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Old 18th April 2008, 03:58 AM   #1
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Default Reverse engineering a JVC stereo amp

Hey folks -

I'd like to build up an audio amplifier for my musical instruments. I know that amps like the gain clone are generally not used as guitar amps, but since I play the electric violin, a good amount of fidelity is useful to me.

Anyhow, I've got an old JVC dual channel stereo tuner that I've taken apart. It doesn't use a single chip for the amplification like the gain clone does; instead, it uses two sets of power-transistors: a pair of 2SB1429 and a pair of 2SD2155, which apparently "complement" one another, one handling (+) voltage and the other handling (-) voltage.

Anyhow, with the parts scavenged from the JVC, I've got a solid power supply, a handful of power transistors, and all kinds of passive components at my disposal.

If I wanted to build a simple high-power amplifier from the ground up, is there a write-up handy? Is there an easy way to wire the power-transistors in place that would work similarly to the LM1875? The gain clone is an easy circuit to build up, and basically, I'm just wondering if there's a way to swap in the power-transistors from the JVC into the circuit.
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Old 18th April 2008, 06:43 AM   #2
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Sadly it's never as easy as swapping things out

I would go for two of BrianGT's kits.

Powersupply wise.

what voltage and VA rating.

Do you want a stereo system? i should think you only need mono if you want to use it with one electric violin.

you will need to search around for a corrent preamp to build.
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Old 18th April 2008, 08:31 AM   #3
e-mos is offline e-mos  Norway
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what about somthing like this?

check out this site for amp projects http://sound.westhost.com/p-list.htm

modifyed two of his schematics so the values should be recalculated.
you can use any transistor you like, also you can use any voltage you like on the output stage as long as the transistors can handle it..
but it is probably best to use the same on both the ic's and the transistors, because of the voltage amlification is taken care of by the ic..

the rule is that the transistor should be able to handel twice volts you choose use.
so if you use +-25volts the transistors need to handle at least 50 volts..
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Old 18th April 2008, 09:16 AM   #4
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Default my sugestion ....

my sugestion :

is first to edit your post from reverse engineering to canibalize .....cause i thing that what you do is riping the guts of the JVC amp .....

then my opinion .....
any transitor amplifier ...especially those so nicelly made by jvc at the time with a lilte bit of love ....some very simple repairs and some even more simple tweaks....will OUTPERFORM !!!!! any gainclone you put next to it .....regarding sonics, safety, control, stability ,repairability .... and a million other things ....

thats my comment

thank you and good luck you ....canibal .....
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Old 18th April 2008, 02:07 PM   #5
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Default Re: my sugestion ....

It doesn't *need* to be a stereo amp, so I suppose I'd only need a single set of transistors instead of both. But the power supply can handle two channels, and I figured it might be handy to have this thing be multi-functional. :: shrug ::

At this point, there's no going back on the JVC; call me a cannibal if you wish, but my goal here is to really learn how simple amps can be built from the ground up. If not the gain-clone circuit (I only mentioned that one because of its popularity; I assumed that it would have a wide knowledge-base here), maybe somebody can point me to a simple transistor amplifier circuit.

Is the (+) and (-) pairing of transistors typical? It doesn't look familiar to me, so I'm not able to simply replace them in some of the simple transistor amplifier circuits I've seen. Any more help would be appreciated.

e-mos -- thanks for the link. I'll check it out.
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Old 18th April 2008, 03:21 PM   #6
jaycee is offline jaycee  United Kingdom
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Using an NPN and PNP pair of power transistors for an amplifier is pretty standard these days. In the good old days a "quasi-complementary" arrangement using two NPN's was more typical because PNP power transistors were rubbish.

With those transistors you could probably build a DX amp or Symasym amp. Search the "Solid State" forum to find out more about those.
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Old 18th April 2008, 04:51 PM   #7
Minion is offline Minion  Canada
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Actually Chip amps are used in a LOT of Guitar amps , Ive seen LM3886/3875 ,TDA2040/2050 and other chips in solid state amps ,I have built 3 Guitar/Bass amps useing the LM3886 and they sound pretty good....

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