One-Bottle Preamp

[Kingston]

It's a shame that other thread disappeared, but it was mostly linked to this one so no big loss there.

I'm waiting for some 12AV7's (and not absolutely sure what input transformer I'll end up using) here so I can't finish the project yet.

Looking forward to that "two bottle" report coming up.


sismofyt, if you're listening, you mentioned about your simple tube pre design in that disappeared thread. You said to start stocking up XZY and XYZ tubes. What were those? and did you finish that design already?

Cheers,
Mike

 

[Kingston]

Seems like I've ran into a bit of a (beginners) problem,

(knowing full well my question is a rather large topic itself)

What choices do I have with the transformers proposed in these designs? It was dawned onto me rather recently that transformers may influence the sound more than the actual tube stages. I then started hoarding this forum looking for the definite transformer thread, but found little conclusive info.

I'm seeing lundahl mentioned everywhere, for example, but I don't think it would be wise to stick something like that to my first project. Would be rather expensive wouldn't it?

Could someone shed some light on this "audio transformer lore" that might not be so obvious for a beginner like me. Or for the fun of it, could you recommend several great alternatives that I could swap around to see how it influences the sound?

 

[Svart]

i haven't been able to get very far in these projects but I am a Lundahl guy. I will pay the extra money for those trafos in a heartbeat. They are above and beyond good. besides, if you buy cheap like OEP, you then have to buy the Mu cans and such separately which ends up costing you 3/4+ the cost of the Lundahls. There is no such thing as being cheap on your first project. spend the money where you need it and take your time or you will regret it later. the worst you can do is do ugly/bad/noisy wiring which is annoyance more than problem.

If you want/have to go cheap you can likely find something on Eb*y that will suit you, just don't get wrapped up in the audiophoolery and pay too much.

EDIT:

here are some quality trafos:

Lundahl
OEP
Lynx(might be called something else, ask Rafa)
Sowter

and many more that don't come to mind

 

[Kingston]

Thanks for the info. The other reason I asked was that I've heard from few people that sourcing lundahl here in finland might not always be straight forward.


(EDIT, all is well now, thanks to viitalahde and some more reading of this comprehensive thread)

 

[jrd]

Here I go thinking out loud about transformers, related of course to New York Dave's One-Bottle design. A three part query.

1. Input iron. I have access to a UTC LS-12X input tx. Primary Imp.s are 500, 333, 200, 125 and 50 Ohm. Secondary is 80K Ohms. Is this a suitable tx, and what will I have to do in the compensation network? Will it be worth my while to think up some switching to make use of variable input impedance? I calculated the turns ratios and they seem rather higher than what NYD originally spec'd for this circuit. Or would it be a good thing having turns ratios in the neighborhood of 1:20? More gain? More better?

2. Output iron. There is a slight chance I could have access to a UTC LS-27 for output. Would this be inappropriate? Primary is 15K Ohms and Secondary is "500/600" Ohms. I calculated turns ratio and got 5:1. Too steep a drop in voltage loss?

3. Power. Would it be kooky to use two transformers for this... I have a 6.3v transformer with enough current to do filaments, and a 120v transformer for the power supply. Dave spec'd a 240v tx, but is there some simple "voltage doubler" trickery that I could employ to use my power tx which has a 120v secondary?

Any insight anyone cares to share would be greatly appreciated.

james

 

[CJ]

Man, that iron might be wasted on anything but a V76.

 

[NewYorkDave]

:? <---Bristling at the suggestion that my preamp isn't worth wasting "good iron."

:razz:

But when did V76s use UTC transformers?

Actually, those UTCs would be perfect for the RCA BC-2B preamp. They're either the same used in the originals (IIRC) or damn close. I haven't tried that circuit myself, but people seem to have a hard-on for it.

 

[CJ]

I was wondering if that was goiung to come off wrong. Part of my rep precedes me I guess. :sad:

It's just that the whole idea to me at least, of a simple pre is also a simple hit on the bank account. But yes, in a case where the parts count is low, using good parts can really make a difference, so go for it.

Those UTC's go for silly money, sometimes 300 a pop for LS X series.

 

[Svart]

Hey CJ and fellows, I have to make some kind of variable attenuator for these pres.. what would you suggest? I assume input attenuation and some kind of U attenuator?

 

[kiira]

so how do I figure out what values to use in the input compensation? I'll use the edcor 10000:600 backwards... hope that'll work ok?

it's nice with a low parts count circuit because you can spend more on fancier stuff if you feel it will make a difference.

Kiira

 

[Kingston]

[quote author="CJ"]
It's just that the whole idea to me at least, of a simple pre is also a simple hit on the bank account. But yes, in a case where the parts count is low, using good parts can really make a difference, so go for it.[/quote]

I've found it the hard way during the last week this thing doesn't come cheap when one hasn't scavenged the parts for it.

Looks like it'll be like 100 euros to get everything "new" and good. But then, this ain't going to be no art or behringer. :green:

 

[Svart]

I need to build some kind of adjustable attenuator for these.. any suggestions?

 

[jrd]

yeah, it kinda doesn't make any sense, but it kinda does. a friend of mine has some of the LS-12x sitting around. i had been talking about the one-bottle design... hoping he'd lend or sell me some altec/utc/whatever iron for prototyping purposes. instead he hands me this massive battleship of a transformer saying, "use this, i've always wanted to hear what it sounds like." so maybe it will be worthwhile trying it in this circuit if it will let us really hear the transformer? who knows. any hints on what i need to be doing to this circuit to optimize it for the LS-12x? Compensation network etc. Where can I find the guidlines for figuring that out?..

 

[vibrolax]

Those transformers would also be perfect for a Pultec MB-1 mic preamp. I used UTC A-11's for inputs and Edcor 15K:600's for the outputs. I did work up an input impedance switching scheme to use the A-11's 50, 200, 500 ohm primary taps.

I'm sure the UTC LS's would be really nice.

Pultec MB-1 clone

Jon

 

[CJ]

There is a gain control already on page one schematic of this thread?

 

[Svart]

I swear I don't see it.. I'll read over it all again.. :shock:

 

[NewYorkDave]

Svart seems to be asking about the CJ preamp.

This thread became really cluttered/confusing by about the second page. :roll:

 

[Svart]

:shock:

no kidding NYD!

i see that I need ~6k:600 for balanced out?

I like the edcor stuff that Kiira mentioned.. will the 10k:600 work? How about a small group buy of some 6k:600 customs?

I am a total trafo noob here.

still don't see any kind of balanced attentuator.. :?

help? :green:

 

[Svart]

ok so I called edcor and bought two XSM10k:600 and had them start on two XSM6k:600(customs). the customs were 11.59 each! not a bad price at all! should take 7 days lead time+shipping.

I'll try them both out and likely build two more pres.


Now i need to figure out an attenuator arrangement..

 

[Kingston]

Ok what am I not understanding here? I'm looking at http://www.jensen-transformers.com/

and transformers with ratios like this one/two bottle design are more than $100!

Why are they so expensive and how come you guys are getting those edcors (even custom!) for so cheap?