** Sanyo MX-720 Line in sensitivity **

Hi Guys,

My Sanyo MX-720 is one of my top 5 boxes. It does everything very well except for one thing.

Whilst the line works, the sensitivity is too low for MP3 playback via an iPhone.
My M9998Ks are the same - nice sounding whilst on line in but not loud enough.

Any tech experts here have any ideas on what I can do internally to improve the line in performance?

Thanks,

James.....

The problem is that the iPhones aren’t very loud anyway. I tend to use my old iPad otherwise the needles don’t bounce like they should!

Hisrudeness said:

The problem is that the iPhones aren’t very loud anyway. I tend to use my old iPad otherwise the needles don’t bounce like they should!

Click to expand...

Hmmm........ the thing is, the iPhone output is actually too high for my Hitachi boxes and is about right for most of my other boxes and the phono input (via attenuators) on my Sanyo M4500K.

Hmm, I have no issue with my M9998K. Maybe yours has dirty contacts or inputs?

Also every phone has a different output. Might need to connect an external DAC for more power.

Reli said:

Hmm, I have no issue with my M9998K. Maybe yours has dirty contacts or inputs?

Also every phone has a different output. Might need to connect an external DAC for more power.

Click to expand...

It does ‘work’ but you need to turn up the volume past the ‘loudness’ part of the volume to get it loud enough.

I’ve tested 6 different M9998Ks with identical results. I thought maybe a resistor change could increase the sensitivity??!?

I only need maybe a 30% increase in sensitivity for it to be similar to my Hitachi TRK-8080.

All boomboxes have differences in input sensitivity and input impedances. The Sanyo M-X720 has an input impedance of 47k Ω, no sensitivity specified. Suggesting that all Hitachi's are the same is anything but the truth. That's because consider the following input impedance & sensitivity specs of these Hitachis:

TRK-8190, 8290 input sensitivity 100mV, 50k Ω
TRK-8600, J5 input sensitivity 200mV, 50k Ω
TRK-7620H input sensitivity 500mV, 680k Ω
3D-30, input impedance 700mv, 40kΩ

So as you can see, the impedances & sensitivity is all over the map. On the M-X720, the input impedance is 47kΩ & if you want to change a resistor, you can change R806 (& the matching one for the R channel), which coincidentally also happens to be.... 47kΩ. If you change that resistor, you might improve the sensitivity but you'll also change the input impedance. However, are you sure you want to alter the input impedance? It's already on the low side (see list above). The sensitivity of the inputs has to do with what the amplifier circuit does with the input signal, and some will have higher gains & some will have lower gains. Sanyo calibrated theirs for a particular reason. Also keep in mind that all of these circuits were designed for "real" line-level signals, not today's quasi earbud/line-out type circuits. The proper way to increase a systems sensitivity is to install an internal buffer amp to jack up the signal level or modify a circuit so that the amplification at that part of the circuit is increased. This would need to be custom designed for that particular circuit. Some service manuals, especially Pioneers, have a diagram called a level diagram. It shows you graphically the "level" of a signal as it travels through the circuit from input to output in DB's. Again, this is all designed and calibrated so that the signal is at a particular level at that particular point in a circuit.

Ideally, the best thing for you to do is get yourself a headphone amp. This will sit between the ipod & your boombox. Ideally, you'll get an adjustable one. That way, you can use it for any boombox and adjust as needed. User mellyselsr is high on and says really good things about ones made by FIIO.

There are a few apps for improving volume and equalisation a little bit.
Might be worth a go trying.

I use an app called Power amp but it’s for Android only.


https://www.imyfone.com/ios-data-erase/top-5-volume-booster-for-iphone-ipad/