This thing is really quiet

[Thijs]

I just wanted to leave a quick post of appreciation on just how quiet the SII operates.
Right now I have the amp coupled to a pair of GPA 604-8HIIIs and it's simply dead quiet. No hiss, no hum, no nothing. This comes as quite the surprise as these are pretty high sensitivity speakers around 99db. (although I can't seem to confirm this spec, it's based on available specs from previous iterations of the driver).

This is a bog standard version of the SII as well, mind you. No internal upgrades, just some different tubes. Telefunken ECC801S and JJ 2a3-40.

Now what to do with the now spare DC filament supply upgrade I bought in advance... 

Cheers,
Thijs

[Paul Birkeland]

With 99dB sensitive speakers, you should be able to hear some 60Hz hum, and likely if you place your hand on the woofer, you'll feel it moving a little bit. 

Having said that, the difference in noisefloor won't be as dramatic as it is when installing the DC filament upgrade on a Kaiju.

[Jay]

I have the same amp and speakers.  I had just a bit of hum with mine before installing the DC filament kit, but now it is very quiet.  To my ears, the SII and the GPA 604s work well together!

[Thijs]

Thanks PB, I'll try to listen/feel for the 60hz hum when I get the chance.

I agree Jay, it sounds like a great combo! Right now I only have them up in JE labs style open baffles and I'm already pretty amazed at the quality of sound. Can't wait to put them into proper cabinets. 

[Thijs]

So my system is currently located at my dads house and I had him check the noise and hum again. He says there is nothing to be heard from the driver. It also doesn’t vibrate at all. And that’s at the maximum volume setting. So, congrats! I’m really happy about this... if only my Eros was this quiet. 

[Paul Birkeland]

For most of the folks I've talked to who haven't been happy with the Eros noise level, they have been using lower output cartridges.  Though the Eros will work with those cartridges, it will be quietest with a 5mV cartridge or a proper MC cart stepped up to about that level with a pair of step-up transformers.

[Thijs]

For most of the folks I've talked to who haven't been happy with the Eros noise level, they have been using lower output cartridges.  Though the Eros will work with those cartridges, it will be quietest with a 5mV cartridge or a proper MC cart stepped up to about that level with a pair of step-up transformers.

Thanks PB

Yes I’ve thought about this as well. I’m using a Dynavector 20x2H cartridge. That’s about 2.8mv output. I’m not too well versed in the world of step up transformers but would there be something I could do to increase the voltage? A 1:2 ratio sut maybe?

[Paul Birkeland]

The Sowter 1090 is setup for that.

[Thijs]

The Sowter 1090 is setup for that.

Thanks for the suggestion, Paul! I'll make sure to look into it. Sending 5.6mv into the Eros will probably be fine, right?

[Paul Birkeland]

5.6mV should be fine.  In reality, the 1:2 step-up will end up being a bit less than that.

[Thijs]

5.6mV should be fine.  In reality, the 1:2 step-up will end up being a bit less than that.

That's great! Thank you so much. I suppose it's safe to assume that the resulting (roughly) 2v output from the Eros won't overdrive or clip the input of the SII?

[Paul Birkeland]

The input of the Stereomour II, assuming it is built stock, can take over 200V before the pots will be marginalized.  The amp would be unusable with this much signal coming into it though because any position of the volume pot other than full mute would indeed overdrive the amp. 

The amp will take 2V at the input and lose 4dB from the volume/balance control, even with everything turned all the way up, so that's now a maximum of 1.26V RMS.  The input stage can take up to 1.4V RMS before being overdriven, and the output stage won't really be able to make use of that full voltage swing, so you'll just barely be able to clip the amp.

[Thijs]

The input of the Stereomour II, assuming it is built stock, can take over 200V before the pots will be marginalized.  The amp would be unusable with this much signal coming into it though because any position of the volume pot other than full mute would indeed overdrive the amp. 

The amp will take 2V at the input and lose 4dB from the volume/balance control, even with everything turned all the way up, so that's now a maximum of 1.26V RMS.  The input stage can take up to 1.4V RMS before being overdriven, and the output stage won't really be able to make use of that full voltage swing, so you'll just barely be able to clip the amp.

More great news, then! Thanks Paul. I think I understand what you're describing. I already have the MourQuiet on hand ready to be installed in the near future, will the loss of signal be the same as the stock pots? Or would I have to look at maybe padding the input of the SII?

[Paul Birkeland]

The MourQuiet and the stock level controls have about the same insertion loss.

If you had 110dB sensitive speakers and maybe some audiophile CD player from 1995 that put out 5V RMS, then maybe padding down the inputs of the Stereomour would be a good idea. 

[Thijs]

The MourQuiet and the stock level controls have about the same insertion loss.

If you had 110dB sensitive speakers and maybe some audiophile CD player from 1995 that put out 5V RMS, then maybe padding down the inputs of the Stereomour would be a good idea.

That's awesome! Thanks so much for your assistance. I've reached out to Sowter about their transformers and ,thanks to you, feel confident in proceeding with everything.

Regards,
Thijs