Hi Tomtest
If you look at your “normal schematics « shown in your previous post you will notice the same configuration ( 1 ohm resistor) I use to provide small isolation between input/feed-back and output/psu ground. This is standard practice and I have not invented it since present in allmost all amplifiers I have seen. Even for preamp a very small 0,25 ohm value for that resistor should not create a noticeable difference in sound (negligible effect on gain). It might be other ground connection (input/pot/preamp/psu/chassis/power amp grounding) that can possibly have this effect (guessing here). Just ensure you really put 0,25 ohms and not higher value. Otherwise you may have found something here...
One thing for sure is that in dual mono configuration it is very easy to not have “hum” issue due to grounding.
There are 2 ways of doing for amplifier ground return for speakers ground return. Either return at amplifier pcb and then to psu or return at PSU directly. In the ussa5 the speaker ground is connected to the psu.
“Warmer and relaxed” sounds right to my ears
and is more my objective...
By the way I am glad you appreciate the USSPA /USSA5 combo
Fab
If you look at your “normal schematics « shown in your previous post you will notice the same configuration ( 1 ohm resistor) I use to provide small isolation between input/feed-back and output/psu ground. This is standard practice and I have not invented it since present in allmost all amplifiers I have seen. Even for preamp a very small 0,25 ohm value for that resistor should not create a noticeable difference in sound (negligible effect on gain). It might be other ground connection (input/pot/preamp/psu/chassis/power amp grounding) that can possibly have this effect (guessing here). Just ensure you really put 0,25 ohms and not higher value. Otherwise you may have found something here...
One thing for sure is that in dual mono configuration it is very easy to not have “hum” issue due to grounding.
There are 2 ways of doing for amplifier ground return for speakers ground return. Either return at amplifier pcb and then to psu or return at PSU directly. In the ussa5 the speaker ground is connected to the psu.
“Warmer and relaxed” sounds right to my ears
and is more my objective...By the way I am glad you appreciate the USSPA /USSA5 combo
Fab
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Hi André
I made this afternoon measurements but in the unheated room so the temperatures seem quite low, for information the heatsinks of my USSA-5 rose to 45 ° in an ambient temperature of 25 °.
The USSPA is powered by +/- 12V with a 60 mA BIAS and the UltraBIB with 200 mA. For resistors R7 to R10, the value is 75R.
Here are the statements:
USSA-5 heatsinks: 37 ° on both channels
USSPA heatsinks: 26 ° and 28 ° on both channels but I did not watch if it was M1 or M2 which was higher.
UltraBIB heat sinks: 34 °
Hi taccodude
Project16 means that you need to select your intended final bias current based on your heatsink size and your own tolerance to heat. I target 50C for heatsink temperature for class A amp but it is my personal choice. Higher the temperature allows higher bias so highest power in class A into lower impedance speaker load.
The manual expects that you will have at least 1.2A final bias current for output stage so when you adjust driver current to obtain 1A for test purpose as per the manual then I suggest about 20ma of driver current. At the end of the manual steps when you will set the final bias you will have to increase P1 and P2 set value which will increase driver current (22-25ma) which will increase driver voltage thus will increase output bias current. In the case where you can not go higher than 1A output bias current then you should select about 23ma for driver current. The exact value is not important but should be roughly about the same between positive and negative sides. For final value 20 ma is the lowest value for driver and 25ma is marginally better.
For your calculations of resistors you got it right so far but have in mind the RV1 value is the result of RV1A and RV1b in parallel and then in series with R13. Same with negative side. If you do not want to consider the RV1b then you can simply remove it to have only RV1A and R13 in series then will match your calculated values. Same for negative side.
Meanie has got it right for 20ma of driver current.
As a tip, I use a standard value of resistor for one side, recalculate the current and then use recalculated value of resistor for the other side.
Fab
Project16 means that you need to select your intended final bias current based on your heatsink size and your own tolerance to heat. I target 50C for heatsink temperature for class A amp but it is my personal choice. Higher the temperature allows higher bias so highest power in class A into lower impedance speaker load.
The manual expects that you will have at least 1.2A final bias current for output stage so when you adjust driver current to obtain 1A for test purpose as per the manual then I suggest about 20ma of driver current. At the end of the manual steps when you will set the final bias you will have to increase P1 and P2 set value which will increase driver current (22-25ma) which will increase driver voltage thus will increase output bias current. In the case where you can not go higher than 1A output bias current then you should select about 23ma for driver current. The exact value is not important but should be roughly about the same between positive and negative sides. For final value 20 ma is the lowest value for driver and 25ma is marginally better.
For your calculations of resistors you got it right so far but have in mind the RV1 value is the result of RV1A and RV1b in parallel and then in series with R13. Same with negative side. If you do not want to consider the RV1b then you can simply remove it to have only RV1A and R13 in series then will match your calculated values. Same for negative side.
Meanie has got it right for 20ma of driver current.
As a tip, I use a standard value of resistor for one side, recalculate the current and then use recalculated value of resistor for the other side.
Fab
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Hi taccodude
Here is the results with 47 ohms as RV1A and 2,2 ohms as RV2A:
Vgsp= 1,548
Requivalent = 47+ 47//100= 79 ohms
IM3pre= 19,6ma
Vgsn= 0,99
Requivalent= 47+ 47//2,2= 49 ohms
IM4pre=0,99 / 49 = 20,16 ma
IMpre Difference = (20,16-19,6) / ((20,16+19,6)/2) * 100 = 2,8 % < 12% — > very good.
When increasing output bias at >= 1,2A at end of test then IMpre will increase to be >= 22ma which will be correct.
Fab
Here is the results with 47 ohms as RV1A and 2,2 ohms as RV2A:
Vgsp= 1,548
Requivalent = 47+ 47//100= 79 ohms
IM3pre= 19,6ma
Vgsn= 0,99
Requivalent= 47+ 47//2,2= 49 ohms
IM4pre=0,99 / 49 = 20,16 ma
IMpre Difference = (20,16-19,6) / ((20,16+19,6)/2) * 100 = 2,8 % < 12% — > very good.
When increasing output bias at >= 1,2A at end of test then IMpre will increase to be >= 22ma which will be correct.
Fab
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Hi André
I made this afternoon measurements but in the unheated room so the temperatures seem quite low, for information the heatsinks of my USSA-5 rose to 45 ° in an ambient temperature of 25 °.
The USSPA is powered by +/- 12V with a 60 mA BIAS and the UltraBIB with 200 mA. For resistors R7 to R10, the value is 75R.
Here are the statements:
USSA-5 heatsinks: 37 ° on both channels
USSPA heatsinks: 26 ° and 28 ° on both channels but I did not watch if it was M1 or M2 which was higher.
UltraBIB heat sinks: 34 °
Hi Olivier,
Thank you for your measurements.
My USSPA is getting a little bit hotter, around 30,5 Grad C (or 9 Grad C above room temperature). What is not surprisingly with the higher current and higher voltage. So everything seems to be alright. I was a little bit afraid that something goes wrong because he is surprisingly “cold”.
Is there a reason why you chose the 75 ohm resistors, smaller gain against 150 ohm resistors?
I came back home today, after a few days in the north of Germany and what surprise, after nearly 7 weeks, the Germany post tried to deliver my LDR during this days. I bet when I have stayed at home nothing would have been delivered!
It is as always.
Have you tried to play around with the ground lanes or will you ever try this?
I will be interested in your findings, but do not make yourself any work.
Bye
André
Hi Tomtest
If you look at your “normal schematics « shown in your previous post you will notice the same configuration ( 1 ohm resistor) I use to provide small isolation between input/feed-back and output/psu ground. This is standard practice and I have not invented it since present in allmost all amplifiers I have seen. Even for preamp a very small 0,25 ohm value for that resistor should not create a noticeable difference in sound (negligible effect on gain). It might be other ground connection (input/pot/preamp/psu/chassis/power amp grounding) that can possibly have this effect (guessing here). Just ensure you really put 0,25 ohms and not higher value. Otherwise you may have found something here...
One thing for sure is that in dual mono configuration it is very easy to not have “hum” issue due to grounding.
There are 2 ways of doing for amplifier ground return for speakers ground return. Either return at amplifier pcb and then to psu or return at PSU directly. In the ussa5 the speaker ground is connected to the psu.
“Warmer and relaxed” sounds right to my ears
By the way I am glad you appreciate the USSPA /USSA5 combo
Fab
Hi Fab,
Thank you for taking the time to answer me and giving me the explanations.
So you made it the way (or why) I thought about.
Even more interesting, that I can hear a difference, where no difference should be (Inaudible). I am talking about the small resistors (I have used 0,22 ohm metal film resistors) and/or bypassing them.
I will try the same with my final setup, to see (hear) if this behavior will last?!
Do you pull down the 0V lines of your power supply to the star ground as “Normal”
, or do you do not make any kind of grounding in this place as some forum members? What are your findings or suggestions for the best sound (your intended sound)?I have built the USSPA-1 version and have not tried to play around with the second harmonic. But I plan to do this after I am sure that everything else is made in the best possible way. So I could be sure to find the version I liked the most. Do you have any new suggestions for finding the preferred version?
I am glad about the really good sound the combination gives too!
And, I could not say it often enough, thank you for your kindness and your constantly support (which must not be always easy), and giving us all the possibility to participate on your genius!
THANK YOU!
André
Hi ClaudeG,
I just finished the final setup for the new input caps and will be giving it a full burn in then listening sessions. I'll be able to tell much more after but so far it sounds quite dynamic and throws a huge soundstage.
Thanks
Do