A THD Hot Plate® is a tuned network of capacitors, resistors and inductors which adjusts the overall EQ as the volume is turned down to compensate for the human ear's frequency response. Your ear perceives sounds differently at different volumes: the louder the sound, the more sensitive your ears are to highs and lows. As the volume drops, your ear becomes more sensitive to the mid-range, and less so for highs and lows. The Hot Plate® compensates for this, working like the "Loudness" switch on a hi-fi. The THD Hot Plate® is the first, and for now, the only attenuator that is frequency compensated.
How do I use it?
The THD Hot Plate® is designed for use strictly with vacuum tube guitar amplifiers, and each version is optimized for a specific impedance (2, 2.7, 4, 8, or 16 ohms.) These inductive loads are frequency compensated, which means it will give you the best possible sound for that impedance speaker and amplifier combination.
To use one: connect the speaker output of the amp into the input of the Hot Plate®, then connect the speaker cabinet to one of the two speaker outputs of the Hot Plate® (doesn't matter which one). The amp thinks the Hot Plate® is a speaker, so the sound stays true even when you turn the volume down.
What else does it do?
Built-in Noise Reduction
The THD Hot Plate® is the only attenuator on the market with built-in noise reduction to reduce the hiss and hum between notes. We've designed a passive, single-ended noise reduction system which provides approximately 10 dB of broad band noise reduction without gating or pumping, and without affecting the tone of the amp. A by-product of the noise reduction circuit is that it generates light as you play. The harder you play, the brighter it glows.
The Hot Plate® is also the only attenuator offering a Bright switch and a Deep switch for tailoring your sound. The Bright switch gives you two different high frequency levels so you can compensate for an overly bright, or dull speaker cabinet. The Deep switch offers two distinct bass settings to help you fill out the bottom end, or reduce the bass in a cabinet with too much low end.
Adjustable Line Out
THD Hot Plates® also feature a Line Out, which is adjustable by its own volume control giving it a wide range of applications. At higher settings, it can provide enough signal to drive the input of a separate power amp for slaving. The middle range of settings is useful for most rack mount effects. And turned most of the way down, the Hot Plate's® Line Out will drive the instrument input of another guitar amplifier for extra power and volume.
Will it hurt my amp?
The THD Hot Plate® will not damage your amplifier. When you play continuously at full output, you cause your tubes to age more quickly than they would at lower volumes. Using a Hot Plate® will maintain the life of your tubes at exactly the same rate, no more or less, as when you play straight through the speaker.
Using a Hot Plate® will also not hurt your transformer any more than playing through a speaker, as long as the impedances are matched (i.e. 8 ohm setting on the amp, 8 ohm speakers and an 8 ohm attenuator). If you are using a well-made amp, then the transformer should last indefinitely, regardless of whether you are driving a speaker or attenuator. If you are using an inferior amp and the transformer blows, it would have done this whether you play through a speaker or an attenuator. The Hot Plate® puts the same load on the transformer as a speaker (which is why it makes such a good dummy load).