I'm using a tube preamp into a Coleman 3-1 line switcher then into a new, cathode biased, homemade by veteran builder, 4 el34 power amp (and/or 2 other amps).Each amp has it's own speakers.
When I switch out the line (or or even unplug the RCA input cables at the amp) to the el34 amp, it hisses like white noise , not a ground noise, more of an input level issue I think.
As long as line level inputs are plugged in and/or active it is very quiet but I can't use my system switching set up the way I'd like to without having to turn the amp off.
I've also tried it with a stepped passive attenuator in line and the el34 amp doesn't like that either, it's noisy like an old radio on all but a couple stages of volume.
The other amps (one being a rebuilt Magnavox 175) are totally quiet when switched out or when using the passive volume control.
Can anyone help me trouble shoot this or recommend what steps I can take, either with outboard gear or internal amp mods, to remedy this input level devil? Much Thanks!
When I switch out the line (or or even unplug the RCA input cables at the amp) to the el34 amp, it hisses like white noise , not a ground noise, more of an input level issue I think.
As long as line level inputs are plugged in and/or active it is very quiet but I can't use my system switching set up the way I'd like to without having to turn the amp off.
I've also tried it with a stepped passive attenuator in line and the el34 amp doesn't like that either, it's noisy like an old radio on all but a couple stages of volume.
The other amps (one being a rebuilt Magnavox 175) are totally quiet when switched out or when using the passive volume control.
Can anyone help me trouble shoot this or recommend what steps I can take, either with outboard gear or internal amp mods, to remedy this input level devil? Much Thanks!
Posting the schematic of the EL34 amp is probably going to help. What does the input circuit of that amp look like?
Yes, a circuit will help. Two possible causes: a high value input resistor is generating noise but this is attenuated when a low impedance input is connected; the first stage is oscillating and needs a grid stopper.
Thanks for the replys.I'm not a tech and I don't have a schematic but this thing is pretty simple ptp wired etc.Is a grid stopper something a novice could install?
If it's an impedance issue do you think using a line buffer between the Coleman and the inputs would send the correct impedance value to the amp?
If it's an impedance issue do you think using a line buffer between the Coleman and the inputs would send the correct impedance value to the amp?
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