Can I operate D-Class amplifier with disconnected power stage?

[lug]

For sake of pure curiosity I opened literally every amp and cabinet I ever had - it's pretty much safe as long as one pulls mains out and puts all things back together and has no remaining parts left


The amp is open from four sides so it's obvious I must make some sheet metal covers. I built five bass cabs, replaced speakers, soldered cables, I'll manage

In some designs, "pulling the mains" and then touching the wrong part can kill you or at the least, ruin your day. This is probably not the case with you small modern amp. Take this from a guy whose been zapped a couple of times in the far past.

 

[sokolasty]

Take this from a guy whose been zapped a couple of times in the far past.

fair point

 

[Tassieviking]

I usually joke that electricity only hurts till you pass out, but I can only still see because I wear glasses with safety lenses in them.
I have been blind and deaf once for 15-20 minutes when I opened a large electric panel and something shorted out in the cabinet, I had burns on my face and arms but only slight and left no scarring. I had holes in my shirt from melted copper from the cables melting and exploding, all because another electrician had done something stupid.
It was a fairly large electrical explosion with only 3 phase 415volts, the 415v is only 3 lots of 240v like we have at home. 220-240v can be fatal if it gets you, I think I am lucky having worked as an electrician my whole life with live machinery and not having any permanent injuries.
Just be careful and work safely, you can't see electricity but it has a nasty bite.
Make sure it is safe for other people who might touch the amp as well.

 

[Tassieviking]

It sounds to me you are ready to start making your own effect pedals as well, start with simple ones and work your way up to hard ones.
Get the kits with everything supplied to start with, then later you can just get the PCB and buy components separately.
There are some pre-amp pedal kits around that would work great for what you want

 

[abarson]

I think I get what you are proposing. You want to remove the amp section and enclose it to become a head that has the full digital effects included.
You don't need to disconnect the power section to do this. Keep it all as one unit.
You will need to enclose the open chassis. It will need ventilation and a speaker jack. I've no idea if this can be done safely.
I still think it's easier and safer to just get a multi-effects pedal that can be used without any amp or with any amp.

 

[sokolasty]

Status report

I am alive and not electrocuted - first success

I unplugged speaker, connected line XLR to Effects Return of other combo, noodled a minute or two and it worked

No smoke, no smell, nothing got warmer

Thank you all for your support and contribution

 

[Artman]

You're playing with fire.
Just buy a preamp or multi-effect with a built-in di.
There are many used ones for sale at bargain prices all over the place.

You could even build a small but excellent sounding pedal board with used boss pedals and an inexpensive di box for far less than your co-pay at the emergency room.

 

[sokolasty]

Luckily in Europe we pay our health insurance in tax (me: 5% of income) and do not co-pay

 

[trevcda]

I can't imagine the pre-amp section of any Rubble amplifier would be worth all that trouble, much less a small Rumble combo. My untrained eye thinks that there's more integration between these modular boards than you think. If you've got the amp to waste and this is simply an exercise in experimentation, go for it. Having once been really into circuit bending, i get it. But you can get better circuits and in a much better form factor by going with a purpose built device.

 

[Hasty]

Read the owner's manual from manufacturers that implement Class D: Gallien-Krueger, Mesa Boogie, Fender, Laney, Trace-Elliot, Traynor, etc. All of them make clear that the head can be used without a speaker load connected. This is by far more authoritative than some rando on a forum who won't even self-identify (FauxFrench).

The amount of butchery you are planning on a lowly combo really means you are pursuing the wrong solution. A preamp pedal would be a better solution.

As long as you do it correctly and follow manufacturer guidelines.

From the Acoustic Image website:

All Acoustic Image amps can be operated without a speaker load if required.

When operating without a speaker attached, turn the master level to zero (all the way counterclockwise). This will prevent the power amp section of the amp from being driven and protect it from damage.

 

[Hasty]

Luckily in Europe we pay our health insurance in tax (me: 5% of income) and do not co-pay

Regardless of who is paying for it... a burn unit is an undesirable experience. Especially with electrical burns.

 

[Plain Old Barry]

Luckily in Europe we pay our health insurance in tax (me: 5% of income) and do not co-pay

You also use 230v electricity.

 

[DJ Bebop]

You're playing with fire.

 

[J Wilson]

The thing that un-nerves me about these threads where one more guy 'got away with it', is somewhere down the line somebody else reads these kinds of threads, thinks he can do it too, inadvertently touches the wrong thing and gets hurt bad. I really wish these types of threads were only available to qualified professionals, if at all.

 

[agedhorse]

First of all, what happened to the power supply? Was that a repair or something that happened accidentally?

Just unplug the speaker, you got (and believed) some incorrect advice based on just a little bit of truth. There may be more integration between the sections than you realize.

I usually joke that electricity only hurts till you pass out, but I can only still see because I wear glasses with safety lenses in them.
I have been blind and deaf once for 15-20 minutes when I opened a large electric panel and something shorted out in the cabinet, I had burns on my face and arms but only slight and left no scarring. I had holes in my shirt from melted copper from the cables melting and exploding, all because another electrician had done something stupid.
It was a fairly large electrical explosion with only 3 phase 415volts, the 415v is only 3 lots of 240v like we have at home. 220-240v can be fatal if it gets you, I think I am lucky having worked as an electrician my whole life with live machinery and not having any permanent injuries.
Just be careful and work safely, you can't see electricity but it has a nasty bite.
Make sure it is safe for other people who might touch the amp as well.

Arc flash injury only hurts while you are conscious. You are very, very fortunate to have survived without even worse injuries imo.

I can't imagine the pre-amp section of any Rubble amplifier would be worth all that trouble, much less a small Rumble combo. My untrained eye thinks that there's more integration between these modular boards than you think. If you've got the amp to waste and this is simply an exercise in experimentation, go for it. Having once been really into circuit bending, i get it. But you can get better circuits and in a much better form factor by going with a purpose built device.

Agreed.

 

[sawzalot]

Oh but what could go wrong? Besides everything.

 

[bherman]

First of all, what happened to the power supply? Was that a repair or something that happened accidentally?

Just unplug the speaker, you got (and believed) some incorrect advice based on just a little bit of truth. There may be more integration between the sections than you realize.



Arc flash injury only hurts while you are conscious. You are very, very fortunate to have survived without even worse injuries imo.



Agreed.

@sokolasty heed this advice - @agedhorse is a high-level pro at amp design & repair, he has done so for many years at the best companies in the busiess, and is the Talkbass resident expert and guru to many of us mere players. When he says that something is not a good idea, I listen.

 

[mmon77]

I usually joke that electricity only hurts till you pass out, but I can only still see because I wear glasses with safety lenses in them.
I have been blind and deaf once for 15-20 minutes when I opened a large electric panel and something shorted out in the cabinet, I had burns on my face and arms but only slight and left no scarring. I had holes in my shirt from melted copper from the cables melting and exploding, all because another electrician had done something stupid.
It was a fairly large electrical explosion with only 3 phase 415volts, the 415v is only 3 lots of 240v like we have at home. 220-240v can be fatal if it gets you, I think I am lucky having worked as an electrician my whole life with live machinery and not having any permanent injuries.
Just be careful and work safely, you can't see electricity but it has a nasty bite.
Make sure it is safe for other people who might touch the amp as well.

You are indeed very lucky. I have to wear Arc Rated clothing at work every day, and even more PPE when I go into an electrical cabinet. But I do that happily rather than suffer the alternative.

I'm all for modifying and learning about amps and equipment, but you should have a certain level of respect and knowledge before you go poking around in line powered devices.

 

[SAlcott]

I asked Fender (specifically about Studio 40) and it's a no-go, answer was:
The Rumble 40 must always be connected to a speaker load.[/QUOTE]

Then don't do that.

 

[sokolasty]

First of all, what happened to the power supply? Was that a repair or something that happened accidentally?

Nothing happened to anything. Everything works perfect.

I knew, apparently wrong, that I could not use my Fender Rumble Studio 40 w/o speaker. This is why I searched options and disconnecting power stage was one of it. Now I was explained I can use my FRS40 w/o speaker, i. e. I need neither to disconnect power stage nor build dummy load.