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Old 30th June 2007, 04:26 PM   #1
joka22 is offline joka22  United Kingdom
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Default Jvc A-x40 Amp Mod Help

Hi i have just recently joined this forum. I would like to mod my JVC a-x40 amp so that it has higher watt output. it delivers 50 watts for each four channels (200watts) so it says on the amp but i want it alot louder. do i just change the transistors and just add bigger power supply. I know basic about electronics. My current power supply in my amplifier has 6 wires going to the amp board and i have four transistors in the amp it a four channel.

here is a image i have taken of my amp without the lid showing the circuit.

http://allyoucanupload.webshots.com/...31536239898827
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Old 30th June 2007, 10:49 PM   #2
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Default Re: Jvc A-x40 Amp Mod Help

Quote:
Originally posted by joka22
Hi i have just recently joined this forum. I would like to mod my JVC a-x40 amp so that it has higher watt output.
I'm thinking the 'ol JVC A-X40 is a two channel integrated amplifier with connections to allow two sets of speakers. The picture in the link looks like the output is left and right with discrete push pull transistor set up. The output transistors would be 2 transistors for each channel i.e. one side of the amp has a PNP & NPN and the other channel has PNP & NPN.

For many reasons I don't think it would be feasible to try and increase the power output of this type of integrated amplifier. You could set the JVC up as your "pre amp" and build a separate power amplifier in another box.

What did you have in mind to try and upgrade it?

Cheers,

Shawn.
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Old 30th June 2007, 10:54 PM   #3
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Default A-X40

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Old 30th June 2007, 11:21 PM   #4
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joka22 you have already started a thread with the same subject. You can post more dialog in one thread, you don't need to start a new topic for every post you make. You'll get the hang of it I'm sure.

Welcome to DIY Audio! It is a good place to hang out. I recommend lots of reading here before posting too much but don't let that stop you.

Cheers,

Shawn.
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Old 1st July 2007, 10:02 AM   #5
joka22 is offline joka22  United Kingdom
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Default any improvements

k then how about any improvements to this jvc amplifier?

alot of ppl say it not worth trying to make the output louder but they never explaine why.
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Old 1st July 2007, 01:15 PM   #6
ilimzn is offline ilimzn  Croatia
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Because it would require changeing so much of the amplifier, you could just as well use these new parts to construct a new amplifier. Transformer, rectifire, filter caps, most semiconductors, heatsink, possibly other parts - and than it would all not fit inside the same box, and you need to know EXACTLY what you are doing. Hence, it is not feasible.

You might want to look at other ways to get a louder output - for example more efficient speakers. For instance, if your speakers have an efficiency of 86dB/1m1W, and you replace them with ones that have, say, 96dB/1m1W, you get double the percieved loudness at the same amplifier output power. You would need an amplifier with 10x the output power to sound as loud as that on the first speakers (yes TEN). So, whan you say you want to increase the loudness, think about what sort of power increase you need - 10x power increase doubles the loudness. Human ears are funny that way. So, if you intend to up the power of your amp from 40 to say 60W, the lodness increase will be literally negligible.
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Old 1st July 2007, 09:19 PM   #7
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Default Re: any improvements

Quote:
Originally posted by joka22
... then how about any improvements to this jvc amplifier?
You could tweak it a little by putting in some new(slightly larger) power supply caps. They may help a little on the low end when heavy bass is required. You could also recap any or all of the coupling caps on the audio signal?

Quote:
a lot of ppl say it not worth trying to make the output louder but they never explaine why.
Basically to make this unit louder you would need more power from a larger power supply and higher supply voltage on the +- rails. This particular amplifier has been designed to work from the power supply that is already in the box. What makes an integrated amplifier hard to upgrade is the fact that there are many other sub-circuits drawing power from the same power source. You would need to somehow maintain these other power supplies sources to continue using the tone controls and phono preamp section etc. It goes on and on.

I think your output power amp is on one PCB mounted with the heat sink. Looks like it could be removed and another power amp section could be dropped in but it also looks like the power supply for the entire pre/phono/display etc. is also coming from the main amp board. Do see the level of difficulty here? This type of operation would require an experienced surgeon and much time and anguish plus the purchase of many new parts, new PCBs, new power supplies and a crazy amount of time. I'm certain it could be done and many folks here at DIY Audio know it can be done but why? Who would waste their precious time when something fresh and new could be created with the same effort?

If you wanted to have some fun you could replace the power supply with a larger one with higher rail voltage and crank it up and watch it self destruct. It could possibly be louder for a few minutes?

You sound like a good candidate to start a DIY amplifier project of your own! There are many DIY kits available with all of the parts to build. Many options. Or you can go to a pawn shop and buy a big fat old amp with lots of power for cheap.

Do you play your HiFi loud? How loud do you like it? Do you want to run multiple sets of speakers? How many?

Big amplifiers are very cool and I like them more than small ones most of the time.

Cheers,

Shawn.
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Old 1st July 2007, 10:07 PM   #8
joka22 is offline joka22  United Kingdom
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thanx tom for reply and advice and others that have responded to my thread.

I have seen 400 watt rms at 4ohms circuit pcb with components already soldered on, on ebay for 40 pound delivered. i do realize i will need power supply and regulater and other stuff. case and heat sink i can take off this old amp.

what do you suggest i just want to build a basic power amp 400 watts 4ohms, 2 channels but in the simplest way possible and with reduce components.

I have ordered a breadboard and multimeter, wire stripper. i already got a hot air station with soldering iron with temp control. i fix mobile phones but i am still need to learn yet when it come to amps.
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Old 1st July 2007, 11:44 PM   #9
ilimzn is offline ilimzn  Croatia
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Just one question, before you go too far with this:
What reasoning makes you think that a heatsink from a 40W amplifier will be enough for a 400W one? Serious question, mind you.
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Old 2nd July 2007, 01:48 AM   #10
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Quote:
Originally posted by ilimzn
Just one question, before you go too far with this:
What reasoning makes you think that a heatsink from a 40W amplifier will be enough for a 400W one? Serious question, mind you.
True words for you joka from ilimzm. There is very little available here to build a 400 watt amplifier...if anything. I think you could modify it into a preamp and then focus on another box, another power supply and other electronics to build a new amp if it is to be BIG.

Take some time hunting in pawn shops or audio shops that repair equipment. Find something broken and use the enclosure and power supply for your new project. Don't forget to look in some surplus stores.

Around here many feel the pain when it comes to getting the enclosure and power supply together for a large amplifier.

I guess you could install a small but powerful class d amp inside your integrated amp but you still have issues with distributing the power to the other circuits and sub systems inside your amp.

Where there is a will there is a way. It may be handy to put a budget $$ together for your project.

Shawn.
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