In many forums all over the world guitarist are searching for the “transparent overdrive”. But what is meant by this and does a transparent overdrive make sense?
Tubscreamer and similar overdrives place great emphasis on the mids. This kind of overdrive is appropriate as an additional booster to an amplifier that is already overdriven. By creating haunting mids the sound of the guitar becomes more assertive and will be perceived much more in the context of the band as a whole.
Transparent overdrives are rather used in the low gain area. The most famous overdrive in this category is the Timmy by Paul Cochrane. The sound is relatively transparent. Usually they are adjusted to produce a clean signal when one hits the strings softly. Playing chords or with more attack it creates overdrives. This kind of overdrive maintains the dynamic of the guitar-play and adds a light compression. The sound should be transformed in very small measure.
Often it is used for an amplifier with much headroom. While small amps easily get closer to saturation by the play with more attack, this becomes pretty complicated with more powerful amps like the Fender Twin Reverb or a Vox AC30. In this case one is able to produce some kind of “dirt” in the frequency peaks by using a transparent overdrive.
But quite often even transparent overdrives produce too much compression anyway (notably when using pickups with high output). In order to display the attack of the strings appropriately and with enough punch, one can additionally insert the overdrive to a parallel looper.
If the parts of the clean and the overdriven signal can be adjusted infinitely, one is able to create a nice and transparent overdrive. By the clean parts of the signal one produces a fast attack. The added overdrive produces the sustain and harmonies. Suitable for this are for example the Parallel L by Lehle or the Xotic X-Blender.
Another possibility to produce less compression is, not to run the overdrive on 18 V but on 9V (as long as this is practicable to the respective overdrive). Many manufactures already declare a power supply for their overdrives from 9 up to 18 V.
Overdrives that run on 18 V got more headroom and distort later. But it also changes its sound. The overdrive might be more harsh as it would be on 9 V. For this it will also sound more transparent. Of course one can experiment with the different current voltage.