Preamp - 18 dB Gain too low?

Still no good here it is again.

Nguyen hi, just looking at the factory specs for your 845 amps they are very sensitive at less than 1v for full output.
There is something not right with your system as Red Book standard for cdp is 2v out and most are higher than this so your Lightspeed should be below half way. What is your cd or source (has it been modded?) please give model no's

Cheers George

The source is Oppo BDP 103.

The amp spec is confusing because the website and the manual state two different spec:

Grant Fidelity website
Output power: 25w
Response: 10Hz to 30KHz
SNR: ≥85dB
THD: ≤1.0%
Input sensitivity: ≤1.0V
Output impedance: 4Ω, 8Ω
Tubes: Standard Shuguang 845B×1, 300B-98 x 1, 6SN7GT ×1 per amp

Manual:
Input impedance: 100kohm
Input Power Voltage: 4.0V
Output Power：28W
Output impedance: 4、8Ω
Frequency Response: 10Hz-30KHz
THD: less than 1.5%
S/N Ratio：85dB
Power supply：AC 115V 60Hz
Power consumption: 170w per channel

Not sure what to believe.

Trust the manufacturer's spec's, especially since they are consonant with your issues.

What is attenuation voltage ratio and what does it tell us?
Nguyen787

read the table header as "rotation", "Db attenuation" & "voltage ratio".
hopefully this clears it up?

The discrepancy between 1V sensitivity (for full rated power output) and 4V is 12dB -- huge! Grant Fidelity and Shuguang really need to get in sync on that one -- it's very confusing/misleading, on such an important spec that can make or break a system.

A 25Watt amp with 4V sensitivity WAY on the low side -- I don't know what the hell they intended that amp to be used with. If would be great for high-output pro sources > 4V. The issues with a typical 2V hifi digital source are one thing; a low-output MC cartridge would be almost impossible to step up enough to coax a satisfying output from those amps.

As a comparison, the Rogue Apollo KT90/KT120 tube amps have a sensitivity of 1V for 250 Watts output. That's 22dB more gain than the Shuguang 845! Yep, they're on the high side of gain.

Another example on the (very) high side: the old Eico HF-87 amp (runs a quad of EL34; cathode bias; 35W/ch), which was spec'd (according to the assembly manual) at 0.34V for +3dB over full output (70 Watts). That's a whopping 26dB over the Shuguangs!

Both the Eico and the Rogue use a 12AX7 input tube...