Here is a low voltage rail-to-rail opamp you could try. Maybe a little too low voltage.
http://focus.ti.com/lit/ds/symlink/opa365.pdf
In other news, I just received some MAX629 500ma DC-DC converter chips. I'm going to build up a circuit to take a single 3.7v lithium battery up to around 20v to use with the OPA551 board I made. I have everything I need except the 47uH SMD inductors.
Still waiting impatiently for the new earbuds to arrive.
http://focus.ti.com/lit/ds/symlink/opa365.pdf
In other news, I just received some MAX629 500ma DC-DC converter chips. I'm going to build up a circuit to take a single 3.7v lithium battery up to around 20v to use with the OPA551 board I made. I have everything I need except the 47uH SMD inductors.
Still waiting impatiently for the new earbuds to arrive.
theAnonymous1 said:
That is nearly the output stage that I'm using, interesting coincidence. That is in the signal path even if it's just producing the ground point.
Using those big caps, why not just put them in series with the output and run the OP amps single ended off the supply? The CMOY caps that produce the ground reference are in the signal path anyway.
Just offering some different perspectives.
Pete B.
I won't be using 220uf caps due to space. I plan on using 100uf tants. The caps ground point won't be connected to the diodes like they are in the diagram from Tangents site. Sijosae's original schematic does not have the caps connected this way (see fig I below).
Going single ended with 100uf tants into 25 ohm phones would pretty much kill all the bass. This wouldn't be such a bad thing for my girlfriend as she can't hear that low anyways, but I might want to use the amp occasionally.
An externally hosted image should be here but it was not working when we last tested it.
Going single ended with 100uf tants into 25 ohm phones would pretty much kill all the bass. This wouldn't be such a bad thing for my girlfriend as she can't hear that low anyways, but I might want to use the amp occasionally.
Yes, 100 uF is a bit low.
I believe that now the Grado phones are the headroom limit as I can hear significant distortion during heavy bass passages at loud listening levels. Phones are obviously going to have excursion limits in the same way as a woofer.
Filtering below 20 Hz might make sense with most phones. You might want to filter higher for your girlfriend if you need very high midrange levels so that the midrange SPL will not be limited by bass excursion.
Pete B.
I believe that now the Grado phones are the headroom limit as I can hear significant distortion during heavy bass passages at loud listening levels. Phones are obviously going to have excursion limits in the same way as a woofer.
Filtering below 20 Hz might make sense with most phones. You might want to filter higher for your girlfriend if you need very high midrange levels so that the midrange SPL will not be limited by bass excursion.
Pete B.
OK, I finally received the new pair of custom buds and I am steaming @#%$ing mad. The new buds were supposed to be 25 ohm and they measure 6.6R. The sick thing is the companies name is Precision Laboratories INC. Not so @#$%ing precise are they.
The proof is in the pudding so they say.......
http://i15.tinypic.com/4c2y3k0.jpg
I'm going to try my best monday to keep my head from exploding when I call Tammy at the earplugstore. She is just the middle man(women) who sells Precision Labs service. I did find it a bit discerning when I first called her with my original complaint and she didn't even know what "impedance" is or why it is an important spec. She sells headphones for a living.
I tried the buds on the OPA551 amp I built and it distorts almost right away. The MP3 player that feeds the headphone amp drives them better, but it also distorts before it plays at a decent volume.
I just purchased $40 worth of parts from digi-key to make a dc-dc converter and rail splitter for the cmoy and now I can't even use any of it.
These were supposed to be a xmas present...... it's @#*$ing March. All I can do is *sigh* at this point.
The specs say "Balanced Armature single driver ", but their specs obviously can't be trusted. It could be a piezo in parallel with a 6.6R resistor for all I know.
My dear friend Tammy told me they are able to make the drivers in any impedance. The only problem seems to be they can't read. How does 25 look anything like 6.6?
My dear friend Tammy told me they are able to make the drivers in any impedance. The only problem seems to be they can't read. How does 25 look anything like 6.6?
Well, good news and bad news.
The good news first......
I finished the headphone amp and it works like a charm. I used it with a pair of cheap 30 ohm headphones and it reaches ear splitting levels.
The tiny amp board is only 1"x2" and contains a DC-DC converter, a discrete rail splitter, and the amp circuit with two OPA551. The DC-DC converter takes a 3.7v lithium cell and converts it to about 23.5v (odd number, don't ask). At full volume into my 30 ohm phones the rails never deviate more than 0.5v from each other and only sag to about +-10.8v. This thing is crazy powerful for it's size and sounds good to boot.
Here is a pic of it powered up and singin' some songs......
http://i15.tinypic.com/2ewhybm.jpg
http://i18.tinypic.com/2ufc11x.jpg
Now the bad news.......
I called my good friend Tammy Bashir of the earplugstore to complain about the second round of screw up. She seemed very aggravated that I expected what I paid for and immediately referred me to a guy named Bill Jr. at Precision Labs. She said she didn't have time to play the middle man. That was nice of her to say considering she had the time to process my $220 credit card order.
So anyway, I call this Bill Jr. guy and explained to him about how imprecise his operation is. He too seemed aggravated at my request to get what I paid for. He said that if they aren't what I want then he can't help me. How nice of him huh? He explained that he just purchases the drivers and they are what they are. It's nice that on his own site he advertises their custom molded buds come with 19 ohm drivers, yet he has no 19 ohm drivers. After a few choice words he said I can mail them back to him AGAIN at my own cost and he will take a look at them, but won't promise he can solve the problem.
At this point I am extremely exhausted and frustrated. I'm not sure if I should send them back again, or go through the painful process of my credit cards buyer protection plan.
*sigh*
The good news first......
I finished the headphone amp and it works like a charm. I used it with a pair of cheap 30 ohm headphones and it reaches ear splitting levels.
The tiny amp board is only 1"x2" and contains a DC-DC converter, a discrete rail splitter, and the amp circuit with two OPA551. The DC-DC converter takes a 3.7v lithium cell and converts it to about 23.5v (odd number, don't ask). At full volume into my 30 ohm phones the rails never deviate more than 0.5v from each other and only sag to about +-10.8v. This thing is crazy powerful for it's size and sounds good to boot.
Here is a pic of it powered up and singin' some songs......
http://i15.tinypic.com/2ewhybm.jpg
http://i18.tinypic.com/2ufc11x.jpg
Now the bad news.......
I called my good friend Tammy Bashir of the earplugstore to complain about the second round of screw up. She seemed very aggravated that I expected what I paid for and immediately referred me to a guy named Bill Jr. at Precision Labs. She said she didn't have time to play the middle man. That was nice of her to say considering she had the time to process my $220 credit card order.
So anyway, I call this Bill Jr. guy and explained to him about how imprecise his operation is. He too seemed aggravated at my request to get what I paid for. He said that if they aren't what I want then he can't help me. How nice of him huh? He explained that he just purchases the drivers and they are what they are. It's nice that on his own site he advertises their custom molded buds come with 19 ohm drivers, yet he has no 19 ohm drivers. After a few choice words he said I can mail them back to him AGAIN at my own cost and he will take a look at them, but won't promise he can solve the problem.
At this point I am extremely exhausted and frustrated. I'm not sure if I should send them back again, or go through the painful process of my credit cards buyer protection plan.
*sigh*
I finished the amp and thought I would post some pics. I dub this amp "Nuclear Winter(green)" because it packs so much power in such a small package, and because well, it's in a wintergreen altoids case.
The cover slides open to gain access to a small connector for charging.
http://i19.tinypic.com/2uqgg9l.jpg
http://i19.tinypic.com/2hp0dqv.jpg
http://i16.tinypic.com/2q1t0dt.jpg
http://i17.tinypic.com/30wplki.jpg
I hesitantly sent the custom earphones back AGAIN, so give it about 3 weeks and we will see what happens. I'm not keeping my hopes up. I am very disappointed with both http://earplugstore.stores.yahoo.net and http://www.precisionweb.com/. Their customer service seems to come second to their profits.
The cover slides open to gain access to a small connector for charging.
http://i19.tinypic.com/2uqgg9l.jpg
http://i19.tinypic.com/2hp0dqv.jpg
http://i16.tinypic.com/2q1t0dt.jpg
http://i17.tinypic.com/30wplki.jpg
I hesitantly sent the custom earphones back AGAIN, so give it about 3 weeks and we will see what happens. I'm not keeping my hopes up. I am very disappointed with both http://earplugstore.stores.yahoo.net and http://www.precisionweb.com/. Their customer service seems to come second to their profits.
Hi Zigis,
Yes, I am using the MAX629. I have the output of the boost circuit set at around 23v. This is a little high for the tantalum caps I'm using, but they don't seem to mind. There was a little audible switching noise from the supply at first, but a 0.1uf cap across pins 3 & 4 completely got rid of it and now the amp is dead silent.
The lithium cell is 900mah. The amp will run at very high output levels for around 5-6hrs per charge. The nice thing about the cell phone battery I am using is that it will automatically cut off the power when the battery reaches 3v to prevent damage to the cell.
I was in a rush to put the thing together and forgot to measure the quiescent current draw of the whole circuit.
In the picture below I outlined each circuit with a colored box. Red is the MAX629, Blue is the discrete rail splitter, and Green is the amplifier.
Yes, I am using the MAX629. I have the output of the boost circuit set at around 23v. This is a little high for the tantalum caps I'm using, but they don't seem to mind. There was a little audible switching noise from the supply at first, but a 0.1uf cap across pins 3 & 4 completely got rid of it and now the amp is dead silent.
The lithium cell is 900mah. The amp will run at very high output levels for around 5-6hrs per charge. The nice thing about the cell phone battery I am using is that it will automatically cut off the power when the battery reaches 3v to prevent damage to the cell.
I was in a rush to put the thing together and forgot to measure the quiescent current draw of the whole circuit.
In the picture below I outlined each circuit with a colored box. Red is the MAX629, Blue is the discrete rail splitter, and Green is the amplifier.
An externally hosted image should be here but it was not working when we last tested it.
refund for incorrect order
Hi,
since you used your credit card (not debit card) you have the power of them behind you.
Write to the supplier (the sales woman that can't be bothered) and ask for a refund of the cost (both if both don't meet the intended specifications) and copy the letter to your credit card company. Make sure the retailer knows you have copied to the credit card by saying so on the letter. The retailer will take heed.
The credit card company will put the sale in dispute and freeze the funds.
If the dispute is not resolved for the wrong goods supplied problem you can use the credit card company to demand your money back for all the goods falsely described.
at least the 6r6 phones are due for refund.
what about the 25r/19r phones? did they meet the original specification?
Now back to the current drive problem way back in posts 1 to 20.
I haven't read those in between 21 and latest.
Power =V^2/R =I^2*R
You know the current limit of the opamp. Therefore use the current power rating.
When using peak currents rather than rms values remember to divide by 2 to obtain the rms based power.
The 2134 has a 40mA current limit.
P=0.04^2*25=0.04Wpk=0.02Wac i.e.20mW.
for 115db/mW phones that equates to a maximum SPL of 115+13=128db.
The average level probably nearer 110 to 115db to avoid clipping.
If the 2134 had been operating correctly it should have been capable of average levels of 110db before clipping.
Reducing the phones to 19r (if they had been manufactured to correct spec) would have REDUCED the power and SPL delivered cf the 25r versions.
Hi,
since you used your credit card (not debit card) you have the power of them behind you.
Write to the supplier (the sales woman that can't be bothered) and ask for a refund of the cost (both if both don't meet the intended specifications) and copy the letter to your credit card company. Make sure the retailer knows you have copied to the credit card by saying so on the letter. The retailer will take heed.
The credit card company will put the sale in dispute and freeze the funds.
If the dispute is not resolved for the wrong goods supplied problem you can use the credit card company to demand your money back for all the goods falsely described.
at least the 6r6 phones are due for refund.
what about the 25r/19r phones? did they meet the original specification?
Now back to the current drive problem way back in posts 1 to 20.
I haven't read those in between 21 and latest.
Power =V^2/R =I^2*R
You know the current limit of the opamp. Therefore use the current power rating.
When using peak currents rather than rms values remember to divide by 2 to obtain the rms based power.
The 2134 has a 40mA current limit.
P=0.04^2*25=0.04Wpk=0.02Wac i.e.20mW.
for 115db/mW phones that equates to a maximum SPL of 115+13=128db.
The average level probably nearer 110 to 115db to avoid clipping.
If the 2134 had been operating correctly it should have been capable of average levels of 110db before clipping.
Reducing the phones to 19r (if they had been manufactured to correct spec) would have REDUCED the power and SPL delivered cf the 25r versions.
I am still waiting for the 3rd set of earbuds to show up. I should probably call Precision Labs and bug them, or they might never show up. If the new phones aren't to spec or if they give me any trouble when I call, then I will go ahead with legal actions.
Zigis,
I bought the battery off ebay and it came with a charger.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160059864568
I should note I bought 2 of the above items and both of the chargers did not work. There is a small transformer inside to provide 5v or so to the charging circuit; this transformer has a manufacturing flaw and does not work. I had to provide a separate 5v supply. Still not a bad deal for the money considering the charging circuit part does work.
I'm not too sure what the other pin on most batteries is for. I think after the battery drains past around 3v that pin might output a small voltage signal.
Zigis,
I bought the battery off ebay and it came with a charger.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=160059864568
I should note I bought 2 of the above items and both of the chargers did not work. There is a small transformer inside to provide 5v or so to the charging circuit; this transformer has a manufacturing flaw and does not work. I had to provide a separate 5v supply. Still not a bad deal for the money considering the charging circuit part does work.
I'm not too sure what the other pin on most batteries is for. I think after the battery drains past around 3v that pin might output a small voltage signal.
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