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active or passive preamp for active speakers

i have some active speakers (dynaudio BM5A MKII monitors) and i want to connect a cd player and tuner to them.

would a passive preamp be sufficient? i'm not looking to spend a lot of money on a preamp, and it seems the passive ones are cheaper, and it also seems i don't really need an active preamp, but maybe i'm missing something?

thanks!
tanglewood

Showing 1 response by almarg

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almarg
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i guess i don't understand the purpose of the preamp. since my active speakers don't have volume control, it seems the only thing i need a 'preamp' for is volume control, assuming at least that the signal coming for the cd player is strong enough. and if i hook a tuner up too, then it would need to switch between sources.

so why not a passive preamp to do those simple jobs?
For a passive preamp to provide good results:

1)It has to be driven by components having low output impedances. That is probably not a problem here if the cdp and tuner have solid state output stages, although it could be a problem if either component has a coupling capacitor at its output, which most tube source components and some solid state components have.

2)The amp or active speaker that it drives has to have an input impedance which is high in relation to the passive preamp's output impedance (which will be much higher than the output impedance of a typical active preamp, and will also vary with volume control setting). This might be a problem here -- the input impedance of the BM5AMkII doesn't appear to be specified.

3)The passive preamp has to be connected with short lengths of low capacitance cabling, especially on its output side, but the input side can be important as well. That may also be a problem here, depending on your setup and on no. 5 below (which determines how much capacitance is acceptable).

4)The gains and sensitivities of the components in the system have to be such that the preamp does not have to provide any gain (i.e., any gain greater than 1). That is probably not a problem here. With the tuner, and perhaps also with the cdp, you will probably not be able to drive the speakers to their maximum possible output level with a passive preamp, but you probably wouldn't want to.

5)The architecture and resistance value of the passive preamp have to be carefully chosen in relation to the impedances of the components it is connected to.

The bottom line: I would not proceed in that direction without first somehow determining the input impedance of the active speakers.

Regards,
-- Al
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