[TenTec] Yamaha CM500 headset and Orion II

[Bob McGraw - K4TAX]

In most cases, the MIC Gain is usually located electrically after one to two 
analog stages of amplification.   Should the first or second analog stage be 
driven into clipping or distortion, adjustment of the MIC Gain, being after 
the first stage, will have no effect on any clipping or distortion occurring 
in the first stage.

Typical mike input circuits are designed for low noise and high gain with 
acceptable input signal levels between -70 dBv and -30 dBv.  If the mike of 
choice is one that has a high output level, and used with a radio lacking an 
input gain control, the first or second stage can be overdriven.  For a 
radio lacking an input level control, not to be confused with the MIC Gain 
control,  but that is one which is pre the first stage, then some value of 
attenuation must be employed to prevent overdrive of the first stage.

We may be talking semantics with regard to terminology.  The mike preamp 
gain is clearly a separate control from the front panel MIC Gain function. 
In the Omni VII, the hardware gain or preamp gain is under the bottom, left 
front of the radio.  The Eagle and the Argonaut VI hardware gain controls 
are on the side and accessed through a small hole.  In general, most Tentec 
radios come from the factory with the hardware gain set for maximum gain. 
This is to accommodate lower output level mikes such as the 707.   For 
higher output mikes, in many to most cases, adjustment to reduce the 
hardware gain is required of the user.   This depends largely on the type 
mike and the mike technique employed by the user.

As a general guideline, I suggest a MIC Gain value to be operated in the 35% 
to 50% range.  If yours is operating 30% or lower, I urge you to reduce the 
hardware mike gain such as to allow normal ALC LED actions with a higher 
value of DSP or MIC Gain value.

73
Bob, K4TAX






----- Original Message ----- 
From: "Jim Brown" <k9yc at audiosystemsgroup.com>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Monday, December 16, 2013 11:49 AM
Subject: Re: [TenTec] Yamaha CM500 headset and Orion II


> On 12/16/2013 5:46 AM, Richards wrote:
>> I chance to disagree with just this one minor point ... and offer my Omni 
>> VII and Orion II as an example.   On the Omni VII one has to turn the 
>> AF-GAIN down to nearly 1 or maybe 2 before it does not cause the ALC 
>> light to come on all the time.   Similarly on a pair of Orion IIs - one 
>> mine and another in a contest shack - although it was not as drastic on 
>> that rig as it is on the Omni VII.
>
> Something does not compute. The function of the AF-GAIN pot is to adjust 
> the mic output level to the rig. The numerical setting (dial setting) does 
> not matter. What matters is the audio drive level that AF-GAIN produces at 
> the output of the audio stage.
>
>>
>> Still,  I venture to recommend a voltage divider or simple L or T pad to 
>> reduce the inherently high output which cuts it down to approximately 
>> what the rig sees from a typical dynamic mic cartridge.  This gives the 
>> ALC more headroom to do its magic.   I believe crowding it down to very 
>> low AF-GAIN kinda crowds the ALC so that it can be difficult to 
>> set -i.e., it is either all on or all off,  and on my Omni VII, the mice 
>> is either on or off by the 2% setting and ALC is on all the time at that 
>> setting.
>
> Nope. ALC action occurs AFTER the audio gain stage that is being adjusted 
> by the AF-GAIN control . The only indication that an attenuator (pad) was 
> needed would be audible distortion on the transmitted signal, which would 
> be the result of the audio stage being overloaded by the mic (and clipping 
> at the input). That is VERY unlikely unless the Ten Tec engineers are a 
> LOT dumber than I think they are.
>
>>
>> Thus, it is my opinion, an attenuator pad is a good idea, and makes the 
>> mic appear to the rig more like a dynamic mic (which I believe it is 
>> designed to expect most often.)
>
> Lessee -- I'm an EE by training and profession, and you're a retired 
> attorney. Last I heard, you hadn't done extensive study of electronics to 
> catch up. I wouldn't consider give legal advice -- heck, even though I 
> know a helluva lot about acoustics, I'm not trained in that field and know 
> my limitations, so I don't give advice on acoustics either.
>
> 73, Jim K9YC
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>