I would like to submit these two measures to you. We have seen that at the output of a transformer preamp, as expected, there is no trace of DC, it is blocked by the transformers.
I wanted to see how much DC was present at the output of my dac. As always I don't know if I used a correct method ...
Dac turned on without signal. On the left channel I measure about 1.0 mV, on the right channel I measure about -0.9 mV.
I didn't expect to find a negative current on a channel.
Would anyone know how to explain these measures (if they are correct and have a meaning)?
Thank you all
Ciao
giacinto
I wanted to see how much DC was present at the output of my dac. As always I don't know if I used a correct method ...
Dac turned on without signal. On the left channel I measure about 1.0 mV, on the right channel I measure about -0.9 mV.
I didn't expect to find a negative current on a channel.
Would anyone know how to explain these measures (if they are correct and have a meaning)?
Thank you all
Ciao
giacinto
Attachments
Yes it is absolutely normal, even more, your result is very good. Your dac is a correctly designed/ executed product.
Output offset can be any polarity, it's normal. Think of it that your dac is producing an AC output, with 0V DC being the center value. The actual momentary magnitude is either above or below in the time; like between +2,8V / -2,8V peak maximum, in case of an average dac output level.
Ciao, George
Output offset can be any polarity, it's normal. Think of it that your dac is producing an AC output, with 0V DC being the center value. The actual momentary magnitude is either above or below in the time; like between +2,8V / -2,8V peak maximum, in case of an average dac output level.
Ciao, George
First, George it is so good to see you back!!!!
The dac measurement is fine. It tells me the dac is dc coupled, a good thing. Also, hook up the TVC and measure again. The dc voltage offset should be even lower when loaded by the dc resistance of the input side of the TVC.
My transformer is on the input of My_Ref. Been running some REW sweeps. Not happy with results. The transformer is raising the noise floor.
Going to play with routing and transformer position to see if there are easy fixes.
The dac measurement is fine. It tells me the dac is dc coupled, a good thing. Also, hook up the TVC and measure again. The dc voltage offset should be even lower when loaded by the dc resistance of the input side of the TVC.
My transformer is on the input of My_Ref. Been running some REW sweeps. Not happy with results. The transformer is raising the noise floor.
Going to play with routing and transformer position to see if there are easy fixes.
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I see saturation in the last plot.. somebody is saturating. Is it possible that You overdrive the transformer? Or the input ADC, given that the signal is -1,6dB, with respect to the -14dB in the first.. -4dB in the second.. when you get close to the Zone, saturation sets in all at once ..
All graphs are using a Cinemag 15/15B line input
Just showing the overload and saturation.The low level is normal listening output. Speakers are three way horns with a sub.
The chain here was REW signal generator, Focusrite Clarett 4Pre output into a Fremen. The measured voltage across the 6 ohm power resistor is fed into an ADC on the Clarett and looped into REW.
All three graphs use the same power resistor and input transformer. High enough input really gets it ringing.
A different signal generator is next, an Akitka 79.00 generator. I hope to install Cinemag CM10/600 4:1 stepdown transformers soon and retest.
Had a pair of Lundahl transformers and configured them for 4:1 step down. Saw a lot of ringing and removed. Guess all ring if driven at a high enough level.
Just showing the overload and saturation.The low level is normal listening output. Speakers are three way horns with a sub.
The chain here was REW signal generator, Focusrite Clarett 4Pre output into a Fremen. The measured voltage across the 6 ohm power resistor is fed into an ADC on the Clarett and looped into REW.
All three graphs use the same power resistor and input transformer. High enough input really gets it ringing.
A different signal generator is next, an Akitka 79.00 generator. I hope to install Cinemag CM10/600 4:1 stepdown transformers soon and retest.
Had a pair of Lundahl transformers and configured them for 4:1 step down. Saw a lot of ringing and removed. Guess all ring if driven at a high enough level.
Do not know. I know it shows using a capacitor to block DC and set a high pass filter is not so bad.
I have a real EVO Rev A in the closet. Need to test it.
GeorgeK and Dario both said it is slightly cleaner than the Fremen due to layout differences. The measurements GeorgeK performed on a Fremen are SOTA. Very few commercial amps are even close.
I have a real EVO Rev A in the closet. Need to test it.
GeorgeK and Dario both said it is slightly cleaner than the Fremen due to layout differences. The measurements GeorgeK performed on a Fremen are SOTA. Very few commercial amps are even close.
Audiophile upgrades
So I took the plunge and installed the Z-foils at R10 & R12, the Amtrans at C12, 30 & 32 and the Cerafine at 9. I already had the Mundorfs at C13 and C101&201. It still sounds fantastic: excellent low end response, clarity and openness and wonderful resolution overall. However, the Mouser BOM build on the Evo A mod was just as wonderful (as I remember) and its really hard to say that doing the upgrades didn’t bias me into thinking that I hear something better than how wowed I was before (with the original build). I’m driving both amps with a single 400VA 28+28 instead of making two monoblocks.
Has anyone actually done a side-by-side real time comparison of the basic build versus with the "audiophile" upgrades? Will dual toroidals bring me anything better? Is it advisable to finish the Z-foil upgrades at R7 & R37?
Thanks
Turion64
So I took the plunge and installed the Z-foils at R10 & R12, the Amtrans at C12, 30 & 32 and the Cerafine at 9. I already had the Mundorfs at C13 and C101&201. It still sounds fantastic: excellent low end response, clarity and openness and wonderful resolution overall. However, the Mouser BOM build on the Evo A mod was just as wonderful (as I remember) and its really hard to say that doing the upgrades didn’t bias me into thinking that I hear something better than how wowed I was before (with the original build). I’m driving both amps with a single 400VA 28+28 instead of making two monoblocks.
Has anyone actually done a side-by-side real time comparison of the basic build versus with the "audiophile" upgrades? Will dual toroidals bring me anything better? Is it advisable to finish the Z-foil upgrades at R7 & R37?
Thanks
Turion64
Turion64,
A long time ago, on a different BOM, I did the single versus two toroids comparison. I couldn't hear any difference and didn't measure any significant difference in hum. If I recall correctly, the reason that two transformers were originally specified by Mauro was to increase the hum immunity. As for sound quality, having a big enough transformer is key to getting the best bass performance and you should be good at 400VA. The Mundorf power supply caps are also said to improve bass sound and are very low ESR which makes sense. In this case, I can't say personally because I have always built with the Mundorfs.
I have done many of the "audiophile" upgrades, but I did them in a different order and, sometimes, with too much time between evaluations to make a proper "back to back" evaluation. However, Dario has done a huge number of back to back evaluations and I have never gone wrong following his advice. The "audiophile" upgrades are based on those evaluations and are meant to offer improvements over the base BOM for those willing to spend the time and money. By the way, we really owe Dario for all his work on this project. You would be amazed at the hours and money Dario has spent working on the best BOMs.
As for Z-foils, others have done evaluations and said that each additional Z-foil in the signal chain offers improvement. The FE I am currently using has all Z-foils in the signal path and I changed them all at once (however, lots of other build variations). I can't say that a big sound difference jumped out immediately after the change, but in the weeks since the change I have been enjoying the amp immensely and it clearly sounds the best of any amps I have ever listened to.
In the end, if you like how your amp sounds with the current build, then enjoy it as is. As you said, the base BOM build sounds amazing. There will always be a tweak or two when you want to play again. Actually, when that time comes, I recommend having a second pair of boards so that you can play with tweaks on one pair and keep a build you like on the other pair.
Jac
A long time ago, on a different BOM, I did the single versus two toroids comparison. I couldn't hear any difference and didn't measure any significant difference in hum. If I recall correctly, the reason that two transformers were originally specified by Mauro was to increase the hum immunity. As for sound quality, having a big enough transformer is key to getting the best bass performance and you should be good at 400VA. The Mundorf power supply caps are also said to improve bass sound and are very low ESR which makes sense. In this case, I can't say personally because I have always built with the Mundorfs.
I have done many of the "audiophile" upgrades, but I did them in a different order and, sometimes, with too much time between evaluations to make a proper "back to back" evaluation. However, Dario has done a huge number of back to back evaluations and I have never gone wrong following his advice. The "audiophile" upgrades are based on those evaluations and are meant to offer improvements over the base BOM for those willing to spend the time and money. By the way, we really owe Dario for all his work on this project. You would be amazed at the hours and money Dario has spent working on the best BOMs.
As for Z-foils, others have done evaluations and said that each additional Z-foil in the signal chain offers improvement. The FE I am currently using has all Z-foils in the signal path and I changed them all at once (however, lots of other build variations). I can't say that a big sound difference jumped out immediately after the change, but in the weeks since the change I have been enjoying the amp immensely and it clearly sounds the best of any amps I have ever listened to.
In the end, if you like how your amp sounds with the current build, then enjoy it as is. As you said, the base BOM build sounds amazing. There will always be a tweak or two when you want to play again. Actually, when that time comes, I recommend having a second pair of boards so that you can play with tweaks on one pair and keep a build you like on the other pair.
Jac
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Mauro's articles are sometimes hard to find. Here is one that overviews the my_ref project.
Dropbox - project_my_ref.pdf - Simplify your life
Jac
Dropbox - project_my_ref.pdf - Simplify your life
Jac
