I have a good sized heatsink and it is cooled by a fan - at this point using 38 volts with ra7's TDV. Biased at 2.6 A the heatsinks never get hot, not even close to hot. Nowhere near as hot as the SIT 1s would get which was HOT.
Would higher voltages allow the use of sightly less current - my scheme is to use closer to 55 volts? Even higher if possible. My capacitors are rated 100 volts and higher. I know the current would be greatly reduced just trying to figure out where to begin ... if at all.
Would the output power go up appreciably or would it be negligible?
Wish I could answer this for myself but I have no idea.
Would higher voltages allow the use of sightly less current - my scheme is to use closer to 55 volts? Even higher if possible. My capacitors are rated 100 volts and higher. I know the current would be greatly reduced just trying to figure out where to begin ... if at all.
Would the output power go up appreciably or would it be negligible?
Wish I could answer this for myself but I have no idea.
The question you are asking is “How do I run the THF51 in its sweet spot?”
This is difficult to determine by just looking at the datasheet.
There are reports from others who have built amplifiers with the THF51 that may provide some guidance. In general big parts like this seem to perform better with both higher voltage and bias current. Maybe the fun part of this DIY project will be further experimentation.
This is difficult to determine by just looking at the datasheet.
There are reports from others who have built amplifiers with the THF51 that may provide some guidance. In general big parts like this seem to perform better with both higher voltage and bias current. Maybe the fun part of this DIY project will be further experimentation.
Hi Rick,
If you want to run a higher voltage, you probably would want to run a higher current too. If you run at higher voltage and lower current, you are not making use of the extra voltage as you also need current for power output. For instance, if you run at 60V and 2.6A, the 2.6A will limit the useable power output. With 8 Ohm speaker, 2.6A will give 2.6A x 8R = 20.8Vp, or 41.6Vpp, which is much less than the available voltage supplied by the 60V power supply. So to take advantage of the higher power supply voltage, the Iq should also be increased.
2.6A is probably close to the optimum current for 38V (perhaps slightly high), taking the voltage drop of the choke and source resistor into account.
If you increase the power supply voltage and decrease Iq, you will actually end up with less maximum power output before clipping. If you increase the power supply voltage and keep Iq the same, the maximum power output before clipping will not increase.
I would like to add that this is from a power output perspective. As TungstenAudio pointed out there is also the "sweet spot", which may also take part in determining your preferred operating point. That is where a FFT test rig comes in handy.
If you want to run a higher voltage, you probably would want to run a higher current too. If you run at higher voltage and lower current, you are not making use of the extra voltage as you also need current for power output. For instance, if you run at 60V and 2.6A, the 2.6A will limit the useable power output. With 8 Ohm speaker, 2.6A will give 2.6A x 8R = 20.8Vp, or 41.6Vpp, which is much less than the available voltage supplied by the 60V power supply. So to take advantage of the higher power supply voltage, the Iq should also be increased.
2.6A is probably close to the optimum current for 38V (perhaps slightly high), taking the voltage drop of the choke and source resistor into account.
If you increase the power supply voltage and decrease Iq, you will actually end up with less maximum power output before clipping. If you increase the power supply voltage and keep Iq the same, the maximum power output before clipping will not increase.
I would like to add that this is from a power output perspective. As TungstenAudio pointed out there is also the "sweet spot", which may also take part in determining your preferred operating point. That is where a FFT test rig comes in handy.
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Thanks to you both for your wise counsel.
I am not concerned about the bias - one of my assumptions that it would have to be decreased. I did not want this since I do not really know what to want. Sorry for being a dilletante.
If I am not asking too much, which is usually the case, what do you think is the maximum voltage and current one should attempt? Looking at the data that is available does not give me much guidance as most have stayed in lower voltages, I suspect it is restrained by the heatsink which I am not concerned about.
If one used 80 volts and stayed with the same current could one assume twice as much power?
I know one could use a mosfet in a mu follower but it seems worthwhile to stay with minimal parts and attempt more power. At least to hear what happens.
I am guessing that the resistor after the choke will be larger in value for the same current and I know this will consume some of the output power.
Is there a point where this meets vanishing returns?
I will learn how to take FFT plots.
I am not concerned about the bias - one of my assumptions that it would have to be decreased. I did not want this since I do not really know what to want. Sorry for being a dilletante.
If I am not asking too much, which is usually the case, what do you think is the maximum voltage and current one should attempt? Looking at the data that is available does not give me much guidance as most have stayed in lower voltages, I suspect it is restrained by the heatsink which I am not concerned about.
If one used 80 volts and stayed with the same current could one assume twice as much power?
I know one could use a mosfet in a mu follower but it seems worthwhile to stay with minimal parts and attempt more power. At least to hear what happens.
I am guessing that the resistor after the choke will be larger in value for the same current and I know this will consume some of the output power.
Is there a point where this meets vanishing returns?
I will learn how to take FFT plots.
Rick, please read my earlier post again. Current needs to be increased if you want more power output.
Another thing to look out for is power dissipation. The THF-51S is a 400W device but you probably wouldn't want it to dissipate more than one third of that amount to keep it from burning up.
Another thing to look out for is power dissipation. The THF-51S is a 400W device but you probably wouldn't want it to dissipate more than one third of that amount to keep it from burning up.
FFT plots can provide some useful information, but more along the lines of is the amp basically working as intended or not. Putting the test equipment and software together is not trivial, though there are people here in the forums who can help.
My preferred method is to use my ears. My recommendation would be to keep the bias current about where you have it (2.6A or maybe 2.8A), and increase the voltage until the heatsinks get nice and warm. Then listen, let the amp run in under this setting (leave it on for a day), and listen some more. How does it sound after the adjustment?
My preferred method is to use my ears. My recommendation would be to keep the bias current about where you have it (2.6A or maybe 2.8A), and increase the voltage until the heatsinks get nice and warm. Then listen, let the amp run in under this setting (leave it on for a day), and listen some more. How does it sound after the adjustment?
I did read it more than once, Ben Mah, as I do with most of your posts. It is my lack of understanding that stymies me!
So, just so I can get an idea of the trend, if I raise the current with the 38 volts I have now could this make a appreciable increase in power?
Over the weekend I made a current source to be able to measure the resistor between the choke and THF51. I made a rather stout one for this - 250 mA - using parts laying about. Unlike the fellow on ELEMENT 14 which made one with a lass than bare minimum power supply I made a good supply (CLC - I have the chokes laying about, why not use them?). When he measured the mV across the resistor being tested his meter was jumping up and down - when I make my measurement the meter is static so I figured gilding the wildflowers was worth the trouble.
All of this leads to: If I slowly lower this resistance down to zero (just the resistance of the choke - which I have not measured yet but specified as 0.85R by LUNDAHL) - my resistor bundle is .56R - any reason not to try with no added resistance on this amplifier as a test? Other than overheating if left on too long (I would turn it off immediately if I felt the heat sink getting too warm) OR if stable it doesn't sound too good.
Sorry for this roundabout: what would you surmise the gain in power to be? Since I have no idea what it is now I am asking for a guess of a percentage increase? Would the increase be minor at best or worth giving it a try?
I will see where I am by supplying a sine wave (from REW) to the amp and measuring the voltage across the speaker leads to get an idea of the power? I know I have to use the formula to get an idea of the power. Better still would be to build up a test resistor, of course. All in good time.
Sorry to ask you to speculate but I am grateful AS ALWAYS for your guidance.
So, just so I can get an idea of the trend, if I raise the current with the 38 volts I have now could this make a appreciable increase in power?
Over the weekend I made a current source to be able to measure the resistor between the choke and THF51. I made a rather stout one for this - 250 mA - using parts laying about. Unlike the fellow on ELEMENT 14 which made one with a lass than bare minimum power supply I made a good supply (CLC - I have the chokes laying about, why not use them?). When he measured the mV across the resistor being tested his meter was jumping up and down - when I make my measurement the meter is static so I figured gilding the wildflowers was worth the trouble.
All of this leads to: If I slowly lower this resistance down to zero (just the resistance of the choke - which I have not measured yet but specified as 0.85R by LUNDAHL) - my resistor bundle is .56R - any reason not to try with no added resistance on this amplifier as a test? Other than overheating if left on too long (I would turn it off immediately if I felt the heat sink getting too warm) OR if stable it doesn't sound too good.
Sorry for this roundabout: what would you surmise the gain in power to be? Since I have no idea what it is now I am asking for a guess of a percentage increase? Would the increase be minor at best or worth giving it a try?
I will see where I am by supplying a sine wave (from REW) to the amp and measuring the voltage across the speaker leads to get an idea of the power? I know I have to use the formula to get an idea of the power. Better still would be to build up a test resistor, of course. All in good time.
Sorry to ask you to speculate but I am grateful AS ALWAYS for your guidance.
Yes, if you raise the current and keep the 38V supply, the power will increase. The good thing with choke loading is the ability to raise the current and have the output voltage swing higher. You will however reach a maximum current that is limited by the DCR of the choke, after you have decreased the source resistor to zero Ohm.
The other limit is the safe power dissipation of the THF-51S. That is where you probably cannot raise the power supply voltage a large amount, as raising the power supply voltage and maintaining the same current or decreasing the current will not increase power output. It will change the operating point though and will change the distortion profile in some way.
The other limit is the safe power dissipation of the THF-51S. That is where you probably cannot raise the power supply voltage a large amount, as raising the power supply voltage and maintaining the same current or decreasing the current will not increase power output. It will change the operating point though and will change the distortion profile in some way.
I will change the current across the resistor - which at the moment is 0.55R - and leave the power transformer alone . The idea of higher voltages was motivated by one of them being noisy and I thought - here is a chance to try higher voltages.
I will go lower and lower and hear what happens. Along with keeping a hand on the heatsink. I need to measure the LL2733's resistance - specified as 0.85.
I am measuring across the resistor. Would it be better, after verifying the resistance of the choke, to measure the voltage across both of them? I figure it would not matter.
THANKS very much for your wise counsel, Ben Mah.
I will go lower and lower and hear what happens. Along with keeping a hand on the heatsink. I need to measure the LL2733's resistance - specified as 0.85.
I am measuring across the resistor. Would it be better, after verifying the resistance of the choke, to measure the voltage across both of them? I figure it would not matter.
THANKS very much for your wise counsel, Ben Mah.
If you are changing the resistor value, it would definitely be easier to measure the current using the choke resistance. That would keep the current calculation constant with less chance of error. An alternate would be to insert an 0.1R resistor in the power supply line for current measurement. Then current is 10X voltage - easy to see and comprehend at a glance.
I have attached the original brochure for the Tokin SITs in case you don't have it.
THF-51S is rated at 600V, 30A, 50 MHz and 400 watts.
2SK182 is slower at 10 MHz, but rated at 800V, 60A, 500 watts.
The harmonic character is a function of Vds and Ids and you can pretty much adjust
one vs the other to get what you want over a fairly broad range. In most of the
projects we might consider its capability will exceed the surrounding hardware.
THF-51S is rated at 600V, 30A, 50 MHz and 400 watts.
2SK182 is slower at 10 MHz, but rated at 800V, 60A, 500 watts.
The harmonic character is a function of Vds and Ids and you can pretty much adjust
one vs the other to get what you want over a fairly broad range. In most of the
projects we might consider its capability will exceed the surrounding hardware.
Thanks, Mr. Pass.
All I had seen was the page you included in one of your articles. Seeing the whole thing is amusing - to know these precious devices would make for one helluva dishwasher and other mundane things that make modern life so good even though we rarely express that sentiment! Thanks.
Would you care to speculate on where the goodness likely ends with Vds and Ids - is there a point where there is too much current - of course, not the point where the device is destroyed but the excellent sonics begin to diminish?
Good morning, Ben Mah,
Thanks for those suggestions. You are a wealth of good ideas. I will measure the choke's DCR this weekend. I had no idea one could do that. I can see the simple logic of it now that you have told me but unfortunately I can only see these things after they are pointed out to me. Just like with my ears and audio gear. I cannot hear the problems but I can hear the improvements.
My thanks to you both for this and a multitude of previous advices given! Of course, Mr. Pass resides in a special place in the Pantheon of audio. How many others who live in that rarefied space are as welcoming to others to get a glance of the inner sanctum of musical pleasure?
All I had seen was the page you included in one of your articles. Seeing the whole thing is amusing - to know these precious devices would make for one helluva dishwasher and other mundane things that make modern life so good even though we rarely express that sentiment! Thanks.
Would you care to speculate on where the goodness likely ends with Vds and Ids - is there a point where there is too much current - of course, not the point where the device is destroyed but the excellent sonics begin to diminish?
Good morning, Ben Mah,
Thanks for those suggestions. You are a wealth of good ideas. I will measure the choke's DCR this weekend. I had no idea one could do that. I can see the simple logic of it now that you have told me but unfortunately I can only see these things after they are pointed out to me. Just like with my ears and audio gear. I cannot hear the problems but I can hear the improvements.
My thanks to you both for this and a multitude of previous advices given! Of course, Mr. Pass resides in a special place in the Pantheon of audio. How many others who live in that rarefied space are as welcoming to others to get a glance of the inner sanctum of musical pleasure?
The goodness thing is quite subjective. You can pick voltage and bias for lowest distortion with little
or no 2nd harmonic, or for an arbitrary value and phase of 2nd, or maximum output power or minimum
dissipation. Any kind of distortion analyzer, even a crappy one, will be your friend in this.
or no 2nd harmonic, or for an arbitrary value and phase of 2nd, or maximum output power or minimum
dissipation. Any kind of distortion analyzer, even a crappy one, will be your friend in this.
Yea, thats how i have been thinking when planning my current THF-51S and 2SK182ES builds.
And. Right or wrong, my thinking is that more voltage and bias availability is more and better when it comes to tuning those Tokins and my sound system, but what sets the final limit for those builds in my case is simply how much heat i would like to add to the listening room.
🔥🎺🙂🎸🔥
I made pair of transformer coupled mono amps a while ago using the 2SK182ES with a 60V power supply. I ended up with a Vd of 51 volts with current of 1.46 amps. This is a power dissipation of almost 75 watts and heat dissipation was not a problem. I used small heatsinks with fan cooling and the heatsinks were only warm to touch. If you use passive cooling, the heatsinks would be quite large and the case would be much larger as well.
The main thing is the power supply becomes bigger. The power transformer and the filter capacitors are much bigger and more expensive. In the end, the amps would end up big and heavy. Even with fan cooling, I ended up with a separate case containing the power supplies and separate chassis for each channel.
The main thing is the power supply becomes bigger. The power transformer and the filter capacitors are much bigger and more expensive. In the end, the amps would end up big and heavy. Even with fan cooling, I ended up with a separate case containing the power supplies and separate chassis for each channel.