To much gain
Hi there,
As anyone who followed my thread "looking for KT88 Circuits", will know I have recently completed a Parafeed adaption of the RH807 circuit. In its final form it just didn't have enough gain with my unity gain line stage preamp. I decided to add a ECC88 as a front end. Initially this introduced a huge amount of hum. A lot of search tracked it down to the input cable coming to close to a power transformer. It forced me to look at the grounding a lot and I am certain I have quietened it down a lot, even though before the ECC88 there wasn't much audable hum. The sound isn't quite as pure with the ECC88 added, but it has a bit more grunt.
The ECC88 has an anode load of 33K and a cathode resistor of 300K with a current of about 5mA and a B+ of about 320V. The cathode isn't bypassed, and neither is the cathode of the following ECC81 driver tube.
The only issue now is that there is just a tad to much gain. Is there any way of reducing it without using the brute force of a voltage dividing network ?
Shoog
Hi there,
As anyone who followed my thread "looking for KT88 Circuits", will know I have recently completed a Parafeed adaption of the RH807 circuit. In its final form it just didn't have enough gain with my unity gain line stage preamp. I decided to add a ECC88 as a front end. Initially this introduced a huge amount of hum. A lot of search tracked it down to the input cable coming to close to a power transformer. It forced me to look at the grounding a lot and I am certain I have quietened it down a lot, even though before the ECC88 there wasn't much audable hum. The sound isn't quite as pure with the ECC88 added, but it has a bit more grunt.
The ECC88 has an anode load of 33K and a cathode resistor of 300K with a current of about 5mA and a B+ of about 320V. The cathode isn't bypassed, and neither is the cathode of the following ECC81 driver tube.
The only issue now is that there is just a tad to much gain. Is there any way of reducing it without using the brute force of a voltage dividing network ?
Shoog