The QSP-20 audio path uses our low noise BE41 class A discrete amplifier design in a balanced configuration at the input feeding a Lundahl audio c-core transformer at the output. Instead of the traditional input transformer we use hi-spec Wima coupling capacitors. The topology is quite different to most other mic preamps in that it is balanced from input to output. The DI inputs feature our BE43 "bootstrapped FET" input interface for a very full sound from your pick ups.
If you use dynamic and/or ribbon microphones you know they sometimes need a lot of gain, which many low cost preamps and audio interfaces cannot provide. The QSP-20 provides up to 70dB of effortless gain for all situations and the transformer-less input matches all microphone types nicely. Think of the QSP as merely an extension of your microphone - everything sounds real.
Having lots of gain is one thing, but importantly the preamp must also be quiet and the QSP does not disappoint here thanks to our perfected design. The very wide frequency response (even at high gain) ensures transients and high frequency content are preserved which make the QSP an excellent choice for percussion and acoustic insturments. But it never sounds "brittle", the output transformer adds that nice touch of warmth to complete the sonic picture. The very high output headroom of +29dBu means it is unlikely you will ever clip the QSP-20 before your DAW audio interface does!.
GAIN - 41 detented pot that sets gain between +22 to 70dB.
0dB/-20dB - this switch introduces a 20dB pad right at the mic input for high level signals.
0/MUTE/180 - this switch changes the polarity (phase) of the output and in the center postion, it mutes the output.
HI Z/LO Z - selects the input impedance as seen by the microphone which can change the overall tone.
48V - locking toggle switch turns the phantom power on and off.
PK - this red led will light up when the QSP output level reaches +22dBu.
There is also a handy power ON/OFF switch.
I'm pleased to say that my new QSP-20 preamps are happily racked and in
heavy rotation here at our shop! As you know, I bought these to replace my
3 API 3124's and I couldn't be more pleased. It's not that the APIs aren't
a good product of course, but to my ears your design suits me better in
every way. BIG, clear and rich sounding with an incredibly even response
across the full 70db of gain...I swear they capture an extra octave on
both ends of the spectrum when compared to the 3124's. The DI inputs sound
fantastic and the stepped gain pots are a really nice touch too. Can you
tell I'm happy? Congratulations on a really great product!
Woodshop Recording Studio
Min Gain Mic; +22dB (-2dB with pad in)
Max Gain Mic; +70dB
Min Gain Instrument; +12dB (-3dB with pad in)
Max Gain Instrument; +60dB
Maximum Output Level; +29dBu into 3k ohm load
Mic; 10Hz to 200kHz @ 20dB gain (-3dB)
Instrument; 10Hz to 120kHz @ 20dB gain (-3dB)
Total Harmonic Distortion (measured at -20dBu input, gain adjusted for +10dBu output level)
Mic; 0.15% @ 100Hz, 0.01% @ 1kHz, 0.005% @ 10kHz
Instrument; 0.15% @ 100Hz, 0.015% @ 1kHz, 0.015% @10kHz
EIN Mic; -131dB A wtg, 150ohm source Z
Signal to Noise Ratio Instrument; -76dB A wtg, input shorted.
CMNR Mic; -78dB @ 100Hz, -100dB @ 1kHz, -100dB @ 10kHz
Input Impedance Mic; 4k ohms/1k2 ohms switchable
Input Impedance Instrument; 1MEG ohms
Power 115V or 230V ac mains, switchable on rear panel, IEC detachable power cable.