Volume Mono pedal

Technical specifications:
• power supply - 9V battery or external 9V DC adapter
• current consumption cca 7mA
• frequency response 50Hz - 20kHz
• dynamic response > 70dB
• battery lifetime cca 140 hours
• dimensions: 230x100x50mm
• weight 1,2kg

Volume Mono pedal

Designed to control the volume of electric guitar and keyboard instruments. Heavy duty mechanical construction and electro-optical control system without pots ensures extended lifetime. The volume at "heel-down" position is adjustable from zero to full signal.

In the late 90's this pedal was also sold by Dunlop Manufacturig under the Rockman RV-1 name.

Here you can read user reviews from Harmony Central:

http://www.harmonycentral.com/reviews/category/guitar-and-bass-effects/subcategory/misc-guitar-effects/product/rockman-rv-1-optical-volume