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

Sprague Vitamin Q capacitors. Old school paper in oil magic for your hi fi!

Hello there tube amp heads.....

This is a little post about the legendary Sprague Vitamin Q paper in oil capacitors. I used to have dozens of these and at one point used to swap caps in and out of my hi fi amps when I had that kind of time. I was never all that impressed with the Vitamin Q caps in the past myself but decided to give them a go again now that I only have one system that I know quite well.

These arrived yesterday and I threw them in to my lovely single ended 45 tube amp.

When you have such a simple circuit like this, every little change makes a difference. For instance, the 6SJ7 driver tubes pictured lived in this amp for a day. They are Sylvania. Really nice tubes. I prefer my 5693 RCA Red series tubes by far so they went back in the box! The Sylvania version I love in a guitar amp. Big, open sound but for my hi fi I found them a bit harsh.

The signal caps were Sprague polyester PS type, .1@600V. I hate the 715P series that has been so popular for the last 30 years. The 716 is better but if I gotta use Orange Drops they gotta be PS types. I find them to be smooth, detailed and musical. Plus they are warm which I need and they don't sound harsh like the beloved 715.

Now the 715 in a mushy old amp? That can work. Not saying they are trash, remember, everything is a relationship so they work for some amps just great.

So when I audition a new cap, tube or transformer, the first thing I do is pick a record I've been listening to for many years of my life, preferably something with vocals. In this case it was "Rastaman Vibration" by Bob Marley. First question is how does Bobs voice sound? Can I make out the words clearly? Second is how does Aston "Family Man" Barrett sound? Does his bass sound natural.

First listen is terrible. No definition, crap bass. But, the amp had also been on a mere 3 minutes. When auditioning a cap let it burn at least an hour. When you rebuild an amp, you must give it time!

So I went about my business and came back to it after a few hours. Liquid.... That's the word I use. Bobs voice sounds clear and natural and the bass is big and fat. The bass however, does have a bit of flab I didn't notice before. These are bigger caps than what I had in there (.15 rather than .1) and I could go down to .05 and get my bass needs met. But I will continue to listen to records and see if it works itself out. As I recall, these Vitamin Q caps got better with weeks of use.

So the jury is still out. Do I spend $30 a cap on Jensen Paper in Oil? Are those worth it? (the answer is YES in my opinion. Those sound beautiful.) Or do I keep on keeping on with these surplus store gems? Time will tell and I will tell you later. For now I dig them about 85%.

And on a final note. Are paper in oil caps worth it in your guitar for tone caps? No.... Those merely bleed a little high end to the copper pipes in your walls. You can get a 50 cent ceramic to do that job. That's all marketing ladies and gentlemen......

JB



And instant update....That was fast!

Listening to my favorite Coltrane record, "Crescent". Side 2..... I wore out my first copy ,I love this side that much.

Jazz has a wonderful way of mixing itself. At least in a quartet fashion. The bass and low drums are the lows, the piano and sax are the mids and the ride cymbal are the highs. Coltrane sounds like he's hanging out in my little apartment playing. How the hell did he get that sound is beyond me! So warm and beautiful on this record. Jimmy Garrisons bass has authority and clarity and McCoy Tyner....crystal clear. The second song on side 2 is called "The Drum Thing". All about Elvin. Such a beautiful, dark drum sound. That piece moved me to change the way I make music. Oh yeah, this is about some caps.....they've been burning in all night. I'm in love.......