Vox mini 3 amp

[midibob]

Re: Vox mini 3 amp

Sure, I'll PM you.

Midibob

[jobo]

Re: Vox mini 3 amp

Hi Midibob,
do you have any more of those daughter boards available, I am new to this site and unable to pm you many thanks joe.

[Paul_5]

Re: Vox mini 3 amp

Will do Midibob.

[midibob]

Re: Vox mini 3 amp

Hi Paul,

Are you able to PM me as I'm unable to send you a message. If you can let me have your Email address I'll forward you the details.

Thanks
Midbob

[Paul_5]

Re: Vox mini 3 amp

Hi all, I've got one that does the same. Are there any daughterboards going spare?

[midibob]

Re: Vox mini 3 amp

Hmm, so it all sounds a bit inconclusive.
I'm still unsure what you are seeing at the headphone socket? Is everything clean there, guitar and Aux? When I test these I use a signal generator so I know what levels I'm putting in to the amp. That way comparisons are easy.

[Microamp]

Re: Vox mini 3 amp

I checked the aux in and it is slightly distorted when I have the MP3 player output volume higher. I guess it wasn't as noticeable when it was lower. The guitar input though is very noticeably distorted when it should be clean (btq clean or line). I guess what still confuses me why I have any sound. It's almost as if the gain stage is bad. When the gain is really low and the master volume is down, it's almost clean. Then again, maybe it's just too quiet to hear the breakup.

[midibob]

Re: Vox mini 3 amp

On these amps the headphone output is before the chip so if all is well there then it further confirms the fault to be the chip. Not sure I understand when you say the Aux in sounds clean? Do you mean that the output isn't distorted at all as if so then it could be something else. All seems a bit unlikely though as it all uses the same path!

Sent you a PM.

[Microamp]

Re: Vox mini 3 amp

Yeah, the problem is still there even with batteries. Any other thoughts on diagnostics? Aux in with a MP3 player sounds clean, as does headphones with the guitar input. The mic input is buzzy like the guitar input. If your daughter board replacement chip isn't too hard of an install and is reasonably price to send across the pond, I'd be willing to give that a shot. Otherwise, I may end up with lots of spare parts to salvage to build another ruby or chime/punch amp and maybe install a 6 inch driver in the cabinet for better tone. PM me with details if you want to keep business off the message board.

[midibob]

Re: Vox mini 3 amp

No problem, the grounds on these little beasts aren't where you'd expect them!

It does sound like the chip is playing up. Have you tried running it from batteries. In theory it won't make any difference and I think then you can be certain it's the chip.

[Microamp]

Re: Vox mini 3 amp

I did measure it wrong the first time. This time I'm taking ground from the master volume potentiometer and do get 5V from ic9 and 2.5V from each speaker lead. I was mistakenly using ground from the power switch. Thanks for bearing with me.

[midibob]

Re: Vox mini 3 amp

That doesn't sound right?
You should only see half the supply voltage between the speaker terminals and ground. Being as the chip should only be fed with 5V you should measure approx 2.5V. Where are you actually measuring?

[Microamp]

Re: Vox mini 3 amp

Hi midibob,

I hope I checked it right. I'm a bit if a novice with a circuit so small and complex. I got over 5v at pin 3 on ic9 and about 9v at the speaker leads. That makes sense since I do get sound. The sound is just buzzy in a bad way, especially on BTQ Clean which was so clean before. It almost sounds like a capacitor is not working to filter out the noise. Are there other tests I could check? My experience is limited (built some small simple circuits like ruby, little gem, and punch amps), but I'm willing to learn.

Thanks,
Microamp

[midibob]

Re: Vox mini 3 amp

Hi Microamp,

I must admit I haven't come across one yet that has been badly distorted. Usually the chip just blows. You could just confirm that the 5V rail is OK that feeds the chip. It's supplied from the surface mount 3 pin regulator chip IC9.

Midibob

[Microamp]

Re: Vox mini 3 amp

Hi midibob,

I think my mini 3 is starting to go, too, but isn't completely blown since I still get a badly distorted sound out of my speaker. I tested the speaker alone with another amp and it's fine. The output from the headphone output is also normal. Since the output chip is completely blown, my resistances are okay. Do you think it could still be the chip or did I blow something else?

Thanks,
Microamp

[midibob]

Re: Vox mini 3 amp

Hi Craciun,

I'll send you a PM.

[craciun]

Re: Vox mini 3 amp

Hi midi Bob,

I have the same problem with my amp. Any chance of you sending me a schematic of your daughter board. Solution.

Thanks in Advanced.

Craciun

[midibob]

Re: Vox mini 3 amp

Hi Taylor.
No problem I'll send you a PM.

[tk5320]

Re: Vox mini 3 amp

Hey midibob, looks like I have the same problem as everyone else. Can you send some help. Thanks, Taylor

[Aimjam]

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