The Comfort preamplifier concept offers an integrated phono preamplifier and a line preamplifier, combined with a state-of-the-art headphone amplifier.
The Comfort preamplifier is a unique combination of three main blocks:
RIAA phono preamplifier for MM or MC portable
Line preamplifier with calibrated volume control with loudness function
Headphone amplifier
The Comfort preamplifier can of course be combined with all standard audio components. We have taken special care to harmonize the set with OldStep monoblocks and Nadral speaker systems, and we are convinced that this set is an excellent choice in the given price category.
OldStep construction philosophy
The value we honor and pass on to our customer is the repeated long-term joy and experience of listening to music. Our constructions are uncompromisingly subordinated to the overall perception and feeling of the music, they are built on the effort to find the most direct path of the audio signal from the carrier to the listener's ears. We love vacuum tubes, but we use a wide range of electrical circuits and wiring concepts and carefully choose to use them in the right place in the audio chain.
Every detail of OldStep components is based on our many years of development, many experiments and experience. The products are handmade and each piece is uncompromisingly controlled for sound, quality and parameters.
- RIAA Phono preamplifier
The signal amplification and equalization block from the turntable is based on a two-stage passive parallel correction of the RIAA curve. This principle is very demanding on the components used and the production process, in which the components must be paired and selected in pieces and the resulting parameters must be carefully measured and checked. The first amplifier stage consists of one ECC88 tube system cathodically excited by a selected legendary Toshiba 2SK369 FET transistor. This is followed by the first stage of RIAA correction (318 and 3180us) to which the second amplifier stage with ECC88 is linked. The output of the second tube system is connected to the second stage of RIAA correction (75us), the correct function of which is ensured by a precisely defined input resistance of the line amplifier. Passive parallel correction is characterized by minimal phase distortion and, according to our tests, brings extremely transparent tool localization and spatiality.
In the basic version, the preamplifier is designed for MM transmissions. The option is a variant for MC laptops. The MC version is complemented by state Swedish Lundahl and Btritish SOWTER step-up transformers and allows you to select a wide input impedance for most MC transmissions, standard input resistance in steps of 10 -100-1000 OHM and capacitance in steps of 100 -330-1000 pF. At the customer's request, the input impedance can be modified exactly to the transmission used.
The design also offers a version with an input transformer for MM transmission where it is used as a balancing or for perfect galvanic separation and minimization of interfering signals.
- Line preamplifier with volume control
In addition to connecting a turntable, the Comfort preamplifier offers up to two audio sources such as a CD and a tuner. Two standard pairs of RCA connectors and an input selector with Takamisawa precision relays are used for connection.
The volume control is a selected tandem potentiometer supplemented by a loudness circuit, which is connected using a relay of the same type as the inputs. When the loudness function is activated, the lower and upper frequencies are amplified by 3 to 5 dB depending on the position of the volume control. The core of the line amplifier is a two-stage driver with a 6SN7 tube. The first system is used as a voltage amplifier with a gain of 15dB and the second system is a cathode tracker in ultimate connection with two MOSFET transistors, which set and stabilize the exact DC operating point of the tube independently of the piece parameters of the tube . This minimizes distortion and precise concurrency of the parameters of both channels. This stage ensures a low output resistance and thus eliminates the influence of the connected power amplifiers. A high quality WIMA capacitor is used at the output.
- Headphone amplifier
The heart of this part of the amplifier is the HIGH END headphone driver LME9600 from Texas Instruments. This integrated circuit is specially developed for this application. Circuit distortion 0.00003% for a load impedance of 600 OHM and a ramp rate of ± 20V / μs with a bandwidth of 55 MHz. These parameters are a very difficult and expensive discrete solution. By comparing different types of connections, we came to the conclusion that this solution has no competition in the given category.
- Auxiliary and protective circuits
The Comfort preamplifier is designed for connection to high-quality components of a higher price category. For this reason, we paid uncompromising attention to protective circuits duringdevelopment. The basic element is the starting circuit, which delays the connection of the output connectors after switching on in the phase of heating the tubes and stabilizing the operating points. The disconnect circuit contains two Takamisawa relays, which are controlled to minimize clicks and transients when turning the amplifier off and on. The second circuit is a DC component monitor at the output of the amplifier, which immediately activates the disconnection and grounding of the outputs whenfailure or improper handling. The third protection circuit is a signal size monitor at the output, which again immediately activates the disconnection of the outputs when the normal level of the nf signal is exceeded, eg in case of incorrect handling of signal cables in the on state, thus protecting especially speaker systems.
- Power supply
The Comfort preamplifier uses a separate power supply to achieve maximum signal distance from interfering voltages. The power supply uses a special audio toroidal transformer, which is connected to the network via an effective filter of interfering voltages and transients of the network. The concept of the source is strictly analogous, the disadvantage is the efficiency, and thus the heating on the other hand the source does not in principle generate any interfering signals as is the case with switched power supplies. The source is equipped with a circuit for standby function, where only the auxiliary transformer supplying the start circuit is connected. The power supply provides stabilized voltages for anodes 250V, heating 6.3V, +30 and -15V for other circuits. The heating and anode sources are equipped with a slow start, which optimizes the life of the tubes.
List for download:
Price: 59 900,- CZK (incl. VAT) - custom production
Specifications:
Phono input
Sensitivity for output -10dBu MM: 3.5 mV | MC: 350 uV
Input Impedance - selectable MM: 47 kOHM
MC: 10 – 100 - 1000 OHM
Input capacitance – selectable MM: 50pF
MC: 100 – 300 – 1000 pF
Gain @ 1KHZ MM: 40 dB
MC: 60 dB
RIAA curve accuracy +/- 0.5 dB 20 Hz-21 kHz
Signal to noise ratio @ 1V output MM: >80 dB | MC: >60 dB
THD+N & SINAD 1KHZ <0.50 %
Overload margin >30 dB
Channel separation @ 10KHZ MM: >85 dB | MC: 75 dB
AUX1, AUX2 input
Sensitivity for output -10 dBu 350 mV
Input Impedance 50 kOHM
Signal to noise ratio >80 dB
THD+N & SINAD 1KHZ <0.05 %
Overload margin >30 dB
Channel separation: >90 dB, 20 Hz-20 kHz
Frequency Response: -0.3 dB, 10 Hz – 20 kHz
Nominal output 775 mV
Maximum signal level: 4V RMS 1kHz
Maximum DC offset: 5 mV
Output impedance: 1.5 kOHM
Phones output: 6.35 mm / 1⁄4″ stereo jack
Phones Impedance 30 – 600 OHM
Power consumption: 50 W max. on, <2 W in Standby
Mains voltage: 230 V AC ±10 %, 50 Hz
Dimensions – Line stage: 240 (w) × 140 (h) × 360 (d) mm
Dimensions – Power supply: 140 (w) × 100 (h) × 280 (d) mm
Weight in total: 6 kg
For listening today in conjunction with ZERO 2 monoblocks and speakers from Nadral.
