Hello nar,
with a current gain of 50% the current source can vary the current between 0 and 2x the DC bias. In case of the Aleph5 with 2A bias this means a peak value of the bias of 4A. This will give about 32watts in 4 ohms and not more. To get the specified 90 watts you´ll have to up the current gain so the current source can give up to about 7A. In this case the current gain is about 70%.
This means that at high power into 4 ohms the Fet´s won´t have any bias for a period of time and you can´t call the amp class A anymore.
This could be the cause for a degrading of the sound quality although at lower power levels (below 4A peak)there´s always some bias left
william
with a current gain of 50% the current source can vary the current between 0 and 2x the DC bias. In case of the Aleph5 with 2A bias this means a peak value of the bias of 4A. This will give about 32watts in 4 ohms and not more. To get the specified 90 watts you´ll have to up the current gain so the current source can give up to about 7A. In this case the current gain is about 70%.
This means that at high power into 4 ohms the Fet´s won´t have any bias for a period of time and you can´t call the amp class A anymore.
This could be the cause for a degrading of the sound quality although at lower power levels (below 4A peak)there´s always some bias left
william
Hello Semikus,
I´m using Thiel CS6 and also tried the amp with small Dynaudio audience 42. I know the thiels very well and have tried a lot of different amps on them so it´s possible for me to compare.
william
I´m using Thiel CS6 and also tried the amp with small Dynaudio audience 42. I know the thiels very well and have tried a lot of different amps on them so it´s possible for me to compare.
william
both superb but both 4Ohms , and ~ 86dB ..... i think that you should make some "auditions" in any hi-fi/end studio with your aleph... try any KEF`s 🙂
Best Regards ,
sernikus
Best Regards ,
sernikus
Hello semikus,
thank you for the advice but I think that at my usual listening level the 4 ohm should be no problem. The Thiels are a bit better than 86dB and have played just fine with an simply845 wich has about 17watt into 4 ohms.
william
thank you for the advice but I think that at my usual listening level the 4 ohm should be no problem. The Thiels are a bit better than 86dB and have played just fine with an simply845 wich has about 17watt into 4 ohms.
william
first mods
Hi,
just a short report. After setting the ac current gain to 50% things have improved a lot🙂
Improvement are noticable over the whole frequency range with the amp sounding smoother and the soundstage getting deeper and more focused.
The 35 or so watts seem to be more than enough for the Thiels.
I´do the other mods one after another and see what happens.
william
Hi,
just a short report. After setting the ac current gain to 50% things have improved a lot🙂
Improvement are noticable over the whole frequency range with the amp sounding smoother and the soundstage getting deeper and more focused.
The 35 or so watts seem to be more than enough for the Thiels.
I´do the other mods one after another and see what happens.
william
William, congratulations on building your amp but maintaining a critical ear when it came to listening. I think too often we get so involved with our "babies" we always expect the work to produce fantastic results. You compared to your present amplifier, what is the amplifier you were using before the 5?
Hello Pete,
my current amp is a mosfet amp in an AB configuration (1A bias current). It´s based upon an elektor design from 1982 (crescendo) with a lot of modifications. (regulated driver supply, dc-servo, different transistors for input and drivers). It uses 3 pairs of 2sk135/2sj50 hitachi mosfets (TO-3) per channel.
Power supply is 450VA transformer and 100000 microF per channel (the 100.000 microF is realised with 100 x 1000microF) for +-42V.
I´ve been building and rebuilding this design for many (17) years now and every new version tends to get better (a next version will come as soon as the Aleph is ready)
I expect from what I´ve heard untill now that the Aleph will eventually win this "contest" exept maybe in the bass department.
william
my current amp is a mosfet amp in an AB configuration (1A bias current). It´s based upon an elektor design from 1982 (crescendo) with a lot of modifications. (regulated driver supply, dc-servo, different transistors for input and drivers). It uses 3 pairs of 2sk135/2sj50 hitachi mosfets (TO-3) per channel.
Power supply is 450VA transformer and 100000 microF per channel (the 100.000 microF is realised with 100 x 1000microF) for +-42V.
I´ve been building and rebuilding this design for many (17) years now and every new version tends to get better (a next version will come as soon as the Aleph is ready)
I expect from what I´ve heard untill now that the Aleph will eventually win this "contest" exept maybe in the bass department.
william
Hi William,
Maybe you could make the move to a bi-amp system with the Aleph on the top end?
Just a thought.
Rodd Yamashita
Maybe you could make the move to a bi-amp system with the Aleph on the top end?
Just a thought.
Rodd Yamashita
Rodd,
nice idea! Problem is that Thiel doesn´t like biwiring and build his crossovers without the possibility to do so.
william
nice idea! Problem is that Thiel doesn´t like biwiring and build his crossovers without the possibility to do so.
william
It's often possible to modify speaker crossovers for bi-wiring. Don't know about yours but it could be worth looking into.
Hi William,
Are the Thiel's 2 or 3 way speakers?
If they are 2 way, there's a good possibility there is some frequency response compensation built into the xover. You would have to be able to separate the woofer compensation circuit from the tweeter compensation circuit (if this is possible). On the other hand, you could experiment and temporarily run without the Theil xover (assuming you're using an electronic xover) and see how it sounds.
If the Thiel's are 3-way and the xover is a parallel design, you should be able to just disconnect the woofer connections to the xover and wire it to the bass amp. Frequency response compensation should not be an issue for the woofer of a 3 way system (check to be sure). Then, to power the upper drivers, you'll have to find your way past the high pass components of the mid driver yet not bypass the any compensation components that may exist.
The easiest way to bi-amp would be to get a sub-woofer and remove the responsibility of the first two octaves from the Thiel's. This can have a pronounced effect (good) on the mid-bass. You may also notice a difference in the upper range as well because there will be less inter-modulation of the high frequencies by the low frequencies in the upper amp.
Try it, you'll like it.
Rodd Yamashita
Are the Thiel's 2 or 3 way speakers?
If they are 2 way, there's a good possibility there is some frequency response compensation built into the xover. You would have to be able to separate the woofer compensation circuit from the tweeter compensation circuit (if this is possible). On the other hand, you could experiment and temporarily run without the Theil xover (assuming you're using an electronic xover) and see how it sounds.
If the Thiel's are 3-way and the xover is a parallel design, you should be able to just disconnect the woofer connections to the xover and wire it to the bass amp. Frequency response compensation should not be an issue for the woofer of a 3 way system (check to be sure). Then, to power the upper drivers, you'll have to find your way past the high pass components of the mid driver yet not bypass the any compensation components that may exist.
The easiest way to bi-amp would be to get a sub-woofer and remove the responsibility of the first two octaves from the Thiel's. This can have a pronounced effect (good) on the mid-bass. You may also notice a difference in the upper range as well because there will be less inter-modulation of the high frequencies by the low frequencies in the upper amp.
Try it, you'll like it.
Rodd Yamashita
Hi Pete,
the Thiels are 3-way and the crossover is 6dB/oct series. See:
http://www.thielaudio.com/THIEL_Web/Pages/cs6.html
I don´t want to fiddle around with these (that's why I bought them in the first place) A subwoofer would certainly be an option but only as an add on from 30Hz downwards or so. Problem is that these are not really small if they´re good and they´re not exactly cheap.......
Building one myself is not really an option cause a day only has 24 hours🙁
william
the Thiels are 3-way and the crossover is 6dB/oct series. See:
http://www.thielaudio.com/THIEL_Web/Pages/cs6.html
I don´t want to fiddle around with these (that's why I bought them in the first place) A subwoofer would certainly be an option but only as an add on from 30Hz downwards or so. Problem is that these are not really small if they´re good and they´re not exactly cheap.......
Building one myself is not really an option cause a day only has 24 hours🙁
william
Yes, subs are very popular in the US. I am not a big fan, I've generally found that they cannot be integrated into the rest of the system particularly well and tend to be in the "more must be better" category. A statement sure to create a disagreement, but just my findings. I have generally not found them especially popular in Europe outside an AV set-up.
I would contact the speaker manufacturer regarding wanting to run multiple amplifiers with the speakers. Some manufacturers are absolutely opposed to the idea of bi/tri-wiring, and that’s fair enough. However there can be no argument about the merits of multiple amplifiers where one is capitalising on the characteristics of each respective amp.
I would contact the speaker manufacturer regarding wanting to run multiple amplifiers with the speakers. Some manufacturers are absolutely opposed to the idea of bi/tri-wiring, and that’s fair enough. However there can be no argument about the merits of multiple amplifiers where one is capitalising on the characteristics of each respective amp.
Hi Pete,
The intention here is not to flame but to enlighten😉 Take a look at this site.
http://www.royaldevice.com/custom3.htm
Let's see,... if I move my furnace over there...
Rodd Yamashita
The intention here is not to flame but to enlighten😉 Take a look at this site.
http://www.royaldevice.com/custom3.htm
Let's see,... if I move my furnace over there...
Rodd Yamashita
I'm not sure I'm any further "enlightened" but thanks for the link. I'm pretty dubious of anyone that claims "The Highest efficiency ever obtained with NO distortion ...".
Think I'll file this one in my monster truck and db drag folder 🙂
Think I'll file this one in my monster truck and db drag folder 🙂
it still works,but better now
Hi all,
just a quick info after a few weeks of listening.
The amp got to sound better with the black gates but bass was still not were I wanted it to be and there were a few other things I wanted to change.
First of all placing the fets on a L-profile wasn´t such a good idea after all. Temperature difference from heatsink to directly next to the fet was about 17°C. I now have placed them on 4 pieces of aluminium (100x25x30mm) bolted directly to the heatsinks and the difference now is only 8°C.
After this I raised the bias to 2.4A. After measuring the power output ac-current gain seemed to have changed from 50% to 42% so it had to be set again. Must have something to do with changing R19 but I can´t really explain why (yet).
Bass has changed and it´s beginning to sound like I want it to.
Since I can´t raise the bias anymore with this setup I´m thinking of building two monoblocks with X5 or X6 and 3-3.2A of bias. The power supply is big enough so it will only cost me new heatsinks🙁 and a few more fets plus a lot of work.
The big question is: will the bass performance be raised again by upping the bias and doubling the amount of fets?
Maybe someone out there has done something along this line and can tell me what happened
william
Hi all,
just a quick info after a few weeks of listening.
The amp got to sound better with the black gates but bass was still not were I wanted it to be and there were a few other things I wanted to change.
First of all placing the fets on a L-profile wasn´t such a good idea after all. Temperature difference from heatsink to directly next to the fet was about 17°C. I now have placed them on 4 pieces of aluminium (100x25x30mm) bolted directly to the heatsinks and the difference now is only 8°C.
After this I raised the bias to 2.4A. After measuring the power output ac-current gain seemed to have changed from 50% to 42% so it had to be set again. Must have something to do with changing R19 but I can´t really explain why (yet).
Bass has changed and it´s beginning to sound like I want it to.
Since I can´t raise the bias anymore with this setup I´m thinking of building two monoblocks with X5 or X6 and 3-3.2A of bias. The power supply is big enough so it will only cost me new heatsinks🙁 and a few more fets plus a lot of work.
The big question is: will the bass performance be raised again by upping the bias and doubling the amount of fets?
Maybe someone out there has done something along this line and can tell me what happened
william
Hi William,
It sounds like the lack of available current is the problem. I noticed on the Thiel link you provided, that the minimum impedance is 2.4ohms! That down in ribbon territory. Impedance that low will suck up the available current pretty fast. I would suspect the the bass is weak in the 100Hz range or maybe a little higher. This would probably be the range where the woofer impedance bottoms out at 2.4ohms. It's too high a frequency to be effected by the inductive reactance of the cone motion at resonance, but too low a frequency to be effected by the inductive reactance due to the voice coil inductance.
It would be nice to get a verification from someone with an Aleph 2 or 4 and similar speakers.
Rodd Yamas***a
It sounds like the lack of available current is the problem. I noticed on the Thiel link you provided, that the minimum impedance is 2.4ohms! That down in ribbon territory. Impedance that low will suck up the available current pretty fast. I would suspect the the bass is weak in the 100Hz range or maybe a little higher. This would probably be the range where the woofer impedance bottoms out at 2.4ohms. It's too high a frequency to be effected by the inductive reactance of the cone motion at resonance, but too low a frequency to be effected by the inductive reactance due to the voice coil inductance.
It would be nice to get a verification from someone with an Aleph 2 or 4 and similar speakers.
Rodd Yamas***a
Hi William,
I think your on the right track by expanding the output of your Aleph. If you went to X6 or 12 devices per channel, If you build them in mono blocks, you would have an Aleph 2 with 32V rails. I'm not sure what adjustments would be necessary on the main board, but I'm sure that some resistor value changes would be required.
This should work and get you the extra current you need for your speakers. Hopefully some of our fellow DIY'er can help with some of the specifics.
Rodd Yamas***a
I think your on the right track by expanding the output of your Aleph. If you went to X6 or 12 devices per channel, If you build them in mono blocks, you would have an Aleph 2 with 32V rails. I'm not sure what adjustments would be necessary on the main board, but I'm sure that some resistor value changes would be required.
This should work and get you the extra current you need for your speakers. Hopefully some of our fellow DIY'er can help with some of the specifics.
Rodd Yamas***a