Pop noise when amp channel switching

[Mick C]

Hi All,
I'm getting a 'pop' noise in my Marshal DSL combo amp when I use the Boss GX-100 Amp CTL to channel switch the amp from Overdrive 2 to Clean (doesn't pop when switching from Clean to OD2). All effects in the GX-100 are off.

But If I don't use the Boss GX-100 to channel switch, and instead use the Marshall supplied footswitch, then no pops.

I've tried different cables between the GX and the Marshall - no difference.

Can anyone suggest why it might be happening, and what I can do / gizmo I can buy to cure it?
Thanks!

[Wonks]

What DSL amp (there are several current ones and I'm sure there are older models) and what model footswitch do you have for it?

If the Boss isn't doing what the Marshall footswitch is doing (which may involve diodes within the footswitch) then don't expect exactly the same results.

[Mick C]

I've had the DSL around 20 years or so and its footswitch is the 10013, where the left button is Clean/OD and the right button is OD1/OD2.

The Boss multi-effects switches channels ok, but does so with the pop that the Marshall footswitch does not.

I need to find some kind of work around because I can't live with the pop and it's therefore preventing me from using the Boss for channel switching

[forumuser931182]

It may that the Marshall pedal is using a simple mechanical switch whereas the Boss is probably using active components to perform the same function… maybe. Could use the Boss to drive a relay circuit to perform a proper mechanical switch.
Is the audio out from the Boss being switched/muted at the same time. Does the Marshall still pop if you feed the same signal to both inputs?

[Wonks]

Can't people answer a simple question FFS!

How long you've had it has no relevance!

[Mick C]

Can't people answer a simple question FFS!

How long you've had it has no relevance!

FFS?? A bit rude don’t you think??
It’s a JCM2000 DSL401. According to the web it was released in 1998 and discontinued around 2012.
I don’t know its exact age as I bought it second hand over 20 years ago, so it could date anywhere between 1998 and 2005-ish.
But having had it over 20 years it’s clearly not a current model, and is therefore definitely an older one.
Hope that helps.

[Mick C]

Is the audio out from the Boss being switched/muted at the same time. Does the Marshall still pop if you feed the same signal to both inputs?

It doesn’t sound like there’s any muting going on.
I’m not sure what you mean by ‘same signal to both inputs’?
The connection between Boss and amp is a single TRS cable that caters for all switching duties.

[Stratman57]

I have a GX 10, a slimmed down version of the GX 100, and there's no way it could be configured to change channels physically on an amp. I use it purely as an effects pedal, amp modelling provided by a VG-800.

It may be able to toggle between amp models, as the VG-800 can do, but it can't toggle between amp channels on a separate amp.

Regards, Simon.

[Mick C]

It may be able to toggle between amp models, as the VG-800 can do, but it can't toggle between amp channels on a separate amp.

Regards, Simon.

The GX-100 has a specific function for switching channels on a separate amp, and has a TRS output jack socket specifically for that purpose. Boss call it ‘Amp CTL’.
It’s the main reason I bought the GX-100 in the first place

[BigRedX]

I have a GX 10, a slimmed down version of the GX 100, and there's no way it could be configured to change channels physically on an amp. I use it purely as an effects pedal, amp modelling provided by a VG-800.

It may be able to toggle between amp models, as the VG-800 can do, but it can't toggle between amp channels on a separate amp.

Regards, Simon.

Looking at the back panel of the GX100 there is a socket labelled AMP CTL 1,2 which offers amp switching. The Roland GP8 multi-effects I used to own had a similar function. This is very useful since it allows amp channel switching along with patch changes on the device. Since it is labelled 1,2 I suspect it offers two switches on a TRS jack socket.

To the OP are you using a standard TS jack lead? It may be worth trying a lead with a TRS jack at one end but remove the connection to one of the tip or ring. You'll need to check the manual to see which contact activates which switch.

[BigRedX]

On other thing to check is to see if the amp is expecting a momentary or latching foot switch input and set the control from the Boss accordingly.

[ef37a]

I have no specific knowledge of the gear mentioned here but switch clicks are almost always caused by the presence of a tiny amount of DC in the signal path.

Tiny indeed, just a few mV can cause a very audible click and few tens of mV quite a POP!

The fix 'in circuit' is a DC isolating capacitor and a 'tie down' resistor. 10uF (at 22V) and 47k Ohms are typical values. There is no reason such a circuit cannot be fitted "outboard".

Ideally you would poke the circuit with a DC mV meter to determine the polarity of the DC offset then connect a capacitor accordingly. The other way is to buy non-polarized electrolytics.

Dave.

[Wonks]

As far as I can make out, when the Marshall footswitch is 'on' i.e. the LED for it lights up, then the switch is open circuit, allowing current to flow through the LED. When the footswitch is off, the switch contact shorts across the LED, linking the voltage fed from the amp to ground.

I believe it's wired like this:



So it may be that the lack of the LED in circuit for the 'on' state may be the cause of the popping.

I also can't find any reference to the maximum switching voltage and current of the relays in the GX100. I think (but I'm not sure) that the switching voltage is round about 12v, but no idea of the current.

From the DSL401 schematics I've found...
https://elektrotanya.com/marshall_dsl40 ... nload.html
...it appears the footswitch jack is JS1 in grid 3A on sheet 2. For one of the switches it seems to switching a transistor on/off which in turn is driving a DC relay. But it becomes difficult to follow after that (for me at least).

The lack of a small current flowing in 'off' might be causing an upset in the switching circuitry that's making its way back into the audio circuitry.

I can't think of anything that you could buy off the shelf, but you could make a DIY box up that had the LEDs and associated current limiting resistors in (they don't even need to be on show, just be wired across the switching lines).

[Mick C]

To the OP are you using a standard TS jack lead? It may be worth trying a lead with a TRS jack at one end but remove the connection to one of the tip or ring. You'll need to check the manual to see which contact activates which switch.

I’m using a TRS lead. It needs TRS to switch between Clean, OD1 and OD2 in any sequence. The switching works fine, it’s just the pops that’s a problem, whether the Boss switching is set to momentary or latching.
Thanks

[ef37a]

As far as I can make out, when the Marshall footswitch is 'on' i.e. the LED for it lights up, then the switch is open circuit, allowing current to flow through the LED. When the footswitch is off, the switch contact shorts across the LED, linking the voltage fed from the amp to ground.

I believe it's wired like this:



So it may be that the lack of the LED in circuit for the 'on' state may be the cause of the popping.

I also can't find any reference to the maximum switching voltage and current of the relays in the GX100. I think (but I'm not sure) that the switching voltage is round about 12v, but no idea of the current.

From the DSL401 schematics I've found...
https://elektrotanya.com/marshall_dsl40 ... nload.html
...it appears the footswitch jack is JS1 in grid 3A on sheet 2. For one of the switches it seems to switching a transistor on/off which in turn is driving a DC relay. But it becomes difficult to follow after that (for me at least).

The lack of a small current flowing in 'off' might be causing an upset in the switching circuitry that's making its way back into the audio circuitry.

I can't think of anything that you could buy off the shelf, but you could make a DIY box up that had the LEDs and associated current limiting resistors in (they don't even need to be on show, just be wired across the switching lines).

Can't see any relays Wonks https://el34world.com/charts/Schematics ... )_v.6_.pdf
and that's a good thing because I have played with them for amp switching uses and found it impossible to stop clicks and pops. May be possible with "Audio Grade" sealed relays?

IMHO OP needs to check the audio paths for DC with a digital meter...BUT! Have main VC at minimum before you start poking!

Dave.

[Mick C]

I have no specific knowledge of the gear mentioned here but switch clicks are almost always caused by the presence of a tiny amount of DC in the signal path.

Tiny indeed, just a few mV can cause a very audible click and few tens of mV quite a POP!

The fix 'in circuit' is a DC isolating capacitor and a 'tie down' resistor. 10uF (at 22V) and 47k Ohms are typical values. There is no reason such a circuit cannot be fitted "outboard".

Ideally you would poke the circuit with a DC mV meter to determine the polarity of the DC offset then connect a capacitor accordingly. The other way is to buy non-polarized electrolytics.

Dave.

I took a punt on Chat GPT and it also suggested the cause could be residual voltage in the signal path in the footswitch circuit.

It suggested a fix was to “make a TRS lead where one end is modified to add a 10kohm ‘pulldown resistor’ across the Tip to Sleeve and another one from Ring to Sleeve. This should safely bleed off any voltage to ground (sleeve)”

Does this sound reasonable?
Is it safe to try without causing any damage?

I can give it a try but I’ve no knowledge about specifying electrical components, therefore do I simply buy 10kohm resistors and that’s it, or do I need to specify anything deeper about the resistors when buying?

[Mick C]

An internet search found this. Sounds like a similar if not identical problem, and a solve.
The device is about £30 so I’ll give it a try

https://forums.prsguitars.com/threads/g ... ter.16449/

[BigRedX]

If you are good with soldering you could probably fit the missing resistors and LEDs in a standard plastic jack plug.

[ef37a]

I have no specific knowledge of the gear mentioned here but switch clicks are almost always caused by the presence of a tiny amount of DC in the signal path.

Tiny indeed, just a few mV can cause a very audible click and few tens of mV quite a POP!

The fix 'in circuit' is a DC isolating capacitor and a 'tie down' resistor. 10uF (at 22V) and 47k Ohms are typical values. There is no reason such a circuit cannot be fitted "outboard".

Ideally you would poke the circuit with a DC mV meter to determine the polarity of the DC offset then connect a capacitor accordingly. The other way is to buy non-polarized electrolytics.

Dave.

I took a punt on Chat GPT and it also suggested the cause could be residual voltage in the signal path in the footswitch circuit.

It suggested a fix was to “make a TRS lead where one end is modified to add a 10kohm ‘pulldown resistor’ across the Tip to Sleeve and another one from Ring to Sleeve. This should safely bleed off any voltage to ground (sleeve)”

Does this sound reasonable?
Is it safe to try without causing any damage?

I can give it a try but I’ve no knowledge about specifying electrical components, therefore do I simply buy 10kohm resistors and that’s it, or do I need to specify anything deeper about the resistors when buying?

If you PM me an address I will post a few values of resistors off to you.

10k might knock the signal back a bit, can't do any harm mind.

Dave.

[Wonks]

Can't see any relays Wonks https://el34world.com/charts/Schematics ... )_v.6_.pdf
and that's a good thing because I have played with them for amp switching uses and found it impossible to stop clicks and pops. May be possible with "Audio Grade" sealed relays?

Definitely a relay. RL1a "coil DPDT 12v" The coil is shown in row 2, below the line between column A and B. Wavy line in a thin rectangle (not how I'm used to seeing them drawn) and there's a 1N4007 snubbing resistor around it to reduce the back EMF spike.

[Wonks]

An internet search found this. Sounds like a similar if not identical problem, and a solve.
The device is about £30 so I’ll give it a try

https://forums.prsguitars.com/threads/g ... ter.16449/

That's for solving a very different problem.

[Wonks]

Why bother with 10k resistors when you can duplicate the footswitch and have an LED and a 1K resistor in series? You already know that is pop-less from using the Marshall foot switch.

[ef37a]

Can't see any relays Wonks https://el34world.com/charts/Schematics ... )_v.6_.pdf
and that's a good thing because I have played with them for amp switching uses and found it impossible to stop clicks and pops. May be possible with "Audio Grade" sealed relays?

Definitely a relay. RL1a "coil DPDT 12v" The coil is shown in row 2, below the line between column A and B. Wavy line in a thin rectangle (not how I'm used to seeing them drawn) and there's a 1N4007 snubbing resistor around it to reduce the back EMF spike.

Yes, got it! Not how I usually see them either. Maybe a 10uF cap across it would help as well?

Dave.

[Hugh Robjohns]

It suggested a fix was to “make a TRS lead where one end is modified to add a 10kohm ‘pulldown resistor’ across the Tip to Sleeve and another one from Ring to Sleeve. This should safely bleed off any voltage to ground (sleeve)”

Does this sound reasonable?
Is it safe to try without causing any damage?

Yes, and yes.

That Marshall schematic is a terrible example of the art of schematics, and really hard to follow...

But I suspect the popping problem is because of DC building up on the line since there's no LED and limit resistor to bleed it off.

The suggested 10K resistors between tip/sleeve and ring/sleeve should take care of that without affecting the DC control voltage too much.

But it might be that you need to go lower since the real footswitch uses 1k resistors.

Either way, there should be space to fit resistors into the plug if you're careful, or you could build a box with sockets either side to contain the resistors, and connect your pedal via that.

I can give it a try but I’ve no knowledge about specifying electrical components, therefore do I simply buy 10kohm resistors and that’s it, or do I need to specify anything deeper about the resistors when buying?

I can send you a couple of resistors if you want. Buying just two resistors is silly and the shipping charge would be ridiculous.

[ef37a]

I have 1/4W MF resistors sorted and a couple of 1uF caps, just need an addy!

Dave.