[BUILD] GIX-51X tube preamp

[irfrench]

Ask and ye shall receive:

http://www.groupdiy.com/index.php?topic=51639.0

Hope it is useful.

Ian.
;D

 

[tonycamp]

cool samples, sounds great!

 

[okgb]

Just for maddness , Radial now has a tube 500 series pre

Radial Powertube Tube Preamplifier
Retail Price: $800.00

High voltage 12AX7 tube drive with 60dB of gain
Smooth sounding Jensen Transformer input
Hand inserted 100% discrete class-A electronics
Single wide module fits all 500 series rack formats

The Radial PowerTube is an 'old school' 100% discrete class-A vacuum tube microphone amplifier intended to capture the essence of the voice or instrument while adding the rich harmonics, warmth, and character of a transformer coupled tube circuit.
Designed to fit inside the Radial Workhorse and other 500 series racks, the 'single-wide' PowerTube begins with an ultra low-noise Jensen input transformer. This exhibits near perfect frequency response while producing the warm Bessel curve Jensen is legendary for. The signal is then amplified via a select 12AX7 tube using an innovative non-radiating charge pump that supplies 140 volts to the tube to deliver the excitement and character of a high-voltage vintage tube amplifier. This feeds a class-A balanced output stage that together, can produce as much as 60dB of gain. This makes the PowerTube ideal for use with all microphones.
Features include an easy-access front panel XLR input with a safely recessed 48V phantom power switch. To optimize signal-to-noise the Powertube is equipped with fully variable trim and gain controls. A 10 segment LED bar graph provides visual feedback and driving the PowerTube into the red is encouraged. This increases the grit, harmonic content and distortion. For even more character, activating the Air adds a slight edge to a male vocal or sparkle on an acoustic guitar. Low frequency resonance is easily tamed using the high-pass filter. For added pleasure, the PowerTube comes factory-loaded with a select 12AX7 tube along with a second Tonebone distortion pedal tube for more grit and madness.
The Radial PowerTube... the true character of a world class vintage tube preamp without the noise!

 

[gemini86]

Sounds pretty cool, maybe I should smack together a one bottle pre and peddle it for 600 bucks a pop and rake in tons of profit.

 

[okgb]

You've done allot of the work already  .............
more curious how they implemented their charge pump , filiment current
and how they get the gain out of one tube [ 40 db from the tube some more from the input xfmr ]
roll music uses the 12dw7 which has a high gain section but the radial doesn't mention an output xfmr

 

[gemini86]

"This feeds a class-A balanced output stage that together, can produce as much as 60dB of gain"

Notice the missing over-hype about an output transformer... I'm going to guess a solid state output, like you would find in maybe an ART pro tube piece. They don't want to loose the gain in an output transformer.

 

[mulletchuck]

So, a bunch of people built this.  but no one has soundbytes of it on drum overheads or vocals or horns or anything? 

 

[gemini86]

I'll probably have some vocals recorded this weekend... probably.

Once I get a little road case built I'm going to loan it out to a local recording studio to put it through it's paces.

 

[Winetree]

Has anybody successfully built one yet? I've been holding off till project was worked out.
Looks like build guide is getting better. Can't print out complete BOM, can't to do a Mouser Cart.
Any help.

 

[irfrench]

Definitely!

And it sounds GREAT! 

I'll be using one in anger this weekend so will hopefully have a better feel for it, but so far I'm very happy.

For reference - I built mine with OEPs.


Ian

 

[gemini86]

Winetree, I'm trying to make the time this weekend to try to iron out the bom and build guide. This is no commercial product and I am making assumptions on peoples troubleshooting skills. There's also the official g9 thread for general circuit troubleshooting. But yeah, I'll definitely try to get all the needed info in one place.

 

[canidoit]

Will this be available as a normal 500 series 16 volts version??

 

[gemini86]

I hadn't planned on it. Two tubes take up way more power than is available in standard 500 format. I wanted this to be a 1U preamp, because rack space isn't plentiful in most studios. It is possible to run it off +-16 though, with modifications.

run the boost converter on +16V, it will suck up a lot of current, probably over 200mA. The tube heaters can run on the -16V rail, but need to be rewired from series to parallel and then they'll need either a voltage dropping resistor (a big one) or a regulator to bring -16 volts up to -12.6V. This will draw 300mA on the -16 rail, so more than 2U worth of power. If you're not running everything in your rack at full power all the time, this will work fine. It's just not VPR compliant.

 

[bruce0]

Have you tried it? With 16v you may want an inductor smaller than 330uH. Duty cycle would be higher and frequency would drop ( probably to 76k hz which is based on the 16usec max on time)but it should work.

If you want to keep it above 100k hz you may need a smaller inductor than330uH I have a spreadsheet calculation and if anyone cares I all take a shot at an initial value.

 

[jandoste]

Hey Guys,
Which tube did you use?  :
Thanks


I found this one... can I go with this tube?
EDIT: http://www.banzaimusic.com/ECC82-12AU7-JJ-Matched-and-Balanced.html

EDIT2: My bad I received all parts! but bad news :-[ this Lorlin switches is the bad one!  Do you think that also will work?
http://fi.mouser.com/ProductDetail/Lorlin/CK2368/?qs=%2fha2pyFadugzyIKxLH3BYupOnqRNmej1oo6IfF6M0Mg%3d

 

[gemini86]

I just used a nice quiet used RCA for V1, V2 didn't seem to make any noise, no matter what tube I used.

Right now I'm messing around with a JJ 12ax7 in V1. Sounds...kinda thin and crunchy. Kinda nice for guitar DI though.

I'm trying to figure out a good switch number. The one I'm using right now is the CK 1458. This is a NON-shorting switch. People are saying that we need a shorting switch, but I'm not convinced. I'm still not hearing any bad pops when gain switching. Maybe a little tick at best. After all, we're only switching AC signals with the switch. there should be no change in DC charge of the cap.

Please somebody correct me if I'm wrong.

 

[emrr]

Gain is always a shorting switch, otherwise there are jumps at best, speaker cone launching pops at worst.  You don't want to change a non-shorting on a low frequency source with a loud sub or bass bin powered, or a 500W amp on your precious NS-10's.  Shorting gets smooth transitions with no breaks in continuity; think about a pot, continuous resistance. 

 

[gemini86]

No, I agree with that. In this specific case, though, is it not a bust? The switch it already bypassed by a 1M resistor, as well as the fact that a momentary open condition between switch positions would result in low gain, not high gain or loud pop.

 

[bruce0]

... a momentary open condition between switch positions would result in low gain, not high gain or loud pop.

My opinion... on the first 3 clicks (steps 2,3 and 4) the momentary open causes a decrease in attenuation so an increase in gain (perhaps 9db or 12db not too much because the attenuation is not much), and clicks 5 through 10 I agree with you completely the momentary open results in lower gain, which is still be audible, but not loud.

But the thing that is odd, is the 4th click.. where the attenuation goes away, and the gain stage steps begin.  That step is where I got a pop when I used non-shorting switches.  The other steps were audible clicks, but not big pops.  But step 4 is a pop.  Oddly the first time I pass step 4 it is a big pop, and after that, if I turn the gain down and back up again, step 4 is no longer a big pop.

The non-shorting switch is usable, but if I change gain levels while tracking I record a click.

 

[gemini86]

I see. I'll have to take measurements from mine while switching, because I'm not getting the same pop.

As far as I can figure out, mouser only carries a shorting switch with a D shaft (with PC pins). That will work with set screw knobs, but I'm not sure about collet knobs. Or you can get a round shaft shorting switch, but with solder lugs instead of PC pins and just snip the lugs off.

Sorry I don't have the time to research exact part numbers at the moment. Will get to that after work today.