A Very Nice Tube Phono Preamp

Yeah, Angela has a lot of sockets. As I said, if we’re building it again I would use something like that instead of the Teflons.
 
I just had an interesting preamp comparison experience. My son brought over his phono preamp during the Thanksgiving holiday and we swapped the two preamps in my system. His preamp is a similar design and uses similar components but there are also a lot of differences. As you can see from the photo, his is a 1-chassis preamp with the power supply and audio circuitry all in the same compact chassis. Not so obvious are some other differences. Like me he uses Slagle copper SUTs but he potted his and mounted them on the preamE0F341E3-0584-45E9-B4C3-38A2F3C1611D.jpegp chassis; he also uses completely different tubes—RCA 280 rectifier and Western Electric 420a and 396a; he has CCS loading for each tube with cap coupling on the output; and he uses a choke-input power supply with vintage PIO filter caps. Similarities include Copper V-Cap coupling caps and several Audio Note Silver tantalum resistors.

With the higher gain 396a, my son’s preamp has more gain. We are estimating his has about 17db more output based on settings of my AVC.

So how does the different yet similar preamp sound? Somewhat to my surprise, the two preamps were very, very close in sound. Similar tonal balance, and very similar detail and dynamics. To my ears the Western Electric version has slightly more solid and weighty bass and slightly brighter top end, and mine has slightly more delicate detail in the midrange. My son said my preamp sounds a bit mellow and his is a bit more lively.

To put things in perspective, we also swapped output cables on my Slagle SUTs, and the differences between the 3 cables we tried were greater than the differences between the preamps themselves.

The preamp swap was as fair an A/B test as I can imagine. We used the same power cord and other cables and each preamp was located on the same shelf of my Box Furniture rack.

All in all, a very interesting listening experience.
 
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In Post #19 I mentioned I was using a different Earth connection for the two chassis. In my original build from 2007, I had a 10 ohm buffer resistor in the PS chassis; in the new build I moved the buffer resistor to the audio chassis. Well, I have now reversed course and am back to the resistor in the PS chassis. This means I no longer have a separate Earth wire in the umbilical. The B- (ground) line is now connected directly to chassis ground in the audio chassis.

In theory my B- line now has power line hash added to it. All I know is that it sounds better in my setup with the buffer resistor in the PS chassis. I would describe it as more solid, more direct, more grounded (pardon the pun). Of course, you don’t need to believe me. Try it both ways and reach your own conclusions.
 
Looks great!

I have quite a few parts that could work for this phono but have learnt that parts make more difference than i ever thought. This was most evident when working on the crossovers of the speakers, so would be wary of using diferent parts.

Having said that i have a PSU from a AudioNote phono that could work for this and id expect it would be good. I have a few D3A tubes but lots of the we417a (actually two matched pairs but loads of uk military equivalent ones), i think i also have a few we420, maybe some deviation would work OK.

I think as soon as this covid stuff is over ill be able to get some boxes made for my power amps and do some boxes for a 2 box phono stage at the same time and give this a go.
 
Since we were talking about trying different components yesterday, i remembered that there are new AN resistors, have you tried them?

Here
 
Since we were talking about trying different components yesterday, i remembered that there are new AN resistors, have you tried them?

Here
I tried a pair of the 2W Niobium resistors - in my DAC on the cathodes of a 27 tube. Overall I prefer AN silver tantalums to the Niobiums, but would use the Niobium before any of the lesser tantalums. The Niobium had smooth, crisply detailed highs and a more full, present, and even/balanced midrange.

The AN silver tantalums are my favorite resistor. They account for half of the resistors in the signal path of my phono stage (2 of 4!).
 
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