Input Transformer Question

[Alonzo]

Searched the forum, didn't find a lot relevant to my situation except for Xavier's BeePre.  Has anyone added input transformers to the BeePree?  What was your outcome?  I'm looking to upgrade from a fully Smashed Smash and a Ingot knockoff, I shouldn't need two preamps but that's where I am for flexibility and sound.  Can a B7 Mexico input transformer BeePre sound good in a variety setting with multiple amps (45 and 2A3) into various dB speakers (86 dB to 101 dB)?  Id plan my setup without the attenuator or the balance circuit, Mike's B7 1:1 10K to 10K input transformers and the P&G pot, Goldpoint selector switch, 3 inputs and 3 outputs, all unbalanced.  Anyone foresee any problems?

[johnsonad]

My thoughts in response are, what impedance does the grid of the 300B want to see and two, that's a really low input impedance and not all sources will play at their best with it.  That P&G pot is nice but what are you gaining by putting hundreds of feet of wire in the form of an input transformer in front of the 300B?

Have you considered trying your Mainline as a preamp? With those taps on the 404 you could easily play around with it.

[Alonzo]

Hmm, that's interesting, Mainline as a preamp. I've already put a switch in place so I can change taps  on the 404.  Right now I could replace the Smash.   

I'm trying to simplify my setup and improve at the same time and maybe make an one off unicorn.  The BeePre may be everything I need stock, I just like to use parts instead of them sitting on a shelf.  Really it's just boredom, need a new project to get into.

I'll look into the input impedances, I didn't anticipate a problem since the BP was already built to accommodate input transformers. 

[BNAL]

Really it's just boredom, need a new project to get into.

Alonzo,

I know what you mean about looking for projects. That's what my wife tells me when I say I'm looking to make a change to the system.

I keep thinking I need to upgrade my preamp, but Right now I'm listening to Eat A Peach on vinyl through my Euros and Quickie PJCCS and it sounds so damb good. The real suprise to me is the Quickie. It is so good for such little money. The only upgrade I made to either was to replace the supplied pot with a eBay DACT step attenuator.

[Alonzo]

I have a couple of Quickies out in the garage, went as far as doing mods to use SLA's for power and it did sound great.  I don't really know why it fell out of favor, I think because the upgrade bug bit again and I moved to the Smash.
The more I ponder this, the more I want to try it out.  Worst thing happens is I wont like it and will have to sell it off.

[Paul Birkeland]

Here's the page that we wrote about adding balanced inputs and input transformers to your BeePre (I still have this particular BeePre)"
http://bottlehead.com/bee-pre-input-transformer-modification/

I do not see any purpose to adding an input transformer to the BeePre (or any other piece of gear for that matter) unless you need the balanced input (for ground loop isolation or very long cable runs).  You can certainly put a 10K:10K pair of transformers between the selector switch and attenuator, then recalculate all of the resistor values in the BeeQuiet to present roughly 10K on the output side of each transformer, but I think you would be doing a lot of work that would diminish the performance of the stock circuit pretty significantly.

-PB

[Alonzo]

Well, seeing that I need a birthday project I reject your common sense and will see how it sounds myself!  I will leave out the BeeQuiet:  RCA's to silver cable to Selector Switch to P&G Pot to input transformers to resistor to 300B. 
If it doesn't work I can return it to stock, but I think I'll be pleasantly surprised... not just in the isolation but in the sound that the transformers will give.  Did you return your transformer input back to stock?

[Paul Birkeland]

Well, seeing that I need a birthday project I reject your common sense and will see how it sounds myself!

That is certainly my highest recommendation. 

Did you return your transformer input back to stock?

No, but the configuration of my BeePre is two unbalanced RCA inputs and one balanced XLR input, therefore the input transformers are only present on one input.  I've left them in, as I end up building equipment with balanced outputs from time to time, and it's nice to be able to test them conveniently. 

[Alonzo]

Installation done.  Not at voltage checks yet, 2 LEDS not lit and some white smoke upon power up.  Will check it out soon as current trip is over.
Going to have to work on the length of the extensions to rotate the transformers since I put in such big caps.

[Alonzo]

Boards out.

[Alonzo]

Touched up some solder joints and voltage checks passed.  Now to burn in till Monday, have to pad the input, way too much gain (also reverse the pot since I have it backwards).  Sounds good so far.

[Alonzo]

Added Harrison -6dB attenuators to the amp input instead of monkeying with the BeePre.  This gives me more range on the P&G pot.  So far the break in is proceeding, some songs sound great, some are horrible, 180 hours or so to go before seriously judging it.

[Alonzo]

Switched to the input transformers.  Doing 10 hours runs on each input during the burn-in.  No hiss, no noise, guess I got lucky on the placement, we'll see if rotating them improves the sound any later.  Sounds pretty good now.

[johnsonad]

I'm curious to your chain and why you did it that way. You wrote your signal Chain is selector, pot, transformers vs the Ingot method of selector, transformers, pot. Was there a reason behind this or did you attempt it both ways and like that way better?

[Alonzo]

I didn't do the planned chain, I thought I would try it out on one channel and see how it compares.  I put the transformers on one input.  So chain is RCA, transformer, selector sw, pot. This seemed the easiest and I used the spare holes for the RCA's.  If its going to stay permanent then I'll reconfigure the transformers behind the selector to get the benefit for all the inputs.