​Headphone amplifier
Röcklinger HPA1 OTL

 A unique product, probably the only pure OTL headphone amplifier on the market.

Construction

Pure Tube® OTL – no output transformator or capacitor.
Double mono amplifiers, thus providing stereo.
High quality potentiometer.
Output power: 0,8W 30 ohm, 1,2W 60 ohm, 1,9W 300 ohm, 1,7W 600 ohm at 1kHz 1%THD
Bandwith 10 – 650 000 Hz -3dB
Dampfactor > 10

Interface

Input: RCA

Output: 6,3 mm stereo jack

Switchable output impedance: 30, 60, 300 and 600 ohm

Volume

Dimensions

Size 230x230x80 cm excluding valves
Weight 4,8 kg

Valves

2  ECC82
1 ECC99
4  6C19
Frequency responce 33ohm 2W
THD @ 1000Hz 33ohm 2W

Circuit solution

The dream of creating a tube amp that does not need an output transformer was born back in the 1930s. But it was not until the 1950s that Julius Futterman managed to solve the problem. The real challenge now was to find a practical, working circuit. It has taken a lot of energy to realize Futtermans idea without spoiling its inherent magic.

In order to construct a tube amplifier with low output impedance you need tubes that have low inner resistance. It is not easy to find tubes that match that criteria. For this construction the NOS Russian tube 6C19 was chosen.

The figure shows the main characteristics of the circuit. You will aslo find the theoretical value for the output impedance.
Read the excellent review the Röcklinger HPA1 OTL headphone amplifier got from one of the biggest Hifi magazines in Sweden (in swedish). Read article.

Behind the specs

Nothing was left unattended. Read up on Röcklingers design decisions.

For the experimental

 Flexible output power 0,8W 30 ohm, 1,2W 60 ohm, 1,9W 300 ohm, 1,7W 600 ohm at 1kHz 1%THD

For the puritan

The amplifier is Pure Tube® OTL  driven– no output transformator or capacitor. THD+N @ 1,0Vrms in @ 1000Hz
    0,09 %,  33 ohm
    0,09 %,  56 ohm
    0,08 %, 330 ohm
    0,08 %, 600 ohm

For the selective

In order to construct a tube amplifier with low output impedance you need tubes that have low inner resistance. It is not easy to find tubes that match that criteria. For this construction the NOS Russian tube 6C19 was choosen.

Read the user manual here

Svenska_HPA1_usermanual.pdf
File Size: 999 kb
File Type: pdf
Download File

Related articles

Output transformerless links
2016-11-09
The first amplifier Röcklinger launched was a headphone amplifer, build with tubes and with OTL technique. OTL stands for Output Transformer Less. To learn more what OTL is we share with you some usefull links for the curious. 
To measure input impedance
​2016-10-22
We at Röcklinger always simulate the electrical design first, then we build the circuit measure and improve the design. This loop will continue until we make sure that the final design is flawless. We also like to share and prove our design. So here is a tip on how to simulateinput impedace using LTspice.