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.
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.
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