One-Bottle Preamp

[skal1]

OK lads

i have just completed one chan of this 1bottle pre , at the moment i have on input tx  to connect at the grid , can i connect a line level feed to the grid? , and would i need to put a resistor in parallel or series to knock do the line level signal ..


thanks

skal1 

 

[Kingston]

It's not optimal, but you could do the MILA-1 (or similar) DI input, unbalanced naturally. Depending on the outputs of the equipment feeding it there's a chance it works fine. But normally, and optimally you should either use a pad before the mic input transformer, or a separate line level (not step up) transformer, keeping it balanced.

 

[skal1]

Ok it passes signal  , i  went unbalanced to grid with a 200 ohm rs in parallel ., sounds alright fat bottom end  .  the only issue i am having is that the 100k pot  is not turning down the signal enough , you  can still  hear a faint signal when pot is turn fullly ccw, is this usually behavior ?. 

thanks

skal1

 

[skipwave]

Yes, the One-Bottle uses the 100k pot as a variable feedback control, not a volume or level control. Turning the pot CCW, you are actually increasing the amount of negative feedback from the output to the first stage cathode, therefore reducing gain.

Notice that Dave provided a gain range specification. +38 to +56dB or +26 to +44dB with a 4:1 turns ratio output transformer. It does not go down to zero like a volume pot would allow.

The MILA does have a level control, where you can ground the pot wiper, and listen to nothing but noise floor. Also see the "Zero Negative Feedback" version of the One-Bottle posted somewhere in this thread, which also sports a potentiometer as resistive voltage divider between first plate and second grid (and bypassed cathode resistors).

 

[skal1]

Thanks skipwave,


for the explanation,the pot does react as you say, so it is not my wiring.

i will try and see if i can find that thread.


skal1

 

[YLab]

Here is a version of that preamp without negative feedback with a pot between the two stages.

Hub

 

[skal1]

Hey thanks YLab ,


i might build that one next...

skal1

 

[skal1]

Ok just some minor details i need some help on.

So the 1 bot is up and running, 2 channels worth  the only detial what is bothering me is that the i am getting 47 vdc  on the plate of the first half of the 12av7 , ny dave spec is 55vdc right, and the cathe cathode voltage is up by 2v, what would i have to do to bring the plate voltage up on the first half of the 12av7?


any help would be nice.


skal1

 

[Denyle Guitars]

You can make the level go to zero by grounding the gain pot.

 

[YLab]

Ok just some minor details i need some help on.

So the 1 bot is up and running, 2 channels worth  the only detial what is bothering me is that the i am getting 47 vdc  on the plate of the first half of the 12av7 , ny dave spec is 55vdc right, and the cathe cathode voltage is up by 2v, what would i have to do to bring the plate voltage up on the first half of the 12av7?

I have reduced r13 to 4.7K on mine to bring the overall voltage up a little.

Hub

 

[Kingston]

So the 1 bot is up and running, 2 channels worth  the only detial what is bothering me is that the i am getting 47 vdc  on the plate of the first half of the 12av7 , ny dave spec is 55vdc right, and the cathe cathode voltage is up by 2v, what would i have to do to bring the plate voltage up on the first half of the 12av7?

47v vs. 55v difference is completely negligible here. NYD designed these in a very tolerant and generic way, and as far as the tube is concerned 47v is the same as 55v.

 

[skal1]

OH that,s cool then , i just have to get me a box, thanks every for your helps , can put this one on the shelf now.


skal1

 

[skal1]

Hi guys,


i have a question for the 1 bot pre gang , how would i connect a line level signal to this pre  , do i need to change tx or can i connect after tx  with resistor in serie with the grid.

thanks

skal1

 

[lassoharp]

Hi guys,


i have a question for the 1 bot pre gang , how would i connect a line level signal to this pre  , do i need to change tx or can i connect after tx  with resistor in serie with the grid.

thanks

skal1

You could use the hi-z input or preferably a direct box or a line to mic pad (~40db).  You can just build a line to mic pad inside the XLR jack and keep it as a designated cable for that purpose. 

 

[skal1]

Hi guys,


i have a question for the 1 bot pre gang , how would i connect a line level signal to this pre  , do i need to change tx or can i connect after tx  with resistor in serie with the grid.

thanks

skal1

You could use the hi-z input or preferably a direct box or a line to mic pad (~40db).  You can just build a line to mic pad inside the XLR jack and keep it as a designated cable for that purpose. 

lassoharp ,  what resistors should i use for a  line to mic pad (~40db).

thanks


skal1

 

[martthie_08]

look at http://www.uneeda-audio.com/pads/ in the bottom table, they show the values for line out --> mic input

cheers, Marten

 

[skal1]

look at http://www.uneeda-audio.com/pads/ in the bottom table, they show the values for line out --> mic input

cheers, Marten

Thanks  martthie_08

skal1

 

[lassoharp]

two 10Ks for the series and a 220ohm for the shunt should give you 40db on the money.

Remember too that the source goes 'into the U' as these pads are for use between unequal impedances.

 

[skal1]

two 10Ks for the series and a 220ohm for the shunt should give you 40db on the money.

Remember too that the source goes 'into the U' as these pads are for use between unequal impedances.

Lassoharp  , is this unbalance or balance? at the moment i have no mic tx in the front end , just a balance line signal going into  the pad,  i use is 10k from pin 2 of my eq too the hot pin on the bottle then put a 100 ohm across  bottle hot pin to ground , is this correct?..


thanks

skal1

 

[lassoharp]

The pad configuration I gave was balanced and intended for use in front of an input transformer.

Each 10K goes in series with pins 2 & 3, the 220 ohm connects across 2 & 3.

If you're not using an input transformer you probably won't need a 40dB pad - maybe more like 10 to 20db - it really depends on what level signal is coming out of your eq.  With no input transformer, 40db is probably too much attenuation.

Do you not plan to use an input transformer?