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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
atmasphere's avatar
atmasphere
12,061 posts
 

@neverlast With full output at only 300mV your amplifier is far too sensitive. Since it can only make 8 Watts, it has to be used on a high efficiency speaker. So you'll be fighting noise. So yes, that's a bit of a mismatch!

Usually SETs (or SEP in this case) have low gain so as to deal with this issue.

I rarely recommend a passive setup but this appears to be a situation where it would be handy. OTOH, finding an amplifier of similar spec that has a more real-world input sensitivity would help with the noise and you may notice greater low level detail as a result.

r1g450
6 posts
 

A volume control can't alter, distort, overdrive, add noise, etc.. to the signal, other than the impact on sound quality the control itself has. (Gain controls can, but not volume.) It can't add or take away noise. The problem lies elsewhere in the system. That said, all audio equipment is prone to the type of noise you are talking about under certain conditions. It doesn't mean anything is wrong. The simplest and easiest solution is to get some Rothwell attenuators that just go inline on a pair of interconnects. They are made for this specific problem and you shouldn't hear any difference in sound at all. 

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cleeds
6,061 posts
 

r1g450

A volume control can't alter, distort, overdrive, add noise, etc.. to the signal ...

I couldn't disagree more. It isn't clear why you'd make such a sweeping claim.

theflattire
228 posts
 

Like others have said, run up the amp to the noise floor.

Let the pre do the rest.

neverlast OP
15 posts
 

Thank you all kindly for the ideas and advice, I will give everything a try.

@atmasphere in theory which specs would the amp need to have to play along with my preamp?

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