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The Audio Gods are tough but fair-Have you had the "Curse of the 300B" ?

These amps can really pull you in to hear the singer. The voice instrument is so spot on it can provide moments of disillusionment. For example, I've always preferred Sam Cooke's Live at the Harlem Square Club over Live at the Coppa.  The former is way more free and pushes the R&B needle.  It's musical and soulful.  On my 300B setup I agree with that but I also can put Live at the Copa on and be drawn in... in so much that I start enjoying that album as much as Harlem Square. My attention gets focused on the music and not that this isn't my favorite Sam Cooke album.  And I start hearing and feeling things in the vocals that weren't present before. It's wonderful in the truest sense. 

The 300B SET also delivers smaller group instrumentals like no other.  Drums in the jazz, acoustic/folk settings are sublime.  You really identify the drum skins. You do this sonically more than viscerally.  It is, however, intoxicating.  

When done right these amps can be captivating.  But the 300B mistress is not without its issues.  

-You have to mate it with more sensitive speakers.  This is huge.  You are no longer looking at the lion's share of state of the art loudspeaker reviews.  No. You are searching for sensitive, efficient speakers because the 300B runs out of gas real quickly. 
-You have few choices in amps, 
-You have few choices in tubes and they get really expensive for the 'premium' makes.
-You are likely listening at below moderate to moderate volumes. 
-You may keep a second system to use outside of 300B time. 

When I go back to push pull, or even solid state, I immediately appreciate the power and increased visceral impact.  My attention, however, gets more easily lost, and while they don't sound "bad", I lose the clear window into pieces of the performance.  Subtle nuances of how the singer's voice has personality arising out of the phrasing and tone of the vocal.  Instruments with the 300B sound more "instrumenty".  I don't consider any of what's lost when switching to push pull to be hyper detail or analytic.  Instead, it's characteristics of the sound that aren't there leaving less of the inherent personality of whatever sound is being reproduced--vocal, instrument, or the room in which the performance is taking place.

And so I've done things with my system to help it when it's in 300B mode and push pull mode.  For 300B, I added an REL subwoofer and a second Sumiko I had laying around.  I use those to load the room and expand low end but increase soundstage and make things sound bigger with few watts.  For the push pull setup, I've got the input source all tube whether digital or vinyl.  

This leaves me with the feeling that the Audio Gods are tough but fair.  It's hard to have it all with SET or PP.  Nonetheless, my mind seems made up that it seems easier to work within the 300B setup to make it better as opposed to the push pull. 

As a total aside, I am not the audiophile sage that many are on this forum or out in the audiophile-wild.  I will say with confidence though that if you love hifi you owe it to yourself to spend a month with a SET amp coupled with efficient speakers. 
jbhiller

Showing 3 responses by cal3713

cal3713's avatar
cal3713
1,421 posts
 
For people with poor matching speakers who still want some of the 300b set magic, there's also the possibility of adding a "booster amp" such as the first watt F4. As outlined in the below 6moons review, you can drive this amp directly from the speaker outputs of your set. The set provides all voltage gain and the F4 provides the full current necessary to respond to difficult loads. Depending on setup, the set can simply see a perfect 8 or 16 ohm load and thus can be run with minimal distortion.

Or, as I will probably do with my Coincident PRE's, if you've got bi-amp compatible speakers, you can use the f4 to take the bass load off your primary amp. Because it has zero gain and is being driven directly by the set, you do not get the normal coherence issues that come with bi-amping. It's no longer available from new from FW/Pass, but thanks to the generosity of Nelson Pass et al. you can build one yourself for under $1k...

https://www.diyaudio.com/forums/pass-labs/234355-guide-building-pass-f4-amplifier.html

https://6moons.com/audioreviews/firstwatt6/f4_3.html
cal3713's avatar
cal3713
1,421 posts
 
@jbhiller  Don't know why my @ didn't work on the last post...
cal3713's avatar
cal3713
1,421 posts
 
@jbhiller You’ve got to use some homebrew cables that are speaker level (spades, bare wire, or whatever) at one end and RCA at the other... use a multi-meter to check whether black or red is tied to ground at your SET output. That will then connect to the outer jacket of the RCA plug. The other wire will be your signal wire going to the RCA pin.

If you’re driving only the F4 with your SET, you’ll also need to add a resistor across the SET’s outputs... probably somewhere between 8 and 16 ohms. When driving only the F4, your SET will essentially be unloaded, so you need to add some resistance to prevent damage to your tubes and transformers. Ideal resistance is whatever the SET was optimally designed to drive... and it should be easy to experiment to see if you get a cleaner signal when it’s seeing a particular load. If you’re using the F4 in a bi-amping setup, then you don’t need to worry about this aspect (as the SET will still be loaded by the midrange & tweeters).

Note that Mark at RenoHiFi used to make these cables for customers, so perhaps you could pitch him to buy a pair if you don’t feel comfortable building your own. Also, I had some trouble decoding this from the writing, but all the quotes you see in the 6moons article are directly from Nelson Pass. I think he’d probably provide a bit of input too if you wanted to get it directly from the source. Unfortunately I haven’t yet implemented any of this, so it’s all still theoretical on my end.
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