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My_Ref Fremen Edition - Build thread and tutorial
My_Ref Fremen Edition - Build thread and tutorial
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Old 26th June 2020, 01:59 PM   #4651
ggerla is offline ggerla  Italy
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Hi all
I want to enhance once again the excellent work done by Dario and the effectiveness of the circuit of this amplifier!
I'm using a raspberry + USB DAC as source of my HiFi. The DAC is directly connected to My_REF. Sound is perfect and no noise or any disturbance is present.
Now I'm try to use a diy preampli and soon as put it between DAC and My_REF 2 problems appears:
1. USB interference from rasberry. It sounds like a prprprpr. I cannot hear this when the DAC is connected directly to My_REF.
2. 50Hz hum from preampli. It sounds as clissical power hum.

To come back to the original good quality of sound I have to power the raspberry with a power bank and the preapli with batteries.

So it seems that My_REF is very proof versus noise. The USB problem is not present and no noise from the power is captured.
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Old 26th June 2020, 04:10 PM   #4652
truepaul is offline truepaul  United States
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My_Ref Fremen Edition - Build thread and tutorial
Default Finding a good trafo

Quote:
Originally Posted by lehmanhill View Post
I can't say from personal experience, but early in the development of this amp, Bob McDaniels compared2 levels of toroidal Antek transformers and, if I recall, found cleaner, better damped bass with the larger levels.
Hi all ! I'm just starting to follow this build thread, and thought I'd search out this question.

So ... At [p.104 post #1038], Bob says he could have shipped ApexJr 125 VA transformers ...

"but though it's been months, I remember feeling the 300 VA units made a significant improvement in the body of the sound. "

That's the only reference I've found. I am also trying to source an affordable pair of transformers, so if for example Antek's 200VA toroid is more than sufficient and the 300VA toroid doesn't make a startling difference, that's probably where I'd land.

Comments and suggestions welcome !
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Old 27th June 2020, 04:51 AM   #4653
Panelhead is offline Panelhead
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No hard answer. Depends on speakers and listening level.
But two 200 watt transformers is plenty. Using 4 ohm rated speakers will pull more current. More current is more watts
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Old 27th June 2020, 02:06 PM   #4654
truepaul is offline truepaul  United States
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My_Ref Fremen Edition - Build thread and tutorial
Default Choices

Thanks for the reply. This is helpful as I assess my project !

I've made surprisingly few changes to my audio set-up over the years -- neglected, I confess -- but I've been reading up on impedance matching and amplifier-to-speaker matching to try to determine if I'm getting it right.

At present, I just switched to a pair of low impedance speakers (4 ohm-- audiophile, circa 1995, with 10" woofer, 6" midrange, 1" tweeter). I'm not getting the sound I'm used to (instruments are now very distinct, versus the more blended sound I've had for ages). I'm not getting the musicality I want, but I continue to listen and test. It may be my turntable and/or cartridge that I need to adjust, as I just installed a new cartridge as well.

So ... I'm bi-amping these speakers, and my two amps each have a gain of approx 27db, so I think this is not too far off from the My_Ref FE gain of 30. I'm hoping to use the My_Ref FE in a bi-amp mode for the upper octaves.

Regarding transformers, the difference in price for 300VA versus 200VA Antek trannys isn't that much. IF it doesn't bump up my chassis cost, I may go with the 300VA version --- with the thought that my "current hungry" low impedance speakers may need it.

In addition, I like the idea of adding a soft start circuit to limit inrush current from possibly degrading any parts.

Are there any other major choices that I should consider before selecting a chassis and starting to source parts (when the new BOM is available, of course)..... ?

Best to all,

Paul B.
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Old 2nd July 2020, 01:59 PM   #4655
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by truepaul View Post
So ... I'm bi-amping these speakers, and my two amps each have a gain of approx 27db, so I think this is not too far off from the My_Ref FE gain of 30. I'm hoping to use the My_Ref FE in a bi-amp mode for the upper octaves.
Hi Paul,

Not to rain on your parade, but a 3 dB difference is really pretty big. From a human perception point of view, something that is 3 dB louder sounds like about twice as loud. That means that you are probably going to have to trim the loudness of the FE's if you are going to bi-amp them with your existing amps.

One thing is that the My_Ref has lots of compensation and interactions that mean changing its gain internally is very difficult to do well. But the good news is that it should be fairly easy to change the sensitivity externally. A simple, 2 resistor voltage divider can drop the input voltage but, as always, there are complications. The impedance ratios of the output of your pre amp to the divider and again from the divider to the input of the amp need to be managed and can affect the sound. The divider could be high impedance and followed by an opamp as a buffer to lower its output impedance, but now you need a +/- power supply.

I know from our off-line conversation that you are thinking about building a second set of FE's if you like the first ones. One solution would be to build 2 FE's so that you can bi-amp both the top and bottom with FE power.

One other question that I should have asked earlier. What is about the speaker sensitivity specification? You might be able to power these speakers with the FE's not bi-amped. I believe I remember some people powering speakers with 86 dB per watt sensitivity without problems.

Hey guys, any other great suggestions for dealing with Paul's issue?

Jac
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Old 2nd July 2020, 02:13 PM   #4656
cyto is offline cyto  United States
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Quote:
Originally Posted by lehmanhill View Post
Hi Paul,

Not to rain on your parade, but a 3 dB difference is really pretty big. From a human perception point of view, something that is 3 dB louder sounds like about twice as loud. That means that you are probably going to have to trim the loudness of the FE's if you are going to bi-amp them with your existing amps.

One thing is that the My_Ref has lots of compensation and interactions that mean changing its gain internally is very difficult to do well. But the good news is that it should be fairly easy to change the sensitivity externally. A simple, 2 resistor voltage divider can drop the input voltage but, as always, there are complications. The impedance ratios of the output of your pre amp to the divider and again from the divider to the input of the amp need to be managed and can affect the sound. The divider could be high impedance and followed by an opamp as a buffer to lower its output impedance, but now you need a +/- power supply.

I know from our off-line conversation that you are thinking about building a second set of FE's if you like the first ones. One solution would be to build 2 FE's so that you can bi-amp both the top and bottom with FE power.

One other question that I should have asked earlier. What is about the speaker sensitivity specification? You might be able to power these speakers with the FE's not bi-amped. I believe I remember some people powering speakers with 86 dB per watt sensitivity without problems.

Hey guys, any other great suggestions for dealing with Paul's issue?

Jac
My understanding is a 3db increase doubles the sound intensity but it takes a 10db increase to double the "percieved " volume to human ears.
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Old 2nd July 2020, 03:17 PM   #4657
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by cyto View Post
My understanding is a 3db increase doubles the sound intensity but it takes a 10db increase to double the "percieved " volume to human ears.
I stand corrected. Thank you.

Once upon a time, when younger, I could hear 1/2 dB difference in sound level, although that was a really small difference.:-)

Jac
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Old 2nd July 2020, 05:41 PM   #4658
MassBoost is offline MassBoost  United States
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A 3db gain is a fairly substantial increase never the less, as it usually takes around double the amplification power to gain a 3db increase.
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Old 4th July 2020, 12:27 PM   #4659
lehmanhill is offline lehmanhill  United States
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Thanks to Stream for reminding us. It is best if build related discussion comes in this thread. Over in the Completed Projects Thread, we got off topic and started talking about building older boards and the new board. That should have probably happened here and if you want to make sure you are caught up, please be sure to read that thread up to about post #34.

Fremen Edition My_Ref Amplifier Completed Projects and Photos

Jac
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Old 4th July 2020, 12:36 PM   #4660
turion64 is offline turion64  United States
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Can those posts be moved over to here then, to keep everything orderly?
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