Great!!!
That makes me feel better!!!
I just sent Mouser a note about the switch and asking them for a replacement!
I am glad you found this one with your golf ball sucking de-soldering system! LOL.
I would have had to physically destroy the switch and remove the legs soldered into the pc board one by one with solder wick....and that is a real pain especially with parts already populated.
The 24 VAC xfmr is boxed and will head your way tomorrow am.
Cool Beans!!
Alex
That makes me feel better!!!
I just sent Mouser a note about the switch and asking them for a replacement!
I am glad you found this one with your golf ball sucking de-soldering system! LOL.
I would have had to physically destroy the switch and remove the legs soldered into the pc board one by one with solder wick....and that is a real pain especially with parts already populated.
The 24 VAC xfmr is boxed and will head your way tomorrow am.
Cool Beans!!
Alex
Ok...
Getting ready for the drill press and drilling out all the front panel holes....simple tape the panel layout agdr provides at the google docs link....print out with a printer and cut and use the 5 holes for alignment.
Then I will carefully punch starter holes with a metal punch and use a small diameter drill to start the holes one at a time.
I start out smaller and enlarge slowly in drill size and checking the fit to the board in the enclosure...
I will post final pix when I am done.
Alex
Getting ready for the drill press and drilling out all the front panel holes....simple tape the panel layout agdr provides at the google docs link....print out with a printer and cut and use the 5 holes for alignment.
Then I will carefully punch starter holes with a metal punch and use a small diameter drill to start the holes one at a time.
I start out smaller and enlarge slowly in drill size and checking the fit to the board in the enclosure...
I will post final pix when I am done.
Alex
Attachments
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Yup...I don't show the center lines in the picture, but have them on it now and will use them. When I did my O2 panels even with the drill centerlines and a punch I still had to file somewhat by hand to get the shapes of the micro-usb openings to mate well.
Its a patient and time consuming job for sure.
I am more worried about how to letter or label the various items....thinking..
Alex
Its a patient and time consuming job for sure.
I am more worried about how to letter or label the various items....thinking..
Alex
ODAC on the way for ODA mounting measurements
I should have an ODAC arrriving this week. I'll take a set of measurements and list where to drill holes in a top-slot board for mounting. I'll also post a rear panel CAD file with the USB slot. I'll post the measurements to locate that slot for anyone else whipping up panels.
I should point out a number of cool things you can do with the ODAC wiring in the ODA. I keep seeing posts from folks who want an output "tap" on the ODAC output along with feeding their O2 headamp for ODACs mounted in O2 amps. Can do, in the case of the ODA...
* You can wire the output of the ODAC to the holes near the ODA's rear RCA input jack (JP1, JP4, JP5). With the ODA's input select switch pushed in the ODAC feeds the ODA input. But the ODAC's output is also available at the ODA's rear RCA jacks to send elsewhere. There is a loading issue with the ODAC. The O2's 10K input impedance is just about the maximum that should be used, from what I read in NwAvGuy's notes. The ODA with the standard build has the same 10K input impedance. BUT... if you push the ODA's input select switch out, so that the ODA's 3.5mm jack is feeding the ODA, then the 10K load is removed from the rear RCA jacks and that ODAC signal passes right through with no loading. In this configuration you can even be feeding the ODA with one signal through the ODA's front 3.5mm jack, while at the same time be sending the ODACs signal somewhere else out through the ODA's rear RCA jacks (no interaction between the ODAC and ODA in this situation). Then remove the 3.5mm input, push the input select switch, and the ODAC is back to feeding the ODA.
* You can additionally wire the ODAC output in parallel with wherever else it is going (rear ODA RCA jack holes or front ODA 3.5mm jack holes) to the ODA's front (pre-amp) RCA jacks (with the pre-amp chip not poplulated).
* You can run the ODAC's output to the holes next to the ODA's 3.5mm jack instead (JP2, JP3) so that the ODAC's signal feed the ODA when the ODA's input select switch is pushed out. This leaves the ODA's rear RCA jack free to hook in some other input. Wired up like this, with the ODA input select switch pushed in you get your rear RCA jack signal. Pushed out you get the ODAC signal fed in through the 3.5mm jack holes.
* Back to the loading issue, you can optionally build up the ODA with the FET-input LME49880 chips instead of the LME49990 bipolar input chips (one of Sergey888's suggestions I believe) which would allow the ODA to have 50K input resistors instead of 10K (at the expense of slighly higher Johnson noise and FET voltage noise). With a 50K load it looks like the ODAC could power another load at the same time, probably down to 14K or so, at the same time.
* You can populate the pre-amp chip wired up as a 1x buffer and use that (via JP20, the inputs to the pre-amp chip) to isolate (act as a current buffer) the ODAC output to keep it from getting loaded. In other words, feed the ODAC output to the holes by the ODA rear RCA jack or front 3.5mm jack, as above, but then run the wires in parallel to the pre-amp 1x buffer chip (JP20). The pre-amp output will now be the ODAC output re-buffered to not load anything.
I have to admit to not having an ODAC, I've been waiting for OPC'c upcomming DAC project.
I should have an ODAC arrriving this week. I'll take a set of measurements and list where to drill holes in a top-slot board for mounting. I'll also post a rear panel CAD file with the USB slot. I'll post the measurements to locate that slot for anyone else whipping up panels.
I should point out a number of cool things you can do with the ODAC wiring in the ODA. I keep seeing posts from folks who want an output "tap" on the ODAC output along with feeding their O2 headamp for ODACs mounted in O2 amps. Can do, in the case of the ODA...
* You can wire the output of the ODAC to the holes near the ODA's rear RCA input jack (JP1, JP4, JP5). With the ODA's input select switch pushed in the ODAC feeds the ODA input. But the ODAC's output is also available at the ODA's rear RCA jacks to send elsewhere. There is a loading issue with the ODAC. The O2's 10K input impedance is just about the maximum that should be used, from what I read in NwAvGuy's notes. The ODA with the standard build has the same 10K input impedance. BUT... if you push the ODA's input select switch out, so that the ODA's 3.5mm jack is feeding the ODA, then the 10K load is removed from the rear RCA jacks and that ODAC signal passes right through with no loading. In this configuration you can even be feeding the ODA with one signal through the ODA's front 3.5mm jack, while at the same time be sending the ODACs signal somewhere else out through the ODA's rear RCA jacks (no interaction between the ODAC and ODA in this situation). Then remove the 3.5mm input, push the input select switch, and the ODAC is back to feeding the ODA.
* You can additionally wire the ODAC output in parallel with wherever else it is going (rear ODA RCA jack holes or front ODA 3.5mm jack holes) to the ODA's front (pre-amp) RCA jacks (with the pre-amp chip not poplulated).
* You can run the ODAC's output to the holes next to the ODA's 3.5mm jack instead (JP2, JP3) so that the ODAC's signal feed the ODA when the ODA's input select switch is pushed out. This leaves the ODA's rear RCA jack free to hook in some other input. Wired up like this, with the ODA input select switch pushed in you get your rear RCA jack signal. Pushed out you get the ODAC signal fed in through the 3.5mm jack holes.
* Back to the loading issue, you can optionally build up the ODA with the FET-input LME49880 chips instead of the LME49990 bipolar input chips (one of Sergey888's suggestions I believe) which would allow the ODA to have 50K input resistors instead of 10K (at the expense of slighly higher Johnson noise and FET voltage noise). With a 50K load it looks like the ODAC could power another load at the same time, probably down to 14K or so, at the same time.
* You can populate the pre-amp chip wired up as a 1x buffer and use that (via JP20, the inputs to the pre-amp chip) to isolate (act as a current buffer) the ODAC output to keep it from getting loaded. In other words, feed the ODAC output to the holes by the ODA rear RCA jack or front 3.5mm jack, as above, but then run the wires in parallel to the pre-amp 1x buffer chip (JP20). The pre-amp output will now be the ODAC output re-buffered to not load anything.
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Pilot holes have been drilled!! Fairly easy so far....
When I get the board I will finish up to custom fit etc....just in case I need to make an adjustment!! LOL.....can u say "file"...
From reading the post about not having the jacks touch the front panel I need to make sure they don't touch the front panel.
Alex
When I get the board I will finish up to custom fit etc....just in case I need to make an adjustment!! LOL.....can u say "file"...
From reading the post about not having the jacks touch the front panel I need to make sure they don't touch the front panel.
Alex
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The Hakko 808 rocks
I had to share these photos of removing the defective gain switch on Alex's board with the Hakko 808. I just can't recommend this tool highly enough. If you are looking for something to drop hints about for Father's day, may I suggest...
From the first three photos you can see that all 10 legs were sucked clean of solder. No damage to the part or to the PC board pads. Even the nearby SMD resistors on the back were spared. Try doing that with solder wick and watch what happens. With wick the best shot is break the part open with pliers or a Dremel, or cut it off at the legs if possible (this works well with SMD op amps), then remove the legs one at time with wick and needle nose pliers. With the Hakko 808 the whole thing is done in about 2 minutes.
That photo of the board with the light behind it just shows that the holes are nice and clean too, ready for the new part.
That beige barrel on the 808 is spring loaded and pops right off for cleaning. At the end of the barrel there is a replaceable ceramic filter and replaceable aluminum "splash plate" that I change after every 20 desolderings or so. It also comes with spring steel cleaning wires to run up the barrel if needed. If things really get stuck they have hand-twisted drill bits for cleaning the nozzle out. I've never had to do that yet. In fact, pretty much every part on this thing is available from Hakko for repair.
I'm kind of a tool freak. I really appreciate running into a well built tool like this that does a job 110%.
I had to share these photos of removing the defective gain switch on Alex's board with the Hakko 808. I just can't recommend this tool highly enough. If you are looking for something to drop hints about for Father's day, may I suggest...
From the first three photos you can see that all 10 legs were sucked clean of solder. No damage to the part or to the PC board pads. Even the nearby SMD resistors on the back were spared. Try doing that with solder wick and watch what happens. With wick the best shot is break the part open with pliers or a Dremel, or cut it off at the legs if possible (this works well with SMD op amps), then remove the legs one at time with wick and needle nose pliers. With the Hakko 808 the whole thing is done in about 2 minutes.
That photo of the board with the light behind it just shows that the holes are nice and clean too, ready for the new part.
That beige barrel on the 808 is spring loaded and pops right off for cleaning. At the end of the barrel there is a replaceable ceramic filter and replaceable aluminum "splash plate" that I change after every 20 desolderings or so. It also comes with spring steel cleaning wires to run up the barrel if needed. If things really get stuck they have hand-twisted drill bits for cleaning the nozzle out. I've never had to do that yet. In fact, pretty much every part on this thing is available from Hakko for repair.
I'm kind of a tool freak.
I really appreciate running into a well built tool like this that does a job 110%.Attachments
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I had to share these photos of removing the defective gain switch on Alex's board with the Hakko 808. I just can't recommend this tool highly enough. If you are looking for something to drop hints about for Father's day, may I suggest...
Ditto on the Hakko 808. This tool has saved hours (days?) of production time in our facility.
Keep up the great work, agdr!
Thanks! I would be happy to take you up on that. The ODAC I have on the way is from JDS. I'll get that installed first.
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Great....
Thanks John as well....it will be nice to see how well this ODA that agdr has put all the time and effort in benchmarks.
I would expect it will be as good as it...."me thinks".... with many nice improvements etc...
JDS labs is where I got my (2) O2 amps and (2) ODACS. John has always been a really accessible and helpful person.
Thanks Again
Alex
Thanks John as well....it will be nice to see how well this ODA that agdr has put all the time and effort in benchmarks.
I would expect it will be as good as it...."me thinks".... with many nice improvements etc...
JDS labs is where I got my (2) O2 amps and (2) ODACS. John has always been a really accessible and helpful person.
Thanks Again
Alex
Hello,
I have had the ODA here for 2 days now and have about 4-5 hrs of listening on a wide variety of headphpones and music.
I have been going back and forth with the O2 amp and 2 other dacs as well.
I will get a helper friend over to do some blind testing to see if we can tell any difference between the two while playing songs etc..
I being an analytical person have bias like we all do and don't want to make subjective claims etc....
My first gut impressions are great, the ODA sounds as good as the O2 to me. With the input removed and the volume and gain all the way up it is totally silent....wonderful.
It has more than enough power to play any of my headphones I have presently to ear splitting levels etc...
Using Beyer T90s. Beyer DT 1350's, AKG Q701's....
I have ODACS and a HRT MSii+ Asynch dac.
With the attenuation resistors shorted out allowing full voltage swing there is no need for me to use any higher gain settings that are provided by the amp.
The volume setting is approx. 10pm to 12 pm for playback for me.
I will take some time and set the levels precisely and do some A/B comparisons between the ODA and my O2's.
Regardless of the outcome this amp is a "keeper" it has the things in it that I wished the O2 had had if only nwavguy would have produced it.
1/4 jack, 3.5mm jack, 3.5 mm input and RCA inputs, multiple gain selection, velvety quiet background...power switch and AC input on the rear...etc. Absolutley no thumps turning on or off. The power LEDs are a nice touch as well.
I really like the idea of a clipping indicator and it works!
At present if I had to choose only one it would be the ODA over the O2 for these reasons alone.
I will post pix when I get the front panel done, find some really nice knobs and figure out how to label the controls and jacks....
For now back to listening, and where in the world is my "reamer???" (I need this to finish up the front panel holes!!! LOL)..
Congratulations to AGDR on all his work getting this design to its present level.....
NwAvGuy would be proud!
Alex
I have had the ODA here for 2 days now and have about 4-5 hrs of listening on a wide variety of headphpones and music.
I have been going back and forth with the O2 amp and 2 other dacs as well.
I will get a helper friend over to do some blind testing to see if we can tell any difference between the two while playing songs etc..
I being an analytical person have bias like we all do and don't want to make subjective claims etc....
My first gut impressions are great, the ODA sounds as good as the O2 to me. With the input removed and the volume and gain all the way up it is totally silent....wonderful.
It has more than enough power to play any of my headphones I have presently to ear splitting levels etc...
Using Beyer T90s. Beyer DT 1350's, AKG Q701's....
I have ODACS and a HRT MSii+ Asynch dac.
With the attenuation resistors shorted out allowing full voltage swing there is no need for me to use any higher gain settings that are provided by the amp.
The volume setting is approx. 10pm to 12 pm for playback for me.
I will take some time and set the levels precisely and do some A/B comparisons between the ODA and my O2's.
Regardless of the outcome this amp is a "keeper" it has the things in it that I wished the O2 had had if only nwavguy would have produced it.
1/4 jack, 3.5mm jack, 3.5 mm input and RCA inputs, multiple gain selection, velvety quiet background...power switch and AC input on the rear...etc. Absolutley no thumps turning on or off. The power LEDs are a nice touch as well.
I really like the idea of a clipping indicator and it works!
At present if I had to choose only one it would be the ODA over the O2 for these reasons alone.
I will post pix when I get the front panel done, find some really nice knobs and figure out how to label the controls and jacks....
For now back to listening, and where in the world is my "reamer???" (I need this to finish up the front panel holes!!! LOL)..
Congratulations to AGDR on all his work getting this design to its present level.....
NwAvGuy would be proud!
Alex
Update on testing... ODAC... part change...V2.1...mods...sound exposure levels
Alex - thank you for the listening impressions! I'll be quite curious what your blind testing turns up. Like NwAvGuy said that really is the gold standard. The one and only thing I ask of anyone here is be completely frank in your reports. If the ODA is worse than anything else than you test against in any area, by all means post it! The "truth is out there" and helps improve the amp.
I have received the ODAC from JDS on Friday but haven't had a chance this weekend to do any more with the mounting. I should have time this week. Keep in mind that you can also do the "2 board" build with the ODA in the longer B4-160 case. Two ODA boards slide in one after the other in the bottom slot. The rear board has just the power supply populated and an ODAC mounted, with the front board just the amp parts.
I'm going to do the B4-080 case ODAC mounting though in the top slot. I've located some 80x160 boards left over from V1.0 of this project that had the wrong case size for the 560uF caps thanks to an error on Mouser's website. That will work just fine as a "substrate" to mount the ODAC on. Once I get the measurements figured out I'll post those. My current thinking is to put the ODAC over the regulators. The USB / Digital noise should be substantially higher than anything in the audio band, assuming a diode junction somewhere or other part nonlinearity doesn't act as a demodulator. I may mount the ODAC on a copper clad board instead to eliminate any chance of digital noise leaking into the amp stages. Still pondering... I'll run some tests on the ODAC again with the QA400 after the ODAC is mounting before forwarding it on to JDS for the dScope testing.
Once I get the ODAC mounting finalized I'll post a second rear panel CAD file with the USB hole in it, along with that good idea of vents from kamilgd. BTW, I don't know if kamilgd intends to sell copies of his nice panels in the vendor forum here or not, but they certainly look better than mine! If he isn't going to sell them maybe he would be willng to post a CAD file. Either way, I should say that I highly encourage ODA add-ons and modifications! Good grief, I've certainly modified the heck out of NwAvGuy's O2 so the same is only fair for this verison of an ODA. That is where the best new ideas come from!
In the meantime you can certainly use your ODA with an external ODAC, like Alex is doing, the JDS ODAC in a box or equivalent.
In other news there is going to be another part change. Credit goes out to Alex again for spotting this one. Resistor R71, a SMD resistor, will change from 82R to 169R, and R70, the end mounted resistor in the relay section, will go back to what it was before, 3.01K, but 1/4 or 1/2W. The changes lower the power dissipation from the regulator IC11. Nothing is lost in performance. I just missed that the 15mA recommended bias current for that chip is with the worst case 125V input and 123V drop across the part. At smaller voltage drops, like what we have here, figure 12 in the datasheet allows smaller bias currents while still staying out of dropout. The change reduces the bias current to 7.5mA and drops the chip dissipation by 200mW. The relay circuit also acts as a safety bleed-down for the large filter caps when the power is turned off, so this change will lengthen that bleed down from about 3 seconds to 6, still acceptable.
The same things applies with any part changes I make here - if any of the folks building V2.0 here have already ordered parts and get nailed by a part change, please just let me know! I'll send out the replacement parts, no charge. Thanks for everyone's interest in the project. At this poiint the BOM is stable again, so it is OK to go ahead and order parts.
Let me know if there is ever anything I can do to facilitate getting your V2.0's completed. Just like Alex discovered, there are a lot of questions that can come up!
There is one other builder now on ODA V2.0, Croxt7. He is overseas and was willing to buy a partially assembled board along with some blank O2 booster boards to get it shipped in the same package and save on shipping costs. I've had some inquiries about assembled boards (in my vendor thread in the vendor forum here) but so far no takers, so this seemed like a good solution for that board before the next V2.1 board run in a few weeks. The next board run will be V2.1 for the folks on the waiting list, which will have the text errors on this board corrected. It will also have that 1N4004 diode hole size problem corrected that Alex found (keep in mind the Gerbers I've posted for V2.0 DO have that issue fixed if anyone is doing a board run). I'm going to do one layout change, rotate JP19 so the disconnect holes are also up and down like JP19 instead of sideways. No change to the board functionality though. I'm going to wait though until any of the V2.0 builders here actively assembling their boards get finished though before sending out V2.1 to fabrication.
Also one more very important thing, the obvious warning for any headphone amp: please protect your hearing like a gold bar! Keep amplifer levels down to the minimum you need and please study the hearing safety chart of sound levels vs. time exposure:
Dangerous Decibels How Loud is Too Loud?
Many headphones and IEMs are quite sensitive these days and can produce levels well into that chart's range with enough voltage swing applied.
Alex - thank you for the listening impressions! I'll be quite curious what your blind testing turns up. Like NwAvGuy said that really is the gold standard. The one and only thing I ask of anyone here is be completely frank in your reports. If the ODA is worse than anything else than you test against in any area, by all means post it! The "truth is out there" and helps improve the amp.
I have received the ODAC from JDS on Friday but haven't had a chance this weekend to do any more with the mounting. I should have time this week. Keep in mind that you can also do the "2 board" build with the ODA in the longer B4-160 case. Two ODA boards slide in one after the other in the bottom slot. The rear board has just the power supply populated and an ODAC mounted, with the front board just the amp parts.
I'm going to do the B4-080 case ODAC mounting though in the top slot. I've located some 80x160 boards left over from V1.0 of this project that had the wrong case size for the 560uF caps thanks to an error on Mouser's website. That will work just fine as a "substrate" to mount the ODAC on. Once I get the measurements figured out I'll post those. My current thinking is to put the ODAC over the regulators. The USB / Digital noise should be substantially higher than anything in the audio band, assuming a diode junction somewhere or other part nonlinearity doesn't act as a demodulator. I may mount the ODAC on a copper clad board instead to eliminate any chance of digital noise leaking into the amp stages. Still pondering... I'll run some tests on the ODAC again with the QA400 after the ODAC is mounting before forwarding it on to JDS for the dScope testing.
Once I get the ODAC mounting finalized I'll post a second rear panel CAD file with the USB hole in it, along with that good idea of vents from kamilgd. BTW, I don't know if kamilgd intends to sell copies of his nice panels in the vendor forum here or not, but they certainly look better than mine!
If he isn't going to sell them maybe he would be willng to post a CAD file. Either way, I should say that I highly encourage ODA add-ons and modifications! Good grief, I've certainly modified the heck out of NwAvGuy's O2 so the same is only fair for this verison of an ODA. That is where the best new ideas come from!In the meantime you can certainly use your ODA with an external ODAC, like Alex is doing, the JDS ODAC in a box or equivalent.
In other news there is going to be another part change. Credit goes out to Alex again for spotting this one. Resistor R71, a SMD resistor, will change from 82R to 169R, and R70, the end mounted resistor in the relay section, will go back to what it was before, 3.01K, but 1/4 or 1/2W. The changes lower the power dissipation from the regulator IC11. Nothing is lost in performance. I just missed that the 15mA recommended bias current for that chip is with the worst case 125V input and 123V drop across the part. At smaller voltage drops, like what we have here, figure 12 in the datasheet allows smaller bias currents while still staying out of dropout. The change reduces the bias current to 7.5mA and drops the chip dissipation by 200mW. The relay circuit also acts as a safety bleed-down for the large filter caps when the power is turned off, so this change will lengthen that bleed down from about 3 seconds to 6, still acceptable.
The same things applies with any part changes I make here - if any of the folks building V2.0 here have already ordered parts and get nailed by a part change, please just let me know! I'll send out the replacement parts, no charge. Thanks for everyone's interest in the project. At this poiint the BOM is stable again, so it is OK to go ahead and order parts.
Let me know if there is ever anything I can do to facilitate getting your V2.0's completed. Just like Alex discovered, there are a lot of questions that can come up!
There is one other builder now on ODA V2.0, Croxt7. He is overseas and was willing to buy a partially assembled board along with some blank O2 booster boards to get it shipped in the same package and save on shipping costs. I've had some inquiries about assembled boards (in my vendor thread in the vendor forum here) but so far no takers, so this seemed like a good solution for that board before the next V2.1 board run in a few weeks. The next board run will be V2.1 for the folks on the waiting list, which will have the text errors on this board corrected. It will also have that 1N4004 diode hole size problem corrected that Alex found (keep in mind the Gerbers I've posted for V2.0 DO have that issue fixed if anyone is doing a board run). I'm going to do one layout change, rotate JP19 so the disconnect holes are also up and down like JP19 instead of sideways. No change to the board functionality though. I'm going to wait though until any of the V2.0 builders here actively assembling their boards get finished though before sending out V2.1 to fabrication.
Also one more very important thing, the obvious warning for any headphone amp: please protect your hearing like a gold bar! Keep amplifer levels down to the minimum you need and please study the hearing safety chart of sound levels vs. time exposure:
Dangerous Decibels How Loud is Too Loud?
Many headphones and IEMs are quite sensitive these days and can produce levels well into that chart's range with enough voltage swing applied.
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Good Morning....
I still cant find my reamer!!! %^$&$%&^
But I have one on the way...LOL...its the small things...
One thing that has popped up that's really quite noticeable.....
In all the back and forth between the ODA and my 2 O2's...the turn off and turn on thumps I have been used to have become more noticeable and annoying.
Again its the little things, with sensitive transducers this can be shocking at times...
Most of my stuff is not that sensitive, but I found my pair of audio technical M50's...and they are 99db sens and 38 ohms.
The ODA is totally anti-thump!!
One other thing is the higher quality jacks are very nice as well. The 3.5 mm Switchcraft jacks are a nice improvement.
Later
Alex
I still cant find my reamer!!! %^$&$%&^
But I have one on the way...LOL...its the small things...
One thing that has popped up that's really quite noticeable.....
In all the back and forth between the ODA and my 2 O2's...the turn off and turn on thumps I have been used to have become more noticeable and annoying.
Again its the little things, with sensitive transducers this can be shocking at times...
Most of my stuff is not that sensitive, but I found my pair of audio technical M50's...and they are 99db sens and 38 ohms.
The ODA is totally anti-thump!!
One other thing is the higher quality jacks are very nice as well. The 3.5 mm Switchcraft jacks are a nice improvement.
Later
Alex
Bass.
Hi.
Is there a percieved change in bass?
This is the one weak point in the O2 in my view. I am wondering where in the signal path one could insert an equilizing circuit to level out whatever hearing imperfections one might have or change the sonic signature to ones liking?
Yes, Thank You agdr for putting all this effort into the project. Time for me to put some orders in a few weeks and catch up
Your efforts Alex to be the first to report on building and listening test calls for a big THANK YOU!
Regards
Hi.
Is there a percieved change in bass?
This is the one weak point in the O2 in my view. I am wondering where in the signal path one could insert an equilizing circuit to level out whatever hearing imperfections one might have or change the sonic signature to ones liking?
Yes, Thank You agdr for putting all this effort into the project. Time for me to put some orders in a few weeks and catch up
Your efforts Alex to be the first to report on building and listening test calls for a big THANK YOU!
Regards
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Turbon,
I did not install the bass boost option in my build. I wanted it to be as flat as the O2 etc...
I am not a real "basshead" and my perception of bass is listening to a real bass violin, or good solid plucks on a bass guitar. The Wood cd by brian Bromberg is a standard I use for testing the quality and tonality of bass. For real low end bass response I use organ music that goes down as low as it goes....27.5hz...
I have listened with both of my Beyers T90 and DT 1350 and the bass seems pretty much the same with both amps.
When I first plugged the ODA in and listened for the first time I was very excited and thought that this was better than the O2. I hadn't listened in awhile since I was in build mode. It really sparkled etc....but I wasn't matching levels etc, just cranking the volume up to where the headphones just sounded awesome....
Upon closer matching the two sound really close to me....I took a SPL meter and set the levels to produce 85db 1Khz tone out of the AKG Q701's....by very carefully coupling the SPL to the transducer in the 701's.
I then listened to a wide variety of songs and went back and forth, it takes me to stop the player, reset, unplug the dac and headphones from one and plug into the other and then start the player again....and listen.
I am pretty fast but its still a 30 second switch etc...and its not blind.
But my gut tells me the ODA is as good as the O2 and in many ways better when it comes to useability and options....
When I get the thing in its case and more "safe" I will train my helper "my wife" to help me do some blind testing and see if I can tell any differences over a set number of changes.
If I had a choice I would pick the ODA over the O2 as it stands right now.
The O2 for the cost, is still a very, very good option for many people. The ODA is more costly but again you get more jacks, switches and customization etc...and better switches etc.
Alex
I did not install the bass boost option in my build. I wanted it to be as flat as the O2 etc...
I am not a real "basshead" and my perception of bass is listening to a real bass violin, or good solid plucks on a bass guitar. The Wood cd by brian Bromberg is a standard I use for testing the quality and tonality of bass. For real low end bass response I use organ music that goes down as low as it goes....27.5hz...
I have listened with both of my Beyers T90 and DT 1350 and the bass seems pretty much the same with both amps.
When I first plugged the ODA in and listened for the first time I was very excited and thought that this was better than the O2. I hadn't listened in awhile since I was in build mode. It really sparkled etc....but I wasn't matching levels etc, just cranking the volume up to where the headphones just sounded awesome....
Upon closer matching the two sound really close to me....I took a SPL meter and set the levels to produce 85db 1Khz tone out of the AKG Q701's....by very carefully coupling the SPL to the transducer in the 701's.
I then listened to a wide variety of songs and went back and forth, it takes me to stop the player, reset, unplug the dac and headphones from one and plug into the other and then start the player again....and listen.
I am pretty fast but its still a 30 second switch etc...and its not blind.
But my gut tells me the ODA is as good as the O2 and in many ways better when it comes to useability and options....
When I get the thing in its case and more "safe" I will train my helper "my wife" to help me do some blind testing and see if I can tell any differences over a set number of changes.
If I had a choice I would pick the ODA over the O2 as it stands right now.
The O2 for the cost, is still a very, very good option for many people. The ODA is more costly but again you get more jacks, switches and customization etc...and better switches etc.
Alex
Ok here is my first set of results doing a real double blind test with a helper.
All that had to be done once the level sets were done was to swap the headphone jack from the ODA to the O2 etc or not! (I choose a level that produced 95 db) enough to make the cans really sound "good" or "loud" etc.
I did a run of 10 samples.
(I used Eva Cassidy's "Ain't No Sunshine" for the test.)
I was not able to successfully pick out either amp to any degree of certainty.
Half the time I was wrong half the time I was correct....but I was never really sure.
It was very hard to detect which one was playing and any differences....very easy to get confused.
This tells me that the amps are very very close, and that's a good thing.
To maintain the same sonic qualities of the O2 is no easy feat to me...to be as transparent and as good as the O2 is awesome.
I have to give kudos to my wife who ran the switching or not switching!!
I also spent an hour just listening, really listening to really low level in he background instruments to see if the resolving was nay better on one or the other. Same conclusion, its all there in both of the amps.
Ok so I am very happy that the ODA to me soncially seems from the same sonic "tree" that the O2 is.
No for some listening!
Alex
All that had to be done once the level sets were done was to swap the headphone jack from the ODA to the O2 etc or not! (I choose a level that produced 95 db) enough to make the cans really sound "good" or "loud" etc.
I did a run of 10 samples.
(I used Eva Cassidy's "Ain't No Sunshine" for the test.)
I was not able to successfully pick out either amp to any degree of certainty.
Half the time I was wrong half the time I was correct....but I was never really sure.
It was very hard to detect which one was playing and any differences....very easy to get confused.
This tells me that the amps are very very close, and that's a good thing.
To maintain the same sonic qualities of the O2 is no easy feat to me...to be as transparent and as good as the O2 is awesome.
I have to give kudos to my wife who ran the switching or not switching!!
I also spent an hour just listening, really listening to really low level in he background instruments to see if the resolving was nay better on one or the other. Same conclusion, its all there in both of the amps.
Ok so I am very happy that the ODA to me soncially seems from the same sonic "tree" that the O2 is.
No for some listening!
Alex
Alex - excellent work! NwAvGuy's good test methods are still alive and well.
All very good news and is exactly what I was hoping for. From your listening report the ODA really does sound like it may be a true desktop O2 if the measurements also stack up. An O2's sound neutrality with 3x the current output, 1/4" jack added, rear power and power switch, rear RCA and input select, clipping detect, more gain settings, pre-amp out.. Plus that ability to build for +/-15Vdc power rails for 300R and 600R cans that can't get enough volume with an O2.
The ODA might very well test better in one or two areas on John's dScope (my big hope here is better noise floor and possibly slightly lower THD) but... like NwAvGuy said, if it is below audible levels for any given person, does it matter? If a tree falls and nobody is around to hear... I know there is one or two enormous philosophical threads going on about that kind of debate.
I also have to admit that I'm not fully sold on measurements only. I tend to go with a quote I saw attributed to Nelson Pass once, that it is possible for an amp to measure well and sound bad. I take that to equate to measurements needed that are not known yet but matter sonically. But measuring well is certainly a good starting point.
As for the specific areas of performance, some thoughts..
* The O2's frequency response curve was mesured to be perfectly flat by NwAvGuy. How do you improve on flat? I increased the roll-off on both ends of the frequency responnse curve slightly. His started rolling off at 5Hz as I recall on the low end. I lowered that to around 2Hz with that big pile of 4.7uF caps. One entire cap in each stack is used up to take the curve from 5Hz to the lower 2Hz. And on the upper end I lowered the gain stage compensation caps to 150pF from 220pf in the O2 amp to increase rolloff to 100Khz, so that a 20KHz square wave would pass looking square. On the O2 he rolls it off closer to the audio spectrum and the 20KHz square wave has sloped edges. But... real music doesn't have square waves, certainly not after going through anti-aliasing filters and a digital signal processing chain at the recording studio. So is the extra 3Hz at the low end and 50Khz on the upper end to pass square waves audible? Probably not.
Also, as for improving on flat, I do think there are headphones out there (and probably some ears) that NEED bass boost to compensate for roll-off on the low end. Hence the bass boost option in the ODA.
* On noise floor, I really am expecting to beat the O2 here. We'll see. Lower noise power supply, lower noise gain chips, lower Johnson noise 1K pot, etc. And I still think I can hear background hiss on my O2s with my 114dB/V AKG K550s, just at the edge of hearing, with the O2s gain and volume all the way up. But... people rarely wind up with a situation of operating their O2 with the gain and volume all the way up. If that background hiss in the O2 isn't heard at lower volumes and gains, where the amp is usually used, does it matter?
* The clipping indicator I do think is a big deal. I tried talking NwAvGuy into that a couple of times with no luck (to his credit through there was simply no room left on the O2 PCB to add more parts without going SMD). With the pot-in-the-middle design, in my view that indicator is REQUIRED to know when your gain stage is going into clipping. With a pot in the front you just turn down the pot. That won't help with the O2 if the gain stage is clipping. You just really do need to know when that is occuring, IMHO.
And other stuff...
I've changed my mind on seending JDS an ODA with the ODAC installed. That ODAC could add digital noise and is a whole different test run in my view. For now I want to see what the ODA tests at with nothing but analog going on inside to get an apples-to-apples comparison with the base O2 amp. Thanks again to JDS for offering to do the dScope tests! There is quite a bit of work and time involved in doing those tests.
All very good news and is exactly what I was hoping for. From your listening report the ODA really does sound like it may be a true desktop O2 if the measurements also stack up. An O2's sound neutrality with 3x the current output, 1/4" jack added, rear power and power switch, rear RCA and input select, clipping detect, more gain settings, pre-amp out.. Plus that ability to build for +/-15Vdc power rails for 300R and 600R cans that can't get enough volume with an O2.
The ODA might very well test better in one or two areas on John's dScope (my big hope here is better noise floor and possibly slightly lower THD) but... like NwAvGuy said, if it is below audible levels for any given person, does it matter? If a tree falls and nobody is around to hear... I know there is one or two enormous philosophical threads going on about that kind of debate.
I also have to admit that I'm not fully sold on measurements only. I tend to go with a quote I saw attributed to Nelson Pass once, that it is possible for an amp to measure well and sound bad. I take that to equate to measurements needed that are not known yet but matter sonically. But measuring well is certainly a good starting point.
As for the specific areas of performance, some thoughts..
* The O2's frequency response curve was mesured to be perfectly flat by NwAvGuy. How do you improve on flat? I increased the roll-off on both ends of the frequency responnse curve slightly. His started rolling off at 5Hz as I recall on the low end. I lowered that to around 2Hz with that big pile of 4.7uF caps. One entire cap in each stack is used up to take the curve from 5Hz to the lower 2Hz. And on the upper end I lowered the gain stage compensation caps to 150pF from 220pf in the O2 amp to increase rolloff to 100Khz, so that a 20KHz square wave would pass looking square. On the O2 he rolls it off closer to the audio spectrum and the 20KHz square wave has sloped edges. But... real music doesn't have square waves, certainly not after going through anti-aliasing filters and a digital signal processing chain at the recording studio. So is the extra 3Hz at the low end and 50Khz on the upper end to pass square waves audible? Probably not.
Also, as for improving on flat, I do think there are headphones out there (and probably some ears) that NEED bass boost to compensate for roll-off on the low end. Hence the bass boost option in the ODA.
* On noise floor, I really am expecting to beat the O2 here. We'll see. Lower noise power supply, lower noise gain chips, lower Johnson noise 1K pot, etc. And I still think I can hear background hiss on my O2s with my 114dB/V AKG K550s, just at the edge of hearing, with the O2s gain and volume all the way up. But... people rarely wind up with a situation of operating their O2 with the gain and volume all the way up. If that background hiss in the O2 isn't heard at lower volumes and gains, where the amp is usually used, does it matter?
* The clipping indicator I do think is a big deal. I tried talking NwAvGuy into that a couple of times with no luck (to his credit through there was simply no room left on the O2 PCB to add more parts without going SMD). With the pot-in-the-middle design, in my view that indicator is REQUIRED to know when your gain stage is going into clipping. With a pot in the front you just turn down the pot. That won't help with the O2 if the gain stage is clipping. You just really do need to know when that is occuring, IMHO.
And other stuff...
I've changed my mind on seending JDS an ODA with the ODAC installed. That ODAC could add digital noise and is a whole different test run in my view. For now I want to see what the ODA tests at with nothing but analog going on inside to get an apples-to-apples comparison with the base O2 amp. Thanks again to JDS for offering to do the dScope tests! There is quite a bit of work and time involved in doing those tests.
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