My Aleph sounds better!

Hi folks,

My question is very simple, but the answer could be complicated...Is there a better sounding Aleph?

My first idea was to build an Aleph4...but someone told me that the Aleph2 had higher bias current and therefore sounds better.

Trying to fit the Aleph2 in my low-profil chassis turned out to be a nightmare and I realized that it would probably never fit in. I've now revised my needs and decided to leave the 100W and go for something less powerful. Something that will suit my low-profil chassis. However, I want to make sure the sound will be as good as the Aleph2...if there is a difference.

So here's the line up:
Aleph0: Monoblock 75W...idles at 250W
Aleph1.2: Monoblock 200W...idles at 500W
Aleph2: Monoblock 100W...idles at 300W
Aleph3: Stereo 30W...idles at 250W (125W/ch.)
Aleph4: Stereo 100W...idles at 500W (250W/ch.)
Aleph5: Stereo 60W...idles at 300W (150W/ch.)

Sorting by idle power/output power ratio:
Aleph1.2: ratio of 2.5
Aleph4: ratio of 2.5
Aleph5: ratio of 2.5
Aleph2: ratio of 3
Aleph0: ratio of 3.33
Aleph3: ratio of 4.16

Is it true to say that the Aleph3 and Aleph0 will have better accoustics performances...or is it just a stupid way to look at this problem?

Is the Aleph5 more comparable to the Aleph2 or the Aleph4 in term of performance?

regards,
Gabriel
 

BrianGT

diyAudio Moderator Emeritus
2002-01-21 2:42 pm
near Atlanta, GA
www.chipamp.com
If you look at the setup on each of the amplifiers, you will see which ones are biased higher.

If you look at the series element with the output device:
Aleph 3 = .5v/.47ohm = 1.064A
Aleph 2 = .5v/1ohm = 500mA
Aleph 5 = .5v/1ohm = 500mA
Aleph 4 = .6v/1.5ohm = 400mA
Aleph 1.2 = .5v/1.5ohm = 333mA

I read somewhere that the amount of power also effects the sound. I read that the Aleph 2 sounds better then the Aleph 4, since it is biased higher, but the Aleph 1.2 sounds better because it has more power.. possibly because it has more devices?

I have not personally listened to any Aleph amplifiers, as I am still making mine, so I am not taking any audio reviews very seriously on the difference of the Aleph amplifiers, since they are conflicting, and I feel that it is partially a subjective opinion. I figure that if someone spends $7k on a pair of monoblocks, the amount of money spent will greatly influence their opinion on how their amplifiers sound best. The same goes for building your own, as you put a lot of time and effort into building the amplifier, so you hold it in a class of it's own.

I think that the bottom line is that all of the Aleph amplifiers sound great. I would decide how much power you need, and pick one in that range. I think that 100W is more then enough for most applications, unless you have very inefficient speakers.

I personally find 100W to be plenty of power, and once I finish my Aleph 2 monoblocks, if it does not run really hot, I can always change some resistors and bias it more and see how it sounds. I am trying to over heatsink it, so that I can do this.

I think you would be safe taking the Aleph 5 design and making a pair of monoblocks. The board layout is the same as the Aleph 2 and 4, so you could always upgrade to a higher power transformer and change a few components later on. (would have to make a bigger case). 60W should be enough output power for most casual listening, and 150W of dissipation is reasonable from one low profile chassis.

Good luck,

--
Brian
[email protected]
 
Well ..... I've built a couple of Pass Class A's over the years.

The Aleph4 I built was done "on the cheap" as a "proof of concept" and bit of fun .... which it certainly is!

Having done this, I am now in the process of building an Aleph5 as my main amp. However, this is a planned and no "short-cut" approach and will be reproducible, so that later I can build a second and bi-amp if I want.

I expect no discernible sonic difference between the two amps, but I will let you know when I finish ;)

This carries on from my posts on required power levels versus "usual" speaker efficiency and listening levels. 60W is fine for me and the extra heat of the Aleph4 is not worth it (I think).

I'll put the whole project together on the web when I finish. I have redesigned the PCBs to include the FETs and to mate to some double-flanged sinks available in Oz. Should be very neat when finished (I hope).

cheers, mark
 
Actually, there's a question in here ....
If you look at the series element with the output device:
Aleph 3 = .5v/.47ohm = 1.064A
Aleph 2 = .5v/1ohm = 500mA
Aleph 5 = .5v/1ohm = 500mA
Aleph 4 = .6v/1.5ohm = 400mA
Aleph 1.2 = .5v/1.5ohm = 333mA

I read somewhere that the amount of power also effects the sound. I read that the Aleph 2 sounds better then the Aleph 4, since it is biased higher, but the Aleph 1.2 sounds better because it has more power ... possibly because it has more devices?
Nelson states that the distortion of a single device decreases with increased bias current. OK, so when we are comparing the bias of amplifiers WRT "sonic quality" should we be looking at the bias per individual device, or should we be looking at the total bias?

I fail to see why increasing the number of devices (all other things being equal) should improve the sound quality. Surely the only effect would be a net increase in gate capacitance and an increase in high frequency roll-off.

If we are comparing total amplifier bias, surely this has to be relative to the maximum current capability of the amp and not just on an absolute scale?

That is, a lower power amplifier may be biased at the same absolute current as a higher power unit, but the relative bias would be higher - or am I going made yet again????

Please remember I'm only a dumb medico, so be gentle .....

cheers, mark
 
Increasing the number of output devices will improve the damping factor and most of the other negative effects can be circumvented by increasing the drive current and lowering the apparent resistance seen by @ the gate of the output device.

Sonic quality has much to do with the ratio of bias vs. required current output. so we must consider bias per device vs. output current from that device... the higher ratio (more bias) the better the sonics.... or @ least that is the theory.
 

macka

Member
2001-12-15 3:07 am
Australia
My Aleph sounds better

Gabriel,

Have you thought about the Aleph 60.

According to ther Pass Owner Manual it mirrors the Aleph 2 in number of areas without the penalty of higher power/heat at 200 vs 300 watts without the trade off of any loss of quality.

This maybe the answer to your payers!

regards

Ian
 
Alright, the Aleph5 sounds to be a good compromise to the Aleph2 (simply a 60W version of this last one). I will build two monoblocks of the design. Furthermore, it will be possible to reuse the same layout later if I want to build the Aleph2.

1) To use my casing design, I need to have a even number of output FETs per half channel...in the current Aleph5 design, there's 3 FETs (X3). Is it possible, like in the other alephs, to have one more FET per block (X3 would become X4)?

Nelson states that the distortion of a single device decreases with increased bias current.OK, so when we are comparing the bias of amplifiers WRT "sonic quality" should we be
looking at the bias per individual device, or should we be looking at the total bias?

I fail to see why increasing the number of devices (all other things being equal) should improve the sound quality. Surely the only effect would be a net increase in gate capacitance and an increase in high frequency roll-off.
mefinnis, how does what you said apply to this modification?

2) What would be a good choice of transformer for each monoblock? I guess that 25Vac 500VA would be a good overkill. What is the transformer originaly used in the Aleph5?

3) I've read some reviews on the Aleph5 and people state that the speakers must be well chosen. That they must have a good sensibility. What range of sensibility should I aim for?

best regards,
Gabriel
 
Increasing the number of output devices will improve the damping factor

This is not always true. The output mosfets transconductance will increase as bias current increases. Lower bias current and an increase in the number devices is also done to decrease power dissapation for each individual output device to increase reliability. This is made neccesary by the higher rail voltages.

The major capacitance is that from gate to source for the output mosfets. With more output devices with with larger source degeneration resistors this voltage from gate to source is not being swung as far for a given transconductance. This eases the current reqirement from the front end. Decreasing the load resistor for the input diff pair from its value of 390 ohms and increasing the bias current and transconductance of the front end diff pair would probably gain some improments though. The T0220 input mosfets will have to have good heat sinking to do this.

H.H.
 
Gabriel,

The rail voltages for the Aleph 60 are +/-35. The amp draws 200 watts. TO-247 packaged devices will be fine.

Consider using IRFP140N's, these will have less distortion but take notice of their lower (94 watt) power dissipation. The IRFP150N would be my second choice, these have a 140 watt PD.

The commercial Aleph 60 has a 600 watt transformer.

Brett
 
My Aleph sounds better

Gabriel,

Question. Are the vac 's quoted full or no load for your transformers?

I any case if this "is " your only choice I'd go with the lower voltage as you will be back in the land of Aleph 2 heat.

But the way, I'm not trying to turn this into a tail chasing thread but if you were to contemplate even very mild fan cooling your low profile concept may be a lot more possible.

I recently saw super - quiet fans on the Farnell catalogue quoting 12 dba @ 1 metre with thermostatic control and they are low voltage!!!!!

I trust this has been discussed on other threads but for example my heatsink manufacturer quotes 0.46 c / watt for natural convection and 0.13 c /watt for 13.5cfm am 0.11 c/watt for 27 cfm

Obviously even relatively low pressure air flow Is most efective

God knows the effect on your layout but you could experiement with a knock up Aleph prototype on the workbench using available parts and try this idea out.

Then with the data you obtain you could then develop a really COOL Alpeh which would be quite something.


best regards
Ian
 
Alright, let's go for the 24Vac then. What are the consequences if the rail voltages are at ±33-34Vdc? Just a little bit less powerful I guess.

I'm really suspicious about fans and I think I will build a set of two aleph 60 for the moment. However, once the aleph 60 built and integrated to my casings I will be able to perform some tests with fans for a upcoming aleph 2.

Below is what I'm planning to do. If you wonder, the thing at the middle is a glass/plexiglass with the power switch. I project to install some kind of blue backlite (this is why it is blue). Note that the heatsinks are missing on the sides (I'm working on it).

ciao,
Gabriel
 

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