The Compactron Integrated Amplifier

Hi!

Here is the last of the initial wave of Compactron gear I built in the recent months. An integrated Stereo Amplifier.

It is based on the same interstage transformer coupled design as the Compactron Power Amp. With Input selector and volume control added.

All inputs are for line level sources. The Phono input is meant to connect to an external phono stage like the Compactron Phono Preamplifier.

The volume control is a stepped resistive attenuator.

Output power is 7W per channel.

This amp is the ideal heart of a minimalistic system.

Add the Compactron DAC and a pair of speakers along with a CD transport and/or laptop or other digital source and you are ready to go.

And the phono stage to cover vinyl playback as well.

Glowing in the dark:

Best regards

Thomas

The integratred 300B Amplifier

 Hi!

The new integrated 300B amplifier for speakers and headphones is finished and passed all tests.

The amplifier uses a pair of 300B directly heated triodes as output tubes and a 6DN7 per channel for the input and driver section. The latter fits this application well and does a much better job than the ubiquitous 6SN7 which seems to be used in 90% of 300B amps. 

One half of a 6SN7 has a too high plate impedance to properly drive a 300B. Using both halves in parallel works well but will then require another tube to get sufficient gain for an integrated amp. Hence my choice of 6DN7 which has a strong system with low plate resistance which is used as driver and the other medium mu section as gain stage.

This build got three inputs but it can be equipped with any number of inputs. Volume control is a stepped attenuator with discrete resistors. The output can be switched between the speaker connectors on the back and the headphone jacks at the front. The speakers can stay connected when using headphones and are muted in that case. Any impedance headphone can be driven. There is an attenuator switch which lowers the output by about 18dB in case of very sensitive headphones. This way a good volume control range is always given.

Power output is about 6-7 W per channel on 8 Ohm speakers. The output impedance is rather low for a SE amp so that a 6 Ohm speaker could still be used.

The high voltage is tube rectified using a pair of 6AX4 TV Dampers or equivalent. These work into a choke input filter (LC) which is followed by separate LC sections per channel (3 chokes total) for decoupling and absolutely hum free operation. The latter also ensured by clean DC filament supplies. 

The dimensions are :

27cm wide, 40cm deep (plus knobs at the front), 30cm high (to the tip of the tubes)

Weight is 24kg.

The unit does not use any PCBs and is completely hand wired point to point.

Here a few photos from the assembly process. The parts are arranged in several layers in a 3D fashion to achieve the compactness.

Only top quality film caps are used in the high voltage supply. 

The amp is designed to work with any 300B compatible tube (No XLS types with increased filament current).

The standard option is with ELROG ER300B output tubes, two pairs NOS rectifiers and two pairs NOS 6DN7 driver tubes. This package comes at 7150,- Euros export price or 8500,- including VAT within the EU. Plus shipping. The amp can also be ordered without output tubes. In that case the price is 5900,- / 7000,-

Of course the amp can also be ordered with ELROG ER300B-Mo: 7900,- Euros export, 9400,- incl VAT.

Or go for the TM300B as output tube for 9000,- / 10700,-

These prices are valid in the introductory phase and will have to be raised by about 500,- due to the materials cost and labour which this amp requires. Also the free spare pairs rectifier and driver tubes are only included in the introductory phase. 

Since each unit is built to order many customisations are possible. For example no headphone outputs or headphone outputs only with selectable impedance. This concept can also be customised to use other tubes like 45, 46, 2A3, 71A.

Best regards

Thomas

Preview of the Integrated 300B Amplifier

 Hi!

The chassis material for the integrated 300B amp arrived. Here a quick preview of how it will look like:

In March I showed the test build which was used to evaluate the concept. Now a version in the final chassis is being built.

The 6DN7 driver tubes in front of the 300Bs. Two power transformers and a choke are hidden under transformer covers.

At the left corner in the back two rectifiers tubes. 6AX4 or equivalent tubes like 6DA4 and 6DQ4 can be used.

Two more chokes and the output transformers will be mounted  under the top plate.

The first version will also get headphone outputs at the front. Any impedance headphone can be used.

Initial pricing will be 8500 Euros (within EU including VAT) / 7150 Euros (export). Price will be raised by 500 Euros later on. The price includes Elrog ER300B and NOS 6DN7 and rectifiers. Any 300b can be used. The unit can also be ordered without output tubes. Stay tuned for photos of the final build when assembly is finished.

Best regards

Thomas

The Integrated 300B Amplifier - Part 1

Hi!

I repeatedly get asked about the possibility to offer an integrated amplifier and also headphone amplifier based on the 300B and preferably in a single chassis.

So I decided do develop one and see if there really is demand. I mocked up a test circuit using a new Lundahl output transformer with a new high bandwidth winding technique and which has optimum values to be used with Elrog ER300B.

Above the bread boarded test circuit, one channel completed. To fit all into a single chassis no interstage transformer and no transformer volume control. Volume control is done via a DACT stepped resistive attenuator (not seen in the pic above yet)

I selected the 6DN7 as driver tube. The two systems offer the right amplification factors and plate resistances for this job.

Initial measurements and listening tests with a bunch of lab supplies gave very good results. So time to bread board a power supply as well.

Some older metal plates got recycled for the test. The result is very pleasing. A headphone version of this will be offered as well with selectable impedances for 32/150/600 Ohm. Now everything will be fitted into a single box and the metal plates for that have to be designed.

Drop me a mail if you are interested to become one of the first owners of a 300B integrated amplifier or headphone amplifier. Other tubes will also be possible.

Best regards

Thomas