Hiwatt Higain 50 - Channel Change Problem

[SteveHiwatt]

Hi all

 

Having a problem with my Hiwatt HiGain 50 combo. When I switch between channels I'm intermittently getting a loud crackle / hiss for a few seconds.

 

I've put a video of the problem below.

 

It doesn't happen every time so not sure what's going on.

 

Anyone have any ideas?

 

Cheers!

[WRGKMC]

Sounds like the channel switch is either loose or dirty to me. The switches that are used for channel selectors like that are multi pin slider switches. They contain multiple contacts. What I'd do is give it a shot of lubricating contact cleaner, the stuff you use for cleaning pots. (do not use zero residue contact cleaner or the problem will get much worse - the cleaner must be lubricating pot cleaner)

 

The tricky part is getting the liquid into the switch so all contacts get cleaned by it. You don't want to have the spray go all over your circuit board and cause issues.

 

I'd normally remove the amp from the chassis, then set the chassis so the switch is in the Vertical position. Then drip the liquid down the shat where the button is by carefully squirting the cleaner. Then work the switch until all the contacts have the liquid on them and your noise issues should go away.

 

I would suggest you get a footswitch and use it for changing channels. Those front PC mount channel switches are made of plastic and unfortunately they don't always hold up very well. When you use a foot switch, the front panel switch will remain stationary, either in or out so once its clean it wont be used and therefore should get any more worn then it is.

 

Its better to use a footswitch in any case. Reaching down to press a button isn't something you can do without interrupting your playing. they expect players to use a foot switch and don't need to use a super heavy duty front panel switch. Nearly all of the channel switches you see on amps are the same plastic junk. They date back to the old tape recorders. The Record/Playback buttons in recorders often had these long multi pinned slider switches that would go bad. Man I must have fixed a thousand of those things. I'd take them apart, tighten the contacts and put them back together with my fingers crossed hoping it would work. Your better recorders used multi contact relays which lasted forever. The cheap gear uses the sliders and they just don't hold up very well.

 

Spend $15 and buy a foot switch and your problems will be solved.

[SteveHiwatt]

Hey

 

Cheers for that info, I should have clarified that I do actually use a footswitch for normal use though and get the same problem.

 

I just used the switch in the amp for the purpose of the video.

 

With that in mind do you still think that using contact cleaner on the switch could still solve the problem?

 

Cheers again!

[WRGKMC]

Maybe not then. What I do hear sound like you have an echo unit is an effects loop. When you switch channels the echo is making the problem sound worse then it actually is.

 

Questions.

 

1. How noisy is it when you have no guitars plugged in, nothing in the effect loop, and any reverb turned off?

2. If you unplug the foot switch and only use the panel switch does it still do it.

3. If you turn the channel volumes all the way down, including the tone and gain knobs down, does this happen. You can try this with the master volume up and down as well.

 

The reason for question #1 is, is you are using pedals before the amp or in the loop there may be DC voltage leaning from the power supplies of those devices into the signal path. We want to eliminate that possibility by removing those from the path. Vintage pedals often have this issue due to their design. A buffer or filter to remove the DC may be an option.

 

Reason for #2 Foot pedals often have DC voltage for the on off LED's. If you are using a generic pedal it may not have the DC voltage routed and its backing up into the amp or isn't being switched properly causing your pop.

 

Reason #3, we want to turn the volumes off to see if there's DC voltage or noise contaminating the signal path.

 

 

This amp may use power relays for switching. I looked at the schematic and its hard to say for sure. These tiny relays look like square boxes on the board. They use an electromagnet to open and close switches. If the switches inside these tine relays get dirty or pitted from arching they can create allot of static noise. When you close that switch in the video, it sounds like the noise is delayed. If they are relays this may account for the delay as they mechanically activate. If its an echo in the effects loop then it may just be the echo that's causing the delay I'm hearing.

 

In any case, an answer to those questions will help me zero in on where the problem is coming from.

 

The schematic also shows some photo conductor devices that come after the switching. Hopefully they aren't involved. Those kinds of devices probably wouldn't cause the noise and when they do go bad, they don't suddenly start working again.

 

For now I think its DC contaminating your signal path. Until we rule that out, we cant assume anything yet. The sound did sound like a bad switch. Its still may be that switch because the foot switch simply runs in parallel to it. The DC that's sent to the footswitch LED's may be causing dirty contacts in the front panel switch to arc out. We just have to rule the easiest and most common issues out first to narrow down the possibilities.

 

[SteveHiwatt]

Here ya go(answers in capitals)

 

1. How noisy is it when you have no guitars plugged in, nothing in the effect loop, and any reverb turned off? IN THE VIDEO THE GUITAR WAS CONNECTES DIRECTLY TO THE AMP, NO PEDALS WERE IN THE CHAIN OR THE LOOP

2. If you unplug the foot switch and only use the panel switch does it still do it. YEAH, THE FOOTSWITCH WAS UNPLUGGED IN THE VIDEO

3. If you turn the channel volumes all the way down, including the tone and gain knobs down, does this happen. You can try this with the master volume up and down as well. IVE JUST TRIED AND TYPICALLY ITS NOT DOING IT AT ALL AT THE MOMENT SO NOT SURE.

 

I did take a look at the circuit board in the amp and it does look like the solder around the channel select switch is a bit darker lookin g than other solder and seems to have somekind of hard clear coating, could be glue I guess though.

 

In the past the noise has happened when the footswitch was connected and when it wasn't, it's also happened when I've had pedals in the chain and when he guitar is plugged directly into the amp.

 

I've been using the Hiwatt footswitch that came with the amp which does have a fault in the reverb switch, this doesn't activate/deactivate the reverb when it's connected but as I said, it happens regardless of whether the footswitch is connected or not so don't think it's the footswitch.

 

The fact that it's intermittent is really annoying too!

[onelife]

I suspect either a direct or indirect low voltage power supply issue. As has been pointed out, there are some optical switches in the signal path. Although the tone stack is shared it is configured a bit differently for each channel and there are optical switches involved in that circuit.

 

If the power supply feeding the LEDs in the optical switch is noisy then there is a possibility that the noise will get introduced into the signal path. If this amplifier uses modern construction then there will be some computer style connectors and ribbon cables inside. If these connectors are not making good contact then that could be where the noise is being introduced.

 

If I was working on this amp, I would carefully reseat all the connectors - after discharging the power supply by grounding pin1 of V1 with a jumper WITH THE POWER CORD REMOVED - then testing it for a while both outside and inside of the case.

 

 

btw, do you have the same problem if you use the front panel switch with the footswitch disconnected?