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Old 08-20-2013, 03:11 AM   #41
midibob
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Default Re: Vox mini 3 amp

Hi Ben7,

I didn't want to complicate the board more than needed although I suppose you only have to click a button on the CAD software, also I didn't want too much exposed area of copper that might touch anything. As both speaker leads are at half the rail voltage the likelihood of a possible short to ground would destroy the chip.
Soldering was done by hot air gun so not sure if you count that as hand soldering?

Midibob
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Old 08-23-2013, 06:19 PM   #42
Thomt
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Cool Re: Vox mini 3 amp

Hi, I'm wondering if it's possible to add a 1/4" line out to my Vox Mini 3. The headphone out is very unreliable, crackles, pops and cuts out. Any help would be appreciated.
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Old 08-24-2013, 12:55 PM   #43
midibob
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Default Re: Vox mini 3 amp

Hi,
I suppose you could just extend the connections from the existing jack socket as it looks like it just signal and ground. I don't know what the voltage level is presented there so you may need an attenuator.

I wouldn't recommend taking it off of the speaker connections as they both sit at half rail potential and if either of them get grounded it will destroy the output chip.

Can't really give you more info than that as I've never looked into that side of things. Have you tried squirting a small amount of switch cleaner into the existing socket, maybe it's just dirty.

Good luck
Midibob
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Old 10-19-2013, 01:06 PM   #44
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Default Re: Vox mini 3 amp

HI, I hope im not too late to jump in on this thread but am hoping these midibob boards are still available? if so how do i go about getting one, well, four.? Only just joined so cant message anyone as yet but would like to kow more about this mini 3 issue. Andy
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Old 10-19-2013, 01:16 PM   #45
midibob
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Default Re: Vox mini 3 amp

Hi Andy,

Yep, made up a few ready for anyone that needs them.
I'll try sending you a PM with my email address and we can correspond.

Cheers
Midibob
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Old 10-19-2013, 01:54 PM   #46
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Default Re: Vox mini 3 amp

Thanks Bob, just replied to your email, let me know if you dont get it.
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Old 01-25-2014, 01:11 AM   #47
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Default Re: Vox mini 3 amp

Hi Bob,

Total novice here, I have the same symptoms: Vox mini3 with no sound from the speaker, but phones are OK. I need to learn how to test for sure whether I have the same problem and can, hopefully, use the same solution.

Thank you in advance
Andrei
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Old 01-25-2014, 02:54 PM   #48
midibob
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Default Re: Vox mini 3 amp

Hi Andrei,

The quick check is to test the resistance between the speaker leads and ground.
Make sure it's turned off and then check the resistance with the speaker disconnected from both leads to a ground on the circuit board.
If the chip's OK, which it probably isn't on yours, both leads (red and black) should measure over 100K Ohms and probably nearer 1M ohms to ground. If either of them measure under 100 Ohms then you know the chip has blown.

On these amps don't assume the black speaker lead is ground, as it isn't, and I suspect many people blow the chips trying to add more speakers.

If it's blown you then need to decide how you want to repair it. All documented in the thread.
I still have spare daughter boards if you need one but I wouldn't recommend anyone without reasonable soldering skills to attempt to fit one.

Let me know how you get on.
Good luck

Midibob
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Old 01-25-2014, 05:56 PM   #49
b0Rn2bL8
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Default Re: Vox mini 3 amp

Hi Bob,

Thank you for the prompt reply and the thorough answer.
I will follow your instructions and let you know what I find out.

Andrei
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Old 01-28-2014, 04:49 PM   #50
b0Rn2bL8
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Default Re: Vox mini 3 amp

Hi Bob,

Here is my progress so far:

bought a multimeter
read the manual
read the tutorial (learned that "OL" stands for "Open Loop", not "Zero Load"

disconnected the speaker
disconnected both an AC adapter and a Battery Pack
switched the power to "Stand By" (there is no "Off" position)

white speaker lead reads .987 on at 2MΩ setting
black speaker lead reads 22.8 on at 200Ω setting

It looks like the amp chip is blown and your daughter board is the solution I need.

Please advise,
Andrei
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Old 01-29-2014, 03:53 AM   #51
midibob
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Default Re: Vox mini 3 amp

Yep, that would appear to be the case as that's the usual problem.
I can send you a board but I suspect you'll need to find someone to fit it for you.
I could do it here but the postage costs each way to the UK would be prohibitive I expect.

I'll PM you the details.

Midibob
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Old 01-29-2014, 01:12 PM   #52
b0Rn2bL8
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Default Re: Vox mini 3 amp

Hi Bob,

I have only rudimentary (pre-PCB) soldering skills.
I'm interested in improving them and learning new ones, so -
What tools would someone attempting this job need? Would a standard 25-watter do?
Can you recommend any tutorials?

Andrei
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Old 01-29-2014, 01:30 PM   #53
midibob
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Default Re: Vox mini 3 amp

I'm sure you'll find many tutorials on Youtube. I can't recommend any specific ones as I've never needed to look.
I've sent you a PM with my mail address. If you reply I'll send you the instruction sheet so you can see what's involved.

Midibob
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Old 01-29-2014, 02:06 PM   #54
b0Rn2bL8
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Default Re: Vox mini 3 amp

thank you Bob
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Old 03-01-2014, 05:20 AM   #55
rhall010861
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Default Re: Vox mini 3 amp

Hi midibob, i have a semi dead vox mini3 too, do you still have any daughterboards left?
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Old 03-02-2014, 12:16 PM   #56
midibob
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Default Re: Vox mini 3 amp

Yep,

I'll send you a PM.

Midibob
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Old 03-03-2014, 06:19 AM   #57
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Default Re: Vox mini 3 amp

midibob. Very interesting thread, just spent the weekend reading it and trying to fix my own Vox Mini 3 without much success. Would you be able to send me details of the daughter board as well. Much appreciated Aimjam
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Old 03-03-2014, 10:45 AM   #58
midibob
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Default Re: Vox mini 3 amp

Hi Aimjam,

I'll PM you.

Midibob
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Old 03-09-2014, 11:03 AM   #59
rhall010861
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Default Re: Vox mini 3 amp

Thanks to Midibob I now have a working Vox Mini 3, had been intermittant, then no power amp at all. Now with daughterboard fitted, all ok - patience and magnifying glasses helped!
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Old 03-18-2014, 02:10 AM   #60
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Default Re: Vox mini 3 amp

Midibob. Thanks for the daughter boards and the instructions how to fit. Very easy to follow and the Amps are now working. Thanks again your work is spot on Aimjam
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