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Author Topic: vox blues  (Read 4469 times)

bluesthug

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vox blues
« on: February 09, 2007, 09:27:28 AM »
hey ya'll, greetings from Texas,my vox pathfinder crapped out due to me not grounding it right.[i'm new at this].But my prob is locating a power chip for the lil'guy,vox/korg are useless!!!a joke at best!Now what i want to do is bump it up from 15watts to 30 and case the amp as a head only unit.That and a 1-12 small cab shoud be just loud enuff to have the cops visit your next backyard thro down.Anyone know where to get one,and exactly what to ask for when looking,would be a great help,also how much these things usally cost?  thanks a lot,bluesthug

joecool85

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Re: vox blues
« Reply #1 on: February 09, 2007, 09:54:00 AM »
Power chips are a few dollars a piece.  Are you going to try to find one that is "plug 'n play" so to speak, or are you building a new poweramp circuit?
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teemuk

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Re: vox blues
« Reply #2 on: February 09, 2007, 11:51:02 AM »
Now what i want to do is bump it up from 15watts to 30 and case the amp as a head only unit.

Are you sure you are up to it? It usually doesn't work that easy: To convert a 15W amplifier to a 30W amplifier you need to convert the power supply so it can give you the 30W, this usually means at least changing the transformer to a higher power model and increasing the supply voltage. ...Which means that you have to change some of the capacitors to higher voltage rating and resistors, diodes etc. to higher power rating. The manufacturer has likely fitted the cheapest stuff inside so with a 80% chance you have to do all of the things above - at least to give some tolerance for the components. And what on earth made you think the PC board can handle the increased current?

If there are delicate bias or settings that require a specific voltage or current you have to reconfigure them. Then the power amp chip... Does the higher power model have the same pinout etc... The heatsink will not be adequate so is there room for a bigger one? I've seen the insides of some of those new Vox amps and there isn't much room for such an extensive mod as this. Have you fully understood the procedures the conversion process requires and are you competent enough to pick the right components for the job.

Frankly put, you already blew your amp by improper grounding - why should I (or anyone) trust that you do not do more damage, or even worse, kill yourself when you start to play with the mains circuit of the amplifier? (You have to do this to make the conversion).

I hope I did not sound too rude but as you see, the thing is a lot more complex than just changing the chip to a higher power model. When I was a beginner in electronics I also thought about converting my 12W practice amp to higher power. I was lucky that someone told me not to do it back then as the amp is still intact and working. So, I've been in the situation as you are. Do yourself a favour and ditch this idea. You will find building a higher power amp easier than modding a low power amplifier into a one. Fix the amp, refit to head cab and...

...If you want loudness, realize that for 6dB increase in SPL (1,5x increase in loudness) the amplifier requires four times more output power and for 10dB increase (doubled loudness) ten times more. Doubling the output power of the amplifier only gives a 3dB increase, which is increasing perceived loudness only about 1,23 times. So, that's not much. Real way to make the amp louder is to use speakers that are efficient. Getting a 6dB increase is a lot more plausible by changing the speaker system than by modding an amp.

Edit: Oh yeah, for getting those power chips I suggest component stores like Radio Shack or whatever they are in your home city. Manufacturer is about the worst source for them and if you ever get anything from them it is likely a complete PC board with a gigantic price tag. If the chip is fairly popular - most of the stuff in new amps is - conventional electronics component stores should be able to sell you one for few bucks.
« Last Edit: February 09, 2007, 12:00:06 PM by teemuk »

joecool85

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Re: vox blues
« Reply #3 on: February 09, 2007, 02:58:58 PM »
Wow, thats a lot to read!

Basically what it boils down to is that changing the chip on your current board will be pretty much impossible unless there was a clone chip (sometimes chips are identical except power output) and even then you'd need to at least upgrade your caps and transformer to allow for more power.  The best way to get more power out of it would be to ditch the current poweramp setup and just build a new one altogether and run your current preamp into that.

Of course you can always just replace your burnt out chip with a new one and go with that.

jameco.com and partsexpress.com are the two places I recommend get your chips.  If you want a whole poweramp setup I would consider chipamp.com
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Crystallas

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Re: vox blues
« Reply #4 on: February 15, 2007, 12:47:15 AM »
awesome post t-uk