Hello!
I have a question concerning preamplifier gain. I designed a preamplifier which is now set for 6dB gain (2x voltage), but I started wondering that my laptop can output higher signal than my mobile phone. Also a RIAA amplifier will output less than the cellphone outputs.
So how is gain controlled in commercial amplifiers? Do they use some sort of autogain or limiting technologies or is it just fixed gain?
I once had an idea of rotary switch which would select the audio input and also select a desired gain level by switching a resistor.
My goal is to amplify or even attenuate the signal to 750mV rms line level using my different audio sources.
I would also be interested in what gain figures are you using in preamplifiers.
Thanks for the answers!
I have a question concerning preamplifier gain. I designed a preamplifier which is now set for 6dB gain (2x voltage), but I started wondering that my laptop can output higher signal than my mobile phone. Also a RIAA amplifier will output less than the cellphone outputs.
So how is gain controlled in commercial amplifiers? Do they use some sort of autogain or limiting technologies or is it just fixed gain?
I once had an idea of rotary switch which would select the audio input and also select a desired gain level by switching a resistor.
My goal is to amplify or even attenuate the signal to 750mV rms line level using my different audio sources.
I would also be interested in what gain figures are you using in preamplifiers.
Thanks for the answers!
Hi . Sources like phone or laptop are partially incorrect for use , they can output different levels of output voltage ,because they have volume control.For best signal to noise ratio, output from source must be close to maximum. But you may have lower distortion at lower levels. Cd player in example , has line out, and not all devices allow to control volume . I had similar problem some time ago, now i don't use any preamplifier, and set volume in pc to about 95percent .
Early preamps had about 20dB line gain, and had a pot at each input, to match the gains of various sources.
Current sources need little or no gain to drive the power amplifier to full output, so the typical line gain now
is from 0dB to 12dB. The less gain, the lower the line stage noise level.
Current sources need little or no gain to drive the power amplifier to full output, so the typical line gain now
is from 0dB to 12dB. The less gain, the lower the line stage noise level.
Search the web for "gain structure". You want to avoid amplifying noise and clipping, which define the "dynamic range" of each stage in the system. If you run a stage at too low a signal level and amplify it later, you bring up the noise with it, so each stage should be operated within, say 10dB of clipping, not more than 20dB. That means run the sources hot and attenuate, ie volume control it at the last possible point. A classic mistake would be to connect a sound card output to a power amplifier without a volume control between them. Each stage should clip soon after the following stage.
Steveu ,very good point about need to have volume control between sound card and power amplifier in between . Regardless how good is sound card ,it will still have some hiss at output ,and when you turn volume down( on pc) , signal gets less loud ,but noise remain . In case there is no volume control .
If you have volume control in between , you can reduce volume lets say 10x times and noise 10x times too . Some power amplifiers have volume control in front input ,thats very poor design . The same apply to preamplifiers .Volume control should be at output . Maybe a buffer with gain=1 can be after volume control , to reduce output resistance and prevent line cable capacity (several hundreds of picofarads) to cut high frequencies .
If you have volume control in between , you can reduce volume lets say 10x times and noise 10x times too . Some power amplifiers have volume control in front input ,thats very poor design . The same apply to preamplifiers .Volume control should be at output . Maybe a buffer with gain=1 can be after volume control , to reduce output resistance and prevent line cable capacity (several hundreds of picofarads) to cut high frequencies .
Putting a volume control potmeter between power amplifier outputs and the loudspeakers has its disadvantages: horrible inefficiency at low volumes, very big potmeters required to dissipate all the power, loudspeaker driving impedance changes with volume setting.
Regarding sound card outputs and audio DACs in general: it can sometimes be a good idea not to drive them as hard as possible, but a few dB softer.
This is related to the so-called intersample overshoot issue; many music recordings have their largest samples normalized to full scale, but that means that the signal has to go above full scale between the samples, and many DACs can't handle that. A bit of digital attenuation can solve that.
This is related to the so-called intersample overshoot issue; many music recordings have their largest samples normalized to full scale, but that means that the signal has to go above full scale between the samples, and many DACs can't handle that. A bit of digital attenuation can solve that.
No, cellphones are not "normal" audio sources; or at least they never were before recent years. (Cellphone audio that didn't suck is 10 years old, High Fidelity is 90 years old.)
Any healthy phono preamp is likely to deliver 3V or more on hot-cut disks, but the average disk can be much less. (Todd's Initiation?)
Have some excess gain in hand.
Put a volume potentiometer where the signal is about 100mV.
There are other ways, and other considerations, but this is an excellent reference. Above universal hiss, but with reasonable headroom for loud sources.
This leads to the classic Hi-Fi staging of gain of 10 in preamp, pot in front. Sensitivity 100mV in to make 1V (near full) at power amp.
If you rule-out some of the extreme sources we used to use, pot into gain of 5 or maybe 3 into 1V-1.5V sensitivity power amp works today.
Any healthy phono preamp is likely to deliver 3V or more on hot-cut disks, but the average disk can be much less. (Todd's Initiation?)
Have some excess gain in hand.
Put a volume potentiometer where the signal is about 100mV.
There are other ways, and other considerations, but this is an excellent reference. Above universal hiss, but with reasonable headroom for loud sources.
This leads to the classic Hi-Fi staging of gain of 10 in preamp, pot in front. Sensitivity 100mV in to make 1V (near full) at power amp.
If you rule-out some of the extreme sources we used to use, pot into gain of 5 or maybe 3 into 1V-1.5V sensitivity power amp works today.
I'm never recommended put volume control before speakers itself , i have meant , volume control must be after preamplifier output and before power amplifier input . But some amplifiers have gain stages after volume control , and and low volume control positions they have audible hiss .
Adjusting volume after amplifier is possible - there are so called line speakers ,120v rated , with transformers inside, used in shops in example, and volume is adjusted in steps for each speaker . They use not potentiometer , but autotransformer and multi position switch yo change taps . Looks like light dimmer pot.