All G.R.A.S. microphone preamplifiers are based on a small ceramic thick-film substrate with a very high input impedance. The ceramic substrate is shielded by a guard ring to minimize the influence of stray capacitance and microphonic interference.The casing is made of stainless steel for maximum strength and durability. This preamplifier ensures reliable operation even under humid conditions owing to the heat generated by internal power dissipation.
G.R.A.S. 26AC can handle both single and dual-sided power supplies. The supply can vary between 28 VDC and 120 VDC single-sided or ±14 VDC and ±60 VDC dual-sided. When using the high supply voltage (120 VDC or ±60 VDC), the dynamic range exceeds 140 dB.
The electrical circuit in G.R.A.S. 26AC is built on a ceramic substrate using selected low-noise componentsto gain very low self-noise. The electrical self-noise is so low that system noise is mainly determined by the microphone cartridge’s thermal noise.
The low-frequency cut-off of the G.R.A.S. 26AC preamplifier is mainly determined by the input impedance of the preamplifier and the capacitance of the microphone cartridge (see Fig. 3). The capacities 20 pF,6.5 pF and 3 pF equal the typical capacitances of 1/2", 1/4"" and 1/8" microphone cartridges respectively. The high-frequency cut-off is determined by the preamplifier’s ability to drive capacitive loads (slew rate), caused by the cable. For large-signals, the effects of these parameters must be accounted for when measurements are performed. Fig. 4 shows the large-signal response for G.R.A.S. 26AC for various capacitive loads corresponding to different cable lengths. The output level is in decibels relative to 1 Volt. Typical capacitance for the cable is 100pF/m (30pF/foot).
The G.R.A.S. 26AC 1/4" Preamplifier is provided with a 3 m lightweight cable terminating in a 7-pin LEMO series 1B plug. The cable is only 2.5 mm in diameter and will withstand temperatures from -40 oC to +150 oC. An adaptor (GR0010) for G.R.A.S. 1/2" microphones is included.
7-pin LEMO plug 1B male (ext. view)
Typical applications and use
|Frequency range (±0.2 dB) with 18 pF microphone dummy||Hz||2.5 to 200 k|
|Input impedance||GΩ // pF||20 // 0.4|
|Output Voltage Swing, max. @ ±14V/+28V power supply||Vp||12|
|Output Voltage Swing, max. @ ±60V/+120V power supply||Vp||50|
|Noise (A-Weighted) max.||µV||2.5|
|Noise (A-Weighted) typ.||µV||1.8|
|Noise (Linear 20 Hz – 20 kHz) max.||µV||6|
|Noise (Linear 20 Hz – 20 kHz) typ.||µV||3.5|
|Power supply, single||V||28 to 120|
|Power supply, balanced||V||±14 to ±60|
|DC-offset, min., single suppy||V||0.5 x Vs - 1|
|DC-offset, max., single suppy||V||0.5 x Vs + 4|
|DC-offset, balanced supply||V||-1 to 4|
|Temperature range, operation||°C / °F||-30 to 70 / -22 to 158|
|Temperature range, storage||°C / °F||-40 to 85 / -40 to 185|
|Humidity range non condensing||% RH||0 to 95|
|Connector type||7-pin LEMO (FGG.1B.307)|
|CE/RoHS compliant/WEEE registered||Yes / Yes, Yes|
|Weight||g / oz||8.0 / 0.28|
|Weight with cable and connector||g / oz||50.0 / 1.76|
1/4" to 1/2" adapter for use with G.R.A.S. 1/2" microphones
1/4" Preamplifier, Short version, customized cable length. Specify the length in cm (e.g. 26AC-CL0350 specifies a 350 cm (3.5 m) cable. Maximum cable length 10 meters
Right-angled (90º) Adapter for½" microphone and ¼" preamplifier
Adapter for 1/2" microphone and 1/4" preamplifier
Angled (90º) Adapter 1/4" to 1/4"
Extension cable, 3 metres
Extension cable, 10 metres
Extension cable, XX metres (customer-specified length)
Tripod adapter for 1/4" preamplifier
Tripod adapter for ¼" preamplifier with angular adjustment