The SissySIT is a different animal. It is a push-pull mosfet/SIT, Depletion / Enhancement Follower (DEF) amp, similar to the FW SIT-3, where the SIT Ugs needs to be in a certain range in order the work with the mosfet.
This common drain mu follower is single ended and does not have the same restriction. So the THF-51S Ugs is not critical. The bias voltage supply is adjustable to accommodate a wide range of THF-51S Ugs.
This common drain mu follower is single ended and does not have the same restriction. So the THF-51S Ugs is not critical. The bias voltage supply is adjustable to accommodate a wide range of THF-51S Ugs.
Hi Ben,
Thanks for the quick reply. I had a feeling since you never mentioned it that would be the case...
Just wanted to double confirm.
I thinking to do this project as my first set of mono blocks. Since my DAC and pre are curently fully balanced and I didn't do a SE curcuit yet, I am thinking to use NP's FE 2022 as a front end, and run this at 2.5A based on your comments.
I will likely do my own PCB layout to get some experience and learning...
I will update you as I proceed, next step is to get some SIT's!
G
Thanks for the quick reply. I had a feeling since you never mentioned it that would be the case...
Just wanted to double confirm.
I thinking to do this project as my first set of mono blocks. Since my DAC and pre are curently fully balanced and I didn't do a SE curcuit yet, I am thinking to use NP's FE 2022 as a front end, and run this at 2.5A based on your comments.
I will likely do my own PCB layout to get some experience and learning...
I will update you as I proceed, next step is to get some SIT's!
G
This amp was my first pcb design too. Now that I have done some projects with my own pcbs, I wish I had started doing pcbs earlier.
I use NP's DIY FE 2022 as a preamp/front end for all of my follower amps and it's a great front end.
Have fun with your project. 🙂
I use NP's DIY FE 2022 as a preamp/front end for all of my follower amps and it's a great front end.
Have fun with your project. 🙂
Hi Ben,
Recieved my SITs today, tested them just to make sure they worked as expected with ZenMods Ugs test curcuit and everything was good, nearly identical but not a good match for his design.
The fun continues..
G
Recieved my SITs today, tested them just to make sure they worked as expected with ZenMods Ugs test curcuit and everything was good, nearly identical but not a good match for his design.
The fun continues..
G
Hi Ben,
I had this question some time on my mind, but as G's question has shoot in the same direction, I'll ask it now.
Forgive me if you had mentioned it in this quite long thread, I've read a lot, but not all in a highly concentrated fashion.
Have you tested different bias points, so let's say maybe from in the 40s upto 70 volts at different current levels? Why have you settled on 65V and 2,5A? I'm asking because of two reasons: most capacitors are rated upto 63V and then 100V or eighty -something. And of cause I have some nice 63V coke bottles waiting for a project. The other one, more important is, that the big 500mm deep and 5U high Modushop case it referring to good soul ZenMod only capable of 120W (and this is for warm days also, as I understood, to have some safety barrier against the magic smoke). (See post #369). Data from Modushop present it a bit different (if you measure different, you get different numbers. I would say from a noob-theoretic point of view that maybe 150W are possible, but then I haven't researched again how they measured -- longer time ago I read the post from modushop but I forgot the details. They are very open about the measurements.).
Could I end somewhere near a sweet spot when I have a heat budget of 120W? Or, if I wanted the maximum fidelity from a SIT follower, have I convince my wife first of the several benefits of mono amplifiers and then build it?
Thank you very much, for everything! I'm eager to listen to a SIT follower!
I had this question some time on my mind, but as G's question has shoot in the same direction, I'll ask it now.
Forgive me if you had mentioned it in this quite long thread, I've read a lot, but not all in a highly concentrated fashion.
Have you tested different bias points, so let's say maybe from in the 40s upto 70 volts at different current levels? Why have you settled on 65V and 2,5A? I'm asking because of two reasons: most capacitors are rated upto 63V and then 100V or eighty -something. And of cause I have some nice 63V coke bottles waiting for a project. The other one, more important is, that the big 500mm deep and 5U high Modushop case it referring to good soul ZenMod only capable of 120W (and this is for warm days also, as I understood, to have some safety barrier against the magic smoke). (See post #369). Data from Modushop present it a bit different (if you measure different, you get different numbers. I would say from a noob-theoretic point of view that maybe 150W are possible, but then I haven't researched again how they measured -- longer time ago I read the post from modushop but I forgot the details. They are very open about the measurements.).
Could I end somewhere near a sweet spot when I have a heat budget of 120W? Or, if I wanted the maximum fidelity from a SIT follower, have I convince my wife first of the several benefits of mono amplifiers and then build it?
Thank you very much, for everything! I'm eager to listen to a SIT follower!
Could you please post the link to his post? Then I could test mine as well. Thanks!
To answer the question of choice of power supply voltage, my amplifier started life as a version of Nelson's BAF2015 SE 50W amplifier. This was a common source amplifier with a power supply voltage of 60VDC. When buying the power transformer, I had the choice of 45VAC or 50VAC secondaries from Antek Transformers. I figured 45VAC would not get me 60VDC so I chose 50VAC which I expected to get me a bit more than 60VDC. To be on the safe side with the power supply capacitors, I went with 80V as 63V capacitors would be borderline.
As for operating point for the THF-51S mu follower follower, there is no reason not to try a lower voltage if you want lower dissipation and cost (and lower power output). 63VDC capacitors should be safe with a 45VAC transformer secondary. The final power supply voltage will be somewhere around 58V plus or minus a couple of volts, assuming Antek transformers. Then try current somewhere between 2A and 2.5A, and make a choice based on heat and FFT distortion measurements. Or even try lower current. These days, all you need is a computer with free software such as REW or Arta, a USB soundcard, and some resistors and cables and you can measure the amplifier's distortion while playing around with operating points. It's DIY. And it is part of the fun and adventure to experiment. You can then say the design is your own! 🙂
As for operating point for the THF-51S mu follower follower, there is no reason not to try a lower voltage if you want lower dissipation and cost (and lower power output). 63VDC capacitors should be safe with a 45VAC transformer secondary. The final power supply voltage will be somewhere around 58V plus or minus a couple of volts, assuming Antek transformers. Then try current somewhere between 2A and 2.5A, and make a choice based on heat and FFT distortion measurements. Or even try lower current. These days, all you need is a computer with free software such as REW or Arta, a USB soundcard, and some resistors and cables and you can measure the amplifier's distortion while playing around with operating points. It's DIY. And it is part of the fun and adventure to experiment. You can then say the design is your own! 🙂
Thank you so much, Ben!
So, you made all the adjustments with your 50VAC Antec which you already had.
Did you try different bias points? I read that you once had 3A, now 2,5A, and I remember that you have very efficient speakers, so that you most of the time use 1W or less. If so, I would be very happy if you could share your findings!
At the moment I have 90dB/W efficient speakers, and the next will be more efficient, and most likely the speaker only has to drive mids and highs, so I won't need lot's of power, too. But, as I'm lazy I want to start with something most promising, and that is the chassis. For sure 65V or 60..62V are not so different, but the bias will play a bigger difference concerning a nice distortion profile.
Most likely I will do 3 things:
1. Look in other places of the forum if somebody has chosen different operating points
2. Talk to my government and prepare her for monoblocks.This would break the limit of 120-135W/channel. Or tocompletely build my own chassis. I By the way fischerelektronik.de has a heat sink 500 or 600m wide with 83mm fins, so this should be enough. My poor back!
3. Go with a voltage slightly lower that 63V and play with my Arta configuration. And I wanted to use REW anyway, so I got this excuse hereby.
3.5 I just came smiling back, as I checked my lab power supply: It has 2 channels of 32V with upto 3A. So I could do tests with upto 3A and 64V! Maybe this is the way to go. A fan will be my friend. Then I know what I like and "need".
Thank you Ben!
So, you made all the adjustments with your 50VAC Antec which you already had.
Did you try different bias points? I read that you once had 3A, now 2,5A, and I remember that you have very efficient speakers, so that you most of the time use 1W or less. If so, I would be very happy if you could share your findings!
At the moment I have 90dB/W efficient speakers, and the next will be more efficient, and most likely the speaker only has to drive mids and highs, so I won't need lot's of power, too. But, as I'm lazy I want to start with something most promising, and that is the chassis. For sure 65V or 60..62V are not so different, but the bias will play a bigger difference concerning a nice distortion profile.
Most likely I will do 3 things:
1. Look in other places of the forum if somebody has chosen different operating points
2. Talk to my government and prepare her for monoblocks.This would break the limit of 120-135W/channel. Or tocompletely build my own chassis. I By the way fischerelektronik.de has a heat sink 500 or 600m wide with 83mm fins, so this should be enough. My poor back!
3. Go with a voltage slightly lower that 63V and play with my Arta configuration. And I wanted to use REW anyway, so I got this excuse hereby.
3.5 I just came smiling back, as I checked my lab power supply: It has 2 channels of 32V with upto 3A. So I could do tests with upto 3A and 64V! Maybe this is the way to go. A fan will be my friend. Then I know what I like and "need".
Thank you Ben!
IMHO,
The bias sets the power output and as you can see if you are at 4 ohms you need more current before you clip. The big variable is the Voltage across the SIT V-DS, the higher, in the 35 volte range and you reduce the distortion and as you drop the voltage the distortion goes up.
You can see a lot of this in these graphs. The Bias is at 2.5 amps. It's all a balancing act between power dissipation, bias, and voltage levels. See MR for a nice load line tutorial at Youtube PassDIY. hope this helps 🙂
The bias sets the power output and as you can see if you are at 4 ohms you need more current before you clip. The big variable is the Voltage across the SIT V-DS, the higher, in the 35 volte range and you reduce the distortion and as you drop the voltage the distortion goes up.
You can see a lot of this in these graphs. The Bias is at 2.5 amps. It's all a balancing act between power dissipation, bias, and voltage levels. See MR for a nice load line tutorial at Youtube PassDIY. hope this helps 🙂
Murdoc, I went from 3.0A to 2.5A to save a bit of electricity. The distortion did go up a bit but since I don't need a lot of power, the distortion was still low enough for me.
3.0A and 2.5A with the same power supply were the only values that I tried. Distortion measurements are in this thread. When comparing the measurements, note that the latest set at 2.5A were done with the DIY FE 2022 preamp doing voltage gain. These measurements should not be compared to my older measurements where my 2SK79 preamp was providing voltage gain, as the 2SK79 preamp has much higher distortion. However the measurements with the 2SK79 preamp were at 3.0A and 2.5A, so the effect of the change in current may be seen.
Since you have a lab power supply, you can play with the operating points and decide what is best for you.
3.0A and 2.5A with the same power supply were the only values that I tried. Distortion measurements are in this thread. When comparing the measurements, note that the latest set at 2.5A were done with the DIY FE 2022 preamp doing voltage gain. These measurements should not be compared to my older measurements where my 2SK79 preamp was providing voltage gain, as the 2SK79 preamp has much higher distortion. However the measurements with the 2SK79 preamp were at 3.0A and 2.5A, so the effect of the change in current may be seen.
Since you have a lab power supply, you can play with the operating points and decide what is best for you.
Thank you very much Botte!
This helps me with the decision!
At how much current did you measure?
Have you compared e.g. to stay at 30V and rise the current? (I understand that then the 4Ohm measurement gets better and the 8Ohm worse).
This place is so great to have all this knowledge arround!
This helps me with the decision!
At how much current did you measure?
Have you compared e.g. to stay at 30V and rise the current? (I understand that then the 4Ohm measurement gets better and the 8Ohm worse).
This place is so great to have all this knowledge arround!
Ben, in the meantime I found both of your postings concerning the distortion. Thank you!
And yes, to play with the lab supply will take the guesswork out of the equation.
And yes, to play with the lab supply will take the guesswork out of the equation.
@Zen Mod
Thanks for sharing the updates. I have only read the first half of the SissySIT thread were a lot of discussion was around finding the right parts, so I am glad you corrected me.
Your SIT test curcuit helped a lot to validate the used parts were not broken, even if it was not needed for the curcuit.
G
Thanks for sharing the updates. I have only read the first half of the SissySIT thread were a lot of discussion was around finding the right parts, so I am glad you corrected me.
Your SIT test curcuit helped a lot to validate the used parts were not broken, even if it was not needed for the curcuit.
G
Ben,
I wondering if I could trouble you to help with some trouble shooting on this circuit.
At step #4 of power up I have the MOSFET attached and an 8R load to the S-D of the SIT position (no SIT attached). With the DBT in place I power up and get ~1.4A throught the 8R, however when I take the DBT tester out the current spikes to 5.5A (I'm uncertain of the exact value as I cut the power very quickly), well beyoud expectations. I replaced the 8R with a 200R and with the DBT in place I get ~0.3A and when the DBT is removed ~0.33A. I have the MOSFET attached to the heatsink, and have not felt any heat coming from it, but I didn't keep any of this test running for very long.
I measured the MOSFET voltage compared to ground and all G/S/D were at rail voltages. I took the MOSFET out of circuit and of course no current flowed and G=-19V, S=0V, D=rail, again all with reference to ground.
I'm using the IXTN90P20P, DS attached.
Any suggestions for my next steps?
One more quick test I did after writing this:
16R accross the SIT S-D and with the DBT in place ~1.2 A and removing the DBT about 3A, again I didn't keep it running for long.
Thanks in advance for any advise to help me move forward.
G
I wondering if I could trouble you to help with some trouble shooting on this circuit.
At step #4 of power up I have the MOSFET attached and an 8R load to the S-D of the SIT position (no SIT attached). With the DBT in place I power up and get ~1.4A throught the 8R, however when I take the DBT tester out the current spikes to 5.5A (I'm uncertain of the exact value as I cut the power very quickly), well beyoud expectations. I replaced the 8R with a 200R and with the DBT in place I get ~0.3A and when the DBT is removed ~0.33A. I have the MOSFET attached to the heatsink, and have not felt any heat coming from it, but I didn't keep any of this test running for very long.
I measured the MOSFET voltage compared to ground and all G/S/D were at rail voltages. I took the MOSFET out of circuit and of course no current flowed and G=-19V, S=0V, D=rail, again all with reference to ground.
I'm using the IXTN90P20P, DS attached.
Any suggestions for my next steps?
One more quick test I did after writing this:
16R accross the SIT S-D and with the DBT in place ~1.2 A and removing the DBT about 3A, again I didn't keep it running for long.
Thanks in advance for any advise to help me move forward.
G
First check the 10k trimmer and make sure that it is set to maximum resistance. If it is installed as I have shown it should be at maximum counterclockwise. That should set current to minimum. Then clockwise rotation should increase the current.
Then with DBT and 8R in place, is the current lower than before? Just to be sure you can adjust the trimmer and observe if the current increases.
Then with DBT and 8R in place, is the current lower than before? Just to be sure you can adjust the trimmer and observe if the current increases.
Ben,
Thanks for the reply.
Yes trimmer was set to max resistance.
With the DBT in place and 8R I see no difference in current from 1 end of the pot to the other...
G
Thanks for the reply.
Yes trimmer was set to max resistance.
With the DBT in place and 8R I see no difference in current from 1 end of the pot to the other...
G
Could it be a bad MOSFET? both of my part act the same but I bought them used so they could be questionable...
Any good way to check them with basic tools or circuit?
G
Any good way to check them with basic tools or circuit?
G