Traynor TVM10 amp

Hi folks! I have been investigating this static POP noise problem for a while now, including talking to the sound shop I bought the amp from and consulting with the manufacturer of the amp.

I am using an Astatic 611 dymamic PTT mic designed for paging/cb systems with an XLR male plug into the female XLR on the Traynor TVM10 amp (left side of diagram). There are only two wires from the mic and one ground connected to the XLR.

Always on the first keying of the mic, there is a very loud static-like POP from the amp. This POP noise reduces significantly with each successive keying of the mic, until the POP sound is at a more normal level - a slight click sound - that you would expect to hear when keying a PTT mic. If the mic sits idle for a few minutes, the dreaded loud POP returns and fades out as mentioned above.

On the advice of the manufacturer, I have tried many different grounding combinations on the XLR male end on the PTT mic with no effect on the POP noise.

It really seems like there is a static build up that dissipates thru the PTT switch when it closes - but where is the static coming from and how to ground it out? A standard dynamic singing/speech mic with an ON/OFF switch does not make this static POP noise at all when plugged into the amp and turned ON.

The amp is portable and powered by an internal 12V/7.2A rechargeable battery. The charger is removed from the battery charging port before using the amp.

  • \$\begingroup\$ Can you post a schematic of the mic's innards? We'll need to know how the PTT is wired to the mic to crack this... \$\endgroup\$ – ThreePhaseEel Jan 17 '16 at 16:14
  • \$\begingroup\$ I take it the POP appears when you press the PTT button; what happens on release? \$\endgroup\$ – CharlieHanson Jan 17 '16 at 17:54
  • \$\begingroup\$ reply to queries...the PTT switch is a very basic slider type switch with a spring inside to return the switch to the OPEN position when the PTT lever is released. Simple wiring: xlr pin3 black to mic, white from mic to switch/white back to xlr pin2. Green from switch case to xlr ground. POP only heard on closing (pressing PTT lever) of switch, not opening (releasing of PTT lever). \$\endgroup\$ – Aaron Jan 17 '16 at 20:42
  • \$\begingroup\$ Is the shell of the XLR connector on the amp connected to anything? Also, is "XLR ground" the shell of the mic's XLR connector, or pin 1 on that connector? \$\endgroup\$ – ThreePhaseEel Jan 17 '16 at 22:22
  • \$\begingroup\$ Guys! I figured it out!! I searched for schematics of simple dynamic mics with ON/OFF switches and they all show the ON/OFF switch in PARALLEL to the mic capsule. So I gave it a try and almost fell off my chair!!! The PTT does not make even the slightest snap, crackle, let alone POP! Just 100% clean, crisp voice coming out of the amp! WOO-HOO! I was chasing this thing for 3 WEEKS! Question: Why/how does this switch work in parallel? \$\endgroup\$ – Aaron Jan 17 '16 at 22:44

The reason why a series switch causes a POP to happen when the PTT is depressed but a shunt switch does not has to do with the DC behavor of a dynamic microphone, combined with charge buildup on the input AC coupling capacitors of the microphone stage.

There is a non-zero current flowing at each input to the microphone amplifier -- this is an input bias current, and is present in all stages that use solid-state inputs. To prevent this bias current from flowing through the mic, and to prevent phantom power from driving the inputs outside the input stage common mode voltage range when dealing with phantom powered condenser microphones, just about all microphone amplifier stages have front-end AC coupling/DC block capacitors. These capacitors charge up to a significant voltage when an open circuit to DC is present (such as a condenser mic, a dynamic mic with a series PTT switch in the open position, or merely nothing at all).

However, dynamic mics, unlike their condenser counterparts, have a very low DC resistance (just the coil of wire). This means that when the PTT switch on your offending microphone is closed, the capacitors can now discharge, forming a transient that creates the POP you are hearing -- the decrease in loudness as you keep using the PTT switch is because the capacitors aren't fully charging before being discharged again.

The reason microphones with a shunt PTT avoid this is because that shunt PTT switch shorts the microphone out when in the OFF position, keeping the capacitors from charging up to begin with.

  • \$\begingroup\$ thanks for this very detailed description! I am just starting to learn about electronics, as a hobby. I am always amazed when I open up an electronic device and all those little components are staring back at me. What are they all for and what do they all do, and who creates this stuff? So complex! It seems strange from my limited knowledge point of view just how many capacitors and resistors are used. It seems that they make up 90% of any electronic device! \$\endgroup\$ – Aaron Jan 17 '16 at 23:16

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