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Boosting Line Input of the Wolfson Audio Card as the Cirrus Logic

Former Member

Hi, I already see the comparison chart between the Wolfson Audio Card and the new Cirrus Logic.

I liked the new one allows to connect more GPIOs because the new RPi B+ have more pins available.

Since i still have the earlier Model B and the original Wolfson Audio Card, the only thing at the moment that didn't like is to the lack of support of classic input microphones (for example the PC external microphones) in the pink 1/8 jack, I have to get a 'boosted' or USB microphone instead.

Apparently, the chip of Wolfson audio card supports 'boosting' microphones, but for some reason they didn't build the card to support it.

Is there way to 'hack' or upgrade the card (soldering, upgrading firmware) to support this feature? The Cirrus Logic one in just script activates the boost

  • 0

    I asked a similar question just now.

     

    If the Cirrus card can provide plug in power for stereo electret condenser microphones, this would transform its potential for fixed audio recording and streaming applications vis a vis the Wolfson.

     

    Thanks

     

    Grant (soundCamp)

  • 0 in reply to shabaz

    Hi,

     

    An easy way to support traditional PC headset (separate headphone and mic connector) would be to use the following adaptor and connect to the headset connector. This adaptor is quite common to allow PC headsets to connect to newer laptop single connector headsets.

    http://www.amazon.co.uk/Startech-com-3-5mm-Headset-Splitter-Adapter/dp/B004SP0WAQ

     

    As is pointed out in both threads the Cirrus card was updated to add the functionality of MICBIAS on both the left and right Line inputs.

     

    Although not pretty the Wolfson card could be modified with a resistor and blue wire to support microphone input. As an example I would suggest unpop C8 and then wire resistor from C8 to junction of C58 / R55. I would point out that the line input connector is wired for stereo input while PC mics are generally wired for mono microphone. So a little care should be taken.

     

    All inputs have gain control on the WM5102 so the gain can be changed in software to the suit the connection being used.

  • 0 in reply to Former Member

    Something like this?

     

    It will be there any chance to turn it off/on with a script like in the Cirrus?

  • 0 in reply to Former Member

    I watched both diagrams and I noticed that the Cirrus have two 2.2k resistors conected before R55 and R56, and then both to the MICBIAS3[4]. Also, there is not a C8 4.7uF capacitor connected in the cirrus, but only to MICBIAS2 (which is for another plug). So, as you said, i have to take out C8, but I think have to connect two resistors in the same place as cirrus diagram instead.

     

    I'm still worried about the activation of Mic bias (or mic boost) with the same drivers.

     

    By the way, that C8 capacitor in the wolfson is for what?

     

    I also noticed there a different component, the PJ-3064A2-5PZ2S in the Wolfson and the JHP-307ST, they have different conections, for example an additional R47 resistor is connected in the Wolfson ( 0R?? ). Why? Is there any impact if I change something?

    F

  • 0 in reply to Former Member

    Hi Ian,

     

    I will try to give you some guidance but suggest there will be some trial and error involved in this approach.

     

    Firstly I would suggest using the 3.12 kernel image for the Wolfson card. MICBIAS3 support has been added to the 3.12 only. The 3.12 image will automatically work correctly on the Wolfson card and also the Cirrus card with no user configuration required.

     

    The primary use of the line input is for typical 2Vrms line input, hence the potential divider on the input. The 2K2 resistor you mention is required to bias ECM microphones. Previously I suggested blue wire with a resistor - the resistor I was meaning was the 2K2. As you point out the 10k resistor could be used as the Bias but I would suspect the sensitivity of the ECM would be too low, you could gain up the signal in the WM5102 but then noise would probably be an issue.

    As a suggestion change R55 for 2k2 and unpop R59. Depending on the external configuration of the microphone you connect you may want to consider unpop R56 and R58. Need to consider the external microphone.

     

    R47 is unpop on the Wolfosn card so ignore this.

    C8 is dependent on the MICBIAS mode selected (bypass / regulator), take a lok at the WM5102 datasheet for more info.

    The connector has changed to low profile, however the connection to the internal circuitry hasn't changed when you plug in a connection.

     

    Recreating Cirrus is the way to go, do remember that the Cirrus is configured for stereo mic (2x 2k2 etc). If you want to connect a mono microphone then you can consider this as one channel.

  • 0 in reply to Former Member

    Thanks for this detailed discussion.

     

    We received our Cirrus cards yesterday.

     

    This may be obvious to others from the above, but would be useful for me to understand:

     

    Is there a simple way to increase the bias voltage to each channel of the Line In? Our microphone capsules need 5V for optimal performance.

     

    Thanks

     

    Grant

  • 0 in reply to soundcamp

    There isn't an option from the WM5102 MICBIAS as the max voltage is 2.8V.

     

    You could blue wire in a 5V supply to the existing MICBIAS resistor (watch back powering of WM5102 micbias pin). My concern with this would be the availability of a suitable clean 5V supply as you need to consider the PSRR of ECM microphones.

  • 0 in reply to Former Member

    Thanks, Scott

     

    I think we've found an equivalent to the Primo EM-172 which works on a lower voltage.

     

    bw

    grant