GA-251 build info
Mic body and grille
The mic body is made of brass, the grille is made of iron.
The grille, which is a critical component affecting the sound character, is similar to the one in the 251.
The GA-251 uses a 34 mm K251 style capsule. Being a dual-sided one, it provides both cardioid and omni polar patterns.
In order to get a good consistency between units, for each production run of 50 pcs GA-251 units, approximately 200 capsules is evaluated in order to find 50 capsules with specifications that lie within the tight tolerances.
Backplate material: brass
Capsule diameter: 34 mm
Membrane diameter: 34 mm
Membrane material: 6 micron gold-coated mylar.
The sensitivity of the front and back side of the capsule do not differ more than 0,3 dB. The sensitivity between different capsules do not differ more than 0,5 dB.
The tight manufacturing tolerance will lead to a very good consistency between different GA-251 units.
The capsule is specially designed to complement the electronic circuit of the GA-251 to achieve a frequency response curve with a nice balance between the high, middle and low frequencies.
The result is a very smooth sound with a warm bottom and airy top end just like ELA M251.
The GA-251 uses a NOS Phillip 5480W super low noise pentode tube connected in triode mode in order to decrease the noise. The tube has the following character:
- balanced sound response
- a smooth and warm sound character and a low noise level
- long lifespan
The GA-251 amplifier features a new proprietary circuit designed around the NOS 5840W tube.
The GA-251 transformer is specially designed with a 10:1 AMI style dual bobbin transformer. It is made from permalloy steel sheet from USA and enamelled wire from Germany. It offers a wonderful sound character with a high resolution and great balance between the low, middle and high frequency bands.
Capacitors and resistors
The coupling capacitor is made by Solen from France. It is a high balanced film capacitor made from MKP material with pure oxygen-free copper connections. It has a very delicate and balanced sound.
The capsule capacitor uses NOS Siemens antique grade polystyrene capacitor to reduce loss.
The tube cathode bypass capacitor uses an ELNA OFC Cerafine high end hifi capacitor from Japan with oxygen free copper connections exhibiting a very sweet and delicate character, not the least for vocals.
The other capacitors are of the low loss polystyrene type.
The resistor used for setting the capsule voltage is a high quality DALE 1% metal film resistor. The result is a very stable and consistent operating level leading to better consistency between different GA-251 units.
The plate resistor uses a non-inductive resistor of the United States IRC audio with pure copper connections. The sound level is rich and full bodied.
The electronic circuit is built with point-to point wiring, All soldering points made with Mudorf Msolder Supreme silvergold solder
All of the inside wire use pure silver wire and decrease the loss during the circuit transmission, also it can ensure the sound quality is transparent.
All components which are connect to electrical ground is connected to the ground plane on the circuit board. All other component connections use point to point wiring which results in virtually zero loss and crosstalk.
Power supply transformer and electrolytic capacitors
The vintage style power supply PSU uses a high power R-style transformer with a low noise level and minimum stray field.
A simple but effective circuit uses dual-stage filtering for the filament voltage. The High voltage is also precisely filtered and stabilized using an ON semiconductor zener diode.
The polar pattern switch is placed on the power supply so that the recording engineer can change the polar pattern between Cardioid and Omni remotely.
A ground lift switch will help to solve mains power related noise issues that can appear in some cases
The cable is specially produced using 99,99% pure oxygen-free copper, Teflon insulation, tin foil and 98% kitmesh, ie with a very high braided density of the cable shield. It has a very open and smooth sound. The mic connector is an aviation style plug providing solid connections and a long life.
- High End, no compromise components and build quality
- Hand Made in small series, 50 units at a time
- Capsules selected with very tight tolerances
- Point-to point wiring with silver-plated wires, no printed circuit board used
- All soldering points made with Mudorf Msolder Supreme SilverGold solder (Sn88, 6Cu, 1,8Ag, 9,5Au
- Solid wood microphone box, tweed style system flight case. Every mic, box and psu has a badge with the serial number.
- Maximum SPL: 136dB
- Frequency range: 20Hz-20KHz
- Signal/Noise: 85dBA
- Impedance: ＜200 Ohm
- Sensitivity: 16mV/Pa
- Microphone dimensions: 50mm(diameter) * 250mm (length)
- Microphone weight: 0,6kg
- PSU dimensions: 200mm (length) * 100mm (width) * 100mm (height)
- PSU weight: 1,5kg