You had better be careful as you don't want to blow it while your driving your amp, it could cause damage. It's not going to give you a warning or put it's hand up when it happens either. Do it quick if you must. Another idea is a dryer element. The wire they use is a resistive element type of wire and you can cut it and set it up for whatever resistance you need. Remember, Nelson used light bulbs in an amp though the resistance on a bulb changes when it heats up. Using the wattage of the bulb and the voltage output you can calculate the resistance using ohms law. Good Luck
Hello,
just did my testing. With a 8 dale 50W 1ohm resistors and a dale 160W 5 ohm resistor...
With 8 ohm, it tops out at 25.4V RMS = +/- 80W
With 5 ohm, it tops out at 15.32V RMS = +/- 46 W
hmm.... Sounds a bit too low doesn't it?
When I change channel, frequency or resistance, sometimes it tops out first and sometimes it bottoms out first... Can someone tell me why?
The current running through my 1.5ohm resistors of the IRFP240's run between 0.565V and 0.588V, can this be why? How can I raise this?
Edwin
just did my testing. With a 8 dale 50W 1ohm resistors and a dale 160W 5 ohm resistor...
With 8 ohm, it tops out at 25.4V RMS = +/- 80W
With 5 ohm, it tops out at 15.32V RMS = +/- 46 W
hmm.... Sounds a bit too low doesn't it?
When I change channel, frequency or resistance, sometimes it tops out first and sometimes it bottoms out first... Can someone tell me why?
The current running through my 1.5ohm resistors of the IRFP240's run between 0.565V and 0.588V, can this be why? How can I raise this?
Edwin
I don't feel like doing any work today, so I'll just put
in my 2 cents.
1) Very few RMS meters have a decent bandwidth, and if
you don't have a bandwidth spec, then measure at 100
Hz or so.
1A) Radio Shack makes fine meters if you observe this
limitation. I keep about 10 around at all times.
2) As long as you are running a sine wave, RMS and averaging
meters will give you the same answer. Again, watch the
bandwidth.
3) You can get away with driving load resistors way over
their rating if you do it fairly quickly.
in my 2 cents.
1) Very few RMS meters have a decent bandwidth, and if
you don't have a bandwidth spec, then measure at 100
Hz or so.
1A) Radio Shack makes fine meters if you observe this
limitation. I keep about 10 around at all times.
2) As long as you are running a sine wave, RMS and averaging
meters will give you the same answer. Again, watch the
bandwidth.
3) You can get away with driving load resistors way over
their rating if you do it fairly quickly.
Hello Edwin,
sounds good to me.
In both cases you´ve got about 3.1A effective current wich means about 4.4A peak. This fits the 2.3A bias I calculate from your voltages/resistors.
You can change this value by raising the value of R19 (Aleph5). Set this with a trimmer and insert the right resistor afterwards.
Depending on the setting of the current source gain you get different values of maximum current. When using 50% you`ll get a maximum of twice the bias current.
When you have less current gain then the max. current will be lower than twice the bias current, when you´ve got more it will be more.
I have to set my Aleph 5 to about 70% current gain to get the specified 90watts/4 Ohms.
I´ve calculated this value for the whole Aleph range looking for max output current specified in the manuals.
For example Aleph5 2A bias and 8A max so 4xthe bias current would mean a current gain setting of 75%
The others (from 1.2 to 60) hoover around 60 to 65%
First check your current gain setting and your bias and you´ll see that it fits.
Normally the amp will always clip on the positive side when the "negative clipper" is set for a generous amount of current. If you want the negative side to be able to sink more amps you´ll have to change this by lowering R16.
william
sounds good to me.
In both cases you´ve got about 3.1A effective current wich means about 4.4A peak. This fits the 2.3A bias I calculate from your voltages/resistors.
You can change this value by raising the value of R19 (Aleph5). Set this with a trimmer and insert the right resistor afterwards.
Depending on the setting of the current source gain you get different values of maximum current. When using 50% you`ll get a maximum of twice the bias current.
When you have less current gain then the max. current will be lower than twice the bias current, when you´ve got more it will be more.
I have to set my Aleph 5 to about 70% current gain to get the specified 90watts/4 Ohms.
I´ve calculated this value for the whole Aleph range looking for max output current specified in the manuals.
For example Aleph5 2A bias and 8A max so 4xthe bias current would mean a current gain setting of 75%
The others (from 1.2 to 60) hoover around 60 to 65%
First check your current gain setting and your bias and you´ll see that it fits.
Normally the amp will always clip on the positive side when the "negative clipper" is set for a generous amount of current. If you want the negative side to be able to sink more amps you´ll have to change this by lowering R16.
william
1) Very few RMS meters have a decent bandwidth
If you look at the pdf's for the Analog Devices AD536 true RMS converters (there are several flavors, I have a ton of AD737's), but the 536 is the device which Charles Hansen uses in his various designs in AudioXpress, you'll note that a capacitor is necessary for integrating, it is root MEAN square, after all. A large cap is needed for low frequencies and vice versa.
"They laughed when I said: "Use the calorimetric method"". Too many p-chem labs, I guess. (Oh, did I forget to mention that Linear Tech once made a true RMS converter which used a heating element. I've never been able to aquire one, however.)
If you look at the pdf's for the Analog Devices AD536 true RMS converters (there are several flavors, I have a ton of AD737's), but the 536 is the device which Charles Hansen uses in his various designs in AudioXpress, you'll note that a capacitor is necessary for integrating, it is root MEAN square, after all. A large cap is needed for low frequencies and vice versa.
"They laughed when I said: "Use the calorimetric method"". Too many p-chem labs, I guess. (Oh, did I forget to mention that Linear Tech once made a true RMS converter which used a heating element. I've never been able to aquire one, however.)
I am getting confused!
In the service manual of the Aleph 4 is written: 100W at 1% at 8 ohm !
Clipping at 80W is hardly 1% is should think. Also there is written bias is slightly higher than 3A (the same is in the Aleph 2 manual). But one runs 2.4A (mine 2.3A) and the other about 3A.
Why do I get 3.1A when the max is about 2.4A at 47% = 4.7A or so...
I am a bit of a novice; I bought a 800page book; Learning Electronics and Electricity just to learn how the Aleph is working. I read a couple of chapters of the passive components but I am not getting a grip of the interaction of the active and the passive. And I am starting to get puzzled about active feedback loops and stuff...
So my question is why is a Aleph 2 running 160W at 4 ohm and 100W at 8 ohm with a current gain of 46% and my Aleph 4 running 46W at 5 ohm and 80W at 8 ohm with a current gain of 50% .
(0.07833 * 1000) / (0.25 * 619) = 0.50
When my calculations are ok the Aleph 5 runs at 1.5A and has a current gain of 78% ...
Edwin
__________________________
Meten is weten ... toch?
In the service manual of the Aleph 4 is written: 100W at 1% at 8 ohm !
Clipping at 80W is hardly 1% is should think. Also there is written bias is slightly higher than 3A (the same is in the Aleph 2 manual). But one runs 2.4A (mine 2.3A) and the other about 3A.
Why do I get 3.1A when the max is about 2.4A at 47% = 4.7A or so...
I am a bit of a novice; I bought a 800page book; Learning Electronics and Electricity just to learn how the Aleph is working. I read a couple of chapters of the passive components but I am not getting a grip of the interaction of the active and the passive. And I am starting to get puzzled about active feedback loops and stuff...
So my question is why is a Aleph 2 running 160W at 4 ohm and 100W at 8 ohm with a current gain of 46% and my Aleph 4 running 46W at 5 ohm and 80W at 8 ohm with a current gain of 50% .
(0.07833 * 1000) / (0.25 * 619) = 0.50
When my calculations are ok the Aleph 5 runs at 1.5A and has a current gain of 78% ...
Edwin
__________________________
Meten is weten ... toch?
Hello Edwin,
don´t get confused
There´s a difference between peak current and rms current. The max peak current at 50% current gain will be twice the bias current.
Max power will be peak current diveded by sqrt2 times the max eff. voltage (this will be reached at just one load)
The bias of the Aleph4 is aprox. 2.6A not just over three as is in the service manual. You can calculate this with the 0,6V over the 1.5ohm resistors or the 250W channel at 96volts supply.
2.6A will give 5.2A peak and 3,67A rms giving 3,67x3,67x8 = 108w into 8 ohm
This fits
Your bias is a bit down so power is also down.
When power is limited by the current it will halve as the load halves so from 80/8 in 40/4ohms
The Aleph 5 has about 2A bias.
Please read the patent again and again, it really helps!
william
don´t get confused
There´s a difference between peak current and rms current. The max peak current at 50% current gain will be twice the bias current.
Max power will be peak current diveded by sqrt2 times the max eff. voltage (this will be reached at just one load)
The bias of the Aleph4 is aprox. 2.6A not just over three as is in the service manual. You can calculate this with the 0,6V over the 1.5ohm resistors or the 250W channel at 96volts supply.
2.6A will give 5.2A peak and 3,67A rms giving 3,67x3,67x8 = 108w into 8 ohm
This fits
Your bias is a bit down so power is also down.
When power is limited by the current it will halve as the load halves so from 80/8 in 40/4ohms
The Aleph 5 has about 2A bias.
Please read the patent again and again, it really helps!
william
Ok, how do you calculate the 2.6A ? When I do;
I = V / R = 0.6 / 1.5 = 0.4 * 6 = 2.4A ...
I still do not understand how Aleph 2 should be able to pull 160W at 4 ohm (ok, I do not understand a lot of things).
0.5 / 1 * 6 = 3A . 47% gives about 3A to 5.9A . For 160W in 4ohm you need about 6.3A rms .
5.9A gives about 5.9 * 0.707 = 4.17A rms = about 70 watt!
So you need a max bias of 6.3A * sqrt2 = 8.9A to pull 160W at 4ohm ...
Some how I am starting to think the services schema's of Nelson are not in sync with the specs... ;-)
Edwin
_________________________________
Please note I am a novice at electronics so be gentle with me!
I = V / R = 0.6 / 1.5 = 0.4 * 6 = 2.4A ...
I still do not understand how Aleph 2 should be able to pull 160W at 4 ohm (ok, I do not understand a lot of things).
0.5 / 1 * 6 = 3A . 47% gives about 3A to 5.9A . For 160W in 4ohm you need about 6.3A rms .
5.9A gives about 5.9 * 0.707 = 4.17A rms = about 70 watt!
So you need a max bias of 6.3A * sqrt2 = 8.9A to pull 160W at 4ohm ...
Some how I am starting to think the services schema's of Nelson are not in sync with the specs... ;-)
Edwin
_________________________________
Please note I am a novice at electronics so be gentle with me!
Edwin,
2.4A is what you get when you use the ca.0.6V value, 2.6A is when you take 500watts/96V/2.
The bias value can only be an estimated value cause it depends on Vgs and the hfe of the biasing transistor so it will vary a bit depending on what you´ve used.
Your calculation for the Aleph2 is right, but where did you get the 47% from?I think somewhere was mentioned that the formula to calculate the current gain is only a aproximation and that it´s much easier to measure.
The Aleph2 will do 200w@4ohm with 3.3A bias and 67% cs gain for 10A peak.
Just try to get your bias up to 2.5-2.7A and set the current gain as you like it best and enjoy the sound, don´t worry too much about the specs
william
2.4A is what you get when you use the ca.0.6V value, 2.6A is when you take 500watts/96V/2.
The bias value can only be an estimated value cause it depends on Vgs and the hfe of the biasing transistor so it will vary a bit depending on what you´ve used.
Your calculation for the Aleph2 is right, but where did you get the 47% from?I think somewhere was mentioned that the formula to calculate the current gain is only a aproximation and that it´s much easier to measure.
The Aleph2 will do 200w@4ohm with 3.3A bias and 67% cs gain for 10A peak.
Just try to get your bias up to 2.5-2.7A and set the current gain as you like it best and enjoy the sound, don´t worry too much about the specs
william
Hello William,
first of all I like to thank you for all the time you took to answer my questions. I could have build the Aleph without knowing how it works (I had enough building, soldering, component reconizing,- skills), but I have to know how it works...
I will read the patent a couple of times more with my electronic books and your comments...
I have used some other serie resistors like the 220 ohm instead of the 221 ohm . I used some E96 for the 392 ohm. I think I used a 4.70 for the 4.75 and a 220K for the 221K ... I will swap some around...
This can account for the lower bias, can it?
Edwin
first of all I like to thank you for all the time you took to answer my questions. I could have build the Aleph without knowing how it works (I had enough building, soldering, component reconizing,- skills), but I have to know how it works...
I will read the patent a couple of times more with my electronic books and your comments...
I have used some other serie resistors like the 220 ohm instead of the 221 ohm . I used some E96 for the 392 ohm. I think I used a 4.70 for the 4.75 and a 220K for the 221K ... I will swap some around...
This can account for the lower bias, can it?
Edwin
Hello Edwin,
I did the same using 220R, 390R, 4k7 etc. This won´t harm and mostly the diff isn´t even 1%.
This normally can´t account for the lower bias. Your bias isn´t that far of so maybe it´ll suffice to raise the value of R26. If this is not enough you can look for a transistor with a lower hfe (can be the same type but a BC550C would work too).
In the last instance you´ll have to change the source resistors to 1ohm or so.
Normally you won´t have to change R23. It only sees to it that the amp won´t sink too much current. If you normally have clipping on the negative side before the positive clips you´ll have to lower the value a bit.
william (he who has just received his black gate caps )
I did the same using 220R, 390R, 4k7 etc. This won´t harm and mostly the diff isn´t even 1%.
This normally can´t account for the lower bias. Your bias isn´t that far of so maybe it´ll suffice to raise the value of R26. If this is not enough you can look for a transistor with a lower hfe (can be the same type but a BC550C would work too).
In the last instance you´ll have to change the source resistors to 1ohm or so.
Normally you won´t have to change R23. It only sees to it that the amp won´t sink too much current. If you normally have clipping on the negative side before the positive clips you´ll have to lower the value a bit.
william (he who has just received his black gate caps
)wuffwaff said:
How much can I raise R26 to keep in the green zone? I Put a 10K in serie which did almost nothing, I put 60K (actually two 120K in parallel) in serie which gave me the 0.6V over the 1.5 ohm resistors. I tried 120K in serie; for a total of 240K which raised it a lot (around .710 but I did not dare to measure long), but it kind of scared me so I switched it back off...
Is 240K still a valid value for R26?
Edwin
wuffwaff said:Hello Edwin,
the only reason it´s there is to reduce the dc bias. You can leave it out without any danger. At 240k it won´t be doing very much anyway (just test it!)
william
With no resistor I have over 2.8A .
With 240k I have about 2.688A of current.
With 190K I have about 2.4A of current.
With 120K I have about 2.3A of current.
So I probably put in a 240k just to be sure it is still limited somehow.
I am still curious over why I need to do this adjustments to get the current up to a 'normal' level!
Edwin
P.s. Just had a big bang *spark* which shook the hell out of me, still do not know what happened but everything is still working! I was with my back to the amp, my girlfriend has seen the spark. I am going back to 20VA trafo instead of these 1000VA ones! I think my turning around I touch a wire on the floor which must have moved another wire which touched another wire and boom... can not find a black spot... Tomorrow I am going back to the amp with new courage...
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