Audio-Technica Lapel/Lavallier convert to +48V

[Migs 31]

Hey folks,
I got this AT831cT5 Lavallier/Lapel mic for a tenner.
I don't have any AT belt packs/systems & buying their "power module" at €100 just to get 5V Bias via Phantom power, looks big/expensive.

To put in an XLR connector + small circuit to drop the +48V to provide 5/9V Bias (pin 2 on TA5F) and Audio (pin 3 TA5F) into a mixer pre-amp, is it faisable?
If any of you has a clear idea/experience with this or a diagram, please share.

Thanks
M

 

[Migs 31]

Tomi Engdahl on epanorama.net has this to say:

"This circuit gives out balanced signals and has around 2 kohms output impedance which enables it to be used successfully with mic cables of several meters or tens of meters.The component "12V" is a 12 Volt zener diode
The 10u capacitors in the HOT and COLD signal leads should be high-quality plastic film types. The values of these may be reduced to 2u2 if the preamp input impedance is 10k or greater. If you for some reason use electrolytics for the capacitors which couple the audio signal then those these mutst have >50V working woltage and you must bypass them with 100n plastic film caps. The 10u capacitor in parallel with the zener should be a tantalum type, and can have a 10n plastic film cap in parallel if you wish.
The cable to the capsule should be twin+shield. The shield should be connected to ground near the zener diode, and left unconnected at the capsule. The pinout given is the standard for XLR3 mic connectors.
Source: PZM Modifications web page by Christopher Hicks."

Would this work on my AT mic?
(thought id' ask before tryin-frying)
See schematic below.

M

 

[Voyager10]

Yes, the schematic shown would work. There's no particular reason to worry about capacitor types, or bypassing them, in this application.

The output impedance is rather high, 4.4K not 2.2K, so you might get treble loss on long cables and a greater susceptibility to noise/interference.

Another option, if there's enough space, is to build an "Alice" style preamp. The original page is here: http://scotthelmke.com/alice-mic.html and the schematic is at http://scotthelmke.com/alice-schematic.jpg

The AT mic has a built-in FET so you don't need the 2N4416 or 1G resistor. Capsule '+' connects where the drain (D) was, and capsule '-' to the source (S).

This has a much lower output impedance (tens of ohms); so will drive longer cables much more easily.

 

[Migs 31]

Made s

Yes, the schematic shown would work. There's no particular reason to worry about capacitor types, or bypassing them, in this application.

The output impedance is rather high, 4.4K not 2.2K, so you might get treble loss on long cables and a greater susceptibility to noise/interference.

Made some progress on this.
I built a “plug-in” version of the circuit above, but got a faint hum and a bit of a dull sound. Tried a different circuit with different values & it’s much better.

Will test tomorrow.
AT 5 pin mini connectors are just a big bluff ( three pins would suffice).
M

 

[k brown]

My suggestion is to look on ebay for just about any AT boundary mic, choir/hanging mic, gooseneck mic; any that are mini electrets (they made countless models over the decades) that use an external power module, and just use the power module. Sometimes you can get just the power module alone (like the AT8533, or AT8531). All these little AT mics use/used the same 2SK660 FET, so nearly all the power modules are designed for it (only the really cheapy lavs don't, as they use just generic electrets with different built-in FETs).

https://www.ebay.com/itm/185937310341?epid=665041507&itmmeta=01HZBSJQ9YQFGWM2CVTK8WXNB4&hash=item2b4aba3285:g:SigAAOSws7dkhlhA&itmprp=enc:AQAJAAAAwGFyfMQCWBXEwvextiJ8rpyfRbRvkeJrBCQNCGE/E8V/OhPg+sKaYcIfZ0wDvsMX9S7yG1ILJfElOU2Pq42S2f1I/J3a0ZHRB0qMcWSgGk43mxk0Fmp6UjsSZzjxymqoK7U8xm7nSeXeUupnKilXcruwH2E78wFc3Mka1I7h/g7Y3Du1S3V+zzb5yibFmhoXxO8w/kEBOQtU0Fm6ob0ncxAAgUkIZapYiuPib+Ax9Da4sTtqlU9kvgq/fHYwIpnTlA==|tkp:Bk9SR471yvn6Yw

https://www.ebay.com/itm/155584179929?itmmeta=01HZBT9RX7P5BG9APWBHKDTNA4&hash=item24398a2ed9:g7wAAOSwa~5kd7fj&itmprp=enc:AQAJAAAAwC5wwVSKYXTfHPcdYf1/8NScWglWcgXyuyzbJQuonesZ2mAMYJt53EaUdZBTV58CDBbFjV4vtjFNWeP7vyQnZlUnBvIfVemPGOxInu27D/hZIR+ce6QMo4zglRa/hdIQSjFTEkGp/kdGnZJMGYJ49AXTW+OI+HebfbF/O2FdZ0ID0RwCZNi69SyW01M0vH0WSZgKRYZjq1S2YtToBXSjna12o5/neOT2+wcoHEWWIfxn20WblC0reBZuH/oaRBJK2A==|tkp:Bk9SR9iOp_r6Yw

These little AT modules are a complete solution to operate your lav with long cables and phantom power; some even have the option of running off a battery without phantom.

The biasing of the Engdahl circuit is nearly identical to a few commercial (not AT) mics that use the 2SK660, so should work fine if the high out-Z is not a concern.

 

[Migs 31]

(like the AT8533, or AT8531). All these little AT mics use/used the same 2SK660 FET, so nearly all the power modules are designed for it (only the really cheapy lavs don't, as they use just generic electrets with different built-in FETs).

The biasing of the Engdahl circuit is nearly identical to a few commercial (not AT) mics that use the 2SK660, so should work fine if the high out-Z is not a concern.

I am not familiar with the Engdahl circuit, but I will look it up.

Useful information about the 2SK660. That means all active AT modules will have a similar-ish design. Food for thought. So far, my passive plug-in solution works well with +48V.

M

 

[k brown]

I am not familiar with the Engdahl circuit, but I will look it up.

Useful information about the 2SK660. That means all active AT modules will have a similar-ish design. Food for thought. So far, my passive plug-in solution works well with +48V.

M

Sorry - I misspoke; it was the Christopher Hicks circuit posted above that I was referring to.

The AT modules I have seen the schems of vary quite a bit; what's relevent is that they are all designed for the 2SK660 (except for the really cheapy mics, like I said).

 

[Voyager10]

The only significant factors relating to the 2SK660 itself are the drain-source voltage and the load resistance. (We don't get to choose the Vgs bias voltage here, and the rest of the circuitry is buffering, power supply and frequency shaping). It's not possible to determine these from the schematics without component values.

For the AT8533 schematic as shown these are 0.6V and 1K, both of which are on the low side and will give lower sensitivity and lower maximum output than the other circuits.

 

[k brown]

The only significant factors relating to the 2SK660 itself are the drain-source voltage and the load resistance. (We don't get to choose the Vgs bias voltage here, and the rest of the circuitry is buffering, power supply and frequency shaping). It's not possible to determine these from the schematics without component values.

For the AT8533 schematic as shown these are 0.6V and 1K, both of which are on the low side and will give lower sensitivity and lower maximum output than the other circuits.

I only posted them to illustrate that the various AT power modules designed for the 2SK660 do not all have "similar-ish designs"..

 

[Migs 31]

I only posted them to illustrate that the various AT power modules designed for the 2SK660 do not all have "similar-ish designs"..

Ok
Gotcha. They are indeed different in their application. Some folks at AT spent some time perfecting their new products/designs instead of using the same old re-heated receipe. Kudos!

BTW, looking at my mic closet (more a drawer) I’m surprised how many Audio-Technica mics are seriously underrated when mic’ing bands, yet real Bad boys: The ATM25, AT 4041 and ATM 63 (original & Neodymium HE versions) & the Double Capsule Bass drum mic, shit can’t remember model (ageing man/memory blank). EDIT: AE 2500

So yeah R&D at AT... top notch
M