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Gain

I have two SM transmitters that I bought two months apart and they seem to have different gains. Why does the newer one have 10 dB more gain?

On the side of the newer units, on the blue metal strip, you should see a +10 dB marking indicating…

On the side of the newer units, on the blue metal strip, you should see a +10 dB marking indicating that these units have an increased gain compared to your older units. Here's what we said on RAMPS (What is RAMPS). Though a little long it explains our rational to making the change and what some users were seeing as far as typical gain settings on the SM transmitter. We didn't make this change lightly because we knew it would cause some confusion. Below is the slightly edited version of the RAMPS thread. The actual thread is at Link to RAMPS thread. We kept the display at 0 to 44 due to memory limitations.



Larry Fisher Sep 6 2006
To the Group: 
After some 6 months or so of field experience with the SM transmitter, we are strongly considering increasing the overall gain of the SM and SM series transmitters by 10 dB. This would increase all input configurations including line level input. The display would now show 10 to 54 dB of gain rather than the current 0 to 44 dB. The same displayed numbers for gain would represent the same gain on either version, i.e., a setting of 30 dB would be the same on either version. Equivalent input noise, response, limiting and so forth would not change. 

From what I've read on RAMPS and various emails, indicates we are a little light on gain. Also, I think some users don't like running the gain at maximum levels even if that is the best setting in a given case. Any and all feedback from the real world would be appreciated. Best Regards, 
Larry Fisher 
Lectrosonics



Scott Farr Sep 6 2006, 9:27 am 
I run my SM transmitters at 38 on the gain setting never any higher and I am using TRAM TR50's 
Scott



Larry Fisher Sep 6 2006, 10:13 am 
Thanks Scott, 
You are within 6 dB of full current gain (44). You would still set the transmitter to 38. What is the lowest you remember setting the transmitter? 
LarryF 
Lectro



Scott Farr Sep 6 2006, 11:10 am 
I think around 32



wyatt Sep 6 2006, 12:05 pm 
I am using 8 SM transmitters on my current production. I am using an assortment of lavs, and my gain settings varry accordingly. The lowest gain I have used to date would be 24 using a cos-11, outdoor scene, times square. the highest would be 44, indoors, using either a b6 (grey band) or a TR-50 (i dont quite recall which at the moment). My normal operating gain for a cos-11 has been between 29 and 31. I think a gain increase would a beneficial improvement, especially considering that you can get most of the lavs that we, as soud mixers, employ daily with attenuated output levels. I have yet go below 24db on my transmitter gain.
Wyatt Tuzo



Larry Fisher Sep 6 2006, 2:29 pm 
Thanks Wyatt, 
More good info. 
LarryF 
Lectro



Scott Smiith Sep 6 2006, 8:20 pm 
Larry, 
This is something I have noticed as well (although the output of the mike used definitely plays into the equation). I would say at least 6 db would be helpful, and there is certainly nothing wrong with 10 db, as long as it doesn't risk overloading the front end preamp. Scott D. Smith C.A.S.



Larry Fisher Sep 7 2006, 12:13 pm 
Hi Scott, 
When the gain is set to minimum, even with the additional gain, the SM will still require 250 uA of peak current from the mic before the limiter even begins to engage. This would require a lavaliere that pulled 500uA of bias. This is higher than any pro mics we have measured. Another way of saying this is that at minimum gain, any known lavalliere will run out of bias (clip) before the limiter starts to limit let alone overdrive the preamp. Further, even at minimum gain there is still more than 30 dB of limiting before the limiter gives up and allows the preamp to overload. As I said earlier, I think we were being way too conservative on gain. Field experience seems to be bearing this out. 
Best Regards, 
LarryF 
Lectro



LaFayette Sep 8 2006, 3:20 am 
Greetings Larry,
Would this be an upgrade mod on existing units or only for new versions? 

I've set mine from 30 w/ Sankens outdoors to 38 w/ Sonotrims indoors. It has been suggested to go w/ red dot Sankens since the regular ones tend to be hot w/ SM's. Although, I also hear that the Sankens wired specifically for the SM sound better anyway, more low end. Should I save my money on new Sankens and just buy the upgrade on the SM? Cheers, S.L.


Larry Fisher Sep 8 2006, 4:42 am 
Hi, 
There is no downside to running the current SM at maximum gain or close to it. Performance of the current units at 44dB gain (wide open) will be exactly the same as the new units at 44 dB gain (10 dB left). So if you have sufficient gain now to handle the mics you have, then it is not necessary to change the units. This is not a necessary "upgrade" and won't be automatically done to units in for other repairs unless the customer requests it, unlike mandatory upgrades that we always make to repairs. Mandatory upgrades are due to a mistake we made and are done at no charge. 

Older units can be changed to the new gain structure and corresponding firmware. There will be a $70 charge to open, test and reseal the unit. This is the same as for the RM addition mentioned earlier on RAMPS. On the other hand, you can get both done at once for the same charge. Depending on the age of the SM you may also pickup a new emulation also.There is no charge for the firmware and new value resistor themselves; just the work involved in opening, closing, sealing and testing the unit. If we are already inside a unit for other reasons, there will be no additional charge for the gain change. As I said above, the customer must request the change since if they are happy with the current gain structure, we are very satisfied to leave it alone. 
Best Regards, 
LarryF 
Lectro



morantzsound (Steve Morantz, C.A.S.) Sep 9 2006, 11:35 pm 
I was told when I bought my SM's anywhere form 24 to 30 was average. I usually stay around 27 or 28 and make adjustments at the board or Deva. It has worked pretty well for me, but will start experimenting with higher outputs. 
Steve Morantz C.A.S.

Posted 5 months agoby LectroAdmin

My UM200B and UM200C transmitters seem to require very different gain settings for the same audio performance. What's going on here?

The previous limit LED indicator on the UM200B was wrong (misleading) and led to many users setting the transmitter gain…

The previous limit LED indicator on the UM200B was wrong (misleading) and led to many users setting the transmitter gain wrong (too low). After 5 years of confused users calling the sales crew, the service troops and yours truly, I decided to change The Damned Thing. The reason I think it was the right thing to do, is that the number of calls about level problems has declined dramatically. 

I didn't do the change casually for the very reason some users have brought up; mixing B's and C's is confusing. If you set the LED's the same, the modulation of the UM200C will be about 10 dB (!) hotter than the B. 

We told users in the UM200B manual to set the limit LED so it was on 10% of the time. The users didn't want to do that since the red LED was worrying them so they were setting it for no limit LED or occasional flashing. The new recommendation on the UM200C is for occasional flashing which is the way most users wanted to set it.

Here's what can be done:
Just use the receiver monitoring. The receiver metering has not changed and the basic audio in the transmitter didn't change either, just the transmitter readout. If you use the metering on the receivers, then the B or C transmitters will be set the same. Also, just remember to set the B's for more LED flashing than the C's.

(See FAQ What are the differences between the UM200B and UM200C transmitters?)

Posted 5 months agoby LectroAdmin

What can I do to prevent audio overload of a transmitter? If I turn the gain down enough to prevent overload, the gain isn't high enough to prevent hiss and noise.

This reply was posted to this question on the RAMPS group: Most wireless systems, even some "pro" systems do not…

This reply was posted to this question on the RAMPS group:

Most wireless systems, even some "pro" systems do not have a limiter-compressor in the transmitter. This forces you to do exactly what you are describing, which is to attenuate the mic input to prevent the occasional overload. All the Lectro transmitters for the last 15 years have a shunt FET limiter before the input preamp. The nice thing about the shunt limiter is that it is out of the audio circuit until a potential overload comes along, then the excess signal is shunted away. The limiter has a range of 25 to 30 dB. At usual gain settings, the transmitter won't overload until after the typical electret lavaliere microphone is already clipping.  

Interestingly, the Vega microphones from years ago had a very effective limiter using an LED/LDR (Light Dependent Resistor). Vega referred to it as a "soft compressor" and it was. Though it wasn't effective when the transmitter gain was set low, for real world use, it was very nice sounding and, in my opinion, one reason Vega was the number one pro wireless. More interestingly is the fact that most current wireless mics have taken a giant step backwards by leaving limiter-compressors out of the bag of design tricks. Check the specs on the data sheets to see if there is an input limiter-compressor. Chances are there isn't one. The COMPANDER used in all current wireless mic systems has nothing to do with the input limiter by the way. The input limiter is in addition to the compander and additionally increases the usable dynamic range.

Posted 5 months agoby LectroAdmin