Extensive compressor reviews and FAQ

Tortenmann TK-23 Kompressor: Originally from the brand "Telenordia", but the company changed hands in 2009 and the brand is now Tortenmann. This boutique optical comp pedal comes from Germany. All of Tortenmann's pedals are based around a germanium transistor gain stage. Germ transistors are often used for the "vintage" wooly coloration they can add to a signal, and that is the case here.
To my ears, this pedal does what the Menatone JAC was supposed to do; they both use a similar optical element followed by a colorful gain stage, but while the Menatone ended up sounding kind of scooped and modern, the Telenordia has thick mids and a warm old-school tone with a sort of "raw" edgy character.
The highest frequencies are gently rolled off, giving the overall tone a dark quality; the lows are quite strong, with maybe a little bit of the lowest frequencies reduced--but not enough to actually bother me, even with a low B on the bass. The make-up gain stage can be pretty noisy, especially at higher levels. I found that if I fed it a nice clean strong input signal, kept the threshold high, and kept the output gain below 12:30, the noise level was not bad, quite tolerable. But if you want to lower the threshold much for heavier squashing compression, that will mean turning the output gain up into the very-noisy range. That's to be expected from most germ gain stages, unfortunately. Another quirk of the germanium is that if this pedal is exposed to heat or direct sunlight for a few hours, it will stop working until it cools down.
The compression action is very smooth and natural at all settings. This is mostly because the ratio is fixed at a very low amount, about 2:1. So while it is possible to get a strong compression effect by setting the threshold very low, it will not act as a peak limiter. It's better suited to thickening and smoothing. The Threshold knob goes clockwise from high to low. There is also a knob labeled "Dry Feed", which is actually a clean blend much like the one in the Barber, Empress, or Wampler for example. This is a great way to bring back some of your original dynamic feel while adding the coloration from the effect. In the original version of the pedal produced by Telenordia, the Dry Feed knob was also a push-pull switch, where the second position included control over the attack time.
The construction is typical of good-quality small-run handbuilt pedals. The housing is plain unpainted aluminum with only minimal engraved markings. There is an internal dip switch that sets the LED light to indicate either on/off status or the amount of compression (but not both). It runs on normal Boss-type 9V DC, although they strongly recommend only using an isolated power supply or battery, not a daisy chain supply. The footswitch is "true bypass".
Compared against some of the other "warm/fat"-sounding comps I have, the TK-23 has more complex texture and more of a rough edge to the tone, but it can be a bit noisier. While the quirks and subtleties of this pedal mean it won't be right for everyone, the action is super smooth and the tone is bold, fat, and "musical", and I like it.

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