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Modified Crown 5000VZ - Help!!

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pczjm View Drop Down
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    Posted: 11 July 2017 at 10:17pm
Hi Guys,

I have a Crown Macro-Tech 5000VZ that was previously used as an amplifier for an NMR machine (similar to MRI) in the chemistry department where I work. It has apparently been modified to some extent for this purpose. 

The obvious thing is that the gain pots have been removed from the front but other than this I am clueless as to how it may have been modified. I popped the top, but never having studied the internals of an amplifier before, this was less than illuminating! There was no obvious/major difference to the pictures I found on the internet of the same model. 

Does anyone out there have experience of this kinda thing? As you might of guessed I wanna use it to power bass bins but am sure if I would need to "convert it back" to any extent. 






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Post Options Post Options   Thanks (0) Thanks(0)   Quote pczjm Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 10:24pm
Here's some pics:


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Post Options Post Options   Thanks (0) Thanks(0)   Quote pczjm Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 10:26pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dub Specialist Sound Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 10:53pm
You need to get in touch with

DjLeco forum member on here, 

ent seen him for quite a while tho

hes a don with them, and amps in general
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 11:14pm
the front pots are connected to the rear board via a pair of screened grey cables, they fit at the back on either a 3 or 4 pin header depending on age. For the amp to work, there may be a jumper, resistor or preset pot fitted on these headers instead. Take a close up picture of the rear board if you're not sure and post it here.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 11:18pm
ok, found a suitable pic.

K. Edwards Electronics Engineers

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pczjm View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pczjm Quote  Post ReplyReply Direct Link To This Post Posted: 11 July 2017 at 11:41pm
Thanks for the replies!! I'll have a proper look tomorrow at work but the best pic I've got atm is this one, I can't see the grey cables!


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 12:01am
Please give me the pictures at original size on mail
 
claudiu971@ yahoo(dot)com
 
On last picture, I see no gray cables for volume potentiometer(s), is missing, maybe potentiometers too.
Make one as mr. kedwardsleisure put above, to see exactly if missing or not potentiometers and cables with connector too.


Edited by DjLeco - 12 July 2017 at 12:06am
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pczjm View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote pczjm Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 10:18am
Hi Guys,

Thanks very much, hope this photo is better:




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Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 3:35pm
It's likely the modification involves DC coupling the output stage, the NMR machine would have required very low-frequency high-current signals with DC components to drive large electromagnet coils. 

I remember using them as an undergrad to determine the structures of molecules, they are eldritch high magick indeed ;)

This will probably mean the speaker protection circuitry has been modified or disabled, because in normal audio operation any DC at the output is a fault. 

There was an industrial version of this amp (branded Amcron not Crown) that had a switch to select DC coupled or AC coupled (audio) mode. That may indicate that the modification is quite trivial.

I see a wire link installed where one of the volume pots was connected. I would hazard a guess that the amp is in parallel-mono or bridge mode with the gain fixed at maximum (in those modes the channel B gain pot does nothing, so wouldn't need to be connected at all). 

I also see an extra trim pot tacked onto the legs of an IC and held in place with hot glue, and a capacitor added in series with a resistor, those do not look like factory installations to me....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DjLeco Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 4:09pm
You must redo to factory construction all those modifications.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 12 July 2017 at 4:51pm
Looks like some of the capacitors have been linked out too. This could be serious!
Oh and the optical compression components are missing

Edited by kedwardsleisure - 12 July 2017 at 4:51pm
K. Edwards Electronics Engineers

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