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Phono inputs, Line inputs, etc.


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#1 Superduper

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Posted 27 December 2010 - 02:22 PM

We frequently have discussions regarding line-inputs, phono inputs, installing an external audio source such as MP3 or CD players onto the phono-in jacks, etc.

The answers to these can frequently be found by simply taking a few moments to do the appropriate search / research. Most contributors don't want to take the time and effort to answer the same question over/over again every couple of weeks. It does take some effort to type all that info into a response.

In General, you can expect the following:

PHONO-IN jacks of most audio devices expect an input from a phonograph. Depending upon the type of cartridge used in the turntable, the output can vary from as low as .3mv to 7mv, +/-. Because that signal level is so low in comparison to normal source voltages of the audio device (boombox), additional circuitry is included in that stage to amplify the signal to the approximate level of the signal level expected by the pre-amp, and before it's passed to the power amp. In fact, the radio, cassette, line-in, phono-in, microphone-in, all have varying signal levels and audio characteristics. If these signal source inputs are available in the boombox, you can expect matching circuitry (which alters those signal sources) will also be present.

LINE-IN jacks expect a completely different set of signal voltage levels. These inputs expect a much higher signal level than the phono inputs. Additionally, these are high impedance inputs meaning the impedance to the input signal will be on the high side. 10,000 ohms would not be uncommon. You can expect signal levels to vary between 300mVrms and can reach as high as 2V's peak to peak. I have heard .7volts is a common line out signal level. Anyhow, the point here is that the signal levels are far far higher than that expected from the phono inputs.

External Device hookups: As you can see, connecting a device that outputs .7 - 2 volts (700mv to 2000mv) to an input that is expecting .3 to 7mv would saturate and overwhelm the circuitry (built in phono-amp). The resulting audio would be too loud and distort due to clipping. If your device has a built in input level control, or if the output device has a volume control, you can try to meter the level to where the audio might sound acceptable, but the tonal curve might not be correct, and those inputs were not intended to be used as such. A far better solution, if your boombox does not have a line-in inputs is to purchase and use one of the commercially available phono to line in adapters. Or you can build one yourself. In short, connecting a line-level device to phono-level inputs is not recommended and although immediate damage to that circuitry may not be realized, sustained use in that manner could result in shortened life of that circuitry as the high signal level takes the amplifer from an active mode to a saturated mode.

While we are on the subject, line-in inputs on most boomboxes were designed back when external portable headphone type audio devices were not commonly used to inject signals into line-in jacks. So they are all pretty much high-impedance inputs. These inputs expect a high voltage level going into a high-impedance load. Portable headphone types of audio devices such as iPods, MP3 players, portable CD players, etc, output a signal expected for headphones, which are considered low impedance loads (8 to 32 ohms). The difference between a device with a high impedance output vs one with a low impedance output is that a low impedance output can output significanly more current. On the other hand, hooking up headphones or speakers to a device with high impedance outputs (true line level) will appear to the output amp as a short and effectively drop the voltage down to near zero. Although the output voltage of line-out signal levels is frequently higher than that of an MP3 player, it can only sustain that voltage if the input impedance of the driven load (boombox) is high. You can observe this for yourself by connecting headphones to the line-out jacks of an audio device. You likely won't hear anything. Headphone outs on the other hand expects a low impedance load and can pass the current without problems. However, it's my experience that the signal voltage level, even at full volume, is frequently lower than that of most standard line-out signals. The point here is that it is not uncommon to observe lower than expected audio signals from the line-in's with a headphone type of portable audio device connected, when compared to the native tape/radio of a boombox.

#2 im_alan_partridge

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Posted 27 December 2010 - 03:19 PM

I was just thinking myself that there seems to be a few similar threads that could maybe be merged.

Maybe what you have just written (or something similar) could be pinned?

#3 redbenjoe

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Posted 27 December 2010 - 03:23 PM

:super: :super: :angelic:

thanks --just bookmarked it -
so its a permanent and available reference for whoever asks next :-)

#4 im_alan_partridge

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Posted 27 December 2010 - 03:39 PM

:cool: Coolio :thumbsup:

#5 Jwrok707

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Posted 27 December 2010 - 10:34 PM

Great info, Thanks!

#6 Fatdog

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Posted 27 December 2010 - 11:48 PM

*Sticky*

:thumbsup: :cool: :super:

#7 mode one

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Posted 30 December 2010 - 12:59 AM

amn maybe someone can put some pictures how to make line in to connect mp3 player? i am makin via volume unit :)

#8 Superduper

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Posted 30 December 2010 - 01:05 AM

amn maybe someone can put some pictures how to make line in to connect mp3 player? i am makin via volume unit :)


THAT would be an interesting project but would be of no value unless you were doing the exact same project on the exact same boombox because each boombox is different, and so each such upgrade/retrofit would only apply to that particular model. There simply is NO one size fits all on such a project.

#9 JVC838

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Posted 30 December 2010 - 05:20 AM

http://en.wikipedia....AA_equalization

or for members who are able to understand german text:

http://de.wikipedia....ki/Phonoeingang

#10 fins5

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Posted 30 December 2010 - 09:36 AM

Superduper, thanks for posting this! Answered a couple of questions for me - I always suspected a true line connection supplied more input power than a portable device designed for headphones, but good to know the details!

#11 Superduper

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Posted 30 December 2010 - 12:19 PM

Superduper, thanks for posting this! Answered a couple of questions for me - I always suspected a true line connection supplied more input power than a portable device designed for headphones, but good to know the details!


Yep, portable devices designed for headphone does have the capacity to pass far more current, just usually not the voltage that the high impedance input needs for max volume.

#12 mode one

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Posted 31 December 2010 - 12:36 AM

THAT would be an interesting project but would be of no value unless you were doing the exact same project on the exact same boombox because each boombox is different, and so each such upgrade/retrofit would only apply to that particular model. There simply is NO one size fits all on such a project.

if u making via volume unit it is the same :) i had done this thing not so many times but it is not so hard to do after u saw one picture how-to :)

#13 Superduper

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Posted 31 December 2010 - 02:07 AM

if u making via volume unit it is the same :) i had done this thing not so many times but it is not so hard to do after u saw one picture how-to :)


Well mode-one, (1) such a project was beyond the scope and intention of this thread and (2) I respectfully disagree that a single such project could be summarily applied to a different box but if you feel differently and believe that any line-in-retrofit project would be sufficient to allow the audience to do the same mod on an entirely different box, member Neko was nice enough to post a thread 3 days ago about adding line in to a JVC B70 complete with pictures. So I suggest you go check that out.

#14 mode one

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Posted 31 December 2010 - 05:56 AM

i dont want to be disrespectful but in that way how he did is the easies and u can easily burn amp chip :)

#15 Superduper

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Posted 31 December 2010 - 01:26 PM

i dont want to be disrespectful but in that way how he did is the easies and u can easily burn amp chip :)


As far as I can see, it is one way to do it and I have absolutely NO problem with how Neko did it. If the input sensitivity was too high to your liking and concerns you, the signal could be attentuated by rigging in a voltage divider setup with a couple of resistors which is exactly why I said no mod will be common to every boombox since each circuit design, topology, signal characteristics, input/output tie-in choices, space on the case to locate the input jacks, etc. etc. etc. is ALL different. And this presumes that anyone needing guidance on such a mod is sufficiently needy of detailed instructions which simply can not be provided on a general basis and may do more harm than good if hooked up wrong.

Based on your comments, I am now convinced that you don't know what you are talking about and instead of asking for other's to post you an example, you should just post one yourself. And please start a new thread when and if you do |-) |-) |-) to prevent cluttering up this one and confusing the audience. That's all I have to say on this subject.

#16 mode one

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Posted 02 January 2011 - 12:55 PM

asking for other's to post you an example

i want to know maybe someone have some new ideas :) and i know about electronics, studiyng telekomunications :)

#17 mellymelsr

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Posted 03 January 2011 - 03:13 AM

asking for other's to post you an example

i want to know maybe someone have some new ideas :) and i know about electronics, studiyng telekomunications :)


...challenging the Super-one is not advised... :nonono: ...as he is many times smarter than us mere mortals, hence the nickname. Just my 2 cents... :-D

#18 mode one

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Posted 03 January 2011 - 03:24 AM

im not challenging :D

#19 baddboybill

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Posted 03 January 2011 - 03:30 AM

asking for other's to post you an example

i want to know maybe someone have some new ideas :) and i know about electronics, studiyng telekomunications :)


...challenging the Super-one is not advised... :nonono: ...as he is many times smarter than us mere mortals, hence the nickname. Just my 2 cents... :-D

:agree: Melly, plus superduper has never steered me wrong :-D

#20 stormsven

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Posted 25 January 2011 - 05:39 PM

A question here? Short story - 2 boomboxes hooked together and all is ok. Tape and radio from the first one sounds perfect on both. But when im hookin to the first one external sound to phono in, the sound on the second one become distorted. First one sounds ok. If i hook the same ext sound (with same levels) to the second boombox directly sounds ok as well. Been thinking and cant solve it :hmmm: . In both cases using phono in :hmmm: . Is it something when im switching the phono switch on the first one? Thanks in advance :-) .

#21 Brownlow

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Posted 29 March 2011 - 09:34 AM

Greetings Everyone,

I was thinking that there must be a way of getting around the onboard phono stage to convert it to line in. Then I remembered an article I saw a few years ago. I've never tried it, but I'll need to :yes: as I am now really into boomers :-)

I haven't seen the solution that Superduper referred to yet, no doubt this will come in time.....

Here's the link I was referring to. If it's been previously posted, please accept my apologies.

http://sound.westhos...m/project80.htm


Cheers


Brownlow

#22 Reli

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Posted 29 March 2011 - 10:24 AM

Greetings Everyone,

I was thinking that there must be a way of getting around the onboard phono stage to convert it to line in. Then I remembered an article I saw a few years ago. I've never tried it, but I'll need to :yes: as I am now really into boomers :-)

I haven't seen the solution that Superduper referred to yet, no doubt this will come in time.....

Here's the link I was referring to. If it's been previously posted, please accept my apologies.

http://sound.westhos...m/project80.htm

If you are trying to connect an MP3 player to your Phono jacks, you can buy an adaptor like Superduper mentioned. Not many people sell them, but there are a couple companies that do. You can velcro it to the side of your boombox.

#23 goodman

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Posted 07 February 2012 - 08:10 AM

I use my boomboxes to listen the radio, cassettes and MP3 player.
There are several options for connecting an MP3 player to the boombox:
1) through FM Transmitter
2) through cassette adapter
3) through the line input
I check 3 MP3 players, volume is on max, but output level is so lower.
In electronics sites found assembled preamplifier with TL 082.
The gain is determined by the value of the resistor in the feedback.
The picture shows how to connect:
Stereo_Pre_Amp_TL082_connections.jpg
I decided to embed this preamplifier in one of my boomboxes.
I found a place to mount the board.
When I finished, it's time to tests.
The level indicators show +3db.
MP3 player  volume is on 40%, equalizer is off or flat.
Now, the sound is good!!!
 



#24 krassi

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Posted 20 July 2012 - 04:12 PM

hiii there i had similar problems and bought myself a passiv line/phono converter..

http://www.amazon.de... ... 02_s00_i01

this one .. quit cheap and im using quit a strange wire setup.. most of my boxes have only a din input so im using a din/rsa cable... for tqo boomboxes together on an mp3 player im using a rsa/ 2x rsa plug ..
well and because my aiwa 660 can handle the mp3 signal directly and my aiwa 950 reacts super sensitiv im using the line/phono converter only for the aiwa950 and direct input for the aiwa660.. and if i wanna use my pana 5500 i use anothe rsa/ 2x ras plug.. ;)) looks like shiat but works ;))

i was thinking about using a car fm-modulator transmitter but they sound like crap...

best sound is pure radio ;)

seeya, daniel