Alpine V12 amplifiers circuit diagrams

[cowasaki]

I have a couple of Alpine V12 amps (MRV-T403 & MRV-T503) which I've not used for years.  Just tried to connect them both up one after the other using my bench PSU and a couple of 8 ohm bookshelf speakers.  The amps should drive 8ohm speakers and both appear to work but they are both extremely crackly.  I've just been looking for a circuit diagram for either and can't find either of them.  I've run out of time tonight but will be having a look tomorrow and was hoping someone might be able to point me in the right direction.  I do plan on being a bit more systematic tomorrow and do have a signal generator and scope etc but was hoping they are just suffering from dodgy caps.....

[oPossum]

MRV-T503 https://www.pacparts.com/part.cfm?sku=82235H96102V78

There is no T403
MRV-T303 https://www.pacparts.com/part.cfm?sku=82235H96101V78
MRV-T407 https://www.pacparts.com/part.cfm?sku=82235H08773V78

You could also ask at the DIYAudio Car Audio forum. Someone may have them.

Crackling can be bad/dirty pots and/or bad coupling caps.

[cowasaki]

MRV-T503 https://www.pacparts.com/part.cfm?sku=82235H96102V78

There is no T403
MRV-T303 https://www.pacparts.com/part.cfm?sku=82235H96101V78
MRV-T407 https://www.pacparts.com/part.cfm?sku=82235H08773V78

You could also ask at the DIYAudio Car Audio forum. Someone may have them.

Crackling can be bad/dirty pots and/or bad coupling caps.

Thanks, they are both straight power amps with no volume adjustment.  I was hoping that someone might have one or the other service manuals/schematic as a PDF.

[cowasaki]

Amplifiers isn't my area....

The speakers I am using are 8ohm speakers and the spec states 2 or 4ohm.  Would/could that cause crackling?

[oPossum]

The max power will be less with 8 ohm, but it will work fine.

There are several pots on the end of the amp for crossover and gain adjustment.

[oPossum]

It could also be a dirty switch. Exercise all the controls and see if it gets better.

[oPossum]

Just tried to connect them both up one after the other using my bench PSU

What is the current rating of the bench supply? These amps will idle at 1 to 2 amps and will need at least 10 amps for moderate volume.

[cowasaki]

It's a 5 amp supply but the amps never used more than about 1.5amps.

The pots and switches had been used or adjusted since the amps were fitted 20 years ago.  I've moved all the switches back and forth as one was for the sub and the other was for the front speakers but with the stereo itself handling the tweeter.  I'll try the pots but it's strange that they both have the same issue.  The speakers I was using were a lot of four which I bought about a year ago but haven't used yet.  I've just tried them on another amp and they all work well so I at least know that it is the amps that are causing the issue.  I will get a pair of 4 ohm speakers out of the garage and try using them after making sure all the contacts are clean.  If there is still an issue then I will take a look inside.

[cowasaki]

Doh!

School boy error...... The V12 really doesn’t drive 8 ohm speakers! Just attached a pair of speakers I took out of another vehicle to replace with decent ones and both amps work perfectly. The smaller pulling a nats under 1 amp at 13.5v and the bigger one 1.5-1.8amps at 13.5v.

[envisionelec]

This is easy. The Alpine V12 amps emitter resistors and sometimes the output devices develop cracks on their solder joints. Remove the board and resolder the joints and you're in business!

I used to work for Alpine Warranty service.

[envisionelec]

Doh!

School boy error...... The V12 really doesn’t drive 8 ohm speakers! Just attached a pair of speakers I took out of another vehicle to replace with decent ones and both amps work perfectly. The smaller pulling a nats under 1 amp at 13.5v and the bigger one 1.5-1.8amps at 13.5v.

The V12 will drive 8 ohm speakers.

[cowasaki]

Doh!

School boy error...... The V12 really doesn’t drive 8 ohm speakers! Just attached a pair of speakers I took out of another vehicle to replace with decent ones and both amps work perfectly. The smaller pulling a nats under 1 amp at 13.5v and the bigger one 1.5-1.8amps at 13.5v.

The V12 will drive 8 ohm speakers.

Neither of mine will!

I have an amp here that will drive 8 ohm speakers. It drives my 8 ohm speakers perfectly.
I have two v12 amps, neither drive the above speakers with awful crackling.
Both v12 amps drive a pair of 4ohm car speakers.

[envisionelec]

Doh!

School boy error...... The V12 really doesn’t drive 8 ohm speakers! Just attached a pair of speakers I took out of another vehicle to replace with decent ones and both amps work perfectly. The smaller pulling a nats under 1 amp at 13.5v and the bigger one 1.5-1.8amps at 13.5v.

The V12 will drive 8 ohm speakers.

Neither of mine will!

I have an amp here that will drive 8 ohm speakers. It drives my 8 ohm speakers perfectly.
I have two v12 amps, neither drive the above speakers with awful crackling.
Both v12 amps drive a pair of 4ohm car speakers.

If a genuine Alpine V12 amplifier won’t drive an 8 ohm speaker without distorting then it’s broken. End of discussion. See my above qualifications.

[oPossum]

Using higher impedance speakers just lowers the maximum attainable power. Power in to 8 ohms will be about half of the 4 ohm rating. There is no maximum impedance. Even unloaded the amp will work properly.

A 4 ohm speaker is nominally 4 ohm. The actual impedance versus frequency curve will show that it often rises significantly above the nominal. So the amp must be stable in to higher impedance loads.

[cowasaki]

Doh!

School boy error...... The V12 really doesn’t drive 8 ohm speakers! Just attached a pair of speakers I took out of another vehicle to replace with decent ones and both amps work perfectly. The smaller pulling a nats under 1 amp at 13.5v and the bigger one 1.5-1.8amps at 13.5v.

The V12 will drive 8 ohm speakers.

Neither of mine will!

I have an amp here that will drive 8 ohm speakers. It drives my 8 ohm speakers perfectly.
I have two v12 amps, neither drive the above speakers with awful crackling.
Both v12 amps drive a pair of 4ohm car speakers.

If a genuine Alpine V12 amplifier won’t drive an 8 ohm speaker without distorting then it’s broken. End of discussion. See my above qualifications.

An 8 ohm speaker is out of spec for a V12 and they are both genuine V12 amps and both work perfectly with a pair of 4 ohm speakers (which are in spec).  It's possible that both the amps have developed EXACTLY the same issue but if, according to the specs, it doesn't drive 8 ohm speakers then its not really a fault.  I've tried it with 4 8 ohm speakers of one make/model and another two of another make/model all of which work with another amp.

[envisionelec]

Ok, you’re clearly the expert here.

But for other people that might happen upon this thread, this person is completely incorrect. This nominal 4 ohm speaker is not a pure resistance and will change its value dramatically over its frequency range. Specifically, it will rise to dozens of times its nominal value at the speaker’s resonance. There isn’t a solid state car amplifier on the market that won’t drive an 8 ohm speaker without massive distortion. I have already stated my qualifications with respect to Alpine amplifiers but I will also add that I have 25 years of amplifier and power supply design experience.

First of all, the amplifier needs at least a 10A power supply to function properly. A 5A supply can cause the amplifier to oscillate between startup and shutdown. It doesn’t matter if the idle  current is low - startup current can be 10-15 Amperes for a few tens of microseconds. Secondly these amplifiers are known for having cold solder joints on in their output stages. This will cause a crackly sound with any load, not just “8 ohm speakers”.

Suspiciously this person says he has an MRV-T503 and he didn’t correct himself. Alpine didn’t make that model and there are many “look alike” knock offs of V12 amplifiers. Perhaps a photo of these amps as well as a video of the supposed distortion is in order. Because what is being portrayed is false characterization of a scientific fact. And this is an engineering forum where most of us don’t take too kindly to misinformation. 

[cowasaki]

Ok, you’re clearly the expert here.

But for other people that might happen upon this thread, this person is completely incorrect. This nominal 4 ohm speaker is not a pure resistance and will change its value dramatically over its frequency range. Specifically, it will rise to dozens of times its nominal value at the speaker’s resonance. There isn’t a solid state car amplifier on the market that won’t drive an 8 ohm speaker without massive distortion. I have already stated my qualifications with respect to Alpine amplifiers but I will also add that I have 25 years of amplifier and power supply design experience.

First of all, the amplifier needs at least a 10A power supply to function properly. A 5A supply can cause the amplifier to oscillate between startup and shutdown. It doesn’t matter if the idle  current is low - startup current can be 10-15 Amperes for a few tens of microseconds. Secondly these amplifiers are known for having cold solder joints on in their output stages. This will cause a crackly sound with any load, not just “8 ohm speakers”.

Suspiciously this person says he has an MRV-T503 and he didn’t correct himself. Alpine didn’t make that model and there are many “look alike” knock offs of V12 amplifiers. Perhaps a photo of these amps as well as a video of the supposed distortion is in order. Because what is being portrayed is false characterization of a scientific fact. And this is an engineering forum where most of us don’t take too kindly to misinformation. 

EVERYTHING that I described is how it is.  I am not pretending to be an expert but I can read.  I didn't correct myself previously because I had nothing to correct.

The imaginary MRV-T503's USER manual is here - https://www.manualslib.com/products/Alpine-Mrv-T503-2762227.html

The photo is attached.

The amplifiers were bought directly from an Alpine main dealer owned by a good friend of mine at the time and I even registered them with Alpine at the time.

I came on here to ask for help finding the repair manual because I believed that these amps SHOULD drive 8 ohm speakers without any problem at all.  Whilst trying to get that manual I tried the speakers attached to a Denon household amplifier and all four worked.  They are Gale 3010S shelf speakers.  I got the same output from both amplifiers when attached to the Gale speakers in that the sound came through with lots of crackling noise. 

When I found, in the manual for the V12s, that they only drive 2 and 4 ohm speakers I got a pair of old 4 ohm speakers out of the garage which, when connected, had no issues at all.

As for the power supply, it IS only rated at 5 amps but at no time, including startup, did it go beyond 2 amps.

I am NOT at all saying that I am the expert!  The whole point is that I am not but I am not a lying or mistaken either.  I've just given the forum the facts as they appear to me!


I really would like these amps to drive 8 ohms!

[cowasaki]

and inside of the MRV-T503...

[cowasaki]

and the model designation there too.

[envisionelec]

I meant there’s no MRV-T403. My apologies.

The manual only shows rated power into 2 and 4 ohms. It says nothing about being unable to drive an 8 ohm speaker.

Those are indeed Alpine manufactured amplifiers and they often have cracked solder connections at the emitter resistors. It might be worth wiggling the resistors while the amp is running to see if the noise returns. These amps also had issues with the RCA shield connection breaking and causing a big DC offset to appear at the speaker terminals. The protection circuits are unusually robust and can appear to be trying to shutdown instead of revealing the true nature of the cause.

Try using a larger power supply when driving the 8 ohm speakers. I know it sounds counterintuitive to need more current at higher impedances but I think it might be having an issue with your 5A power supply.