On 17/05/2011 01:26, IVP wrote: >> Or just use an electret mic (or a dynamic) and leave the electronics >> until after the isolation transformer. > 'isolation' in this context refers to impedance isolation doesn't it ? Not sure quite what you mean here - if you mean impedance matching then=20 it could do that too (e.g. the DI box would), but a 1:1 transformer=20 would just be for galvanic isolation purposes. I can remember using DI=20 boxes with the ground lifted and similar to help with issues with dodgy=20 ground and dangerous old equipment (I can remember getting a small shock=20 from the mic whilst singing plenty of times) As long as the transformer had a suitable voltage rating across its=20 windings, then it probably shouldn't matter much what exact form it=20 comes in. I was thinking of something roughly along these lines (or=20 whatever ratio is needed to match the equipment the OP is intending to=20 connect to): http://uk.rs-online.com/web/search/searchBrowseAction.html?method=3DgetProd= uct&R=3D2106431=20 Seems to be tested to 1kV according to datasheet. With shield between=20 windings. Search page it came from with other options: http://bit.ly/jKbMph --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .