I built another one of these today. Its meant to drive my Sennheiser HD650 headphones, and it´s running a OPA637AP + BUF634 at a gain of 11. Sounds good at first try. Will hopefully get some measurements next week.
In my preamp, I prefer to use just one single OPA627BP for each channel, and no BUF at all... but this is of course up to everyone to make their own choice.
Im now running the DIL version of BUF634, and it´s getting pretty hot. Maybe I´ll have to try the TO220 version later on..
In my preamp, I prefer to use just one single OPA627BP for each channel, and no BUF at all... but this is of course up to everyone to make their own choice.
Im now running the DIL version of BUF634, and it´s getting pretty hot. Maybe I´ll have to try the TO220 version later on..
I haven't tested myself but you can get a very small reduction of distortion by using max current but I'm perfectly happy with "medium" speed which is 3.9 kohms from pin 1. In my case I gain so little when I listen (Carlos I do listen to my stuff!) so the only advantage is a hotter amp.... and I have limited resources in that particaluar design.
Schematic can be found here, here and here.
Distortion with medium speed is less than my sound card, 0.008%
In the QRV-04 design I have also a current source for the opamp but with OPA627 and AD8610 I can't pick any significant difference with and without class A biasing but I have circuit on the pcb as an option.
Schematic can be found here, here and here.
Distortion with medium speed is less than my sound card, 0.008%
In the QRV-04 design I have also a current source for the opamp but with OPA627 and AD8610 I can't pick any significant difference with and without class A biasing but I have circuit on the pcb as an option.
peranders said:
May I ask what soundcard and software you are using, and how you perform the measurements?
I tried measuring with my crappy integreted soundcard using a software called "Spectralyzer" (demo). All I did find out, is that I should get a new sound card
At first I measured with the mic input grounded to recieve the noise from the soundcard itself.
The second measurement was with headphoneamp connected to mic input, and inputs to headphoneamp grounded. This showed almost exactly the same as the first measurement.
Third one, I connected the input of the headphoneamp to the output on the soundcard (playing an infnite zero track). Now I got some really ugly noise, even with the sound pot turned to zero.
Is this the way to measure, or how should I proceed? (probably with a better source of course)
I have a Turtle Beach Santa Cruz SC and I have used the russian freeware Rightmark Audio Analyzer.
http://audio.rightmark.org
The amp QRV-07 with TPA6120
http://www.sjostromaudio.com/hifi_files/qrv/qrv07_testreport/QRV07_HD545.htm
http://audio.rightmark.org
The amp QRV-07 with TPA6120
http://www.sjostromaudio.com/hifi_files/qrv/qrv07_testreport/QRV07_HD545.htm
Hetsinks for DIL
Or use these:
Search for 75-611-52 at ELFA
I use these on the BUF634 and AD811 in my preamp...
air said:Ooops.
I did miss the part in the datasheet, where it says that Wide BandWith mode sets Iq to 15mA. That explains the heat in my Buf´s
Well, I´ll just have to change them to TO220 and use heatsinks, like Carlos suggests.
Or use these:
An externally hosted image should be here but it was not working when we last tested it.
Search for 75-611-52 at ELFA
I use these on the BUF634 and AD811 in my preamp...
peranders said:
Thanks!
I have measured now, with my crappy soundcard. Tested both with Sennheiser HD650 (300ohm) and with my old Philips SBC3388 (34ohm).
http://people.arcada.fi/~nylundj/rmaa/headphoneamp.htm
peranders said:
As you know, I use them in wide BW mode, with +/-18v PSU.
And I use the TO220 version.
They get hot without the heasinks, but no problem with any "normal", small heatsink like those we use for regulators.
Also, as I said some pages ago, the TO220 allows a much better layout.
Better PSU arrangement, bypass, smaller feedback loop.
Yes, your soundcard isn't the best around these days. I wonder though why you have so much distortion, much more than I have with OPA637+BUF634air said:
Maybe the difference is the pcb?Here is the test for my OPA627+BUF634
http://www.sjostromaudio.com/hifi_files/qrv/qrv04_testreport/qrv04_test.htm
The test is done with resistive load but unfortunately I don't know how much I used. I will make a more detailed measurement later.
peranders said:
I wonder though why you have so much distortion, much more than I have with OPA637+BUF634
Do you mean the IMD? Maybe it has to do with the new measuring system they have implemented. Your measurements are made with an older version, without this type of measurement. It is implemented from 5.1 and on.
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