[Kenwood] Matching transformer for mike

Fri Jul 10 14:45:24 EDT 2020

   That makes sense because the line output is at a much higher 
level. There should be specs fro this thing. Do you have an 
instruction book for it?  If not check BAMA.
   You should not need a transformer for it on either input or 
output sides.
   There is much confusion about microphone impedance partly 
because the conventional spec is for the microphone as a source 
impedance and partly because its not very consistent. The 
American system is to state the source impedance of the mic. The 
input to the amplifier being much higher. The British also give 
mic impedance as a source but assume the amplifier provides a 
termination. The BBC published a technical note justifying this 
method but it seems to be that it lowers signal to noise by 6db 
and is not a good method. For microphones with internal 
amplifiers, which includes all condenser and electret mics, the 
impedance is generally of little consequence. Level is important. 
High impedance mics generally put out more voltage. The use of a 
transformer in old equipment was primarily to increase the 
voltage at the amplifier input. I am not sure what the practice 
is now, much of the terminology was established in the vacuum 
tube era.

On 7/10/2020 3:54 AM, Steve H wrote:
> Thanks Rich, yes, its got a mike and line level option and 
> inside the compressor on the main board there is a switch that 
> changes the output
> from line or mike. I was told to put that into the mike 
> position, which I did, and it made a huge difference and 
> eliminated alot of humm
> and artifacts from the signal.
>
> This is the mike I am now using:
> https://www.newark.com/stellar-labs/cm-2250/studio-condenser-cardioid-microphone/dp/53Y1921 
>
>
> Since its designed around needing phantom power, and the 528E 
> can supply it, figured it was a good match. When I tried it 
> with just my headphones monitoring the output of the 
> compressor, it really did sound great.
>
> But no matter what I did last night with it set like that, 
> could not get a whole lot of modulation into the Kenwood where 
> it was an upgrade over the MC50 Kenwood mike. If I put the mike 
> gain on the Kenwood past 3, I get lots of distorting and 
> oscillations without even speaking into the mike. I can cut the 
> mike gain control or the main level out from the 528E down to 
> eliminate it, but at the cost of the percent modulation 
> decreasing way down so its nearly unreadable.
>
> So far the MC50 mike sounds way better than what I can get from 
> this setup and it seems like more mike gain would get me more % 
> modulation, however
> as I get it better and hit 3, it just distorts. If I put the 
> Kenwoods built in compressor on, I can get past 3 and 
> modulation will improve as I go up, but even with the mike gain 
> at max, the modulation % is just not very robust at all.
>
> Steve Hearns
> KA2PTE
>
> ----- Original Message ----- From: "Richard Knoppow" 
> <1oldlens1 at ix.netcom.com>
> To: <kenwood at mailman.qth.net>
> Sent: Thursday, July 09, 2020 11:18 PM
> Subject: Re: [Kenwood] Matching transformer for mike
>
>
>> Level are important. If the output level of the processor is 
>> high you need a resistive attenuator which will also serve to 
>> match the impedance.
>>  In general, American practice is to state microphone input 
>> impedance as the expected source impedance, usually there is 
>> no need to match impedances because the source is a voltage 
>> source not a power source. For instance, in historical 
>> broadcast equipment and sound equipment designed to work from 
>> low impedance microphones the the typical input impedance was 
>> on the order of 5K ohms or more while the source impedance was 
>> on the order of 150 ohms. For equipment that runs at line 
>> level the impedance is usually a terminating impedance, source 
>> impedance can be the same or sometimes not.
>>  See if the processor is meant to drive a microphone input or 
>> a line level input. If a line level input you need an 
>> attenuator to get the level down to mic level, maybe as much 
>> as thirty db. The exact impedance is not critical.
>>
>> On 7/9/2020 7:53 PM, Steve H wrote:
>>> I am trying to hook up a Symetrix 528E voice processor to my 
>>> Kenwood Hybrid 830S and was told that the mike input is about 
>>> 150 ohms
>>> to the rigg and the processors output is 600 ohms.
>>>
>>> Other hams I think use a matching transformer, I guess 4 to 
>>> 1? Anyone out there have any experience selecting a matching 
>>> xfmr for the Hybrids?
>>>
>>> Steve Hearns
>>> KA2PTE
>>>
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>>
>> -- 
>> Richard Knoppow
>> 1oldlens1 at ix.netcom.com
>> WB6KBL
>>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL