WE SHIP WORLDWIDE
  • FAQs
  • Privacy
  • Terms
Analog Classics
Login / Register
0 items $0.00
Menu
Analog Classics
0 items $0.00
Browse Categories
  • PCBs
  • Batteries
  • Switches
  • Encoders
  • Knobs
  • Bulbs
  • Potentiometers
  • Jacks & Plugs
  • ICs
  • Op-Amps
  • Transformers
  • ALL CATEGORIES
  • Home
  • Shop
  • Free Resources
  • Contact Us
JOIN OUR NEWSLETTER
Gyraf G7 Tube Mic PCB Set on a white background
Gyraf G7 Tube Mic PCB Set on a white background
Click to enlarge
Home PCBs Gyraf PCBs Gyraf G7 Tube Mic PCB Set
Gyraf G7 Tube Mic PCB Set on a white background
API 500 Series Female Card Edge Connector $24.95
Back to products
Gyraf G7 Tube Mic PCB Set on a white background
1176 Input/Output Knob $11.95
Gyraf

Gyraf G7 Tube Mic PCB Set

$24.95

70 in stock

SKU: 101053 Categories: Gyraf PCBs, PCBs Tags: diy mic, gyraf, pcb, tube mic
  • Description
  • Additional information
  • Documentation
  • Reviews (0)
Description

This PCB set is the starting point for the Gyraf Audio G7 DIY Tube Microphone with power supply PCB.  Please see the “Documentation” tab for build info.

 

The Gyraf G7 Microphone

This is a true variable-pattern microphone, capable of doing omni, cardiod and figure-of-eight. This is acheived by polarizing the front and back diagphram of the capsule in different ways with respect to the center electrode.

To act like a microphone, we need a voltage charge across the capsule. When the capsule changes capacitance (that is: the distance between the electrodes are changed by sound pressure) is changed, so does the amount of energy that can be held stored in this capacitor. But as we are charging/discharging with a hell of a small current – the 1GigaOhm resistor – the current really has nowhere to go, and so results in a varying voltage potential across the capsule.

The polarization scheme can be a little difficult to understand at first. To acheive simple remote switching of the polar patterns, a single variable voltage is used for this, only changing the charge of the back part of the capsule.

We want to keep the front electrode of the capsule at ground potential – 0V – at all times, both to act as a shield for incoming electrical disturbance and to avoid electrostatically attracting too much dust from the environment. So to keep a voltage charge across the capsule, we bias the center electrode by the means of two 470K resistors dividing our 160V supply voltage in half – resulting in +80V.

Now we have -80 volts at the front electrode, referred to the center electrode. If we now bias the back electrode with the same (-80V ref. Center = 0V polarization voltage), a positive sound pressure on the back capsule will have the same voltage-potential effect on the center as when applied on the front capsule. This sensitivity pattern is then OMNI directional.

If we polarize the back electrode at +80 Volts, no voltage difference will exist between this and the center electrode, already offset at +80V. This in effect mutes the back capsule, resulting in the CARDIOD directionality.

At last, if we polarize the back capsule at +160 Volts, we’ll have a charge of +80 Volts relative to the center electrode. Now a positive sound pressure applied to the back electrode will produce an 180 degrees out-of-phase signal compared to the front capsule. When applying a sound pressure from the side of the microphone, so both capsules sees the same sound pressure, the signals coming from the two capsules will be in opposite phases, effectively canceling each other. This is the FIGURE-OF-EIGHT directionality.

The changing voltage potential on the center electrode of the capsule is picked up and amplified by the EF86 Pentode, which is wired in triode mode – just like the VF14 pentode in the U47. It’s input resistance has to be kept VERY high not to disturb the charge/discharge of the capsule, so we use a 1G resistor to bias the grid to 0VDC.

From the anode of the EF86 we take the signal thru’ a 2u2 DC blocking capacitor to the output transformer, a Lundahl LL1538 microphone input transformer, here used the “wrong” way around, converting the 15K output impedance of the tube into more useable 600R, and so driving the cable and your microphone preamp with low impedance.

On the PCB board there’s an option for adding a trimmer and a capacitor in order to introduce cathode feedback to the tube amplifier stage. This lowers both distortion figures and output impedance, but cancels out a lot of the “tubey” sound – the reason we bother to make a tube microphone in the first place. The reason I have’nt removed this option, is for purely educational reasons – if you want to do some experimenting yourself. This is also where you can put in various equalizations if you like that. But for the best sound – at least to me – leave the tube undisturbed by feedback and other dirty tricks. “

 

The Power Supply

This is a very simple power supply. You only need a couple of mA at 160V for the anode, and about 200mA at 6.3V for the heater. The PSU is based on standard transformers to make it easier for you get hold on them. First there’s a mains-to-9V about 5VA transformer, that is rectified and regulated to 6.3V DC by a LM317T regulator. This is sent to pin 6(+) and 7(0) on the XLR, to power the heater in the microphone.

The 9VAC from the first transformer is also taken to the secondary(“the wrong way around”) of a 220:15V transformer. Now we have about 135V AC on the primary of this second transformer. We rectify this and remove ripple with a 220uF/200V (or maybe larger)electrolytic. We take this DC thru another ripple filter consisting of a 10K resistor and another 220uF/200V (or maybe larger)electrolytic. Now we have our 160VDC for the anode (HT) voltage of our EF86 tube, and run this to pin 2 on the XLR, the ground goes to pin 1.

Now we need the polarizing voltages: 0V, 80V and 160V. The 0 and the 160 are easy, we have them already from the HT supply. We do the 80V simply by dividing the 160V by two 100K resistors, that will also work as “bleeders” ensuring that when you power off the mic, it should be safe to open after 10 to 15 minutes.

BUT ALWAYS CHECK YOUR VOLTAGES BEFORE TOUCHING ANYWAY!!! ( Burnt out bleeders often results in burned out tecnicians. And we dont want that!)

OK – the three different polarization voltages are taken to a 3-pole switch that selects the pattern you want, and goes to XLR pin 5.

Additional information
Weight 3 oz
Dimensions 6 × 2.5 × 0.35 in
Brand

Gyraf

Condition

New

Documentation

Documentation

Schematic

Component Layout

PSU Component Layout

Component List

 

Reviews (0)

Reviews

There are no reviews yet.

Be the first to review “Gyraf G7 Tube Mic PCB Set” Cancel reply

Your email address will not be published. Required fields are marked *


You may also like…

Gyraf Calrec PQ1549 Equalizer PCB Kit on a white background

Gyraf Calrec PQ1549 Equalizer PCB Kit

$29.95
Add to cart
Gyraf SSL/GSSL Bus Compressor PCB Kit on a white background

Gyraf SSL/GSSL Bus Compressor PCB Kit

5
$29.95
Add to cart
EZ1290 Preamp PCB on a white background

EZ1290 Preamp PCB

5
$29.95
Add to cart
Gyraf Pultec Tube EQ PCB Set on a white background

Gyraf Pultec Tube EQ PCB Set

$29.95
Add to cart
Gyraf G9 Tube Mic Pre-Amp PCB Set on a white background

Gyraf G9 Tube Mic Pre-Amp PCB Set

$29.95
Add to cart
Gyraf 1176 Compressor PCB Set on a white background

Gyraf 1176 Compressor PCB Set

5
$29.95
Add to cart

Related products

3PDT Footswitch Wiring Board/PCB on a white background

3PDT Footswitch Wiring Board/PCB

5
$0.75
Add to cart
Mutated Edges PCB on a white background

Mutated Edges PCB

$9.45
Add to cart
DIY Bench Power Supply DC Splitter PCB on a white background

DIY Bench Power Supply DC Splitter PCB

$5.95
Add to cart
Neve 80 Series Male Card Edge Connector on a white background

Neve 80 Series Male Card Edge Connector

$9.95
Add to cart
Mutable Instruments Plaits PCB on a white background

Mutable Instruments Plaits PCB

$7.45
Add to cart
Mutated Grids PCB on a white background

Mutated Grids PCB

$8.45
Add to cart
Neve BA438 Replica PCB on a white background

Neve BA438 Replica PCB

$9.95
Add to cart
Plum Audio DSO150 mk2 Oscilloscope Eurorack Conversion Kit on a white background

Plum Audio DSO150 mk2 Oscilloscope Eurorack Conversion Kit

$14.95
Add to cart
Close
Categories
  • Adapters
    • Hub Adapters
    • Mic Stand Adapters
    • Op-Amp Adapters
    • Thread Adapters
  • Amplifier Boards
  • Batteries
    • Battery Holders
      • Battery Boxes
  • Bulbs
    • Indicator Bulbs
    • Revox Replacement Bulbs
    • Universal Audio Replacement Bulbs
    • VU Meter Lamps
  • Buttons
  • Connectors
    • Card Edge Connectors
    • Terminal Block Connectors
  • Cooling Fans
    • Marshall Fans
    • QSC Fans
  • Displays
    • Roland Displays
  • DIY Kits
  • Encoders
    • E-mu Encoders
    • Ensoniq Encoders
    • TC Helicon Encoders
    • Yamaha Encoders
  • Fader & Slider Caps
  • Fuse Holders & Caps
  • Gears & Pulleys
  • ICs
    • Diodes
    • FETs
    • Transistors
    • Voltage Regulators
  • Jacks & Plugs
    • 1/4" Jacks
    • 1/8" Jacks
    • Jack Hardware
    • MIDI Jacks
    • Power Jacks
    • Power Plugs
    • USB Ports
      • Alesis Replacement USB Ports
    • XLR Jacks
  • Knobs
    • DBX Knobs
    • Neve/Marconi Knobs
    • Pultec Knobs
    • UREI Knobs
    • Yamaha Knobs
  • LEDs
  • Microphone Diaphragms
  • Monitors & Drivers
    • Diaphragms
      • Klipsch Tweeter Diaphragms
    • Hardware
  • Op-Amps
  • Other Components
  • PCBs
    • Adapter PCBs
    • Eurorack PCBs & Panels
      • Erica Synths PCBs & Panels
      • Plum Audio
    • Gyraf PCBs
  • Potentiometers
    • Slide Potentiometers
    • Trimpots
  • Relays
  • Rubber Feet
  • Screws
    • Thumbscrews
  • Switches
    • Marshall Switches
    • Mute Switches
    • Power Switches
    • Pushbutton Caps
    • Slide Switches
    • Tact & Button Switches
    • Toggle Switch Nuts & Washers
    • Toggle Switches
      • Peavey Toggle Switches
  • Tape Machine Parts
    • Cams
      • Akai Reel To Reel Replacement Cams
  • Thumbscrews
  • Transformers
    • Microphone Transformers
  • Turntable Parts
  • Uncategorized
  • VU Meters
  • Wireless Streaming
  • Wiring Adapters / Cable Harnesses
© 2023 Analog Classics LLC
payments
Close
  • Home
  • Shop
  • Free Resources
  • FAQs
  • Contact Us
  • Join Our Newsletter
  • Privacy
  • Terms
  • Login / Register
Sign in
Close

Lost your password?

No account yet?

Create an Account

This website uses cookies. By continuing here, you agree to the use of cookies.
More information