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Constantin

DPA with C amp and Lectro HM

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Hello, 

 

I‘m curious: who here has successfully paired a 4017C with a Lectrosonics HM or HMa transmitter? 
I know there‘ve been various discussions about this in the past, and I thought that DPA had solved, but just today I tried my third, brand new, C preamp and it’s still terribly noisy. Not as bad as it once was, but clearly too noisy. And it’s not just hiss, there is a lot of lower freq noise. 
?

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I don't have one Constantin to try, but a thought.  What happens if you add a length of XLR cable between the C preamp and the HM transmitter.

I realize you wouldn't be using it with a cable, but curious if there is an RF issue.  Also if you have a cable with a Neutrik EMC connector on the mic end try that.

David

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I thought it was to do with the current draw from the DPA the HMa couldnt handle the current draw from DPA.... edit looking at specs  i think i remembered wrongly..

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2 hours ago, r.paterson said:

I thought it was to do with the current draw from the DPA the HMa couldnt handle the current draw from DPA.... edit looking at specs  i think i remembered wrongly..

The original H and UH plug-ons from dinosaur days to the present day were setup with a non-DIN input powering circuit so that the plug-ons could deliver higher than DIN levels of current to some of the popular mics back then . The current plug-ons can deliver 2 to 4 times the usual current of the 48 Volt DIN spec.

Best Regards,

Larry Fisher

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11 hours ago, LarryF said:

The original H and UH plug-ons from dinosaur days to the present day were setup with a non-DIN input powering circuit so that the plug-ons could deliver higher than DIN levels of current to some of the popular mics back then . The current plug-ons can deliver 2 to 4 times the usual current of the 48 Volt DIN spec.

Best Regards,

Larry Fisher


If I remember correctly, the issue may have been with the tx only supplying 45V. I don’t know why that causes an issue, as most mics are capable of running on even 12V. 
But I also stopped using Schoeps CMC641 mics, because they sound a bit anaemic through the HM. That may be due to other reasons, though. 
I was told though that DPA had fixed this on their end and the noise now is different from what it was before, but it’s still unbearable. 

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Hi Constantin,

The UH series does indeed only start out at 42 Volts but the series resistance to the mike is only 1k versus the 3.4k (two 6.8k resistors) of the DIN standard. In actual operation, the UH series can provide more voltage at the mic, particularly for high current mics.

Best Regards,

Larry Fisher

 

 

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28 minutes ago, LarryF said:

Hi Constantin,

The UH series does indeed only start out at 42 Volts but the series resistance to the mike is only 1k versus the 3.4k (two 6.8k resistors) of the DIN standard. In actual operation, the UH series can provide more voltage at the mic, particularly for high current mics.

Best Regards,

Larry Fisher

 

 


Thanks, Larry. I actually meant the HM and HMa transmitters. Do those provide the full 48V? 
 

I just tried the transmitter set at 15V and this eliminates the awful background noise. I just did a quick test only, though, and I don’t know how reduced the mic‘s specs maybe at this setting, but this could indicate that the mic expects the full 48V at the 48V setting, and won’t tolerate 45V. The tx only has a 15V setting and maybe that works better to supply more than the required voltage?

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The 15 Volt setting was for the low voltage, high current Schoeps of yesteryear. There's not many of them still around. The 15 Volt setting was also used for some Shure mics that really wanted something at or slightly above 12 Volts. The first thing the Shure mics did was Zener the 48 Volts down to 12 Volts. By having a 15 Volt setting on the transmitter, a lot of power was saved, extending the battery life.

 

The voltage at the pins of a 48 Volt mic is never 48 Volts. If the mic pulls 3 mA then there is a 10.2 Volt drop across the two 6.8k resistors specified in the DIN standard. In this instance, the mic would see 37.8 Volts at its XLR pins. With the HM and HMa at 3 mA the mic would see 39 Volts.

 

That doesn't explain your noise problem. I did find this on Trew's site: "The Schoeps CMC6U is designed for standard 48- and 12-Volt phantom powering. Its circuitry recognizes the supply voltage and adjusts itself automatically. "  Perhaps the 42 Volts isn't enough to kick the mic into the 48 Volt mode but the 15 Volts is fine for the 12 Volt mode (as were the older Schoeps I mentioned above). If so, you probably can get better battery life running the HM at 15 Volts.

 

Also, all the Lecto plug-ons from the H185 (first one) on, have used the same input arrangement, i.e., 1k series resistor and 42 Volts. The 15 Volt and 5 Volt settings were added fairly early in the series.

 

Best Regards,

Larry Fisher

 

 

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Larry, I have two questions:

1. what is the exact slope and fcy cutoff of the LowCut filter in the HM and HMa ?

2. Does the HM or HMa have a specific internal antenna or is it a "Pin1" version ?

 

Constantin: you talk about a " lower freq noise ". Does it have something to do with handling rumbles, or is it a part of the electrical unexpected noise, even if you do NOT (at all) touch the microphone/boom ?

 

If the issue has nothing to do with power supply, I would be pleased to make a loan to Constantin (specific suspension/windshield with RF filter in the XLRF).

Philippe@Cinela

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16 hours ago, LarryF said:

Perhaps the 42 Volts isn't enough to kick the mic into the 48 Volt mode but the 15 Volts is fine for the 12 Volt mode (as were the older Schoeps I mentioned above).


Thank you Larry, that’s very helpful. It pretty much confirms what I have been thinking now. 
So how come the HM only supplies 42V? Maybe this can be increased for the HMb? 
This makes me wonder now if the Schoeps CMK641 also sounds better in the 15V mode. I always found it lacking in low end when working off the HM. 

So now I should probably contact DPA (shame they don’t have a presence here), and ask about the performance of the 4017c at 15V. 
 

 

10 hours ago, cineli said:

 

Constantin: you talk about a " lower freq noise ". Does it have something to do with handling rumbles, or is it a part of the electrical unexpected noise, even if you do NOT (at all) touch the microphone/boom ?

 

If the issue has nothing to do with power supply, I would be pleased to make a loan to Constantin (specific suspension/windshield with RF filter in the XLRF)


Thank you as well, Philippe, for this and the kind offer. The noise I am talking about is fairly certainly not handling noise. It sounds more like brown noise. The low cut at the tx is set at 70dB. Still a good filter might help. I am somewhat optimistic that this might be a voltage issue as the sound seems improved with the 15V setting. I would like to try the RF filtered suspenion anyway, though, as I can still imagine this to be helpful with this mic. 
Thank you!

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The plug on series were 42 Volts because with their relatively low 1k series resistance, this gave a similar voltage at the mic pins as the 3.4k series resistance of the 48 Volt DIN supply. A secondary benefit, is that the battery didn't have to provide as much power.

Best Regards,

Larry Fisher 

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5 hours ago, LarryF said:

The plug on series were 42 Volts because with their relatively low 1k series resistance, this gave a similar voltage at the mic pins as the 3.4k series resistance of the 48 Volt DIN supply. A secondary benefit, is that the battery didn't have to provide as much power.

Best Regards,

Larry Fisher 

Thank you Larry for these precisions. The well known inconvenient of a "low value DC resistance" technique is the decreasing of the dynamic impedance...down to 1k in this case. The C preamp has 100 ohms output impedance, but is claimed to support loads...down to 2k and not less (or is it 2k per phase ?...I don't know). Who knows what may be "affected" (max SPL, or else) but I suppose this is a minor inconvenient and may not be the pb of Constantin (and others ?).

 

Larry, in order to make a loan to Constantin (suspension or windshield), just curious:

1. what is the exact slope and fcy cutoff of the LowCut filter in the HM and HMa ?

2. Does the HM or HMa have a specific internal antenna or is it a "Pin1" version ?

Philippe@Cinela

 

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Hi Philippe,

From the HMa data sheet "Adjustable for -3dB @30, 50, 70, 100, 120 or 150 Hz)"  The slope is 12 dB octave though it is steeper at the lowest frequencies since several roll offs pile up on one another.

 

There is RF on all pins of the XLR so that the mic is part of the antenna structure. You will see a thin plastic separator at the mic plate, just below the twist ring. The main case is circuit ground and the mic is RF hot though in free space the case and mic look like a dipole. 

Best Regards,

Larry Fisher 

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7 hours ago, LarryF said:

Hi Philippe,

From the HMa data sheet "Adjustable for -3dB @30, 50, 70, 100, 120 or 150 Hz)"  The slope is 12 dB octave though it is steeper at the lowest frequencies since several roll offs pile up on one another.

 

There is RF on all pins of the XLR so that the mic is part of the antenna structure. You will see a thin plastic separator at the mic plate, just below the twist ring. The main case is circuit ground and the mic is RF hot though in free space the case and mic look like a dipole. 

Best Regards,

Larry Fisher 

 

Thank you Larry, I'll contact Constantin to make him test a unit with a special filter (triple choke) inside the XLRF. Any experience and feedback regarding adaptations between microphones and Plug-On Txs is good to know for everyone.

Philippe@Cinela

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Thanks for sharing your notes on this issue, all. Agreed, it is a shame DPA don't have a presence here. We are certainly fortunate to have active members like Larry and Philippe, though.

I have contacted DPA about the same problem with noise when used with my Lectrosonics HMa at ph48v setting, but I have been reluctant to send my C pre amp to Denmark as it seems this RF noise is STILL an issue even with new units out of the factory.. and there may be less costly workarounds that will allow me to keep the mic in action here, instead of shipping it out for service. Definitely encouraging to try it out at 15v supplied by the HMa, it's almost clean.. I would be very interested to hear about your results with the triple choke filter in the XLRF, Phillippe and Constantin. Maybe I could replicate your filter.. or I'd happily offer to test one of yours out too!

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Hey!
I am using a MMP C with a Lectro HM and don't have any issue. When i first bought the MMP C it did have a lot of noise, rendering the Preamp unusable. I went to my distributor and they changed it for a newer version (see my last post on that topic)

It works both on 48V and 15V. I actually tried it on 15V for the first time right now and to my ears and during a very quick test in my flat it sounds the same, if not with a little bit less noise. And same level on the output. I bought it about a year ago now and did 2 films with it since. No complains from post and i am happy as well.

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So I heard from DPA back. Took me a long time unfortunately to write to them, but they  responded very quickly. 
However, the response was a bit lame, to be honest. 
But it leads me to ask Larry if the input of the HMa and HM is balanced or unbalanced? The tech seemed to think it had something to do with that. 
 

On 11/9/2019 at 6:28 PM, Ben B said:

I went to my distributor and they changed it for a newer version (see my last post on that topic)


Thanks, yes I remember that other thread. As I posted there, I thought the c preamp was still a little noisy, but hadn’t used it since. But now I have and want to more, I find it’s still unusable. I have in the meantime pretty much determined that RFI is not the issue. 
The DPA respondent also didn’t tell me if the preamp works to full spec when run on 15V. 

 

However, an interesting aside, I always found the Schoeps CMC preamp to sound a bit weak with the HMa. And following this a friend of mine (who shared my view about the CMC/HMa combo) tried the mic with the 15V mode and has found that it also sounds much better with a much better bass response. 

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5 hours ago, Constantin said:

So I heard from DPA back. Took me a long time unfortunately to write to them, but they  responded very quickly. 
However, the response was a bit lame, to be honest. 
But it leads me to ask Larry if the input of the HMa and HM is balanced or unbalanced? The tech seemed to think it had something to do with that. [snip]

The input is unbalanced but both pins have the same bias voltage applied. Pin 3 has a large cap to ground fed by a 1k resistor from the bias supply and pin 2 has a 1k resistor (no cap) to the bias voltage. The signal developed across the 1k resistor in the signal input.

 

Swapping pins 2 and 3 with a barrel type phase switcher might be an interesting experiment.

Best Regards,

Larry Fisher

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2 hours ago, LarryF said:

The input is unbalanced but both pins have the same bias voltage applied. Pin 3 has a large cap to ground fed by a 1k resistor from the bias supply and pin 2 has a 1k resistor (no cap) to the bias voltage. The signal developed across the 1k resistor in the signal input.

 

Swapping pins 2 and 3 with a barrel type phase switcher might be an interesting experiment.

Best Regards,

Larry Fisher


thank you Larry for your response! I shall try that this weekend, I will have to resolder for this.

DPA recommended sending the preamp to my dealer to get it fixed (that would be the third time), but I‘d like to try this first. 

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So that's the diagram Larry is talking about. Classical one, but a bit unsusual concerning values. OK about DC currents and voltages, but the (low) dynamic impedance could be a clue. Just saying. Forget me if I'm wrong...

HM-Input.JPG

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