Hi Piotr,
Is the Musical Fidelity a MOSFET? Is it single ended? My prediction is it is a bipolar, and not a single-ended class A.
"Good" amp doesn't have to "sound" good because it is only a small part in the audio chain. Look at an equalizer or tone control, they "ruin" the signal by their existence in the audio path, but at the same time they give something to the system. Many good amps (and even speakers) are "flat", in that they don't ruin the signal as much the bad amps but they also don't give anything (Why it has to give something if there's no disefficiency in the system? What it needs to do is to amplify the input signal as close as possible to the input)
IMO, bipolars tend to be musical due to the dynamics or the high transconductance. If this is the case, you have to pay attention to this aspect in your Aleph 5: the POWER SUPPLY.
I can't see the picture of your amp clearly from this public computer, but it seems like you are using budget components as I can see it clearly from the resistors.
1. Do not use cheap diode! There is no expensive diode so using a bad one is a big mistake. This will affect your system more than changing those resistors. (I don't have enough statistics to be sure but usually ultra fast ones, down to 35ns in smaller diodes, have great impact on dynamics. As for the component build, I trust Motorola for all their products)
2. I hope your transformer is not under-rated. Aleph 5 requires big current. From the not-so-clear picture, your amp (dimension/heatsink/transformer) looks so small for an Aleph 5 (I know it is a monoblock, but my Aleph 3 seems bigger). But this is another story because transformers are the most expensive part in your amp.
3. I cannot see the capacitors. "Standard" Alephs use inductors in the DC rails. This will filter the noise to a great degree, but at the same time ruin the dynamic/sonic (or whatever they call it) capability. If you use these inductors, make sure you have a massive capacitance after the inductor.
4. Well, Aleph 5 has a constant current source that will provide the current anytime it is needed. But that is too ideal than what happened in reality. Make sure you don't underestimate the capacitance and had measured the bias current exactly as intended.
5. If those do not fix the problem, somebody else had mentioned about the speaker. But that is the most expensive and difficult area. Those guys like Dave who knows about speaker design are more lucky than those who knows about amp design like Mr. Pass you know
(Just kidding, Mr. Pass!) Frankly, your impression about the downside of the Aleph is the same with many others who had built them including me. Your comments are welcome on my philosophy: "Got a lot of money, build a tube amp. Got a few money, build a bipolar" (And I'm bulding a bipolar! 
)
Is the Musical Fidelity a MOSFET? Is it single ended? My prediction is it is a bipolar, and not a single-ended class A.
"Good" amp doesn't have to "sound" good because it is only a small part in the audio chain. Look at an equalizer or tone control, they "ruin" the signal by their existence in the audio path, but at the same time they give something to the system. Many good amps (and even speakers) are "flat", in that they don't ruin the signal as much the bad amps but they also don't give anything (Why it has to give something if there's no disefficiency in the system? What it needs to do is to amplify the input signal as close as possible to the input)
IMO, bipolars tend to be musical due to the dynamics or the high transconductance. If this is the case, you have to pay attention to this aspect in your Aleph 5: the POWER SUPPLY.
I can't see the picture of your amp clearly from this public computer, but it seems like you are using budget components as I can see it clearly from the resistors.
1. Do not use cheap diode! There is no expensive diode so using a bad one is a big mistake. This will affect your system more than changing those resistors. (I don't have enough statistics to be sure but usually ultra fast ones, down to 35ns in smaller diodes, have great impact on dynamics. As for the component build, I trust Motorola for all their products)
2. I hope your transformer is not under-rated. Aleph 5 requires big current. From the not-so-clear picture, your amp (dimension/heatsink/transformer) looks so small for an Aleph 5 (I know it is a monoblock, but my Aleph 3 seems bigger). But this is another story because transformers are the most expensive part in your amp.
3. I cannot see the capacitors. "Standard" Alephs use inductors in the DC rails. This will filter the noise to a great degree, but at the same time ruin the dynamic/sonic (or whatever they call it) capability. If you use these inductors, make sure you have a massive capacitance after the inductor.
4. Well, Aleph 5 has a constant current source that will provide the current anytime it is needed. But that is too ideal than what happened in reality. Make sure you don't underestimate the capacitance and had measured the bias current exactly as intended.
5. If those do not fix the problem, somebody else had mentioned about the speaker. But that is the most expensive and difficult area. Those guys like Dave who knows about speaker design are more lucky than those who knows about amp design like Mr. Pass you know
(Just kidding, Mr. Pass!) Frankly, your impression about the downside of the Aleph is the same with many others who had built them including me. Your comments are welcome on my philosophy: "Got a lot of money, build a tube amp. Got a few money, build a bipolar" (And I'm bulding a bipolar! )
One definite improvement is to double the number of fets in the output like the Aleph 60, and then re set the DC bias to as high as you dare.
ie 12 fets per channel
You will find the amp noticably more dynamic with better control in the bass. ie the benefits of the Aleph 2 without power/heat.
This is quite an easy modification with only hardware issues to consider.
The wiring may also be an issue.
The supply rail wiring from R14 should be as short as possible to the output stage power and I would tend to run seperate power wires to both the driver board and the output fets, this will add more spark and open up the sound stage.
Having the caps under the board and high current wiriing from the rectifiers may be causing induced hum into the input stage.
Check that you are running the positive input to the unbalanced input (+) and that the negative (-) of the balanced input is shorted to ground if you are using unbalanced input for best performance.
macka
ie 12 fets per channel
You will find the amp noticably more dynamic with better control in the bass. ie the benefits of the Aleph 2 without power/heat.
This is quite an easy modification with only hardware issues to consider.
The wiring may also be an issue.
The supply rail wiring from R14 should be as short as possible to the output stage power and I would tend to run seperate power wires to both the driver board and the output fets, this will add more spark and open up the sound stage.
Having the caps under the board and high current wiriing from the rectifiers may be causing induced hum into the input stage.
Check that you are running the positive input to the unbalanced input (+) and that the negative (-) of the balanced input is shorted to ground if you are using unbalanced input for best performance.
macka
Hi guys! I made some Aleph (A30) too. http://koy.hi-end.org/Audio/Bastleni/Aleph3.html . And I experienced the same feeling.Loss of details and space ( comparing to Thule Audio). I rised bias ( to about 1.2A per IRFP), used metal resistors, bypassed electrolyts, changed % of modulation of the bias current, I tried blue LED, painted heatsinks, drunk some whisky and ... nothing changed. I am afraid it belongs to Aleph. Somebody likes it somebody not.
I spend some time ( I build and tuned it allmost one year, on evenings) with Aleph. I have build A30, and all measuremens http://koy.hi-end.org/Audio/Clanky/A3cln.html - unfortunatelly in czech. I am going to translate it in more known language ) I have done was on A30. After all I successed to burn ( screwdriver in wrong position) one IFRP and I turned it to A3. On the other hand output IRFPs are much better matched now. On the picture you can see A30 in time of experiments ( that-s why the nest of cables).
Grounding? I tried to do my best. I can not hear allmost no humm. But I am not sure it helps.
) I have done was on A30. After all I successed to burn ( screwdriver in wrong position) one IFRP and I turned it to A3. On the other hand output IRFPs are much better matched now. On the picture you can see A30 in time of experiments ( that-s why the nest of cables).Grounding? I tried to do my best. I can not hear allmost no humm. But I am not sure it helps.
Koy said:
When I first built the Aleph, It drove me crazy. This is because my definition of a good system is the one who can make me enjoy the music. This is not the amp fault, because in an audio system an amp must work in synergy with other components. You have to tweak your system to achieve a good result. I like the Aleph only after I tweak the speaker (sealed the vent and changed the crossover).
IMO, the good things about Aleph are:
1. It is a class A (you know what it means). Class A amps usually have "separated" and sweet vocal. I think the Aleph's vocal is wonderfull compared to other class A amps.
2. It is very efficient as a class A (You know what a high power amp can do to the overall system, even though you never drive the system more than a few percentage of it's capacity).
3. It is a MOSFET. IMO, it is the bass performance of MOSFET that attracts most people.
4. It has the capability to "ghost" the load? Or work with many speakers. Well, there are many other technicall things, but they are not important to pure music listeners (We care only what we hear).
PMA said something about trying an amp with lower distortion. If you think Aleph "has" distortion, I agree. The current feedback apparently introduced some distortion (so you must use quality caps there). But I prefer to remove the current feedback with the price of much reduced power.
During past few days i did following changes to my Aleph :
1. Rised current on fets up to 1 A per fet
2. Used IRFP 250 N instead of IRFP 244
3. mooved source and gate resistors directly to fets. (As u know i have fets on a wires
And now finally I an 100% satissfied with my Aleph. It is sweet, dynamic and spacious. I like it. Really !!!
1. Rised current on fets up to 1 A per fet
2. Used IRFP 250 N instead of IRFP 244
3. mooved source and gate resistors directly to fets. (As u know i have fets on a wires
And now finally I an 100% satissfied with my Aleph. It is sweet, dynamic and spacious. I like it. Really !!!
just remove R19 (around 523 ohms) or the 220uF Cap that connects the output and the current source.
This will give you a constant current source. The only problem could be that peak output current is halved so output power will only be 25%.
Power into 4 ohms for 2.5A bias would be 2.5x2.5x4/2=12.5 watts
william
This will give you a constant current source. The only problem could be that peak output current is halved so output power will only be 25%.
Power into 4 ohms for 2.5A bias would be 2.5x2.5x4/2=12.5 watts
william
you're right. I was thinking the reverse way (didn't see the need for the 2 components, if you build the amp from zero. But he isn't building it from zero, it's already working. So removing one component will be easier, of course)wuffwaff said:
I didn't, for sure: I have no aleph :/Jaskier said:
But since it's a so easy mod, try it! You found a difference between 2 positions for a resistor, you'll certainly head the difference here.
And tell us your results
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