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Can A Mic Pre Kill You?

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Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 3:02 pm
by ManFromGlass
I can do basic soldering and don’t have an electronics background. My 15+ year old ART mic pre with a tube in it now only works with the Gain at 100%. The unit cost $150 back then and it’s not worth taking to a tech for repairs. A tech friend suggested WD40 on all pots while the unit is turned on to see if it helps.
I’m asking if the unit could be as dangerous as a tube guitar amp which I understand can give one quite a shock if you don’t know what you are doing. I figure I could open it up to take a peak at solder connections while the unit is unplugged. Should I let it sit for a few minutes while some component drains itself of a charge? Anything else to watch out for?

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 3:32 pm
by DGL.
It will all primarily depend on what the plate voltage of the vacuum tubes are and if it is mains powered as to whether or not there are high voltages inside the unit. Suppression and primary side capacitors can retain quite the charge if no bleed resistors are fitted, and yes I know from experience.
As such any large higher voltage capacitors should be drained before going near them (using a high value resistor (470k 0.5W?) is usually the best option).
If you have ever removed a plug, touched the pins quickly afterwards and got a "nip" off them then you have experienced this, and it is why a lot of suppression capacitors will have bleed resistors connected across them.

Might be worth asking the question over at the vintage radio forums, vintage-radio.net , as valve circuits are their bred and butter.

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 3:46 pm
by Sam Spoons
I've managed to download a couple of ART Tube Preamp schematics and they both show low voltage 'HT' supplies (63V electrolytic caps in the grid circuit). A PSU for another supplies 5.7VDC and 33VDC in addition to 48V (for spook power). However I don't know if any other ART preamps use 'proper' HT to the valve. Which model do you have?

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 3:50 pm
by Murray B
Like Sam I'm fairly convinced that the valve is run at a fairly low voltage, but I'm not qualified to advise you on any potential risks.

However don't use standard WD40 to clean the pots it's got the potential to do more damage than good (although WD40 also make a contact cleaner so this can confuse the issue and perhaps me in this case). There are special chemicals for cleaning pots and faders that will clean and lubricate them.

For example:

https://caig.com/fader-f-series/, other manufacturers make similar stuff.

It's not super cheap, but you can use it to maintain the rest of your gear too.

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:01 pm
by Sam Spoons
+1 for Caig products, expensive but a can will last for years.

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:05 pm
by DGL.
Contact cleaner with remove any lubrication form pots/faders and as such the proper fader cleaning/lubing products should be used, I know my DX9's sliders did not take kindly to contact cleaner, and are no longer as smooth as they should be, but then they are knackered anyway.

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:09 pm
by Tomás Mulcahy
Servisol Super 10 is much easier to purchase in Europe, effectively the same thing as Caig deoxit.

That would be the first thing to do, clean the pot. The ART is actually a nice pre.

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:15 pm
by zenguitar
Can a mic pre kill you?

Depends on how high it's dropped from :D

Andy :beamup:

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:22 pm
by Sam Spoons
No need to drop, overarm from behind should do it :D

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 4:34 pm
by Eddy Deegan
DGL. wrote: I know my DX9's sliders did not take kindly to contact cleaner ...

DX9! There's a blast from the past. My first 'proper' synth and one of only 2 keyboards I've ever sold (not because I wanted to, I had to in order to pay some bills at the time). I don't think I've ever seen it mentioned in casual conversation. Not generally well regarded due to it being compared to, and significantly less powerful than, the DX7 but there was a lead patch I programmed into it (pretty much by happy mistake) that to this day is the best synth lead in my head I've ever heard and I have a secret love for it even though I've not owned one for 30 years.

Thanks for the nostalgia! :thumbup: :thumbup:

Re: Can A Mic Pre Kill You?

PostPosted: Sat Mar 06, 2021 7:47 pm
by CS70
zenguitar wrote:Can a mic pre kill you?

Depends on how high it's dropped from :D


Haha, that's the first thing that came to my head as well when reading the title! :lol:

Re: Can A Mic Pre Kill You?

PostPosted: Sun Mar 07, 2021 2:21 pm
by ManFromGlass
One of the joys of the English language!
I have the ART Tube Pac. I can see 1 small tube through a little window. It says - Warning do not open, shock hazard. It has a proper mains cable, no wall wart. It could be 20 years old. It’s a half rack unit, quite solid and would do some damage falling from a modest height. :D
I better look into the Craig vs WD40 a bit more before proceeding.

Re: Can A Mic Pre Kill You?

PostPosted: Sun Mar 07, 2021 2:34 pm
by desmond
Eddy Deegan wrote:there was a lead patch I programmed into it (pretty much by happy mistake) that to this day is the best synth lead in my head I've ever heard

And if you'd done it on the DX7, it could have even been velocity/aftertouch sensitive... :headbang:

The DX9 had very few redeeming features, in comparison to the DX7 (which was all everyone did, as the DX7 was a genuine game-changer as we all know).

Even the DX21, effectively the DX9's replacement, was quite a bit better...

Re: Can A Mic Pre Kill You?

PostPosted: Sun Mar 07, 2021 2:41 pm
by ManFromGlass
Ahh! :thumbup:
I still have my DX21 in working condition. Good memories of ancient gigs.

Re: Can A Mic Pre Kill You?

PostPosted: Sun Mar 07, 2021 2:50 pm
by desmond
ManFromGlass wrote:I still have my DX21 in working condition. Good memories of ancient gigs.

This image in an early Making Music issue always made me want one:

Image

I'm still rather drawn to that Yamaha 80's design language and palette...