My 1st Tube Equipment Experience

I just purchased a used Herron Audio VTSP-3A(r02) tube preamp, as a replacement for a NAD M12.  I paired the M12 with a NAD M22 v2.  My first impressions are the M12 has more detail, the VTSP is much warmer, which is what I wanted.  The VTSP sound is definitely different.  And while it lacks the M12 detail, I do like it.  

With the M12, my speakers were dead silent when music was not playing.  With the VTSP, I hear a slight hiss when I put my ear very near a speaker.  With the M12, I used XLR from the M12 to the M22; XLR from my Parasound JC3 jr; and RCA from my Liberty DAC.  With the VTSP, everything now is RCA.

Is a little hiss common when using a tube preamp and SS power amp with RCA cables?
Did you try both gain levels on the preamp with all three gain levels on the amp to try and find the best match?  Other than that with a speaker of average or higher sensitivity it is not uncommon to hear some small level of tube hiss if your put your ear right up to the tweeter. 
Dropping the gain level on the Herron to the low gain position should pretty much eliminate any noise even right at the tweeter. Then you can leave the amp on the default(shipped) position. Should also give you more "travel" on the volume control. 
For my taste, it sounds like you made a backward move. Never give up detail.
Frank Van Alstine used the 5751 tube in place of the stock 12AX7 in his Dynaco PAS pre-amp mod. Quietest tube pre-amp I've owned, or even heard. The 5751 is a little lower in gain than the 12AX7 though. Has anyone tried a 5751 in the Herron?
@noromance  In general I would agree.  The M12 is a too bright; I also don't use it's DAC, BluOS module, or phono inputs.  If the Heron doesn't pan out, I'll look for something else.  
@bdp24 " Has anyone tried a 5751 in the Herron "
Tubes in Herron's are 6992s not 12ax7s/5751s
Ah, I was thinking of the Herron RIAA phono amps, which use 12AX7's and 12AT7's. Never mind ;-) .
With the Heron volume level set to 60 and the M22 gain set to Low, the sound was hollow.  With the Heron volume level set to 60 and the M22 gain set to Mid, everything opened up.  The detail is there, and the sound is so much more musical with a wider soundstage than the M12.  The M12 is a good piece, but as my system has evolved, the Heron fits soooo much better.

While the hiss is still slightly there, it is less with the M22 gain set to Mid.  I’m satisfied (at least for now).

Is that with the preamp’s gain set to high or low? Also what speaker are you using?  If you are having to put your ear to the tweeter to hear the hiss then you are good to go so just enjoy what the Herron brings to the table. 
This preamp has no gain setting that I can find, at least on the outside.  My speakers are Tannoy 8 dcti.  And yes, I have to put my ear to the tweeter to hear the hiss.  

I like the Heron paired with the M22 v2.  I’m hearing all of the detail I heard with the M12, without the “glare.” 
@jmolsberg.  I see said the blind man!

I'm not yet sure what mode the Heron is set to.  I like what I hear now, but I'm definitely going to play with the M22 and Heron gain modes today to see what happens.  

Thanks to everyone for your help.  I'm really enjoying my 1st tube preamp experience.
@oldschool (:

that is one fine pre amp good sir. and if you bought it new, it is only get better. match this to the Herron VTPH-2A!
@jmolsberg.  I bought it used.  The VTPH-2A would be a nice addition I’m sure - if I could only sneak it in the house without my wife noticing (:

Herron gain was set to Low.  I set it to High and left the M12 at Mid.  I had to lower the volume to around 35.  Sounds OK, but I like it better the way it was.  I’m going to play with different combinations later today.  Of course, the tweeter hiss is a little louder in the High position.
The tube hiss probably because of poor AC filtering.  Adding a choke ot filter the AC may help and may also add the details back.

Happy Listening.
All of my components are plugged into a Furman Elite-15 PF power conditioner. The Furman is plugged into a PS Audio receptacle, which is connected to a dedicated AC line.  I use WireWorld and VooDoo power cables; with a VooDoo cable to the Herron.

Regarding the AC filter, are you referring to something like this:  

I was researching the viability of using an RCA to XLR cable, with RCA on the Herron and XLR on the M22.  Might that help, or is it a bad idea.
I was researching the viability of using an RCA to XLR cable, with RCA on the Herron and XLR on the M22. Might that help, or is it a bad idea.
It won't make any difference. What might help though is to make sure you have a jumper installed in the M22 between pins 1 and 3 of the XLR when using the RCA input. This will prevent pin 3 from picking up noise.

The RCA connection is single ended and that won't change if the other end of the cable has an XLR connector on it.
I've finally found my sweet spot with the Herron and NAD settings.  The Herron gain is set to low; the NAD M22 v2 gain is set to mid.  Now I understand why many here have recommended a tube preamp and SS poweramp.  I'm quite happy with the Herron/NAD combination.

I also re-positioned my speakers.  I have a small 11x12 listening room.  I placed the Tannoy's 36" from the back and side walls, and toed them in about 3/4 of an inch.  My two listening chars are a little more than equidistant between the speakers.  No more glare and I can listen for hours with no music fatigue.  I'm finally enjoying digital music as much as analog. 

Now I'm wondering what a better DAC would do.  I have a Mytek Liberty, which sounds pretty good with my current setup.  My planning budget is ~ $2.5K.  Suggestions anyone?
My preference is a tubed NOS R2R dac, very analog sounding. 
I have been very pleased with my Audio Mirror Tubadour III. Sound wise it comes pretty darn close to my analog - VPI, dynavector, Herron audio vtph-2a. 
The Tubadour III looks interesting, the Tubadour Signature edition even more so.  Audio Mirror's trial period makes this even more interesting. 

@jmolsberg   Thanks for the suggestion.

@atmasphere I'm also wondering how much better a Herron VTPH-2H would sound than my Parasound JC3 junior :)
Couldn't tell you as I've not heard them but I can tell you I prefer tubes especially in preamps. You need them to get things right at the front end of the system; no amount of the best amps and speakers can bring back missing elements in the signal if the preamp doesn't do its job.
@oldschool1948-  When you're ready to try a little experiment, PM me.  I'll send you a nice pair of Amperex 6922s(no strings), to try in your Herron.  Even two out of six, should give you an idea of what's available, if you roll.  btw: Would your Old School 1948, happen to be a Pan?
I re-read my post. Blows away is not accurate. I am passionate with regards to the vtph-a, it is the best I have heard.
@rodman99999 I’m new to tubes and have never rolled tubes. All 6 tubes in the Herron VTSP-3A are of the type 6922.  What's different about the one's you are offering?
There’s a 99.99% chance that they are much better, than what you got with your preamp, without exaggeration. It appears you have an ear for sound. I’m simply offering an opportunity, to hear what’s available, without spending any money, outside of the postage to return them to me, after you’ve experimented. Call a couple tube vendors and ask them about 1960 to 1962, Amperex, Navy 6922s(gold pins).
@ oldschool1948      My email service(Spectrum/Roadrunner) is down. Lots of angry postings, regarding the situation, online. Now, the link to PM you with, isn’t available here either, for some reason.
My Tubadour Signature arrived today.  The DAC came expertly packed.  The build quality is excellent and it looks good.  And, it was a pleasure doing business with Vlad.

Out of the box, the Tubadour sounds much better than my Liberty DAC. It should considering it cost more than twice as much.  I didn’t know what to expect; better sounding for sure, but in comparison, this DAC is in a different league.

The Tubadour sound is lush, more detailed, with a wider soundstage.  I fits very well with my existing equipment.  I can’t imagine how much better it will sound once it’s broken in.  I plan to do some serious listening over the next couple of weeks.  

I’ll be selling my Mytek Liberty DAC starting tomorrow :-)

@jmolsberg  Thank you for mentioning the Tubadour DAC.  Next up, a better phone preamp than my Parasound JC3 Jr.  I think I see a Herron  VTPH-2A in my Christmas stocking.
A quick follow-up after a half-day of listening to music with the Tubadour DAC in my system.  I get the best SQ with the Herron pre-amp gain set to Hi and the NAD pwr amp gain set to Lo.  (With the Liberty, the Herron was set to Lo and the NAD to Mid.)  

I've also noticed a larger difference in sound volume when I switch between my analog and digital sources (Analog: Technics SL-1200G w/ Ortofon Quintet Black/Parasound JC3 Jr; Digital: Innous Zenith MKII/ sonicTransporter with Roon DSP/Tubadour DAC.)  In summary, at the same volume setting, when I switch between inputs, the digital music is noticeably louder.  With the Liberty DAC, the music was also louder, but there was much less of a difference.

I was thinking of adding an Ortofon ST-7 SUT to get more analog gain, or buying a better phone pre.  Thoughts anyone?

It's normal enough to have louder digital. As long as your vinyl sounds good, don't get hung up on the difference. 
@noromance  That's good food for thought.  I have to increase the volume, but the vinyl sounds awesome.
you're welcome. i certainly wouldn’t worry about two different sources being at a matched volume. it’s cool for A/B-ing, but thats about it. more importantly is how is the sound? the vtph-2a will take your vinyl experience to another level.....
It's normal enough to have louder digital. As long as your vinyl sounds good, don't get hung up on the difference.
+1 really good advice!
@atmasphere I'm also wondering how much better a Herron VTPH-2H would sound than my Parasound JC3 junior :)
I finally purchased a Herron VTPH-2A. As it say's on Keith's site, "Immediately you know!"  As recommended in the manual, I started listening without loading plugs.  Paired with my Herron VTSP-3A(r02) pre amp, out of the box, everything is better than the JC3jr, but, I wasn't blown away by the sound.  After a few days, I tried a couple of different loading plugs.  When I installed the 500 plug, the difference in SQ was everything I could hope for.  The sound is rich and full, with much better imaging, sound stage, and definition. 

I have a Technics SL1200G w/ Ortofon Quintet Black cartridge. For the last several days, I've been listening to my old Marvin Gaye, Maze, War, etc., albums that I've had for over 40 years and have played many times on other TT/system setups.  It's hard to put into words how much better they sound.  I certainly expected improvement. I had no idea how much better it would be.  I am one happy camper!

Congrats. I've heard so much about the Herron but it's expensive and I'm not sure it would beat my modded Croft. 
Expensive is relative.  Having said that, I felt the same way.  I was fortunate enough to find a used mint condition one at a very good price.