hi there,
i need some help, i built a EL34 amp with ECC83 pro-amp for my quitar.
at the 1st level (the ecc83) i`m try to built an equalizer (bass&treble) and there is hum.
the input is the A point
if i move the input on the 2nd gril (pin 7)of the tube, the amp play`s perfect,without hum.
i bielive that i got some kind of feedback betwin 2 levels of ecc83.
how can i remove it....
any suggestions?
i need some help, i built a EL34 amp with ECC83 pro-amp for my quitar.
at the 1st level (the ecc83) i`m try to built an equalizer (bass&treble) and there is hum.
the input is the A point
if i move the input on the 2nd gril (pin 7)of the tube, the amp play`s perfect,without hum.
i bielive that i got some kind of feedback betwin 2 levels of ecc83.
how can i remove it....
any suggestions?
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I presume that you mean that the input is at the grid of the first valve (not the plate) when you are getting hum.
There is something strange about that circuit. Is it really a 5.6k plate load resistor on the first triode. Seems way too low for a 12AX7. And where does that capacitor on the grid of the first valve go? Some kind of global feedback?
There is something strange about that circuit. Is it really a 5.6k plate load resistor on the first triode. Seems way too low for a 12AX7. And where does that capacitor on the grid of the first valve go? Some kind of global feedback?
There should be no global feedback in circuits which contain bass-treble controls.
The hum problem might be due to ground loops or a poor layout in the tone control circuit. If the wire runs are long, shielded cable is absolutely necessary because the tone control circuit impedances are high.
A full schematic of the preamp would help.
The hum problem might be due to ground loops or a poor layout in the tone control circuit. If the wire runs are long, shielded cable is absolutely necessary because the tone control circuit impedances are high.
A full schematic of the preamp would help.
shielded cables are already used.
something i didnt said ,i `m not use pcb for the equalizer. just wiring the compoment on ponts.
and are as short as i can.
something i didnt said ,i `m not use pcb for the equalizer. just wiring the compoment on ponts.
and are as short as i can.
looking at this schematic it is not correct for a guitar amp.
input impedence must be stabilized first. the volume knob should be after the first tube stage. this looks like a hi-fi amp the way the input is set up.
a very good example is :
http://www.drtube.com/schematics/vox/ac501976.gif
and
http://www.drtube.com/schematics/gibson/ga-1rt.gif
and
http://www.drtube.com/schematics/marshall/jtm45tr.gif
input impedence must be stabilized first. the volume knob should be after the first tube stage. this looks like a hi-fi amp the way the input is set up.
a very good example is :
http://www.drtube.com/schematics/vox/ac501976.gif
and
http://www.drtube.com/schematics/gibson/ga-1rt.gif
and
http://www.drtube.com/schematics/marshall/jtm45tr.gif
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If you bypass the first stage cathode resistor it will help reduce hum.
But for a guitar amp you would be better to choose a different circuit that is designed for guitar rather than hi-fi.
But for a guitar amp you would be better to choose a different circuit that is designed for guitar rather than hi-fi.
Not really. Nothing to say a Bandaxall tone control can not be used in a guitar amp. In fact Traynor and other amp makers use it. As long as the values are selected for guitar frequencies all is good.
Why do you have the 0.1uF cap C127, if I read it correctly, from anode 2 (point B) to feed the amplified signal back into the tone circuit?
Also, if doing the above removes the hum then in my opinion you have layout issues with the tone stack.
By the way this is a very weird connection of a Baxandall tone stack! Have not seen it connected this way before!
Also, if doing the above removes the hum then in my opinion you have layout issues with the tone stack.
By the way this is a very weird connection of a Baxandall tone stack! Have not seen it connected this way before!
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