Agdr, actually in 2.0 R3 and R4 are not surface mounted as described in the build guide. Another small standard is to keep the direction of non polar parts in line with the pcb text - so in that context direction matters even with resistors 😉
Regards
Regards
You are right! That is one of the "clean-up" changes I made in V2.1.
The 274R R5 & R6 have to be surface mount to fit (front 3.5mm jack) but the 274R R3 & R4 on the rear RCA could go either way. Originally I tried to keep as much stuff through-hole as possible, so those went TH. With V2.1 though I decided that reducing the number of different types of parts was better and just made all 4 SMD.
Did I send you SMD instead of TH for those? If so and you can't get them locally just shoot me a PM and I'll send you a pair. 1/8W 1% metal fim.
The 274R R5 & R6 have to be surface mount to fit (front 3.5mm jack) but the 274R R3 & R4 on the rear RCA could go either way. Originally I tried to keep as much stuff through-hole as possible, so those went TH. With V2.1 though I decided that reducing the number of different types of parts was better and just made all 4 SMD.
Did I send you SMD instead of TH for those? If so and you can't get them locally just shoot me a PM and I'll send you a pair. 1/8W 1% metal fim.
No problems agdr, you have provided both types for R3/R4 🙂
Not either way, reading the text R3 from left to right on the board then the red band should be to the left 😉
Regards
Not either way, reading the text R3 from left to right on the board then the red band should be to the left 😉
Regards
Would there be any use of soldering pins to all the JP's and use connectors to make the connections to other pins on the board?
Regards
Regards
Only IC8 and surroundings left and some connectors.
So what about all the JP's? Should I solder pins on them and use females to connect parts or should I solder cables directly to the board?
Regards
So what about all the JP's? Should I solder pins on them and use females to connect parts or should I solder cables directly to the board?
Regards
I didn't use any pins at all.
I think AGDR has used some for making measurements easier.
I usually find a part to attach to for measurements etch...
You getting close!
Alex
I think AGDR has used some for making measurements easier.
I usually find a part to attach to for measurements etch...
You getting close!
Alex
Sorry about the delayed reply guys, I was tied up all day. 🙂
No need to populate those JPs. I just put those in for maximum flexibility on ways to hook things up. The holes near the rear RCA jack can be used to wire in an ODAC output, same with the holes near the front 3.5mm jack. Or either set of holes can be used to tap off that input and route it to the pre-amp chip, via that set of JP holes, or directly to the pre-amp out jack via the set of holes just in back of that jack.
The set of JP holes near the input select switch can be used to route to the pre-amp chip or pre-amp out jack directly, to just use whichever input is selected. There there are JP holes on the output of each gain stage channel which are just there as test points. There is a set of JP holes between the relay and 1/4" output that can be used to tap the output off for some other panel mounted jack.
So... I would leave them all blank until you had a need, then just solder a wire in directly.
Also Turbon - great soldering job!! You and Alex both have done fantastic soldering work on all those SMD parts.
Remember that on your V2.0 board the power JP18 power supply disconnect jumpers left and right (once you have the output tested, of course), while JP19 jumpers up and down. That is another one of those annoying hiccups I fixed on V2.1. OK to only jumper 1/2 of JP18 and JP19. I put the extra set of holes in there in case some future top slot board wanted power from the power supply. I see another too, looking at your pictures. I biffed the text label on the 1/4" jack, but fixed that on V2.1. 🙂
So Tubon, as per the build instructions the first thing to do once you have it all soldered on and the voltage regulators in place is test those power supply voltages before jumpering JP18 and JP19. Make sure you measure the correct (power supply) side of those disconnects. Then do the resistance check to ground on the other side of the disconnect and make sure you don't have a power rail dead short on either rail. Then connect the disconnects with jumpers, power it up, and you should immediately get the two green power LEDs in the front and those blue voltage reference LEDs near the comparator chip. If those work you have power, then it is on to measuring the output DC offset and setting that with the two trimpots. Remember about the headphone relay delay! 🙂 I forget that myself sometimes and instinctively hit the on/off switch when no sound or DC voltage has shown up at the headphone output after a few seconds, lol.
No need to populate those JPs. I just put those in for maximum flexibility on ways to hook things up. The holes near the rear RCA jack can be used to wire in an ODAC output, same with the holes near the front 3.5mm jack. Or either set of holes can be used to tap off that input and route it to the pre-amp chip, via that set of JP holes, or directly to the pre-amp out jack via the set of holes just in back of that jack.
The set of JP holes near the input select switch can be used to route to the pre-amp chip or pre-amp out jack directly, to just use whichever input is selected. There there are JP holes on the output of each gain stage channel which are just there as test points. There is a set of JP holes between the relay and 1/4" output that can be used to tap the output off for some other panel mounted jack.
So... I would leave them all blank until you had a need, then just solder a wire in directly.
Also Turbon - great soldering job!! You and Alex both have done fantastic soldering work on all those SMD parts.
Remember that on your V2.0 board the power JP18 power supply disconnect jumpers left and right (once you have the output tested, of course), while JP19 jumpers up and down. That is another one of those annoying hiccups I fixed on V2.1. OK to only jumper 1/2 of JP18 and JP19. I put the extra set of holes in there in case some future top slot board wanted power from the power supply. I see another too, looking at your pictures. I biffed the text label on the 1/4" jack, but fixed that on V2.1. 🙂
So Tubon, as per the build instructions the first thing to do once you have it all soldered on and the voltage regulators in place is test those power supply voltages before jumpering JP18 and JP19. Make sure you measure the correct (power supply) side of those disconnects. Then do the resistance check to ground on the other side of the disconnect and make sure you don't have a power rail dead short on either rail. Then connect the disconnects with jumpers, power it up, and you should immediately get the two green power LEDs in the front and those blue voltage reference LEDs near the comparator chip. If those work you have power, then it is on to measuring the output DC offset and setting that with the two trimpots. Remember about the headphone relay delay! 🙂 I forget that myself sometimes and instinctively hit the on/off switch when no sound or DC voltage has shown up at the headphone output after a few seconds, lol.
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Hi agdr et al.
I found myself back to an earlier question/idea I had. Where do we get the signal out of the circuit and where do we inject it again after tweaking? Very few of us have the same hearingabilities on both ears and in the same spectral spans. I would like to open this area up - as I don't have the neccesary skills to do it myself I rather fish and see if others might find this exiting as I do. I rather listen to something I percieve as sounding equal to my ears than looking on a scope to see that the signal is perfectly equal between channels. The reason to step forward? Now I wouldn't give a sh*t about what those not in the need or really have perfectly synced ears thinks - this is not for them. The reason is simple - if we can control this in a good way we can listen to our favourites with the same enjoinment we do today in 50 years 🙂 Sounds good? Yes I know - lets go to work with the experts as agdr and nikolaj if they agree... I would liked to have proposed this to RS as well as he is of the same spirit as so many in the original thread as in the spinnoffs like this thread.
Right, I proposed the idea on another forum as well - at lenco heaven http://www.lencoheaven.net/forum/index.php?topic=17709.0
You do recognise the need and benefit don't you - whoever reads this?
Yeees, we also recognize that needs means money - so much better if we take care of it ourselves so the money stays with us. 🙂
I found myself back to an earlier question/idea I had. Where do we get the signal out of the circuit and where do we inject it again after tweaking? Very few of us have the same hearingabilities on both ears and in the same spectral spans. I would like to open this area up - as I don't have the neccesary skills to do it myself I rather fish and see if others might find this exiting as I do. I rather listen to something I percieve as sounding equal to my ears than looking on a scope to see that the signal is perfectly equal between channels. The reason to step forward? Now I wouldn't give a sh*t about what those not in the need or really have perfectly synced ears thinks - this is not for them. The reason is simple - if we can control this in a good way we can listen to our favourites with the same enjoinment we do today in 50 years 🙂 Sounds good? Yes I know - lets go to work with the experts as agdr and nikolaj if they agree... I would liked to have proposed this to RS as well as he is of the same spirit as so many in the original thread as in the spinnoffs like this thread.
Right, I proposed the idea on another forum as well - at lenco heaven http://www.lencoheaven.net/forum/index.php?topic=17709.0
You do recognise the need and benefit don't you - whoever reads this?
Yeees, we also recognize that needs means money - so much better if we take care of it ourselves so the money stays with us. 🙂
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That is a fascinating idea. I have some "holes" in my hearing that are different from ear to ear. Would be interesting to run an EQ of sorts to work that difference out.
Hey Turbon! 🙂
I'm not sure I follow. Are you after something like a parametric equalizer where the frequency and amplitude can be set individually for the bass cut/boost, and same for the treble? With parametric EQ like that the amplitude for each channel could be adjusted individually, at least for the treble and bass, which would help with ear-to-ear differences.
On the ODA board I set things up where taking a signal off the board and then returning it is easy, with the thought in mind for a top slot board that does something someday. Specifically those attenuation resistors which are in series between the output of the gain stage and the pot. They can be left out and the holes used for signal send/return instead. I also included extra holes on the power supply disconnect pads to allow power to be taken off for a top slot board.
The problem though is that so far it seems like software is the most effective place for EQ. But that is assuming the source is digital. 🙂 Your link goes to a turntable forum so I'm guessing that your source(s) are primarily analog, hence the need for an analog EQ?
I'm not sure I follow. Are you after something like a parametric equalizer where the frequency and amplitude can be set individually for the bass cut/boost, and same for the treble? With parametric EQ like that the amplitude for each channel could be adjusted individually, at least for the treble and bass, which would help with ear-to-ear differences.
On the ODA board I set things up where taking a signal off the board and then returning it is easy, with the thought in mind for a top slot board that does something someday. Specifically those attenuation resistors which are in series between the output of the gain stage and the pot. They can be left out and the holes used for signal send/return instead. I also included extra holes on the power supply disconnect pads to allow power to be taken off for a top slot board.
The problem though is that so far it seems like software is the most effective place for EQ. But that is assuming the source is digital. 🙂 Your link goes to a turntable forum so I'm guessing that your source(s) are primarily analog, hence the need for an analog EQ?
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Hi agdr.
Yes, analog is of interest too - found this one that could be modernized Gyraf Audio - DIY Calrec EQ , maybe there are better analogue circuits out there today but they didn't show up during a swift search. The Calreq seems to be 4 ways and could probably do for one mans ears giving it better speced components and keeping the channels apart. Probably I would need to use the ODA as a piggyback to it 🙂. I could of course live with an digital dsp but it would need a builtin CPU and so forth for steering it as I don't want a laptop hanging in the chain. It must be easy to handle, one button or knob selection to different listeners, clear display to see whats going on, easy to save subprofiles depending on the source... So a digital solution will be very complicated indeed. Well, as it is capable of so much more of course the demands on it has to be higher 🙂. It would more be as a programmable hearing aid steered by a remote control. Now, I don't ask you to design it but I would be very interested in such an gadget if anyone would get into the fire 🙂.
Regards
Yes, analog is of interest too - found this one that could be modernized Gyraf Audio - DIY Calrec EQ , maybe there are better analogue circuits out there today but they didn't show up during a swift search. The Calreq seems to be 4 ways and could probably do for one mans ears giving it better speced components and keeping the channels apart. Probably I would need to use the ODA as a piggyback to it 🙂. I could of course live with an digital dsp but it would need a builtin CPU and so forth for steering it as I don't want a laptop hanging in the chain. It must be easy to handle, one button or knob selection to different listeners, clear display to see whats going on, easy to save subprofiles depending on the source... So a digital solution will be very complicated indeed. Well, as it is capable of so much more of course the demands on it has to be higher 🙂. It would more be as a programmable hearing aid steered by a remote control. Now, I don't ask you to design it but I would be very interested in such an gadget if anyone would get into the fire 🙂.
Regards
Turbon - sorry about the delayed reply! Between the hoiidays here and a few projects in the works I'm just now getting back to this thread.
That link you posted looks fantastic! I've looked into eq circuits a couple of times and it would be quite a project in its own right. I wouldn't be surprised if there were some existing boxes like this out there. If so that would probably be the best solution, feed the source into the eq box then on to the ODA.
That link you posted looks fantastic! I've looked into eq circuits a couple of times and it would be quite a project in its own right. I wouldn't be surprised if there were some existing boxes like this out there. If so that would probably be the best solution, feed the source into the eq box then on to the ODA.
I finally have all my parts lined up for my ODA build -- Mouser was back-ordered on a few items but parts have finally arrived. I only have one item left to figure out before I start putting everything together.
I would like to wire up the pre-amp output so that I can drive a small amp and a set of desktop speakers for times when I cannot be tethered to my amp or if I want to share the music with someone else in the room. I would like to wire up the pre-amp buffer after the 1K pot so that I can use the same volume knob to control either the speakers or the headphones, whichever is hooked up.
Additionally, I would like to be able to be able to enable or disable the output to either the headphones or the speakers depending on which I am listening to at the time. I was thinking of adding two switches to accomplish this - one for headphone enable/disable and another for the pre-amp out enable/disable, but I need some help thinking this through about what would work best.
The pre-amp buffer amp input (JP20) could be wired through a panel mounted DPDT switch to either switch in the signal from the output side of the volume pot, or ground the pre-amp input signal lines to disable the pre-amp output to the speakers. Since I did not see an appropriate test point on the output side of the pot, I was thinking of picking up the signal by soldering on a wire to the output side of one of the 4.7 uF caps, or R63/R64, or ??? (any ideas welcome here).
To control the heaphone output I was thinking of adding a switch that would be able to de-energize the coil to the output relay K1 if the headphone output switch is set to off. Or, when the headphone output switch is set to on, the relay would perform as intended as a power on delay circuit. I like this idea because I would be able to disable the headphone output without having to wire an additional switch into the signal path, or have to run the high current output signals through any additional wiring. The problem is that I am not certain how best to add this switch into the relay circuit yet, but I figured someone might have some ideas about what would work best and easiest to implement.
I would like to wire up the pre-amp output so that I can drive a small amp and a set of desktop speakers for times when I cannot be tethered to my amp or if I want to share the music with someone else in the room. I would like to wire up the pre-amp buffer after the 1K pot so that I can use the same volume knob to control either the speakers or the headphones, whichever is hooked up.
Additionally, I would like to be able to be able to enable or disable the output to either the headphones or the speakers depending on which I am listening to at the time. I was thinking of adding two switches to accomplish this - one for headphone enable/disable and another for the pre-amp out enable/disable, but I need some help thinking this through about what would work best.
The pre-amp buffer amp input (JP20) could be wired through a panel mounted DPDT switch to either switch in the signal from the output side of the volume pot, or ground the pre-amp input signal lines to disable the pre-amp output to the speakers. Since I did not see an appropriate test point on the output side of the pot, I was thinking of picking up the signal by soldering on a wire to the output side of one of the 4.7 uF caps, or R63/R64, or ??? (any ideas welcome here).
To control the heaphone output I was thinking of adding a switch that would be able to de-energize the coil to the output relay K1 if the headphone output switch is set to off. Or, when the headphone output switch is set to on, the relay would perform as intended as a power on delay circuit. I like this idea because I would be able to disable the headphone output without having to wire an additional switch into the signal path, or have to run the high current output signals through any additional wiring. The problem is that I am not certain how best to add this switch into the relay circuit yet, but I figured someone might have some ideas about what would work best and easiest to implement.
Good deal! 🙂 Just a reminder for anyone out there building an ODA, I have all the parts here, so if you find something out of stock please send me a PM and I can sell it to you at-cost (whatever Mouser's price is) plus actual shipping cost.
Sounds good, but I just want to verify that you do have another amp between the ODA pre-amp out and your speakers (sounds that way, but I just want to make sure I'm understanding the system design). The pre-amp out is line level and by itself wouldn't stand a chance of powering speakers, of course. 🙂
Which headphones are you using (or impedance + sensitivity numbers)? Apologies in advance if you have already told me via PM in the past, I've chatted with so many folks everything sort of runs together. I would like to run the math and see how much voltage swing you are going to need. In the ODA - same as in NwAvGuy's O2 amp - the full signal swing goes through the pot since that output stage it feeds is a unity (voltage) gain current buffer. The ODA can swing up to 7.25Vrms.
With a headphone that requires maximum voltage swing from the ODA you would be getting up to that 7.25Vrms off the pot, which would be way above the 1V or so line level input needed to your amp. That would be easy enough to fix with a resistive divider though. Depending on your headphone model though it may not be an issue and the maximum voltage swing needed may be (a lot) less.
So there is a good place to start - please post the headphone and lets see how much swing you will have on the pot.
Yes, I will have an amp for the speakers after the ODA. Something small, maybe 5-10 watts.
The headphones are Grado 325's -- 32 ohms, 99.8 dB/ mW, so I think they will be < 1 Volt in normal listening.
fmcclell - for the Grados I get 1.8Vrms at 120dB SPL and 0.0326Vrms at a more normal listening level of 85dB. Looks like you could run the pot to the amp input.
The best place to take a signal from to feed that J20 pre-amp buffer input would be after the coupling capacitors so that there would be no DC offset feeding through. Right after the pot you would get the DC offset from the gain stage (although it should be fairly small with the LME49990 chips). Once you make the connection you might want to tweak the DC offset zeroing trimmers a tiny bit since the input bias current for the pre-amp buffer will be added to the circuit, along with that of the ODA output buffers.
Hmm... Lemme think about it a bit today to give you the best suggestion on the switches. 🙂 I'll post a pictore with some good connection points to take the signal from after the caps.
By the way, I have a new favorite chip for the pre-amp buffer, the OPA2140. It wasn't a shipping part yet earlier in the year as I discovered when I designed it into one of the first versions of the O2 booster board then went to Mouser to buy one, lol. If you haven't soldered your pre-amp buffer in yet, or if you would be willing to try to get the chip out if you have (Chip Quick!), let me know. I'll send you one no charge if you want to give it a try. The OPA2140 is FET input and will have vanishing small DC output offset. You wouldn't have to re-adjust your DC offset trimmers at all with the 2140.
It doesn't have a lot of current/capacitance drive though, so the two output series resistors in the pre-amp section need to be populated with 20R resistors R62 and R57. I'll send those along too. The BOM has those as zero ohm jumpers if using the surface mount NJM4556A, since it has lots of capacitive drive ability. The resistors just decouple the output capacitance from the chip and shouldn't make any difference at all in the pre-amp output at line levels.
The best place to take a signal from to feed that J20 pre-amp buffer input would be after the coupling capacitors so that there would be no DC offset feeding through. Right after the pot you would get the DC offset from the gain stage (although it should be fairly small with the LME49990 chips). Once you make the connection you might want to tweak the DC offset zeroing trimmers a tiny bit since the input bias current for the pre-amp buffer will be added to the circuit, along with that of the ODA output buffers.
Hmm... Lemme think about it a bit today to give you the best suggestion on the switches. 🙂 I'll post a pictore with some good connection points to take the signal from after the caps.
By the way, I have a new favorite chip for the pre-amp buffer, the OPA2140. It wasn't a shipping part yet earlier in the year as I discovered when I designed it into one of the first versions of the O2 booster board then went to Mouser to buy one, lol. If you haven't soldered your pre-amp buffer in yet, or if you would be willing to try to get the chip out if you have (Chip Quick!), let me know. I'll send you one no charge if you want to give it a try. The OPA2140 is FET input and will have vanishing small DC output offset. You wouldn't have to re-adjust your DC offset trimmers at all with the 2140.
It doesn't have a lot of current/capacitance drive though, so the two output series resistors in the pre-amp section need to be populated with 20R resistors R62 and R57. I'll send those along too. The BOM has those as zero ohm jumpers if using the surface mount NJM4556A, since it has lots of capacitive drive ability. The resistors just decouple the output capacitance from the chip and shouldn't make any difference at all in the pre-amp output at line levels.
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Hi agdr et al. Happy New Year!
Actually, I got noticed and can understand that the gyraf eq is a serial one.
I got some other leads to look at a bloke named Massenburg's gadgets which are parallel in construction. Still looking for a schematic or circuit that seems to be right. Signed myself for the FreeDSP project as well to find out what the digital domain can deliver. But I would really like to have an rock steady analogue solution.
Regards
agdr,
Yes, good point about picking up the signal after the coupling capacitors to minimize offset -- will do. Also, your OPA2140 looks like a good chip as well. I do not know what amp I will have hooked up to this pre-amp output, but having a very small DC output offset might allow me to run it DC coupled. So, yes, I will solder in the OPA2140 if you want to send one to me. I am starting with the board that you sent me with all the surface mount parts already installed, so I will have to remove the old op-amp first. I do not have the right tools to do that cleanly, but in the past I have just cut the leads of the old chip first, then de-solder just the legs. The old chip is sacrificed in the process, but it is much easier to do cleanly.
As far as wiring in a selector switch to switch between headphones and speaker output, I ordered a 3PDT chassis mount ON-none-ON switch. I will use two of the poles to switch in the signal to the op-amp's input, or ground the op-amp input when the headphones are selected. The third pole will be wired in-line with the coil to the K1 relay so that it will cut off the output to the headphones when the speaker output is selected.
I haven't figured out where to wire those in on the layout to be easiest, but it looks OK from the schematic point of view. Will have to cut some traces though.