Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: J3ona1 on April 01, 2026, 09:52:12 pm

Title: Tweed pre with XLR out
Post by: J3ona1 on April 01, 2026, 09:52:12 pm

Hi good people. I'm putting together a fender tweed pre with XLR out and wanted some eyeballs on the XLR out portion of the circuit. I have a cathode follower feeding a Hammond 1:1 line matching transformer (Model 1140-LU-B) https://www.amplifiedparts.com/products/transformer-hammond-line-output-1140-series to get the balanced feed for the XLR out. Will this schematic get the output impedance to a good enough place where it can drive a long run to a mixing console. Schematic attached. Thanks in advance for your help.

Title: Re: Tweed pre with XLR out
Post by: J3ona1 on April 02, 2026, 08:20:19 am

Updated schematics to reflect actual pt and xlr pinout

Title: Re: Tweed pre with XLR out
Post by: Merlin on April 03, 2026, 04:30:50 am

Looks OK. The output impedance will be roughly 1/gm, so less than 1k for a 12AU7. The ground lift switch is kinda redundant, just tie XLR pin-1 to chassis.

Title: Re: Tweed pre with XLR out
Post by: J3ona1 on April 03, 2026, 07:09:10 am

Thanks Merlin!