SNR, THD+N, Dynamic Range and Impedance

[Johnseye]

Uh, how they sound? My guess is either would be a good choice. One advantage most tube pres have over most SS preamps for phono inputs is the tubes have very high voltage overload so better handle the dynamic range of ticks and pops of records without clipping and splattering harmonics.

Tube components are notoriously under-specified though these days tend to do better. Let me get back to you, or more likely someone else will pick this up. I'm just fly-by posting awaiting a conference call. A quick look does not show SNR specs so hard to compare noise floors.

Do you need a phono stage? AFAIK the LS28 is a line stage only...

I like the balanced design of the MP-3. There are no SNR specs that I saw but everything else looks really good. If you need a phono stage that is the obvious choice, and it appears to have good reviews as well. I've owned ARC gear in the past (still have an SP3A1a in storage) but have a soft spot for Atma-Sphere because they seem more down-to-earth with a little less marketing gloss than some other companies. Note tube phono stages tend to be a bit noisier than SS, probably not a big deal with MM cartridges but in the past I used a transformer with a MC cartridge into a tube preamp.

Probably not much in the way of concrete help, sorry...

They both sound great. I've auditioned about 7 different pre's over the past month. Most tube and a few SS. These two are the final picks. Both sound remarkably similar, and completely different than all the other pre's I've heard. Ironically they're both made in Minnesota. Go figure, must be something in the water.

I don't need another phono stage but I am curious to know how a tube one sounds as mine now is a SS Simaudio Moon. My cart is an MC so my guess is things are going to be a bit noisier. That would be unfortunate if that's the case. I asked Ralph at Atma-Sphere specifically about SNR and I quoted what he told me in my first post. There isn't much info on it and so that concerns me.

Doing a comparison of the two by turning up the volume with nothing playing I can get a rough idea of the difference in noise levels. My hope was to see if I could better understand the specs in the subject, and if there was any way to determine the differences between the two pre's by those specs.

 

[Johnseye]

Ah, now you tell us . There are much more useful measurements there than the spec sheet. Let's review them:

This says there is a very mild 0.5 db roll off at 20 Khz. I am not going to hear that but if you are much younger or have better hearing, you may hear a slight roll off.

That is fairly noisy at low volumes.

Other than that, this is a type of tube amp that tries hard to not be a tube amp with all the problems that brings .

Thanks Amir. Yes, I was trying to keep the names anonymous so the feedback would be as unbiased as possible, but that's tough to do when there isn't enough info to form a conclusion.

 

[amirm]

Pre 2 is an Atma-Sphere MP-3. I haven't found any spectrum for it.

I will be happy to measure it for you.

 

[Johnseye]

I will be happy to measure it for you.

Shipping these things isn't cheap. I appreciate the offer though.

 

[DonH56]

The specs are not complete enough to tell a good story, or paint a good picture, or (insert your favorite analogy here).

My guess is the MP-3 has enough gain for a MC cartridge but will be noisier than your SS preamp. One thing to check is that, with balanced inputs, if the circuits are differential then they will suppress even-order harmonics. This should provide lower distortion overall but also cost some of the stereotypical tube sound that arises from the second harmonic distortion. Many years ago I built (and sold) a fully differential preamp, a one-off DIY project. I also cascoded the input tubes to reduce Miller capacitance, which rolled off the bandwidth of many tube preamps when driven from a high-impedance source. It measured fine, and did OK in listening tests, but a typical comment was that it "sounded too solid-state". IOW, it was a better preamp, but did not provide the sound that tube lovers desired.

I did try a number of phono preamps but liked my ARC's tube input the best. It was not balanced and did have a bit more noise, but overall measured and sounded very well to me. But, as I think I mentioned earlier, it had neither the gain nor the noise floor to support a MC cartridge, so I used a pre-preamp or (most often) a transformer before the ARC to provide an additional voltage gain stage. Most of the carts I actually owned were MM (working for local audio stores with understanding bosses let me try out far more stuff than I had a right to as a cheap college kid).