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-   -   Balder, OPA2134+BUF634 Headphone Amplifier (https://www.diyaudio.com/forums/headphone-systems/222369-balder-opa2134-buf634-headphone-amplifier.html)

theAnonymous1 28th October 2012 06:01 PM

I've built quite a few different amps based on the LME49600 circuit (with servo), and even though it nulls any offset injected into the inputs, there has always been some offset on the outputs without an input signal present or even with the input grounded. I'm not experienced enough to figure out why that is.

Neutrality 28th October 2012 06:10 PM

Quote:

Originally Posted by theAnonymous1 (https://www.diyaudio.com/forums/headphone-systems/222369-balder-opa2134-buf634-headphone-amplifier-post3218686.html#post3218686)
I've built quite a few different amps based on the LME49600 circuit (with servo), and even though it nulls any offset injected into the inputs, there has always been some offset on the outputs without an input signal present or even with the input grounded. I'm not experienced enough to figure out why that is.

How much are we talking about? When I use a DC Servo on my other designs I get an offset of +/- a few mV, the output offset basically swings around 0V, +/- a few mV. This is quite normal behaviour and nothing to be worried about

theAnonymous1 28th October 2012 10:43 PM

I would say the average of all the different boards was around ~10mV.

qusp 29th October 2012 03:25 PM

i've built 4 different iterations of the wire with lme49600/10, none have any offset worth mentioning. LPUHP had some (~25-30mV) without the input grounded or connected, thats only logical as its a floating amp, with a floating power supply and a floating input, its a hugely wideband amp so will amplify noise pickup. the LPUHP has 21db of gain, far more than the other 3, it vanished when the input was grounded or fed signal. the others had none to speak of at any time.

a servo isnt going to stop a sudden an extreme transient from outside the amp, or a sudden failure inside the amp

so its my opinion the servo doesnt solve anythung more than good layout would and brings its own set of problems, if the servo fails....

Neutrality 30th October 2012 07:10 PM

2 Attachment(s)
Changed to OPA2132 instead of OPA2134, more or less same performance but half the worst case input offset.

I dropped the idea of using a DC Servo and instead I added an 1uF input cap and increased R7/R8 to 100K so I would still be getting a good and extended low end response.

Input DC blocking cap will be a Wima film type in SMD, cap in RC filter will be a Panasonic film cap also in SMD.

Electrolytes will be 16V/1000uF os-cons.

Going with +/-12 VDC, more than enough power for my 250 Ohm DT880 PRO.

Neutrality 5th November 2012 06:12 PM

Just got word from the manufacturer, PCBs are on their way.

Neutrality 14th November 2012 04:36 PM

Received the PCBs today, now I just have to get it built. I am planning on having some first impressions this Friday.

Neutrality 19th November 2012 04:56 PM

Got it up and running today together with my ES9023 DAC.

First impressions are very positive.

Detailed without being bright and plenty of control and power.

Tomorrow I will try it with a pair of cheap Sennheiser HD415 110dB/32 Ohm headphones as well as my "highendish" 96dB/250 Ohm Beyerdynamic DT 880 Pro headphones.

Neutrality 20th November 2012 06:00 PM

Did some listening today, it sound absolutely wonderful.

See pictures here : pictures

Jenyok 22nd February 2013 06:14 AM

1 Attachment(s)
Could I use opamp preamplifier in "class A" for LME 49600 ?
As is example, "class A" opamp preamplifier for BUF634.
.


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