LOUD POP noise when switching between channels/voices

[zedzetzed]

Hi!

as of today, I am proud to be a part of the Blackstar community with buying my own Blackstar HT-60 Stage combo. I bought it second hand for a great price, however, when it arrived I noticed loud poping sounds when I am swithing the Voice in Clean channel, and also in Distorted channels. The only way the channel switching works without these awful noises is CLEAN - voice not pushed and D1 + D2 pushed voices. Also, the noise is there even with Standby on and it is getting louder when I turn the volume up.

Here is a video of it: https://youtu.be/IECjyev7Hak

I am really desperate and do not know what to do with it. I think it is a problem with speakers, because when I quickly tried it without the speakers connected (only with Emulated Output), there was no sound in the output when switching voices/channels. And here (https://www.flickr.com/photos/zedzetzed ... 7626961045) are photos of the speakers and its connection - I think it was done pretty badly regarding how it looks...

MANY THANKS FOR ANY TIPS.

Zdenek

[rschleicher]

Zdenek,

That's interesting, that you don't hear the popping sound when you listen to the emulated-out. That doesn't rule out a problem with the circuitry that's downstream from the emulated-out, but it does rule out (I think) the pre-amp circuitry.

I suppose some switching noise might be coupling into the speaker wires, although that seems a bit doubtful to me. One experiment you might try would be to disconnect the red/black twisted-pair wires that tie the two speakers together, and then run the main speaker cable to just one speaker at a time. (You'd need to plug the speaker cable into the 1x16 ohm jack, of course.) If the popping sound is still present, when using either speaker one at a time, that would tend to rule out a speaker problem, as well as the wires that had been between the two speakers. But if the problem is not present when trying one speaker at a time, or only presnet on one of the two speakers (used one at a time), that would support the problem being speaker, or speaker-wiring, related.

I am still thinking that it is a noise-coupling issue into a part of the circuit that is downstream of the emulated out, such as in the power amp section. (Although, I am not sure what to make of your statement that the popping noise is still there when on standby?) I think it is the case that the voice switches (or at least the clean channel voice switch) do something with the amount of damping/feedback of the power-amp (in addition to affecting their respective pre-amp sections). So that may be where the problem lies. Just speculating, obviously...

[thephantum]

Switching channels is mechanical...there is a physical switch that's thrown. Regardless of how quiet a switch is, it will make noise. However, that noise should be barely audible. So, that means it's either a bad switch or a coupling issue which is causing an normally inaudible pop to be amplified by the output stage. It doesn't sound like you have a problem with a single switch as you don't hear it in the EO AND it's happening regardless of whether or not it's in standby. So it's very possible that you do have some kind of noise coupling issue that's manifesting itself in power amp. That could mean a bad tube...

As you've already observed, that speaker wire is not the original and whoever put it on did a total hack job on it. Things like that always make me wonder what else did they try and "fix" and how bad did they botch it...

So the first things I would do is replace the tubes (potentially worn parts), properly bias the amp (tune up), fix those wires (an obvious problem), then look for any other shoddy work and fix it. If it still pops after all that, then a deeper dive will be needed.