Ok thanks, I was working off instructions on the wiki page here:
"The Wire" Headphone Amp Build Wiki - diyAudio
But I cant see a schematic for the power supply there.
"The Wire" Headphone Amp Build Wiki - diyAudio
But I cant see a schematic for the power supply there.
Owen has posted the gain equations for the SE-SE in post #1020:
http://www.diyaudio.com/forums/head...headphone-amplifier-pcbs-102.html#post2809927
If you built the amp to the standard BOM, the amp is built at unity gain. This means the amp acts as a current buffer and does not amplify the voltage levels of the signal coming from the source. You may want gain depending upon your source, your headphones and the listening level you like.
I think a lot of folks are coming from using high gain amps (gains of 10x and higher are not uncommon) and get somewhat frustrated when their selected attenuation solution does not yield the same results it did on other gear. If you really want , you can bump the gain to mimic the gain you are getting from your other amps. Just be advised, that sort of defeats the point of "The Wire". At least in my opinion.
Hi jdkJake,
Indeed that would be the better way to go. In the scenario I'm describing, I'm assuming that the pot is permanently attached to the input, and the likelihood of failure on a stepped attenuator is very low.
It would be best though to populate something between 100k and 1M for R14 and R18 just in case you happen see a failure on the pot, or on the wiring somehow.
As for your previous post, you are exactly correct about the low gain being an intentional and integral part of "The Wire" design.
Unity gain will serve the vast majority of sources and headphones which is why it was chosen. For some IEMs and high sensitivity headphones even unity gain can be far too much if you have a source that can output 2VRMS.
Nelson Pass talks about this in great detail in the B1 article, and it's a very good read for anyone who is currently hung up on high gain systems. Most people are used to having far too much gain in their systems, and as a result, they often feel like "it's not loud enough" if they have to exceed 1/2 volume on their volume control. In reality, you should plan your entire system gain out so that the volume control is at or near 100% for a comfortable listening level. Anything less than that, and you're throwing away gain which always comes at a cost somewhere else in the system. If you want the highest possible dynamic range, and the lowest possible noise, you should have just enough gain to get the levels you want, and nothing more. If you've never exceeded the half-way mark on your volume control, you're doing it wrong
There are of course exceptions to the unity gain set up, and headphones like the HE6 and others that sit in the mid 80's sensitivity levels will need significantly more gain. While using the HE6 with a true 2VRMS source, I found that a gain of between 2 and 3 worked quite well. This produced levels loud enough to hurt my ears at maximum volume. If you have a lower output from your source, you might need even more. If you feel the need to maximize the potential power output from The Wire, then just work your way backwards from the clipping point of the headphone amp and plan your gain such that your maximum output voltage from your source results in a signal level that is just below clipping on the headphone amp. In the case of an SE-SE set up, you'll clip right around 15V peak if you have 18V rails. If your source can output 2V peak then you'd need a gain of roughly 7.5 to fully utilize the output capabilities of the amp at full volume.
Cheers,
Owen
Indeed that would be the better way to go. In the scenario I'm describing, I'm assuming that the pot is permanently attached to the input, and the likelihood of failure on a stepped attenuator is very low.
It would be best though to populate something between 100k and 1M for R14 and R18 just in case you happen see a failure on the pot, or on the wiring somehow.
As for your previous post, you are exactly correct about the low gain being an intentional and integral part of "The Wire" design.
Unity gain will serve the vast majority of sources and headphones which is why it was chosen. For some IEMs and high sensitivity headphones even unity gain can be far too much if you have a source that can output 2VRMS.
Nelson Pass talks about this in great detail in the B1 article, and it's a very good read for anyone who is currently hung up on high gain systems. Most people are used to having far too much gain in their systems, and as a result, they often feel like "it's not loud enough" if they have to exceed 1/2 volume on their volume control. In reality, you should plan your entire system gain out so that the volume control is at or near 100% for a comfortable listening level. Anything less than that, and you're throwing away gain which always comes at a cost somewhere else in the system. If you want the highest possible dynamic range, and the lowest possible noise, you should have just enough gain to get the levels you want, and nothing more. If you've never exceeded the half-way mark on your volume control, you're doing it wrong
There are of course exceptions to the unity gain set up, and headphones like the HE6 and others that sit in the mid 80's sensitivity levels will need significantly more gain. While using the HE6 with a true 2VRMS source, I found that a gain of between 2 and 3 worked quite well. This produced levels loud enough to hurt my ears at maximum volume. If you have a lower output from your source, you might need even more. If you feel the need to maximize the potential power output from The Wire, then just work your way backwards from the clipping point of the headphone amp and plan your gain such that your maximum output voltage from your source results in a signal level that is just below clipping on the headphone amp. In the case of an SE-SE set up, you'll clip right around 15V peak if you have 18V rails. If your source can output 2V peak then you'd need a gain of roughly 7.5 to fully utilize the output capabilities of the amp at full volume.
Cheers,
Owen
Thanks Gents; for both the specifics and the gain discussion. I'm still very much a noob, and it has definitely helped my understanding.
So then to clarify:
1. Short R13 and R17
2. Use 1M for R14 and R18
3. For a gain of 2, use 833 Ohms for R15 and R19
I'm driving a pair of HE-5's, and the Wire is sourced by a BIII/Legato build.
So then to clarify:
1. Short R13 and R17
2. Use 1M for R14 and R18
3. For a gain of 2, use 833 Ohms for R15 and R19
I'm driving a pair of HE-5's, and the Wire is sourced by a BIII/Legato build.
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So, R13/R14 and R17/R18 form a simple voltage divider. With no pot in the circuit, the gain from the L-pad is (R2/(R1+R2)) or (10k/(1k+10k)) = 0.909
If you simply insert a 50k pot in series, the equation becomes (10k/(51k+10k)) = 0.164
To get the same gain characteristic, you need to increase the value of R2. Once you do this, the relatively low default value of the R1 resistor (1k) becomes inconsequential when added in series with the 50k pot. So, using a 1M resistor for R2 yields (1000k/(51k+1000k)) = 0.951. A 500k resistor in R2 will yield 0.907 or close enough.
In any case, you get the idea. Just swap R14/R18 with a 500k to 1M resistor and bump R15/R19 to 833R (2X gain) and see what you think. I would have 435R (3X) and 295R (4X) on hand in case you need more gain. Personally, I would not go beyond that, but, that is always a matter of perspective and taste.
owc -- thanks for a better clarification on how the gain works in this amp.
I had used what I thought was a gain of 4, which in actuality had only netted me a gain of ~0.711 because of the 50k pot, which is acceptable to my ears, but I understand isn't exactly correct. If I switch to a 10k pot then my gain goes up to 2 using the same values for R15 and R19.
Does this make sense?
I had used what I thought was a gain of 4, which in actuality had only netted me a gain of ~0.711 because of the 50k pot, which is acceptable to my ears, but I understand isn't exactly correct. If I switch to a 10k pot then my gain goes up to 2 using the same values for R15 and R19.
Does this make sense?
You are going about this somewhat in the wrong way. You need to resolve the attenuation situation first and then worry about the gain of the amp. You do not want to solve gain through manipulating attenuation. You want to allow as much signal as possible through the attenuation circuit when the attenuator is fully reduced (no attenuation). Then, if still not loud enough, you want to amplify that signal with gain from the amp.
The size of the attenuator should be chosen such that it presents a load your source can effectively drive. Most modern sources can drive a 10k load, but, other sources may struggle. Hence the desire to bump up to a 25k or 50k pot. The noise level goes up a little, but, the load is easier for the source to drive. Once you select the pot based upon your source, you calibrate the L-pad to optimize the selected pot. The goal is to optimize the amount of signal allowed through the attenuator circuit. Remember, you can only subtract at this step, not add to the signal level. This is important to ensure you do not waste precious signal through excess attenuation before it hits the amp.
Note that most L-Pad circuits in this position/application are 1:10 ratio. Play with the math a bit and you will see why this works best. Again, the actual value of the pot drives the resistor values of the L-Pad. In the circuit for “The Wire”, the R13/R17 resistor can be represented by the pot and the pot alone or you can leave a smaller resistor in series, just remember they sum when used like that. The R14/R18 resistor should be sized to maintain the 1:10 ratio with the resistance in front of it. The R14/R18 resistor also provides a path to ground in the event no signal is connected (or in this case, the pot or pot wiring fails). So, for a 10k pot, the R14/R18 resistor should be 100k. For a 50k pot, the R14/R18 resistor should be 500k. Some would just put a 1M there and be done with it as that accommodates up to a 100k pot (and everything below it). Be advised, it you ever remove or change the pot, this circuit need to be revisited and possibly corrected with different resistor values applicable to the new pot (or complete lack thereof).
Once you have optimized your attenuation solution, then you can worry about the overall amp gain. I would be surprised if you require more than 2X out of “The Wire” for the vast majority of sources and phones out there. But, you can always bump it to 3 or 4 if you want more oomph. “The Wire” can certainly provide it.
Just my two cents…
Hi Guys,
jdkJake is exactly correct in what he's saying above. You don't really want to replace your pot, you just want to increase the input impedance of The Wire so your pot works correctly with it.
To do this, you just increase the value of R14 and R18 to 500k or 1M ohm and short out R13 and R17. Job done. You don't even need to short out R13/17, but I would suggest it since it's free and easy, and makes for one less series component.
As Jake said, you can look at R13/14 and R17/18 as fixed value pots on the input with a ratio of 0.909. The wire was originally intended to be directly driven by a low impedance source without a pot, so the input impedance was optimized for that exact scenario. The relatively low input impedance is easily driven by the output of most modern DAC circuits, and the low input impedance helps keep noise as low as possible when no source is connected. If you want to use a 50k pot, just increase the input impedance to work best with that. The beauty of the SE-SE and BAL-SE versions of The Wire is that you can make the input impedance whatever you want, and as long as your source impedance is low, there's not really any noise penalty to pay.
To summarize, the 50k pot you have now basically takes the place of R13/14 and R17/18 to form the input voltage divider of the amp. The only difference is that now you can dynamically change the two resistor values by moving the pot, which gives you volume control. The pot's impedance becomes the amp's new input impedance, and you're off to the races. Keeping R14 in the circuit and changing its value to 1M ohm simply gives you a safety bypass in the event your pot fails. If that happens, the 1M resistor in R14 will ensure the amp always has a GND reference at the input which will prevent DC on the output.
Cheers,
Owen
jdkJake is exactly correct in what he's saying above. You don't really want to replace your pot, you just want to increase the input impedance of The Wire so your pot works correctly with it.
To do this, you just increase the value of R14 and R18 to 500k or 1M ohm and short out R13 and R17. Job done. You don't even need to short out R13/17, but I would suggest it since it's free and easy, and makes for one less series component.
As Jake said, you can look at R13/14 and R17/18 as fixed value pots on the input with a ratio of 0.909. The wire was originally intended to be directly driven by a low impedance source without a pot, so the input impedance was optimized for that exact scenario. The relatively low input impedance is easily driven by the output of most modern DAC circuits, and the low input impedance helps keep noise as low as possible when no source is connected. If you want to use a 50k pot, just increase the input impedance to work best with that. The beauty of the SE-SE and BAL-SE versions of The Wire is that you can make the input impedance whatever you want, and as long as your source impedance is low, there's not really any noise penalty to pay.
To summarize, the 50k pot you have now basically takes the place of R13/14 and R17/18 to form the input voltage divider of the amp. The only difference is that now you can dynamically change the two resistor values by moving the pot, which gives you volume control. The pot's impedance becomes the amp's new input impedance, and you're off to the races. Keeping R14 in the circuit and changing its value to 1M ohm simply gives you a safety bypass in the event your pot fails. If that happens, the 1M resistor in R14 will ensure the amp always has a GND reference at the input which will prevent DC on the output.
Cheers,
Owen
An OT tangent but here goes:
Imitation is apparently flattery and Burson Audio have created a new headphone system and named it 'The Conductor'. Do you think they have heard of Owen's projects, perhaps? Obviously a different amplifier stage entirely to Owen's designs, but have seemingly taken some inspiration from Owen's project name here.
Digital Audio Review by John Darko Burson Audio prep successor to HA-160D: The Conductor
Imitation is apparently flattery and Burson Audio have created a new headphone system and named it 'The Conductor'. Do you think they have heard of Owen's projects, perhaps? Obviously a different amplifier stage entirely to Owen's designs, but have seemingly taken some inspiration from Owen's project name here.
Digital Audio Review by John Darko Burson Audio prep successor to HA-160D: The Conductor
Hochopeper:
Great link! I always like reading product descriptions and in this case seeing how a very questionable layout can be turned into an $1800 product. Makes me want to be less of a perfectionist and just get something out the door
I honestly do wonder if it was inspired by the kits sold here. Then again, maybe they're referring to the conductor of an orchestra? May we'll see versions on eBay called "The Pure Transmission Medium".
Mull3t:
Glad to hear you're going to give it a shot. I can promise you it will be worthwhile.
For shorting, qusp's suggestions are spot on. I personally would use a small piece of solid copper wire, cut to length and flattened with a hammer to look like a solid copper 0805 resistor. Just solder that in place and you're ready to go. Otherwise, a 0R 0805 resistor would work, or a blob of solder that shorts the two pads.
qusp:
Did seeing that ESS DAC floating on a cheap 2-layer board scare you as much as it scared me? There's no possible way you can do a proper layout for that DAC with anything less than 4 layers...
It always shocks me what passes for a "polished" consumer product.
Cheers,
Owen
Great link! I always like reading product descriptions and in this case seeing how a very questionable layout can be turned into an $1800 product. Makes me want to be less of a perfectionist and just get something out the door
I honestly do wonder if it was inspired by the kits sold here. Then again, maybe they're referring to the conductor of an orchestra? May we'll see versions on eBay called "The Pure Transmission Medium".
Mull3t:
Glad to hear you're going to give it a shot. I can promise you it will be worthwhile.
For shorting, qusp's suggestions are spot on. I personally would use a small piece of solid copper wire, cut to length and flattened with a hammer to look like a solid copper 0805 resistor. Just solder that in place and you're ready to go. Otherwise, a 0R 0805 resistor would work, or a blob of solder that shorts the two pads.
qusp:
Did seeing that ESS DAC floating on a cheap 2-layer board scare you as much as it scared me? There's no possible way you can do a proper layout for that DAC with anything less than 4 layers...
It always shocks me what passes for a "polished" consumer product.
Cheers,
Owen
Hochopeper:
Great link! I always like reading product descriptions and in this case seeing how a very questionable layout can be turned into an $1800 product. Makes me want to be less of a perfectionist and just get something out the door
I honestly do wonder if it was inspired by the kits sold here. Then again, maybe they're referring to the conductor of an orchestra? May we'll see versions on eBay called "The Pure Transmission Medium".
The rest of us cannot thank you enough for being the perfectionist! I believe the perfectionist engineers mostly specialise in technical fields and the rest are 'managers'!
I saw that DAC (there are a few iterations of it now unfortunately). It is my most ardent hope that no-one actually exchanged money for the 2-layer ESS DAC that you refer to! It is like an oppo spinning disk machine with absolutely butchered insides and calling it 'development'.
Finally finished up my Wire build. I ended up going 4x with my gain as I drive orthos (HE-5). 4x has me at 3:00 for my max listening. 3x didn't quite give me the headroom. This build is using the Khozmo 50K attenuator.
It's sitting on my BIII using eXD I2S/DSD board with Paul Hynes regs throughout. IV is IVY, but I hope to replace it with an NTD1 someday.
Qusp - thanks for supplying the power supply. It was very much appreciated. Opc, JDJake, Mull3T - as always, thanks for your help.
It's sitting on my BIII using eXD I2S/DSD board with Paul Hynes regs throughout. IV is IVY, but I hope to replace it with an NTD1 someday.
Qusp - thanks for supplying the power supply. It was very much appreciated. Opc, JDJake, Mull3T - as always, thanks for your help.
An externally hosted image should be here but it was not working when we last tested it.
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