Carl Martin Chorus II hum issue

I have Carl Martin Chorus II, and I'm having a small hum issue. I know
this pedal should excel in clean sound, that's why I would like to check
on this issue.

It works fine except that when I stop playing I can tell a very small
hum even when the guitar volume is turned OFF. My guitar chords are
very of high quality. I have tried to swap the power cord polarity or
move it to a different outlet but it made no difference, the small hum
remained. I have other pedals such as BOSS, but they do not give such a
hum.

I am not sure if this hum is expect and within specs or if anything is
wrong. The pedal's ON/OFF switch is not a true bypass and does not
allow me to completely get rid of the hum.

I am using Fender Black Face Deluxe Reverb tube amp.

I usually use the pedal as MONO, and my measurements are MONO as well
(i.e. one input at a time). I have measured its output using
oscilloscope and here's what it's like:

When guitar was played to it, its output was about 300mv pp.

When its input was short (guitar volume set to zero):

Output L:
has 5-8mv DC offset and some <1mv pp hum 50Hz signal.

Output R:
Has 2mv DC and has 100kH-300kHz (beyond our hearing spectral range)
slowly varying periodic comb signal of amplitude 3mv pp when L chorus is
selected or when R chorus is selected and is OFF. It also some <1mv pp
hum 50Hz signal.

Does anyone know if that's normal, and what could be done to improve that?

Does anyone know which output is the "mono" one (should such exist)?

Thanks!

Gonzo <Gonzo@nospamplease . com > schrieb:

Hi!

Can you use it with batteries? Is it then still humming?

greets
Jürgen
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Juergen Klein wrote:
> Gonzo <Gonzo@nospamplease . com > schrieb:
>
> Hi!
>
> Can you use it with batteries? Is it then still humming?
>
> greets
> Jürgen
No,
It does not some with battery option, it uses internal 12v power supply,
and they say it can suck up a battery within 30 minutes.

Gonzo <Gonzo@nospamplease . com > schrieb:

>Juergen Klein wrote:
>> Gonzo <Gonzo@nospamplease . com > schrieb:
>>
>> Hi!
>>
>> Can you use it with batteries? Is it then still humming?
>>
>> greets
>> Jürgen
>No,
>It does not some with battery option, it uses internal 12v power supply,
>and they say it can suck up a battery within 30 minutes.

I think the internal power supply is not filtered enough. Add some
caps or better a LC-Filter to the supply.
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