The series resistor in the output from the mosfet changes the SITs tracking of the load line. So the question is what do you like? It’s easy to see the changes in the spectrum it’s much harder to decide what it should sound like.
Here is 10w at 8 ohms
Here is with a 4 ohm load. About 20w. With the output resistance at .7 ohms
At a resistance of .55 the load line holds and you don’t get the H2 dropping below the H3.
What sounds best? That’s the secret sauce!
Here is 10w at 8 ohms
Here is with a 4 ohm load. About 20w. With the output resistance at .7 ohms
At a resistance of .55 the load line holds and you don’t get the H2 dropping below the H3.
What sounds best? That’s the secret sauce!
Attachments
I think someone who is sure that his build is good enough to give it to another diyaudio friend will PM you.
I think the possible candidates might still be occupied with their own baby.
Some might not like a public run on their boards or...or....
I think Nelson has no problem with our tries to follow his SIT-5 idea as good as we can.
I have more the impression that he might like the wave of activity and excitement his builds make here at Pass Labs forum.
exactly same thing I suggested earlier, I used this approach when I took my measurements. Had 8r Lpads laying around so I used them.
Also good music
Here is a very informative review by the one and only mr. Guttenberg.
Seems to be fantastic amps! 🎺🙂🎸
Seems to be fantastic amps! 🎺🙂🎸
Seems there is at the output a resistor combination comparable to the one at the 30.5 output?
Only guessing.....
Only guessing.....
This article from Nelson might be interesting https://www.firstwatt.com/wp-content/uploads/2023/12/art_sweet_spot.pdf
Here is one of the possibilities to "search for the sweet spot" that might be used in SIT-5 too in a passive way like XA30.5.
"Here's a technique we use at Pass Labs – the use of some single-ended bias in a push-pull output stage to reduce distortion. The distortion curve below shows what you can get if you simply put a small value current source in parallel with one of the JFETs as shown on the middle circuit. The current source displaces the bias current values on the JFETs until they achieve a more perfect distortion cancellation:"
So I have something new to search if I can see it in Spice.
Nelson is a genius as the "Audiophiliac" said.....
:--))
Here is one of the possibilities to "search for the sweet spot" that might be used in SIT-5 too in a passive way like XA30.5.
"Here's a technique we use at Pass Labs – the use of some single-ended bias in a push-pull output stage to reduce distortion. The distortion curve below shows what you can get if you simply put a small value current source in parallel with one of the JFETs as shown on the middle circuit. The current source displaces the bias current values on the JFETs until they achieve a more perfect distortion cancellation:"
So I have something new to search if I can see it in Spice.
Nelson is a genius as the "Audiophiliac" said.....
:--))
Attachments
Ben for the 8r test it was around 80vdc with 1.6a bias so class AB, same stuff for the 4r test, 60v with 1.8a bias.
I am attaching another measurement at 75w/4r but this time at 0.4a bias 🙂) which is practically identical to the one at 1.8a bias.
I am attaching another measurement at 75w/4r but this time at 0.4a bias 🙂) which is practically identical to the one at 1.8a bias.
It`s no problem .. we all learn by reading these graphs. +h2 in my graphs is actually -h2
Attachments
Forgetting again one thing..
To have this circuit protected you will need a ocp protection like in the f3.
It will save you some trouble if you short the output or if you decide to make it class ab and push a lot of power through your 4r speakers.
To have this circuit protected you will need a ocp protection like in the f3.
It will save you some trouble if you short the output or if you decide to make it class ab and push a lot of power through your 4r speakers.
That is definitely Class AB efficiency, push-pull action.
Is that a typo in post #374: 0.4A bias?
Is that a typo in post #374: 0.4A bias?
I created some simulations using LTSpice to determine the THD values.
I used Botte's circuit as a basis.
For all outputs, the VDS on the SIT was set to 27V.
The IRFP9240 was used for the MOSFET.
The values with a slash between the values refer to a load of 4 and 8 ohms.
The following values were used as input voltage: 3V, 5V, 10V, 15V and 20V.
The supply voltages were -55V, -60V, and -65V, with a current of 1.5A and 2.0A, respectively.
The output power is approximately as follows:
3V => 0.9W / 0.5W
5V => 2.7W / 1.4W
10V => 10.6W / 5.6W
15V => 22.6W / 12.2W
20V => 40.5W / 21.0W
The resistance Ra is between the two source pins and Rb is the resistance at the MOSFET source to the speaker.
I used Botte's circuit as a basis.
For all outputs, the VDS on the SIT was set to 27V.
The IRFP9240 was used for the MOSFET.
The values with a slash between the values refer to a load of 4 and 8 ohms.
The following values were used as input voltage: 3V, 5V, 10V, 15V and 20V.
The supply voltages were -55V, -60V, and -65V, with a current of 1.5A and 2.0A, respectively.
The output power is approximately as follows:
3V => 0.9W / 0.5W
5V => 2.7W / 1.4W
10V => 10.6W / 5.6W
15V => 22.6W / 12.2W
20V => 40.5W / 21.0W
The resistance Ra is between the two source pins and Rb is the resistance at the MOSFET source to the speaker.
Code:
****************
*** Ra = 3.0 ***
-55V 1.5A -55V 2.0A -60V 1.5A -60V 2.0A -65V 1.5A -65V 2.0A
R2=22K5 R3=4K R2=22K4 R3=5K3 R2=22K2 R3=3K9 R2=22K1 R3=5K2 R2=22K R3=3K8 R2=21K9 R3=5K1
*** Rb = 0.2 ***
3V => 0.056% / 0.047% 0.043% / 0.041% 0.063% / 0.050% 0.049% / 0.043% 0.068% / 0.053% 0.052% / 0.045%
5V => 0.091% / 0.063% 0.056% / 0.048% 0.104% / 0.071% 0.066% / 0.055% 0.115% / 0.077% 0.074% / 0.059%
10V => 0.458% / 0.225% 0.220% / 0.176% 0.518% / 0.243% 0.243% / 0.185% 0.569% / 0.257% 0.262% / 0.192%
15V => 0.927% / 0.594% 0.605% / 0.271% 0.997% / 0.653% 0.688% / 0.310% 1.047% / 0.698% 0.739% / 0.337%
20V => 0.968% / 1.182% 0.931% / 1.180% 1.129% / 1.003% 0.981% / 0.732% 1.189% / 1.053% 1.040% / 0.779%
*** Rb = 0.5 ***
3V => 0.038% / 0.044% 0.038% / 0.042% 0.038% / 0.046% 0.038% / 0.044% 0.038% / 0.048% 0.038% / 0.045%
5V => 0.040% / 0.055% 0.039% / 0.050% 0.039% / 0.060% 0.038% / 0.055% 0.040% / 0.063% 0.039% / 0.058%
10V => 0.175% / 0.176% 0.148% / 0.165% 0.174% / 0.182% 0.160% / 0.171% 0.176% / 0.188% 0.159% / 0.174%
15V => 0.377% / 0.263% 0.208% / 0.209% 0.406% / 0.286% 0.182% / 0.224% 0.429% / 0.304% 0.196% / 0.233%
20V => 0.560% / 0.821% 0.569% / 0.819% 0.597% / 0.608% 0.455% / 0.362% 0.596% / 0.639% 0.462% / 0.386%
*** Rb = 0.6 ***
3V => 0.042% / 0.043% 0.040% / 0.042% 0.040% / 0.045% 0.038% / 0.044% 0.039% / 0.046% 0.038% / 0.045%
5V => 0.049% / 0.053% 0.043% / 0.050% 0.044% / 0.058% 0.040% / 0.055% 0.042% / 0.060% 0.038% / 0.057%
10V => 0.173% / 0.172% 0.147% / 0.164% 0.166% / 0.177% 0.146% / 0.169% 0.172% / 0.181% 0.145% / 0.173%
15V => 0.345% / 0.238% 0.207% / 0.206% 0.330% / 0.255% 0.170% / 0.219% 0.337% / 0.267% 0.163% / 0.227%
20V => 0.787% / 0.733% 0.794% / 0.732% 0.676% / 0.524% 0.396% / 0.328% 0.630% / 0.552% 0.389% / 0.345%
*** Rb = 0.7 ***
3V => 0.048% / 0.042% 0.042% / 0.042% 0.045% / 0.044% 0.040% / 0.043% 0.043% / 0.045% 0.039% / 0.045%
5V => 0.062% / 0.052% 0.049% / 0.050% 0.056% / 0.055% 0.045% / 0.054% 0.052% / 0.058% 0.042% / 0.058%
10V => 0.198% / 0.167% 0.164% / 0.164% 0.185% / 0.173% 0.152% / 0.169% 0.178% / 0.177% 0.148% / 0.172%
15V => 0.395% / 0.223% 0.237% / 0.204% 0.350% / 0.236% 0.205% / 0.216% 0.345% / 0.246% 0.190% / 0.223%
20V => 1.044% / 0.659% 1.041% / 0.657% 0.846% / 0.454% 0.448% / 0.312% 0.781% / 0.480% 0.395% / 0.326%
*** Rb = 0.8 ***
3V => 0.054% / 0.041% 0.045% / 0.042% 0.051% / 0.043% 0.043% / 0.043% 0.049% / 0.044% 0.041% / 0.044%
5V => 0.075% / 0.050% 0.056% / 0.050% 0.069% / 0.053% 0.050% / 0.054% 0.065% / 0.056% 0.047% / 0.056%
10V => 0.236% / 0.165% 0.177% / 0.163% 0.212% / 0.169% 0.166% / 0.167% 0.204% / 0.172% 0.159% / 0.171%
15V => 0.531% / 0.213% 0.260% / 0.202% 0.467% / 0.225% 0.229% / 0.213% 0.439% / 0.232% 0.211% / 0.219%
20V => 1.298% / 0.594% 1.286% / 0.590% 1.047% / 0.398% 0.587% / 0.303% 0.977% / 0.419% 0.507% / 0.314%
*** Rb = 1.1 ***
3V => 0.071% / 0.040% 0.054% / 0.041% 0.069% / 0.041% 0.051% / 0.042% 0.067% / 0.042% 0.050% / 0.043%
5V => 0.111% / 0.046% 0.075% / 0.048% 0.105% / 0.049% 0.069% / 0.051% 0.102% / 0.050% 0.066% / 0.053%
10V => 0.327% / 0.159% 0.219% / 0.161% 0.313% / 0.162% 0.206% / 0.165% 0.306% / 0.164% 0.198% / 0.167%
15V => 1.040% / 0.196% 0.406% / 0.198% 0.970% / 0.204% 0.363% / 0.206% 0.937% / 0.208% 0.341% / 0.211%
20V => 1.990% / 0.442% 1.955% / 0.432% 1.656% / 0.303% 1.106% / 0.288% 1.596% / 0.314% 1.034% / 0.297%
****************
*** Ra = 2.0 ***
-55V 1.5A -55V 2.0A -60V 1.5A -60V 2.0A -65V 1.5A -65V 2.0A
R2=22K5 R3=2K9 R2=22K4 R3=3K9 R2=22K2 R3=2K8 R2=22K1 R3=3K7 R2=22K R3=2K75 R2=21K85 R3=3K65
*** Rb = 0.2 ***
3V => 0.059% / 0.048% 0.046% / 0.041% 0.066% / 0.051% 0.051% / 0.044% 0.070% / 0.053% 0.054% / 0.046%
5V => 0.096% / 0.066% 0.058% / 0.050% 0.111% / 0.073% 0.072% / 0.057% 0.119% / 0.078% 0.078% / 0.061%
10V => 0.480% / 0.231% 0.224% / 0.178% 0.572% / 0.251% 0.261% / 0.189% 0.580% / 0.261% 0.277% / 0.195%
15V => 0.954% / 0.614% 0.615% / 0.279% 1.024% / 0.680% 0.735% / 0.337% 1.063% / 0.710% 0.774% / 0.360%
20V => 1.101% / 1.014% 1.081% / 0.958% 1.164% / 1.031% 1.025% / 0.774% 1.214% / 1.061% 1.075% / 0.813%
*** Rb = 0.5 ***
3V => 0.038% / 0.045% 0.038% / 0.042% 0.038% / 0.047% 0.038% / 0.044% 0.038% / 0.048% 0.038% / 0.046%
5V => 0.039% / 0.057% 0.038% / 0.052% 0.041% / 0.062% 0.040% / 0.057% 0.043% / 0.065% 0.041% / 0.060%
10V => 0.175% / 0.180% 0.160% / 0.173% 0.184% / 0.187% 0.162% / 0.180% 0.197% / 0.198% 0.163% / 0.184%
15V => 0.419% / 0.283% 0.193% / 0.215% 0.456% / 0.309% 0.218% / 0.232% 0.476% / 0.323% 0.228% / 0.241%
20V => 0.614% / 0.661% 0.589% / 0.600% 0.612% / 0.655% 0.498% / 0.407% 0.616% / 0.677% 0.521% / 0.428%
*** Rb = 0.6 ***
3V => 0.039% / 0.044% 0.038% / 0.042% 0.038% / 0.046% 0.038% / 0.044% 0.038% / 0.047% 0.038% / 0.046%
5V => 0.042% / 0.056% 0.039% / 0.053% 0.040% / 0.060% 0.038% / 0.056% 0.039% / 0.062% 0.038% / 0.059%
10V => 0.174% / 0.175% 0.147% / 0.166% 0.153% / 0.182% 0.146% / 0.172% 0.161% / 0.186% 0.145% / 0.176%
15V => 0.340% / 0.254% 0.170% / 0.211% 0.361% / 0.275% 0.172% / 0.226% 0.373% / 0.285% 0.173% / 0.234%
20V => 0.665% / 0.584% 0.613% / 0.523% 0.597% / 0.577% 0.424% / 0.358% 0.573% / 0.597% 0.423% / 0.375%
*** Rb = 0.7 ***
3V => 0.043% / 0.043% 0.039% / 0.043% 0.041% / 0.045% 0.038% / 0.044% 0.040% / 0.045% 0.038% / 0.046%
5V => 0.050% / 0.054% 0.042% / 0.052% 0.046% / 0.058% 0.040% / 0.056% 0.043% / 0.060% 0.039% / 0.058%
10V => 0.175% / 0.172% 0.144% / 0.166% 0.167% / 0.177% 0.146% / 0.172% 0.163% / 0.181% 0.145% / 0.175%
15V => 0.333% / 0.237% 0.195% / 0.209% 0.321% / 0.253% 0.181% / 0.222% 0.318% / 0.261% 0.175% / 0.230%
20V => 0.789% / 0.519% 0.698% / 0.459% 0.682% / 0.514% 0.389% / 0.333% 0.632% / 0.532% 0.378% / 0.347%
*** Rb = 0.8 ***
3V => 0.047% / 0.043% 0.041% / 0.043% 0.045% / 0.044% 0.040% / 0.044% 0.043% / 0.045% 0.039% / 0.045%
5V => 0.060% / 0.053% 0.046% / 0.052% 0.055% / 0.056% 0.043% / 0.055% 0.052% / 0.058% 0.041% / 0.058%
10V => 0.193% / 0.169% 0.158% / 0.166% 0.184% / 0.174% 0.151% / 0.170% 0.176% / 0.177% 0.147% / 0.174%
15V => 0.372% / 0.226% 0.217% / 0.208% 0.343% / 0.239% 0.195% / 0.219% 0.320% / 0.246% 0.182% / 0.226%
20V => 0.942% / 0.468% 0.834% / 0.407% 0.815% / 0.460% 0.433% / 0.320% 0.753% / 0.477% 0.382% / 0.333%
*** Rb = 1.1 ***
3V => 0.060% / 0.041% 0.047% / 0.042% 0.058% / 0.042% 0.046% / 0.043% 0.056% / 0.043% 0.044% / 0.044%
5V => 0.088% / 0.049% 0.060% / 0.051% 0.084% / 0.052% 0.057% / 0.054% 0.081% / 0.054% 0.054% / 0.056%
10V => 0.268% / 0.163% 0.185% / 0.164% 0.258% / 0.167% 0.180% / 0.168% 0.238% / 0.169% 0.173% / 0.170%
15V => 0.698% / 0.207% 0.298% / 0.204% 0.658% / 0.216% 0.285% / 0.213% 0.608% / 0.221% 0.262% / 0.219%
20V => 1.412% / 0.351% 1.261% / 0.312% 1.266% / 0.351% 0.795% / 0.301% 1.193% / 0.363% 0.690% / 0.312%
****************
*** Ra = 1.0 ***
-55V 1.5A -55V 2.0A -60V 1.5A -60V 2.0A -65V 1.5A -65V 2.0A
R2=22K5 R3=1K75 R2=22K4 R3=2K3 R2=22K2 R3=1K72 R2=22K1 R3=2K25 R2=22K R3=1K68 R2=21K85 R3=2K22
*** Rb = 0.2 ***
3V => 0.066% / 0.050% 0.050% / 0.043% 0.072% / 0.052% 0.054% / 0.045% 0.076% / 0.054% 0.057% / 0.047%
5V => 0.111% / 0.070% 0.070% / 0.054% 0.121% / 0.076% 0.078% / 0.059% 0.129% / 0.080% 0.084% / 0.062%
10V => 0.581% / 0.250% 0.267% / 0.186% 0.596% / 0.263% 0.281% / 0.194% 0.636% / 0.274% 0.295% / 0.200%
15V => 1.015% / 0.678% 0.737% / 0.339% 1.064% / 0.704% 0.791% / 0.373% 1.101% / 0.745% 0.823% / 0.393%
20V => 1.147% / 1.009% 1.011% / 0.771% 1.214% / 1.055% 1.089% / 0.824% 1.259% / 1.085% 1.132% / 0.855%
*** Rb = 0.5 ***
3V => 0.040% / 0.046% 0.039% / 0.044% 0.042% / 0.049% 0.040% / 0.046% 0.044% / 0.050% 0.041% / 0.047%
5V => 0.048% / 0.061% 0.041% / 0.055% 0.053% / 0.066% 0.045% / 0.059% 0.057% / 0.069% 0.048% / 0.061%
10V => 0.224% / 0.198% 0.169% / 0.177% 0.237% / 0.204% 0.174% / 0.183% 0.251% / 0.209% 0.178% / 0.186%
15V => 0.554% / 0.361% 0.290% / 0.234% 0.586% / 0.382% 0.317% / 0.248% 0.612% / 0.401% 0.353% / 0.256%
20V => 0.692% / 0.717% 0.586% / 0.470% 0.736% / 0.749% 0.629% / 0.504% 0.768% / 0.772% 0.657% / 0.523%
*** Rb = 0.6 ***
3V => 0.038% / 0.046% 0.038% / 0.044% 0.039% / 0.048% 0.039% / 0.046% 0.040% / 0.049% 0.039% / 0.047%
5V => 0.042% / 0.060% 0.039% / 0.055% 0.045% / 0.064% 0.041% / 0.059% 0.048% / 0.067% 0.043% / 0.061%
10V => 0.199% / 0.185% 0.153% / 0.177% 0.205% / 0.191% 0.157% / 0.182% 0.207% / 0.196% 0.167% / 0.185%
15V => 0.471% / 0.317% 0.232% / 0.227% 0.496% / 0.335% 0.267% / 0.240% 0.518% / 0.351% 0.279% / 0.248%
20V => 0.622% / 0.659% 0.523% / 0.415% 0.643% / 0.689% 0.544% / 0.450% 0.669% / 0.710% 0.567% / 0.467%
*** Rb = 0.7 ***
3V => 0.038% / 0.046% 0.038% / 0.044% 0.038% / 0.048% 0.038% / 0.046% 0.038% / 0.049% 0.038% / 0.047%
5V => 0.039% / 0.059% 0.038% / 0.055% 0.040% / 0.063% 0.040% / 0.058% 0.042% / 0.065% 0.040% / 0.061%
10V => 0.176% / 0.182% 0.161% / 0.169% 0.178% / 0.187% 0.161% / 0.174% 0.191% / 0.191% 0.162% / 0.178%
15V => 0.409% / 0.292% 0.200% / 0.219% 0.428% / 0.304% 0.209% / 0.235% 0.446% / 0.317% 0.216% / 0.233%
20V => 0.585% / 0.612% 0.465% / 0.379% 0.591% / 0.640% 0.479% / 0.409% 0.597% / 0.660% 0.497% / 0.425%
*** Rb = 0.8 ***
3V => 0.038% / 0.045% 0.038% / 0.044% 0.036% / 0.047% 0.038% / 0.046% 0.038% / 0.048% 0.038% / 0.046%
5V => 0.040% / 0.058% 0.038% / 0.055% 0.039% / 0.062% 0.038% / 0.058% 0.039% / 0.065% 0.039% / 0.060%
10V => 0.165% / 0.180% 0.147% / 0.170% 0.161% / 0.185% 0.147% / 0.180% 0.171% / 0.188% 0.143% / 0.177%
15V => 0.361% / 0.273% 0.176% / 0.216% 0.378% / 0.287% 0.179% / 0.228% 0.392% / 0.297% 0.190% / 0.238%
20V => 0.590% / 0.573% 0.426% / 0.354% 0.563% / 0.599% 0.430% / 0.381% 0.566% / 0.619% 0.442% / 0.395%
*** Rb = 1.1 ***
3V => 0.042% / 0.044% 0.039% / 0.043% 0.041% / 0.045% 0.038% / 0.045% 0.040% / 0.046% 0.038% / 0.046%
5V => 0.050% / 0.055% 0.042% / 0.054% 0.046% / 0.059% 0.039% / 0.057% 0.043% / 0.061% 0.038% / 0.060%
10V => 0.175% / 0.173% 0.159% / 0.168% 0.166% / 0.178% 0.146% / 0.172% 0.162% / 0.181% 0.144% / 0.176%
15V => 0.330% / 0.243% 0.194% / 0.215% 0.315% / 0.254% 0.178% / 0.226% 0.305% / 0.262% 0.159% / 0.232%
20V => 0.716% / 0.488% 0.400% / 0.319% 0.636% / 0.511% 0.357% / 0.340% 0.596% / 0.528% 0.347% / 0.351%