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!


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.

Thanks for the input guys,

@mulveling the noise does not bother me much when the music sounds good so thats not really a problem, only problem is that Im controlling my volume with the preamps remote and the jumps are too high when the amp is fully open. Read somewhere that the pots balance is usually better in the later stages.

@theflattire I would also consider using only the amp but I have 4 sources connected one of which is the phono and since the preamp has the section I would need to alter my system quite a bit.


Try backing off on the amp volume control to where you can use the preamps volume between 9 and 12 o'clock.  That may eliminate the noise while not influencing the sonics. Another approach might be to have the preamp modified to reduce the gain if that is possible. 

There's no technically best answer here, since the actual gain isn't being adjusted.  I think @mesch answer is pretty sweet though.

That is, I don't think the amp volume control will affect the character of the sound at all, just noise, so make yourself comfortable and find the range that works for you.

It's generally true though that most preamps have much more gain than we ever really need, some of that is historical, so you can turn up the volume to hear the faintest of signals on a radio, but in modern times I think it's time for that to be rethought.

@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.