Custom Preamp for Jrebman

[Paul Birkeland]

In a prior post, Jim was asking what credentials were necessary for a good shunt regulator tube in our hybrid shunt reg. setup, and somehow that turned into discussing a 6J5 parallel feed transformer coupled linestage.

Well, Jim had an extended Foreplay III on order, and that batch of plates just happened to have holes for Magnequest B7 transformers, so we cooked up this custom preamp.  Jim had the plate powder coated to match his other components, found solid copper RCA jacks, high quality octal sockets, and some additional hardware.

I used this preamp as a little bit of a test bed for some of the BeePre components like the input wiring and the attenuator upgrade.  Jim selected V-cap OIMP parallel feed capacitors, and I selected Vishay RN55D resistors for the majority of the positions in the piece.  Interestingly, I managed to build the preamp without any terminal strips, which certainly presents an extra challenge. 

Naturally, Jim went for a custom bamboo base from Blumenstein, all that's missing is Jim's set of brass knobs! (No pun or innuendo here)

 

[johnsonad]

Nice work Paul! 

 

[4krow]

Just when I've grown fond of those copper jacks, then I see the underbelly, and look at Goldpoints. Very good indeed.

 

[Wanderer]

....... all that's missing is Jim's set of brass knobs! (No pun or innuendo here).......

Oh thank heavens!!!! Hate to think that on a website that sells a phono pre call a "Seduction", a simple pre-amp called a "Quickie" and an amp called "S.E.X." anyone would fall into the trap of puns and innuendo.

No jokeing -  that looks lovely.

How much of a PITA are copper jacks? Constant cleaning? I have wondered about the gold plating, often gold over nickel, on "normal" audiophile jacks. 

 

[Paul Birkeland]

How much of a PITA are copper jacks?

Only time will tell, I think that I have had the best luck with nickel plated jacks, but finding solid copper jacks with nickel plating can't be that easy.

 

[jrebman]

Many thanks to PB and the whole BH crew -- I'm really looking forward to giving this a listen.  BTW, the knobs are gold plated but made of brass (audionote).

The thing with the copper jacks is probably going to be dependent on where you live and your tolerance for regular cleaning.  In Colorado where it is bone dry and with the use of caig de-oxit and pro gold, it is not as big a deal as it would be in a humid or coastal area, and about every 6 months seems to be fine in this dry environment.

BTW, the other matching components will be the Eros and eventually the rebuild of the SR-45s

And yes, all this goes back to questions I raised on the fpIII forum about building a transformer coupled version with a single gain stage, and specifically the 6j5, and eliminating the cathode follower.

Thanks for all the nice comments,

Jim

 

[4krow]

Well, not to beat a dead horse, but simply put, I doubt that you will have much of an issue with the jacks. If so, maybe a light coat of clear(or RED  hehehheheh) nail polish on the non-contact ares will keep things at bay.

 

[Grainger49]

I still use a bottle of Red Cramolin.  That is the predecessor to De-Oxit.  Cramolin is an industrial/electronic product that seems to have disappeared.

 

[4krow]

I said I would give it back when I was finished

 

[ditdah]

Great looking build.  So many talented folks around here.

 

[jrebman]

A quick update...

The finished preamp arrived last evening and this morning I unpacked it, and wow, PB did what anybody would call a superb job on the wiring and layout -- fantastic workmanship!  Wow, I had no idea those B7s were such tiny little buggers and I had to do some gentle poking around to find the  V-cap coupling caps.  Nice also to find some 4-pole electrolytics in the power supply -- thanks Paul!  So, here's the rundown on all the goodies:  Started with a basic foreplay III+, but with a P7 power transformer and eliminating the second cathode follower output stage.  Instead the gain tubes are 6j5s -- essentially a single triode version that is something like half a 6sn7, coupled to the outside world through a MQ Cobalt B7 parafeed preamp transformer.  The shunt reg tube is a 6bx7. The volume control is essentially the same as the BeeQuiet for the BeePre, but using goldpoint switches, and the input selector is also the same goldpoint many of you upgraded your FP IIIs with  (and which I'll also be using in my stereomour).  The input and output jacks are all solid OFC copper and pretty much everything else is standard bottlehead fare.  Of course the whole thing is point to point wired with no terminal strips as well.

I hope to take it downstairs later today, replace the knobs with the gold ones I have for it, put some Herbie's baby booties feet on it for better airflow, and then crown it off with a bottlehead badge.

This is a real gem of a preamp already and I consider myself very fortunate to have such a work of art and one of the few preampsanywhere  with mq cobalt output transformers.  A very sincere thanks to Paul, Doc and Eileen and of course PJ for the original design.

Now I only hope I can do right by it and do as good a job on the Eros that will be it's companion piece at the heart of my referrence system.

 

[4krow]

One of the things that I appreciate most about this build is it's simplicity. It is further enhanced by parts selection. Then, as the first two facets compliment each other, the build itself is striking. Beautiful and exact. I DO want to see a photo of the amp with brass knobs. Brass can be the perfect touch, but for me there is a limit as to how much can be added without overdoing it. I have  a feeling that this will go quite well with the amp as a whole.

 

[Hank Murrow]

Jim, you are going to love those B7 cobalts. I have a pair in the linestage that Paul built for me and in comparison with the BeePre sans BeeQuiet attenuators, it held up surprisingly well, even to Doc's fine ears. In a week I will be taking my Birkeland-built phono and linestages up for a Friday the 15th BHeadquarters comparison to the house phonostage and the BeeQuieted BeePre. Should provide some meaty lunchtime palaver at a nearby Bainbridge bistro.

While your project and my projects are unlikely ever to appear as BH kit products, they seem to stimulate much useful thinking in the comparison with current BH 'best efforts'.

As Clark mentioned in a recent post, progress is incremental, and best enjoyed in good company_____ BH/Blumenstein(and The Crew here on the Forum) are damn fine company.

Cheers, Hank in Eugene

 

[jrebman]

Hank,

It's the one real thing I miss -- good, easy going audio buddies who are as into it as I am and can really appreciate not only fine music, but fine design and artisan craftsmanship.

I'm truly jealous of the community that exists in the Seattle area and all the wonderful exchhanges of ideas, music, bevvies and just plainold technical geek time and hanging out.

Boulder is also a mecca of sorts for audio companies, though mostly solid state stuuff and way out of my price range, and as I've also heard most of them, not really to my tastes either.  Though there are a couple local turntable makers whose products I certainly wouldn't mind owning.

 

[balancedtriode]

From a circuit design perspective that is one of the most beautiful FP-III's I have ever seen. And it's not too bad on the eyes either 
Congrats' Jim you own a work of art, it has even given me a few Ideas for my FP-III build.
-Coltrane

 

[jrebman]

Coltrane,

Yes, it should be a fantastic preamp in every way, but I also have to thank PB for suggesting and doing the silver vein powdercoat on the transformer covers and of course Clark for the base it all sits in.

Glad you see some things you can use -- that is one of the great things about this forum -- lots of creative people doing their own things and sowing the seeds of creativity for others.  I like your idea of the plate chokes in the stereomour, and in turn you can takee something from this for your FP III.  Now, that's cool.

 

[balancedtriode]

Jim,
I agree this is a great community, we bounce idea's off of each other an make the listening experience better for every one involved.
I just ordered  heat-sinks like the ones you have on your foreplay's regulators  (at the very least it increases the life of the component). I also love the base. Clark may be getting an order for one soon, Its  listed as the foreplay base on his site, right? even though its a FP- III
-Coltrane

 

[Grainger49]

Coltrane,

Funny you said that about Foreplay vs FP III.  Since I have a FP 2 it wouldn't fit mine. Or my Paramours either.  The only new, full plate, kit I have is the Eros.  I have received remarks like, "So, the big one is the phono stage only?  The smaller ones here are the amps?"

 

[Natural Sound]

Coltrane,

Funny you said that about Foreplay vs FP III.  Since I have a FP 2 it wouldn't fit mine. Or my Paramours either.  The only new, full plate, kit I have is the Eros.  I have received remarks like, "So, the big one is the phono stage only?  The smaller ones here are the amps?"

Clark offers a base for "seduction" which uses the smaller plate.

 

[balancedtriode]

technically, the seduction base would work for the FP 1&2 as well as other older bottle head gear Because the have the same chassis plate size right?
sorry for taking this off topic I am just curious.
-Coltrane