The Truth Line Stage & Active Buffer With Light Dependent Volume Control

The Truth as it sits in my system today

By mrgoodsound

I would like to write about a pre-amp (specifically a line stage) that has been part of my system since late 2018, and will continue as a mainstay for the foreseeable future.

Background

The 'Truth' line stage is built by Ed Schilling of thehornshoppe. I am inspired to write an article about it as it is certainly a unique component which defies the mainstream, and some internet discussions about this unit have some misinformed opinions. I first learned of the 'Truth' from Arthur Salvatore's original essay on it in 2016. At the time, it unseated his reference active Coincident Statement Line Stage and passive EMIA autoformer volume control, and his writing on it made me extremely curious - though I wouldn't be able to act on that curiosity until years later. I will note that while I do not agree with everything Arthur Salvatore has ever published, I admire his application of deductive reasoning and rational thinking towards audio. His original essay on the 'Truth' contains the most coherent explanation of the active vs. passive line stage argument I have ever read.

I will try to keep the technical explanation simple. The Truth is a unity gain (0dB) solid-state buffer which uses light-dependent resistors (also referred to as a photoresistor or photocell) to attenuate the input signal and provide balance control. Basically a LDR is a resistor which has variable resistance based on the intensity of light reflected on its surface. The Truth contains two potentiometers, however the signal does not pass through the contacts of either. Instead, these are used to adjust the intensity of a light source (an LED) being reflected onto the photocells, to control the level of attenuation or balance.

The Truth is not the only device on the market which uses LDRs in this manner, there are the more commonly known Tortuga LDR and Lightspeed Attenuator. However, it is critical to point out both of these devices are passive - they have no input or output buffering - and in my opinion markedly inferior to The Truth for this very reason.

The Truth also contains a simple transistor-based input and output buffer; and two regulated switch-mode power supplies, one per channel. My unit has the optional remote control, which adds another IR sensor board and motorizes the potentiometer. A picture of the internals of The Truth are below, borrowed from Roger McCuaig of TNT Audio with my labeling in red. I did not take a photo inside my own unit as it is actually rather difficult to open. Roger did provide the only other decent review of The Truth I have seen apart from Arthur Salvatore's, so check that out here. As an aside, I am a fan of TNT Audio's publications with their independent writing team and exploration of less mainstream components.

My Experience

Throughout the period of time I have owned The Truth, I have been able to use it in a wide variety of system configurations with a variety of power amplifiers and speakers. I have also loaned it to several local audiophiles, just to get their opinion. Only in one case was The Truth not a good match - the system's owner had a CD player with 2.0V RMS output, 90dB/w Yamaha NS-1000s, and an Audio Research VT200 power amplifier with an input sensitivity of 2.5V RMS for full rated output. There was not enough gain, though replacing his existing active pre-amp with The Truth yielded much better sound, even without the ability to crank it up. In every other case, The Truth immediately and undeniably outperformed every pre-amp or line stage it replaced. It simply has the least electronic character of any component I have owned and in many cases cannot be distinguished from a direct connection to the source! Sometimes, it even sounds better than a direct connection, as its buffering capability resolves impedance mismatch or input stage drive issues.

Internals of The Truth line stage

My current system configuration is perfect for The Truth. I have a DAC and phono stage with low-impedance 4.0V RMS triode output stages, a valve amplifier with three cascades and no volume control. I definitely do not require gain, but I do need a way to adjust volume, adjust balance and switch between multiple sources. The Truth is perfect for my application as it allows me to do these things while being barely distinguishable from a direct connection between my source and my amplifier. In his original essay, Arthur Salvatore rated a direct connection as '100', and The Truth as '97'. I would agree with this, the loss of 3 points can be attributed to the slightest softening of transients, and it is difficult to even assign this solely to The Truth, as another pair of interconnects are also present versus a direct connection.

In some ways, it is the perfect separate box line stage, though it is not a perfect component. It is not a component for the faint of heart. There are no on/off, mute or mono switches. Though I am personally a fan of scrappy looking gear, it is a rather cheap looking black box that barely weighs 1 lbs. Due to the nature of the balance control, the balance drifts once the unit is turned off and on, and the center position on the balance knob is not the center between the two channels, so balance must be set by ear. Due to the nature of the volume control, there is a very large portion of the volume pot which is useless and a small portion which is critical, though this will depend on the efficiency of your speakers and the gain structure of your system. I have 100dB+ efficient speakers and can hear mechanical noise from the motorized potentiometer when adjusting volume. The remote volume control is extremely finicky, the remote must be pointed directly at the unit for it to register any input, and the + and - buttons on the remote must be gently tapped, or you will get major adjustments.

I live with all these quirks because of what The Truth offers. Describing its sound is rather pointless as it has little electronic character of its own. It is easier to describe what is often observed when replacing an existing pre-amp or line stage with it.

When replacing an active line stage with The Truth, you will lose the coloration of that specific component (this can be a good or bad thing), but you will almost certainly gain sharper transients and leading edge; greater intelligibility; vividness; spatial impression; emotional mobility and a sense of appropriateness with regards to the distribution of sound, as it relates to intonation, rhythm, dynamics, etc.

When replacing a passive line stage with The Truth, the above still applies varying with the quality and application of the passive line stage - but even more emphasis on vitality, dynamics, energy, life!

Future Considerations

Is The Truth a must-have? No, it is not actually necessary in all system configurations to have a separate line stage. Pretty soon, this will likely include my own system. I have also not been able to compare it critically to an active line stage with gain that I consider worthy, though I am conflicted on what this would look like, even theoretically. Certain designs, such as those involving capacitor or transformer coupling, are likely out of the question if clarity of sound is to be matched. However, the sound character of an active line stage with gain may be desired or even necessary in some systems. I hope to be able to compare it in the near future with two OTL tube buffers, using standard ALPS potentiometers for signal attenuation, and draw more concrete conclusions about its sound character (or absence thereof).