Crack as full function preamp
- Thread starter Ritchie
- Start date
Cool project!
I'm curious about the heater supply for the tubes, 2.8A is a pretty demanding load!
-PB
I'm curious about the heater supply for the tubes, 2.8A is a pretty demanding load!
-PB
Sorry for the late reply.
I decided to try the crack circuit for a preamp as I needed something to drive long interconnects into a low input impedance.
The circuit is the the Crack with speedball. The power supply transformer is the same except I'm using a CLCLCRC config. The chokes are Lundhals and are wired in common mode, so there is filtering in the positive and negative leg.
The output caps are Mundorf M-cap supreme 22uf. I am using a goldpoint selector switch and a hybrid resistor attenuator remote control from Bent Audio. http://bentaudio.com/index2.html
The circuit boards at the rear of the chassis are timers with relay contacts I am using as a home theater bypass. When the preamp is off, my home theater front speakers signal is switched directly to the pre outputs and when the preamp is turned on, after 30 seconds the contacts switch to my preamp output. This allows me to share my front speakers with my 2 channel and home theater. Prefer to not have the preamp on every time the family watches tv, tubes aren't getting any cheaper. The other circuit board is power for the timer boards and remote attenuator boards. I am using AC on the heaters with an artificial center tap biased at 1/4 B+. It is surprisingly quiet but I can hear a slight hum when a couple feet from the speakers. Will try a dc heater supply if this becomes an issue. This is a great circuit especially when driving a difficult load.
Thanks to the Bottlehead guys for providing such great stuff at a reasonable price.
Ritchie
I decided to try the crack circuit for a preamp as I needed something to drive long interconnects into a low input impedance.
The circuit is the the Crack with speedball. The power supply transformer is the same except I'm using a CLCLCRC config. The chokes are Lundhals and are wired in common mode, so there is filtering in the positive and negative leg.
The output caps are Mundorf M-cap supreme 22uf. I am using a goldpoint selector switch and a hybrid resistor attenuator remote control from Bent Audio. http://bentaudio.com/index2.html
The circuit boards at the rear of the chassis are timers with relay contacts I am using as a home theater bypass. When the preamp is off, my home theater front speakers signal is switched directly to the pre outputs and when the preamp is turned on, after 30 seconds the contacts switch to my preamp output. This allows me to share my front speakers with my 2 channel and home theater. Prefer to not have the preamp on every time the family watches tv, tubes aren't getting any cheaper. The other circuit board is power for the timer boards and remote attenuator boards. I am using AC on the heaters with an artificial center tap biased at 1/4 B+. It is surprisingly quiet but I can hear a slight hum when a couple feet from the speakers. Will try a dc heater supply if this becomes an issue. This is a great circuit especially when driving a difficult load.
Thanks to the Bottlehead guys for providing such great stuff at a reasonable price.
Ritchie
