B.L. said:
Nelson Pass said:
Nelson is once again showing us all just how patient he is I think that we are pushing this; I would have no worries about what transistor to use I would just measure the ACIG once built you only need a multimeter and a sinewave generator. I assume that nobody in there right mind would attempt to build an amp without a multimeter and we all have a PC, software can be found here for those that don't have a signal gen.
Give me a few days and I may be able to point you in the right direction regarding how to chose the correct value resistor right 1st time based on measurement without "R0" and difference found with a given resistor value. to save soldering in pots or different values.
I will bet that nelson and clan have this mastered or know that it is not possible
It's not like the value is that critical. You can easily run the
gain figure from 0 to maybe 75%, and if you trust your ears,
then you can just stick a potentiometer in and see what you
like - you can adjust it over a wide range safely, just put a
resistor in series to set what you think the maximum gain
will want to be, so as to avoid accidents.
gain figure from 0 to maybe 75%, and if you trust your ears,
then you can just stick a potentiometer in and see what you
like - you can adjust it over a wide range safely, just put a
resistor in series to set what you think the maximum gain
will want to be, so as to avoid accidents.
Nelson Pass said:It's not like the value is that critical. You can easily run the
gain figure from 0 to maybe 75%, and if you trust your ears,
then you can just stick a potentiometer in and see what you
like - you can adjust it over a wide range safely, just put a
resistor in series to set what you think the maximum gain
will want to be, so as to avoid accidents.
I followed your advice, put in a pot listened while twiddling it until my ears were happiest (trying to ignore the voices in-between them that were nagging about technical correctness and stuff was hard). Upon measuring the result, I found that it was set at 52% (suddenly the voices in-between my ears silenced with shame).
sbear said:
It’s often the simplest method that gets overlooked.
Ok, question af a newbie :
I have a pair of aleph 2 running (for 2 years now), but I've never set anything.
So now is the time to make it works really as it should.
So I would like to set the bias and the curent source.
I have understood how to measure the bias and how to adjust it by playing with R19 value.
I have also understood that to adjust the current source, I have to take off R21, measure something, put again R21, re-measure and find R21 value so that the measure is half the measure without R21.
But then I have two problems :
- Nelson said : set the amplifier driving a sine wave into a load (let's say 16 Vrms into 8 ohms at 100 Hz). I have dowloaded Test tone generator. So I can create a sine wave at 100HZ. But what about the 8ohms load and the 16Vrms ? I should use the output of my sound card and use the generated signal at the input of the amplifier (using the RCA for example). I have to adjust the output level of the sound card so that I get 16V at the speakers output ? what about 8 ohms ? (yes I know, I am going from deep, but with a good explanation, I am sure that I will succeed)
- where exactly do I have to make the measurement ?
in the attached file, there is the board I used (but with the values for an aleph 2) : where should I take the measure ?
Thank you for spending a part of your time with me !
I have a pair of aleph 2 running (for 2 years now), but I've never set anything.
So now is the time to make it works really as it should.
So I would like to set the bias and the curent source.
I have understood how to measure the bias and how to adjust it by playing with R19 value.
I have also understood that to adjust the current source, I have to take off R21, measure something, put again R21, re-measure and find R21 value so that the measure is half the measure without R21.
But then I have two problems :
- Nelson said : set the amplifier driving a sine wave into a load (let's say 16 Vrms into 8 ohms at 100 Hz). I have dowloaded Test tone generator. So I can create a sine wave at 100HZ. But what about the 8ohms load and the 16Vrms ? I should use the output of my sound card and use the generated signal at the input of the amplifier (using the RCA for example). I have to adjust the output level of the sound card so that I get 16V at the speakers output ? what about 8 ohms ? (yes I know, I am going from deep, but with a good explanation, I am sure that I will succeed)
- where exactly do I have to make the measurement ?
in the attached file, there is the board I used (but with the values for an aleph 2) : where should I take the measure ?
Thank you for spending a part of your time with me !
ndhennin said:
First, you need to connect a resistor as the loading instead of a speaker, i.e. connect a 8 ohm 100W resistor (you can parallel 5 pieces of 39 ohm 20W ones) at the speaker output.
Second, you need an AC volt meter, a multi-meter will do, but you have to use low frequency (100 Hz for example) because a multi-meter does not work well at high frequency. Use the "Out" terminal if your meter has one, to avoid including DC voltage in the measurement.
Actually the figures given by Mr. Pass are just an example. They need not be exact. You just need to produce a signal across the speaker output high enough so that the AC voltage at the source resistors can be measured. What you must do is to keep the input signal the same at all time and the output is not clipped.
You can measure the AC voltage across S, s at the lower right corner of your PCB diagram. The reading is around 0.1 to 0.3 volt depends on the output voltage (and current) so it is a bit difficult to read with an analog multi meter. A digital one may work better.
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