Hi! I'm a hobbyist trying to learn about amps, etc.
I wonder why is the power supply in this amp so much more complicated than the original O2? What are the improvements? Why 3 more voltage regulators and a lot more caps?
What's the purpose of the TL064?
I've searched a bit about the Zobel network but i'm having some difficulties on understanding it. What's it's purpose? Won't it increase the output resistance?
I also have some questions about the bass boost. Is it really only a RC filter that's suppressing the higher frequencies? If so, won't the high's suffer a lot more than the mids?
I wonder why is the power supply in this amp so much more complicated than the original O2? What are the improvements? Why 3 more voltage regulators and a lot more caps?
What's the purpose of the TL064?
I've searched a bit about the Zobel network but i'm having some difficulties on understanding it. What's it's purpose? Won't it increase the output resistance?
I also have some questions about the bass boost. Is it really only a RC filter that's suppressing the higher frequencies? If so, won't the high's suffer a lot more than the mids?
Hi, I can help out there.
I don't recommend people using the bass boost part of the circuit anymore. If works fine, but the corner frequency (where the boost cuts in) is fixed, as is the amount of boost and the slope of the transition region. A hardware or software equalizer between the audio source and the amplifier would give a lot more flexibility over these parameters.
One of NwAvGuy's design parameters with the O2 was also not to mess with the signal in any way other than amplitude (volume). Bass boost really should be elsewhere in the signal chain.
As for how it works: Each op amp has a feedback resistor, lets call it R1, in parallel with another series resistor + capacitor (call that one R2). Lets also say R1 = R2 = R, all the same value. So for low frequencies that capacitor blocks the signal from resistor R2. The gain is then R1/Rg = R/Rg (Rg = gain switch selection resistor). But at high frequencies the capacitor lets signal pass. Now you have R1 in parallel with R2, which gives 1/2R. Plug that in the gain forumula above and you get half the gain. (0.5*R)/Rg.
As for the (optional) Zobel circuit on the output, I threw that in there at design-time just because it had been an big issue with AMB's b22 headphone amp, which I was familiar with at the time, to stop oscillations. As it turned out the ODA doesn't have that problem, with any load I've tried or anyone else has reported, so the Zobel has never been used to my knowledge. I have "optional" next to the Zobel parts in the BOM.
The TL064 is wired up as a dual channel (left and right) window comparator, as I recall.
It is part of the clipping indicator circuit, the LEDs that let you know of the input is being overdriven. The O2 headamp can suffer from that problem. I wanted to "fix" it with an indicator here. So the audio signal path does not pass through the TL064 circuit. Just a side thing.Op-amps can be used as comparators in certain situations. Comparators usually switch faster but often have an open collector output that requires a pull up resistor. Here, just driving indicator leds, blazing speed wasn't important but having outputs that swung high and low was helpful. Also that quad package since a window comparator requires 2 comparators.
There are actually 2 voltage regulators in the O2, a positive and a negative.
I used a two stage design for a few reasons. The Linear Tech LDO final regulators have slightly lower noise figures, but only slightly if you properly "gain up" their datasheet noise numbers for the voltage setting. Like most things from Linear Tech they are supposed to be a complimentary voltage regulator pair (positive and negative regulator), but are not...quite... if you really dig into the datasheet. One thing is the input voltage difference. One, the positive reg I believe it was, is 20V max. The other is 30. 20V is just barely too low with the standard transformer voltages out there. So the pre-regulators (which are slightly noisier but have a 35V input) drop the voltage down low enough to meet specs on that one LDO.Past that having two stages reduces ripple more. And the big one: power dissipation. Gets spread out over two VRs on each power rail, with most of it getting burned off by the pre-reg. That leaves the LDOs with relatively little to do, which is a good thing for the final regular.
I hope this helps!
Last edited:
Noise When Changing Volume
First off, this amp is still awesome, been using it nearly every day since I built it.
But, recently I have started getting noises when changing volume... kinda like static. I got them before every once in a while but could only hear them when no source was playing and they were very, very quiet. Now it is starting to get louder and I can hear when music is playing.
Did I have a bad volume pot from the beginning and should have replaced? Or maybe some other part is starting to fail. It seems the worst right when I turn it on and more noticeable on my powered monitors than on my headphones. The gain setting seems to have no effect on the loudness of the static.
Any ideas?
First off, this amp is still awesome, been using it nearly every day since I built it.
But, recently I have started getting noises when changing volume... kinda like static. I got them before every once in a while but could only hear them when no source was playing and they were very, very quiet. Now it is starting to get louder and I can hear when music is playing.
Did I have a bad volume pot from the beginning and should have replaced? Or maybe some other part is starting to fail. It seems the worst right when I turn it on and more noticeable on my powered monitors than on my headphones. The gain setting seems to have no effect on the loudness of the static.
Any ideas?
If its happening when you rotate the volume knob its probably the pot....I have had the same issue with mine for awhile as well. Been going to replace it but just too many things get in the way!! I dont know if this pot is still available from Mouser or other vendors? Will look into this.
My scratchiness is in the 9am to 10 am area...where I listen the most with the 2x gain with my high impedance cans. I rotate it a few times and it cleans up nicely until the next time...so thats my solution for right now.
Alex
Still available at mouser.
PTD902-1015K-B102 Bourns | Mouser
My scratchiness is in the 9am to 10 am area...where I listen the most with the 2x gain with my high impedance cans. I rotate it a few times and it cleans up nicely until the next time...so thats my solution for right now.
Alex
Still available at mouser.
PTD902-1015K-B102 Bourns | Mouser
Last edited:
I recently ran into this problem with a different headphone amp, the whammy, and found that tying the body of the pot to signal ground removed this hum.
No hum here... just scratchy, static like sounds, and yes they only occur when rotating the volume knob. For me, they occur between 10 o'clock and 2 o'clock positions of the knob and I do notice that the more I turn the knob back and forth, the more the sounds decrease.
I've even tried to stop the rotation of the knob when the static starts to try and see if I can "lock in" the static just as a test, but every time I stop rotation, the sounds stop too.
I will look up tomorrow if the same part is still available on Mouser or Digikey.
I've even tried to stop the rotation of the knob when the static starts to try and see if I can "lock in" the static just as a test, but every time I stop rotation, the sounds stop too.
I will look up tomorrow if the same part is still available on Mouser or Digikey.
4x4F150 and adydula - yep, sounds like a classic worn-pot description. Hey I'm curious - please refresh my memory - roughly how many years have your ODAs been in use? Just like to get a feel for how long the pot lasts.
Are you both using the 1K linear pot, the mouser #652-PTD902-1015KB102 (the standard one in the BOM)?
Pots can be somewhere between hard to impossible to remove without a solder sucker (I have one). If you guys would want to mail your amps to me I can replace the pot and mail back. PM me here if you want.
Alex - that is good news that Mouser has them in stock!
adam1016 - you are right, it is very important to ground the pot shaft (in this case the body is plastic, but there is a metal face plate connected to the shaft). Without the shaft grounded the pot can become sensitive to "hand noise" too (hum), just from proximity to someone's hand. In the ODA the shaft gets grounded with the nut - the front panel and the rest of the case is single-point grounded at the ground of the input jack, same as with NwAvGuy's O2 headamp.
Are you both using the 1K linear pot, the mouser #652-PTD902-1015KB102 (the standard one in the BOM)?
Pots can be somewhere between hard to impossible to remove without a solder sucker (I have one). If you guys would want to mail your amps to me I can replace the pot and mail back. PM me here if you want.
Alex - that is good news that Mouser has them in stock!
adam1016 - you are right, it is very important to ground the pot shaft (in this case the body is plastic, but there is a metal face plate connected to the shaft). Without the shaft grounded the pot can become sensitive to "hand noise" too (hum), just from proximity to someone's hand. In the ODA the shaft gets grounded with the nut - the front panel and the rest of the case is single-point grounded at the ground of the input jack, same as with NwAvGuy's O2 headamp.
Last edited:
Built mine in 2014.
I dont have the Hakko solder sucker....I would physically break up the pot carefully with a pair of pliers etc..slowly etc...remove all the plastic/ceramic emnclosure to expose the actual pins and desolder one at a time, I have done this before and if done carefully it will work...just needs patience....heat only pin at a time, heat and remove pin quickly...then de-solder the hole where the pin was....prevents heating the entiire area etc and possible causing board damage or land de-lamination...
Alex
I dont have the Hakko solder sucker....I would physically break up the pot carefully with a pair of pliers etc..slowly etc...remove all the plastic/ceramic emnclosure to expose the actual pins and desolder one at a time, I have done this before and if done carefully it will work...just needs patience....heat only pin at a time, heat and remove pin quickly...then de-solder the hole where the pin was....prevents heating the entiire area etc and possible causing board damage or land de-lamination...
Alex
If you're looking for a good solder sucker and don't have the budget for say a Hakko FR 300/301 etc. these are worth their weight in gold.
Professional Silicone-Tip Solder Sucker ID: 1597 - $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits
They're surprisingly small but powerful. All metal construction and the silicone tip forms a much better seal than those typical white teflon tips because it actually conforms around the solder joint
As for removing multi-pin components like pots, one method I've developed and had great luck with is to mount the PCB in a vise or some kind of holder (component side down) and attach and hang something weighted to the component you're wanting to remove. Ensuring two main things: 1 that the board is level so that gravity is pulling the component at a nice perpendicular angle to the PCB. And 2 the weight is heavy enough to actually pull on the component but light enough to be gentle on the PCB.
After it's all set up I'll add some excess solder to the joints and then bridge the solder joints all together (taking breaks as needed to keep the temperature from heating the board too much) After all the solder joints are bridged from the excess solder I'll gently lay the long edge of the soldering tip across all the solder around the pins at once and then gravity just pulls the component out. Afterward, I'll clean up the holes with a solder sucker, solder wick, isopropyl, and q-tips. You can also mask off the solder side with some Kapton tape to prevent disturbing other solder joints and cut down on clean up afterword
Professional Silicone-Tip Solder Sucker ID: 1597 - $17.50 : Adafruit Industries, Unique & fun DIY electronics and kits
They're surprisingly small but powerful. All metal construction and the silicone tip forms a much better seal than those typical white teflon tips because it actually conforms around the solder joint
As for removing multi-pin components like pots, one method I've developed and had great luck with is to mount the PCB in a vise or some kind of holder (component side down) and attach and hang something weighted to the component you're wanting to remove. Ensuring two main things: 1 that the board is level so that gravity is pulling the component at a nice perpendicular angle to the PCB. And 2 the weight is heavy enough to actually pull on the component but light enough to be gentle on the PCB.
After it's all set up I'll add some excess solder to the joints and then bridge the solder joints all together (taking breaks as needed to keep the temperature from heating the board too much) After all the solder joints are bridged from the excess solder I'll gently lay the long edge of the soldering tip across all the solder around the pins at once and then gravity just pulls the component out. Afterward, I'll clean up the holes with a solder sucker, solder wick, isopropyl, and q-tips. You can also mask off the solder side with some Kapton tape to prevent disturbing other solder joints and cut down on clean up afterword
Thanks guys for all the feedback!
OK, interesting, so let's say around 3 years (cumulative) of near-daily use for the ODA volume pots. Alex it sounds like yours may have made it to 4+, but since both have been scratchy for a little while the "non-scratchy" period sounds like maybe 2.5-3 years of total time, if it were all lumped together.
Yep, for better or worse, with near-daily use around 3 years is probably what a person will get out of the small 9 mm pots before they start going scratchy. Less frequent use would add time to that, as would a larger pot (which wouldn't fit of course).
Alex - that would be my default method if I didn't have the solder sucker. Exactly as you say, cut/crush the pot body, then go after the pins one at a time with solder wick and pliers.
4x4F150 - please do feel free to send it to me, if you want, at any point!
Definitely watch out for solder wick here. Quite possible to lift the traces off the board with the stuff before the pot pins are out of the hole. If I don't have the solder sucker out I will sometimes clear holes (after the lead for something is out) by just heating the hole up and then tapping the board on the table.
Lavalier - interesting! I can see how that would be effective. Could use something like hot glue to temporarily stick a fishing weight on the top of the pot. Great pointer to that spring loaded sucker too. Like you say, I can see how the conformal tip would be wayyy better than rigid Teflon (which I've tried to use myself in the past and is semi-useless because it doesn't conform).
In fact, funny story there, regarding NwAvGuy's O2 headamp and gravity helping part extractions. He made the PCB holes for the voltage regulators a bit too large, either by accident or design, who knows. So to get them out all I have to do is lay the soldering iron tip sideways so it contacts all 3 holes (lead-ends) at once with the board turned upside down. Once the solder for all 3 holes melts after a few seconds the regulator drops right onto the floor by gravity. Works every time.
OK, interesting, so let's say around 3 years (cumulative) of near-daily use for the ODA volume pots. Alex it sounds like yours may have made it to 4+, but since both have been scratchy for a little while the "non-scratchy" period sounds like maybe 2.5-3 years of total time, if it were all lumped together.
Yep, for better or worse, with near-daily use around 3 years is probably what a person will get out of the small 9 mm pots before they start going scratchy. Less frequent use would add time to that, as would a larger pot (which wouldn't fit of course).
Alex - that would be my default method if I didn't have the solder sucker. Exactly as you say, cut/crush the pot body, then go after the pins one at a time with solder wick and pliers.
4x4F150 - please do feel free to send it to me, if you want, at any point!
Definitely watch out for solder wick here. Quite possible to lift the traces off the board with the stuff before the pot pins are out of the hole. If I don't have the solder sucker out I will sometimes clear holes (after the lead for something is out) by just heating the hole up and then tapping the board on the table.
Lavalier - interesting! I can see how that would be effective. Could use something like hot glue to temporarily stick a fishing weight on the top of the pot. Great pointer to that spring loaded sucker too. Like you say, I can see how the conformal tip would be wayyy better than rigid Teflon (which I've tried to use myself in the past and is semi-useless because it doesn't conform).
In fact, funny story there, regarding NwAvGuy's O2 headamp and gravity helping part extractions. He made the PCB holes for the voltage regulators a bit too large, either by accident or design, who knows. So to get them out all I have to do is lay the soldering iron tip sideways so it contacts all 3 holes (lead-ends) at once with the board turned upside down. Once the solder for all 3 holes melts after a few seconds the regulator drops right onto the floor by gravity.
Works every time.
Last edited:
Alex - I was thinking that myself! The pot is a "wear" item in any amplifier (unless an optical encoder I suppose). They really should be a socketed thing.
4x4F150 - Good choice! The odds of lifting a trace, given that many pins and fairly small traces, are really high with anything other than a solder vac. PM sent..
4x4F150 - Good choice! The odds of lifting a trace, given that many pins and fairly small traces, are really high with anything other than a solder vac. PM sent..
Oops! I screwed up on a PM on Tuesday - pls check your PM for details.
I have some questions. I have some questions.
Reply sent... responding here too just in case you forget where the PMs are...
Reply sent... responding here too just in case you forget where the PMs are...
Haha!
PM back your way.Just wanted to post results now that I have my amp back after the volume pot swap... And it is back to dead silent; no static sounds here now.
Alex, I highly recommend that you get yours swapped out... it has made a world of difference. The funny thing is that when agdr had my amp, he could not hear any noise at all. For me, I could hear the amp make static every time I turned the knob from minimum to maximum, but now all is good.
Thanks again agdr!
Alex, I highly recommend that you get yours swapped out... it has made a world of difference. The funny thing is that when agdr had my amp, he could not hear any noise at all. For me, I could hear the amp make static every time I turned the knob from minimum to maximum, but now all is good.
Thanks again agdr!