One-Bottle Preamp

[offramp]

Sorry - kind of - for bringing this back up to the front. I've had to put this project on hold for a long while, and am forcing myself to get back on it, in the midst of all the other s**t I have going on. Hopefully it'll be therapeutic.

So... I've had the luxury of going through all the resistors here at work and hand-picking the ones with the tightest tolerances. Nice.  8)
But now, I'm wondering about caps... is there an overall consensus on what types of caps are best in this circuit?

 

[ruffrecords]

I doubt there is a consensus! I would say use film for coupling and aluminium electrolytic for decoupling.

Cheers

Ian

 

[offramp]

I doubt there is a consensus!

Yeah, I know... I have bouts of stupid optimism from time to time. 

 

[ruffrecords]

I doubt there is a consensus!

Yeah, I know... I have bouts of stupid optimism from time to time. 

As long as they are balanced by bouts of common sense and sanity you will be fine!

Cheers

Ian

 

[Adam Smith]

I'm starting on on a couple of these with transformers that are hanging around, not getting used. My input transformer is 200:47k, made for this sort of thing, no problem there. However, my OT is a plate to line that calls for 0mA on the primaries. So, I figure I need to run it as a parafeed kind of thing. Would this basically be the correct way to do something like that? I figure I'll need to change up R10 and maybe C4. Also, has anyone tried to do this?

 

[Kingston]

Please post the information on what exact output transformer you are using. Sounds to me like you can use it the way you have drawn.

What this configuration calls for is an impedance matching 5:1 or 4:1 ratio transformer (10k:600 or 15k:600) like you have drawn.  C4 can be higher to extend bass response a bit but is not critical (2,2-10uF). R10 is the load for unbalanced out and not actually needed with a transformer at all, also not critical at all. I would also ignore R4/C1 zobel network completely unless you actually hear any transient ringing (you won't).

 

[Adam Smith]

Thanks.

I'm using utc ls 50's

these are the specs i could find...
http://wevtt.com/UTCLS50specs.jpg

I suppose I could sell them and get some OT's that can take DC on the primaries, but they are kind of rusted up. I found 'em on craigslist an am actually not sure what shape they are in. If they are busted, I'm just gonna go without the OT.

 

[lassoharp]

get some OT's that can take DC on the primaries

Putting DC on the pri = redesign.  Besides, this circuit was designed for parafeed.  LS 50 would work great, so would the Edcor 15K:600.

 

[Adam Smith]

get some OT's that can take DC on the primaries

Putting DC on the pri = redesign.  Besides, this circuit was designed for parafeed.  LS 50 would work great, so would the Edcor 15K:600.

that's awesome news. thanks a ton guys.

 

[theaterguy]

Hello, is this PT enough for one or two channels? The secondary voltage is only 230. Any problem here?

Small power transformer for tube projects. Primary 230V, secondary 230V 0,12A, 20V 0,12A and 6.3V 4A.

The price is only 27€.

So far I have found two versions of the PSU; one with two zeners and one with four. Which one would you recommend?
Somewhere I saw a version without a output tranny. How is de-coupling done without or should I take the tranny instead?

Thanks

 

[Kingston]

Hello, is this PT enough for one or two channels? The secondary voltage is only 230. Any problem here?

Small power transformer for tube projects. Primary 230V, secondary 230V 0,12A, 20V 0,12A and 6.3V 4A.

The price is only 27€.

So far I have found two versions of the PSU; one with two zeners and one with four. Which one would you recommend?
Somewhere I saw a version without a output tranny. How is de-coupling done without or should I take the tranny instead?

Thanks

That PSU transformer looks great but build the PSU set up from MILA-1 project instead. It's generic and will work better than any of the one bottle PSU's NYD originally designed for random transformers he happened to have around.

One bottle works fine with no output transformer. Maybe change R10 to a bit lower value like 50-100k and C4 higher 4.7-10uF. Just remember it won't drive low impedance inputs without the output transformer. Not much of an issue in modern studio and AD/DA's.

 

[theaterguy]

Yep, Mila could be better choose. The trafos are anyway the biggest expense, not the tubes.

 

[Kingston]

Yep, Mila could be better choose.

I didn't mean to suggest you should build the whole of MILA-1, but just the PSU part to power the one bottle design.

And yes, input transformer is going to be the single most expensive part, whichever project you choose.

 

[theaterguy]

Yep, Mila could be better choose.

I didn't mean to suggest you should build the whole of MILA-1, but just the PSU part to power the one bottle design.

And yes, input transformer is going to be the single most expensive part, whichever project you choose.

I must have been half asleep when I replied  your post but now One-Bottle-Pre is working. Yes, I did the Mila-1 PSU and it's pretty hum free until highest gains but totally ok when singing to a dynamic mic (and the top lid was open).
I connected heater feeds to pin 4&5  and pin 9. The HT voltage is  7V, is this something to worry?

On some schemas there was a 1M resistor between input trafo secondary but on some designs it was left out, what is the purpose of that? I have mine without.

 

 

[Kingston]

I connected heater feeds to pin 4&5  and pin 9. The HT voltage is  7V, is this something to worry?

I couldn't find the exact spec for 12AV7 but most of these smaller 9-pin tubes can happily take 10% over- or under-voltage on heaters. 7V should be fine.

On some schemas there was a 1M resistor between input trafo secondary but on some designs it was left out, what is the purpose of that? I have mine without.

It's needed if you have a DI input jack so that the instrument sees a bit lower impedance than the tube grid. If you have no DI input, there's no need for it. Again, MILA-1 schematic has the best guide for this.

 

[theaterguy]

Ok, mine is working nicely. The sound is surprisingly clean and with dynamic mikes it was not all that different compared to solid state pres. Testing with condensers revealed it is slightly darker and kinda "slower".  The hum level is very low but I would't record quiet solo instruments with a ribbon mike. With Cinemag irons it's output is pretty hot, so hot that I need to think some kind of output pad. But hey, now I can get some nice transformer saturation as well!

 

[ForthMonkey]

Hi,

Now i'm building this preamp.And it's my thread;

http://www.groupdiy.com/index.php?topic=53606.0

I have some questions,can you look? I found lots of answer about my design but i'm still have questions.

And there are a resistor and cap in input.What are values? 150K & 100pF?

 

[rock soderstrom]

It is a Zobel network.

check this reply #725

http://www.groupdiy.com/index.php?topic=6711.msg614285;topicseen#msg614285

You will find nearly all about this fantastic amp in this thread. Read it!  8)

 

[ForthMonkey]

It is a Zobel network.

check this reply #725

http://www.groupdiy.com/index.php?topic=6711.msg614285;topicseen#msg614285

You will find nearly all about this fantastic amp in this thread. Read it!  8)

Thanks for quick reply!

Zobel network is impedance stabilizer,right?Mostly using with speakers i guess.I'm learning. ;D

Now i will use cheap 1:10 transformer for now(NTE 10/3). It has 200/50K source/load impedance and 200:20K impedance ratio.I want more bass response.How should i calculate Zobel R & C? Original circuit's Rz is 100K but for Cz it says select for best reproduction.Can use 0.1uf or 0.01uf? Or what?

 

[gemini86]

Zobel network is usually calculated once you know what the transformer's frequency response is. Some have a 'ringing' or a frequency which will resonate if not loaded properly.

Found this thread after a quick search...

http://www.groupdiy.com/index.php?topic=28976.msg350646#msg350646