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planning on making this headphone amp (capacitor and other questions)

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Triode

Active Member
I'm planning on trying to make this headphone amp, I'm going to set it up for guitar. I know to just get a headphone amp it would be better to just spend the $30 to buy one, but I'm trying to get started with understanding amplifiers. I'll probably have several specific questions as I work though it.

HeadWize - Project: Not Just Another Headphone Amp by Alan Gary Campbell

To start with, how much does it matter what kind of capacitor I use? It calls for film capacitors. I could eventually get some electrolytic ones but right now I only have access to a wide variety of ceramic caps. I'm guessing since it specifies the type of capacitor must effect audio in some way. Response time maybe?
 

amitak

New Member
Film capacitors are characterized by high insulation resistance, good capacitance stability, low losses , and high pulse handling capabilities.
Ceramic capacitors are used for noise filtering and coupling and are usually much smaller value.
Electrolytic capacitors are usually higher value and used to store enough charge to provide the current during the circuit operation and change of states.
 

Triode

Active Member
so then it probably does make a difference, i guess i can get the film type, breadboard it, and see what difference it makes if i plug in an equivalent ceramic type.

So does "film" only mean polyester film, or is it a broader category of capacitor?
 

audioguru

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Most Helpful Member
I use film capacitors for coupling audio. Ceramic is microphonic (picks up vibrations) and is used only for bypassing noise to ground. Electrolytic causes distortion and is used for bypassing a power supply voltage to ground as a filter.

The LM386 is noisy (hissss) and is not suitable for headphones unless they are 8 ohms ones. Headwize has circuits using OPA2134 dual low noise and fairly high current opamps driving 32 ohm to 600 ohm headphones.

Many guitar articles say that the preamp does not need much gain and should have an input impedance of at least 1M, not just 100k. an OPA2134 can have a 1M input impedance but an LM386 cannot without adding more parts.
 

Triode

Active Member
I havent ordered any parts yet so I can certainly change to a different plan. Thanks for the advice, I definitely dont want any hiss. I'll look at the diagram you mentioned

(later)
There are actually a lot more headphone amp projects out there than I expected, hundreds atleast. The site I found that first one on seems like it might be a good source for one. I'm trying to choose one thats cheap, beginner level, and works well with a guitar, and of course sound quality would be nice too but obviously the first two rule out it being top quality.
 
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Triode

Active Member
I just want to make sure, by film they mean metal film right? not polyester film.
 

audioguru

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Most Helpful Member
A film capacitor has an extremely thin film of metal deposited on the extremely thin plastic film. Many types of plastic film are available. Polyester, polypropylene, mylar and others.
 

Triode

Active Member
So, at this point I've built a simple amplifier with two darlingtons and one with an op amp. The darlington one was just really quiet and consumed a lot of power, the chip one was ok, the tone was very clipped and fuzzy, then the regulator blew up.

So, theres thousands of amp designs online, and its hard for a newcomer to filter them, I don't want to be like the people who show up here asking for a project handed to them, but if anyone can suggest a diagram/plan for a simple amp, preferably not chip based, to drive headphones from a guitar, I would appreciate it.
 

audioguru

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Many years ago I made good but low power amplifiers with many transistors.
Then the semiconductor manufacturers copied my designs and made them as ICs.
The IC amplifiers are better because the transistors in an IC are extremely well matched. Also more transistors are used to make the IC amplifier perform better.

Modern ICs for driving headphones are tiny so they can be used in small MP3 players and cell phones. They are very difficult to solder.
 

Triode

Active Member
The IC amplifiers are better because the transistors in an IC are extremely well matched. Also more transistors are used to make the IC amplifier perform better.
that makes sense to me, since the chips are made to amplify it seems like they would be good at it. But for some reason people keep telling me they clip the highs and lows and sound bad. Perhaps outdated experience?

Ive seen that headbanger amp, ive been looking at a lot of designs. It does look good.
 

audioguru

Well-Known Member
Most Helpful Member
An IC amplifier goes as low in frequency as you want. The low frequency response is determined by the size (value) of the coupling capacitors. 20Hz is easy.

The LM386 little IC amplifier has an upper cutoff frequency of 300kHz which is much higher than you can hear.

The distortion is almost nothing.
 
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Triode

Active Member
Well you know how it is, when it comes to guitar amplifiers the things people will tell you start to seem almost superstitious more often than technical.
 
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