I recently finished a 12B4 preamp that makes a nasty pop when turned on (SS recto, regulated HV & LV PSU, no standby switch). I have decided to add a simple 555 timer/relay circuit to mute the output for 45 sec upon start up.
I breadboarded the 555 timer circuit (see attached), powered it off my bench PSU and it worked great, no issues, nice 45 sec delay.
Next I installed long flying leads from the breadboard and hooked the circuit up to my preamp. At this point I powered the circuit off the amp’s 12V DC heaters.
When the circuit was installed in the amp the relay tripped almost instantly. I believe this is because my 12V heaters are “elevated” and referenced to +40V DC and not ground. The amp’s heaters are referenced to 1/3 of the B+ using a 300K-100K voltage divider. The 100K resistor is bypassed by a 10nF cap. I believe this 100K||10nF that is in series with the 555 timer circuit’s ground is what is screwing up the timing of the circuit.
What can I do to fix this issue? I was thinking of splitting the 300K-100K into 350K-50K-50K and taking the output from the 50K-50K node and powering the 555 circuit off that. Is there another way I can isolate the two circuits/grounds?
I breadboarded the 555 timer circuit (see attached), powered it off my bench PSU and it worked great, no issues, nice 45 sec delay.
Next I installed long flying leads from the breadboard and hooked the circuit up to my preamp. At this point I powered the circuit off the amp’s 12V DC heaters.
When the circuit was installed in the amp the relay tripped almost instantly. I believe this is because my 12V heaters are “elevated” and referenced to +40V DC and not ground. The amp’s heaters are referenced to 1/3 of the B+ using a 300K-100K voltage divider. The 100K resistor is bypassed by a 10nF cap. I believe this 100K||10nF that is in series with the 555 timer circuit’s ground is what is screwing up the timing of the circuit.
What can I do to fix this issue? I was thinking of splitting the 300K-100K into 350K-50K-50K and taking the output from the 50K-50K node and powering the 555 circuit off that. Is there another way I can isolate the two circuits/grounds?