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#### eyevancsu

##### New Member
I was wondering how you would go about to increase the volume of some headphones with a device that you connect inbetween say the cd player and headphones. I know that simply adding a pot you can mute or lower the volume, but how would the volume be increased?

regards,

ivan

#### daviddoria

##### New Member
you have to have another power source. you could put a transistor with the base hooked up to the input (out from the cd player), the collector hooked up to the new power source, and the emmiter out to the headphones.

give that a shot.

david

#### eyevancsu

##### New Member
thx alot david, i have one question regarding your advice, to what do you connect the transistor, i mean to the negative or positive of each? i "recon" its the positive, or am i wrong?
also, would any transistor do the job, like the common 2222,3904,3906 etc, and approximately what value power source would be most recomended, sorry about the questions, i dont want to mess up my headphones/cd player.

thx alot for the help
regards

ivan

#### daviddoria

##### New Member
yea, i would definitely use the schematic that Gene posted... however, gene, why could you not just boost the signal with an NPN transistor (3904 or the like)?

what is the rest of that doing??

#### bogdanfirst

##### New Member
that circuit looks fine to me. but you have to build 2 of them since the cd-player is stereo . also, you might check, because there are a lot of IC's designed for headphone amplifier. also check your circuit before plugging it into the cd-player, so that you will not 'hurt' the cd-player.
http://sound.westhost.com/project24.htm

#### daviddoria

##### New Member
wow! still so complicated... whats wrong with a simple transistor to boost the signal?

#### bogdanfirst

##### New Member
i agree. a simple transistor like a BC547 is ok.

#### Gene

##### New Member
David - Of course you could boost a signal with a transistor and the 3904 will work. In fact, almost any transistor will amplify an audio signal. The reason I posted the schematic was that the conversation was sounding a little like - all you needed was a transistor and, presto, you have an amp.

I'm sure that you actually meant that a transistor (in the proper configuration, with the proper biasing, balanced for input/output, considerate of feedback, and with the proper voltage) will work. Also, transistors are used for different purposes - some are specifically made for audio, some for RF, some for switching, etc.

I don't have a drawing handy but, if it were me, I would search for a single IC amp (8 pins or less) or a stereo amp on a chip to recommend. Maybe someone has one handy....

#### daviddoria

##### New Member
haha that is my point... i've seen (even built) audio amplifiers... but after responding to this questions i don't understand what all that does... if you simply want to make it louder, send more power to the speaker (via transistor), right?

i am in no way arguing with you as i'm sure you are correct, i'm just wondering why lol

#### Gene

##### New Member
You are absolutely right. More POWER, yea! Some transistors have a better gain than others and some circuits seem to favor multiple stages of amplification and can get really complex because each stage has to accept the previous stage's output, and have all the particulars added for an audio amp. Whew, lots of parts to deal with.

If I were going to make this project, this is a circuit that would interest me.

#### eyevancsu

##### New Member
thx alot for that last link GENE, ive almost got it all done except for the grounding process. i read the grounding section in his main "headbanger" page but am still confused. according to me there are grounds on: r3,r5,c1,c5, pin 2 on both IC's, 100k pot, headphone plug and headphone jack, c9, c10, neg batt, and FINALLY DC NEG. do i just connect all of these together or what, i woujld appreciate any help on this, grounding has always been my problem.

#### Gene

##### New Member
Recommend you follow the section titled "Headbanger Grounding". There is a photo also that may help:

http://www.minidisc.org/ground.jpg

Grounding is critical for an amp. I mean, if ya gonna take the time to build the thing, you sure don't want to deal with distortion, hum, etc.

#### eyevancsu

##### New Member
sadly, i did read the section on grounding and looked at the pic as well but am still kinda lost. First of all, where do both grounds end up in the end?, the -9v? and what goes connected to the ground 'lug', all of the input ground?

input: phoneplug, pin 2, pin 4, pot
output: R3, R5, headphone jack, dc neg, C10, C9

am i right on these?

#### Gene

##### New Member
Yes - you are right. The confusion may be because, electrically these points all connect . . . but, it is important WHERE they connect to a common bus (wire). Amplifiers and RF circuits are funny that way. I think that's why the author wrote an entire section on this topic - it IS confusing. He also suggested that you ground the case of the volume control. In a normal amp application this would happen automatically because the chassis would be metal. A long piece of skinned wire can be wrapped around the front of the pot before it is bolted down to get this done. Because of the number of photos and the length of the descriptions, I think you will do well. If you end up with a problem, perhaps there is someone in your community or a school science teacher that can give your project a first-hand look. Do not put the ICs in their sockets until you are finished soldering - they hate heat. Also, if you are not using the rechargeable battery, you can omit R6, C10, and C9.

#### eyevancsu

##### New Member
here are the pics of the main circuit board: Note the 470 UF is missing, (noticed i reversed its polarity, have to replace):
i separated the 2 separate grounds, would these then go to the -9v (not shown)? i have yet to connect the heaphone jack, pot(ordering it) headphone plug. (excluding batt charg)

ivan

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#### Gene

##### New Member
I regret that I can't follow your wiring but I'll assume you have things under control. I sometimes make a photocopy of a schematic. Then, as I trace the connections with an ohmmeter, I highlight (yellow pen) the checked section on the schematic diagram. This is especially easy when there are no diodes/ICs installed. Something to do while you wait for your other parts to arrive. In the future you may want to use the componet leads or a smaller gauge wire for the hook-ups between components and consider using a vertical placement for resistors to save space. Lookin' good!

#### eyevancsu

##### New Member
thx alot for your help, ill do that about using smaller wire , it does look rather messy.

regards

ivan

#### eyevancsu

##### New Member
just a simple note,
i saw a device similar to this at soundproffesionals.com that sold for $170 and another version for$100, it looks pretty much like the one im making from the site gene posted.
i dont think its worth that much but who knows.....

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