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Failed Headphone Amp


AndrewCE

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ok, so i just checked, and the lead temp for soldering is 260C. I use a 450C soldering iron. I probably burnt the chip. I shouldve used a socket. Now i cant even remove the probably-burnt chip. Maybe i'll convert it into a fuzz box effect pedal.

I think i'll retry this with a socket, and get one of those higher quality opamps. If in the meantime anybody sees an error in my schem that can be fixed, please notify me. I have switched the leads of the power supply so that it matches the schematic exactly. The current state of operation is:

with battery power, I get a lo-fi fuzz effect with almost no sustain; it just craps out when the volume gets low. When plugging in the power supply(and therefore cutting off the battery power) i just get a whooshing sound, completely devoid of my guitar signal. I'm not chained up to any other pedals, so thats not the problem.

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ok, so i just checked, and the lead temp for soldering is 260C. I use a 450C soldering iron. I probably burnt the chip. I shouldve used a socket. Now i cant even remove the probably-burnt chip. Maybe i'll convert it into a fuzz box effect pedal.

I think i'll retry this with a socket, and get one of those higher quality opamps. If in the meantime anybody sees an error in my schem that can be fixed, please notify me. I have switched the leads of the power supply so that it matches the schematic exactly. The current state of operation is:

with battery power, I get a lo-fi fuzz effect with almost no sustain; it just craps out when the volume gets low. When plugging in the power supply(and therefore cutting off the battery power) i just get a whooshing sound, completely devoid of my guitar signal. I'm not chained up to any other pedals, so thats not the problem.

That could very well have done it.

Another thing that could have done it is an ESD (electrostatic discharge) event... a shock transferred from your body or an object to the device during handling which causes damage in the form of frying an internal pathway,either partially or fully. We often neglect this phenomena in the DIY world as it's not really given much attention in the standard tutorials. It's the very reason why you get electronic circuit boards for PC's packaged in silver metallized bags. They're static shielding, designed to protect, until the consumer gets their hands on them. In the industrial world, we spend thousands of dollars on bench setups designed specifically to reduce and neutralize static buildup and discharge around sensitive devices. They constantly monitor the operator for proper grounding to keep the operator, the bench, and the product at ground potential to avoid static. Op amps are among these sensitive devices, as are most semiconductor devices. When an ESD event occurs and damages a component, it is all but untraceable without using specialized X-ray equipment with very high magnification.

Yes, I agree on using sockets, but why can't you just remove the chip and try replacing it? No matter what you've done, it is always removeable,even if you've clinched the leads over. Get yourself some wicking braid and liquid flux on your next visit to the electronics shop. You flux the braid, lay it across your joint and apply heat to both braid and solder joint. When the solder melts, the braid sucks it up. When you have enough sucked up, the chip should be easily coerced out of the holes. It's at least an opportunity to give it a try.

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Yes, I agree on using sockets, but why can't you just remove the chip and try replacing it? No matter what you've done, it is always removeable,even if you've clinched the leads over. Get yourself some wicking braid and liquid flux on your next visit to the electronics shop. You flux the braid, lay it across your joint and apply heat to both braid and solder joint. When the solder melts, the braid sucks it up. When you have enough sucked up, the chip should be easily coerced out of the holes. It's at least an opportunity to give it a try.

eh, my pcb is extremely cluttered. i'll show you a pic as soon as i get one. i think its possible to remove it, but not worth the effort. especially since i would have to remove, and maybe even desolder, some of the jack and pot connections to remove it from the chassis. i think it's easier just to build another one. and i got a larger enclosure this time, bigger than my 1x2x4 that my amp is in now, so it should be easier. i'll just have to reacquire all the parts.

i might even re-breadboard

are you absolutely sure that i want the lowest possible impedance? i know from speaker cabinets that you want your impedances to match for max power transfer. but i also know that headphone/earphone impedance vary considerably. i'm wondering if i can get by with a lot less gain if only i could match the impedance. is a transformer the only way to do this?

p.s. how do you even measure an earphone's impedance? i can only get a DC resistance. and how do you measure output impedance of the amp?

Edited by AndrewCE
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Oh well. I'm sure all of this has been a learning experience for you to say the least. You and I are on much the same path and so I can identify with your interest, enthusiasm, confusion, disappointment, etc. No worries though, let's look at it as "right of passage". :D

A low impedence output can handle going into a higher impedence input, but not the other way around. This is what I've learned, but it is 2nd hand knowledge from a member of the nerd herd at my employer and other threads within this and other electronics forums, for a basic bit of evidence, it's stated about 2/3 down this page... http://www.kpsec.freeuk.com/imped.htm

In practical termns, if you think about how things like op amp based stomp boxes work, they are always very low output impedence and very high input impedence (this is why they're used as buffers and how they avoid "loading" the guitar circuit). They have no issues interfacing with the input of a guitar amp. If there is any issue with a low output impedence, then I'd also like to know why.

Impedence is not so easily measured. It's a combination of resistance, inductance, capacitance, reactance (variation with frequency), all brought together. You would need an LCR meter to measure the individual values and use some math (that I'v enot ventured to fully understand) to come up with the impedence value. I also believe there is a difference powered vs unpowered. However, I believe that for the most part, with something as simple as headphones, you can factor it down to an estimate, based on only the resistance of the headphones. I think your biggest issue is going to be the output current, not impedence. Like I said a few posts back, I hooked this up with a TL082 driving my Bose headphones (quite high output) using dual 9V supplies and it was very nice. I do not think the dual 9V supplies change the output impedence, but the output current of the op amp does go up with increased voltage supplied to the op amp.

Some of your questions are very valid and I'm not sure you're going to get the answers you really need here... notice no one else seems to be chiming in?

I would recommend joining the forums at www.allaboutcircuits.com. They have a subforum ccalled "projects" and some serious nerds there that will guaranteed be able to answer your questions better than me if not fully to your satisfaction. They have helped me out recently when I was very frustrated with a project of my own and I personally will go there first for any electronics questions after that experience.

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Oh well. I'm sure all of this has been a learning experience for you to say the least. You and I are on much the same path and so I can identify with your interest, enthusiasm, confusion, disappointment, etc. No worries though, let's look at it as "right of passage". :D

A low impedence output can handle going into a higher impedence input, but not the other way around. This is what I've learned, but it is 2nd hand knowledge from a member of the nerd herd at my employer and other threads within this and other electronics forums, for a basic bit of evidence, it's stated about 2/3 down this page... http://www.kpsec.freeuk.com/imped.htm

In practical termns, if you think about how things like op amp based stomp boxes work, they are always very low output impedence and very high input impedence (this is why they're used as buffers and how they avoid "loading" the guitar circuit). They have no issues interfacing with the input of a guitar amp. If there is any issue with a low output impedence, then I'd also like to know why.

Impedence is not so easily measured. It's a combination of resistance, inductance, capacitance, reactance (variation with frequency), all brought together. You would need an LCR meter to measure the individual values and use some math (that I'v enot ventured to fully understand) to come up with the impedence value. I also believe there is a difference powered vs unpowered. However, I believe that for the most part, with something as simple as headphones, you can factor it down to an estimate, based on only the resistance of the headphones. I think your biggest issue is going to be the output current, not impedence. Like I said a few posts back, I hooked this up with a TL082 driving my Bose headphones (quite high output) using dual 9V supplies and it was very nice. I do not think the dual 9V supplies change the output impedence, but the output current of the op amp does go up with increased voltage supplied to the op amp.

Some of your questions are very valid and I'm not sure you're going to get the answers you really need here... notice no one else seems to be chiming in?

I would recommend joining the forums at www.allaboutcircuits.com. They have a subforum ccalled "projects" and some serious nerds there that will guaranteed be able to answer your questions better than me if not fully to your satisfaction. They have helped me out recently when I was very frustrated with a project of my own and I personally will go there first for any electronics questions after that experience.

yes, i've read many articles like this before, and the "low output impedance, high input impedance" system is the best for stompbox-to-stompbox, or from guitar to amp, etc etc, but like the article says, when driving speakers you need a matched impedance for maximum power transfer. i'm sure the concept applies when driving a 0.3" speaker just the same

as when driving a 12".

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Yep, you're right, I missed that point. It sounds as though with a lower than matched output impedence, some power is lost. This would make sense why when I built the 18V version it sounded much better than the 9V version if it was because it was able to supply more power and make up for what was being lost. I did not measure the output current.

I found a thread where someone with a similar set of circumstances found a secondary buffer on the ouptut makes a positive impact.

http://www.electro-tech-online.com/electro...dphone-amp.html

Edited by Donovan
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Yep, you're right, I missed that point. It sounds as though with a lower than matched output impedence, some power is lost. This would make sense why when I built the 18V version it sounded much better than the 9V version if it was because it was able to supply more power and make up for what was being lost. I did not measure the output current.

I found a thread where someone with a similar set of circumstances found a secondary buffer on the ouptut makes a positive impact.

http://www.electro-tech-online.com/electro...dphone-amp.html

thanks, but i dont think I'm quite ready to deal with transistors yet. i know how they work, but to actually see them implemented in a circuit spins my head around. (maybe you could refer me to a good site/article on transistor tips and how to read transistor schems?)

by the way, i have an updated schem, now with an LED and switch. Also, i fixed the wall-wart power supply problem.

headphoneampschematic7final.jpg

unfortunately i think radio shack STOPPED stocking and selling op amp sockets, and my town only has one other electronics store (which doesnt stock them) so i seem to be at a dead end as far as soldering up a board goes.

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