My ReMus preamp. Pandemic project number 3,84whatever

 Today was pandemic project number three thousand two hundred and whatever. It entailed me spending a whopping 2 hours re-vamping the ReMus preamp I built way back in 1998 when I lived on the corner of Missouri and Failing (yes it actually was a dead end!) in Portland Oregon. 

It was an early build of mine with the classic "bowl o' spaghetti" construction. But it worked shockingly well so I never bothered to fix a few annoying issues. 

First was eliminating the tape out buffer. This preamp has one too many gain stages. The beauty of it is it's simplicity (I'll provide an updated schematic here).  So I put this part of the circuit on a switch as I like to use it for putting vinyl to digital. But audio should not pass through it going to the output. It's redundant and likely causes phase issues. There was something about the original design that I simply didn't like but couldn't put my finger on. I figured less is more and this did the trick. The whole thing sounds dramatically better.

Second was back in the day I used 1Meg pots. The original calls for 250K. I couldn't even turn it up past one before it gets too loud for my room using the phono stage! I fell into a rabbit hole trying to decide what to throw in there. This is my hi fi.... guitar amp pots aren't gonna do. One can obsess over this stuff. I wound up using pots by Tokyo Cosmos cause, well, Cosmos. I like the name!! I got them through Antique Audio Supply:  https://www.tubesandmore.com/products/potentiometer-tocos-rv24-audio-10-6mm-shaft

Again, major improvement. Everything sounds better and is much more in control!

My preamp is kinda "dual mono" rather than "stereo". In other words I have two mono volume pots for left and right rather than a dual pot. This eliminates the possibility of having one side behave differently than the other. 

I also replaced the output caps with Sprague Paper in Oil. Not Vitamin Q but I'm sure very similar. They're 1uf@ 400V.  Before I had these beautiful Angela polypropylene caps that were 1.5uf. I love those but wanted to try something else and love the Spragues more. The rest of the caps are Angela / Jensen PIO caps. Sadly none of these are made any longer. I think the business has gotten so spread out with competition. I don't know that anyone is making better stuff than what he was offering in the 90's.

Last but not least..... I used some cheapass RCA jacks. Total Jive dig?!? 

What was I thinking? They were always getting loose! The phono, line and output stage I did years ago with nice Switchcraft 3501. So today I finally did the rest, 24 years later! Typical tech. The last thing you want to do after a long day is your own stuff so it's easy to tolerate. One of my favorite luthiers plays bass. I asked him how his basses play and knew the likely answer: "dude they all play like crap!" he replied laughing.

Much better! I also added a center channel output should I want to experiment with a sub woofer. I've been fantasizing about that. Building a 50 watt mono block only to be used for symphonic music, reggae, soul, Afrobeat, electronic stuff. I'm kind of afraid I'll like it too much and get addicted to it but hey....

I also finally color coded my wires, left and right channel..... It was difficult to get Mogami hookup wire back then. Finally have a source and they have plenty of pretty colors! Cheap as chips too. That stuff is great. Warm, rich, full bodied wire and easy to work with. I could only buy it in blue back then!! 

Buy it here: 

https://www.performanceaudio.com/mogami-w2514-hi-fi-red-hook-up-wire-by-the-foot.html

Apparently you can get this on Amazon now but, well, ew......

So now I have one final task. The power supply is separate. It uses a 5U4 tube with all oil filtering, two chokes (another choke inside the preamp housing for a total of three!) and 6.3V DC filament voltage. I built it this way so I can have it far away from the audio. No AC voltage enters the preamp except for the signal itself. But...... I used an old Kenton transformer I scored at a Ham Fest.  And it buzzes.... I once had a 1967 Plexi 100 Watt Marshall with the same annoying problem. I couldn't do anything about that one cause no one made a replacement part for that old beast and, well, it was vintage. I think I sold that one to Mick Mars. He bought a few from me back then. Nice fella!

Anyway, that transformer has gotta go. It's ironic to have gone to such great lengths to create something quiet only to live with a stupid mechanical buzz! That will be my mid-April project.

For those who are interested in the schematic, here is the modern "no tape buffer' circuit. Brilliantly simple.

https://www.lencoheaven.net/forum/index.php?topic=28010.0

My own version used octal preamp tubes, substitute 6SL7 for 12AX7 and 6SN7 for 12AU7. I prefer these for hi fi. The modern little 12 volters sound a bit hyper for my taste. I like a bit more euphonic presentation. Plus I can still find high quality octal preamp tubes for much cheaper than tubes all the guitar freaks need! And they tend to last forever.

So there you have it. In it's 24 year life it burned out two resistors (the 22k cathode follower resistors on the output tubes.) I upped those to 5 watt wire wound resistors, nice Allen Bradley ones. Yes, I like to overbuild things. I don't want to open this up until 2031 now. I've changed tubes a few times just for fun. I think this set has been going since I moved to Brooklyn in 2011. Still making music!

I also didn't use their power supply schematic. I just went with a simple 3 stage dual choke loaded power supply like they've been using since the 1920's. Why so many chokes? Why big oil caps? I used to live by a surplus shop, actually two: R5D3 on 82nd Ave and Cascade Electronics way up in the northernmost tip of Portland and they had so much of this junk! These oil caps will last forever and they look super hip. Plus, again, relaxed sound...  I avoid electrolytics when I can, and sometimes you really can't, I find they just don't work as well. Besides, if you are only going to build one thing, why not go all out into the land of the ridiculous??? Just please, don't do what I did and skimp on cheap RCA jacks that get loose when you look at them wrong, or right, or whatever....

J

50's Russian 6SL7 and new 6SJ7 tubes, review. Nice glass!

Just a brief bit of impressions on some Russian glass I received recently from a great seller in Ukraine.

First up is the metal base Melz made 6SL7.

And the test LPs were Charlie Byrd Trio: Charlie's Choice and Stan Getz's Jazz Samba.

I usually have a set of run of the mill inexpensive nothing special RCA 6SL7 tubes burning away. I know how they sound as I spend hours listening to my setup. I'm also familiar with these records. They spend a good amount of time on my turntable.

My RCA tubes:

So how did they stack up against the RCA? The difference was pretty drastic. First let me say I wasn't expecting them to outshine what I have. I choose my hi-fi tubes carefully. If I don't like something it goes in my box to sell to guitar players.

The Melz has impressively low microphonics. Great for my phono stage. Sonically they are far more aggressive than my RCA. Very forward. Stan Getz's sometimes harsh tenor sound gets harsher, not in a bad way, just more in your face. I find the RCA tubes to be more clear and relaxed. Since I don't listen to much metal these days, the Melz tubes will go back in the box. I like to relax in my tiny universe.

I bet these will kick some ass in a guitar amp. I do have one Magnatone that used the 6SL7 tube. I have a new RCA in right now and prior to that I had a Sovtek there which I didn't find sounded objectionable at all. I have a feeling the Melz will melt some faces. I didn't find it objectionable for my hi fi either, I just prefer the RCA.

A word about 6SL7 tubes. The big octal 6SL7, 6SN7 tubes are my favorite for hi fi. They relax more for me than the more common and sought after 12AX7, 12AU7 which are obviously more in demand and more valuable. I built my own preamp to use 6SL7 tubes in the phono and line stage, 6SN7 for the cathode follower driving the power amp. I do not covet any vintage or modern preamps. I built mine 20 years ago from a Swedish schematic called "Remus". It's a fantastic circuit! Simple and honest. No Marantz 7 for me, this sounds better to my ears!

Ok next. A tube I'm really picky about. The 6SJ7. My 45 power amp uses these as a driver stage. Also my favorite guitar amps use these, Magnatone Varsity and "B" amplifier of my own design. They have something psychedelic about them, a shimmer, when in a guitar circuit. I thought it was an Echoplex I used to have but that's gone and that characteristic is still there on my recordings. I don't get it with other amps that don't use these.

So I have the fancy 5693 red RCA 6SJ7 tubes in mine. I love these for hi fi, guitar I prefer the standard 6SJ7. I have a set of metal base Sylvania 6SJ7s that I rejected in this circuit after 10 minutes. I missed the warmth and euphonic quality of these red tubes:

So I got these Russian babies. Cheap as a bag of fancy chips. No joke. A couple bucks each. How do they stack up?

I wasn't hopeful. But....they are pretty damned good! Again more forward and aggressive but not like the 6SL7 tubes. The sound was nice and round, not cold or harsh like my Sylvania tubes. In a pinch I would gladly burn these up. There is no markings on these, just a #7 in a box on the side. Charlie Byrd's guitar sounded nice and round, the percussion deep and warm with a nice top end. No, they don't beat my RCAs, but they don't offend me one bit either.

So, hope this was helpful! I will try these out in my guitar amps and do a bit about that as well. And remember just because something doesn't work for me doesn't mean it won't work for you. Give these a try if you are curious! I'd love to hear your impressions.

JB