One-Bottle Preamp

[Svart]

call Edcor up. From what I read they don't hand wind and they do high volume with a limited variety other than winding ratios.. thats the key to cheap. other manufacturers do this by hand or have some kind of proprietary material/winding arrangement/etc. that make them charge more. may or may not make them better..

EDIT: we'll see how these work.. they were cheap enough for me to purchase a few for testing.. CJ might get and extra one to open up if he's lucky..

 

[CJ]

It's probably a bobbin wound, pri sec, easy to wind coil on some barn roof laminations. But don't laugh, barn roofs are in a lot of those WE's, and I just tested a 60 hz step down transformer that was very flat from 10 to 30k. Ten bucks a pop.

 

[Svart]

http://www.edcorusa.com/classx/matching/xsm/XSM10k-600.htm

tell me what you think CJ..

 

[kiira]

If I were going to buy something nice and something new this might be what I'd go for... to use with a ribbon at -2dbu. I might call them up and see what they want because it's really small 22mmx27mm.

http://www.cinemag.biz/mic_input/CMMI-10PCA.pdf

 

[Svart]

I just wanted something quick to try out for the output trafos. We should all build some with different trafos to see what we get and what is better. A team effort is better than trying to afford 10 different trafos.. :green:

I have some of the tiny beyers for the inputs for two, but if these turn out as nice as i think I will be building more. let us know how much the cinemags are.

 

[Kingston]

Svart,

It looks like I'll be using Jensen 1:8 to 5:1, or OEP 1:13 to lundahl 4:1 depending on which ones I'll get first in case you want team effort. They're reasonably small with good prices I've managed to find. (viitalahde helped)

It's the two bottle configuration I'll be building. Then another one depending on success (read sound).

I still haven't figured what kind of PSU transformers (toroidal? what's that) I should be looking for good sound, and how they influence these things.

Then there's the cap/resistor conpensation values after the input trafo which I haven't figured out... and do I need to compensate for the output trafo as well?

 

[Svart]

toroidal is how the trafo is shaped and wound.. in layman's terms it's a donut shaped transformer. very useful for many reasons but the main one is the very small field it generates.

the manufacturer of the transformer you use should have the info about the zobel/snubber network (R/C) in the data sheets for the transformer

 

[pstamler]

If you're using the Jensen 1:8...that would be the JT-110***, the recommended termination resistor is 100k (10xsecondary impedance). The Zobel network, placed in parallel with the 100k resistor, would be 30.1k in series with 56pF.

Peace,
Paul

 

[Kingston]

well that was fast!

thanks guys. I'm new to this so I didn't know I'd find it in the data sheets.

 

[NewYorkDave]

Kiira, that's one hell of a hot ribbon you have there, if it's putting out -2dBU!

Svart, are you still talking about the CJ preamp now, or mine? I think Kingston is talking about mine. I know Kiira is.

This should really be two threads...

 

[Kingston]

I thought we've been talking about dave's pre all the time. I hope we have, because this is getting a tad confusing.

 

[kiira]

[quote author="Kingston"]I thought we've been talking about dave's pre all the time. I hope we have, because this is getting a tad confusing.[/quote]

LOL, I think I have it figured out:

Kiira - building 2 bottle version of Dave's one-bottle pre
Kingston - building 2 bottle (??) version of Dave's one bottle pre
Svart - confusing everyone by asking about gain switches so prolly building CJs 417a one-bottle pre.
Kiira - confusing everyone by giving wrong answers to simple arithmetic questions about impedance ratios.

Next we'll hash out who is using what transformers. :razz:

Kiira

 

[CJ]

Sorry, I screwed up the thread with that 417 thingy. You can run that tube with no output trans, as the output of the tube is semi low impedance.

 

[Svart]

Hey, Yeah I'm focused on CJ's preamp right now, as soon as i build it I'll be on to yours NYD, so don't worry!

Cj, i need a balanced out for this as I will be running a pretty long distance with these.

sorry to be bugging about the gain switches! If i build some kind of switchable U pad, and the primary impedence of my trafo is 200R, how do i figure the shunt R and does that change with the two series Rs or stay the same?

 

[skipwave]

I'm aboard the NYD One-Bottle Express, making a two channel box.

Power supply built, NOS GE AV7s arrived yesterday, and placing order for the last few components right now.

Input iron is Sescom MI-70 or Peerless 15095A.
Output iron (with 1/4" switching jack for bypassing) is Triad A-69J.

Go team. Go. :thumb:

What are you all using for the 100k pot?

 

[NewYorkDave]

A modest proposal to bring some order to this thread:

Let's call the preamp I posted at the top of the thread, the One-Bottle Pre.

The same circuit, with the 5879 input stage added, C5 replaced by 1uF film, and R11/R12 replaced by a 100K fixed resistor, is the Two-Bottle Pre.

The circuit CJ posted with the single WE triode is the CJ Pre.

Just mention which preamp you're talking about in your messages and there should be no confusion. Capiche? :wink:

 

[soundguy]

[quote author="CJ"]Talk to Bill Yacey, even though I have not seem him here for a while. Maybe his Johnson blew a head gasket somewhere in the backwaters of Lake Titicaca.

[/quote]

yeah! yeah!

heh heh

dave

 

[NewYorkDave]

A couple of comments pertaining to the "Two-Bottle":

Pins 2 and 6 on the 5879 should be grounded to the chassis--and use at least 47uF for the cathode bypass cap, especially with AC heaters.

The three-stage circuit inverts signal polarity. You can compensate for this by wiring the output transformer to invert. I say the output transformer because if you reversed it at the input transformer, it wouldn't help when you used the a Hi-Z (DI) input--assuming you had a DI input in the first place.

Personally, I wouldn't bother with a Hi-Z output on the "Two-Bottle" because there's gain to spare and that extra 12dB won't be missed in most situations. And not only does the stepdown transformer give you a balanced-floating output, it frees you from having to make sure your load impedance is 10K or greater.

If/when anybody actually builds this thing, we should probably start a new thread for it because it seems silly to be discussing a two-bottle preamp in a thread entitled "One-Bottle preamp." :wink:

 

[Svart]

got my edcor trafos today! now i just have to figure out some kind of attenuation network for gain control and it'll be done!

 

[skipwave]

In the NYD One Bottle, are cheapo carbon pots okay for gain control? I've got some Alphas lying around.

How much influence does the type of pot have on the sound in this application, meaning in the feedback loop and not the signal path? Maybe that's a can of worms I shouldn't open, but I'm just sooooo green. :green: