One-Bottle Preamp

[pstamler]

[quote author="Marik"]Unless I am missing something (sorry did not read much before last couple messages), with 3-0-3 you get 6x1.41=8.46V. You still have some margin to smooth it out even further with a small value resistor and cap.[/quote]

Not really; the diodes in the full-wave bridge rectifier lose 2.5V, give or take a bit. So instead of 8.48V you get 5.98V, which leaves you no margin for further smoothing or for undervoltage from the wall.

Peace,
Paul

 

[Marik]

[quote author="pstamler"][quote author="Marik"]Unless I am missing something (sorry did not read much before last couple messages), with 3-0-3 you get 6x1.41=8.46V. You still have some margin to smooth it out even further with a small value resistor and cap.[/quote]

Not really; the diodes in the full-wave bridge rectifier lose 2.5V, give or take a bit. So instead of 8.48V you get 5.98V, which leaves you no margin for further smoothing or for undervoltage from the wall.

Peace,
Paul[/quote]

In my pre I have a rectified 6.3V winding. Just re-measured it again--it gives 8.03V before smothing. I am using Shottky diodes.

 

[pstamler]

Aha! An end run around the problem. So if you use the Schottkys and a 2-stage filter (3300µF-2 ohms-3300µF) you'd get an additional 14dB of filtering from the second stage. You'll still be down to 5.4V at low line voltage, though. But then, you'd be down to 5.7V with AC filaments too. No free lunch.

Peace,
Paul

 

[Marik]

[quote author="pstamler"]Aha! An end run around the problem. So if you use the Schottkys and a 2-stage filter (3300µF-2 ohms-3300µF) you'd get an additional 14dB of filtering from the second stage. You'll still be down to 5.4V at low line voltage, though. But then, you'd be down to 5.7V with AC filaments too. No free lunch.
[/quote]

:grin: :grin: :grin:

Whole my life is just a run around the problems... or else... getting into the problem and then trying to realize: "How the heck I am gonna get out of this shit". :grin:

I actually run a four stage filtering 4700-0.75 Ohm-4700--0.47 Ohm--4700--0.33 Ohm--4700 and get 6.2V. I selected the resistors out the bunch for lower values and got around 1.5 Ohm total, IIRC. I tried three stage 6800--1 Ohm--6800--0.47--6800 and still got some residual hum at appr. 70db of gain. With the four stage it is ABSOLUTELY hum free.

If I had a transformer with a 9V tap, the problem would be easily resolved with a high current regulator.
I never was able to get a zero hum at the high gains with AC.

 

[emrr]

Referring to the two bottle with 5879 input sage:

[quote author="PRR"]> I always wanted to build a pentode pre too

Just FYI: NYDave's plan has you buy a Pentode and then convert it to a Triode. A waste of two grids!

However, triode is better here: Pentodes have noise issues, and we don't want the tremendous gain that a pentode is capable of. He picked that particular 5879 tube because it was manufactured for audio applications, including low-noise when triode strapped. There are a half-ton of other triodes you could use instead, but you may have to buy several extras and select for low noise. With 5879, you are unlikely to run into a hisser, and it isn't expensive. (It has also been featured in some notoriously famous audio gear, but so what?)[/quote]


I'm not seeing this mentioned anywhere else here; sorry if it is and I missed it: The antique literature almost always refers to triode connected pentodes as having noise advantages over regular triodes. There must be something to it, given the predominance of triode connected pentodes in pro gear before 1955 or so. Still seen in the Langevin, Gates and Collins preamps up until the 1960's.

I'd guess that as more and more loop feedback got used, the desire/need to stick with triode connected pentodes for noise purposes lessened. I'd also bet that the move towards a pentode front end followed by a triode connected pentode output stage had a lot to do with gain compensation for the increasing use of loop feedback, and the desire to still hit that magic 40 db mark with two stages.

 

[emrr]

[quote author="PRR"]>

Tubes do NOT belong on printed circuit boards. Call me old-fashioned, but that's the way I see it.

[/quote]

Nothing like the fun of working on older PCB tube gear. Usually you have many spots that are very burnt from the heat, and it's not unusual to find traces that are floating off the boards like pieces of wire - and with no insulation to prevent shorts! Even if not burnt, how many years of flex stress do you have from pulling and reinserting tubes? Even worse; add some transformer weight to the PCB. To hell with PCB's for tubes!

 

[skipwave]

My first pair of One-Bottles are on a PCB recycled from a Dyna PAM. Sturdy enough, but I've since converted to entirely point to point for tube gear.

 

[emrr]

[quote author="skipwave"]My first pair of One-Bottles are on a PCB recycled from a Dyna PAM. Sturdy enough, but I've since converted to entirely point to point for tube gear.[/quote]

Hey, if you can cannibalize, and get it done faster, go for it. I'm thinking mainly about new building from scratch I guess. And to my own taste.

 

[Freddy G]

Finally got my NewYorkDave two bottle fired up....
It's passing audio and it sounds very sweeeeeeet!
One thing I'm hoping for some help with....the wire going from the output of the input transformer to pin 1 of the 5879 tube is unbelievably sensitive.
If I even go near it with my finger or a screwdriver the hum gets pretty loud.
I've tried using a shielded cable here, with the sheild only hooked up at one end. It was an improvement, but still very sensitive.
Is this normal?
BTW, I'm not using a Zobel or RC network or whatever you call it between the tranny and the 5879..... just a straight wire. Could that have something to do with it?
Kevin Carter from K&K kindly suggested that I terminate the secondary of the input transformer (Lundahl LL1636) with an impedance defining resistor of about 200k. I tried this but it changed the tone for the worse (made it really thin). Maybe I did'nt put the resistor in the right place? I thought it just went from the + output of the 1636 to ground, no?
One more question....on Dave's drawing of how to install a HI-Z direct in, there is an extra resistor right after the 1/4" jack to ground. What value should that be.
Thanks a lot,
Freddy G :sam:

 

[mich]

The resistor after the input Jack is usually 1 Mega.

 

[hodad]

Somewhere way upstream Paul Stamler suggested using a 500K resistor on the input transformer. NYDave thought it unnecessary with the UTC he used on the input. I have one with & 1 w/o on my two-channel (with Bozak xformers), & there's a slight difference with the resistor there, possibly a slight improvement. It's worth futzing around with a little bit to see what works or doesn't.

Tom

 

[Freddy G]

1 meg? ....ok thanks Mich.
Hodad, I'll try a 500k, thanks for the tip.
I have not actually closed the box up yet, so I'm hoping that some of the weird issues like
~the supersensitve wire from tranny to pin 1 of the 5879 tube~
~some low level hum~
get sorted when I close it up for complete sheilding.

If I have not said it before.....
Thank you New York Dave for posting this design :thumb:
Freddy

 

[jaygunn]

I have a pair of UTC O-1 input transformers. NYD used O-11 I think I recall, back about 30 pages ago.

Is the O-1 comparable/suitable especially for the One-bottle?

Also, especially if the answer is Yes, there is a pair of UTC O-1's on eBay right now (ending in 9 days--this guy is not taking any changes) with no reserve. I bid $40.30 on them just for the heck of it, just trying to 'steal' them if there's no competition. No hard feelings if you DIY guys outbid me if you're tempted and they are good candidates for NYD"s designs. I probably won't bid again on the pair. How many do I need anyway?

Last question--I have also printed out and studied the MILA schematic as well as the OBMP. I don't mind that it's a bit more complex (and I'd leave off the DI.) But for a warm, clean Demeter/Manley-like preamp for vocals using a LDC like the Audio-Technica AT4047 (no clipping/fuzz/overdrive required), where 40-50 dB of gain is plenty, would someone be able to say the One-bottle, with its variable feedback would be more/less suitable than the MILA?

 

[Nadege]

Hi,

I've some question as I'm totaly new at tube DIY

I was wondering if this transformer (oep X187B) http://www.rsonline.de/elektronische-bauelemente-de/indexb866.html will suit the one bottle project?

Which kind of output transformer should I use?

Which resistor and/or capacitor should I used just after the input transformer ? What's those component for?

Thanks a lot for your help

 

[rafafredd]

Yes, it would probably work very well. you hve a 1:15 ratio aproximately there, so start with a 330k resistor across the secondar of the transformer. If it rings too much, you will need a RC circuit, but it would most probably work fine with just a 330k and a tube grid.

You can use this circuit without output transformers, if you do not have a big studio with messy and long wiring, EMI, and such... More gain and probably more clear also.

 

[Nadege]

hi, thanks for the answer. :grin:

for the output transformer, I have a big studio with very long wiring,.. maybee it's a good idea to put one ? would, the same transformer reversed work for this ?

thanks

 

[rafafredd]

No. You need a bigger core for the output. Use a 20k:600 and you should be fine. You will loose some 16dB gain. If you run it directly to a 20k or higher input, the gain is 16dB higher, but you get too hot maximum output, like 39dBu into 20kohms, and it can also be a problem, smoking some inputs. The transformer should bring the maximum output down to 24dBu into 600ohms, wich is a good figure.

 

[Nadege]

Hi,

rafafred, thanks for your help.

I had a quick look over thze catalogue of different audio tranformer seller, but couldn't find a 20k:600 tranformer.

Do you have any idea where I can find such a transfo?

Thanks a lot

 

[rafafredd]

Edcor. Sowter. Probably Lundahl. I would go EDCOR. You see, you are using the low cost OEP at the input, so low cost EDCOR is a good match for your unit. Just ask for a 20k:600 output and they will do it. For aproximatelly $10.00....

 

[NewYorkDave]

15K:600 is fine for the output. The plate resistance of the output stage in this circuit is close to 7.5K, so it's a good match.