What is the TLP?
The TLP (tube line preamplifier) is a unity gain vacuum tube stage in cathode follower configuration. It is inserted into the signal chain between the signal source and the power amplifier, and uses a very carefully chosen tube and operating point to confer the 'tube magic' people rave about the world over.
Does the TLP have any voltage gain?
No. Its gain is around 0.95. However this represents an insertion loss of less than 0.5dB, and in practice this is inaudible, particularly if used with the AKSA, which has a voltage gain of almost 32dB.
Generally, a line preamplifier does not need gain if the signal source is digital and the amplifier is sufficiently sensitive. This is the reason passive preamplifiers are sold for just this purpose.
Why would you ever use a unity gain tube stage between a CD/DVD player and a power amp?
A unity gain tube stage is used solely for its sonic contribution to the overall sound of the system. It is difficult to explain what the tube does to the sound, but it is true to say that it adds palpably to the 'engagement' of the music, the ability of the system to communicate emotionally with the listener.
Can the TLP drive long cables without sonic penalty?
Yes. This is a strong suit of the cathode follower, which has very low output impedance and excellent drive. The cathode follower has been likened to an 'electronic transformer' since it gives current gain, without losing voltage.
How big is the TLP, and where can I mount it?
The TLP is mounted on a pcb of dimensions 3.3" (84mm) x 2.6" (66mm). The tube and all other components except the rectifier diodes for the HT tube supply are mounted on this pcb. The TLP is best mounted in its own small enclosure, or behind a metal screen inside the power amplifier enclosure.
What sort of power supply is required for the TLP?
The TLP requires a 150Vact 10mA winding for the tube high tension supply, and a 6.3Vac 500mA winding for the tube filament. A custom transformer is supplied with the TLP which features precisely these windings, and in addition, a 15-0-15Vac supply for future developments. This transformer is built with grain oriented high quality laminations, and designed for universal use across the world.
What benefits does the Nirvana upgrade bring to the TLP?
The TLP Nirvana upgrade brings subtle improvements to image depth and resolution. It also adds a little more slam and impact to the sound. However, these improvements make the TLP quite demanding of source quality.
Is the TLP a genuine two channel, stereo design?
Yes. The two channels are powered from separate, split power supplies, and use entirely separate circuitry. Each section has its own triode within the same envelope, but there is a large shield between the channels which utterly prevents any crosstalk. In practice, the imaging qualities of the TLP are remarkable.
Can I get replacements of the tube?
At this stage, yes. Aspen is steadily upgrading its tube stock with a view to offering a full replacement service in the years to come. However, the TLP does not overstress its tube, and all indications are that the life will be measured in years, approaching ten.
How difficult is the TLP to make?
Of all the AKSA project kits, this is the simplest and quickest to build - and this is reflected in the short instructions, running to only 13 pages and 5000 words, compared to 13,200 words for the 55W power amplifier! A conservative estimate is three hours, including testing. Nothing could be simpler, although good soldering skills are desirable. When you also consider that in use it is almost impossible to electrically damage the tube, this is a walk in the park for most DIYers and a great project for a beginner!