Is this preamp appropriate?

Two things to try: firstly, the Alpine stereo might have an input-level adjustment (either hardware or software) that can be changed. (it'd be embarassing to find that there was a 'mute' selection, or the auxiliary input source wasn't selected, but... I've seen it happen). One Alpine manual refers to 'AUX SETUP mode' ...

Second, a coupling transformer can match the headphone-output (100 ohms or maybe less) to the line-input (usually 1000 ohms, sometimes as high as 50k ohms) of the stereo. It'll take two, of course, for stereo; they're small.

schreef in bericht news: snipped-for-privacy@4ax.com...

Well, as too often it's a maybe.

To tell something more I have to make some assumptions:

- Suppose the output of the MP3 player is meant to drive a low impedance headphone. That requires (relative) low voltage and high curent.

- Suppose the Alpines input is a line input. That has a (relative again) high input impedance so it requires high voltage but has no need for high current.

Suppose you see the mismatch :)

Theoretically you can solve the problem using two audio tranformers with a windings ratio of about 1:30. I don't know wether or not this transformers are made but 1:8 or 1:10 will also do. Price tags I saw from about $20,- up a piece (ex. VAT and shipment).

Now you amplifier comes into play. As an amplifier it will amplify the voltage level by 40dB that's a 100 times. That may be way to much for your Alpine but the volume control of the amplifier can handle this. So with a little luck you're done.

But without luck? Well you may get noise or hum or distortion or even all of them.

Noise is hard to fight. Putting a 100 Ohm or so resistor parallel to the input of the amplifier may help.

Hum can be prevented by using well shielded cables and putting the amplifier in a metal shield box.

Distortion may be caused by overloading the amplifier input. The 100 Ohm resistor mentioned earlier may help. It can be lowered down to 33 Ohm if it needs to.

I did, off course, not mention all possibilities but I, once more, suppose, you can at least go for a try.

petrus bitbyter

But what kind of low voltage?

"Line in" is always pretty vague. I have an amplifier fed from a VCR, a DVD player and misc and I tend to have to adjust the volume control when switching sources, proving that the standard isn't really much of a standard.

That said, it seems to be generally assumed that "line level" is about 1 volt. And surely even a headphone output can supply somewhere around that. The mismatch doesn't matter.

I've plugged various portable devices into that amplifier, my Sansa Fuze, various portable CD players, a small am/fm headphone radio, and while there might be some lower level with those as the source (I can't remember) it wasn't a massive difference.

I like the comment from someone suggesting there's some mute or other setting that needs to be changed on the radio. There seems to be way too much difference in sound level.

Let's not forget that if some car radio has a jack intended for external devices, it likely is expecting an MP3 player or a portable CD player, plugging into their headphone jack. Why else would there be an input jack?

The only other possibility is that the MP3 player has some blocking so the volume can't be turned up too high. SOme of them do have a menu setting to disable or enable this sort of thing, and if the problem isnt' a setting on the radio, then the poster should look for some setting on the MP3 player.

Michael

Yeah, even now the list of possibilities has not been exhausted yet. But I - once more - suppose the OP has enough info to try for a solution. If he fails he can come back to report. You and I can be more specific once we know more about the specifications of the equipment involved.

petrus bitbyter

Following your suggestions I plugged the MP3 player into the minijack and fiddled with the menus on the radio. Of all the options there is no input level option for the minijack. So I think everything I can do as far as plugging in and listening has been done. So then I looked for a transformer as you suggested and was unable to find any that match the specs you gave. So maybe I am looking in the wrong place. Any links? Thanks, Eric

Greetings Petrus, I'm going to look for small transformers in my junk pile to see if any match the 1:30 or thereabouts spec and if I find any give 'em a try. Thanks, Eric

Whether I plug in an iPad or a Sansa the result is the same. I need to turn the volume up high on the player and pretty high on the radio. I have tried to get a manual for the radio just in case I am not doing something right but Alpine says talk to Toyota and Toyota says to talk to their manual printer and their manual printer says it's not available. And the Scion forums have not been any help either. Eric

ce

he

I don't suppose you have 'scope or other test gear? (maybe a signal generat or?) I'd like to know the signal level from the mp3 and then see if it goes down when you plug it into the car stereo. (maybe you could split the audio co rd and listen as you plug it in.) The amp you posted looks fine. As long as you power it from the car battery I assume there is not much chance it w ill overload the stereo input.

George H.

Greetings George, I do have a scope. A Tek 465B. Bought because it was recommended on this group when I asked about one years ago. I will try to make up a setup where I can measure the output from the MP3 player. What should I look for? How many volts/div? Thanks, Eric

any

or

so

eft

dance

, a

hen

t 1

uze,

too

nal

o the

ing

the

rator?)

own when you plug it into the car stereo. (maybe you could split the audio cord and listen as you plug it in.) The amp you posted looks fine. As lo ng as you power it from the car battery I assume there is not much chance i t will overload the stereo input.

Geesh I have no idea. :^)...(we need some audio guy to answer.) OK my computer has a little audio output. I plug a ~35 ohm ear bud into i t. There's about 100 mV p-p (peak to peak) with the ear bud plugged in. Witho ut the ear bud the signal is more like 400-500 mV p-p. So I'd like to see that the mp3 output doesn't drop too much when it's plugged into the amp.

George H.

schreef in bericht news: snipped-for-privacy@4ax.com...

Just to try any small transformer between 220:5V to 220:24V will be of interest. Though I think you will loose higher frequencies as these are mains transformers. I expect output transformers from old transistor amplifiers will do better... If only you can still find them. Remember the

petrus bitbyter

In terms of places to look, if you can find a similar non-OEM stereo at you can try to download its manual for more info.

As for a good source of audio matching transformers: I dunno. There's microphone adapter units (somewhat pricey), and maybe (but I've not done any business with them). Audio matching transformers have kinda ... dried up and disappeared from the usual distributors.

There was a time, likely brief, when tv sets seemed to include audio transformers to feed external circuits.

There was a period 20 years ago when one tv repair store reliably tossed tv sets once a week, and I'd come upon them. And I have a scrap of circuit board from that period, two matching audio transformers that must have been for isolating the headphone jack or even "audio output" jacks. I have no idea how common that was, and likely by now those tv sets have already all been scrapped.

Michael