A Very Nice Tube Phono Preamp
- Thread starter Salectric
- Start date
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 pream
p 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.
p 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.
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.
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.
Sadly, yes I never wrote anything down. I will try to sketch out the basic circuit this weekend and post some more details in another thread.
I haven’t tried them but Michael has so I will let him reply.
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!).
Thanks Michael, ive been pleased with the 2w magnetic ones so far and havent tried the silver ones yet (i have 2 of the 1/2w silver ones to try on my earphones when i get the soldering iron out next). I need to get a few resistors, one being a cathode resistor for the driver tube so will give the Niobium ones a go there.
Hope you like them. Peter Q has indicated there will be a silver niobium resistor at some point, which could be better yet.
Hi all,
My first post at this Forum
A question to Salectric: you have used Slagle 1:1 as OPT. I believe you used this because you had it on hand. 1:1 turns ratio is not common to use as OPT, do you see this as optimum or would you recommend something else? Others can give their opinions as well on optimum OPT specs for this specific case.
My first post at this Forum
A question to Salectric: you have used Slagle 1:1 as OPT. I believe you used this because you had it on hand. 1:1 turns ratio is not common to use as OPT, do you see this as optimum or would you recommend something else? Others can give their opinions as well on optimum OPT specs for this specific case.
If this were a linestage, an OPT with a stepdown ratio would make more sense since it gives a low output impedance and typically a linestage these days needs minimal gain so the loss of gain would not be a problem. It's different with a phono stage. You usually don't want to throw away gain, and that's especially true with this design where the gain is adequate but there is none to spare. Also, output impedance is usually not a major issue with a phono stage since it typically feeds an active linestage via relatively short cables.Hi all,
My first post at this Forum
A question to Salectric: you have used Slagle 1:1 as OPT. I believe you used this because you had it on hand. 1:1 turns ratio is not common to use as OPT, do you see this as optimum or would you recommend something else? Others can give their opinions as well on optimum OPT specs for this specific case.
Lastly, Dave Slagle says a 1:1 sounds better than a stepdown transformer.
Thanks Salectric. My system has a passive Slagle AVC + 300B SET amp, if I remember right you had a very similar type of a system. So there should be no issues with compatibility?
It is few months since last posts in this thread. It would be nice to hear if anybody has built a unit with this schematic. I think I will give it a try and start a build. I have a really nice solid state phono pre by Whest Audio, and it has been playing already over a decade. However, it would be nice to do some DIY work and see how this tube amp will cope with Whest.
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