{"id":1158,"date":"2016-11-18T17:19:19","date_gmt":"2016-11-18T17:19:19","guid":{"rendered":"http:\/\/stompville.co.uk\/?p=1158"},"modified":"2020-10-11T11:54:00","modified_gmt":"2020-10-11T11:54:00","slug":"unbalanced-piezo-preamp","status":"publish","type":"post","link":"https:\/\/stompville.co.uk\/?p=1158","title":{"rendered":"Unbalanced Piezo Preamp"},"content":{"rendered":"

Update: Modules are available in the shop here<\/a> now.<\/p>\n

I finally decided to retire the Altoids Piezo Preamp Kit<\/a> and Altoids Piezo DI kit<\/a> projects from the shop; I received good feedback from customers – but not enough people bought them.\u00a0 Fully built and tested Altoids Piezo Preamps are available from the shop here<\/a>.<\/p>\n

The Phantom Piezo Preamp Module has been a great success and has sold very well. However, we have been getting a significant number of enquiries about deploying the Phantom Piezo Preamp without the Phantom power so I decided to adapt the Altoids Piezo Preamp design to make a complimentary module to the Phantom Piezo Preamp. In the absence of a better idea, I am calling it the Unbalanced Piezo Preamp. Here is the schematic:<\/p>\n

\"242SV\"<\/a><\/p>\n

This is a slightly cut-down version of the Altoids Piezo Preamp design. It is worth noting that this is an impedance buffer rather than a preamp as it has no voltage gain (in fact the voltage gain is slightly less than unity). Battery life is a few hundred hours and the design will work down to about 4V. If you want to connect a quantity of these up to a power supply (which must be smoothed and regulated), the maximum supply voltage is 24V (but there is little mileage in going above 15-18V). If you do connect several preamps to a power supply then you should create a star grounding point adjacent to the power supply output and take the negative battery wires separately from each channel to the power supply -ve.\"P180SV\"<\/a><\/p>\n

The PCB is 38mm x 31mm (approx 1.5″ x 1.25″). Input and battery connections are via solder pads. However, space has been allowed to fit terminal blocks with 3.81mm (0.15″) spacing. Terminals will be available in the shop as an optional extra. Output connection is a stereo jack socket which takes a mono jack plug. The output is wired so the battery negative is disconnected when there is no plug inserted in the output jack. If you don’t want this functionality, you need to solder a link between the ring and shield connections for the output jack. Do not be confused by the stereo jack on the output – both the input and output of this design are wired unbalanced.<\/p>\n

\"P177SV\"<\/p>\n

If you want to experiment with this design, here’s the low down:<\/p>\n