Ming Da MC34B....passive or active pre amp?

[Paul Dimaline]

I have the above amp but I am a bit confussed as to wether the pre amp is an active stage or just a simple volume pot.

It has a pair of 6N1 driver tubes and a pair of 6N2 pre amp tubes. I was under the impresion that the driver tubes are a part of the power amp section, but are the pre amp tubes just that....a pre amp?

I only want to know as I was considering using it as just a power amp. I dont have a scematic but have traced the signal from the selector switch to the volume pot, then to the pre amp tubes and then to the drivers. The pre amp tubes are center bottom and the driver tubes on the outside. You can just see the black signal wires going to the 6N2's

Sorry if this is a dumb question but I just dont get it!

[jo-briggs]

As far as I was aware, it is basically a power amp, feed it from your CD/Tape/Tuner or whatever - why worry about the circuitry, just play the music. The only problem is that it has no facility for recording to tape, so you would have to make your own arrangements.

[lt cdr data]

Hi Paul, its a bit of a misnomer a preamp stage.

What happens in this kind of amp is that the output stage is called push pull.

This means that one el34 amplifies half the waveform, the other the other half.

To do that, you need a phase splitter which is the middle valve.

The purpose of the first valve isn't really a preamp as such, preamp means before amplification.

It goes back to the old days of vinyl, when your cartridge was amplified by your riaa amp, it didn't have enough volume, so it was amplified some more, by a pre amplifier.

so a phono stage is a pre pre amplifier, and you even get a pre pre pre amplifier with an moving coil head amp by which its more commonly known.

Pre amps come now in a number of forms, because cd gives much more 'volume', we don't need an amplifying preamp, so we can use a passive, just a volume control.

There are a few amplifying preamps, you can use tubes, chips or discrete transistors.

You can also do it with transformers.

So yours is really an integrated amplifier( some integrated amps have a passive preamp built in and some an active, techically, power amps typcially have 3 stages, so you can say its either a power amp with a vol control, an integrated, or a power with a passive preamp, its not that straightforward), with a volume control on the front, the first valves job is to boost the 'volume' of the signal, it is 'pre' or before the phase splitter, but to truly understand what the preamp stage is, you have to know where the output is taken.

Its a passive if after the volume pot, or active if after the tube.

look to the output and you will understand