hiss/noise from jcm clone

[subwaysavage]

Hello,

I recently finished building a jcm 800 2204 clone but found an annoying background hiss.

With the guitar unplugged, The hiss reacts with eq and master volume adjustments.
The hiss will only go away if i pull out the phase inverter and/or power tubes. If i bias the tubes really cold the hiss goes silent.

I poked around the components with a wooden stick and moved wires around but found nothing that affectes the hiss.

What can i do??


Thanks.

 

[funk1980]

Without hearing the actual hiss/noise it's hard to tell. But if it's the typical white/johnson noise, it might just be high value carbon (or metal film FWIW) resistors in series with a high gain stage, like huge grid stopper for example. But you'll have to come up with a bit more info the prevent this from becoming a guessing game. Schematics would be helpful.

 

[subwaysavage]

Schematic: http://site.triodestore.com/JCM8002204Stock.pdf

yes its white noise and it also occasionally picks up radio signals. i have the inputs shielded like the schematic stated. the noise is more prominent in the high sensitivity jack which is very annoying. when i put the amp on standby it fades off in about a second.

 

[JonSnell Electronic]

It won't be output issues. If you effectively switch off the EL34's by increasing the bias voltage, the hiss will be inside the crossover point and not so noticeable. Connect a 22k 1/4 resistor in series with the control grids and the feeds. Connect the resistors to the valve base pins 2 and 7 on the ECC83. Try grounding the grids, one each in turn to stop input noise. Have you a circuit diagramme?

 

[FabioZzzz]

It won't be output issues. If you effectively switch off the EL34's by increasing the bias voltage, the hiss will be inside the crossover point and not so noticeable. Connect a 22k 1/4 resistor in series with the control grids and the feeds. Connect the resistors to the valve base pins 2 and 7 on the ECC83. Try grounding the grids, one each in turn to stop input noise. Have you a circuit diagramme?

sorry mate.I can't understand were to insert the resistor. Do only have to solder a 22k resistor between pins 2 and 7 of the second 12AX7 ?

I am racing the same issue here . A 60 or 120 Hz at the pin 7 of the second 12AX7. It's Dave form is like a horizontal " { " .
It is a clone of a classic jcm800 2204 I have made.

Other than that the sound is great.


Thanks.

 

[boobtube]

Without hearing the actual hiss/noise it's hard to tell. But if it's the typical white/johnson noise, it might just be high value carbon (or metal film FWIW) resistors in series with a high gain stage, like huge grid stopper for example. But you'll have to come up with a bit more info the prevent this from becoming a guessing game. Schematics would be helpful.

Try reducing the 68K input resistor that goes to pin 7 of the first tube to 15K or so. If it is carbon comp, change it to metal film.

 

[AudioFreak88]

Try reducing the 68K input resistor that goes to pin 7 of the first tube to 15K or so. If it is carbon comp, change it to metal film.

Yeah drop the input good bit does help...very common for the Carbon's to go noisey as hell....Metal Film, while pretty damn quiet... adds bunch of damn brightness though to me...