That will be pretty simple then. You could even keep the same MOSFETs in the same threaded holes as the AN uses the amazing quick release Molex connectors and flying leads for the MOSFETs.
I have pulled the AN out of an amp, did a quick solder mod on the board and returned it to the chassis in 5min. Talk about user friendly.
All Aksa/JPS64/jhofland/XRK amps will use this format going forward. We might as well just leave the N and P Chan MOSFETs attached and just swap boards.
I have pulled the AN out of an amp, did a quick solder mod on the board and returned it to the chassis in 5min. Talk about user friendly.
All Aksa/JPS64/jhofland/XRK amps will use this format going forward. We might as well just leave the N and P Chan MOSFETs attached and just swap boards.
Hi Danny,
For us to get a better idea of the drive requirements of your speakers, can you please share an impedance vs frequency plot? Either simulated from XO designer program or from measurement with a DATS etc is fine. I know it is “4ohms” but some 4ohm speakers dip to 2ohms and have peaks as high as 250ohms. A wide range.
Cheers,
X
Still the current XO schematic?
For us to get a better idea of the drive requirements of your speakers, can you please share an impedance vs frequency plot? Either simulated from XO designer program or from measurement with a DATS etc is fine. I know it is “4ohms” but some 4ohm speakers dip to 2ohms and have peaks as high as 250ohms. A wide range.
Cheers,
X
Still the current XO schematic?
Hi X,
The crossover has changed a little for version 2.
Here are some measurements.
I already made plenty of impedance measurements during development, the last for tuning the vent to 24Hz.
When designing the crossover I made attention to keep the impedance as high as possible,
not that easy because there are 3 drivers (two woofers and a mid) playing together in the 100-400Hz xo region and all three are trying to push the impedance down.
In the impedance plot you see the minimum at 3.3ohm, the purple line is the phase plot.
Besides amplifier friendly impedance, you also want a nice frequency response on and off axis, a smooth phase and good sound, balanced with all kind of music.
The frequency response is made in-room between mid and tweeter at 1m20 distance, no smoothing but windowed,
don't pay too much attention to the measurements below 500Hz, that's where the dragons live, those that create roommodes
For below 500Hz in-room measurements it's better to use RTA, on RTA the FR is smooth and hits the mid 20s.
But back to the Alpha,
the question for 4R or 8R amplifier is not so obvious,
I think it also depends a lot on the sensitivity of the speaker.
How much voltage you need can be easily be checked by playing some sine and putting an oscilloscope or DMM on the speaker outputs.
My 4R speakers(93db) go very loud with 4vpp but with 8R 82db speakers you need already 48vpp for the same level of output on the speakers.
So which load is the easiest for an amplifier like the Nirvana 8R: 4R at 4vpp or 8R at 48vpp ?
Regards,
Danny
The crossover has changed a little for version 2.
Here are some measurements.
I already made plenty of impedance measurements during development, the last for tuning the vent to 24Hz.
When designing the crossover I made attention to keep the impedance as high as possible,
not that easy because there are 3 drivers (two woofers and a mid) playing together in the 100-400Hz xo region and all three are trying to push the impedance down.
In the impedance plot you see the minimum at 3.3ohm, the purple line is the phase plot.
Besides amplifier friendly impedance, you also want a nice frequency response on and off axis, a smooth phase and good sound, balanced with all kind of music.
The frequency response is made in-room between mid and tweeter at 1m20 distance, no smoothing but windowed,
don't pay too much attention to the measurements below 500Hz, that's where the dragons live, those that create roommodes
For below 500Hz in-room measurements it's better to use RTA, on RTA the FR is smooth and hits the mid 20s.
But back to the Alpha,
the question for 4R or 8R amplifier is not so obvious,
I think it also depends a lot on the sensitivity of the speaker.
How much voltage you need can be easily be checked by playing some sine and putting an oscilloscope or DMM on the speaker outputs.
My 4R speakers(93db) go very loud with 4vpp but with 8R 82db speakers you need already 48vpp for the same level of output on the speakers.
So which load is the easiest for an amplifier like the Nirvana 8R: 4R at 4vpp or 8R at 48vpp ?
Regards,
Danny
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Danny,
It really depends on how much current you pass to your speakers. If they are efficient, then maybe 3-4A max is just fine, particularly orchestral or rock. From 65Hz to 500Hz, a very large swath of music, you have less than 5R there, but it dips to 3.3R at about 95Hz which is critical for slam and percussion. You could simply keep rail voltage down, and bump up the quiescent to 3.5A, and this will give you up to 6.9A undistorted, max output current.
That is a very heavy crossover, that midrange would be difficult to drive at power. Are all the drivers at nominal 6.8R? From your 4Vpp//4R speakers figures, I would go for the 4R.
HD
It really depends on how much current you pass to your speakers. If they are efficient, then maybe 3-4A max is just fine, particularly orchestral or rock. From 65Hz to 500Hz, a very large swath of music, you have less than 5R there, but it dips to 3.3R at about 95Hz which is critical for slam and percussion. You could simply keep rail voltage down, and bump up the quiescent to 3.5A, and this will give you up to 6.9A undistorted, max output current.
That is a very heavy crossover, that midrange would be difficult to drive at power. Are all the drivers at nominal 6.8R? From your 4Vpp//4R speakers figures, I would go for the 4R.
HD
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IMO you would gain a lot when bi-amping.
A potent A/B amp for the woofers which will be happy to drive the 4 ohm load.
The Nirvana for mid-high.
Further advantage is you would get rid off the "ugly" 88 uF capacitor of your midrange crossover by providing the input of the Nirvana with for example a high quality silver mica capacitor (or whatever) of the appropriate value (to be calculated with the input impedance of Nirvana).
I am afraid that the load presented by the parallelled woofers sucks out too much current out of the Nirvana; that's not what you want to maintain the highest quality higher up in frequency.
A potent A/B amp for the woofers which will be happy to drive the 4 ohm load.
The Nirvana for mid-high.
Further advantage is you would get rid off the "ugly" 88 uF capacitor of your midrange crossover by providing the input of the Nirvana with for example a high quality silver mica capacitor (or whatever) of the appropriate value (to be calculated with the input impedance of Nirvana).
I am afraid that the load presented by the parallelled woofers sucks out too much current out of the Nirvana; that's not what you want to maintain the highest quality higher up in frequency.
Yes, bi-amping Troels style is also on my to-do list.
With bi-amping the adjustable phase and level matching between bass and midhighs should be nice,
because bass level is never correct for all songs.
The 88uf is not so ugly, it's a mix of Mundorf Evo Supreme, Russian NOS K71 polystyrene and Audyn Reference caps, although it looks a bit ugly
With bi-amping the adjustable phase and level matching between bass and midhighs should be nice,
because bass level is never correct for all songs.
The 88uf is not so ugly, it's a mix of Mundorf Evo Supreme, Russian NOS K71 polystyrene and Audyn Reference caps, although it looks a bit ugly
Hi Danny,
Thanks so much for the detailed view of your impedance sweeps. The 3.3ohms is rather low, but since you only need 4Vpp (1.41Vrms) that is not a lot of current. I=V/R=1.41V/3.3ohm=700mA rms or 2A p-p. Lets give it 6dB headroom, so 4A p-p should suffice. IMO, you culd get away with the 8ohm Alpha Nirvana, but don't play it above 4Vpp program level with 6dB headroom. That's about 88dB program level (which is same as middle of dance floor in a nightclub circa 89dB). You have to yell to speak to someone next to you. If you went with 4R version, certainly it will work even better.
As a comparison to your speakers, I play all my amps through my reference 10F/RS225 FAST monitors. Although 82.5dB sensitive (the reality of -5dB baffle step fall off for being an in the open stand mount with an 87dB nominal woofer) , the impedance is very well behaved almost steady 8ohms with a peak at woofer box tuning frequency:
The measured acoustical phase is flat and varies only +/-15deg from 200Hz to 15kHz, so percussive transients are very distinct and lifelike:
This is the simple 2-way first order XO:
The 1st order XO achieves a good trick though, a nice right angle triangle step response:
Thanks so much for the detailed view of your impedance sweeps. The 3.3ohms is rather low, but since you only need 4Vpp (1.41Vrms) that is not a lot of current. I=V/R=1.41V/3.3ohm=700mA rms or 2A p-p. Lets give it 6dB headroom, so 4A p-p should suffice. IMO, you culd get away with the 8ohm Alpha Nirvana, but don't play it above 4Vpp program level with 6dB headroom. That's about 88dB program level (which is same as middle of dance floor in a nightclub circa 89dB). You have to yell to speak to someone next to you. If you went with 4R version, certainly it will work even better.
As a comparison to your speakers, I play all my amps through my reference 10F/RS225 FAST monitors. Although 82.5dB sensitive (the reality of -5dB baffle step fall off for being an in the open stand mount with an 87dB nominal woofer) , the impedance is very well behaved almost steady 8ohms with a peak at woofer box tuning frequency:
The measured acoustical phase is flat and varies only +/-15deg from 200Hz to 15kHz, so percussive transients are very distinct and lifelike:
This is the simple 2-way first order XO:
The 1st order XO achieves a good trick though, a nice right angle triangle step response:
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Hi X,
That's a very impressive impedance and phase plot ! Very nicely done !
Now something like that but with 90db sensitivity
I have to photoshop to get such impedance and phase plots with the drivers and the 2nd/3rd order xo I used
Yes, 89db is very loud, last weekend I played a 1kHz sine wave at 90db and measured about 4vpp on the speaker binding posts, of course I used earplugs.
Normal listening is done at 1-2vpp.
Since I will use the PS of my Alpha4R with 25vdc rails, I'll go for the 8R.
Maybe one day I'll bi-amp the woofers with some class A/B or D.
Thanks for calculating the needed amps, I didn't knew I had to convert to rms and back.
Danny
That's a very impressive impedance and phase plot ! Very nicely done !
Now something like that but with 90db sensitivity
I have to photoshop to get such impedance and phase plots with the drivers and the 2nd/3rd order xo I used
Yes, 89db is very loud, last weekend I played a 1kHz sine wave at 90db and measured about 4vpp on the speaker binding posts, of course I used earplugs.
Normal listening is done at 1-2vpp.
Since I will use the PS of my Alpha4R with 25vdc rails, I'll go for the 8R.
Maybe one day I'll bi-amp the woofers with some class A/B or D.
Thanks for calculating the needed amps, I didn't knew I had to convert to rms and back.
Danny
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