Hello from Danilo,
As you can understand, I am not an expert:
How do I measure the input sensitivity of an amplifier?
I have a multimeter and some resistors.
The power amp is Hiraga Class A (20W).
Thanks a lot!!!
Danilo
As you can understand, I am not an expert:
How do I measure the input sensitivity of an amplifier?
I have a multimeter and some resistors.
The power amp is Hiraga Class A (20W).
Thanks a lot!!!
Danilo
You need a suitable load for the amplifier at full rated output power.
Make sure your meter can accurately measure the voltage of a 1kHz sine.
With a 1kHz sine input, increase the input level to just barely the output clipping point,
as observed on a scope, and then measure the rms input voltage.
That is the input required for full output (input sensitivity). It would be difficult to measure
the input sensitivity without a scope, though. It could be estimated by calculating the
output rms voltage at full rated power, and dividing by the rated voltage gain factor (not dB).
If the rated power is 20W into 8R, then the rms output voltage at clipping would be sqrt (20 x 8) = 12.6Vrms.
The gain factor from the schematic appears to be x 21, so 12.6Vrms / 21 = 0.6Vrms input sensitivity.
Make sure your meter can accurately measure the voltage of a 1kHz sine.
With a 1kHz sine input, increase the input level to just barely the output clipping point,
as observed on a scope, and then measure the rms input voltage.
That is the input required for full output (input sensitivity). It would be difficult to measure
the input sensitivity without a scope, though. It could be estimated by calculating the
output rms voltage at full rated power, and dividing by the rated voltage gain factor (not dB).
If the rated power is 20W into 8R, then the rms output voltage at clipping would be sqrt (20 x 8) = 12.6Vrms.
The gain factor from the schematic appears to be x 21, so 12.6Vrms / 21 = 0.6Vrms input sensitivity.
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No, have not an oscilloscope.
So I need to know Voltage gain factor, isn't It?
The problem Is that Hiraga Classe A specs are hard top find!
Danilo
So I need to know Voltage gain factor, isn't It?
The problem Is that Hiraga Classe A specs are hard top find!
Danilo
If you can measure the gain at 1kHz at around 1W output, that's fine for the gain factor.
Or just calculate the gain factor by adding 1 to the ratio of the two feedback resistors.
In this schematic they are 200R and 10r, so 1 + 200/10 = 21.
Without a scope it's hard to know the exact clipping point into a resistor load,
so I would go by the rated output power instead.
P = Vrms x Vrms / R
or Vrms = sqrt (P x R)
so Vrms = sqrt ( 20W x 8R ) = 12.6 Vrms maximum output rms voltage at clipping into 8R load.
Then the input voltage sensitivity for rated output is 12.6Vrms / 21 = 0.6 Vrms
Or just calculate the gain factor by adding 1 to the ratio of the two feedback resistors.
In this schematic they are 200R and 10r, so 1 + 200/10 = 21.
Without a scope it's hard to know the exact clipping point into a resistor load,
so I would go by the rated output power instead.
P = Vrms x Vrms / R
or Vrms = sqrt (P x R)
so Vrms = sqrt ( 20W x 8R ) = 12.6 Vrms maximum output rms voltage at clipping into 8R load.
Then the input voltage sensitivity for rated output is 12.6Vrms / 21 = 0.6 Vrms
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Thanks a lot, Rayma.
The only thing I don't understand Is this messurement procedure:
If you can measure the gain at 1kHz at around 1W output, that's fine for the gain factor.
Danilo
The only thing I don't understand Is this messurement procedure:
If you can measure the gain at 1kHz at around 1W output, that's fine for the gain factor.
Danilo
Sure, do you have a sine wave generator? Some use an app on their phone.
You have to be able to vary the size of the voltage from 0V up to
whatever you need to clip the amp. But this won't help if you don't have a scope.
You have to determine clipping either visually on the scope, or else by calculation.
If you can't do that, just calculate the gain factor by 1 + ratio of feedback resistors.
If the feedback resistors are 200R and 10R like in the schematic above,
the gain is 1 + 200 / 10 = 21 times.
You have to be able to vary the size of the voltage from 0V up to
whatever you need to clip the amp. But this won't help if you don't have a scope.
You have to determine clipping either visually on the scope, or else by calculation.
If you can't do that, just calculate the gain factor by 1 + ratio of feedback resistors.
If the feedback resistors are 200R and 10R like in the schematic above,
the gain is 1 + 200 / 10 = 21 times.
If a Power amp has 0.6V of input sensitivity (It seems to be low!) means that if the preamp reaches that output value at one tenth of the knob rotation, does the power amp go into saturation from that position on?
Yes, it does. The amp has enough gain that you only need 0.6Vrms for full output.
Part of the reason is that it is a low power amp, with a small maximum output voltage.
Lots of amps were designed with a small input sensitivity about like 0.6V, years ago.
Newer amps will be higher, roughly 1V to 2V.
You could add a couple of resistors at the preamp output for each channel to reduce the output
for a given volume knob setting. For example, change the sensitivity to 1.2V instead of 0.6V.
Add a series 5k and then a shunt 5k to each preamp output. That will cut them in about half,
so the 0.6V effectively becomes 1.2V instead.
Then the volume knob would have to be turned up higher for the same speaker volume.
Often times that is good, since volume controls often don't track as well at lower settings.
Part of the reason is that it is a low power amp, with a small maximum output voltage.
Lots of amps were designed with a small input sensitivity about like 0.6V, years ago.
Newer amps will be higher, roughly 1V to 2V.
You could add a couple of resistors at the preamp output for each channel to reduce the output
for a given volume knob setting. For example, change the sensitivity to 1.2V instead of 0.6V.
Add a series 5k and then a shunt 5k to each preamp output. That will cut them in about half,
so the 0.6V effectively becomes 1.2V instead.
Then the volume knob would have to be turned up higher for the same speaker volume.
Often times that is good, since volume controls often don't track as well at lower settings.
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Rayma, I've found an used preampli Musical fidelity M8 with 9.5 Vrms.
Is It top much in comparison with 0.6?
Which Is the Gold preampli output Voltage value?
Danilo
Is It top much in comparison with 0.6?
Which Is the Gold preampli output Voltage value?
Danilo
That Musical Fidelity preamp appears to have x 27 gain factor in the line stage, which is higher than
many preamps. You might have to keep the volume'control setting low for even loudly playing the speakers.
However, the volume control provided in this preamp is a very precise digital control, and can be set
at any level and still have proper tracking. I would not worry about this, it should not be a problem at all.
many preamps. You might have to keep the volume'control setting low for even loudly playing the speakers.
However, the volume control provided in this preamp is a very precise digital control, and can be set
at any level and still have proper tracking. I would not worry about this, it should not be a problem at all.
Just remember to start with the volume setting at zero to start, on either the remote or on the front panel,
until you get used to the normal playing setting.
until you get used to the normal playing setting.
In your opinion, which Is the optimal ratio between pre-output and power-sensitivity?
That depends how loud you listen.
If you are planning on using amp to full power, then you need preamp with enough output to drive the amp to full power, and some reserve.
Reserve is needed as not to clip preamp before even feeding the amp. That tends to sound awfull.
If you only need few watts for highly efficient speakers, no need for preamp, as almost any line source will be enough.
I see you ignore my suggestion about putting pot on the input of your amp. Fine with me, but it would allow you to use any preamp with any gain. Or no preamp whatsoever. Instead you are asking weird question. Buy.
If you are planning on using amp to full power, then you need preamp with enough output to drive the amp to full power, and some reserve.
Reserve is needed as not to clip preamp before even feeding the amp. That tends to sound awfull.
If you only need few watts for highly efficient speakers, no need for preamp, as almost any line source will be enough.
I see you ignore my suggestion about putting pot on the input of your amp. Fine with me, but it would allow you to use any preamp with any gain. Or no preamp whatsoever. Instead you are asking weird question. Buy.
Pot on the input... Maybe a good idea.
I have 99dB speakers and I listen orchestral music.
Which value of Pre.output/Power.sensitivity di you suggest?
Can you work on electronic circuits, like installing a volume control your amp?
What preamp and sources do you use. LP, CD, tape?
What preamp and sources do you use. LP, CD, tape?
Rayma,
No, I'm not able to work, sorry.
Source is CD.
The power amplifier is the Hiraga (20 Watt, sensitivity = 0.6V (thanks again, Ryama)) and speakers are Klipsch RF7 (100 dB @ 8Ohm).
The question is this: I have to buy a new preamplifier.
First, I want to know its electrical characteristics to avoid a wrong purchase.
So, I need to know in advance the optimal range of input impedance and sensitivity.
No, I'm not able to work, sorry.
Source is CD.
The power amplifier is the Hiraga (20 Watt, sensitivity = 0.6V (thanks again, Ryama)) and speakers are Klipsch RF7 (100 dB @ 8Ohm).
The question is this: I have to buy a new preamplifier.
First, I want to know its electrical characteristics to avoid a wrong purchase.
So, I need to know in advance the optimal range of input impedance and sensitivity.