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Tyran
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Last seen: 3 years 3 months ago
Joined: Dec 23 2015 - 5:05am
Headphone Amplifier

Hi Guys,

I just finished building my latest headphone amplifier project, and this one is definitely worth sharing with the community. After a few prototypes, I went ahead and had some PCB's made, and there are plenty extra available if people are interested.

I basically wanted a headphone amplifier that was as close as could be to a wire with current gain. I didn't want it to impart anything at all to the source signal. That led me to the following design criteria:

- Perfectly flat FR from DC to over 100kHz
- No phase shift from 0-100kHz
- No capacitors (except for PSU)
- Extremely low harmonic distortion
- Extremely low IM distortion
- Extremely low noise floor
- Ability to drive down to 4 ohms with no load dependence
- Enough voltage swing to drive any reasonable headphone set.
- Excellent input CMRR
- Simple circuitry using the best parts available.

I needed a balanced input, and wanted to use a standard 1/4" jack for the output.

The resulting amplifier is basically an instrumentation amp using three LME49990 op-amps and an LME 49600 buffer nested into the last stage. These parts represent the absolute best you can get for this sort of application. I used all 0.1% Susumu thin film resistors, and all X7R ceramic bypass capacitors placed directly on the supply pins. Bulk caps are all solid polymer for the absolute lowest ESR and best HF performance. Layout was optimized for short signal length, low noise and low crosstalk.

The circuit provides differential input, or the option to ground one phase and drive the circuit with an SE input. Gain is set to 1, but can easily be changed to pretty much anything with just two resistors It runs on +/-5VDC up to +/- 15VDC and has enough drive to run anything you can throw at it.

As for sound, having a DC coupled amplifier makes for some of the most stunning bass I have ever heard. I'm driving a pair of Denon AH-D2000 headphones, and there's a world of difference between this amplifier and every other source I have ever tried when it comes to performance below 100Hz. It has incredible impact, depth and cleanliness. In the midrange and top end, it passes on the characteristics of the source like nothing I have ever heard. I've driven it with an Aikido linestage, a BZLS, straight from a DAC and a multitude of other devices, and all you hear is the device driving it. I now use this setup as my primary means of evaluating all preamps and sources since nothing else I have ever used even comes close to exposing the true nature of the sources like this circuit does. It's honestly like it's not even there... hence the name.

ultrabike
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Awesome!!!

I don't think one can upload images here, but I think one can definitively link them and would love to see some pics of your build along with some characterization results.

If you run it with SE inputs, will it still have instrumentation amp level performance? Any output bias issues?

Tyran
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Joined: Dec 23 2015 - 5:05am
Headphone Amplifier
ultrabike wrote:

I don't think one can upload images here, but I think one can definitively link them and would love to see some pics of your build along with some characterization results.

If you run it with SE inputs, will it still have instrumentation amp level performance? Any output bias issues?

One I completely forgot to mention in the original post. The DC offset is less than 1mV at the output with the input floating, or connected to ground. I was initially worried about this since the reference board for the LME49600 has a full servo to minimize DC, but to my surprise, the DC offset was actually lower on the reference board with the servo removed from the circuit. Of course, if you have DC from the previous stage, the servo would help to null it out, but I'm assuming nobody here would be foolish enough to feed a DC coupled circuit from something with a DC offset. Obviously it will make it through with a gain of 1.

I didn't run it in SE mode during testing, but I can run a few tests tomorrow to see what the performance is like

walian
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Great!!!

Hi I am interested in buying 1-2 boards from you~

Tyran
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walian wrote:

Hi I am interested in buying 1-2 boards from you~

Hi,
I do not have spare kits for sale.But you can make one by yourself. I would consider doing a group buy kit for the boards and parts.
A group buy for the LME parts would indeed be wise. http://www.digikey.com/? has the worst pricing for these parts, and they can be had for half as much at other sites.

Either way, I've got 25 boards and that's 150 LME49990 and 50 LME49600.
For pcbs, I bought them from http://www.pcbway.com/n, cause I prefer their website design, the better filtering system, low price, and the more logical pcb organization.

For 100pcs of LME49990 you've got:

Avnet = 2.57 each
Newark = 3.00 each
Digikey = 4.15 each
Arrow = 2.95 each
Future = 3.12 each

Digikey's single part price is $5.70.

For 50pcs of LME49600 you've got:

Newark = 6.98 each
Digikey = 9.47 each
Arrow = 6.53 each
Future = 6.90 each

Digikey's single part price is $11.56.

walian
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Tyran wrote:walian wrote:Hi I
Tyran wrote:
walian wrote:

Hi I am interested in buying 1-2 boards from you~

Hi,
I do not have spare kits for sale.But you can make one by yourself. I would consider doing a group buy kit for the boards and parts.
A group buy for the LME parts would indeed be wise. http://www.digikey.com/? has the worst pricing for these parts, and they can be had for half as much at other sites.

Either way, I've got 25 boards and that's 150 LME49990 and 50 LME49600.
For pcbs, I bought them from http://www.pcbway.com/n, cause I prefer their website design, the better filtering system, low price, and the more logical pcb organization.

For 100pcs of LME49990 you've got:

Avnet = 2.57 each
Newark = 3.00 each
Digikey = 4.15 each
Arrow = 2.95 each
Future = 3.12 each

Digikey's single part price is $5.70.

For 50pcs of LME49600 you've got:

Newark = 6.98 each
Digikey = 9.47 each
Arrow = 6.53 each
Future = 6.90 each

Digikey's single part price is $11.56.

Can I have the parts list?

digiOS
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Joined: Jun 25 2016 - 12:23pm
Interested

Just what i was looking for . Can you send me your contact info I would like to discuss an idea and possibly prototype for purchase from you.
Regards.

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