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PostPosted: 05 Oct 2016, 06:24 
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Thanks Bruce. The circuit is pretty much the same as the OPA2134 data sheet minus the phono section. I have built and use your phono pre.
On the data sheet it looked so simple that I thought maybe something else should be added.


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PostPosted: 17 Oct 2016, 20:54 
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I built the preamplifier using the OPA2134 today in just a few hours. The PS section and amplification section fit on one small perfboard. Very easy simple build. I have spent much more on more complicated preamplifier builds that do not sound as good as this one does. Just use the section from the volume control forward that Bruce provided. I built the PS section from the phono OPA2134 build guide. Not much difference from the one provided on the same amplifier schematic. I did use 1000uf 16V caps in the PS section being that the cost is so low. I have not listened to it for long so my opinion is subject to change but being that the OPA2134 us such a fine chip I doubt my opinion is going to change.


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PostPosted: 17 Oct 2016, 21:19 
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wdecho wrote:
I built the preamplifier using the OPA2134 today in just a few hours. The PS section and amplification section fit on one small perfboard. Very easy simple build. I have spent much more on more complicated preamplifier builds that do not sound as good as this one does. Just use the section from the volume control forward that Bruce provided. I built the PS section from the phono OPA2134 build guide. Not much difference from the one provided on the same amplifier schematic. I did use 1000uf 16V caps in the PS section being that the cost is so low. I have not listened to it for long so my opinion is subject to change but being that the OPA2134 us such a fine chip I doubt my opinion is going to change.


Sounds good.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 19 Oct 2016, 10:21 
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I made some changes in the feedback circuit. I changed out the 100K and 10K resistors for two 2.2K ones and it lowered the gain and noise level. It worked fine with most of my amps as is but on some the gain was too much with too much noise. With the phono section added you would probably want to use the values shown. As a standalone preamp I believe the 2.2K resistors are better in the feedback circuit. I am open to opinions and other options.


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PostPosted: 19 Oct 2016, 16:48 
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wdecho wrote:
I made some changes in the feedback circuit. I changed out the 100K and 10K resistors for two 2.2K ones and it lowered the gain and noise level. It worked fine with most of my amps as is but on some the gain was too much with too much noise. With the phono section added you would probably want to use the values shown. As a standalone preamp I believe the 2.2K resistors are better in the feedback circuit. I am open to opinions and other options.

So you have opted for unity gain?

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 19 Oct 2016, 17:12 
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I believe it is 2X gain and not unity gain. I do know there is gain from knowing my components. When first built it worked fine with my Firstwatt amps but not with some of the D boards I have been playing with lately. I thought it may just be an impedance mismatch but after making the changes it works and sounds great with them as well. I did omit the 2.2K resistor on the output. I saw no need for it the way I am using the pre. I just finished using it with the 50ASX2 ICEpower board which did not sound good at all before and it sounds fine now. From looking at Rod Elliotts 2 stage pre design he uses 10K resistors in his feedback circuits. I am considering building Rod's pre and compare how it sounds to this one. One thing for sure, this one is an easy and quick build that sounds really fine now.


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PostPosted: 19 Oct 2016, 19:03 
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wdecho wrote:
I believe it is 2X gain and not unity gain. I do know there is gain from knowing my components. When first built it worked fine with my Firstwatt amps but not with some of the D boards I have been playing with lately. I thought it may just be an impedance mismatch but after making the changes it works and sounds great with them as well. I did omit the 2.2K resistor on the output. I saw no need for it the way I am using the pre. I just finished using it with the 50ASX2 ICEpower board which did not sound good at all before and it sounds fine now. From looking at Rod Elliotts 2 stage pre design he uses 10K resistors in his feedback circuits. I am considering building Rod's pre and compare how it sounds to this one. One thing for sure, this one is an easy and quick build that sounds really fine now.


I built Elliott's preamp with the original hand made Jupiter beeswax caps. Got sold to a guy in America.

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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PostPosted: 26 Dec 2016, 16:33 
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Joined: 26 Dec 2016, 03:46
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I compared a lot of opamps including 2134, OPA2604/OPA604( single), LMH4562 and many others. OPA2134 is good, but I like the OPA2604/OPA604 a little better. They all have very low distortion particular LMH4562. But I don't like the sound of the 4562. 2134 is close to 2604, but just does not have the fullness of the 2604.

I designed my own preamp pcb with remote motorized volume pot and I put two together and have switch to choose one or the other. I put different opamps in each board so I can A/B compare by just a flick of a switch, no remembering the sound while changing the opamp.

I am actually surprise how much difference between different opamps even though they are flat gain of about 1.2!!! They are have high frequency respond and good slew rates. But the sound are different.


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PostPosted: 26 Dec 2016, 17:52 
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I recently built a phono preamp based on the LM833. It was an old kit from 2006. It is a two stage affair with the second stage a bufferhigh pass filter. I had built a number of Bruce's OPAMP based (2134) phono stages and loved the sound. But there is something really appealing about this preamp and I'm blaming the OPAMP.

It does state in the instructions you can replace the OPAMP with the 2134 but I like the upfront and dynamic sound. Of course I'm not just listening to an OPAMP here, it's a whole different design with different EQ values but the kit really sounds excellent.

It's a blast from the past but have you tried the LM833. Depending on your build you may be able to drop the OPAMP straight in.

http://diyaudioprojects.com/Forum/viewtopic.php?f=10&t=5742

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Projects: "Sanctum" - 12AU7 and 6AS7 direct coupled headphone amp | "retro-Oatley 6J6" - 6J6 push-pull headphone amp with OPTs | "Mimic Carbon" - carbon resistors and PIO caps. MM phono preamp
Website: retro-thermionic


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