just a "One Bottle" mod

Hi all !

i would like you give me your point of view about this joined schematic for a pair of one bottle.

-> first i want to validate the schematic ; it's a mod of the original with some new features like 48v, phase, pad - 20, and i would like a "warn" pot /or switch to adjust tube temp.

-> second i want find the right materials like transformer & tubes

thanks for your help

christophe

What tube do you plan to use?

i could be wrong, but I think one tube stage will struggle to drive a 15K:600 output transformer
and a flat-ish freq response.

More common to use a paralleled pair of stages with a parafeed output transformer.

Maybe the 12AV7 will do it. Or some other higher dissipating tube like an ecc99 or so.

Having said that, I've done a preamp exactly that way, but it had high gain input stages
and a weird output transformer, something like 38K:600 and it was a guitar preamp.
It works great for guitar with it's low freq (and high freq!) rolloffs.

Cheers

alexc said:

i could be wrong, but I think one tube stage will struggle to drive a 15K:600 output transformer
and a flat-ish freq response.

Click to expand...

The only parameter we need to look at with driving an output like this is the plate resistance. And 12AV7 has nice lowish plate resistance for this 5:1 ratio output. It works very well. No need for paralleled triode sections here.

There are some easy opportunities to adjust tube "warmth". Cathode bias (R8/R20) and dropping B+ voltage a lot(R29). Those will give you some control over the sound. Test them on bench first before you put anything behind a switch.

Also, which tubes are you planning on using? 12AV7 sounds pretty awful with no feedback.

That 220k/47pF zobel is lifted from NYD schematics. If you don't have the exact same input transformer as him, do not assume they will work for you as well. Leave them out for now.

hi !

thank for your answers

[quote author=alexc]Having said that, I've done a preamp exactly that way, but it had high gain input stages
and a weird output transformer, something like 38K:600 and it was a guitar preamp.
It works great for guitar with it's low freq (and high freq!) rolloffs.[/quote]

this preamp will be for microphones

i think also a 12av7 could be good.

[quote author=Kingston]That 220k/47pF zobel is lifted from NYD schematics. If you don't have the exact same input transformer as him, do not assume they will work for you as well. Leave them out for now.[/quote]

yes i know this zobel was for the original transformer but how can i calculate the right network for one or another transformer what are the characteristics to include ?


does the 48v phantom power schematic right ?

where can i find the adequate power transformer ? also input and out put transformer ?  with no compromise of course

does the 48v phantom power schematic right ?

Click to expand...

I would add a resistor before the 47uf capacitor, like 470ohm. This allows the capacitor to function as a reservoir and a filter.

input and out put transformer ?  with no compromise of course

Click to expand...

There are several threads discussing the NYD one bottle preamp. It would be wise to read them first before buying or designing further, since others have tried many things that you can learn from. I used an Edcor for the output as have many others. I am still searching for inputs, but another member reported good results with a Cinemag and Lundhal.

12AV7 sounds pretty awful with no feedback.

Click to expand...

I used a 1meg pot for the feedback in my one bottle and it doesn't sound awful at high values , I don't think (nearly no feedback). I wouldn't want to omit the feedback loop entirely, however! Neodyms, why have you cut this out?

dmp said:

I used a 1meg pot for the feedback in my one bottle and it doesn't sound awful at high values , I don't think (nearly no feedback).

Click to expand...

Perhaps awful was a strong word but 12AV7 really is the wrong tube for plans with no feedback. Maybe try 6SN7/12AU7 or perhaps ECC88 equivalent. Might need some tweaking of bias.

[quote author=dmp]Neodyms, why have you cut this out?[/quote]

i was inspired by "no feedback one bottle" just because the input schematic include a DI input with 1 mOhm impedance but you surely right about the feedback.

how can i mix this two features ?

how can i mix this two features ?

Click to expand...

In NYD's design there is feedback from V1B pin 6 to V1A pin 3 through a ~10uf cap, a 100k pot and a 22k resistor, all in series. The cap needs to be rated for high voltage like c4, and it should block the high voltage from the pot for safety. To go to 'no feedback' increase the pot to a higher value, like I did, or put in a switch.

yes i know this zobel was for the original transformer but how can i calculate the right network for one or another transformer what are the characteristics to include ?

Click to expand...

A. Read the datasheet for the transformer, sometimes they tell you.
B. Search the forum for 'zobel', 'calculating zobel', etc... spend hours reading

ok

thanks a lot for your help

i will modify this  schematic with the precious help of your advices  and come back to you after.

best regards

read soon


christophe

The plan that Chris posted is the "6SN7" (NYDave) version of a One Bottle preamp - it is not the original One Bottle 12AV7 plan.

No feedback, simple interstage volume control. 

Any good mic to grid transformer will work on the input.  A 10K:600 will also work fine on the output - an easy buy at Edcor.

Make sure the 2.5K PS dropping resistor is speced for proper dissipation.  Around 20 +ma total if doing two channels on a single supply.

zobel:

There is no simple way to calculate the series RC damping networks for microphone input transformers.
The simplest way to determine the proper damping network for a microphone input transformer is experimentally.

>> http://www.groupdiy.com/index.php?topic=32441.msg393923#msg393923

One very small practical point. The output connector on the schematic is specified as nc3fd-v-bag, which is a female Neutrik XLR. You probably want the male version 3 pole XLR on the output = part number nc3md-lx, and the female version nc3fd-lx on the input. (Postfix LX depending on what colour, solder pins etc)

On a deeper level of change, the Russian 6n6p (sort of similar to ECC99) might also be worth a look for this design u=22 Rp ±2K  (might require some resistor jigging) YMMV Haven't tried this myself yet but am tempted to do so for a cheap and cheerful test.

As has already been pointed out, the original had -ve feedback: schematic can be found here. http://electronicdave.myhosting.net/miscimages/onebottlepreampschem.gif

MeToo2 said:

On a deeper level of change, the Russian 6n6p (sort of similar to ECC99) might also be worth a look for this design u=22 Rp ±2K  (might require some resistor jigging) YMMV Haven't tried this myself yet but am tempted to do so for a cheap and cheerful test.

Click to expand...

The gain is low and that's why it's not good for one bottle projects, ie. extracting lots of gain from a small package. It's a great driver tube. I've used it in line amps many times and like it very much. You only need a 2:1 ratio output transformer which is nice. But you're looking at low gain, 30-40dB (including the very high step up input transformer) which is too low to be called a preamp these days.

well i think it all depends on what microphone is being used with it and what type of source is being recorded, 40 dB overall gain is sufficient for a sensitive mic (like most Audio Technicas for exemple) especially in front of loud sources.
i have a similar tube mic preamp with about 45dB overall gain but with a double cathode follower output design (no output transformer)
that i use a lot with my pair of 451e, it sounds terrific !
For the pwr transformer have a look at musikding.be they have a bunch of nice and very affordable power transformers for projects like this one.
best of luck

A pentode front end to a 6n6p/ecc99 configured somewhat like the above one bottle would work very well. For example 5879 or ef86 configured as a triode is 20-25dB of very linear gain. No feedback needed.

Somewhat similar to what NYD himself suggested for the "two bottle" project actually. Warm sound guaranteed.

Kingston said:

MeToo2 said:

On a deeper level of change, the Russian 6n6p (sort of similar to ECC99) might also be worth a look for this design u=22 Rp ±2K  (might require some resistor jigging) YMMV Haven't tried this myself yet but am tempted to do so for a cheap and cheerful test.

Click to expand...

The gain is low and that's why it's not good for one bottle projects, ie. extracting lots of gain from a small package. It's a great driver tube. I've used it in line amps many times and like it very much. You only need a 2:1 ratio output transformer which is nice. But you're looking at low gain, 30-40dB (including the very high step up input transformer) which is too low to be called a preamp these days.

Click to expand...

Didn't mean to hijack the original thread. My main reason for posting was to place the link to the original schematic from NYD for the OP. Forgive me if my maths is screwy on the 6n6p. Not sure I follow why voltage gain should be so low as just 7-17dB for 2 stages (excluding the 23dB or so gain delivered by the input transformer but including the output transformer). A 12av7 has a mu of between 35 and 40 which is coupled to a 4:1 output transformer (-12dB). By using a 2:1 output transformer on the 6n6p don't you make up for one set of 6dB for the difference in lower voltage gain due to the 6dB higher current drive capability of this tube e.g. biassing it at 20mA rather than 10mA? So that just leaves the difference in the first stage, where overall gain is governed by negative feedback rather than mu? I think the main limit on this design is probably going to be the quality of the input transformer which has to deliver 20+dB of the gain. Anyway this is diverging off topic and I haven't built this particular combination, so I'd best stop now.....

A few questions/points:

1. Is this going to be built in a single enclosure along with its PSU? If it is then you need to be careful where you position the mains transformer relative to the input transformers and I would recommend using an aluminium enclosure rather than a steel one. If the power supply is to be separate then you need to revise your grounding scheme to take that into account.

2. With a 50VAC secondary for the phantom PSU you will have nearly 70V dc to play with so you might just as well use a TL783 regulator instead of the zener which will give you a much cleaner phantom supply.

3.  R25 and R26 should probably be 100 ohms rather than the 100K shown.

Cheers

Ian

ok

back to start!!  



my first wants was to make a very simple, but efficient mic preamp

the NYDave one preamp was a good foundation.

then add to this one :
48v phantom power
HIZ DI input
-20dB pad  
phase inverter
balanced output

this was the real reasons i did this previous bad schematic sorry for that


so will see joined a new one with less modification of the NYDave one bottle and the previous features added.

for phantom psuu I find this http://www.eleccircuit.com/48v-phantom-power-supply-with-tl783c/

thanks for all you comments


***joined file error ***

this the pdf

sorry

Looks good to me. Some notes,

C7/C23 doesn't have to be electrolytic. A big film cap also works here, the value is kind of non-critical, as long as it's more than 1uF. For electrolytic you could go as high as 100uF. You could even take the feedback loop from behind the output coupling cap and skip the separate feedback cap completely (saves one potentially expensive film cap).

R12 feedback potentiometer could also be 470k-1M. Gives you even more gain range.

The output transformer doesn't necessarily have to be 15k:600 (5:1 ratio). Even 10k:600 (4:1 ratio) works and you will have slightly more gain left.

Keep in mind it might be difficult to find a good quality 200:50k (1:15 ratio) input transformer with enough headroom and bandwidth. Something like 1:7 to 1:10 (150:15k) will also work fine, and will be easier to find.

About the zobel network C1/R4,

Sometimes the datasheet might only suggest a loading resistor. There might not be a cap at all. If your input transformers datasheet doesn't tell you what values these should be just leave it all out. It will probably sound just as good without it and tuning them by hand is a very delicate and longwinded process.