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Amp, Preamp, two volume pots, there can be only one!

Hello everybody,

I have a question regarding the two volume knobs in my system and how they

should co-relate.

Here is my gear, both units are tubed:

Amp: Coincident Dynamo 34SE Mk1 (Output power: 8Wpc, Sensitivity: 300mV for full output, Input impedance: 100k ohms, S/N ratio: 92dB)

Preamp: Doge 8 2018 (Output impedance: 600 ohms, Input impedance: 50K ohms, Input sensitivity: 200mV)

Speaker: Proac 140 Mk1 (Sensitivity 91db, Amplifier Power Range 15 - 250 watts)

Now here is the dilemma, Coincident says if Dynamo is used a power amp the volume pot should be left open (heard that some call it a sensitivity pot too) but this introduces noise in the system (albeit when music is not playing) and leaves a very small usable range on the preamp volume knob, and hard to hit the sweet spot as at 9 o clock its already very loud.

So what would be the best way to run things without losing signal quality? And is there any mismatch between my power/pre?

Thanks in advance for any suggestions!

neverlast

Showing 1 response by mulveling

mulveling's avatar
mulveling
2,190 posts
 

It’s not a serious mismatch per say, it just appears you’ve got a high gain tube preamp without the highest signal-to-noise ratio. Your Doge lists "200mV sensitivity" - if that is in reference to a 2V output, that’s 20dB gain which is very high. Generally, when you get a tube pre up in that range you’re gonna hear low level hiss noise at output (from speakers) unless your speakers and/or amps are low sensitivity. Your amp’s gain (27.6dB) and speakers (91dB) are sufficiently high that this noise floor is totally expected. Tube power amps almost always have pretty high sensitivity / gain - even low power ones like yours! 

So now it’s just whether the noise bothers you enough to cut it down with that amp potentiometer. You might try a little and see if that sounds "transparent enough" for you.

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