JVC A-X3 integrated amp doesn't play loud

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Hi all,

Been reading this forum for a while - great stuff. This is my first post.

I recently acquired a JVC A-X3 55W rms/ch integrated amplifier. The amp sounds nice, functions well and shows thoughtful engineering - except that it does not play as loud as other amps I have using same sources and speakers. My main speakers are Polk Audio RTA-11T and my sources are a Marantz CD player and a TT with MM Shure M91ED.

Although it doesn't get very loud, it sounds distortion free till passing the 3 o'clock mark. I also tested it with my other pair of Polks: Monitor 5 Series 2. Same loudness. Replacing it with an old Kenwood 35W rms/ch amp gives significantly louder sound (comparable to my other amp, a Pioneer 65W rms/ch.

Pushing all controls to the max on my HK equalizer makes the amp play 'normal' loud with no distortion till past the 3 o'clock mark. This makes me think there is something wrong in the preamp section. I cleaned the controls, replaced all electrolytics (except on the LED driver board), redid the heatsink compound, and adjusted idle and dc offset to specs: no improvement!

The amp runs reasonably warm. However, I noticed that the driver amp board (PCB #6 in the service manual) gets too warm for a circuit handling line levels. Also, half of that board is slightly darker that the rest, but no components show signs of thermal damage.

What are your thoughts on the cause and remedy?

Thank you,
Bill
 
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Hi Bill,
The other amps have higher distortion and therefore sound louder would be my guess. I used to sell JVC when they came out with the "Super-A" and they sounded a lot better than the other products.

Lose the EQ! You don't need it and all you've done is add enough distortion to make it sound as bad as the others. To compare levels, send a tone through and measure it with a meter on any systems you want to compare. Use dummy loads because this will destroy a speaker. Try 400 Hz as most meters will respond to that kinda okay. Most meters will read properly at 60 Hz and not much higher. So don't try to calculate power output. Power measurements must be made on an 8R dummy load. You can get these on Ebay. The real ones will run you about $60 each now and still need a big heat sink.

If the PCB is discoloured, the components are heat damaged no matter how they look, not unless they were changed recently. There is nothing you can do with the designed operating levels. So accept it and keep on going until you have problems, then fix the problems.

-Chris
 
Thanks Chris. Do you remember the other JVC amps being not very loud like I'm describing? My other amps don't sound distorted at all till they near clipping. Not sure I get your point about higher distortion amps being louder. Something doesn't seem right about my unit. I had an equally powered Onkyo and it played much louder. Either something is attenuating the signal at the preamp stage or the power amp section doesn't reach high gain for some reason. The rail voltages are 1.5V higher than specs (so no problem there). :confused::confused::confused:
 
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Something doesn't seem right about my unit.

The line input sensitivity is 150mV for full output, so the gain spec is normal.

BTW, you did turn OFF the -20dB muting switch, right?

Since the volume is the same in both channels, perhaps the line section +/- 38VDC supply voltages
are too low. The dropping resistor(s) could be off value. Did you measure these voltages specifically,
and not just the power amp rail voltages?
 
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Hi nabzan,
If equipment is a lot lower distortion and lower noise than other equipment, it won't sound as loud. Sometimes people take added distortion as an indication of power output. JVC stuff is generally very clean sounding.

The only way you can prove or disprove this is to measure power output into a dummy load. It's either putting out "x" number of watts, or it isn't. Human beings make lousy test instruments. Do you have a friend with an electronics bench by chance? Too bad you are so far away or we could have done exactly that here.

-Chris
 
Hi again,

So I finally got some time to check further: I had suspected a 2W 1.2K resistor in the preamp circuit (because it was running a bit too hot), but it turned out to be within acceptable tolerance at 1.06K. Other voltages read within +/- 10% of specs (more on the + side), which is probably due to component tolerances.

Maximum output voltage reached 28.8V using a 100mV 60Hz test signal, read at the speakers terminals with speakers connected and using a DMM (channels were within 200mV). I guess that is OK for a rail of 35.4V. Turning the volume knob caused the output voltage to change in an seemingly linear fashion.

Both channels behaved very close and the lack of high volume and 'punch' seemed to be equal in both. It only got 'quite' loud towards the max volume setting but with noticeable distortion. One thing I noticed is that when I switched to mono, the output voltage dropped a max of 22.6V (and the LED meter dropped one notch) although there was no perceived drop in loudness.

I can't figure the problem out and I'm not sure how to test further. Any ideas?

Thanks,
Bill
 
FUSES

Hi.

I serviced a few amplifiers in my life. Part of theme had resistors parellel to fuses.

Amplifier recting with really quiet, no deep bass sound. Static measurements are quite ok - resistor is not big - around 100Ohm or so, and allow amplifier to still have "0" offset etc...

Just try to measure voltage on fuses - if You get some around 1V or more then switch off the amp and check a fuses, or better check a fuses at first.

This is first thing to check for me ( with commercial amps like aura from B&W ).

Best.
 
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