co.uk/en/audio-...rubber-lead-gold-2m-008444-5055383484447.html

Cable 1 is what is working best at the moment, cable 2 and 3 are causing squeal and a background hum. From reading their specs only one of them (2) mentions TRRS.

I've been going down the route of four pole as I need stereo audio plus the mic in a single jack.

Kind regards,

Owen
 
The audio shield socket does not have microphone connection, and is definitely intended for a TRS cable. If you need a microphone connection
you'll need a splitter.

Thinking about the SGTL5000 headphone output some more, I suspect its not designed for a highly capacitive cable, in particular
the virtual ground output(*) may be susceptible to this as its basically an opamp output straight into a low impedance load (normally
avoided).

So the problem may simply be that the SGTL5000 headphone output is not intended to drive a long extended cable.

Perhaps the way to go is carry the audio signal as a line-level signal along an extension cable to a headphone amp near the destination.

(*) the common "ground" line for the headphone output is not actual ground, but held at a DC level actively by the SGTL5000.
This done to avoid needing large value DC-blocking capacitors in the headphone output, as this chip is intended for small audio
devices (hence the assumption of a short headphone cable).
 
(*) the common "ground" line for the headphone output is not actual ground, but held at a DC level actively by the SGTL5000.
This done to avoid needing large value DC-blocking capacitors in the headphone output, as this chip is intended for small audio
devices (hence the assumption of a short headphone cable).

Hey Mark, sorry to re-open this, but I was wondering if you might be able to help me. I'm currently having issues with getting audio from the audio shield (outputs fine through the jack) across to a sparkfun breakout board from where it is going into an old telephone (https://www.youtube.com/watch?v=dI6ielrP1SE&lc=UgxCDFtArey5Ej38ha54AaABAg.9cWGX7lc_6j9d6AocAtrev - building this project).

When I connected it all up, it worked fine. Today, just buzzing. I'm wondering if it is something to do with the 3.5mm cable I'm using, though I have tried another cable without any success. I'm an amateur, but from research I've used a multimeter to beep test all the cables and contact points, and checked the voltage which sits around 1.5v. I know the audio shield is outputting because I can plug ear buds into it and hear it fine, and as I said, this all worked the first time I connected it up. I'm just using the tip and sleeve of the breakout board, and I've soldered the cables directly on to it in an effort to make sure the connection is good. Any tips would be greatly appreciated.
 
Hello all,

I've got an odd issue with some 4-pole 3.5mm audio extension cables that I'm using with the Teensy 4.1 and audio shield. I've got three different branded cables and a sketch that links an I2C input (mic) to a set of headphones. With one of the cables it works fine and you can hear yourself perfectly, however, with the other two cables the audio is distorted and there's a lot of background squeeling. Other than the obvious potential quality issues, could the distortion and squeeling be reduced or removed by manipulating settings on the sglt5000?

I'm going to spend the afternoon playing with some settings but was wondering whether anyone had experienced this before and might be able to put me out of my misery.

Kind regards Toca Boca,

Owen
Hi, I am purchasing an extension cable 6 inches long for my earphones. Alot of extension cables are using 3.5mm 4 pole male. I think my current earphones have 2 poles. Will the 4 pole extension work fine? I just want to make sure I won't lose any sound quality or anything. Thanks.
 
Hi, I am purchasing an extension cable 6 inches long for my earphones. Alot of extension cables are using 3.5mm 4 pole male. I think my current earphones have 2 poles. Will the 4 pole extension work fine? I just want to make sure I won't lose any sound quality or anything. Thanks.
You would want to get a 3 pole extension cord, not a 4 pole extension cord. What you want to do is search for "TRS 3.5mm extension cord". If you can only get 4 pole extension cords, I would imagine you want to get a converter plug.

  • TS, TRS, and TRRS explanation
  • TS is 2 pole, typically mono output
  • TRS is 3 pole, typically stereo output (for example desktop computers have 2 TRS plugs, one for output and one for input)
  • TRRS is 4 pole, typically stereo output and mono input (for example laptop computers and phones typically have a 1 TRRS plug to combine output and input).
 
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