WAHOO new hiss in bypass

[henrykaiserguitar]

My Wahoo has been on my board for almost a year. It never hissed in bypass. And I understood that it is true bypass.
Suddenly something changed and it hisses in bypass. On batteries or external power, the hiss is the same.
Have not updated software or anything. Have not changed any settings and I have been using the same 5 presets that I wrote for a year.
I tried the pedal alone with a guitar and amp = same hiss in bypass. I am sure this his was not there before last week. Any suggestions? HK

just to be clear I mean bypass to be when the stomp button for bypass has been switched to bypass

[james]

Oh, that is strange.

If you remove the batteries and PSU does it stop hissing? It is true bypass, so the signal path is the same with no power, or when powered-up and in bypass mode.

If there is noise only when powered, is there anything else in the signal chain? Does it still happen if all you have connected is guitar -> Wahoo -> amp?

If the noise only happens when powered, and happens with nothing else connected, all I can think of is some problem internal shielding that separates the digital side (control panel etc) from the analogue electronics. Or maybe some kind of short circuit... it's hard to be sure, I've never heard of this before.

[henrykaiserguitar]

if one removes the batteries with no ac it stops hissing and passes clean signal

however I just ran a bunch of tests and discovered that this is the case in bypass

1) no battery no AC no hiss

2) no ac low batteries but not low enough so that effect does not work fine hiss in bypass

3) no ac freshly charged batteries no hiss

4) ac no batteries hiss in bypass

5) ac low batteries hiss in bypass

could something be funky with the power supply circuit internally that is causing this?

[james]

Thank you for the detailed measurements. It is certainly strange that it is hissing in bypass mode.

Have you noticed any problems when not bypassed? Does it sound normal? Is the noise level normal, or is it higher?

It's certainly easy to check the power supplies if you have a multimeter, then open the bottom of the Wahoo -- I can give you details if you want to check this.

[henrykaiserguitar]

it is perfectly normal and its usual excellent self
when not in bypass

I am about to be on the road until the 18th
and can do voltage check then
(I can't seem to find my multi-meter around the studio it's probably under a couch or something)

I have never updated the firmware, since I got the pedal I keep meaning to do that

I suppose it could be the external wall wart that I am using the tests
but maybe not since the unit is not supposed to work fine, but hiss in bypass when the battery set is lower than freshly charged

[henrykaiserguitar]

it seems that it has the hiss if I power it 400 MA which is what the power supply on my board is.....
I know it's supposed to be 500 MA
if I power with a 2AMP 9V supply (enloop) no hiss
if I power it with rechargeable Li batteries HISS even if batteries were just charged
if I power it with fresh alkaline batteries there is no hiss for about an hour then the hiss begins

so I guess it's just a current required issue?

it also suddenly developed a new issue when powered with the Li batteries or 400 MA supply
which is that the bypass stomp switch does nothing will not turn processing on or off
it will turn the unit on if I toe down the pedal but then it won't turn off

now... my unit did not do these things for the first year
and I used it A LOT on many gigs and recordings
it worked with the 400MA power supply
and it worked with the li batteries
so MAYBE SOMETHING CHANGED IN THE UNIT? what do you think?

I just reinstalled the newest firmware and that had no effect

HK

[james]

I agree it sounds like a power problem.

If you can open the Wahoo and measure a voltage, it may show the cause of the problem (if my guess is correct).

When you open the Wahoo, you can see the back of the analogue PCB (the big one). R123 (highlighted on the attached drawing) is where you need to measure. "Ground", or 0V is the big fat track at the top (one side of C23 is touching it). You want to measure each side of R123 to see what the voltage is.

What I am guessing is some problem with that resistor. It is used to filter the power between the digital and analogue circuits. The voltage on each side should be similar. If there is too much voltage loss across the resistor the analogue circuits won't have enough power and will get very noisy. It will also cause problems with the relays switching.

If this is the problem, a new resistor will fix it.

Alternatively, if you send it back to me I will check it and make sure it's working correctly for you.

[henrykaiserguitar]

will do and report
will check with proper external supply and with batts
off to some gigs until THURS will check then

thank you! HK

[henrykaiserguitar]

with a proper external proper power supply:

we get 0.131 V drop across the resistor
8.35 and 8.22 are the two sides' measurements

what does this tell you?


with brand new AA alkaline batteries: same voltage drop and measurements


identity-wise, my left board says v 1.24a

[james]

This suggests that resistor is working fine... when bad the voltage drop is very high so the "output" is around 4V or less, so you get lots of noise on the analogue side.

It might be best to return it for repair... but I will think about it some more and reply to you again tomorrow.