Gain problem

[GoranB]

Hi,

I have 3 way speakers (diamond 10.4) crossower 140hz/3800hz, they are passive.

I would like to build an active 3 way crossower.

1. For bass Frequencies i think it will be the best to use powerfull solid state push-pull amplifier it will work bellow 140Hz.

2. For bass-midrange 140-3800 i would like to use my power follower 99 SE (designed by Andrea Ciuffoli)

3.Above 3800 - also another PF 99.

All amplifiers should have the same gain.


The power follower 99 doesnt have gain, so, im using the tube preamp with gain about 30.

My problem is Push-pull solid state amplifier (Marantz PM44SE) which i like to use for frequencies bellow 140HZ. I dont know the gain of this amplifier, and if there is posibility to change the gain (not using the Volume control), I mean changeing the gain by changeing elements in circuit.

Another question: how can i meassure gain?

Any suggestions are welcomed

[nightanole]

I dont think you can change the gain of the amp very easily, if at all. its Not like a tube preamp where you can swap a 12ax for a 12au.

You could attenuate the signal in with resistors, which would sound better then a pot.

To measure gain, you need a signal gen and a scope or peak to peak multi meter. Then using anything (pc) send a 60hz signal into the amp if it can take it. measure the pp of the input, and measure the pp of the amp out put. Then just do the math. Id try something like 50-100mv for the input as i dont know the gain of the amp. some peak at 100-150mv, some peak at 3volt.

[GoranB]

Thanks for your answer


If i understood you well, for example: I should produce a signal (i think it could be from PC) and bring it to the input of amplifier. I should meassure the voltage on output using the ressistor instead of speaker.
Using the same level of input signal to all amps i should achieve (by changeing resistors on input) the same voltage on the output of every amplifier. That will means they have simillar gain and i could use the active crossover?

[nightanole]

You need use speakers as your load(or a huge resistor) for your tube amps. You shouldnt need a load for your solid state amps.

Yes you can use your pc for a sine wave generator.

yes measure the input, then measure the output. this will give you your gain.

You can attenuate the input on the amps with too much gain by making a resistor network instead of a pot. I would find a pot. Use it to find the right values. then measure the pot and make the resistors from the measurements.

Im alittle off today but this should work. So lets say amp 1 needs 1 volt in to get 100 volts out. It has a gain of 100. Amp 2 needs 2 volts in to get 100 volts out. It has a gain of 50. So you would have to attenuate the signal to amp1 by half.

[GoranB]

Thanks man, i appriciate your help a lot.
Ill do what you suggest. I really hope active system will be worth to build.

Thanks again