mabell313

CAD GXL3000 zener diode?
« on: August 18, 2013, 10:06:27 AM »
I have been reading that the CAD 3000(or the Apex 480) have an issue with slightly low voltage to the capsule resulting in poor response in Figure-8. As recommended, I would like to change the zener in the mic's power supply. The problem is I can not read the value/model of the zener and do not want to remove it just to see the value. I would prefer to know all of the parts I need before ordering. Does anyone have any experience changing out this zener? It is D1 on the power supply board. Any help would be much appreciated.


RuudNL

Re: CAD GXL3000 zener diode?
« Reply #1 on: August 18, 2013, 12:45:52 PM »
What is the problem to 'unsolder' one leg of the zener diode?
It is probably the fastest way to find out...
(If you want to change the zener, you will have to remove it anyway!)
There is a solution for every problem!

http://www.vansteenisaudio.nl

mabell313

Re: CAD GXL3000 zener diode?
« Reply #2 on: August 18, 2013, 02:44:57 PM »
What is the problem to 'unsolder' one leg of the zener diode?
It is probably the fastest way to find out...
(If you want to change the zener, you will have to remove it anyway!)

You are right! The only problem is the value/model number is gone. It has been rubbed off. I probably should have said that in the first place to avoid someone pointing out the obvious to me. Once removed, is there a way to test a zener to determine what voltage it is? That would be a giant help!

mabell313

Re: CAD GXL3000 zener diode?
« Reply #3 on: August 18, 2013, 03:27:23 PM »
OK! Just started a small fire! I used a 24VDC wallwart and a resistor to find the zener voltage and ended up starting a damn fire! I was not careful with where I placed the resistor and my hook ups were sloppy as hell. Does anyone know the value of this zener diode? Please help before I end up burning down my whole damn house! :o

mabell313

Re: CAD GXL3000 zener diode?
« Reply #4 on: August 20, 2013, 07:14:47 PM »
I did some testing a few minutes ago. The zener seems to be 8.2V. The reading was 8.1V on the DDM so, pretty close. I removed the zener and the voltage shot up to 18.8V! Over 120V at the capsule total, 60V each diaphram. I still not able to read the stock zener's markings. I am going to replace the stock 8.2V zener with a 16V and do some more testing. This should put the capsule at a better voltage for figure-8. Painfully weak stock in figure-8! I'll post pics soon.

Khron

Re: CAD GXL3000 zener diode?
« Reply #5 on: August 22, 2013, 07:46:31 AM »
I've got a strong hunch, the bulk of the circuit is very similar to the Apex 480 (FET, transformer-coupled), and indeed, the zener (far right) is 8.2v.

http://www.gearslutz.com/board/attachments/geekslutz-forum/181381d1278276199-anybody-mod-apex-480-apex480-schematic.jpg
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

mabell313

Re: CAD GXL3000 zener diode?
« Reply #6 on: August 25, 2013, 07:55:46 AM »
I've got a strong hunch, the bulk of the circuit is very similar to the Apex 480 (FET, transformer-coupled), and indeed, the zener (far right) is 8.2v.

http://www.gearslutz.com/board/attachments/geekslutz-forum/181381d1278276199-anybody-mod-apex-480-apex480-schematic.jpg

The CAD GXL3000 is indeed the same mic as the Apex 480. After I PROPERLY connected a wallwart, I did test the zener with success. It is indeed a 8.2V zener. The mic's capsule voltages without the zener seem to be a bit erratic and jump up pretty high. I measured 168V at one "surge"! The total capsule voltage is around 120V without the zener but, again it was erratic. I am thinking a 16V zener will do the trick. It should give a high enough capsule voltage as well as some regulation. Someone let me know if I am barking up the wrong tree!

Khron

Re: CAD GXL3000 zener diode?
« Reply #7 on: August 25, 2013, 08:12:49 AM »
For what it's worth, i seem to remember reading somewhere that in these fet + transformer-coupled "chinese mics", the biasing for the BJT that's driving the transformer was often quite "off", which leads to distortion way earlier than if the biasing was done properly.

Unfortunately i can't recall exactly where i've read that, but some googling should reveal the source :)
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mabell313

Re: CAD GXL3000 zener diode?
« Reply #8 on: August 26, 2013, 07:32:02 AM »
For what it's worth, i seem to remember reading somewhere that in these fet + transformer-coupled "chinese mics", the biasing for the BJT that's driving the transformer was often quite "off", which leads to distortion way earlier than if the biasing was done properly.

Unfortunately i can't recall exactly where i've read that, but some googling should reveal the source :)

You are right, the emitter follower's bias is way off. I have been reading about it for some time now. I am following the ideas of Fox Audio Research's FET 47. His mods are for the Apex 480 but, the CAD 3000 is the same mic damn near. It should be awesome with a 47-style capsule once the mods are completed.

Khron

Re: CAD GXL3000 zener diode?
« Reply #9 on: August 26, 2013, 01:32:59 PM »
... Or with some U87-type internal EQ-ing :)

Could you post some link to those Apex 480 mods?
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mabell313

Re: CAD GXL3000 zener diode?
« Reply #11 on: August 27, 2013, 08:02:43 AM »
Some of the info is outdated. Check the Fox Audio Research website for the updates. It is the FAR FET47.

Re: CAD GXL3000 zener diode?
« Reply #12 on: March 25, 2018, 01:31:55 AM »
I know this is an old topic, but I just picked one of these up.  Just curious...what value Zener did you replace the stock Zener with?