Hah - that is the $64,000 question! 🙂
Yes, my new bias current is ~2.5a, I think, Nikos.
As I use a 20mm diam washer on top of the mosfets ... it is hard to measure the temperature of the body. So I point my laser temp gun at the head of the bolt which clamps the mosfet to the heatsink.
What are your measurements even with the laser on the body of the mosfet but also on the heatsinks?
The IR temp gun will not give an accurate reading aiming at shiny metal objects like washers and hardware. Apply kapton tape to the washer for better accuracy.
Be aware that ir sensor and laser pointer originate in two different spots...meeting at a distance. In close proximity, they do not coincide yet. Just my personal observation with my handheld device.
During the beautiful journey of building this particular amplifier for me, I tried to place the mosfets in a common heatsink 41cm x16 x 5 , the ambient temp now in my room in Greece is 29-31 C we always talk about version 4R and I know it's forbidden. The temperature that develops in the body of the mosfet scared me quite a bit. Since I have nothing else hahahah. Τhe transistors of the power supply must not be placed together with the mosfets outputs. I have mentioned this in my previous post...I said NO WAY.....
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Then I'm fine...I measure on the metal surface of the mosfet about 50C and on the housing on the mosfet about 45 degrees Celsius. This with the second stage setup 40-55C of the controller pwm fan where the fans play much more relaxed and are not heard at a distance of half a meter .
Thanks Mr Hugh.
Thanks Mr Hugh.
Attachments
Hi, I found this information about the "Sonus Faber Olympica Nova III" speakers. Maybe it can help @rdb64
Regards
https://www.hifi-voice.com/testy-a-...-podlahove/2332-sonus-faber-olympica-nova-iii
Regards
https://www.hifi-voice.com/testy-a-...-podlahove/2332-sonus-faber-olympica-nova-iii
Wow, thank you so much @karucho. This is somewhat new territory for me, so based on this impedance curve, if anyone has advice on whether I should build 4R or 8R, I sure would appreciate it.
@rdb64
Looking at the region from 50Hz to 5khz, much of it is in the 4-6 ohm range. Usually if it’s a true 8 ohm speaker, I usually don’t see much of the range below 80% of 8 ohms or to be accurate, not less than 6.4 ohms. We can round down to 6 ohms to make it simple. Your Sonus Faber’s have several large ranges where it is comfortably below 6 ohms and even at around 5 ohms from 10khz to 20khz (where there is comparatively little music). As such, I would choose a 4 ohm version of the AN39.
Keep in mind there is still a lot of musical information particularly midbass, between 50Hz and 200Hz and you are solidly in a 5 ohm region there.
And finally, your phase angles are fine for the most part although at 40Hz, you do have -36 degrees and 4 ohm, which will demand current from your amplifier.
Best,
Anand.
Looking at the region from 50Hz to 5khz, much of it is in the 4-6 ohm range. Usually if it’s a true 8 ohm speaker, I usually don’t see much of the range below 80% of 8 ohms or to be accurate, not less than 6.4 ohms. We can round down to 6 ohms to make it simple. Your Sonus Faber’s have several large ranges where it is comfortably below 6 ohms and even at around 5 ohms from 10khz to 20khz (where there is comparatively little music). As such, I would choose a 4 ohm version of the AN39.
Keep in mind there is still a lot of musical information particularly midbass, between 50Hz and 200Hz and you are solidly in a 5 ohm region there.
And finally, your phase angles are fine for the most part although at 40Hz, you do have -36 degrees and 4 ohm, which will demand current from your amplifier.
Best,
Anand.
Great analysis, Anand! 👍
Totally agree with your conclusions. (And the TAS review I found put them as 4ohm spkrs!)
The only thing I would worry about ... is the power available from the AN. I suspect these SFs need more than 40w to make them sound their best.
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Michael,
There is a huge, contentious paradigm in the belief of measured distortion with audio systems.
The purists, often very well-educated engineers and scientists, are quite sure that THD, the root mean square addition of all the harmonic distortions, should be zero, or, to be reasonable, say no more than 0.002%. The ASR Forum publish many such figures and argue cogently that zero distortion is a wonderful achievement and should be striven for in all cases of sound amplification, including the speaker drivers.
The subjectivists, a colourful lot wherein I throw my hat, are a little more blase about it. They say distortion is OK as long as certain harmonics are NOT included in the THD level. This means we need to examine the harmonic spread before we make a judgment. This is how it gets difficult however.
As an aside, there are problematic amps (let's talk only of amps at present) which sound glorious but have HUGE THD; tube amps. A typical single ended tube amp, say a 300B with a three tube line up of 6SL7 - 6SN7 - 300B, output around 8W into 8R with a 3.5k:8R OPT, measures up to 3% at 6W. This is outrageous and based on the principles of zero THD this should sound dreadful. But it doesn't, or at least in my view. I think the sound is quite entrancing. Admittedly it's a 'sound effect', no question, but then why do some musicians only ever use Marshall, or Vox, or Fender? All three guitar amps use TUBES, and all sound different.
What is going on? It turns out that if you design an amp for a particularly harmonic profile, it will sound 'different'. Not better, no worse, but different. I have found that Class A amplifiers using a single ended topology, like the 300B amp I referred to above, create a dominant second harmonic (H2), with a linear decreasing harmonic of higher end, so HIGH levels to LOW levels are H2, H3, H4, H5, H6, H7, H8 and so on. With most tube amps, and particularly of zero global feedback designs, there are very few harmonics beyond H4, typically below -100dB.
The idea of designing amplifiers for distortion is a hundred years old, because that is what tube designs do with every design they create. There are some tubes which in conventional topologies sound wonderful; examples are 6SL7, 6SN7, 300B, 2A3, 1626, 845, 211, EL84, 6V6, and hundreds of others. The distortion of triode in plate load is horrendous; typically H2 at -42dB, H3 at -90dB and H4 and beyond beyond -100dB. This confers warmth, but with lots of H2 you can take away some of the resolution, nothing like as sharp as a good SS amp.
On the Alpha Nirvana 39 H2 at listening levels starts at about -80dB. This is trivial compared to a tube amp, yet, the profile is monotonically decreasing, and I think this is the key to the good sound
Let us open the thread to diametrical viewpoints; all have a place in the sun.
Cheers,
Hugh
There is a huge, contentious paradigm in the belief of measured distortion with audio systems.
The purists, often very well-educated engineers and scientists, are quite sure that THD, the root mean square addition of all the harmonic distortions, should be zero, or, to be reasonable, say no more than 0.002%. The ASR Forum publish many such figures and argue cogently that zero distortion is a wonderful achievement and should be striven for in all cases of sound amplification, including the speaker drivers.
The subjectivists, a colourful lot wherein I throw my hat, are a little more blase about it. They say distortion is OK as long as certain harmonics are NOT included in the THD level. This means we need to examine the harmonic spread before we make a judgment. This is how it gets difficult however.
As an aside, there are problematic amps (let's talk only of amps at present) which sound glorious but have HUGE THD; tube amps. A typical single ended tube amp, say a 300B with a three tube line up of 6SL7 - 6SN7 - 300B, output around 8W into 8R with a 3.5k:8R OPT, measures up to 3% at 6W. This is outrageous and based on the principles of zero THD this should sound dreadful. But it doesn't, or at least in my view. I think the sound is quite entrancing. Admittedly it's a 'sound effect', no question, but then why do some musicians only ever use Marshall, or Vox, or Fender? All three guitar amps use TUBES, and all sound different.
What is going on? It turns out that if you design an amp for a particularly harmonic profile, it will sound 'different'. Not better, no worse, but different. I have found that Class A amplifiers using a single ended topology, like the 300B amp I referred to above, create a dominant second harmonic (H2), with a linear decreasing harmonic of higher end, so HIGH levels to LOW levels are H2, H3, H4, H5, H6, H7, H8 and so on. With most tube amps, and particularly of zero global feedback designs, there are very few harmonics beyond H4, typically below -100dB.
The idea of designing amplifiers for distortion is a hundred years old, because that is what tube designs do with every design they create. There are some tubes which in conventional topologies sound wonderful; examples are 6SL7, 6SN7, 300B, 2A3, 1626, 845, 211, EL84, 6V6, and hundreds of others. The distortion of triode in plate load is horrendous; typically H2 at -42dB, H3 at -90dB and H4 and beyond beyond -100dB. This confers warmth, but with lots of H2 you can take away some of the resolution, nothing like as sharp as a good SS amp.
On the Alpha Nirvana 39 H2 at listening levels starts at about -80dB. This is trivial compared to a tube amp, yet, the profile is monotonically decreasing, and I think this is the key to the good sound
Let us open the thread to diametrical viewpoints; all have a place in the sun.
Cheers,
Hugh
Hugh i believe theres more to it than distortion.there is a continuos_ ness with se that alows the music to be absorbed and allows one to engage in music eithout resistance to what one is hearing. Thanks for a great amp.
But Michael ... the AN circuit is not 'SE' (which stands for 'single ended'). It has +/- DC rails - not a single +DC rail?
Andy,
It looks push pull but because ALL the signal is processed by only the upper device (NMOS) it can be considered Single Ended. The lower device, PMOS, supplies only current during the negative halfcycle and has no voltage setting influence over the load. It is an unusual topology, sometimes described as Single Ended Push Pull, SEPP.
The bipolar supplies are not related in fact.
HD
It looks push pull but because ALL the signal is processed by only the upper device (NMOS) it can be considered Single Ended. The lower device, PMOS, supplies only current during the negative halfcycle and has no voltage setting influence over the load. It is an unusual topology, sometimes described as Single Ended Push Pull, SEPP.
The bipolar supplies are not related in fact.
HD
Aah OK ... thanks Hugh. 'SEPP' I can understand! 👍
As Michael said "there is a continuous_ness with SE that allows the music to be absorbed and allows one to engage in the music without any resistance to what one is hearing"! 😵
I agree with Michael. It may relate to the way that the music signal is handled solely with one output device rather than being 'split' to two halfcycles in push pull...
HD
HD