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Re: A hum while on charge

Subject: Re: A hum while on charge
From: Walter Knapp <>
Date: Sat, 08 Mar 2003 16:28:26 -0500
jyoung1113 wrote:

> Thank you Walt for your quick response.
> Yes the hum comes when I use the Portadisc ac/dc plug in or using the 
> Portadisc using the "mains".
> When I unplug teh Portadisc all is fine, but plug it in and I get this 
> hum.
>   I tried different mics and they don't give me this problem, just the 
> DAT-stereo
>   You sure are right about the mic being sensitive and strong though,
> I have never experienced anything like it.
>   Well I guess I should have the Portadisc looked at, I just hate to 
> go with out it for 2 weeks.
> Thanks again Walt,

I absolutely never use the Telinga with the Portadisc plugged into AC, 
that would take one long extension cord! Based on Klas' comment I went 
and checked. Yes, if the Portadisc is plugged into AC and the Telinga 
connected I get a hum, which goes away when I unplug the power for the 
Portadisc. I've been using the two together for several years, and this 
is the first time I've had occasion to do this.

I've tested other mics while the Portadisc was plugged in without that 
happening, so Klas is probably right, the Telinga is not shielded enough 
for AC operation.

I don't consider it a problem. And no reason to have the Portadisc in 
the shop.

It's not the cable between the Telinga and Portadisc. I've replaced that 
cable and am using a 5 pin XLR connector and Canare star quad cable. So, 
it's all balanced cabling as far as the Telinga handle. There is no 
connection between signal minus and shield in mine. The circuit in the 
handle is not shielded in any case. Note that this also means if I 
forget and leave phantom power on there is no problem. Shuffling mics 
for the samples I've already done that.

Only time I've had hum pickup out in the field was under some high 
tension lines, and I could practically feel my hair standing on end 
then. That was only a fairly faint hum. And was back when I was using a 
Sony MZ-R30.

Walt






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