Certainly. But the more important question is: do you have speakers that can make use of such an amp?
I don't understand how this is a reply that means anything to the person who asked the question. What is it about speakers that in your mind make them able to "make use of" this amp? Impedance, sensitivity?
Good morning, gentlemen. I will ask my question again.
Is it possible to build this amplifier with THF-51S?
If yes, same idle current (2.3 A to 2.5 A) and 35 Vds?
By thanking you in advance.
Is it possible to build this amplifier with THF-51S?
If yes, same idle current (2.3 A to 2.5 A) and 35 Vds?
By thanking you in advance.
Yes, it is possible. That operating point is one that does work for the THF-51S. There are variations among the THF-51S, so you may have to adjust a bit. I have amps where I run at 38V and 2.1A.
everything pretty much the same with THF51
finding sweet spot for your taste is strictly optional
finding sweet spot for your taste is strictly optional
I tried this circuit about 6 months ago with THF51-S but with 25VAC transformer. Never was able to get a stable bias. Maybe the higher voltage (30VAC) is the key or maybe I didn't have the patience 😱
Best
Bob
Best
Bob
Sensitivity is not as important as a controlled impedance. The vast majority of ordinary speakers are extremely unhappy when driven from a 5-7 ohm source.
Some Bad News, and Some Good News To Follow
I did not experience instability when I tested the amplifier section with my lab power supply, and no instability when I first had the amplifiers running with their own power supplies. That was in December when the weather was cold and the ambient temperature was lower.
However lately the amplifiers have not been stable. The current has been wandering upwards, especially when the line AC drifts up to 121V or so from a low of 117 to 118V. It would wander up and up with no sign of stopping.
I tried adding source resistors, starting at 0.1R and increasing in 0.1R increments until the right channel stabilized with 0.4R and the left channel at 0.6R. Interestingly, the right channel's Vgs before the addition of source resistors was lower then the left channel's Vgs.
The plus with the addition of the source resistors was lower harmonic distortion but a negative was the lowering of the power output. I measured the maximum output of the left channel at 15W.
Since testing with the regulated lab supply gave stable results, I put together a simple regulation stage with a low dropout LT1084 regulator and installed it between the power supply and the 193V, and removed the source resistors. Unfortunately, that did not stabilize the current. Yet during testing with the regulated lab supply, the amplifier stage was stable. The lab supply has a current regulator but I did not recall it being activated. So perhaps the 2SK180 changed a bit after burn-in?
So in frustration, I pulled the 2SK180 and put in a recently purchased THF-51S. No problem with the THF-51S at all. The current was stable, with only small fluctuations that followed th AC line voltage.
So at this point I would say that the THF-51S is preferred SIT to use in this implementation. So it should be "25W Single Ended Hammond 193V Choke Loaded THF-51S L'Amp".
So that is the bad news for the 2SK180 (but good news for the THF-51S).
Now for the good news for the 2SK180. I still wanted to make use of the 2SK180 in some way. I decided to put the 2SK180 back into the amplifier but use it in a different implementation. I wired it up as a follower, putting the 193V after the 2SK180 and taking the speaker out from between the 1SK180 and 193V, and it was stable. Being a follower, it has no voltage gain so it needs a preamp with enough voltage output or a voltage gain stage in front of the 2SLK180 output stage. The harmonic distortion is also significantly lower as a follower.
In my system my Luminaria preamp has about 17dB of gain (50X). It is nearly but not quite enough since my digital source, a TDA1541A dac with only a 60R I/V resistor and no voltage gain stage, has an output voltage of about 0.1V. So I inserted my ACP+ headphone amp/preamp in between the DAC and Luminaria and that provided enough voltage.
I have some Russian 2KP296 on the way from Eastern Europe and I will do a voltage gain stage for the amp. It will be SIT voltage gain with SIT current gain.
I have listened to this for several hours now and I really like the sound. The 2SK180 follower amp seems to have a clarity that the 2SK180/THF-51S 193V L'Amp and my BAF2015 THF-51S amp do not have. It is a subtle but noticeable difference. Due to the follower's lower harmonic distortion? More listening to do and distortion measurements to come.
So my experience:
-2SK180 needs source resistor if implemented as common source amplifier (voltage and current gain).
-THF-51S (drop-in replacement for 2SK180) is stable as common source amplifier.
-2SK180 and Hammond 193V as common drain amplifier (follower with only current gain) is stable and seems to have an edge in sound. Appropriate source/preamp with high voltage output required.
So far I really like the sound of the 2SK180 as a follower.
I did not experience instability when I tested the amplifier section with my lab power supply, and no instability when I first had the amplifiers running with their own power supplies. That was in December when the weather was cold and the ambient temperature was lower.
However lately the amplifiers have not been stable. The current has been wandering upwards, especially when the line AC drifts up to 121V or so from a low of 117 to 118V. It would wander up and up with no sign of stopping.
I tried adding source resistors, starting at 0.1R and increasing in 0.1R increments until the right channel stabilized with 0.4R and the left channel at 0.6R. Interestingly, the right channel's Vgs before the addition of source resistors was lower then the left channel's Vgs.
The plus with the addition of the source resistors was lower harmonic distortion but a negative was the lowering of the power output. I measured the maximum output of the left channel at 15W.
Since testing with the regulated lab supply gave stable results, I put together a simple regulation stage with a low dropout LT1084 regulator and installed it between the power supply and the 193V, and removed the source resistors. Unfortunately, that did not stabilize the current. Yet during testing with the regulated lab supply, the amplifier stage was stable. The lab supply has a current regulator but I did not recall it being activated. So perhaps the 2SK180 changed a bit after burn-in?
So in frustration, I pulled the 2SK180 and put in a recently purchased THF-51S. No problem with the THF-51S at all. The current was stable, with only small fluctuations that followed th AC line voltage.
So at this point I would say that the THF-51S is preferred SIT to use in this implementation. So it should be "25W Single Ended Hammond 193V Choke Loaded THF-51S L'Amp".
So that is the bad news for the 2SK180 (but good news for the THF-51S).
Now for the good news for the 2SK180. I still wanted to make use of the 2SK180 in some way. I decided to put the 2SK180 back into the amplifier but use it in a different implementation. I wired it up as a follower, putting the 193V after the 2SK180 and taking the speaker out from between the 1SK180 and 193V, and it was stable. Being a follower, it has no voltage gain so it needs a preamp with enough voltage output or a voltage gain stage in front of the 2SLK180 output stage. The harmonic distortion is also significantly lower as a follower.
In my system my Luminaria preamp has about 17dB of gain (50X). It is nearly but not quite enough since my digital source, a TDA1541A dac with only a 60R I/V resistor and no voltage gain stage, has an output voltage of about 0.1V. So I inserted my ACP+ headphone amp/preamp in between the DAC and Luminaria and that provided enough voltage.
I have some Russian 2KP296 on the way from Eastern Europe and I will do a voltage gain stage for the amp. It will be SIT voltage gain with SIT current gain.
I have listened to this for several hours now and I really like the sound. The 2SK180 follower amp seems to have a clarity that the 2SK180/THF-51S 193V L'Amp and my BAF2015 THF-51S amp do not have. It is a subtle but noticeable difference. Due to the follower's lower harmonic distortion? More listening to do and distortion measurements to come.
So my experience:
-2SK180 needs source resistor if implemented as common source amplifier (voltage and current gain).
-THF-51S (drop-in replacement for 2SK180) is stable as common source amplifier.
-2SK180 and Hammond 193V as common drain amplifier (follower with only current gain) is stable and seems to have an edge in sound. Appropriate source/preamp with high voltage output required.
So far I really like the sound of the 2SK180 as a follower.
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Interesting results! I may add that my SK82 build with the Hammond had no bias stability problems ten years ago.
And yes I had the THF51 as well in common drain and common source configuration with a chain of 9 x 5 Ohm resistors and high voltage around 90V and the sound of the common drain version had this touch of more clarity you described. (three years ago)
:--))
And yes I had the THF51 as well in common drain and common source configuration with a chain of 9 x 5 Ohm resistors and high voltage around 90V and the sound of the common drain version had this touch of more clarity you described. (three years ago)
:--))
The Hammond 193V came from my 2SJ28 193V L'Amp and it had no stability problems either. However not so with the 2SK180.
I find it interesting that the THS51 does not go into thermal runaway. It is, after all, the obvious thing to do. Perhaps the cooling is very efficient and keeps the temperature low.
Interesting too, but not unexpected, that the follower sounds better. Minimalism looks cool but seldom sounds good.
Interesting too, but not unexpected, that the follower sounds better. Minimalism looks cool but seldom sounds good.
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The sound differences with these simple SIT amps using neg or ps phase of H2 were big.
I checked it with Diana.
I checked it with Diana.
As I told 45R and 90V, the 45R were combined out of 9 x5R TO247 resistors on the heatsink.The 45R either in the drain or source line. Voltage at the drain around 15V. Of course a 10000uF output cap.
Monoblocks.
Monoblocks.
