Like Aborza in post 3519, I'm also considering leaving out the power on/anti-thump circuitry.
The thing is I want to integrate the amp along another project which features a separate very high quality +/-15V DC supply which features a slow power up functionality.
I see the op-amps support up to +/-18V supply. Would there be any problems when I just feed the op-amps directly from the +/-15V supply, or does the power-on circuitry provide additional features that are really essential?
Like Aborza's solution, I do not need this amp to be powered up separately.
If the power-on circuit is crucial, would I need to change out any resistor or capacitor values to accommodate +/- 15V ? I'll do a Spice simulation tomorrow, since the rough transfer function I made from it doesn't seem right.
The thing is I want to integrate the amp along another project which features a separate very high quality +/-15V DC supply which features a slow power up functionality.
I see the op-amps support up to +/-18V supply. Would there be any problems when I just feed the op-amps directly from the +/-15V supply, or does the power-on circuitry provide additional features that are really essential?
Like Aborza's solution, I do not need this amp to be powered up separately.
If the power-on circuit is crucial, would I need to change out any resistor or capacitor values to accommodate +/- 15V ? I'll do a Spice simulation tomorrow, since the rough transfer function I made from it doesn't seem right.
All your O2 amp +/-15Vdc questions answered in the build instructions for my O2 booster board project.
Go to the google drive link in the first post here:http://www.diyaudio.com/forums/headphone-systems/244473-o2-headamp-output-booster-pcb.html
Then go to the 1_18_2014 V3.0 folder, then build instructions, then search or scroll down around 7 headings under "description" for "running on higher voltages". Also at the very end of the build instructions there is an appendix on exactly how to upgrade the O2 to +/-15Vdc. In addition to changing the voltage regulators you have to change one capacitor (upgrade its voltage rating) and the two battery charging resistors have to be increased. Plus you have to make sure you are using the mosfets in the O2 BOM with the +/-30V maximum gate-source voltage, as it says. The O2 booster board BOM also lists the parts for the +/-15Vdc upgrade and their Mouser part numbers. I'm aware of at least two folks who have built the booster board and did the +/-15Vdc O2 amp upgrade in the process.
In a nutshell the O2's NJM4556A output buffer chips in their DIP8 packages would overheat on some loads running on +/-15Vdc power rails according to the O2 designer in his blog, and the math confirms it. If your headphones are high impedance and/or high sensitivity (requiring less current through the O2's NJM4556A chips) it may work just fine. You just need to run the math on the dissipation produced in those O2 output chips, taking ambient de-rating (hotter inside the case) into account.
The booster board I whipped up replaces the NJM4556A chips with LME49600s that don't have the dissipation problem at +/-15Vdc. I had instructions in there for a +/-18Vdc upgrade with the booster board at one time, but removed them. One big problem at +/-18V is no comparator chips (U2 in the O2) I could find rated that high. The existing chip's maximum voltage is 36Vdc, and the power rails are both down one diode drop, so it *should" work in theory but too close to the maximum to feel comfortable about long term reliability at +/-18Vdc. Then the other issue is battery charging. If the O2 is still using batteries the change of charging resistor works just fine to charge them, but once on battery power the rails are back down to +/-9V or so (from the +/-15 or +/-18 on AC).
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agdr,
Thanks a lot for the very informative reply, this is certainly an interesting mod. But it quickly might become an overkill - here's why:
The other project I'm working on is P.-A.'s QSXM02 phono amplifier. It will drive headphones directly, but it is in need of a volume control to become really useable. I can't just add a volume control at the input due to a semi-critical input impedance requirement and I can't just add it at the output since it would then be in series with the headphones, which will also alter their frequency response.
So what I need is a buffer and a volume control. Normal buffers have comparatively large input offsets to be usable without feedback, so it's a no-go with this pre-amp.
What me consider the O2 was the cheap parts, a pre-made PCB with no SMD components that I had to take care of.
Thanks a lot for the very informative reply, this is certainly an interesting mod. But it quickly might become an overkill - here's why:
The other project I'm working on is P.-A.'s QSXM02 phono amplifier. It will drive headphones directly, but it is in need of a volume control to become really useable. I can't just add a volume control at the input due to a semi-critical input impedance requirement and I can't just add it at the output since it would then be in series with the headphones, which will also alter their frequency response.
So what I need is a buffer and a volume control. Normal buffers have comparatively large input offsets to be usable without feedback, so it's a no-go with this pre-amp.
What me consider the O2 was the cheap parts, a pre-made PCB with no SMD components that I had to take care of
.
What me consider the O2 was the cheap parts, a pre-made PCB with no SMD components that I had to take care of
P-A has some excellent project boards! Yep the O2 booster board would be overkill.
Here you go: https://docs.google.com/file/d/0B52...i00YjA4LTk1NzgtZTMwNTAzMWQ3Y2Iy/edit?hl=en_US
The google spreadsheet viewer doesn't do a good job. You can download it at file -> download then open it in Excel.
Don't know if this question has been asked before. I have an O2 that gets a ridiculously small amount of time on 2x9v Tenergy NiMH batteries. I think I might get 1 hr to an 1.5hr at best when being charged for quite a while. Most of the time I've powered the amp off of the 16VAC wallwart with the batteries in tact. Thus I know the batteries should be fully charged. I opened the O2 up and took some VDC readings with my DMM on the batteries and noticed a mismatch in voltage. One battery had 9.05v and the other had 7.63v. From the initial notes on NWAVGUY's website it looks like the batteries should be below 7 volts before the amp shuts off. Also, it seems like they should be even with each other. I'm not even that low. Is a battery mismatch that common? Or could something else be awry? I've decided to plug in the battery that read 9.05v turn on the O2 and then try to get it down to ~7.6v. Then I'll recharge and see what happens. Thoughts?
A problem with the O2 charging circuit is that the charging current depends on battery voltage.
Its common to see the voltage across a 9v pack rise considerably during charging, perhaps to as high as 9.5 volts (or more). Measure it and see. That means that the 12 volts available for charging (less the 0.65v drop of diode D1 or D5) means that as little as (12-0.65)/220 = 8.4 milliamps is available for charging. That could take 30 hours or more. Depending on the battery voltage it may be even less.
You need to check the battery packs marked voltage. Some are higher than others because they include an "extra" cell in the pack. That makes the O2 even worse because it can't fully charge the packs, the packs develop "memory effect" problems and you end up with poor battery performance.
Its common to see the voltage across a 9v pack rise considerably during charging, perhaps to as high as 9.5 volts (or more). Measure it and see. That means that the 12 volts available for charging (less the 0.65v drop of diode D1 or D5) means that as little as (12-0.65)/220 = 8.4 milliamps is available for charging. That could take 30 hours or more. Depending on the battery voltage it may be even less.
You need to check the battery packs marked voltage. Some are higher than others because they include an "extra" cell in the pack. That makes the O2 even worse because it can't fully charge the packs, the packs develop "memory effect" problems and you end up with poor battery performance.
@Mooly
In my reading, I was under the impression that only NiCD batteries develop "memory effect" problems.
Is that 12v you refer based on the AC adapter? If so, then I have the 16v version. How did you come up with 8.4 mA? I did that same equation and came up with .05159090909.
The spec sheet says that "End of Voltage Discharge" is 7v. So I'm assuming I can draw it down to as little as 7v. The nominal voltage is 8.4v.
In my reading, I was under the impression that only NiCD batteries develop "memory effect" problems.
Is that 12v you refer based on the AC adapter? If so, then I have the 16v version. How did you come up with 8.4 mA? I did that same equation and came up with .05159090909.
The spec sheet says that "End of Voltage Discharge" is 7v. So I'm assuming I can draw it down to as little as 7v. The nominal voltage is 8.4v.
That's not a safe assumption. First, which spec sheet? Second, is that the lowest DoD at which they'll continue to supply current, or is that the lowest DoD that will produce the full rated cycle life of the battery? We take batteries for granted. Turns out, they're actually fickle little beasties that are extremely easy to kill.
Ni-cads certainly have a memory effect, that's well know and documented... for Ni-mh there are various opinions, some say yes, some say no. If you look it up you'll find conflicting opinions. I've always felt that they can benefit from an occasional full discharge though, to maintain capacity.
Formulas
Each battery is charged from the appropriate stabilised 12 volt rail via series diode. So you have at most a voltage of around 11.2 to 11.8 ish depending on the exact output of each reg. Subtract from that figure the actual voltage of the battery and divide by 220 and you get the charging current.
A 12 volt AC input will give around -/+ 16 volts DC unregulated, while a 16 VAC input will give around -/+ 22 volts dc unregulated. The O2 doesn't make use of the unregulated rails though.
@williaty - noted. I'm not going to play with fire and I'll just try recharging both for a more substantial period of time to see if I can get the voltage to even out that way. If all else fails it's time for a few more 9v batteries. Need them anyhow for a PINT and PPA-S project I'm working on. Here's the spec sheet I was speaking of... http://www.all-battery.com/datasheet/10001_datasheet.pdf
@Mooly - understood. I'll have to look it up to see the opinions. I get regulated rail aspect vs. unregulated. Where does the 220 figure come from?
@Mooly - understood. I'll have to look it up to see the opinions. I get regulated rail aspect vs. unregulated. Where does the 220 figure come from?
True Memory Effect is way overblown, (and is centralised around a specific NiCd design), it was originally found by aerospace industry in satellites with very tight discharge-charge cycles caused by orbital periods, we are talking discharging to a percentage with 0.01% margin of error, a simple tweak of allowing overcharge fixed this and we are also talking aerospace grade batteries, which I hope don't need to be replaced every 2-3 years because of age.
Well this is at least according to quote from a Bob Myers (in 1996) referring to a GE technical bulletin, but I can't find anything more scientific than the rest of the conjecture on the internet.
Problems with "Initial DIY-Testing"
Hello diyaudio!
I've got some Problems with finishing my Objective2. I have a Kit from Headnhifi in Switzerland.
The Problem is, when measuring the Resistors some of the Values are not Correct.
So for example R25 is 457kOhms instead of ~330... most others seem to be correct. But when I measure the Supply Voltages, things get weird. When i just plug the AC-Adaptor in, the DMM says about 22.6Volts, which is still OK I think?
However, when I Turn the O2 on, the Voltage drops to 18V and doesn't stay at 24V. I checked all the Joints and reheated them but the Problem still occurs. Do you guys have any ideas what could be wrong?
Thank you in Advance and excuse me for my bad English. Describing technical things is harder than i thought it would be.
P.S.: I've got a real cheap DMM, it looks exactly like the one on nwavguys Site. Might this be an Issue?
Hello diyaudio!
I've got some Problems with finishing my Objective2. I have a Kit from Headnhifi in Switzerland.
The Problem is, when measuring the Resistors some of the Values are not Correct.
So for example R25 is 457kOhms instead of ~330... most others seem to be correct. But when I measure the Supply Voltages, things get weird. When i just plug the AC-Adaptor in, the DMM says about 22.6Volts, which is still OK I think?
However, when I Turn the O2 on, the Voltage drops to 18V and doesn't stay at 24V. I checked all the Joints and reheated them but the Problem still occurs. Do you guys have any ideas what could be wrong?
Thank you in Advance and excuse me for my bad English. Describing technical things is harder than i thought it would be.
P.S.: I've got a real cheap DMM, it looks exactly like the one on nwavguys Site. Might this be an Issue?
His sgtstan and welcome to diyAudio
Have you followed and read the fault finding guide I compiled. Post #3775 here,
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667
Have you followed and read the fault finding guide I compiled. Post #3775 here,
http://www.diyaudio.com/forums/head...eadphone-amp-diy-project-189.html#post3806667