Hi!
I friend of mine decided yesterday to make pretty detailed measurements of his Aleph ...
We were not able yet to comment the results in "live" - so I'm not too detailed informed yet ...
As far as I understood this are his finding outs:
- it doesn't develop 60W but only around 15-20!?!?!
- that's because the bias is only around 1,3A!! - altough all values should be pretty close to the ones in original schemtaic - but it is true, that PSU gives out 32 instead of 34V - can that cause such difference? Or are the tolerances of those 1R resistors the guilty ones?
- then it also cuts one half of the signal much much before than the other - but when he put -1V DC offset on the input - everything became much better - is that the problem with input differential pair (their matching) or something else?
Thanks for tips and help!
I friend of mine decided yesterday to make pretty detailed measurements of his Aleph ...
We were not able yet to comment the results in "live" - so I'm not too detailed informed yet ...
As far as I understood this are his finding outs:
- it doesn't develop 60W but only around 15-20!?!?!
- that's because the bias is only around 1,3A!! - altough all values should be pretty close to the ones in original schemtaic - but it is true, that PSU gives out 32 instead of 34V - can that cause such difference? Or are the tolerances of those 1R resistors the guilty ones?
- then it also cuts one half of the signal much much before than the other - but when he put -1V DC offset on the input - everything became much better - is that the problem with input differential pair (their matching) or something else?
Thanks for tips and help!
Hi Stabist,
power depends on bias and ac-current gain. With 1.3A bias and 50% you can expect aprox. 25 watts into 8 ohms (12.5 into 4 ohms). The voltage is more than high enough for the little bias your friend is using.
Bias should be set with R19 (use a pot then replace with a resistor). After that you should measure ac-current-gain and set as you like (between 50% and 65%.........)
The Aleph will clip unsymmetrically by design. Positive swing is limited by bias, voltage, ac-current-gain, negative is limited by voltage and the current limiter. This is only there to protect the amp in case of a shortcut at the output.
If the DC offset is allright (<50-100mV) then the input pair is matched allright.
William
power depends on bias and ac-current gain. With 1.3A bias and 50% you can expect aprox. 25 watts into 8 ohms (12.5 into 4 ohms). The voltage is more than high enough for the little bias your friend is using.
Bias should be set with R19 (use a pot then replace with a resistor). After that you should measure ac-current-gain and set as you like (between 50% and 65%.........)
The Aleph will clip unsymmetrically by design. Positive swing is limited by bias, voltage, ac-current-gain, negative is limited by voltage and the current limiter. This is only there to protect the amp in case of a shortcut at the output.
If the DC offset is allright (<50-100mV) then the input pair is matched allright.
William
Thanks wuffwaff!
The thing is - he thought he has "full" (2+A) bias - considering his A5 is built with same resistor values as in original schematic ... The differences are just in transistors (his version uses irfp240, irf9620 and ZTX450) and in fact that PSU voltage is 32V instead of 34V ....
We just wonder how come that it is such big difference betwen original A5 and this one ...
OK now when we know that we must lift bias - no problem (I hope) ...
The thing is - he thought he has "full" (2+A) bias - considering his A5 is built with same resistor values as in original schematic ... The differences are just in transistors (his version uses irfp240, irf9620 and ZTX450) and in fact that PSU voltage is 32V instead of 34V ....
We just wonder how come that it is such big difference betwen original A5 and this one ...
OK now when we know that we must lift bias - no problem (I hope) ...
Considering resistors - I can just believe that they are really pretty much same values as noted (and they are supposed to be 2% ones)- because my multimeter is very inaccurate for resistors below cuople ten Ohms ...
So - a combination of resistors in Zen gives me 0,33R - and voltage drop is around 0,75V
But when measuring current with meter in series in PSU line - it shows it draws only 1,3A ... ?!? OK I said to myself - also the mutlimeter ain't pretty precise - but still - to get such difference - there must be something wrong ...
So - a combination of resistors in Zen gives me 0,33R - and voltage drop is around 0,75V
But when measuring current with meter in series in PSU line - it shows it draws only 1,3A ... ?!? OK I said to myself - also the mutlimeter ain't pretty precise - but still - to get such difference - there must be something wrong ...
Hi Stabist,
I think the only thing that is wrong is the measurement
Current can´t disappear or appear so if it flows through 0,33R it must come out of the power supply.
Did you look at the signals with a scope?
What you could do is to put another 0,33R in the power supply line and measure the voltage there and calculate the current.
william
I think the only thing that is wrong is the measurement
Current can´t disappear or appear so if it flows through 0,33R it must come out of the power supply.Did you look at the signals with a scope?
What you could do is to put another 0,33R in the power supply line and measure the voltage there and calculate the current.
william
My Aleph 5
Hi!
Right values of bias are:
Left channel: +1.57A, -1.57A
Right channel: +1,59A, -1.59A
Power supply voltage on power capacitor:
+32.08V, -32.08V
Trannie power:
P=218,8W
S=339,9VA
Maksimum power is 30W on 8ohm and 12.5W on 4ohm.
All measurment was taken by professional equipment (curruent probe - Omicron, and power analyser,...)
Picture of maksimum sinus wave without a disstorsion on 8ohm load.
Hi!
Right values of bias are:
Left channel: +1.57A, -1.57A
Right channel: +1,59A, -1.59A
Power supply voltage on power capacitor:
+32.08V, -32.08V
Trannie power:
P=218,8W
S=339,9VA
Maksimum power is 30W on 8ohm and 12.5W on 4ohm.
All measurment was taken by professional equipment (curruent probe - Omicron, and power analyser,...)
Picture of maksimum sinus wave without a disstorsion on 8ohm load.
Hi!
I know it's not the right thread - but nevertheless - after spending few days with trying to reanrange Zen - I've decided to STOP the Zen project for some time - and instead - A5 is going to born! FINNALY So today I've filled PCB with parts Tomorrow I'm going to order some Al plates for my chassis And I hope it will be finished during November
Btw wuffwaff - great tip
I know it's not the right thread - but nevertheless - after spending few days with trying to reanrange Zen - I've decided to STOP the Zen project for some time - and instead - A5 is going to born! FINNALY
So today I've filled PCB with parts Tomorrow I'm going to order some Al plates for my chassis And I hope it will be finished during November Btw wuffwaff - great tip
No change
Hi!
Kirc asled me if I can report his findings - he has fiddled quite a lot with the "bias resistor" - but nevertheless if he increases or decreases the value - the bias goes just down
But he said that it is truth he made quite big "jumps" between values ... So should he use a pot and very careffuly trying to get higher bias or is there something else that doesn't work OK?
THANKS!!
Hi!
Kirc asled me if I can report his findings - he has fiddled quite a lot with the "bias resistor" - but nevertheless if he increases or decreases the value - the bias goes just down
But he said that it is truth he made quite big "jumps" between values ... So should he use a pot and very careffuly trying to get higher bias or is there something else that doesn't work OK?
THANKS!!
I put out R19 and bias is still only 1.62A. No matter what I put instead of 221K the bias is still the same. I can only lower bias with resistor lower then 180K. I replace ZTX450 wizh BC546B, but there is still no difference in bias value. I don't have an idea what can it be wrong with my sweet Aleph ?
Now I measure voltage drop across R40-42 (1ohm) and on each is about .6V so if the value of resistors are 1ohm, the current across resistor are about 0.6A and complete bias is about 1.8A, with Omicron current clamp 1.62A.
All resistor are 1% tollerance, only R40-42 are 2%.
I use IRF9620 and IRF240.
All resistor are 1% tollerance, only R40-42 are 2%.
I use IRF9620 and IRF240.
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