>> 2) If I amp calculating system gain in Db, it should be
>> db= 10 log (X1/X2) , should the loss be 0.9db instead
>> of 1.8db?
No, I think that 20log() is correct as we are dealing with power ratios: V2^2/R2 div-by V1^2/R1 where the 2 voltages cancel out & the impedances are ratioed 1:0.81.
>> 3) Does preamp increase current to maintain constant
>> voltage?
yes. that's what Eldartford was stating as well. The preamp should have some negative feedback around it. Thus, as its output impedance increases, it'll draw more current to output the same voltage per the volume knob setting. The power supply should have enough capacity for the job. If it didn't then only would the output voltage drop. So, under the elevated output impedance condition, there'll be more power dissipated in the preamp i.e. lossier load power transfer.
>> 11-03-06: Bob_reynolds
>> But, since its internal impedance increases there will
>> be a larger voltage drop internally. So less voltage
>> will reach the amp.
no, more power dissipated in the pre internally.
less voltage ONLY if the preamp power supply runs out of ability to supply current. Hopefully an expensive pre like the 51SE will have that headroom!
>> db= 10 log (X1/X2) , should the loss be 0.9db instead
>> of 1.8db?
No, I think that 20log() is correct as we are dealing with power ratios: V2^2/R2 div-by V1^2/R1 where the 2 voltages cancel out & the impedances are ratioed 1:0.81.
>> 3) Does preamp increase current to maintain constant
>> voltage?
yes. that's what Eldartford was stating as well. The preamp should have some negative feedback around it. Thus, as its output impedance increases, it'll draw more current to output the same voltage per the volume knob setting. The power supply should have enough capacity for the job. If it didn't then only would the output voltage drop. So, under the elevated output impedance condition, there'll be more power dissipated in the preamp i.e. lossier load power transfer.
>> 11-03-06: Bob_reynolds
>> But, since its internal impedance increases there will
>> be a larger voltage drop internally. So less voltage
>> will reach the amp.
no, more power dissipated in the pre internally.
less voltage ONLY if the preamp power supply runs out of ability to supply current. Hopefully an expensive pre like the 51SE will have that headroom!