A Very Nice Tube Phono Preamp

There is a long-running thread at the Haven titled "Building the World's Best Tube Phono Preamp." It's now up to 46 pages and is chock full of interesting information but unfortunately it can be difficult to locate particular posts in the thread due to its length. In fact, it takes some real digging just to find the schematic of the D3a/5687 design. Therefore, I thought it would be best to start a new thread to share details of some recent changes. For anyone who hasn't seen the original discussion, it's right here:

HiFi Haven Group Project - Building The "World's Best Tube Phono Preamp"

First of all, let's clarify the title. I am not in any way claiming this design is the world's best phono preamp, tube or otherwise. The original title on the other thread originated with the Prime Minister (who was probably just trying to stir up trouble). I will just say that this is a very nice sounding preamp that can hold its own in comparisons with some pretty expensive commercial preamps. How close it gets to "World's Best" will ultimately be up to each builder.

Secondly, this is hardly a kit with detailed construction details. This is a project for someone who already has some experience in building electronic gear, can read a schematic, identify parts, and knows something about circuit layout. If you qualify and you would like a nice sounding phono stage, then this might be just the ticket. Otherwise maybe you can get a custom builder to build one for you.

Lastly, let me state at the outset that the circuit as I built it uses BlackGate WKZ capacitors which are no longer made and no longer available at pretty much any price. That's unfortunate because the WKZ caps are the best sounding caps I have ever used. Of course, the circuit will work just fine with other filter capacitors; it just won't sound the same as the version I am using. Also unfortunately I can't recommend a substitute because I haven't tried any caps in this design except BGs. I used to recommend Jensen 500v electrolytics but they were discontinued recently as well.

I first built the original version of this design way back in 2007. It was based on a build diary written by Stephen Robinson (a/k/a "Izzy Wizzy") who chronicled his evolution in DIY phono preamps. The one I built was closest to his Mk 15 which gives you an idea how many variations he tried up to that point. Check out Izzy's site for full details on his evolution up to that point as well as afterwards.

Development Phono – Izzy Wizzy Audio

Anyway, my build turned out so well that it has remained a fixture in my system for the past 13 years. Not that it has remained the same during those years. Quite the contrary. I tried all sorts of variations in power supply topology and audio circuitry as well as component parts before finally settling down with the version described in the "World's Best" thread. Yet it has always been my intention to build a "final" version once the design choices settled down. I guess after 13 years it's time to do just that.

The big change in the schematic is I am now using Output Transformers instead of coupling caps. I actually installed the OPTs in the old preamp so I could do a fair A/B against the plate CCS/coupling cap design. To my surprise the sound did not change much at all. The OPTs sound slightly more direct and less "mechanical" than the CCS/coupling caps; but these were slight differences. I wasn't even aware of a "mechanical" coloration in the old version until I heard the preamp without it. Sorry if that term sounds too wishy washy but that word is what popped into my head when I heard the sound with OPTs. What I am trying to describe is the CCS/coupling cap had some artificial colorations that I wasn't aware of until they were gone. However, the OPTs do not have quite as much weight in the bass as my old version, probably due to the big 2uf V-Cap couplers I used before. In any case, the take-away is the OPTs sound very good and they are certainly simpler for a DIY project. They will even save some money compared to a pair of expensive output caps.

I also simplified the power supply filtering for the D3a input tubes, eliminating a resistor and one cap for each tube. I did that primarily because I wanted separate caps for the final filtering for the second stage since there was no longer a CCS to isolate the channels from one another. I can't say whether the simplified PS for the input tubes helped the sound or not, but it may have. In the past I have generally noted improved sound quality whenever a filter stage was eliminated. The circuit is still very quiet so I would opt for the simpler design even if I didn't need the extra filtering for the second stage.

I haven't tried any other OPTs than the Slagle 1:1 nickel trannies so I can't say they are the best, but they certainly sound good to me. I used these previously as ITs in my 46 SE amps so they were already broken in.

One more comment about components. With the exception of the BG caps, nearly all of the parts I used are still available. In my schematic I am very specific about the parts I used for the simple reason that I have tried many different types of resistors and capacitors and the ones listed are the ones I found to sound the best. Considering all the time and effort I put into the part sampling, I am happy to share my findings and recommend them to others. However, they are by no means required for the preamp to work and sound decent. You can build this design (or the CCS/coupling cap version) for much less money and you should still have a pretty good sounding and quiet phono stage. Nevertheless the parts I used are the ones I think sound the best. This circuit can be built at all sorts of different levels all depending on your interest and budget.

With a circuit this simple, everything matters. Every part, every wire affects the sound. That's probably true with every hifi component but with a simple circuit I think it's easier to hear the effect each time you try a different part. For example I have literally spent the last month trying different chokes for the 5687 filter (8 at the last count) and even more types of wire for the power supply lines. Every part affects the sound, and every part requires time to settle in which makes the evaluation process even more time consuming.

Photos will follow.IMG_1924.jpgIMG_1926.jpgIMG_1925.jpg
 
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And some progress shots during the construction.
 

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Hmm. Not sure why the photos are so fuzzy. I will try reposting them from home to see if I can improve on the picture quality.
 
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Wntrmute2

Not So Mediocre Member
I remember when someone said we don't do enough DIY to merit its own forum. I beg to differ at this point - not that I think we need to add one - just interesting how much DIY goes on here and the cast of characters we have slapping stuff together!
 
For some reason a couple of my under-the-hood photos didn’t post. So I will try again.
 

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The detachable power umbilical has been a godsend considering how many times I have removed a chassis to try a different part.
 

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MrEd

Senior Nobody
Thank you for sharing Sal.
I will dig in and read later after work... goofing off right now...
Vert excited about this.
 

marantzfan

Administrator
Staff member
I remember when someone said we don't do enough DIY to merit its own forum. I beg to differ at this point - not that I think we need to add one - just interesting how much DIY goes on here and the cast of characters we have slapping stuff together!
Oh, it was never a question as to whether or not we had enough DIY content. Rather, the decision was made to not separate out DIY as our intent was not to silo groups into smaller forums.

DIY has it's place in this hobby and there is no reason we shouldn't discuss DIY and off the shelf solutions in the same place. Both are equally valid.
 
In my schematic of the power supply, I forgot to label the choke in the power supply chassis. It is a vintage Chicago RH-1085 rated at 10H @ 85 ma. I bought it on EBay as NOS still wrapped in paper and in the original Chicago box. I have to confess—this choke is the one thing in my preamp that I have no idea how it sounds. It looks so cool I just had to use it.
 

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MrEd

Senior Nobody
I like the Slagle iron, but have to ask about the the 4 henry choke.
Ihow you arived at that value and is there a reason for having Dave wind it?
Inquiring mind here :)
 
I am glad you asked about the Slagle choke because that's a spot where I spent a long time trying different units. The others varied in value from the 4H Slagle to a 30H Hammond. The chokes all sounded different but I don't think the inductance value was a significant factor. For example, one of the Hammonds I tried was a 5H and it sounded more like a 30H Hammond than the Slagle.

For whatever reason, I preferred the sound of the Slagle choke over the others I tried. The Slagle is a bit more detailed and has deeper, tighter bass and more extended highs. It is not warm or rich sounding like the Hammonds (and I happen to like a warm, rich sound) but ultimately I chose the Slagle for its faster, more extended highs and better detail.

One of the things I like about the Slagle is you can use your own choice of connecting leads and those make quite a difference in sound. I tried a half dozen types of wire on the Slagle before settling on the particular wire shown in my photos of the completed preamp. The blue wires in the photo are Neotech 20g solid Silver with Teflon insulation. The Neotech wire has a warmth in the lower mids that nicely complements the Slagle's own sound.

Most of the other B+ wiring is a thick white bundle. These wires are VH Labs CU-21 which has four 21g solid copper conductors. I used a pair of conductors in parallel for each lead. The CU-21 sounds really good as a power supply wire with a neutral tonal balance and excellent speed and detail. It is just very slightly lean in the lower midrange and very slightly tipped up in the highs. That's what led me to use a single Neotech Silver wire in the outboard power supply. It counteracts the very mild colorations of the CU-21.

Of course, maybe this is all in my mind since everybody knows all wire sounds the same......
 

MrEd

Senior Nobody
Thank you for the details.
I have been studying this and deciding how much I want to sub for your exact component to preserve your design vs what I have in stash.
All comments on how specific items effected the sound character are greatly apriciated.
We can now put you in the certified crazy camp... your psyciatric chart will read " hears difference in wires" 🤣
 

Wntrmute2

Not So Mediocre Member
I built his prior phono-stage as closely as I could within reason. Subbed in Jensen's for the Black Gates and some very close tolerance polystyrene caps in the RIAA section. Also, I couldn't afford the V-Cap coupling caps at the outputs. Used solid silver wire for all signal path.
I can't comment on how things would have sounded if I had fine differently but I was somewhat constrained by cost and availability. It does sound as good as anything I've heard.
 
I just edited my first post above to include photos of the schematics instead of PDF copies. Not very elegant and I am sure there is a better way of posting scan copies but that's all I know how to do.

I also wanted to mention that I changed the chassis earthing from the old design based on comments from Izzy and Paul@Bottlehead. They both recommended that the connection between the IEC earth and the power supply ground should take place in the audio chassis and not in the power supply chassis. I wired it that way and it works fine. I am still using a 10 ohm buffer resistor but it's now in the audio chassis. There were enough changes between the two preamps that I can't say the earthing change made a difference. I do know that from an audible noise standpoint, it didn't change things. The preamp was very quiet before and it's very quiet now. But perhaps it affected the sound quality. I can't say one way or the other but I am comfortable leaving it as it is.

EDIT: But see Post #26 below for further thoughts.
 
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I also forgot to mention that I used Teflon tube sockets for the 9-pin tubes in the audio chassis. These are the sockets sold by PCX under their Connex brand name. The only reason I used them is that my previous go-to sockets are no longer available. My previous favorite was a ceramic socket with silver pins made by Azuma. I used to buy them from Angela Instruments and they always delivered the goods. Very high quality construction and easy to solder. Then, a few years ago, I found Angela was no longer carrying them but, lo and behold, Audio Note had picked them up and was selling them under their own name. Same quality socket, just twice the price. I was ok with that and ordered a number for projects during the last couple years. But now the Audio Note sockets are gone. Angela now explains on their website that Azuma has ceased manufacturing them so they are no longer available under any brand name.

It was for that reason only that I went with the Connex Teflons. I know they must sound good since they are used in my Emotive Audio preamp and power amps (I am not about to do an A/B of tube sockets), but I also know from experience they are very difficult to work with. The pins are just straight pins; they can't be bent the way normal socket terminals can be so the wire connections for a 9-pin socket are very tight. And to make matters worse the pins rotate so there is a risk a solder joint could end up touching an adjacent solder joint if the connecting wires or component leads move around. This makes the wiring much more tedious than with a normal socket. To be honest, if I were building this again I would use a conventional socket, ANY conventional socket, instead of the Teflons.
 
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