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Hi there,

just ordered "The brick" from the US. Now I need to change the internal voltage switching from 110V to 230V as I live in Germany. I just had a look inside the unit but I cannot find any switch for my purpose.

Any help ?



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Kev Sun, 01/15/2006 - 18:20

IF the power transformer has dual primaries then it may be possible to re-configure the input

sorry I just can't see enough detail to be sure
you need a tech to look inside for your

please be careful of the 220 / 230 mains power

There was a thread here with better inside pictures but I can't find it right now

anonymous Mon, 01/16/2006 - 08:38

Voltage switch

Thanks for your posts !!! As our bassplayer is a great tech engineer I'll ask him to do it. What I do not understand is why Groove Tubes claims that Pirmary Voltage is switchable inside; it's not that easy I think as there's no real switch at all...

I'll tell you if I proceed...



anonymous Tue, 01/17/2006 - 06:05

...have asked Groove Tubes last week already

I've asked GT last week but didn't receive any answer 'til yesterday. They've got the solution, here's their statement:

"Find the two inside wires (RED, BLACK) off the power transformer
follow them up to the power switch and cut them off at the power switch
being carefull not to cut the other black and red wires.
Now strip and twist them together.
Also insulate.

Done.... now you have just converted it from 120v to 230volts"

Will check this out today & inform ya on the result...[/code]

robbi Wed, 07/10/2019 - 08:57


I have tried to convert the Brick I have from 115v to 230v using this method, however, blowing fuses (250mA, as per the back of the unit). It's entirely possible that I've messed up the conversion some how--do you have any pictures of how you did it?

Here is how I did it:

(please excuse crappy job).

These are the "top" pair of red and black from the transformer.

Another view of the top of the xformer:

Any help is appreciated!

Many thanks,

Boswell Wed, 07/10/2019 - 09:48

The 2006 post that quoted the GT instructions said find the inside red and black wires at the transformer and cut these two off the switch, then join the free ends together. Your first photo shows two wires taped together, but there are other wires in the photo, so it's hard to tell for certain whether the taped pair are a red and a black. They are presumably wires that used to go to different sets of contacts on the switch. Please confirm.

I take it that GT meant that the two 120V mains windings are wound layered on top of one another, and that the modification effectively creates a single continuous 240V winding. If so, you would get the order from outside inwards (or vv) red-black-red-black, so by "inside" they mean "middle". What they don't say is whether red and black sleeving has been put on each winding to denote the start and finish (normal) or whether there is a winding with red sleeves and another with black sleeves (crazy).

I would hope and expect that each winding has a red and a black sleeve. The easiest way to check this is to disconnect the mains and temporarily undo your join. Measure continuity using a battery-powerd Ohm-meter of each red-black pair, where you should find that a winding will be something like 20 Ohms. There should be no continuity shown from one winding to the other with your join un-made.

robbi Sat, 07/13/2019 - 03:12

Yes, thanks for the help with it.

I have a different issue with it, sonically; it sounds very thin and lacking bass, neutered, compared to a Focusrite Trakmaster. I have swapped the 12AX7, waiting on a 12AU7 to be delivered to check it.

Is there any thing else I might be missing if the tube swap doesn't help? Maybe time to take to a tech...

Many thanks,

Boswell Sat, 07/13/2019 - 03:33

OK, a few questions: Is this "thin" sound heard when you are using the microphone input or the DI? If microphone, what model of microphone, and what's the sound source? What are you feeding the output of The Brick into? What type of cabling are you using at the input and output of The Brick?

The reason for all this probing is that it is technically possible that your connecting 240V to a 120V mains winding on the transformer caused some over-stressing of internal components for the few tens of milliseconds before the fuse blew. This is not very likely, but it would be good to eliminate external effects first.

robbi Sat, 07/13/2019 - 06:02

It's both the instrument input and the mic input that are sounding this way. I've fed the mic input with a speaker simulator (XLR -> XLR) coming from my amp/attenuator, and then the DI with guitar (TR instrument cable), and an iMPC app, from my phone. I am sending all these signals into a Tascam 388, which was leaving the Brick with an XLR -> TRS cable into the line input of the mixer. All of these signals sound thin, especially in comparison to the Trackmaster, hooked up and used in similar ways to the Brick.

Many thanks,

Boswell Sun, 07/14/2019 - 05:29

Well, that's interesting information. I would have said the input transformer was a suspect for this effect, but since the DI input does not go through the transformer or the first valve stage, that's ruled out.

The only repair work I've done on a Brick that had similar symptoms to those you describe was to de-gauss an input transformer. This was after an intermittent XLR cable short when phantom power was applied caused core magnetisation. However, in that case there was evident distortion at higher amplitudes, which you haven't mentioned.

How confident do you feel about prodding around inside the Brick with a multimeter and (possibly) an oscilloscope? I must warn you that there are some lethal voltages in there.

robbi Sun, 07/21/2019 - 07:00

Thanks Boswell--I would give it a shot with a multi meter, if needs be! It's about time I took a deeper dive into some equipment. What is the purpose of an oscilloscope in the instance? If I need it to generate a tone, could I do that another way?

Today, I have de-mag'd/de-gaussed the transformers and there's been no change in the sound. Popped in a different 12AU7 as well.

Here's a quick video of the difference in DI'd sound compared to a Trakmaster; might illuminate something else:

Many thanks,

paulears Sun, 07/21/2019 - 07:17

it's to see what waveforms look like - if you need to inject a tone, then that comes from somewhere else. Handy to see the distortion you can often hear. Let's you also detect unwanted DC on lines that shouldn't have it, and of course measure voltages. Withe the probe, you can follow the signal in to out, and this is a great way of detecting which stage is the culprit for things like noise and distortion. A handy tool.

Boswell Sun, 07/21/2019 - 11:00

robbi, post: 461544, member: 51638 wrote: Is an oscilloscope app, say, on my laptop or phone a good working alternative to the real deal?

No, an app like that can only work on digitised waveforms and cannot use probes that connect to different points in a real circuit. Some scope apps can be switched to use the mobile's microphone as an input, but these are quick-look toys that give you a low-fi representation of acoustic sounds.

The guitar in your video is making the sort of sound you get by plugging a piezo pickup into a low impedance input. However, it can't be that if other sources all do the same. It's more likely that a similar effect is replicated further along the circuit inside the Brick, for example, an inter-stage coupling capacitor has failed through having had the momentary over-voltage.

Sorry to appear to be judging you, but from what you say, I'm going to recommend that you do NOT start probing around on the circuit board of the Brick when it is powered up. I'll send you a pm.

robbi Sun, 07/21/2019 - 12:03

Boswell, post: 461549, member: 29034 wrote: Sorry to appear to be judging you, but from what you say, I'm going to recommend that you do NOT start probing around on the circuit board of the Brick when it is powered up. I'll send you a pm.

Aha, that is a completely fine judgement to make and I agree--maybe one day I'll be up to the task.

Thanks very much for all the help thus far! Will PM.

paulears Mon, 07/22/2019 - 01:09

I actually disagree with this. Heath and safety rules, and an assumption of lack of common sense is killing experimentation and people's access pathways into science and engineering.

Of course there is a risk, and yes, you could die. When I was a teen, I soon learned that 240V hurts, badly. I quickly learned which things inside electronic items hurt, and most critically, why! Prodding around inside is how most engineers learned their trade. Nowadays, you go to university having never even held a soldering iron, or knowing where test probes go - and they spend the first few weeks teaching you safety before they can let you loose - that's your formative years gone before you even try.

Can you imagine discovering electricity, or radiation, or chemistry without risk? If you stick your finger in and it hurts you don't do it again. If you do it while grabbing a radiator with your other hand, you'll probably die. Back in my youth we fixed TV and radio sets by banging valves (tubes) with a screwdriver, and then seeing which one made the fault better or worse. Powered up, working and dangerous. Nowadays, we aren't allowed to do dangerous things. I'm not sure this is actually sensible. We learn from mistakes, and statistically, electrocution is a very rare cause of death. The odd burn I can live with. In a way - a scope that doesn't blow up when mains voltage is applied instead of microvolts is a great diagnostic tool.