| percy |
Are there any headphone amp designs that use only a buffer opamp ? Just a standalone buffer.
All I need is something to provide high impedance to the source and boost the output current high enough for a typical 32ohm heaphone, ofcourse low output impedance. |
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| lineup |
| quote: | Originally posted by percy
Are there any headphone amp designs that use only a buffer opamp ?
Just a standalone buffer.
All I need is something to provide high impedance to the source
and boost the output current high enough for a typical 32ohm headphone,
of course low output impedance. |
A good option is to use a dual Op-Amp, like for example OPA2134 (good quality/price)
and parallel the dual to give double current output.
Will power most every 32 Ohm headphones, more than enough.
At Raymond's DIY Audio Pages I found such a project.
Pictures and schematics, including power supply.
Very nice documentation indeed!
He has also two other headphone amplifiers and more good audio projects.
| quote: | Opamp Headphone Amplifier
This is an headphone amplifier, based on the OPA2134 from Burr-Brown.
Two opamps are used, with one half of each buffering the output of the other half
for increased current capability. |
A guy from Finland has built Raymond's project and documented this with images.
He uses PCB he made himself.
http://www.kolumbus.fi/antti.penttala/ele/headamp/
This is schematic:
He uses 100k/10k gain=11.
This is changed easily.
Removing 10k resistor (R3) gives gain=1. (Unity gain buffer)
Making R3=100k gives gain=2.
Amplifier image:
The small heatsinks are for LM317 LM337 voltage regulator chips. |
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| lineup |
This is a picture of guy from Finland's amplifier a la Raymond.
From link in post above.
You see the two OPA2134 and components placement here:
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| tlmadsen |
Percy
Try the BUF634T from BB/Texas
Have fun
Thomas |
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| percy |
I have seen BUF634 being used in a few diy headphone amps as an output stage preceeded by another opamp but have yet to come across one by itself.
thanks all for the project links. I will check them out. |
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| karahara |
| Look at the LT1010, imo a very good choice for that app. |
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| percy |
| or the LT1210 maybe ? anyone tried it yet ? |
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| chumi |
percy,
I used LT1210 and it works like a best sounding chip headphone amp in my collection :D My Sony MDR-F1 headphones have only 12 Ohm and are driven perfectly - so deep bass I never heard form a small chip :) |
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| karahara |
Wow, looks good. Maybe you want to share your layout, I would be very interested.
Here's my LT1010, no listening yet because I currently building the amp. PCB is ready but PSU and Case not. |
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| percy |
Hi Chumi, great work. Its good to know that the LT1210 will not dissappoint.
| quote: | | I used LT1210 and it works like a best sounding chip headphone amp in my collection My Sony MDR-F1 headphones have only 12 Ohm and are driven perfectly - so deep bass I never heard form a small chip |
Since you already have an opamp (OPA627) driving the buffer I'd imagine the buffer would be within the feedback loop of the opamp ?
I am trying to see if its possible, or if anyone has already made a buffer-only headphone amp. Although the LT1210 does seem well suited for the task.
Anyone willing to throw some ideas together to build such an amp ? |
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| chumi |
Unfortunately this time the PCB is not my design :( but works as great as my first project assembled on protoboard :) I ordered PCBs from www.unisonus.com - fully recommended source of PCBs - high quality at low price :)
Percy - DIL8 opamp (OPA627 - last time changed to MAX400) works as a DC servo to reduce DC voltage on output. It's quite important when driving low impedance headphones :) LT1210 works also great without DC servo (<40mV output DC) however only the best possible solutions are good enough :)
I still have 4 spare PCBs - 2 stereo amps could be made. So, if You (Percy, Karahara) want to have a pair I can share with You :) just send me a delivery address me via email :)
Now I'm testing +/-12V PSU units (4*MUR860, Rubycon ZL) with voltage regulators (LM2941/LM2991 as well as LT317/LT337) and without and ... unregulated is going to be my favorite! but final verdict is not jet announced :) What is yours experience in this area? |
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| chumi |
| ... one more thing - complete documentation including schematic you can find also on www.unisonus.com -> last project LT1210 pre/power amplifier |
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| percy |
in my quest to find a simple compact headphone amp solution, I have now also found the TPA6120 !
Now I am two minds whether to go with the TPA6120 or the LT1210 ? For the TPA I again see two options - the TPA6120 board from unisonus, or the EVM from TI direct. I like the simplicity of the unisonus TPA amp but I am gravitating to the TI EVM.
http://focus.ti.com/lit/ug/slou169/slou169.pdf
Help me decide! |
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| chumi |
| I have experience with both. LT1210 were better to low extremely low impedance like my 12ohm. Specially better bass and dynamics. Bought are very detailed, high grade in high frequency and overall quality of bought is very good :) LT is already better from mechanical point of view – it is simple TO220 housing :) For TPA you need a special PCB with solderable PowerPad. My choice for the real best power headphone chip amp is LT :) but for a compact one … could be TPA :) |
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| percy |
yeah I have seen perander's project but I'd really like to keep it simple.
Chumi, whats your impression of the LT1010 though ? |
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| chumi |
I do not have any experience with LT1010. But it is just a simple buffer and max. current is just 150mA :( In my opinion even BUF634 could be a better choice :) and TPA for sure. But nobody knows really without listening – this is the final test – always :) so try it and tell us how it sounds :)
If you are looking for really simple but high grade designs perander’s projects are not a best choice - are rather complicated and first impression is a little bit oversized. But Veteran www.unisonus.com seems to be good source – sometimes those projects looks like too universal but all the time keep high grade and are simple :) |
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| Granholm |
I just received the 2 PCB's from Damian! Looking just fine! Now I just have to source tha last components to complete the project and fire up my MDR F1's ;o)
Anyone with an availabel partlist? Or recomandations for capacitors/Diodes etc??
Rgds. |
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| kalin oleg |
I have just today finished similar project.
it is OPA 2134 buffered with 2x BUF634P.
very nice sounding, glad of this choise.
some pictures here
http://kalin.euweb.cz/index.html |
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| Granholm |
| quote: | Originally posted by kalin oleg
I have just today finished similar project.
it is OPA 2134 buffered with 2x BUF634P.
very nice sounding, glad of this choise.
some pictures here
http://kalin.euweb.cz/index.html |
Sure looks nice! What impedance are the headphones the amp will be driving?
Rgds. |
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| kalin oleg |
Granholm,
16 Ohms |
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| TB |
Hello, I would like to build LT1210 buffer amp based on schematic posted on website mentioned by Chumi. The only difference would be not to use current source. I understand that without use of current source I will have to protect inputs and outputs with caps, what really do not mind. Could someone advised me how to change the circuit to accomodate that change? Which parts are not necessary with use of only LT chip?
Thanks for the help. |
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| Granholm |
| quote: | Originally posted by TB
Hello, I would like to build LT1210 buffer amp based on schematic posted on website mentioned by Chumi. The only difference would be not to use current source. I understand that without use of current source I will have to protect inputs and outputs with caps, what really do not mind. Could someone advised me how to change the circuit to accomodate that change? Which parts are not necessary with use of only LT chip?
Thanks for the help. |
Why not contact Damian that made the layout? I got a pair of PCB,s from him after reading this tread and have only positive experience with the information and fast responce from Damian.
Have Fun |
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| peranders |
| quote: | Originally posted by percy
Since you already have an opamp (OPA627) driving the buffer I'd imagine the buffer would be within the feedback loop of the opamp ?
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The LT1210 is a current feedback amp so it's not possible to use it with no local feedback but if you have so local feedback you can also use global feedback too.
I have designed four current feedback headphone amps and I really like current feedback. I wonder why so few have tested current feedback? |
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| Dxvideo |
Hi all,
I plan to make a good headphone amplifier for myself. And I have some LT1210. So I want to use them. I've searched a lot of site to find a good design with it but I couldnt.
Youre talking about the "backdoor" however there is no schematics of LT1210 head amp in this site.
Does anybody know a working good schematics. I have never made a headphone amp and as my supposition it should be like a gainclone. But I saw more complex circuits on web, like DC servo, pre buffer etc..
May anybody give me some tips to make a good headamp pls?
Best regards,
Ozgur |
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| Dxvideo |
Thank you Naim,
I've already examined that sites. Thats interesting but I couldnt see the schematics of LT headamp in backdoor.
Anyway,
What kind of headamp PCBs you have? I can buy one of them from you if possible.
By the way; why youre not one of our members?
forum.diyaudiotr.com
Best regards,
Ozgur |
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| Dxvideo |
Thats the Damian's circuit for LT1210;
But I am confused that whats OPA604 for? Its a kind of POSITIVE FEEDBACK or what? If so :bigeyes: he has a big trouble!
Does anybody have any idea? |
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| endia |
Hi Ozgur,
i have some cmoy, a47, meta42 and sijosae design zen headamp pcbs, plus a few but can't remember their names now.. they all single sided and etched in a small pcb house. i'm not planning to use most of them and of course free for you..
also, i have not an excuse and as soon as joining the forum.
naim |
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| gfiandy |
The OP604 is eing used as a DC servo so that the design does not need any coupling caps and won't have any bias DC offset on its output.
Regards,
Andy |
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| Dxvideo |
Hi Naim,
What a nice proposal! Thank you. I will contact you about that matter in next week.
Looking forward for your membership to our club.
And for GFiandy,
Its interesting. I have never had any experience with DC servo circuits. Op-amp choosing is important on this design? I mean does this feedback carry any kind of signal? If its important for just its precision then I can use another more available alternative like TL071?
Thx. |
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| ybserge |
Theres another way to get rid of DC at the output when working with 1210. One has to change the feedback resistor value from
2K to 1K. However the gain is reduced. In this case some nice sounding previous stage should be added before 1210, possibly an opamp, that OPA604 might happily do. |
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| Dxvideo |
Is it a rule to put a buffer before headamp? I can run a 80W power LM3886 without any buffer, and it works fine! But I did not see any kind of "nude" and good sounding headamp.
Whats that? Somebody like to make things more complex? |
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| gfiandy |
The servo opamp carries a very heavly low pass version of the signal. This means that you get minimal interaction from the DC opamp on the main path. However for best sound quality a good opamp here will out perform a cheap one.
The most inportant characterisitic of the DC servo opamp is the input offset. However it will carry signal upto 1K at very low levels this can interact with the main path.
I have also noticed in listening trials that the quality of the low pass capacitor (C4) significantly affects the sound quality of the main path.
Also note that this circuit has significant noise gain if the input to the main opamp is not driven from a low impedance source.
Regards,
Andrew |
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| Dxvideo |
So if we use the DC servo to cancel input cap. because of the input cap is important on sound quality and the C4 is still critical on sound quality even while DC servo exists:
The DC servo idea is not effective as guessed.
Am I true? |
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| gfiandy |
I think this is rather over stating the case. When AC coupling the cap is directly in the audio path and can introduce measurable distortion.
The DC servo works to much lower frequency using a much higher quality dielectric than can be used for AC coupling. All I am saying is that the type of capacitor is still significant to the sound quality.
If cost is not a problem I would go with a DC servo as you will get a better result.
If you want a simpler or cheaper solution then AC coupling makes sense.
Regards,
Andrew |
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