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Jeff Wexler

DPA 4098 - first impressions

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Good find, Constantin. I don't know for sure who wrote this Lectrosonics FAQ answer, but it seems to have Larry Fisher all over it!

 

To save time with the link, here is the text:

 

For a typical two wire lavaliere mic that specifies 5 Volts, the manufacturer is actually assuming that the transmitter has a 5 Volt supply in series with a bias resistor of 1k to 5k, depending on the brand of transmitter. The actual voltage at the mic will be 5 Volts minus the drop across the bias resistor. For example, a mic that is listed to draw 500 uAmp would produce a 2.5 Volt drop across a 5k bias resistor. The mic would only see 2.5 Volts (5V minus 2.5V drop). A different mic that pulled only 100 uA would see 4.5 Volts. So for most all transmitters, the voltage to the mic is all over the map. Generally the mics still work, because they actually can handle a wide range of voltages.

All the current Lectro transmitter models, such as the LMa, have a servo input that regulates the bias voltage to exactly 4 Volts under any condition of bias current. The voltage is set to 4 Volts by using the pin 2 to pin 4 wiring. This allows us to handle a wide range of microphones with any current draw with no concern about excessive voltage drop across the bias resistor and is unique to the Lectro transmitters. We chose 4 Volts because this was a typical design voltage and all the professional lavaliere mics we looked at worked very well at that voltage. The one exception is the tiny Countryman B6 and E6 models which require 2 Volts at high current. For the Countryman mics Pin 4 is NOT connected to Pin 2 and this sets the servo input to a regulated 2 Volts which is ideal for those lavaliere mics.

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Yeah, that one is mine. The DPA's we measured  drew whatever current necessary to have 1.8 Volts across the mic. They would draw as low as 20uA to as much 3000uA(!) to stabilize around that voltage depending on the value of the bias resistor. Since we provide 4 Volts and that is twice the idle voltage, there is no "headroom" problem or "high noise" due to low voltage. Their head engineers understand this. Some of their techs don't understand the servo circuit and are just looking at raw specs.

 

As an aside, you can vary the "gain" of the DPA mics by choosing the bias resistor in the connector; smaller values give more gain (1k) and larger values (4k) give 12 dB less. 2k is a good middling value.

Best,

Larry F

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Thank you Constantin for the forensic work on finding the thread on the Lectro site. And thank you Larry for always chimming in on the neccessary info.

 

I recieved an email from the Distributor here is what they said,

 

"As for the Adapter, if it’s a Cabled item, we have a few people that can customize the resistor value inside and adjust the Gain.
The factory adapter is padded down for use with “Most” devices, but you can have a custom one made that better matches the 4098 with the Lectro Units."

 

 Who knew? My 4098's are microdot terminated like most of my DPA's to be used with the appropriate adapter for SSM,SM,SMQV etc. If I'm using a DAD3056 adapter how would I change the resister? Are they serviceable? I think this email is referirng to the DAD6001 which is a XLR to microdot. That I can see being serviceable. I will write back to the distributor and verify. Am I the only one noticing the noise floor? I thought I was doing something wrong?

 

Bill

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9 hours ago, Sound Intuition said:

Am I the only one noticing the noise floor? I thought I was doing something wrong?

 

Bill

 

I would say no to both of those questions, although of course I can't know for sure about the second one ;)

But a higher noise floor compared to what? A 4060? Or a 4017? 

I think many of us here are using the mics for car work and perhaps as a quick-fix spot mic. 

In cars the noise doesn't bother me, especially if the car's engine is running. Previously I used to hide Schoeps mics, which sounded much better, but were much more difficult to hide. Before that I used DPA lav mics, which are very easy to hide, but rarely sound nice (I'm only talking about car work). 

The biggest issue I found was that I usually connect the mic straight to the tx and every little movement the transmitter makes gets transferred to the mic. This can be solved by suspending the tx in one way or another. 

9 hours ago, Sound Intuition said:

 

"As for the Adapter, if it’s a Cabled item, we have a few people that can customize the resistor value inside and adjust the Gain.
The factory adapter is padded down for use with “Most” devices, but you can have a custom one made that better matches the 4098 with the Lectro Units."

 

Bill

 

I have a feeling they are not actually talking about the MicroDot adapter, but about the TA5 connector soldered to the cable. 

Younshpuld probably follow this up with them

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The DPA microdot/TA5 adapter they make for Lectrosonics has a 3.9K resistor inside. I haven't tried to open one to see if it could be changed, but I agree that a bit more level would be better for TV/dialog.

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14 hours ago, Glen Trew said:

The DPA microdot/TA5 adapter they make for Lectrosonics has a 3.9K resistor inside. I haven't tried to open one to see if it could be changed, but I agree that a bit more level would be better for TV/dialog.

 

Thanks Glen, I guess this could well apply to the 3 pin Lemo adapter too, and may have scope for being changed?

I will have to educate myself better as I realized I don't understand how the resistors work, as Larry's contribution -

"As an aside, you can vary the "gain" of the DPA mics by choosing the bias resistor in the connector; smaller values give more gain (1k) and larger values (4k) give 12 dB less. 2k is a good middling value."
is the opposite of what I thought, as I thought the resistor worked by leaking some of the signal to earth, so a higher value resistor would leak less to earth and hence give more gain.

I obviously need to find out how it works.......

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The resistor is in series with 4 Volt servo input so larger values reduce the DPA current. The Lectro servo input is current driven. Less current, less "gain". Keep in mind, increased gain at the mic element may gain up the noise just as much as the desired audio. My guess is that increasing the gain won't improve the signal to noise ratio, which is the only important  number. The transmitter has enough gain range to make high or low resistor values work. The clipping levels, distortion numbers, limiter range  and transmitter input noise are all independent of that resistor value. It may be comforting to see a middle value on the transmitter gain setting but it makes no real difference. As long as you don't run out of range.

Best,

Larry Fisher 

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On 29/10/2017 at 12:45 PM, LarryF said:

Keep in mind, increased gain at the mic element may gain up the noise just as much as the desired audio. My guess is that increasing the gain won't improve the signal to noise ratio, which is the only important  number.

 

 You are correct Larry increasing the gain does not help with the signal to noise.

On 28/10/2017 at 6:33 PM, Constantin said:


 

Previously I used to hide Schoeps mics, which sounded much better, but were much more difficult to hide.

 

 

I used to use Neumann 150's with the active goose neck which were great for years but now seem to be impossible to hide. I love my DPA 4060's, 4061's and the slims as Lavs but saddly I'm not impressed with the 4098 as a car plant. I will follow up with the distributor and see what they can do resister wise.

Bill

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