LP-1HE

RIAA phono amplifier

Built-in regenerative power supply

Pure Class A regulated power supply

Completely feedback-free CAST technology

Linear fax RIAA technology.

LP-1HE MM：Available for MM phonostage only，

LP-1HE MC: Available for MC phonostage only，

LP-1HE Overview :

Built-in regenerative power supply.

Four pure Class A regulated power supplies are built in to power the regenerative power supplies and RIAA amplifiers.

Completely feedback-free CAST current transfer design.

Uses the best sounding FET 2SK170 field tube as a buffer.

MM version:

The input impedance can be user-configured to 10K, 22K, 33K, 47K, 100K and 200K to match the needs of different character phonostages or listening preferences. (Please note: Normally this should be set at 47K or adjusted to suit the user's preference)

The input capacitance can be configured by the user to 50P, 100P, 150P and 200P to match the needs of different characteristics of the cartridge. (Please note: Typically, the input capacitance is set to 100P for a smaller capacitance and better transparency, and a larger capacitance for a thicker, warmer and softer sound)

This unit offers 4 steps of +1.5DB each for a total of +6 gain, which can be adjusted by the user to correspond to the 3-5mV output of the phono head.

MC version:

The input impedance can be user-configured to 20, 30, 50, 100, 150, 300 and 600 ohms to match different characteristics of the phono head or listening preferences.

The input capacitance can be user-configured to 100P, 500P, 1000P and 1500P to match the needs of different characteristics of the cartridge.

The unit offers 4 steps of +2DB each for a total of +8 gain, which can be adjusted by the user to correspond to the output of 0.2-0.5mV cartridges.

Translated with www.DeepL.com/Translator (free version)

What is the "Linear Fax Technology" of RIAA design:

Over the years, it has become popular to use attenuated RIAA networks for vinyl preamplifier designs. This is due to the fact that feedback network designs are only found in inexpensive products because of the large intermodulation distortion, which always makes the upper and midrange frequencies less pleasant to listen to.

The attenuated RIAA design is shown below.

However, there is a problem with this decaying design. See the RIAA equalisation characteristics graph below.

The graph shows that the phono head outputs a signal that is 20DB higher at 20KHz than at 1KHz. This means that if the amplifier outputs a level of 500mV 1KHz, then the amplifier needs to output a level of up to 5V at 20KHz.

The question is not whether the amplifier can output a 5V level, but rather that there must be a considerable difference in the distortion of the amplifier by outputting a 5V level at 20KHz and 500mV at 1K. And this frequency band is in the sensitive region of the human ear.

I'm not trying to design an ultra-low distortion RIAA amplifier, the vinyl configuration itself has a high level of distortion and it is perhaps this distortion that makes the sound so pleasing and analogue sounding.

I wanted the RIAA amplifier to have a flat distortion characteristic.

The frequency bands of the different instruments can be seen in the chart above.

The different distortion levels must affect how the instrument sounds when played back. For example, if a piano is played back, if the distortion level of the different bands is different, the low band may sound like a piano of brand A, the middle band like a piano of brand B, and the high band like a piano of brand C. The whole recording will sound like a mix of several piano clips of different brands.

The diagram and detailed schematic of the LP-1HE MM are shown below.

In our design, a 75uS low-pass filter is fitted to the input of the amplifier, which will attenuate the input signal from 1KHz and ultimately the input signal to the amplifier will be flat from 1KHz to 20KHz, and the output of the amplifier will be flat from 1KHz to 20KHz, ensuring better distortion consistency.

I don't know if anyone else uses the same design, but I call it the "linear fax technology" RIAA design.

Fully analogue regenerative power technology:

The regenerative power supply is like having a private generator built into the machine.

It filters out the maximum amount of interference from the power lines and provides a super pure power supply to the audio amplifier, restoring a very low-dyed, analogue signal to the audio system and the user.

The regenerative power supply is designed so that 120V / 220V AC power is converted to DC power via a regenerative power input transformer, and then to a Class A parallel regulated power supply for the regenerative waveform generator and driver.

A balanced regenerative standard waveform generator generates an ultra-low distortion 50Hz waveform, which is balanced by a gain amplifier and a powerful driver stage to drive the three regenerative output transformers to produce a pure, stable voltage and frequency supply.

The regenerative waveform generators and drivers are powered by the Class A regulators so that their operation is not affected by changes in mains power or interference.

The Class A shunt regulator has a very high input impedance to prevent interference from entering the audio circuitry through the mains supply, and also to avoid crosstalk between the left and right sound signals through the supply to improve separation. The low output impedance provides excellent linearity and speed, making it an excellent power supply regulator design.

Audio-gd's arguments for regenerative power supply design:

1, The pure analogue regenerative standard waveform generator has much lower distortion than the digital synthesis generator, as demonstrated by internal design analysis and practical testing of the AP SYS-2722.

2, The digital driver stage can have higher power conversion efficiency, but the fully analogue driver stage has more analogue flavour.

3, The 400Hz regenerative waveform frequency has a higher power conversion efficiency, and the 50Hz regenerative waveform frequency is further away from the human hearing zone than 400Hz, resulting in a more mellow and natural sound quality.

Please note:

This product is specially designed, so please make sure that the phono head is connected before switching on. Please switch off the unit before plugging in the phono cable.

The LP-1HE needs to be switched on for 20 minutes to warm up before it meets its design expectations. Music can be played during this time.

To change the on/off status of the product, the amplifier volume must be turned down.

GND terminal connection:

The GND terminal is for the ground connection of the turntable.

Switch on the power socket :

Turns the power of the unit on or off.

The unit can be powered on for long periods of time.

Make sure that the amplifier is not powered on when switching the unit on or off.

The unit's CAST and XLR outputs are single-ended signals.

Here there are two corresponding switches to configure the parameters for both channels.

The user must change both switches to configure the parameters for both channels.

Please note that the switches with the same configuration for the left and right channels have the suffix number opposite to the ON direction. The switches are clearly marked.

To change the status of the switches, use a small screwdriver such as a stylus.

MM version:

Most heads are recommended to be set to 100P and 47K, but customers are free to experiment with different capacitor-resistance values for a more suitable tone.

MC version:

The higher the electrical capacity of the configuration, the softer the sound. The lower the configured impedance, the more dynamic the sound usually is.