One-Bottle Preamp

[tk@halmi]

Hey, Dave's preamp could be really cool coupled with his Line Output circuit and drive a 600 ohm transformer. Hmm...

 

[NewYorkDave]

:grin:

I've been thinking the same thing, myself. You'd have 70dB or more of total gain available--perfect for ribbons.

This is the most recent version of the line amp ckt:
http://electronicdave.myhosting.net/miscimages/nydave_lineamp1.gif

 

[tk@halmi]

Dave,

Thank You for the updated line driver. Combining them will be pretty slick because decent 600:600 transformers are easy to source. (Edit: I just noticed that the pic shows a 2:1 transformer.)

As far as the preamp section goes, I was wondering if using a 12AT7 instead of the 12AV7 may help reduce distortion through increased loop gain. However, the current is too large for that part in the second triode.

Then after a little thinking I realized that with the line driver added the preamp stage will not have to put more than a few dBu out, and the distortion would be much less than what you measured at 24dBu.

Cheers,
Tamas

 

[NewYorkDave]

Plus, the preamp will be driving the easy load of the 100K volume control--as opposed to the 10K load I used for my measurements--reducing distortion further.

The 12AT7 has higher gain, but is less linear--and, at current prices, costs more than the humble, cheap AV7 :wink:

The output stage CAN drive 600 directly, but maximum level before clipping is a few dB less than with a 2:1 stepdown transformer. You'd probably never notice if you're running at sane output levels; I was going for real hefty maximum output in the old tradition of real line amplifiers. Change the feedback resistor to 27K and its associated coupling cap to 2.2uF, if you want to try a 1:1 output transformer.

 

[NewYorkDave]

Here's a followup to my One-Bottle pre circuit. Today, I thought of a simple add-on stage to turn the One-Bottle into a Two-Bottle for when a lot of gain is needed.

This add-on requires an additional 150mA of heater and about 1mA of plate current.

Other changes: Replace R11 with a 100K fixed resistor, change C5 to 1uF film. Assuming a 1:10 input transformer, max gain is 63dB with a 4:1 output xfmr, or 78dB if no output xfmr is used (high-Z load).

I haven't breadboarded this yet but it's on my list of "to do" projects and I'll report back when I get around to trying it.

 

[kiira]

[quote author="NewYorkDave"]Here's a followup to my One-Bottle pre circuit. Today, I thought of a simple add-on stage to turn the One-Bottle into a Two-Bottle for when a lot of gain is needed. [/quote]

I'll build it. It will be simpler than the 3 tube high gain pre.

Kiira

 

[NewYorkDave]

Excellent. I hereby anoint you my research assistant... Here's your lab coat.

:thumb:

 

[kiira]

[quote author="NewYorkDave"]Excellent. I hereby anoint you my research assistant... Here's your lab coat.

:thumb:[/quote]

kewl. I almost have all the metalwork done... just gotta make another tube socket hole and mount the input/output xformers then the fun part starts. I always wanted to build a pentode pre too. This is my cutest project ever.

Kiira

 

[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?)

 

[kiira]

[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![/quote]

oops... I missed it.

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?)

They're nice and cheap too. Actually, I have a dead Tek which might have some in it.

Dave... can I use an Edcor 10000:600 wired with half the input winding for the output xformer? I have no 2:1 handy. I have a pair of Haufe 5:1 wish I could use them they're so small.

thanks all... I'm having fun.

edit: oops again! I read the whole thread and see you did that too with the edcor. hokay.

Kiira

 

[rafafredd]

You could try the Haufe at the input, wired 1:5.

 

[NewYorkDave]

Kiira, I think you're thinking of one of my other circuits (the line amp with the 12BH7 WCF output). For the One-Bottle pre, or this new "Two-Bottle" idea, you'd use a 10K:600 output, wired in the normal fashion (using the whole primary and the whole secondary). A 5:1 (15K:600) output would work fine, too. Your max output level would be less, but the distortion near max output would be reduced, too (due to slightly lighter loading of the output stage). Just make sure those small 5:1 jobs are intended for use as output xfmrs, not inputs! They should be rated to handle +20dBM or more.

PRR, those are exactly the reasons why I used a triode-wired 5879. Good call! The fact that it only draws 150mA of heater was a big plus, too, since I'm planning to build mine using a power transformer that isn't going to have much extra heater current to spare in the first place.

 

[skipwave]

[quote author="NewYorkDave"]PRR, those are exactly the reasons why I used a triode-wired 5879. Good call! The fact that it only draws 150mA of heater was a big plus, too, since I'm planning to build mine using a power transformer that isn't going to have much extra heater current to spare in the first place.[/quote]

It's nice that the datasheet gives seperate figures for Triode connected:
http://www.triodeel.com/5879p2.gif


Hey, Moderators. Who deleted the seperate One Bottle thread that on the Drawing Board? I think the title was "Simple Tube Preamp with a Good Sound." It was there yesterday, and now I can't see it or search it. There was some good information unique to that thread.

 

[Viitalahde]

[quote author="skipwave"]Hey, Moderators. Who deleted the seperate One Bottle thread that on the Drawing Board?[/quote]

Forum error that erased some other posts too. Unrecoverable, and all of my previous posts are not linked to my user account either. Major error! :shock:

 

[kiira]

[quote author="NewYorkDave"]Kiira, I think you're thinking of one of my other circuits (the line amp with the 12BH7 WCF output).
[/quote]

gah. I've been reading so many schematics and making layouts my brain has turned to mush.

For the One-Bottle pre, or this new "Two-Bottle" idea, you'd use a 10K:600 output, wired in the normal fashion (using the whole primary and the whole secondary). A 5:1 (15K:600) output would work fine, too. Your max output level would be less, but the distortion near max output would be reduced, too (due to slightly lighter loading of the output stage). Just make sure those small 5:1 jobs are intended for use as output xfmrs, not inputs! They should be rated to handle +20dBM or more.

I see. I'll have to double check... I know that they are officially out put xformers, 5:1 but I am not sure of the impedances or how many decibels they will carry.

thanks! I thought I'd build this from my junk box but I had to order a Edcor today... a 10000:10000K for the line input. They will custom wind a xformer for $5 extra! So a wsm 2500:600 would be only $14. That's amazing.

Kiira

 

[NewYorkDave]

Speaking of 5879 datasheets, here's a nice one from RCA, courtesy of the always-excellent online tube data collection known as "Frank's Electron tube Pages."

PDF

 

[kiira]

[quote author="NewYorkDave"]Speaking of 5879 datasheets, here's a nice one from RCA, courtesy of the always-excellent online tube data collection known as "Frank's Electron tube Pages."

PDF[/quote]

Ha :razz: I won those tubes for $1 apiece.... his pair of 12bh7a the same. :roll: I was hoping to finish it this weekend but my transformer hasn't gotten here yet.

Kiira

 

[jrd]

hi all. i seem to remember that NYD posted an improved version of the power supply for this one-bottle project, but can't find it anywhere. can anyone furnish a link? many thanks.

 

[NewYorkDave]

You can't find it because that thread disappeared during the recent message board malfunction. But here's the file:

PDF

And also some input/output options:

PDF

 

[kiira]

Since the 2 bottle version of the one bottle pre does more gain maybe the heaters should be rectified? It's really crowded in this DI sizd box!

Kiira