I've always used a Johnny Stewart. I started off with a record player but some times you'd bump it when moving away and the needle would slide across the record. NOT good for calling in crows.
I changed to a cassette player type and have killed untold numbers of crows over that caller.
I no longer get out and hunt them and if you're interested in that caller with a bunch of cassettes to call crows and predators drop me a PM and we can talk price. It has a 25 watt speaker to really reach out to them. I've held on to it for all this time thinking some day I might get back out and do it again but my health just really doesn't allow that.