I recently picked up a used VPC-1, to dip my toes into the whole passive preamp thing
I am using it in a secondary two-channel system, consisting of just two digital sources (Squeezebox SB3 and the digital output feed from my cable box, for Music Choice). These go into a M-Audio CO3 for digital conversion and switching, then into a Behringer DEQ2496 unit, for EQ and DAC. The VPC-1 passive goes between the DEQ and my power amp, an Aragon 8002 modded with Jensen input trannys on the XLR inputs.
I checked the CI unit out by using some spare Kimber 3-conductor PBJ interconnects, with one end of each cable converted to XLR. On the Behringer end, I only used pin 1 and 2, (hot + and ground) which forces the EQ to output a lower than "full pro" voltage level (but still over 2 volts). The Aragon is set up so that the input XLR connector pins 2 and 3 feed the internally mounted Jensen transformers, which in turn feed the single ended inputs of the amp. Pin 1 goes to the Aragon's chassis ground (I originally did this Jensen mod the Aragon for another system/ setup, which involved long cables). The cables in this new setup only need to be 12-18" long, but I still may need proper shielding.
In this setup, the passive worked OK, with good output at the 12 o'clock setting of the volume control.
Now I am ready to make some permanent cables, using Belden 89207, which is a twisted pair w/ shield cable. I discovered that the CI unit does not ground it's RCA "-" to the chassis.
So I am thinking I can try using all three pins from the Behringer, which will output a higher voltage level signal. This will allow me to ground the shield of both the input and output cables to the chassis of the VPC-1, which means the shielding will go straight through from the Behringer to the Aragon, and not be in the cable's "-" signal path. I can then compare that with the Kimbers.
So...to my questions. First, will the VPC-1 handle a full voltage "pro equipment" signal? I am assuming I need to remove a jumper inside the unit, to reduce the level "seen" by the volume control? I didn't get a manual with this unit, what screws does one remove to access the internal jumpers? Also, what effect if any, does the Jensen input transformers (JT-11-P1) have on the output of the VPC-1? I'm thinking the tranny actually increases the input impedance a little, which would be a good thing, right?
Thanks
John
