owen offre juste les pcb mais la on est en train d organiser un achat de groupe pour les ampli op
translation: owen only offers pcb but we are organizing something for the opamps.
Looks nice and clean 
From the schematic, the input is balanced, from balanced source, without any volume pot. Are you driving this amp using a balanced pre amplifier? Or balanced audio interface?
If the balanced source is in close distance with the amplifier and the balanced interference reduction is not necessary, you might want to drive the headphone in balanced set-up instead It might sounds better than unbalanced headphone set-up.
Just my2cents
From the schematic, the input is balanced, from balanced source, without any volume pot. Are you driving this amp using a balanced pre amplifier? Or balanced audio interface?
If the balanced source is in close distance with the amplifier and the balanced interference reduction is not necessary, you might want to drive the headphone in balanced set-up instead
It might sounds better than unbalanced headphone set-up.Just my2cents
Hi Guys,
Looks like the kit thing is causing a bit of an upheaval, so maybe I should reconsider.
If the number does indeed hit 25 kits, then I'll re-offer the option. I just don't think it's a good idea to make everyone wait for a month while the last few people trickle in.
If there are 25 takers by the end of the week, then I'll go ahead and order the parts and offer the kits. On that note, if you want a kit, then let me know ASAP.
I have a grand total of 35 boards to sell (I was going to keep some for a later project, but I'll just order more if I ever get around to it). I've updated the list with the latest people interested, so keep it coming.
So far, we need three more people to take boards and kits, and one person with just a board to take a kit as well.
IanAS:
I'm going to say that the differences in those plots are purely due to issues with headphone measurement consistency. Measuring headphones requires the use of a fake ear and a clamp mechanism, and depending on the exact position of the headphone on the ear and the pressure applied by the clamp, you'll see huge variances in acoustic headphone measurements, especially in the bottom end where the seal to the head can make all the difference.
Running "balanced" cables from the drivers in your headphones to the amplifier will not alter the frequency response, but it can drastically improve crosstalk depending on how the headphones were originally wired.
I do love that webpage though, my hat goes off to them for actually having useful data on their products!
Here's a link to a brief intro on headphone measurement:
Between the Ears: the art and science of measuring headphones | Stereophile.com
Cheers,
Owen
Looks like the kit thing is causing a bit of an upheaval, so maybe I should reconsider.
If the number does indeed hit 25 kits, then I'll re-offer the option. I just don't think it's a good idea to make everyone wait for a month while the last few people trickle in.
If there are 25 takers by the end of the week, then I'll go ahead and order the parts and offer the kits. On that note, if you want a kit, then let me know ASAP.
I have a grand total of 35 boards to sell (I was going to keep some for a later project, but I'll just order more if I ever get around to it). I've updated the list with the latest people interested, so keep it coming.
So far, we need three more people to take boards and kits, and one person with just a board to take a kit as well.
IanAS:
I'm going to say that the differences in those plots are purely due to issues with headphone measurement consistency. Measuring headphones requires the use of a fake ear and a clamp mechanism, and depending on the exact position of the headphone on the ear and the pressure applied by the clamp, you'll see huge variances in acoustic headphone measurements, especially in the bottom end where the seal to the head can make all the difference.
Running "balanced" cables from the drivers in your headphones to the amplifier will not alter the frequency response, but it can drastically improve crosstalk depending on how the headphones were originally wired.
I do love that webpage though, my hat goes off to them for actually having useful data on their products!
Here's a link to a brief intro on headphone measurement:
Between the Ears: the art and science of measuring headphones | Stereophile.com
Cheers,
Owen
Hi Guys,
I've updated the list yet again. A few people have dropped off, and a few more have taken their place, so we're about even from the beginning of the week.
I will personally take a kit (I forgot to include myself) so that means we need two more takers for kits to make it 25. If we get there by Friday, then I'll give people the weekend to do a final check on the list, then I'll place the order on Monday which will lock the list down. That should allow me to start shipping kits by the following Monday providing people have paid.
On that note, if you don't intend to take a kit and you're on the list, you'll have until Monday to notify me.
Cheers,
Owen
I've updated the list yet again. A few people have dropped off, and a few more have taken their place, so we're about even from the beginning of the week.
I will personally take a kit (I forgot to include myself) so that means we need two more takers for kits to make it 25. If we get there by Friday, then I'll give people the weekend to do a final check on the list, then I'll place the order on Monday which will lock the list down. That should allow me to start shipping kits by the following Monday providing people have paid.
On that note, if you don't intend to take a kit and you're on the list, you'll have until Monday to notify me.
Cheers,
Owen
Hi Guys,
Well, that makes 25 which is good news for the kits.
Here's the plan:
1. The list is now full, and if you want a kit, I will start a waiting list.
2. I'm giving everyone until Sunday evening to request changes, and after that, the list is locked, and I'm considering you to be committed for whatever is beside your name. It would be in very poor taste to request changes after Sunday when I will be ordering the parts.
3. If between now and Sunday, I have more than five people drop off the list, then I'll be putting the kit on hold until the numbers are back up. I don't expect that to happen, however, so all should be fine.
4. The parts will be ordered first thing Monday (Jan 17th) morning, and should arrive a few days later. Once here, I will separate the parts into kits, and start shipping kits out the following Monday (Jan 24th)
5. I will start officially accepting payments for boards and kits on Monday January 17 (after I confirm that the list is locked and parts are ordered). I expect to have all payments made by the following Monday (Jan 24th) so I can ship the boards in a timely manner.
I've attached an updated list with 24 kit requests, and the 25th will be for me. If you are on the list, and you only want boards, you can make payment immediately and that will expedite your board shipment.
Thanks to everyone for the interest, and I'll keep everyone updated on progress!
Cheers,
Owen
Well, that makes 25 which is good news for the kits.
Here's the plan:
1. The list is now full, and if you want a kit, I will start a waiting list.
2. I'm giving everyone until Sunday evening to request changes, and after that, the list is locked, and I'm considering you to be committed for whatever is beside your name. It would be in very poor taste to request changes after Sunday when I will be ordering the parts.
3. If between now and Sunday, I have more than five people drop off the list, then I'll be putting the kit on hold until the numbers are back up. I don't expect that to happen, however, so all should be fine.
4. The parts will be ordered first thing Monday (Jan 17th) morning, and should arrive a few days later. Once here, I will separate the parts into kits, and start shipping kits out the following Monday (Jan 24th)
5. I will start officially accepting payments for boards and kits on Monday January 17 (after I confirm that the list is locked and parts are ordered). I expect to have all payments made by the following Monday (Jan 24th) so I can ship the boards in a timely manner.
I've attached an updated list with 24 kit requests, and the 25th will be for me. If you are on the list, and you only want boards, you can make payment immediately and that will expedite your board shipment.
Thanks to everyone for the interest, and I'll keep everyone updated on progress!
Cheers,
Owen
Hi,
into the instrumentation amplifier design could easily be integrated a couple of tweaks that raise practicality and safety.
As a first tweak, I´had expected to see some current limiting resistors in the feedback path of the input stages anyway. 4 equal resistors Rx of a couple of kOhms value going from the outputs of U1,3,4 and U6 to the respective inverting input pins. Then a stereo-Pot Px connected between the negative inverting inputs U1 and U3, resp. U4 and U6, would allow to change the gain setting after A=1+2Rx/Px. Without Px the gain would be 1 as it is now, but with Px gain and as such volume could be set to any desired level >1.
As a second tweak, one could easily include a DC-protection, that prevented the connected HP to suffer from possible high levels of DC. The voice coils of HPs are quite fragile and any differential DC appearing at the input of amp will show at the output (proportional to the gain of the amp).
besides the possibility to add DC-blocking caps the instrumentation amp may easily be DC-nulled with an active DC-servo.
For this an inverting integrator (1 OP, 1 R, 1 Cap) could be connected to the output of A1, resp. A2 and it´s output feeding into R6, resp. R12, at the gnd-connection (the gnd-connection of these pins itself must be broken).
As a third tweak one may want to bandwidth limit (to prevent the input from picking up HF) and protect the amp and HP of excessive input levels. A RC-input filter and protection diodes help in safeguarding the amp and HP.
All tweaks could be implemented as options on the PCB hardly increasing dimensions and cost, without sacrificing performance, but raising practicality and safety.
jauu
Calvin
into the instrumentation amplifier design could easily be integrated a couple of tweaks that raise practicality and safety.
As a first tweak, I´had expected to see some current limiting resistors in the feedback path of the input stages anyway. 4 equal resistors Rx of a couple of kOhms value going from the outputs of U1,3,4 and U6 to the respective inverting input pins. Then a stereo-Pot Px connected between the negative inverting inputs U1 and U3, resp. U4 and U6, would allow to change the gain setting after A=1+2Rx/Px. Without Px the gain would be 1 as it is now, but with Px gain and as such volume could be set to any desired level >1.
As a second tweak, one could easily include a DC-protection, that prevented the connected HP to suffer from possible high levels of DC. The voice coils of HPs are quite fragile and any differential DC appearing at the input of amp will show at the output (proportional to the gain of the amp).
besides the possibility to add DC-blocking caps the instrumentation amp may easily be DC-nulled with an active DC-servo.
For this an inverting integrator (1 OP, 1 R, 1 Cap) could be connected to the output of A1, resp. A2 and it´s output feeding into R6, resp. R12, at the gnd-connection (the gnd-connection of these pins itself must be broken).
As a third tweak one may want to bandwidth limit (to prevent the input from picking up HF) and protect the amp and HP of excessive input levels. A RC-input filter and protection diodes help in safeguarding the amp and HP.
All tweaks could be implemented as options on the PCB hardly increasing dimensions and cost, without sacrificing performance, but raising practicality and safety.
jauu
Calvin
Hi Calvin,
Those are some interesting comments, most of which were considered during the design of the amplifier, and intentionally omitted.
I'll try to highlight my design reasoning behind what did and what didn't make it into the amp.
Any series resistance would have introduced some level of noise, and was therefore omitted. Why would you add a part when the circuit works perfectly without that part? Adding a resistor here means more cost, more parts, and more sacrifices in layout, and I don't see what the benefit would be. If the circuit wasn't working, or the op-amps were overheating, it would be a different story.
A stereo pot would present terrible channel matching, so at the very least, wouldn't you want a stepped attenuator with proper discrete resistors? Why spoil 0.1% channel matching with a 10% pot? Why not use a proper volume control before the amp?
Also, having the ability to set the gain only higher than 1 isn't really a volume control, especially when a typical source is over 2VRMS and the average headphone needs less than 250mV RMS to play at a loud level. I set the gain to 1 which is high enough for 95% of the headphones out there (less than 600R impedance). If people want more gain to drive something outside the norm, then they're free to up the gain by changing discrete resistor values.
The design was intended to be used with either a good passive attenuator before the input, or directly coupled to a DAC that has volume control.
Once again, these are issues that would have sacrificed performance and offered minimal benefit to the end used if the amplifier is used correctly. With a gain of only 1, small DC offsets at the output of attached equipment will remain small at the output of the amplifier. Besides, a good preamp should NEVER have DC on the output.
Adding a DC servo would have been easy, and the reference circuit for the the LME49600 does indeed have one. It would, however, add cost, complexity, and degrade both noise and LF performance. That means is has no place in this circuit.
The bottom line is, it's a DC coupled amplifier and that's a good thing. You put DC in, you get DC out, and that's the sacrifice you make to have an amplifier with perfect response and phase from DC to 50kHz.
The DC offset of the amplifier by itself, with inputs open or grounded is less than 1mV. That's what's important.
Once again, the BW liming on the LME 49600 can be used, or a cap can be put in parallel with the input resistors to form a low pass. People who add a cap will do so at the cost of HF phase response, but the option is there if you want it.
BW limiting the LME49600 is probably a good idea, and it simply involves lifting one pin.
As for ESD protection, there's a lot more to it than just slapping some diodes on the inputs. Proper ESD protection would require several diodes, caps, and lossy ferrite beads on the inputs, outputs, and power supply. It would add quite a bit of complexity, and nobody I know has the means to properly test ESD protection levels once implemented. Adding a zener from input to ground provides very little protection which begs the question: "Why do it at all?". Especially when most people will simply omit those parts.
As above though, if you want to, add a few PTH parts across the XLR input jacks. Easy enough to hand solder onto the exposed pins below of the XLR jacks. I'd like to hear a headcount on the number of people who actually do this once the kits are built.
Overall, your suggestions are good, and would be the sort of things I would likely add to the circuit if I were to sell it commercially. The problem with selling things commercially is that you have to assume the users are idiots, and you have to assume the people who designed the equipment it will be attached to are idiots. Because of this, you have to pepper any circuit with piles of protection and safeguards to make sure nobody can ruin anything no matter how foolish they are. This also requires a lot of testing to prove everything is fool proof, which costs a lot of money and takes a lot of time. It also inevitably reduces performance, and can often double or triple the parts count and complexity of the circuit. If that's what you want, you're free to pay $1500 for a commercial amplifier that performs less than half as well.
I certainly don't mean to come across as harsh, and I do appreciate the comments, I just don't think they fit the intended purpose of the amplifier. This is a "performance first" amplifier, and that means some sacrifices have to be made. If all you need to do as a user is show a little bit of caution, then I think that's a fair price to pay for this kind of performance.
Regards,
Owen
Those are some interesting comments, most of which were considered during the design of the amplifier, and intentionally omitted.
I'll try to highlight my design reasoning behind what did and what didn't make it into the amp.
Any series resistance would have introduced some level of noise, and was therefore omitted. Why would you add a part when the circuit works perfectly without that part? Adding a resistor here means more cost, more parts, and more sacrifices in layout, and I don't see what the benefit would be. If the circuit wasn't working, or the op-amps were overheating, it would be a different story.
A stereo pot would present terrible channel matching, so at the very least, wouldn't you want a stepped attenuator with proper discrete resistors? Why spoil 0.1% channel matching with a 10% pot? Why not use a proper volume control before the amp?
Also, having the ability to set the gain only higher than 1 isn't really a volume control, especially when a typical source is over 2VRMS and the average headphone needs less than 250mV RMS to play at a loud level. I set the gain to 1 which is high enough for 95% of the headphones out there (less than 600R impedance). If people want more gain to drive something outside the norm, then they're free to up the gain by changing discrete resistor values.
The design was intended to be used with either a good passive attenuator before the input, or directly coupled to a DAC that has volume control.
Once again, these are issues that would have sacrificed performance and offered minimal benefit to the end used if the amplifier is used correctly. With a gain of only 1, small DC offsets at the output of attached equipment will remain small at the output of the amplifier. Besides, a good preamp should NEVER have DC on the output.
Adding a DC servo would have been easy, and the reference circuit for the the LME49600 does indeed have one. It would, however, add cost, complexity, and degrade both noise and LF performance. That means is has no place in this circuit.
The bottom line is, it's a DC coupled amplifier and that's a good thing. You put DC in, you get DC out, and that's the sacrifice you make to have an amplifier with perfect response and phase from DC to 50kHz.
The DC offset of the amplifier by itself, with inputs open or grounded is less than 1mV. That's what's important.
Once again, the BW liming on the LME 49600 can be used, or a cap can be put in parallel with the input resistors to form a low pass. People who add a cap will do so at the cost of HF phase response, but the option is there if you want it.
BW limiting the LME49600 is probably a good idea, and it simply involves lifting one pin.
As for ESD protection, there's a lot more to it than just slapping some diodes on the inputs. Proper ESD protection would require several diodes, caps, and lossy ferrite beads on the inputs, outputs, and power supply. It would add quite a bit of complexity, and nobody I know has the means to properly test ESD protection levels once implemented. Adding a zener from input to ground provides very little protection which begs the question: "Why do it at all?". Especially when most people will simply omit those parts.
As above though, if you want to, add a few PTH parts across the XLR input jacks. Easy enough to hand solder onto the exposed pins below of the XLR jacks. I'd like to hear a headcount on the number of people who actually do this once the kits are built.
Overall, your suggestions are good, and would be the sort of things I would likely add to the circuit if I were to sell it commercially. The problem with selling things commercially is that you have to assume the users are idiots, and you have to assume the people who designed the equipment it will be attached to are idiots. Because of this, you have to pepper any circuit with piles of protection and safeguards to make sure nobody can ruin anything no matter how foolish they are. This also requires a lot of testing to prove everything is fool proof, which costs a lot of money and takes a lot of time. It also inevitably reduces performance, and can often double or triple the parts count and complexity of the circuit. If that's what you want, you're free to pay $1500 for a commercial amplifier that performs less than half as well.
I certainly don't mean to come across as harsh, and I do appreciate the comments, I just don't think they fit the intended purpose of the amplifier. This is a "performance first" amplifier, and that means some sacrifices have to be made. If all you need to do as a user is show a little bit of caution, then I think that's a fair price to pay for this kind of performance.
Regards,
Owen
Hi Guys,
I've had a few questions and some confusion around the "Boards" "kits" and "parts kits" terminology, and it is admittedly confusing.
I re-made the list to better reflect exactly what people are getting, and exactly what the cost is.
The options are as follows:
1. Only Boards - cost includes one amp board, one PSU board and shipping anywhere. - $20
2. Only Parts - cost includes only the parts, no boards, and shipping anywhere. - $80
3. Boards and Parts - Cost includes one amp board, one PSU board, and all SMD parts previously listed, as well as shipping anywhere. - $95
I've separated the list into these categories to better clarify things.
Please double check the list one last time to make sure I have you down for the correct items. Some people seemed to be under the impression that the "kit" didn't come with boards, but it was already included in the $95 cost.
From now on, it you want to be added to the list, ask specifically for one of the three categories.
All the boards are spoken for, but the number of kits can be anything. 25 was the minimum for pricing, so if you still want a kit, feel free to request one and I will add you to the list.
Regards,
Owen
I've had a few questions and some confusion around the "Boards" "kits" and "parts kits" terminology, and it is admittedly confusing.
I re-made the list to better reflect exactly what people are getting, and exactly what the cost is.
The options are as follows:
1. Only Boards - cost includes one amp board, one PSU board and shipping anywhere. - $20
2. Only Parts - cost includes only the parts, no boards, and shipping anywhere. - $80
3. Boards and Parts - Cost includes one amp board, one PSU board, and all SMD parts previously listed, as well as shipping anywhere. - $95
I've separated the list into these categories to better clarify things.
Please double check the list one last time to make sure I have you down for the correct items. Some people seemed to be under the impression that the "kit" didn't come with boards, but it was already included in the $95 cost.
From now on, it you want to be added to the list, ask specifically for one of the three categories.
All the boards are spoken for, but the number of kits can be anything. 25 was the minimum for pricing, so if you still want a kit, feel free to request one and I will add you to the list.
Regards,
Owen
Ready Set Go!
Hello,
While we are waiting for the Ready Set Go, to send our payments!
I tried what I think is as a similar point to point version using a BUF634 installed in the feedback loop of a LM4562, parts I had in a plastic box on the shelf.
Lots of good potential with this PCB / KIT.
The next iteration might be balanced all the way through the output. Getting rid of the shared single end ground, that makes an audible difference at the headphones. People do not normally try to test the as used installation.
DT
All just for fun!
Hello,
While we are waiting for the Ready Set Go, to send our payments!
I tried what I think is as a similar point to point version using a BUF634 installed in the feedback loop of a LM4562, parts I had in a plastic box on the shelf.
Lots of good potential with this PCB / KIT.
The next iteration might be balanced all the way through the output. Getting rid of the shared single end ground, that makes an audible difference at the headphones. People do not normally try to test the as used installation.
DT
All just for fun!
to balance or not to balance...
Owen,
Thanks for the link to the Stereophile review and for your reply.
At headphone.com they appear to have better measuring equipment with the dummy head and the anechoic chamber largely or completely ruling out extraneous and reflected sound. I don't know if their published plots are the mean of numerous readings or taken until they achieved enough agreeing results, but the 'balanced' ones are a fair bit variant from the 'unbalanced' at the higher frequency, perhaps more than the Stereophile article suggested would be expected from small positional changes, clamping being provided by a given headphone itself for each reading of that headphone so would be consistent for each reading. I also don't know if they 'selected' their results to in some way promote their more expensive 'balanced' amplifiers.
The Stereophile article pointed out the effect of differing output impedance on the loudness measurements across the headphones impedance curve and we can be reasonably confident that the Headroom amp will have different output impedance with the two choices. Maybe they are both very low, but maybe that still accounts for some variance?
As you have a balanced source, when you were prototyping, did you build and try a balanced version?
There are significant disadvantages with balanced; double the output impedance, double noise, perhaps double the distortion, double components in the signal path, half the damping factor, cancelling the even order harmonics and leaving all the odd order possibly making it sound harsh. Does doubling the slew rate and deleting the ground reference really outweigh? Many people and reviewers say that to their ears it does. Are they enjoying the extra distortion?
I wonder if some of the change is from the XLRs instead of the Jack plug or whatever it's called. Plug and sockets can make an audible change to the sound.
Owen,
Thanks for the link to the Stereophile review and for your reply.
At headphone.com they appear to have better measuring equipment with the dummy head and the anechoic chamber largely or completely ruling out extraneous and reflected sound. I don't know if their published plots are the mean of numerous readings or taken until they achieved enough agreeing results, but the 'balanced' ones are a fair bit variant from the 'unbalanced' at the higher frequency, perhaps more than the Stereophile article suggested would be expected from small positional changes, clamping being provided by a given headphone itself for each reading of that headphone so would be consistent for each reading. I also don't know if they 'selected' their results to in some way promote their more expensive 'balanced' amplifiers.
The Stereophile article pointed out the effect of differing output impedance on the loudness measurements across the headphones impedance curve and we can be reasonably confident that the Headroom amp will have different output impedance with the two choices. Maybe they are both very low, but maybe that still accounts for some variance?
As you have a balanced source, when you were prototyping, did you build and try a balanced version?
There are significant disadvantages with balanced; double the output impedance, double noise, perhaps double the distortion, double components in the signal path, half the damping factor, cancelling the even order harmonics and leaving all the odd order possibly making it sound harsh. Does doubling the slew rate and deleting the ground reference really outweigh? Many people and reviewers say that to their ears it does. Are they enjoying the extra distortion?
I wonder if some of the change is from the XLRs instead of the Jack plug or whatever it's called. Plug and sockets can make an audible change to the sound.
Last edited: